1

Chapter One

Introduction to the Green River Formation

and research approach

2 1. INTRODUCTION

The Green River Formation of southwestern Wyoming has been the focus of

hundreds of studies over the past century. This growing database documents the current

understanding of the mineralogy, paleohydrology, paleogeography, paleoenvironment,

vertebrate and invertebrate paleontology, stratigraphy, geochemistry, structure, hydrocarbon

potential, paleofloral, paleoclimate, and paleolimnology of the sediments deposited in and

around Eocene Lake Gosiute. This wealth of information provides a framework from which

to develop lacustrine stratigraphic principles and to test paleohydrologic tools. This

introductory chapter is intended to summarize the stratigraphy and paleogeography of the

Green River Formation, the tectonic and climatic setting of Lake Gosiute, recent advances in

lacustrine stratigraphy, and the utility and limitations of the strontium isotopic analysis.

2. GEOLOGIC SETTING

The Green River Formation represents a ~5 Ma interval of lacustrine deposition

during the early to middle Eocene time (Smith et al., in review). It exists within the greater

Green River Basin of southwestern Wyoming, northwestern Colorado, and northeastern Utah

(Figure 1.1). The basin is in the foreland of the Sevier Thrust Front and is bounded to the

north, east, and south by Precambrian cored Laramide style uplifts from

Cretaceous/Paleocene time. The uplifts are (clockwise from the west) the Sevier thrust belt,

the Wind River Mountains, Granite Mountains, Sierra Madre, and the Uinta Mountains. The

lacustrine strata of the Green River Formation were deposited during the final stages of

Laramide uplift. The formation includes the clay rich Luman Tongue, carbonate rich oil

shales of the Tipton Shale Member, evaporites of the Wilkins Peak Member, and the

3

Figure 1.1. Geologic map of the Green River Basin and surrounding uplifts

(modified from Witkind and Grose, 1972).

4 limestone, oil shale, and tuffaceous sands of the Laney Member (Roehler, 1993; Figure 1.2).

The Greater Green River Basin (43,500 km2) is divided into four sub-basins by

structural arches; the western Green River Basin, northeastern Great Divide Basin, eastern

Washakie Basin, and southeastern Sand Wash Basin. Laterally extensive tuff deposits within

Laney strata indicate that deposition within the sub-basins was time transgressive during the

final stages of lacustrine deposition, infilling north to south (Roehler, 1993).

Stratigraphic relationships between the lacustrine Green River Formation and the time

equivalent alluvial Wasatch and Bridger Formations suggest that the aerial extent of Lake

Gosiute was highly variable throughout its existence (Figure 1.3; Roehler, 1993). Expansion

and contraction of Lake Gosiute has previously been attributed to fluctuations in the early to

middle Eocene climatic regime (Roehler, 1993), but more recent studies suggest that tectonic

and magmatic controls on the geomorphic evolution of the basin and its drainage played an

integral part in the lake size and type (Surdam and Stanley, 1980; Carroll and Bohacs, 1999;

Wilf, 2000; Morrill et al., 2001; Pietras et al., in press; Rhodes et al., in review).

The Luman Tongue of the Green River Formation covers an area of approximately

17,200 km2 centered around the Uinta Mountain trough. Roehler (1993) interpreted a

decrease in precipitation and temperature caused the lake to contract and fill in following

Luman Tongue deposition. Lake Gosiute re-expanded to cover the Uinta Mountain trough

and spill over into the Greater Green River Basin. This lake expansion is represented by the

Tipton Shale Member and is estimated to have covered close to 38,900 km2 of the basin at its

maximum extent (Roehler, 1992). Tipton lake expansion was punctuated by the progradation

of deltaic sediments from the north (Farson Sandstone). Contraction of the Tipton lake is

interpreted by Roehler (1993) to represent hotter and drier conditions. However, Pietras et

5

Figure 1.2. Cross section through the Green River Basin illustrating the stratigraphic

relationships between the members of the Green River Formation (modified from

Roehler, 1992).

6

7

Figure 1.3. Tectonic uplifts, paleocurrent directions, and maximum lake size for the

members of the Green River Formation. Active uplifts are gray. A) represents

sedimentation in the GRB prior to the existence of Lake Gosiute (earliest Eocene).

B) shows the maximum extent of the lake during Luman and Tipton deposition. C)

illustrates the margins of the Wilkins Peak Member, and D) shows the extent of the

Laney Member. (maps modified from Surdam and Stanley, 1980; lake extent and

paleocurrents from Roehler (1993) and Sullivan (1985); uplift data from DeCelles,

1994; Dorr et al, 1977; Bell, 1954; Keefer, 1965; Love, 1970; MacLeod, 1981;

Steidtmann et al., 1983; Steidtmann et al.,1986; Steidtmann and Middleton, 1991;

Hail, 1965; Anderman, 1955).

8 al. (2003) interpret a tectonic control that forced the lake to retreat back to the Uinta

Mountain trough where it occupied an area of ~ 18,000 km2.

Roehler (1993) interpreted the deposition of the Wilkins Peak Member to represent a

period of intense climatic cyclicity from hot and dry to warm and temperate conditions,

causing the expansion, contraction, and extinction of Lake Gosiute, approximately 77 times,

during Wilkins Peak time. To test for precessional forcing as a control for Wilkins Peak

depositional cycles Pietras et al., (2002) combined detailed stratigraphic analysis with

40Ar/39Ar dating of tuffs to reveal a 10.2 +/- 3.6 kyr cyclicity, precluding precessional

controls on cycle level stratigraphic expression. Paleocurrent indicators suggest that

sediment was brought in to the basin from the south and east during this time (Figure 1.3).

The lake depocenter migrated into the central Green River Basin, just west of the Rock

Springs uplift (Roehler, 1992).

Lake Gosiute reached its maximum size of 39,900 km2, roughly half the area of Lake

Superior, during the deposition of the Laney Member of the Green River Formation

(Roehler, 1992). During Laney Deposition, paleocurrent measurements indicate the majority

of clastic sediment was brought in from north of the basin (Surdam and Stanley, 1980; Figure

1.3). During Laney time, the depocenter shifted toward the eastern Uinta trough as the basin

was infilled with sediment from north to south (Roehler, 1993). The Laney Member

represents the final transition in the basin from lacustrine to alluvial environments.

3. PALEOGEOGRAPHY

Paleogeography plays a very large role in zonal climate distributions on a continental

and regional scale. During Eocene time, the continents were nearly in the same position as

9 they are today (www.scotese.com). The Green River Basin was located approximately 35° N

(5º to 8º south of present latitude) near the descending limbs of the Hadley and Ferrel

atmospheric circulation cells. Prevailing winds were from the west-northwest in the Green

River Basin during lacustrine deposition as indicated by the east-southeastward thinning of

air-laid volcanic ash deposits preserved in the sediments (Roehler, 1993).

Paleoflora, oxygen isotope, and apatite fission track studies have lead to a number of

paleoelevation approximations for the Green River basin floor and surrounding uplifts during

the deposition of the Green River Formation. Bradley (1929) speculated that the basin was at

an altitude of 330 meters, whereas Axelrod (1968) used floral assemblages to determine a

450 meter elevation for the Green River Basin. Floral evidence led MacGinitie (1969) to

suggest that the surrounding uplifts were 1000 to 1200 meters higher than the basin floor

during early to middle Eocene time.

Norris et al. (1996) studied oxygen isotopes within the Wilkins Peak and Laney

Members of the Green River Formation and measured intervals within the Wilkins

Peak/Laney transition that were depleted in 18O. The δ18O values from lacustrine

stromatolites are too negative to be explained by atmospheric distillation but are consistent

with isotopic values derived from snowmelt. Norris et al. (1996) concluded that the

mountains surrounding the paleolake must have been high enough to supply the lake with

glacial melt water, which would require the mountains to be in excess of 3000 meters higher

than the basin floor. However, this study was based on the analysis of microbial carbonates

that are difficult to test for diagenetic alteration. A study by Wolfe (1998) supports the

conclusions of Norris et al. (1996) through a multivariate statistical approach relating leaf

characters to environment, and concluded that the elevations surrounding the Green River

10 Basin were equal to or greater than modern elevations (~2.9 +/- 0.8 km). However, a recent

investigation by Morrill and Koch (2002) suggested that there is no convincing evidence for

high elevations surrounding the Green River Basin because the low oxygen isotope values

measured from mollusks are found to correlate to the presence of calcite, a diagenetic

precipitate.

Apatite fission track ages in the Wind River Range suggest total uplift to have been

4.5-6.5 km relative to the modern day surface (Cerveny and Steidtmann 1993). From this

data, measured from samples collected in a series of north to south transects across the Wind

River Range, Cerveny and Steidtmann (1993) concluded that the southern margin of the

range underwent gradual uplift throughout regional Laramide deformation and the northern

margin uplifted more rapidly over a shorter period of time.

4. TECTONICS

Green River Basin bounding ranges typify Laramide-style uplift. The mechanism for

this “thick-skinned” uplift remains controversial. Dickinson and Snyder (1978) and

Dickinson (1979) called for low angle slab subduction as the primary force driving

Laramide-style uplifts. In this model, the uplift of Laramide blocks bound by high angle

reverse faults occurred in the vicinity of a magmatic gap, which is analogous to the structural

setting in the central Andes where the cessation of volcanism was found to be associated with

the sub-horizontal subduction of the oceanic plate beneath the continent (Barazangi and

Isacks, 1976; Megard and Philip, 1976). Gries (1983) argued that while Laramide uplift may

have been intensified by low angle slab subduction, the attitude of Laramide structures

changed through time in response to more than one direction of compression. Different

11 compressional regimes are expressed in three stages of uplift associated with the opening of

the North Atlantic-Arctic Oceans which produced north-south, northwest-southeast, and east-

west trending uplifts. Noting the similarity of Laramide structures to those of other

collisional orogens such as the Himalayas, an alternative model was proposed by Maxson

and Tikoff (1996). The “hit-and-run” collision model for Laramide uplift, suggested that the

Baja-BC terrane hit the North American plate at the latitude of Baja, California, and

translated northward to its modern latitude in British Columbia and Alaska. The oblique

convergence of the Baja-BC terrane coincided with the timing and location of Laramide

uplift.

More recently, Marshak (1999) proposed rift inversion of the Proterozoic cratonic

platform as a mechanism for Laramide style uplift. This interpretation is based on the

recognition of Proterozoic rift sediments that underlie some Laramide structures and

attempted to explain conflicting fault vergence of Laramide structures through the

reactivation of basement penetrating faults with opposing dip in the Laramide compressional

regime. Although mechanisms for Laramide uplift remain controversial, the timing of uplifts

has been deduced by documenting structural relationships within strata deposited along the

margins of adjacent basins, geochronologic investigrations, and apatite fission track study.

Figure 1.3 illustrates the relative timing of tectonic uplift within the Green River

Basin and the resultant sediment dispersal patterns in the Green River Basin (see Figure 1.3

for references). The majority of uplift took place prior to Green River deposition. All uplifts

were active during the deposition of the late Cretaceous strata that underlies the basin. The

Wind River Range, Granite Mountains, and Uinta Mountains were tectonically active

throughout the Late Cretaceous to early-Early Eocene time when they contributed to the

12 deposition of the alluvial, Paleocene Fort Union Formation (Figure 1.3A). Sevier thrusting

and Gros Ventre uplift took place for a period of time around the end of Cretaceous time to

the beginning of the Paleocene, and then again from late Paleocene to early Eocene time

when they contributed to the deposition of the alluvial Wasatch Formation.

The Uinta Mountains uplifted throughout the deposition of the Green River

Formation. Luman Tongue and Tipton Shale Members of the Green River Formation were

influenced by tectonism to the south (Uinta Mountains), west (Sevier Thrusts), and north

(Gros Ventre Mountains and Wind River Range) of the basin (Figure 1.3B). Renewed uplift

in the Granite Mountains and activity along the continental fault in the Wind River Range

coincided with the deposition of the Wilkins Peak Member (Figure 1.3C). Finally, the Laney

Member of the Green River Formation was deposited during the waning stages of Laramide

deformation, and coincided with the beginning stages of Absaroka volcanism (Figure 1.3D).

The Eocene Absaroka Volcanic Province grew to the north-northwest of the Green

River Basin. Sundell (1993) reported that volcanism occurred between 53 and 38 Ma, and

that the center of eruption and deposition shifted southeastward with time. Andesitic

stratovolcanoes are interpreted to have risen to heights of nearly 3 km throughout the

evolution of the Absarokan volcanic terrane. These volcanoes quickly eroded and formed a

thick, regional volcaniclastic deposit. Surdam and Stanley (1980) documented a hydrologic

connection between the Green River Basin and the Absaroka volcanics based on paleocurrent

measurements and clastic provenance study of the Sand Butte Bed of the Laney Member.

This hydrologic connection is further examined in this dissertation through geochemical and

stratigraphic means.

13 Within the Absaroka Volcanic Province exists one of the most structurally enigmatic

features in North America, the Heart Mountain detachment (HMD). In short, the HMD,

exposed over a 3400 km2 area of northwestern Wyoming, is composed of a break-away fault

where the upper plate of the detachment is interpreted to have originated, a bedding plane

fault that follows resistant Ordovician dolomite, and a transgressive fault over which

Paleozoic strata and Tertiary volcanics co-exist and overlie the Eocene land surface. This

controversial structure was first described by Dake (1918), and has subsequently been the

focus of an ongoing structural debate regarding emplacement rate: was the HMD formed

catastrophically as suggested in variations of the “tectonic denudation” model of Pierce

(1973, 1987), or was it the result of a slower process as proposed in the continuous

allochthon model of Hauge (1985, 1990). Malone (1995, 1996, 1997) argued for

catastrophic emplacement based on his interpretation of a large debris avalanche deposit

associated with Heart Mountain faulting, mapped as the Deer Creek Member of the Wapiti

Formation. Given evidence of a hydrologic connection between the Absaroka region and the

Green River Basin (Surdam and Stanley, 1980), and the current geochronologic constraints

for Heart Mountain faulting (49.5-47.5 Ma; Pierce, 1973, 1987; Torres and Gingerich, 1983)

and Laney Member deposition (49.02 ± 0.15 Ma; Smith et al., 2001), it is possible that a

sedimentary record of Heart Mountain faulting exists in the Green River Basin, and that it

will elucidate one of the proposed emplacement models.

14 5. CLIMATE STUDIES

5.1. Paleofauna

The paleofauna of the Green River Basin consists of numerous lacustrine and

terrestrial organisms through which paleoenvironment and paleoclimate interpretations have

been drawn. Lacustrine environments were filled with gastropods, bivalves, ostracodes, and

fish, while turtles, crocodiles, and birds lived along the lake margins (Hanley, 1974). The

faunal assemblages that characterized lacustrine environments in general can be used to

interpret water conditions due to variations in salinity tolerance. However, the lacustrine

fauna of the Green River Formation is likely very endemic and any information about water

chemistry is better derived from isotopic study of their tests.

Terrestrial faunal assemblages are either directly related to climate conditions (such

as the occurrence of reptiles) or indirectly related to climate through their relationship with

vegetation. The number of arboreal mammals increased throughout the middle early Eocene

time, which indicates a tropical forested vegetative landscape (Wilf, personal

communication, 1999). Mammal size distributions are used to approximate climatic

conditions (Clyde et al., 1997), however during this time, mammals started to move into

habitats that were previously held by reptiles. This may have had an evolutionary impact on

body size, independent of climate.

Mammalian stratigraphy is relatively coarse and its utility depends upon precise

correlation from terrestrial environments to laterally equivalent lacustrine equivalents. To

make paleontologic observations meaningful in a global stratigraphic framework, Clyde et al.

(1997) attempted to correlate North American Land Mammal Ages (NALMA) in the Green

River Basin to the Geomagnetic Polarity Time Scale to constrain relative ages. They

15 concluded that the Wasatchian/Bridgerian NALMA is either correlative within Chron23r (52

Ma), or Chron22r (50.5 Ma). Recent work by Smith et al. (in review) reinterpreted this

correlation and concluded that the major faunal turnover event occurred after Chron23n.

It is widely known that the Cenozoic global temperature maximum occurred during

early Eocene time (Clyde et al., 1997, and references therein). This fact has prompted many

evolutionary studies and consequently, there have been a number of fossil mammals

collected from the marginal alluvial facies in the Green River Basin. Important vertebrate

fossils recovered from the early to middle Eocene strata are, Lambdotherium and Cantius

from the Wasatchian fauna; and from the beginning of Bridger NALMA, Hyrachus,

Palaeosyops, Omomys, Notharctus, and Smilodectes (Krishtalka et al., 1987). This was also

a time of maximum reptilian diversity which indicates the tropical nature of the climate

(Hutchison, 1982; Markwick, 1994).

Ostracodes represented in the Green River Formation include Hemicyprinotus

watsonensis, Heterocypris, Procyprois, Potamocypris, Pseudoeucypris, and Cypridea, of the

superfamily Cypridacea. Forester (personal communication, 1999) determined that most of

the Green River ostracodes have subtropical to tropical affinities. From this data, he

suggested that any early to middle Eocene seasonality may be related to moisture rather than

temperature.

5.2. Models

Paleoclimate models are used as a way to understand climate boundary conditions for

particular time periods. Paleoclimate models are created with detailed observations about

paleogeography, paleoflora, and paleofauna. Sloan (1994) constructed a computer model for

16 Eocene time to improve previous models for which the modeled climate did not agree with

the paleodata available (Sloan and Barron, 1992). Sloan (1994) considered the “lake effect”

of the Green River Lakes on paleoclimate models. She found that the model of Eocene

climate in North America with atmospheric CO2 levels that are 6 times modern levels was

similar to the model with 2 times CO2 levels plus the presence of a large paleolake.

However, with the paleolake included in the model, the winter freeze line was deflected too

far poleward which, again, did not honor the paleodata.

Most recently, Morrill et al. (2001) simulated a general circulation model and used

the output to drive lake energy balance, and lake water balance models for Lake Gosiute for

the two climate end members of the precessional cycle to test for a possible connection

between orbital cyclicity and sedimentation. They concluded that the effects of changing

shortwave radiation were likely more important than temperature and moisture on lake level

fluctuations. This result may be model dependent because their general circulation model

predicted little or no precipitation changes in response to orbital forcing. Changes in

seasonality were predicted during a precessional cycle which would likely affected

vegetation, the amount of snowmelt runoff, and the area of exposed mudflats that surrounded

the lake, all variables that would greatly influence the water balance of the lake. Model

results suggested that the stratigraphic stacking patterns within the Green River Formation

could have been greatly influenced by local non-climate variables (Morrill et al., 2001).

Hydrologic models of Kutzbach (1980) and Morrill et al. (2001) illustrate an

important relationship between the size of the lake and the size its associated drainage basin.

A small lake relative to the size of its drainage area is more sensitive to changes in runoff and

precipitation than a large lake with a small drainage basin. A reasonable estimate of the size

17 of Lake Gosiute in comparison to the size of its drainage basin is roughly 1:10. This ratio

indicates that Lake Gosiute could have had a significant response to changes in its hydrologic

budget.

5.3. Paleoflora

Paleofloral analysis has been used in the Green River Formation to approximate

climatic conditions through early to middle Eocene time (Brown, 1928, 1934; MacGinitie,

1969; Axelrod, 1968; Leopold and MacGinitie, 1972; Wolfe, 1998; Wilf, 2000). Eocene

floral assemblages that contain species that exist today or have a modern analog can be used

to make direct climate interpretations. Species that do not exist in modern assemblages or

have no modern analog can be studied for paleoclimate interpretations using a technique

called Leaf Margin Analysis. Leaf Margin Analysis is a univariate technique based on the

positive correlation of mean annual temperature to the proportion of species in an assemblage

with untoothed margins (Wilf, 1997).

Thousands of plant fossils in the Green River Basin comprising about 200 species

were collected for paleobotanical analysis (Wilf, 2000). The climate in the latest Paleocene

time is interpreted to have been a humid, warm-temperate floodplain forest dominated by

trees in the birch, laurel, and bald cypress families (Wilf, personal communication 1999) with

a mean annual temperature of about 15° C and rainfall of 1.5 m/yr. The early Eocene

assemblages (dominated by alders, tree ferns, and a genus called Platycarya) indicate a

humid subtropical swamp forest with a mean annual temperature interpreted to be around 22°

C. This is an important interpretation for the Green River Basin floras because it means that

a warm, wet climate existed in the area before Lake Gosiute existed. The latest early Eocene

18 was warm (about 19° C) and more arid than the early and middle early Eocene (< 1m/y

precipitation). The dominant floras had shifted again to include plants of the bean, sumac,

and elm families (Wilf, 2000).

The Little Mountain floral assemblage from the upper Wilkins Peak and lower Laney

members is a transitional assemblage between a period of maximum aridity during Tipton

and lower Wilkins Peak deposition and a very moist climate represented by the upper

LaClede Bed of the Laney Member (Wilf, 2000).

6. RESEARCH APPROACH

6.1. Lacustrine sequence stratigraphy

With little exception, the majority of lacustrine sequence stratigraphic research has

focused on applying marine sequence stratigraphic concepts to understand the stratigraphic

packaging in modern and ancient extensional lacustrine basins. Analysis of the stratal

geometries within the African rift lakes has resulted in important contributions to the

understanding of development and evolution of petroleum systems in young ocean basins

(Tiercelin et al., 1992; Scholtz and Finney, 1994; Dam et al., 1995; Johnson et al., 1995;

Scholtz, 1995; Soreghan and Cohen, 1996). Marine sequence stratigraphic terminology and

processes were adapted to Cretaceous rift deposits in NE China to advance petroleum

systems concepts and to bring into question the relative importance of sequence boundaries

vs. flooding surfaces for non-marine environments where the presence and extent of water

(and its resultant sedimentation) is more significant than the dominant processes of erosion

and non-deposition (Xue and Galloway, 1993). Olsen et al (1996) and Smoot (1991)

interpreted complex tectonic and climatic controls on sedimentary facies and lacustrine

19 stratigraphy in the Mesozoic Newark Supergroup, a rift basin in eastern North America.

Several sequence stratigraphic investigations have been completed within Quaternary Lake

Bonneville (Oviatt et al., 1994; Milligan and Chan, 1998; Lemons and Chan, 1999) as the

fine and coarse-grained deltas into basin provide an excellent outcrop analog for subsurface

exploration of closed lacustrine basins in an extensional tectonic regime. Seismic facies

analysis and sequence stratigraphic interpretation of the strata within the Neogene Pannonian

Basin, a Mediterranean type back-arc basin, concluded that the lacustrine stratal geometries

are the same as have been described for marine sequences (Vakarcs et al., 1994). These

sequences have been correlated to the global eustatic sea level curve, indicating a possible

marine teleconnection.

The Green River Basin is a unique tectonic setting within which to conduct sequence

stratigraphic studies. Until very recently (Pietras et al., 2000; Rhodes and Carroll, 2001,

2002), very few studies have been sequence stratigraphic in nature. Extending traditional

marine sequence stratigraphic concepts, Bartels and Zonnenfeld (1997) proposed the term

“terrasequences” for intervals bounded by lacustrine flooding surfaces in the alluvial

Wasatch and Bridger Formations and the laterally equivalent lacustrine Green River

Formation. Bohacs (1998) addressed the utility of geophysical and geochemical indicators in

establishing a sequence stratigraphic framework for lacustrine mudrocks, with examples

from the Green River Formation. Lake basin type, for which the Green River Basin has

provided descriptive examples (Carroll and Bohacs, 1999), is interpreted to have an influence

on the sequence stratigraphic expression and hydrocarbon potential of the strata preserved.

Shaney and McCabe (1994) addressed the inherent differences between marine and

non-marine sequence stratigraphy (base-level, role of climate, environments of deposition).

20 They argued that marine sequence stratigraphic terminology can “easily be applied to

lacustrine systems”. However, lake levels, unlike sea level, are highly variable because there

are many more controls on the presence or absence of water within the system. For example,

the amount of water in a basin is a function of local climate which drives the precipitation,

evaporation, and the development of local and regional groundwater tables. The evolution of

tectonic and geomorphic sills, along with basin subsidence and physiography, control the size

of the basin and its potential accommodation (Milligan and Chan; 1998; Lemons and Chan,

1999; Carroll and Bohacs, 1999; Pietras et al., in press). Variation in the size of the

catchment area through stream piracy or by vertical growth of volcanic edifices in the

drainage basin provides another potential control on the amount of water available to a lake.

Because sedimentation is directly tied to the delivery of water to a basin, the controls on

sedimentation in lacustrine environments are fundamentally different than for marine

environments. High frequency fluctuations in lake level cause numerous unconformable

surfaces to develop. It is difficult to recognize the surfaces that are significant enough to be

labeled as sequence boundaries and whether or not those boundaries separate genetically

unrelated stratigraphic packages. The development and preservation of lacustrine sequences,

sequence boundaries, and other significant surfaces may depend upon a number of pre-

existing basin conditions.

Carroll and Bohacs (1999) recognized the need to develop a method by which to

classify lake types. They define three genetic lake types constrained by potential

accommodation rate and water + sediment fill rate. Each lake type (overfilled, balance-filled,

and underfilled) corresponds to a separate lacustrine facies association in the stratigraphic

record. The large-scale packaging of the Green River Formation exemplifies their lake type

21 classification. The evaporative facies association is typified by the aggradational stacking of

evaporitic units in the basin center and alluvial sheetfloods on the shoreline. This association

is indicative of an underfilled lake and is characterized by the upper Wilkins Peak Member of

the Green River Formation. The fluctuating profundal facies association is composed of

progradational carbonate and siliciclastic units, and strata that represent cyclic flooding,

progradation, and desiccation. The lower LaClede Bed of the Laney Member typifies this

facies association, where organic rich micritic mudstone capped by lake marginal dolomitic

mudstone suggests lake expansion and contraction, indicative of a balance-filled lake. The

Fluvial-Lacustrine Facies Association is characterized by thick, progradational

parasequences of micritic mudstone and siltstone, shelly coquinas, sandy deltas, and coals

typical of overfilled, hydrologically open lakes. The Luman Tongue and the uppermost

Laney Member contains facies characteristic of the fluvial-lacustrine facies association.

Important paleogeomorphic and paleohydrologic interpretations can be made by

recognizing the evolution of these facies associations, such as the relationship of lake level to

sill level and the relative size of the drainage network. These interpretations are enhanced

when considered in a sequence stratigraphic framework. In Chapter 2, the interpreted

lacustrine sequence stratigraphy and its relationship to shifting lake-types within the Laney

Member is described in detail.

6.2. Strontium isotope composition

The utility of Sr isotopic analysis of lacustrine carbonate material for paleohydrologic

study has been demonstrated for several late Cenozoic lake deposits (Jones and Faure, 1972;

Rosenthal et al., 1989; Stewart et al., 1993; Ullman and Collerson, 1994; Bensen and

22 Peterman, 1995; Lent et al., 1997; Stein et al., 1997; Bouchard et al., 1998; Stewart, 1998;

Talbot et al., 2000). In these studies, freshwater limestones, tufa deposits, evaporites, shell

material, brines, groundwaters, surface waters, and precipitation were analyzed for their Sr

isotope composition in order to trace sources of water into particular lacustrine systems over

time. Because a limited range in the 87Sr/86Sr ratio for Phanerozoic seawater has been

previously established (~0.707-0.709; Burke et al., 1982), many studies have analyzed the Sr

isotope composition of carbonates to simply verify that it lies outside of this range and

therefore represents a non-marine depositional environment (Faure and Barret, 1973;

Donnelly and Jackson, 1988; McCulloch and DeDeckker, 1989; Spencer and Patchett, 1997;

Poyato-Ariza et al., 1998; Vonhoff et al., 1998). Other than the work presented in this

dissertation, there have been very few Sr isotopic studies of older lacustrine units (Neat et al.,

1979; Albarede and Michard, 1987; Pietras et al., 1999). Neat et al. (1979) documented

significant variation in the 87Sr/86Sr ratio (0.70890 – 0.71260) from the carbonate facies of

the Paleocene-Eocene lacustrine Flagstaff Formation and attribute that variation to the

occurrence of geological events in the drainage basin combined with a possible influence

from the period influx of volcaniclastic material to the lake. Given the framework

established from the numerous studies completed in the Green River Basin, variations in the

Sr isotope composition of carbonate material in the Laney Member of the Green River

Formation can be interpreted to be the result of specific controls on lake evolution (ie.

climatic vs. tectonic). The specifics of the Sr isotope system are as follows.

Strontium (Sr) is an alkaline earth element with chemical properties that are very

similar to those of calcium (Ca) allowing Sr to substitute for Ca in carbonate mineral

matrices. Rubidium (Rb) is approximately the same size and charge as potassium (K) and

23 therefore commonly substitutes for K in crystal lattices (typically feldspar and clay minerals).

With a half life of ~48.8 x 109 years, 87Rb radiogenically decays to 87Sr over time (β- decay),

therefore the abundance of 87Sr is slowly being adjusted in the system. The abundance of the

four naturally occurring Sr isotopes known (84Sr, 86Sr, 87Sr, 88Sr) and therefore the 87Sr/86Sr

ratio of a rock/mineral, is a measurement of the amount of natural 87Sr isotope plus the

amount of radiogenic 87Sr. (86Sr has a similar natural abundance making the 87Sr/86Sr ratio

sensitive to change). The 87Sr/86Sr ratio of a rock depends on its age and Rb/Sr. Through the

processes of mechanical and chemical (differential) weathering, the isotope composition of

an uplift will be incorporated into surface water runoff (Sr like Ca, is easily carried in

solution) and the sediment that will ultimately be deposited into an adjacent basin (Faure,

1991). Therefore, the isotopic composition of Sr in a lake is a function of the 87Sr/86Sr ratios

of the surrounding uplifts.

To determine the Sr isotopic composition of ancient Lake Gosiute, carbonate minerals

were analyzed from micritic and dolomicritic mudstone, tufas, stromatolites, and dolomitic

and volcaniclastic siltstone (methods are described in chapters 3 and 4). Previously reported

paleocurrent directions (Figure 1.3) suggest there was a shift in provenance from the south

and east (Uinta Mountains, Granite Mountains, and Sierra Madres) to sediment derived from

the north (Absaroka volcanics) coincident with the deposition of the Laney Member. Surdam

and Stanley (1980) determined, in a petrographic study, that the Sand Butte Bed of the Laney

Member was derived from the Absaroka Volcanic Range. This indicates that less radiogenic

drainage was incorporated into the basin during Laney time, and highlights the probable

utility of Sr as a lakewater provenance tool for Laney Member carbonates. Table 1.1

summarizes the average 87Sr/86Sr ratios of uplifts surrounding the Green River Basin.

24 All specimens referenced in this thesis are in the collections of the Department of

Geology and Geophysics, University of Wisconsin – Madison, under file number UW1941.

25

Table 1.1.

Location Area/lithology No. of analyses reported

Rb a

(ppm)Sr a

(ppm)

87Sr/86Sr b Reference

Absaroka Range andesite, trachybasalt, rhyodacite welded tuff, absarokite 14 109 1 032 0.706 16 Peterman et al., 1970Independence Volcano 19 161 577 0.705 81 Meen and Eggler, 1987average 27 86 972 0.705 06 Hiza, 1999

Owl Creek Mountains Archean volcanics 18 61 169 0.743 82 Mueller et al., 1985Archean granite 20 192 190 0.939 92 Hedge et al., 1986

Granite Mountains granites 33 245 150 0.877 32 Peterman and Hildreth, 1978metamorphics 15 204 216 0.838 38 Peterman and Hildreth, 1978

Wind River Range banded gray gneiss, Native Lake gneiss, Bridger batholith, Louis Lake batholith, Bears Ears batholith, South Pass granites 39 82 445 0.724 51 Frost et al., 1998

Laramie Range Sherman Granite 4 164 137 0.774 40 Zielinski et al., 1981Cheyenne Belt 20 96 75 0.830 26 Patel et al., 1999

Sierra Madre quartz biotite gneiss, Baggot Rocks Granite, Encampment River Granodiorite, Green Mountain Formation, Big Creek Gneiss, Sierra Madre Granite, white quartz monzonite, North Park Granite 40 120 331 0.731 10 Divis, 1977

Uinta Mountains Uinta Mountain Group, Red Pine Shale 3 190 111 0.782 94 Critenden and Peterman, 1975

Uinta, Sevier Thrust, Wind Rivers

Paleozoic marine clastics and carbonates

1000 - 10000 0.707-0.709 Burke et al., 1982

a Average ppm. b Concentration weighted average.

Reported strontium isotopic composition for Greater Green River Basin bounding uplifts

26

Chapter Two

Lacustrine Sequence Stratigraphy of the Laney Member, Green River Formation, southwestern Wyoming

27 ABSTRACT

The complex sequence stratigraphic packaging of the Laney Member records an

overall trend toward decreasing basin subsidence, erosion of basin sills, and increasing

sediment + water supply. At the base of the Laney Member, balanced fill strata of the lower

LaClede Bed constitute a sequence set that is divided into 4 sequences, each of which is

recognized by an exposure surface and basinward shift in facies at its base. Internally each

of these sequences comprises repeated 1-3 m lacustrine parasequences. The 4 sequences thin

upward in succession, which we interpret to record net expansion of Lake Gosiute and a

resultant decrease in sedimentation rates near the basin center. Near the top of this

succession alluvial facies are closely interbedded with profundal muds, suggesting a decrease

in basin-floor gradient.

The overlying “buff marker” bed and upper LaClede and Sand Butte Beds together

are interpreted as a single sequence that includes both balanced fill and overfilled strata.

Deposition of this sequence coincided with a major re-organization of the basin, and by a

shift in profundal sedimentation from west to east across the Rock Spring Uplift. The basal

sequence boundary represents a major desiccation event, marked by desiccation cracks up to

3 m deep that formed in underlying profundal mudstone. Volcaniclastic and intraclastic

fluvial strata were deposited above this sequence boundary, followed by a series of

retrogradational, balanced-fill lacustrine parasequences that culminate in a maximum

expansion surface. This surface marks a threshold above which the basin remained

hydrologically open. The basin was subsequently infilled by progradation of volcaniclastic

deltaic sediments as lake level remained relatively stable.

28 1. INTRODUCTION

Lacustrine sequence stratigraphy has been pioneered in recent decades by researchers

who recognized the need to understand the depositional controls on and geometries for some

of the most economically and scientifically important sedimentary basins in the world (Xue

and Galloway, 1993; Scholz, 1995; Scholz et al., 1998; Vakarcs et al., 1994; Oviatt et al.,

1994; Dam et al., 1995; Milligan and Chan, 1998; Lemons and Chan, 1999; Bohacs, 1998;

Bohacs et al., 2000; Shanley and McCabe, 1994). Within many studies, marine sequence

stratigraphic concepts have been used to describe the lacustrine sequence stratigraphic

evolution of lake basins. While superficially this may seem appropriate, this analogy has

serious limitations, particularly with respect to isolating sediment supply from highly

variable lake levels. The sensitivity of lacustrine systems to changes in the hydrologic

budget of a basin (climatically and tectonically controlled) is apparent due to the preservation

of rapid facies changes and numerous genetically insignificant erosional surfaces in

lacustrine strata, adding to the complexity of lacustrine sequence stratigraphic interpretation.

While local climate drives the amount of water available to a drainage basin, neither

modern lake size, depth, or salinity correlate to prevailing climate conditions indicating that

the potential accommodation (primarily a tectonic control) of a basin exerts a major control

on the presence or absence of lacustrine environments (Carroll and Bohacs, 1999). From this

observation, the structural history of a lake basin can be interpreted to have a major influence

on lacustrine stratal architecture. This structural control on stratal geometries has been

demonstrated within rift basins (Xue and Galloway, 1993; Dam et al., 1995; Scholz, 1995;

Johnson et al., 1995; Scholz et al., 1998) and extensional basin and range settings (Oviatt et

29 al., 1994; Milligan and Chan, 1998; Lemons and Chan, 1999), but is less understood for other

basin types.

The Green River Formation is perhaps the best known interval of lacustrine strata in

the world, making it ideal for studying the stratigraphic expression of and probable

mechanisms for the formation and preservation of lacustrine sequences and significant

lacustrine surfaces. Additionally, the Laramide dissected Sevier foreland basin within which

Eocene Lake Gosiute was impounded to deposit the Green River Formation is a unique

structural regime. The development and subsequent interpretation of lacustrine sequence

boundaries in a foreland basin surrounded by compressional orogens may broaden our

understanding of patterns of sedimentation in lacustrine environments.

Despite being the focus of extensive previous studies, there has been relatively little

research on the sequence stratigraphy of the Green River Basin strata (Bartels and

Zonnenfeld, 1997; Bohacs, 1998; Bohacs et al., 2000; Pietras et al., 2000; Rhodes and

Carroll, 2001, 2002) or for specific controls on deposition vs. erosion within different

stratigraphic levels (Rhodes et al., 2002; Pietras et al., 2001; Pietras et al., in press; Rhodes et

al., in review). The strata of the Laney Member of the Green River Formation mark the final

stages of Eocene Lake Gosiute and represent the shift in genetic lake types from balanced fill

to overfilled (Roehler, 1973; Surdam and Stanley, 1979; 1980; Carroll and Bohacs, 1999).

Previous work on lake basin type and the geophysical response of fine-grained lacustrine

sediments facilitate the development of a detailed correlation and sequence stratigraphic

interpretation across this change in lake type (Bohacs, 1998; Carroll and Bohacs, 1999).

The Laney Member is composed of oil shales that characterize the LaClede Bed,

volcaniclastic mudstone to sandstone of the Sand Butte Bed, and shallow freshwater facies of

30 the Hartt Cabin Bed (Roehler, 1973). The stratigraphic relationship between the LaClede

and Sand Butte beds has been interpreted to be either unconformable (Roehler, 1992) or

gradational (Surdam and Stanley, 1979, 1980). The sequence stratigraphic analysis of Laney

strata can be used to better understand stratigraphic relationships observed in the field.

This study is a detailed lithologic description and sequence stratigraphic interpretation

across the major shift in basin hydrology within the Laney Member exposed along the

Delaney and Kinney Rims of the Washakie Basin and correlated to Firehole Canyon in the

Green River Basin, highlighting the facies, facies associations, lateral facies changes,

conditions of formation and preservation of significant stratal surfaces, and the evolution of

lacustrine stratigraphic stacking patterns (Figure 2.1).

31

Figure 2.1. The geology of the Greater Green River Basin, southwestern Wyoming

(modified from Witkind and Grose, 1972). The inset box marks the location of the

Figure 2.2.

32 1.1. Geologic setting

During Early to Middle Eocene time, Lake Gosiute was impounded in the subsiding

Green River Basin of southwestern Wyoming by Laramide-style uplifts that dissected the

foreland of the Sevier Thrust Front (Bradley, 1964; Roehler, 1993 Figure 2.1). The Laney

Member of the Green River Formation marks the final transition from a saline lake to a

freshwater lake that was progressively in-filled with sediment from the north during the

waning stages of Laramide deformation (Surdam and Stanley, 1980; Roehler, 1993; Carroll

and Bohacs, 1999). It is comprised of the LaClede Bed that is dominated by oil shales, Sand

Butte Bed composed of volcaniclastic siltstone and sandstone, and the Hartt Cabin Bed

composed of shallow, freshwater deposits (Roehler, 1973). The LaClede Bed records the

maximum extent of Lake Gosiute (Roehler, 1993) and is divided into upper and lower units

by a dolomitic volcaniclastic unit informally known for its distinctive appearance in outcrop

as the “buff marker” bed (Roehler, 1973). Roehler (1992) interpreted the depocenter of the

LaClede bed to be along the northeast side of the Uinta Mountains in the Washakie subbasin

of the Greater Green River Basin where roughly 240 meters of stratigraphic section recorded.

The Sand Butte Bed of the Laney Member is a volcaniclastic deltaic unit that overlies the

lower LaClede Bed and, as previously mentioned, has been interpreted to unconformably or

gradationally overlie the upper LaClede bed (Roehler, 1992; Surdam and Stanley, 1979,

1980). The Sand Butte Bed currently exposed in outcrop along the flanks of the Rock

Springs Uplift. Paleocurrent measurements and petrographic analysis of this strata indicate

that the delta prograded across the basin from the north to the south and that the sediment

was sourced in the Absaroka volcanic region (Surdam and Stanley, 1980).

33 2. FIELD LOCATIONS AND DATA COLLECTION

Correlation of strata along the Delaney and Kinney Rims of the Washakie Basin and

to Firehole Canyon in the Green River Basin was completed by describing 11 stratigraphic

sections in centimeter scale detail and logging 2 subsurface cores taken from near the outcrop

exposures (Figure 2.2, see Appendix B for measured sections). Two of the sections, Dirt Hill

and Section Line, are poorly exposed but were measured in an attempt to extend the upper

LaClede correlation northward along the Delaney Rim. The two cores, Arco Oil and Gas

WB1 and Arco Oil and Gas 2WB, are housed in the USGS Core Repository in Denver, CO,

and were logged and correlated to outcrop sections (Figure 2.2).

Outcrop correlation was facilitated by measuring the ppm U, ppm Th, %K, and total

gamma radiation at 50-cm intervals throughout 7 sections with a hand held gamma ray

scintillometer (GR-320 enviSPEC portable gamma ray spectrometer, manufactured by

Exploranium). Each interval was measured for a total of 60 seconds. Gamma ray

calculations were processed using Explore software (Exploranium Radiation Detection

Systems, 1998, Software Version 3V02; see Appendix C for gamma ray data). The natural

gamma ray spectrum of lacustrine strata reflects changes in volcanic input (K, Th) and

detrital heavy minerals (U) (Bohacs, 1998), and has proven to be an excellent correlation tool

for Laney strata. In lacustrine environments influenced by volcaniclastic sands, %K

measures the potassium feldspar within the sandstone, ppm Th measures volcanic ash input,

and ppm U measures detrital heavy minerals (Bohacs, 1998).

34

Figure 2.2. Location map of the measured sections and core along the Delaney and Kinney

Rims, Washakie Basin and in Firehole Canyon, Green River Basin. NBS = North

Barrel Springs; WB = Wells Bluff; SL = Section Line; TR = Table Rock; DH = Dirt

Hill; RW = Red Wash; DE = Delaney East; DW = Delaney West; AC = Antelope

Creek; SB = Sand Butte; TD = Trail Dugway; FC = Firehole Canyon.

35 3. FACIES DESCRIPTIONS

Several past studies have documented details of the Laney Member sedimentary

facies (Bradley, 1964; Roehler, 1992; Buchheim, 1978; Stanley and Surdam, 1978; Surdam

and Stanley, 1979, 1980; and Kornegay and Surdam, 1980). The descriptions that follow

summarize aspects of these previous studies and add our own new observations. The

organization of the facies presented here provides the basis for the sequence stratigraphic

interpretation that follows.

Nine separate facies of the Laney Member (and 1 from the Wasatch Fm.) along the

Delaney and Kinney Rims are described here in detail for the purposes of building a

hierarchy of strata. These facies include laminated dolomicritic mudstone, laminated micritic

mudstone, massive dolomicritic mudstone, algal stromatolite, massive dolomicritic silty

mudstone, ostracode, oolitic, and intraclastic grainstone, dolomitic volcaniclastic siltstone

and sandstone, volcaniclastic sandstone, lithic sandstone, and variegated silty mudstone

(Table 2.1).

3.1. Laminated dolomicritic mudstone

Laminated dolomicritic mudstone is brown in color and characterized by mm-scale

interbedded laminae of organic matter and dolomicrite. Ostracodes and fish fossils are

common in this facies. Laterally extensive mm- to cm-scale analcimated tuff stringers are

found throughout this facies.

This facies is interpreted to represent profundal deposition from brines along the lake

bottom during initial lake expansion over evaporatively concentrated mudflats. Dolomite,

formed by evaporative pumping from the groundwater table, was transported to the lake for

36 deposition or re-precipitation, (Desborough, 1978) in anoxic bottom waters (Wolfbauer and

Surdam, 1974).

3.2. Laminated micritic mudstone

Laminated micritic mudstone is the dominant facies in the LaClede Bed of the Laney

Member (Figure 2.3). It is characterized by tan to gray-brown organic-rich micritic

mudstone (oil shale) that contains µm-scale parallel to wavy lamination, abundant ostracode

and fish fossils, and mm- to cm-scale analcimated tuff stringers.

This facies is interpreted to represent a profundal lacustrine environment due to the

preservation of fish fossils and mm-scale laminations (Bradley, 1929; Buchheim and

Surdam, 1977). The preservation of µm-scale laminations indicates the absence of bottom

dwelling organisms and the deposition of sediments on a broad flat lake bottom below wave

base and unaffected by internal lacustrine currents. From this, anoxic bottom-waters can be

interpreted, similar to those conditions that exist in modern day Green Lake of Fayetteville,

New York (Ludlam, 1969) or Lake Zurich, Switzerland (Bradley, 1929; Kelts and Hsü,

1978). However, as Buchheim and Surdam (1977) reported, the recovery of catfish fossils

from the laminated micritic mudstone facies of the Laney Member indicates that aerobic

hypolimnetic waters must have periodically existed.

3.3. Massive dolomicritic mudstone

The massive dolomicritic mudstone contains tan to dark brown, massive dolomicritic

mudstone with ostracodes, evaporite casts, algal laminations, and mudcracks.

37 This facies is interpreted to represent the transition from sublittoral to littoral to

supralittoral lacustrine environments that occurs during lake contraction. Wolfbauer and

Surdam (1974) investigated the possible origin of dolomite in the Laney mudstone and

concluded that it formed penecontemporaneously through evaporative pumping in a mudflat

environment. This mechanism of dolomite formation has been documented in the

Quaternary Coorong region of South Australia (von der Borch et al., 1975). Dolomite

created in the mudflat environment may have then been available for transport into profundal

lacustrine environments where it was deposited as laminated dolomicritic (cf. Smoot, 1983).

Alternatively, the dolomite in laminated profundal facies may have originated through

microbial sulfate reduction associated with the anaerobic degradation of organic matter

(Baker and Kastner, 1981; Powell, 1986; Kelts, 1988; Bohacs et al., 2000).

38 Table 2.1. Facies of the Laney Member and laterally equivalent strata.

Facies

Description

Occurrence

Interpretation

laminated dolomicritic mudstone

Brown to blue-gray mm-scale laminated mudstone, ostracode and fish fossils common

Minor component within the Lower LaClede Bed at DE, DW, AC, and FC sections.

Deposition in profundal lacustrine environment during initial lacustrine expansion

laminated micritic mudstone

Brown to blue-gray planar to wavy millimeter-scale organic and carbonate laminations, abundant ostracode and fish fossils

Dominant lithology within DE, DW, AC, WB2, SB, TD, FC, and WB1 sections/core

Profundal lacustrine

massive dolomicritic mudstone

massive tan dolomicritic mudstone, evaporites and mudcracks are common near the top of massive beds

Minor component within the Lower LaClede Bed at DE, DW, AC, and FC sections. More commonly found within the Lower and Upper LaClede Beds at SB, TD, and WB1.

Littoral (massive beds) lacustrine environment. Dolomite from exposed mudflats through evaporative pumping and washed into the lake during contraction and lowstand.

algal stromatolites algal mats elongate stromatolites individual domal stromatolites

Laterally continuous thin (cm-scale) algal mats, associated with rip-up clasts, oolites, and ostracodes Individual elongate (~40-cm long) stromatolites associated with lithic sandstone Individual domal (~50 to 60-cm diameter) stromatolites weather by concentric delamination

Dominant morphology within the Lower LaClede (and lowermost Upper LaClede) at TR, DE, DW, WB2, AC, TD, and WB1. Found only at the TR section Ridge forming unit at NBS

Broad, low relief lake marginal environment unaffected by wave scour. Fluvial environment where strong currents (normal to shoreline) influenced morphology Fluvial/lacustrine environment influenced by currents multi-directional currents

massive dolomicritic silty mudstone

Massive tan to pink silty dolomicritic mudstone with chert nodules, root casts

Found at AC and TD Paleosol

Ostracode, oolitic, and intraclastic grainstone

Massive white-tan med-coarse grained ostracode, oolitic, and intraclastic grainstone, silicified to very friable in outcrop, rare gastropods

Predominantly found at the NBS, WB, SL, and TR sections. Found associated with algal facies at DE, DW, AC, WB2, SB, WB1, and TD.

Littoral lacustrine shoal or beach environment

dolomitic volcaniclastic siltstone and sandstone

Silt to medium sized volcaniclastic sand, beds coarsen and thicken upward, then fine and thin upward. Rip-up clasts occur in discrete horizons before the unit thins upward. Dolomite rhombs make up > 50%.

Found at DW, WB2, AC, SB, WB1, TD, and FC. The best exposure is at the TD section.

A progradational to transgressive unit that is interpreted to represent rapid sedimentation into the basin as a result of an extrabasinal event.

volcaniclastic sandstone Gray brown silty mudstone with plant fragments, gray siltstone, and very fine gray brown volcaniclastic sandstone

Caps the sections along the Kinney Rim, AC, DW, and DE. Caps the section in Firehole Canyon.

Fluvial/Deltaic

lithic sandstone

Fine to coarse grained micaceous lenticular to laterally continuous sandstone with trough cross beds, asymmetrical ripples, burrows, and iron nodules.

Found in the NBS, WB, TR, and DW sections

Fluvial sandstone and sheet flood sands

variegated silty mudstone

Variegated silty mudstone with claystone, and fine sand to pebble sized clasts

Found at the NBS section and at the base of the WB, TR, DE, DW, and AC sections

Alluvial flood plain environment.

39

Figure 2.3. The laminated micritic mudstone facies in outcrop along the Kinney Rim in the

Washakie Basin, LaClede Bed of the Laney Member, Green River Formation.

40 3.4. Algal stromatolite

The algal stromatolite facies contains within it a number of different stromatolite

morphologies; laterally extensive algal mats, individual elongate stromatolites, and solitary

domal stromatolites. Laterally extensive algal mats are found within the Antelope Creek

(AC) section. These units are 10-30 cm thick, weather black and tan in outcrop, and are

typically underlain by dolomicritic rip-up clasts and interbedded with ostracode, oolitic, and

intraclastic grainstone (Figure 2.4a). Individual elongate stromatolites occur in the Table

Rock section in a more lake marginal position than the algal mats at Antelope Creek (Figure

2.4b). These stromatolites were formed over a scoured surface and are more intimately

associated with lithic sandstone and ostracode and oolite facies. Solitary domal stromatolites

in the North Barrel Springs (NBS) section are 0.5- to 1.0- m in diameter and are also found in

association with lithic sandstone and associated variegated silty mudstone facies (Figure

2.4c).

Modern stromatolites have formed in Green Lake of Fayetteville, New York

(Eggleston and Dean, 1976), the Great Salt Lake (Halley, 1976), and Lake Tanganyika

(Cohen and Thouin, 1987; Casanova and Hillaire-Marcel, 1992). These algal buildups have

been documented to occur in lake marginal and fluvial environments. Additionally, changes

in stromatolite morphology can be interpreted to indicate variations in lake water energy

(Gebelein, 1969) and shoreline topography. Stromatolites in the Laney strata are interpreted

to have been formed during lake expansion (Buchheim, 1978). Algal mats in the Laney

Member are interpreted to have formed along a low gradient lake margin where wave energy

was insufficient to scour (Buchheim, 1978). The shape of elongate and domal stromatolites

41

Figure 2.4. Stromatolite morphologies within the Laney Member. A) Top view of algal mats

from the Antelope Creek section; B) Elongate stromatolites from the Table Rock

section; C) Domal stromatolite from the North Barrel Springs section.

42 in Laney strata was likely influenced by unidirectional currents within fluvial environments

or a result of increasing wave scour closer to the lake margin (Platt and Wright, 1991).

3.5. Massive dolomicritic silty mudstone

The massive dolomicritic silty mudstone facies weathers pinkish-tan and spheroidally

in outcrop (Figure 2.5). In outcrop, this facies is typically 0.5 to 2.0 meters thick and is

commonly associated with cm-scale chert nodules and root traces. Massive dolomicritic silty

muds are slightly brecciated with interbeds of subhorizontally laminated silty mud. These

beds also contain mudcracks. Lacustrine fossils are absent from this facies.

Root traces in this facies indicate that the sediments were colonized by floral

communities and the lack of lacustrine fossils and presence of mudcracks further indicate

that the sediments were subaerially exposed. The chert nodules are interpreted to be Magadi-

type chert, diagenetically altered from magadiiate, a hydrous sodium silicate, created by the

interaction of saline lacustrine pore-water with meteoric water (Eugster, 1967, 1969).

Although there are no obvious soil structures, this facies is interpreted to represent a poorly

developed alluvial paleosol.

3.6. Ostracode, oolite, and intraclastic grainstone

The ostracode and intraclastic grainstone contains medium sand-sized ostracode and

intraclast grains that are very poorly lithified and often poorly exposed (Figure 2.6).

Consequently, sedimentary structures within this facies are difficult to discern. These poorly

lithified sediments are commonly associated with thin lignite beds, whispy laminated green

mudstone, gastropod fossils, tufa, and algal stromatolites. Intraclasts are composed of algal

43

Figure 2.5. The massive dolomicritic silty mudstone facies in outcrop at Antelope Creek.

44

Figure 2.6. The ostracode, oolitic, and intraclastic grainstone facies in the Sand Butte

section. A) photograph of the surface of an ostracode, ooid, and intraclast pavement

and, B) photomicrograph of the rock shown in A (SB-48.75; UW1941/01).

45 material or lithic clasts and, together with ostracodes, are often lithified as a grapestone

(Winland and Matthews, 1974).

Similar to marine oolites, lacustrine oolites are restricted to shallow, wave-agitated

lake marginal areas (Talbot and Allen, 1996). Inorganic carbonate can precipitate in

lacustrine environments when chemically different water masses are mixed (such as

groundwater and lake water) or as a result of photosynthetic activity (Kelts & Hsü, 1978).

The ostracode, oolitic, and intraclastic grainstone in the Laney Member are

interpreted to represent beach sands and littoral shoals. This facies can exist along lacustrine

shorelines that lack clastic input, as is the case for certain stretches along the shoreline of

Lake Tanganyika (Cohen and Thouin, 1987), or along lacustrine shorelines that are by-

passed by clastic influx.

3.7. Dolomitic volcaniclastic siltstone and sandstone

This facies is restricted to one stratigraphic interval that is informally known as the

“buff marker bed” (Roehler, 1973). This unit is roughly 12.5 meters thick at its best

exposure in the Trail Dugway (TD) section where it is composed of silt to medium sized

micaceous sand, tuffaceous material, and dolomite, interbedded with mudstone (Figure 2.7a).

The beds near the bottom are siltstone to fine sandstone, medium and parallel to sub-parallel

bedded with wavy mudstone laminations. The beds coarsen and thicken upward in the

section and are composed of medium wavy bedded fine to medium grained sand interbedded

with mudcracked mudstone. Sandstone units contain ripple cross laminations, trough cross

beds, and some massive laterally discontinuous beds. The beds fine and thin upward and are

composed of thin dolomitic siltstone and mudstone beds with rip-up clasts 3-4-cm in length.

46 The beds that compose the volcaniclastic siltstone and sandstone facies are very dolomitic

(up to 50% - Figure 2.7b, Figure 2.8).

This facies, and the laterally equivalent “orange marker” of Buchheim (1978), has

been interpreted to be an evaporative facies deposited in an arid environment when lake

levels were very low (Surdam and Stanley, 1979). The only fossils that have been recovered

from this facies include crocodile and insects (Buchheim, 1978). An alternative explanation

for the contracted lake levels and the presence of dolomite is the elimination of a major

drainage into Lake Gosiute and the subsequent formation of dolomite through evaporative

pumping of groundwater through the newly exposed lake sediments (Rhodes et al., in

review).

3.8. Volcaniclastic sandstone

The Sand Butte Bed of the Laney Member is characterized by volcaniclastic

sandstone and mudstone. The Sand Butte Bed outcrops along the Delaney Rim from the

Delaney East section to the Antelope Creek section, along the entire Kinney Rim, and caps

the Laney sections in Firehole Canyon. It is composed of tuffaceous material and

interbedded gray brown silty mudstone with plant fragments, gray siltstone, and very fine

gray brown volcaniclastic sandstone (Figure 2.8). Surdam and Stanley (1980) documented

basaltic and andesitic fragments within the Sand Butte Bed with an increasing component of

pyroclastic material toward its southern extent in the Green River Basin. There are also

recessive, vegetated intervals near the top of the unit in outcrops within the Washakie basin.

The uppermost sandstone bed in the Antelope Creek section is a very fine, purple, cross

bedded, sandstone with bone and carbonaceous material. Volcaniclastic strata in Firehole

47

Figure 2.7. A) The buff marker bed as seen from the Trail Dugway section represents the

dolomitic volcaniclastic siltstone and sandstone facies. The coarsening and

thickening upward beds are shown here. B) photomicrograph from within the buff

marker bed, note abundance of dolomite rhombs (TD-34.25; UW1941/2.1).

48 Canyon coarsen and thicken upward, is medium to coarse grained and characterized by syn-

depositional slumping features including fluid injection structures, internal growth faulting,

and convolute bedding.

Bradley (1964), Roehler (1973), and Stanley and Surdam (1978) interpreted the Sand

Butte Bed as a fluvial/deltaic deposit with individual bottomset, foreset, and topset strata that

can be mapped in outcrops along the Delaney Rim. The thickness and bedding within the

deltaic foresets suggests progradation into a shallow lacustrine environment (Stanley and

Surdam, 1978). The presence of significant soft sediment deformation at the base of the

deltas suggests that this facies was rapidly deposited across a soft substrate. The Sand Butte

deltas have been compared to the late Quaternary Truckee River deltaic deposits in Pyramid

Lake, Nevada (Stanley and Surdam, 1978).

3.9. Lithic sandstone

The lithic sandstone facies is characterized by gray-tan to purple-red medium to

coarse-grained sandstone with cm-scale iron concretions, low and high angle planar cross

beds, 0.5 to 1-meter scale trough cross beds, plant fragments, lignite, ripple marks and

surfaces that have been scoured to ~ 1 meter (Figure 2.9). Resistant sandstones are more

calcareous and interbedded with green, bluish, and/or brown mudstone.

We interpret this facies to have been deposited by fluvial processes (cf. Ramos et al.,

1986). In the North Barrel Springs section, lithic sandstone forms the resistant unit that caps

and consequently provides measurable section in some of the outcrops.

49

Figure 2.8. The Sand Butte Bed of the Laney Member represents the volcaniclastic

sandstone facies, seen here along Kinney Rim. Note the outcrop expression of the

buff marker bed (~ 12 m thick).

Figure 2.9. Sandstone with well developed trough crossbeds (0.5 meter scale) typifies the

lithic sandstone facies in the North Barrel Springs section. The sand is interbedded

with the variegated silty mudstone facies. Hammer for scale in lower left corner.

50 3.10. Variegated silty mudstone

Variegated silty mudstone outcrops along most of the Delaney Rim, and along the

base of Kinney Rim. It is characterized by red, purple, green, and white laterally continuous

mottled bands of claystone to mudstone with varying amounts of silt and sand (Figure 2.9).

This facies represents the alluvial Wasatch Formation that intertongues with the

lacustrine members of the Green River Formation along the margins of the basin (see Figure

2.2). The variegated beds have been described in detail by Braunagel and Stanley (1977) to

represent sedimentary couplets that fine upward and are interpreted to have been deposited

between channels during flooding events.

4. FACIES ASSOCIATIONS

The above facies may be grouped into two major facies associations based primarily

on their stratigraphic position within the Laney Member (c.f. Carroll and Bohacs, 1999). A

fluctuating profundal facies association occurs within the lower LaClede and lower part of

the upper LaClede bed, and includes the algal stromatolite, laminated dolomicritic mudstone,

laminated micritic mudstone, massive dolomicritic mudstone, massive dolomicritic silty

mudstone facies, and the ostracode, oolitic, and intraclastic grainstone, and lithic sandstone

facies. The lithic sandstone and variegated silty mudstone facies also characterize this facies

association and are laterally equivalent to the lower LaClede in the Wasatch Formation. In

contrast, the uppermost LaClede and Sand Butte beds are characterized by a fluvial-

lacustrine facies association, which include only the volcaniclastic sandstone, laminated

micritic and dolomicritic mudstone facies.

51 4.1. Fluctuating profundal facies association

The fluctuating profundal facies association is composed of lithologically different,

laterally equivalent stratigraphic packages. In LaClede strata, ~ 1-5 meter thick cycles of

algal stromatolite, laminated dolomicritic mudstone, laminated micritic mudstone, and

massive dolomicritic mudstone facies predominate (Figures 2.10 and 2.11). The massive

dolomicritic silty mudstone facies is a minor component of this association, and is located

stratigraphically above massive dolomicritic mudstone when present. Well developed

stromatolitic horizons pinch out basinward, leaving alternating beds of laminated micritic and

dolomicritic mudstone. Buchheim (1978) and Surdam and Stanley (1979) interpreted these

carbonate cycles to indicate the rise and fall of lake level; the basal stromatolite was

deposited during lake transgression, laminated dolomicritic mudstone, laminated micritic

mudstone as the lake expanded, and dolomicritic mudstone deposited as the lake contracted.

Alternating amalgamated beds of ostracode, oolitic, and intraclastic grainstone, lithic

sandstone facies, mudstone, and lignite or whispy carbonaceous mudstone with minor

occurrences of the algal stromatolite facies are another component of the fluctuating

profundal facies association (Figures 2.10, 2.12 and 2.13). These strata indicate a shift from

carbonate dominated lacustrine sedimentation to clastic dominated fluvial systems near the

lake margin.

The alluvial Wasatch Formation, characterized by sandstone and variegated silty

mudstone, interfingers with the fluctuating profundal facies of the LaClede bed. Laterally

discontinuous, medium to thick bedded lithic sandstone beds punctuate the variegated silty

mudstone facies and cap sinuous outcrop ridges. These sinuous sand-capped ridges appear to

represent paleo-channel fill and would therefore be the exhumed Eocene inlets to Lake

52

Figure 2.10. Idealized chronostratigraphy of the fluctuating profundal facies association

(modified from Surdam and Stanley, 1979).

53

Figure 2.11. Detailed measured section of the fluctuating profundal facies from the Delaney

West section (see Figure 2.2 for location).

54

Figure 2.12. The lake marginal expression of the fluctuating profundal facies association at

the Table Rock section (see Figure 2.2 for location). The star marks the location of

the photograph in Figure 2.13.

55

Figure 2.13. Laterally equivalent to the stromatolite mudstone cycles are ostracode-oolite

grainstone and lithic sandstone facies. The photo was taken at the Table Rock

section.

56 Gosiute. The variegated silty mudstone that surrounds the sandstone is interpreted to be the

result of alluvial flood plain deposition (Braunagel and Stanley, 1977).

The stratigraphic stacking of the facies within the fluctuating profundal association

indicates the repeated expansion and contraction of Lake Gosiute (Buchheim, 1978; Surdam

and Stanley, 1979; Braunagel and Stanley, 1977; see Figure 2.10). During periods of low

lake level, fluvial systems crossed a large lake plain to deliver water and sediment to the lake.

As the lake expanded, mm-laminated micritic mudstone was deposited in profundal

environments, algal stromatolites transgressed the lake margins, and clastic sediments were

increasingly restricted to the extreme margins of the basin allowing oolitic and ostracode-rich

shoals and beaches to dominate in the newly formed lacustrine environment.

4.2. Fluvial - lacustrine facies association

The fluvial-lacustrine facies association is interpreted to indicate lacustrine

sedimentation within an overfilled lake basin and is typified by progradational geometries.

This association is composed of alternating beds of laminated micritic and laminated to

massive dolomicritic mudstone, and volcaniclastic sandstone facies (Figure 2.14). Micritic

mudstone dominates in this facies association along the Delaney and Kinney Rims, and

where present, the interbedded dolomicritic mudstone facies lacks desiccation features and

evaporite casts, indicating that it is deposited subaqueously in profundal to sublittoral

lacustrine environments. Freshwater lacustrine mollusks are more abundant within the

mudstone of this facies association. The volcaniclastic sandstone facies, as previously

described, is interpreted as a deltaic deposit, and is interbedded with micritic and dolomicritic

mudstone near its base (Figure 2.14 and 2.15).

57

Figure 2.14. Idealized cross section through the fluvial-lacustrine facies association.

58

Figure 2.15. Detailed measured section showing fluvial-lacustrine facies association within

the Sand Butte section (see Figure 2.2 for location).

59 There is no evidence of exposure within the facies of the fluvial-lacustrine

association. This association is interpreted to indicate the infill of the lacustrine basin due to

continuously open hydrologic conditions, and not the expansion and contraction of lake level.

Lake level during the deposition of these facies is constrained by the elevation of the lake’s

outlet (Carroll and Bohacs, 1999).

5. SIGNIFICANT STRATAL SURFACES

The significant stratigraphic surfaces within the Laney Member, those surfaces that

aid in the correlation and interpretation of the strata, include exposure surfaces and laterally

extensive transgressive deposits such as flat pebble conglomerates and associated algal

stromatolite horizons. Exposure surfaces occur at a variety of scales in the Laney Member

ranging from cycle boundaries within fluctuating profundal facies to meter scale mudcracks

marking a unique period of sudden basin-wide desiccation. Exposure surfaces and

transgressive deposits represent important and easily recognizable stratigraphic boundaries

that may be used to subdivide the Laney Member into genetically related sub-units.

5.1. Cycle boundaries within fluctuating profundal facies

Within strata of the fluctuating profundal facies association are centimeter to 0.5-

meter scale mudcracks along surfaces that are typically capped by the algal stromatolite

facies (Figure 2.16a). Recognized by Buchheim (1978), these mudcracks are within massive

dolomicritic mudstone, are evenly spaced, characterized by up-warped laminae, and are

infilled with silt to pebble-sized sediment. They are often associated with chert nodules, root

casts, and/or flat pebble conglomerates.

60 5.2. Flat-pebble conglomerates and algal stromatolite facies

Flat-pebble conglomerates and algal stromatolite facies mark significant surfaces in

the absence of well developed centimeter to decimeter-scale mudcracks. These associated

facies are laterally continuous and form very resistant beds in outcrop that allow for the easy

identification of profundal lacustrine cycle boundaries. Flat-pebble conglomerates,

composed of algal rip-ups and chert clasts, are interpreted to form during storm events, where

algal mats and resistant chert clasts are eroded and re-deposited in a transgressive lag.

Stromatolites and oolites were deposited on top of this new substrate as the lake expanded.

The occurrence of flat-pebble conglomerates and algal stromatolite facies indicates a lake

level below the sill elevation and are therefore important indicators of lake type.

5.3. Meter-scale mudcracks

Mudcracks that penetrate to a depth of 1 to 3-meters are found at the base of the

dolomitic volcanic siltstone and sandstone facies (buff marker bed), within the fluctuating

profundal facies association (Figure 2.16b). This surface can be traced from the Delaney

West, to Trail Dugway, to the Firehole Canyon section. Figure 2.17 is an aerial photo of the

Antelope Creek area along the Delaney Rim where there appears to be three dimensional

evidence of this mudcracked surface at the base of the buff marker bed. Within the Antelope

Creek section, the mudcracks at the base of the buff marker bed are at least 3-meters deep,

and are infilled with an algal stromatolite flat pebble conglomerate. These 3-meter

mudcracks are difficult to locate in the Trail Dugway section because they have been infilled

with the recessive dolomitic and volcaniclastic siltstone of the buff marker bed. Here, the

61

Figure 2.16. A) Decimeter scale mudcracks within the Antelope Creek section and, B)

Meter scale mudcracks at the base of the buff marker bed in the Sand Butte section.

62

Figure 2.17. Aerial photo showing the desiccated surface below the buff marker bed at

Antelope Creek (see Figure 2.2 for location). The field of view for this photograph is

approximately 0.25 km.

63 profundal mudstone that had been desiccated forms resistant exposures that dip back into the

outcrop at a 5 to 10-meter spacing where, at a closer look, you can see the relationship

between laminated micritic mudstone and the massive dolomitic and volcaniclastic siltstone

that infills the cracks. This surface in the Firehole Canyon section is characterized by 0.5

meter mudcracks that are infilled with dolomitic algal rip up clasts.

6. CORRELATION AND STRATIGRAPHIC EVOLUTION

Measured sections were correlated using a combination of tuff beds, distinctive

lithologic markers, gamma-ray spectroscopy, and facies associations (Figure 2.18 – in

pocket, original paper copy in the University of Wisconsin - Madison Geology library, Dept.

of Geology and Geophysics). For most of the sections, the correlations can be demonstrated

with a high degree of confidence, and reinforced by visually tracing continuous beds across

much of the study area. For some sections the correlation is less certain due to incomplete

exposures.

There are “floating” datums due to the very recessive and highly vegetated nature of

the upper LaClede bed along the Delaney Rim. A blue colored tuff that outcrops at the top of

the Dirt Hill section is likely correlative to a blue colored tuff within the Antelope Creek

section. Another tuff, called the Analcite tuff (48.94 +/- 0.12 Ma – Smith et al., in review),

outcrops ~7 meters above the buff marker bed serves as a datum along the Kinney Rim.

Correlation across the Rock Springs Uplift to Firehole Canyon is interpreted based on the

recognition of a major desiccation surface. A description of the correlation, from basin

center to basin margin follows for each stratigraphic unit within the Laney Member.

64 6.1. Lower LaClede Bed

Correlation of strata within the lower LaClede bed parallels a near shore to profundal

transect with the depocenter near the Firehole Canyon section. Firehole Canyon strata were

lithologically correlated toward the lake margin, while the correlation of Delaney and Kinney

Rim sections (NBS to TD) was largely based on outcrop gamma ray measurements. Fisher

assay data from Roehler (1991) were also utilized in correlation. Lower LaClede strata are

interpreted to represent the sedimentary fill within a balanced fill basin. The fine-grained

strata within the Firehole Canyon section are interpreted to be entirely within the lower

LaClede bed, based on the recognition of a major desiccation surface that caps the lower

LaClede along the Delaney and Kinney rims, represented by 0.5 meter deep mudcracks

within profundal mudstone near the base of the Sand Butte Bed (Figure 2.19).

Lower LaClede strata in the basin center are composed of thick beds of micritic

mudstone interbedded with dolomicritic mudstone and siltstone. Dolomitic strata correlate to

alluvial/fluvial facies or shallow lacustrine strata near the lake margin. Thick beds of organic

rich dolomicritic mudstone (oil shale) called “blue beds”, because they weather light gray

with a blue cast, are interpreted to form in a deep stratified lake, just after the lake has

expanded when organic production is increased by nutrient input from fluvial systems but not

inhibited by clastic influx near the lake margins (for detailed discussion, see Bohacs et al,

2000). Micritic mudstone packages are correlated to fluctuating profundal facies toward the

basin margin.

65

66

Figure 2.19. The stratigraphic section illustrates the fluctuating profundal strata of the lower

LaClede bed. A) Photograph of the section, illustrating the strata in the measured

section to the left and the approximate location of the mudcracked surface that caps

lower LaClede strata. B) Close up photo of the mudcracked surface, notice the

laterally continuous intraclastic bed above the desiccated surface. C) The

mudcracked surface is highlighted by differential compaction around the crack fill.

67 The base of the lower LaClede bed at Trail Dugway, Antelope Creek, Delaney East,

and Delaney West, is characterized by ~ 13, 1-to 3- meter cycles of the fluctuating profundal

facies association punctuated by a 10-meter outcropping of the lithic sandstone and

variegated silty mudstone facies. There are at least 4 mudstone-stromatolite cycles preserved

below this interval, and at least 9 preserved above it. Many of these cycles are separated by

decimeter-scale mudcracks, and they are thicker near the top of the section.

The laterally equivalent lower LaClede bed lake margin facies within the Wells Bluff

section are ostracode, oolitic, and intraclastic grainstone facies, beyond which are lithic

sandstone and variegated silty mudstone facies at North Barrel Springs. The upper part of

the lower LaClede bed does not outcrop along the Delaney Rim between Red Wash and

Wells Bluff: the facies changes are not clear behind Delaney Rim because the gently dipping

slopes in this region are highly vegetated.

6.2. Buff Marker Bed

The dolomitic volcanic siltstone and sandstone facies (buff marker bed) overlies the

lower LaClede bed from Firehole Canyon to Delaney East and was either eroded, never

deposited, or not recognized from Dirt Hill to North Barrel Springs. The buff marker bed is

separated from the lower LaClede bed by a major desiccation event recorded by 0.5 to 3.0

meter mudcracks. The bed also marks a shift in the deposition of profundal facies from near

Firehole Canyon to near the Delaney and Kinney Rims. The buff marker bed is very

recessive in outcrop along the Kinney Rim. In its best exposure (Trail Dugway, Figure 2.20),

the buff marker bed overlies ~3.0 meter mudcracks that are infilled with dolomitic siltstone.

It is roughly 12.5 meters thick, coarsening and thickening upward over the first 6.5 meters,

68

Figure 2.20. Stratigraphic section through the buff marker bed at Trail Dugway, illustrating

the coarsening and thickening upward to fining and thinning upward beds.

69 and fining and thinning upward throughout the remaining ~6 meters. The entire unit thins

toward the north and to the west. At Antelope Creek, the buff marker bed overlies ~3.0

meter mudcracks that are infilled with algal rip ups. The Firehole Canyon section has

roughly ~4 meters of the buff marker bed, expressed as a thinning upward package of

dolomitic siltstone interbedded with micritic mudstone and preserved above 0.5 m mudcracks

infilled with intraclastic sediment, including algal material. Overall, the stratigraphy of the

buff marker indicates a depocenter close to Trail Dugway and expansion of the lake north-

ward and west-ward, filling desiccation cracks with stromatolitic intraclasts along the way.

The sedimentary structures and bed thicknesses of the buff marker strata indicate the

progradation and subsequent retrogradation of fluvial-deltaic beds that include a mixture of

volcanic and dolomitic provenances.

6.3. Upper LaClede Bed to Sand Butte Bed

The upper LaClede bed is predominantly micritic mudstone, and as such, is poorly

exposed and often vegetated in many accessible outcrops. There are 3 marker beds that aided

in correlation across the Delaney and Kinney Rims; the Analcite tuff, a thick

stromatolite/oolite algal rip up bed, and a laterally extensive blue tuff. Limited gamma ray

measurements facilitated correlation of the balanced fill strata immediately above the buff

marker bed.

The upper LaClede bed conformably overlies the buff marker bed. The depocenter

for upper LaClede strata appears to be within the Washakie Basin during the initial stages of

sedimentation where dolomicritic organic rich mudstone dominates in the balanced fill strata.

Within the lowermost upper LaClede strata in the Sand Butte and Antelope Creek sections

70 are at least two balanced fill fluctuating profundal cycles that are each roughly 5-meters

thick. The uppermost cycle is capped by a chert rip-up – stromatolite horizon that is overlain

by 30 to 50 meters of the thickening upward cycles of micritic and dolomicritic mudstone.

Based on the correlation presented here, there was an influx of sand into the Sand

Butte section prior to the major progradation of the Sand Butte Bed across the basin. The

lower LaClede bed in the Sand Butte section is interpreted to be the most profundal section in

along the Delaney and Kinney Rims, indicating that there may have been less sedimentation

here (Buchheim and Eugster, 1998), which would have created more accommodation space

for the coarser clastic sediment entering the basin.

The recessive upper LaClede bed presumably interfingers with facies of the recessive

Hartt Cabin Bed toward the east, the base of which is marked by a turretellid agate unit that

caps the North Barrel Springs section. Based on the stratigraphic relationship of the lower

LaClede and Sand Butte beds in Firehole Canyon, the Sand Butte Bed is interpreted to be

laterally equivalent to the upper LaClede Bed and time transgressive across the basin where

strata are missing in the Rock Springs Uplift (Surdam and Stanley, 1979; 1980). The

progradation of volcaniclastic sandstone, nearly perpendicular to the line of section, forced

lacustrine facies to migrate toward the southeastern portion of the basin through time, and

ultimately marks the end of lacustrine deposition in the basin (Surdam and Stanley, 1980).

The correlation of Laney strata presented here differs from a previously documented

correlation (Roehler, 1992). The most important difference is the correlation from Firehole

Canyon in the Green River Basin to the outcrops along the Delaney and Kinney Rims in the

Washakie Basin. Roehler (1992) identified a split buff marker bed in the Firehole Canyon

section, which divided the section into lower and upper LaClede beds, unconformably

71 overlain by the Sand Butte Bed. The correlation (and sequence stratigraphic interpretation)

presented here interprets the 2 buff colored beds in Firehole Canyon to represent contracted

stages of Lake Gosiute. A major desiccation surface near the base of the Sand Butte Bed is

correlated to the base of the buff marker bed in the Washakie Basin, indicating that the entire

Laney section below this surface at Firehole Canyon is lower LaClede equivalent. This

interpretation highlights the change in locus of profundal deposition from the Firehole

Canyon area to the Trail Dugway area across the major desiccation surface. The LaClede

Bed is interpreted to represent the maximum extent of Lake Gosiute, as mapped by Bradley

(1964). The separation of the lower and upper LaClede beds into 2 distinctly different

depocenters may have implications for the interpretation of the maximum extent of Lake

Gosiute.

7. SEQUENCE STRATIGRAPHIC INTERPRETATION

We interpret a nested hierarchy of stratigraphic packaging to occur within the Laney

Member, including lacustrine parasequences, to parasequence sets, sequences, and sequence

sets (see Figure 2.18, in pocket). Parasequences composed of single 1-3 meter stromatolite-

micritic-dolomicritic mudstone cycles are interpreted in the lower LaClede strata along the

Delaney and Kinney Rims. Aggradational, retrogradational, and progradational

parasequence sets construct 4 sequences in the balanced fill strata of the lower LaClede Bed.

The base of each sequence is recognized as a basin ward shift in facies, marked by either

alluvial/fluvial or paleosol facies, and is interpreted to have been formed/deposited in a

closed lacustrine basin. In the basin center, dolomicritic mudstone overlies the sequence

boundary, likely derived from the exposed mudflats during the contracted lake stage.

72 Retrogradational parasequence sets identify lake transgression to a maximum expansion

surface. Maximum expansion is identified lithologically within the most shoreward sections

by the occurrence of lake marginal stromatolites and geophysically by a sharp decrease in the

total gamma-ray activity (Bohacs, 1998). In the basin center, the maximum expansion

surface is placed below thick organic rich “blue beds” (Bohacs et al., 2000). Micritic

mudstone dominates in the basin center during lacustrine highstand, which is also marked by

minor shoreline progradation. The 4 sequences of the lower LaClede bed stack together to

form a balanced fill sequence set within which the sequences thin upward in succession.

This is interpreted to record net expansion of Lake Gosiute and a resultant decrease in

sedimentation rates near the basin center. Near the top of this sequence set alluvial facies are

closely interbedded with profundal muds, suggesting a decrease in basin-floor gradient.

The lower LaClede balanced fill sequence set is bound on top by a major desiccation

event, recorded by 3 m deep mudcracks that formed in the underlying profundal mudstone.

The overlying “buff marker”, upper LaClede, and Sand Butte beds together are interpreted as

a single sequence. The buff marker is a record of the initial deposition above the sequence

boundary, in the lowstand position of the sequence. Internal stratal stacking patterns and

composition of mudcrack fill suggest that the earliest deposition occurred near the Trail

Dugway section, where progradational stacking patterns prevail and mudcracks are infilled

with dolomitic siltstone. Upsection in the buff marker bed at Trail Dugway, rip up clasts and

fining and thinning strata suggest transgression, supported by intraclastic/stromatolitic strata

and infill of mudcracks at Antelope Creek and Firehole Canyon. A very organic rich

mudstone package directly above the buff marker bed in the base of the upper LaClede bed

suggests continued transgression/early progradation of lacustrine strata. A series of

73 progradational balanced fill lacustrine parasequences follow, and culminate in a significant

surface interpreted as a maximum expansion surface. This surface, interpreted to be on top

of a 0.5 meter chert and algal rip up bed that is overlain by laterally equivalent stromatolites

and oolitic grainstone, marks a threshold above which the basin remained hydrologically

open. The basin was subsequently infilled by the progradation of volcaniclastic deltaic

sediments and laterally equivalent micritic and dolomicritic mudstone as lake level remained

relatively stable.

8. DISCUSSION

8.1. Sequence Stratigraphic Implications

Previous workers have tended to interpret lacustrine sequence stratigraphy in the

same way that they would interpret shallow marine strata (Oviatt et al., 1994; Vakarcs et al.,

1994; Dam et al., 1995; Lemons and Chan, 1999). However, unlike in the marine realm, it is

clear that sediment supply and lake level are in many cases intimately linked, and that large-

magnitude lake-level fluctuations can occur much more rapidly than equivalent sea-level

changes (Shanley and McCabe, 1994; Bohacs, 1998, Carroll and Bohacs, 1999). Below, we

compare sequence stratigraphic approaches developed for marine settings with our

observations from the Laney Member.

Whereas marine parasequences are bound by flooding surfaces (Van Wagoner, 1985;

Van Wagoner et al., 1988), lacustrine parasequences in the Laney Member are defined as a

genetically related succession of beds bound by unconformities commonly recognized by

mudcracks in lake marginal environments. Parasequences are easily identified in balanced

fill, fluctuating profundal lower LaClede strata due to the preservation of resistant lake

74 marginal carbonates above desiccated surfaces (see Figure 2.11., lower LaClede near

Antelope Creek in Figure. 2.18). They represent the expansion and contraction of the lake

and likely record effect that climatic fluctuations have on the hydrologic budget of the basin

(Rhodes et al., 2002). Parasequences are indistinct in the overfilled strata, as desiccation

rarely occurs in this lake type.

Retrogradational, aggradational, and progradational packages can be recognized

because lacustrine parasequences stack to form parasequence sets, similar to marine

parasequence sets (Van Wagoner et al., 1990). This implies that transgressive and regressive

lacustrine shorelines can be interpreted as the amount of water and sediment entering (and

stored in) the basin changes. Strata of the lower LaClede Bed (Figure 2.18) form

aggradational and retrogradational parasequence sets.

Marine sequences are defined as a “relatively conformable, genetically related

succession of strata bound by unconformities or their correlative conformities (Mitchum et

al., 1977)”. Fundamentally, lacustrine sequences in the Laney Member do not strictly adhere

to this definition because they are less conformable than marine sequences because they are

constructed by lacustrine parasequences (bound by unconformities), and are highly variable

depending on the basin physiography and hydrology. For example, if there is no water

entering the basin, then there is no sediment entering the basin. They are identified in the

balanced fill Laney Member by a significant basinward shift in facies, which probably either

record changes in basin subsidence or tectonic or geomorphic processes in the drainage basin

(Rhodes et al., in review). In overfilled strata, there are no significant unconformable

surfaces to interpret as sequence boundaries (Neal et al., 1997).

75 Marine sequences are comprised of lowstand, transgressive, and highstand systems

tracts (Brown and Fisher, 1977; Fisher and McGowen, 1967). The lowstand systems tract is

at the base of the sequence, is typically composed of a sand dominated basin floor fan, and

bound by a transgressive surface above (Van Wagoner et al., 1990). The lacustrine

depositional system in the lowstand position is dependent upon the basin type. In balanced

fill Laney strata lowstand deposits are thin and aggradational (see strata of lower LaClede

bed at Firehole Canyon, Figure 2.18) whereas in the overfilled strata of the Laney there are

no deposits in a strictly lowstand position. The marine transgressive systems tract, deposited

when sea level rises, is capped by a maximum flooding surface. Transgressive strata are the

dominant component of balanced fill Laney sequences and were similarly deposited when the

lake expanded until the lake overflowed its sill level or where maximum expansion of the

lake was reached. The surface above which Lake Gosiute remained hydrologically open is

recognized here as a maximum expansion surface, and identified in the field in a location

directly above the last major transgressive deposit (Figure 2.18). Marine highstand systems

tract, deposited as sea level falls, is bound on top by a sequence boundary. Highstand

deposits are difficult to recognize in balanced fill Laney strata because as the lake contracted,

water and sediment input were eliminated. In overfilled Laney strata progradational

geometries are identified as highstand deposits, which dominate the overfilled sequence.

A lacustrine sequence set is defined as the stack of consecutive sequences associated

with specific genetic lake types.

76 8.2. Controls on lacustrine sequence stratigraphic expression

The complex sequence stratigraphic packaging of the Laney Member records an

overall trend toward decreasing basin subsidence, erosion of basin sills, or increasing

sediment + water supply (see Figure 2.21 for summary). The lower LaClede is composed of

four thinning upward sequences that stack together in a balanced fill sequence set. The

uppermost strata of the Laney is interpreted to represent a single lacustrine sequence because

the deposits represent a predictable succession of strata within the terminal basin fill.

Figure 2.21 – 1 illustrates the change in potential accommodation interpreted from

lower LaClede strata. Basin subsidence and lake level define the potential accommodation of

a basin, which changes within a balanced fill basin as a single lacustrine parasequence is

deposited as the lake level fluctuated around sill level (Carroll and Bohacs, 1999). On a

larger scale, the potential accommodation of the entire lower LaClede bed is interpreted to be

decreasing with time, as evidenced by the thinning of lacustrine sequences. The record of

more closely interbedded alluvial and profundal lacustrine facies up-sequence indicates that

the supply of water to the basin may not have increased, but the rate of basin subsidence

likely decreased and slowly changed the geometry of the basin margin during this time.

Figure 2.21-2 illustrates our hypothesis regarding the desiccation event that caps

lower LaClede strata. The basin-wide desiccation of profundal lacustrine mudstone is

interpreted to represent the sudden elimination of the lake from the basin when a large

debris-avalanche deposit associated with the emplacement of the upper plate of the Heart

Mountain Detachment blocked the major inlet to Lake Gosiute, temporarily disrupting the

hydrologic balance of the basin (Rhodes et al., in review). The event caused the groundwater

table to lower enough to accommodate the development of at least 3 meter deep mudcracks.

77

Figure 2.21. (see next page for caption)

78

Figure 2.21. Summary of the interpreted paleohydrology, changes in subsidence, sediment

supply, and water during the deposition of the Laney Member. The left side of the

figure is a generalized oblique view of the basin. The line across the basin indicates

the location of the cross section illustrated on the right side of the figure. See text for

full description.

79 The depth of the mudcracks at the base of the buff marker bed and the distance between them

decreases from the Kinney and Delaney rims (~ 3 meters deep, ~10 – 15 meters apart) to

Firehole Canyon (~ 0.5 meters, ~ 2-3 meters apart). Mudcracks of this magnitude have been

documented to occur within modern playas of the Great Basin (Neal et al., 1968) and more

specifically the Black Rock and Smoke Creek Deserts (Willden and Mabey, 1961). This

basin-wide desiccation is the basal sequence boundary for the overlying upper LaClede –

Sand Butte Bed basin infill sequence, which is interpreted to have formed geomorphically.

Figure 2.21-3 illustrates the re-organization of drainage to the basin and the

deposition of the buff marker bed which formed the basal strata of the overlying basin infill

sequence. Transgressive beds within the buff marker indicate the re-expansion of Lake

Gosiute back to its sill level, and therefore the increase in water + sediment to the basin. The

depth to the groundwater table is interpreted to have decreased toward Firehole Canyon due

to the decrease in the depth of the mudcracks, indicating that Firehole Canyon was perhaps

topographically lower than the Delaney and Kinney rim region. Therefore, as indicated by

the depocenter of the buff marker bed in the Washakie Basin, when Lake Gosiute

transgressed, the sediment of the buff marker bed was trapped near the lake margin.

Figure 2.21-4 illustrates the re-establishment of a balanced fill basin, and the

deposition of thicker, prograding fluctuating profundal cycles, which is interpreted to

represent the continued decrease in basin subsidence and the expansion of drainage basin

boundaries to increase the water + sediment delivered to the basin. The upper LaClede bed

parasequences exhibit progradational stacking, as stromatolitic horizons preserved along the

Delaney Rim prograded south and westward toward the basin depocenter. The presence of

this package suggests shoreline progradation, also observed in the Firehole Canyon section as

80 volcaniclastic material prograded into the basin at this time, further evidence of the increase

in sediment + water to the basin. These parasequences are capped by the maximum

expansion surface, which marks the shift to permanent overfilled basin conditions.

Figure 2.21-5 shows the final stages of lacustrine deposition in Lake Gosiute

represented by progradational “highstand” deposition of the Sand Butte and upper LaClede

beds and the shift in depocenter of profundal lacustrine muds. The shift in profundal

lacustrine deposition could have been the result of tectonic and/or sedimentary processes.

The Absaroka volcanic center was documented to have migrated southeastward through time

(Sundell, 1993) and may have imparted a regional tilt to the basin to shift the position of the

depocenter, as well as shifted the sedimentary provenance of the Sand Butte Bed closer to the

Green River Basin. The progradation of Sand Butte deltas prograded across Green River

sub-basin promoted its “fill and spill” into the Washakie sub-basin, which would also have

shifted the locus of profundal deposition.

The decrease in basin subsidence was coincident with the end of Laramide

deformation. The increase in sediment + water to basin could have been the result of the

evolution of a wetter climate that enhanced chemical and physical weather within the

drainage basin, the erosion or tectonic shift of geomorphic sills upstream and therefore the

increase in size of the drainage basin, or the increase in water to the drainage basin as the

growing volcanic edifices captured additional precipitation and increased the surface area

drained in the basin. Surdam and Stanley (1980) documented the increase in size of the

hydrographic basin by identifying the provenance of the Sand Butte Bed to be within the

Absaroka volcanic range. They suggested that this was a result of tectonic activity enhanced

by the prevailing climate conditions, despite the lack of lithologic evidence for climate

81 change. We suggest that the increase in water + sediment is a combination of the expansion

of the hydrographic basin coincident with decrease basin subsidence, and exaggerated by the

increase in clastic source rock provided by the collapse of large volcanoes in the drainage

basin.

The shift toward overfilled conditions was a gradual shift, beginning with the

decrease in basin subsidence interpreted from the lower LaClede sequence set. Subsidence

continued to decrease while the sediment + water began to increase as interpreted from the

transgression of the buff marker bed, progradation of the balanced fill strata in the upper

LaClede bed, and finally culminating in the continuously profundal mudstone and

progradation of volcaniclastic sandstone of the upper LaClede and Sand Butte beds. The

uppermost sequence of the Laney Member, which contains balanced fill and overfilled strata,

can be described as a terminal basin fill sequence, and interpreted to have been driven by

geomorphic processes in the drainage basin, preserved in a basin with decreasing potential

accommodation. This study highlights the importance of detailed correlation and

interpretation of lacustrine sequence stratigraphic expression to interpret major controls on

lacustrine deposition.

82 9. CONCLUSIONS

1) Ten lacustrine and alluvial facies within the Laney Member comprise 2 facies

associations; fluctuating profundal and fluvial – lacustrine. The lower

LaClede bed is characterized by the fluctuating profundal facies association

which typifies deposition in a balanced fill lake basin. The upper LaClede bed

and Sand Butte bed is constructed of fluctuating profundal to fluvial –

lacustrine facies associations, indicating the shift to deposition in an overfilled

lake basin.

2) Gamma-ray measurements are an excellent correlation tool for the lacustrine

strata of the Laney Member.

3) The lower LaClede bed contains 1 sequence set, constructed of 4 thinning

upward sequences, interpreted to represent the expansion of Lake Gosiute and

the change in basin geometry due to the decrease in basin subsidence.

4) A major desiccation event at the base of the buff marker is correlative across

the basin. We interpret this to record sudden elimination of a major drainage

to the basin and the consequent lowering of the groundwater table to allow for

0.5 to 3.0 meter deep mudcracks to form.

5) Based on the recognition of the desiccation event described above, Laney

strata in Firehole Canyon (Green River Basin) are correlative to lower

LaClede Bed strata in the Washakie Basin. This indicates that there was a

shift in profundal sedimentation from west to east across the Rock Springs

Uplift which may have implications for the interpretation of the maximum

extent of Lake Gosiute.

83 6) The Sand Butte Bed is laterally equivalent to the upper LaClede Bed.

7) The buff marker, upper LaClede, and Sand Butte beds represent a single basin

fill sequence characterized by progradational to retrogradational geometries

(in balanced fill strata) during lowstand and transgression, and progradation

(in balanced fill and overfilled strata) during highstand. The maximum

expansion surface in this sequence marks the threshold after which the lake

was continuously open (overfilled basin).

8) The sequence stratigraphic packaging within the Laney Member highlights the

gradual shift to overfilled basin conditions due to the decrease in basin

subsidence and the increase in sediment + water input.

84

Chapter Three

Strontium isotope record of paleohydrology and continental weathering,

Eocene Green River Formation, Wyoming

85 Rhodes, M.K., Carroll, A.R., Pietras, J.T., Beard, B.L., and Johnson, C.M., 2002, Strontium

isotope record of paleohydrology and continental weathering, Eocene Green River

Formation, Wyoming, Geology, v. 30, no. 2, p. 167-170.

ABSTRACT

Sr isotope ratios in carbonate-rich lacustrine strata provide highly resolved and

geographically specific records of past changes in weathering and regional drainage patterns.

The Eocene Green River Formation is perhaps the best documented pre-Quaternary

lacustrine unit in the world; therefore, these strata are ideally suited for studying the behavior

of Sr. 87Sr/86Sr ratios measured for primary carbonate in lake expansion-contraction cycles

of the Laney Member are directly linked to changing lake facies. Four distinct cycles are

preserved in a 6.4 m interval of the Arco Washakie Basin No. 1 core, each represented by a

vertical succession of transgressive stromatolite facies containing dolomicritic intraclasts,

laminated micrite facies deposited during lake highstands, and lake-marginal dolomicrite

facies which represents subsequent lowstands. Initial 87Sr/86Sr ratios range from 0.711 99 to

0.713 31. The least radiogenic isotope compositions are associated with laminated micrite

that records increased regional runoff from Phanerozoic marine carbonate and Tertiary

volcanic rocks during lacustrine highstands. The most radiogenic isotope compositions are

associated with dolomicrite, recording a higher proportion of runoff from basin-bounding

Precambrian uplifts and the exposed lake-plain during lacustrine lowstand. The observed

87Sr/86Sr variations may also be due in part to changes in differential weathering of the

surrounding landscape, where drier climates are associated with decreased differential

weathering and, therefore, higher 87Sr/86Sr in runoff.

86 1. INTRODUCTION

Lacustrine basins are uniquely positioned to capture the weathering products of

continental uplifts and often provide relatively complete records of local geomorphic

processes. Because the 87Sr/86Sr ratio in minerals is not fractionated during precipitation

from fluids, Sr isotope compositions preserved in lacustrine carbonate rocks should record

the isotopic composition of the lake water and, therefore, the flux-weighted compositional

average of runoff and groundwater that entered the lake (e.g., Faure, 1986; Palmer and

Edmond, 1992; Capo et al., 1998; Singh et al., 1998; White et al., 1999; English et al., 2000).

In contrast to the globally mixed marine realm, 87Sr/86Sr ratios preserved in lake deposits can

be tied to paleo-river systems that drained specific areas (e.g., Stewart et al., 1993; Benson

and Peterman, 1995; Pedone, 2000). Lacustrine records, therefore, hold considerable

potential for helping to reconstruct local patterns of continental weathering.

Lake Gosiute occupied the greater Green River Basin of southwestern Wyoming

during most of early Eocene time (Figure 3.1, Bradley, 1964; Roehler, 1993). The greater

Green River Basin is a segment of the Sevier foreland basin, bounded by Laramide-style

Precambrian-cored uplifts to the north, east, and south. This study focuses on changes in the

87Sr/86Sr ratio that occur within individual lake expansion-contraction cycles in the Laney

Member, which may reflect relatively short-term climatic fluctuations.

2. GEOLOGIC SETTING OF EOCENE LAKE GOSIUTE

The Wilkins Peak and overlying Laney Members of the Green River Formation

record a transition from a hydrologically closed basin that contained hypersaline lakes and

playas to a hydrologically open basin that contained large freshwater lakes (Carroll and

87

Figure 3.1. Green River Basin of southwestern Wyoming and surrounding uplifts

(modified from Witkind and Grose, 1972). Cross section A-A’ shown in Figure

2. WB-Washakie Basin, GRB-Green River Basin. Strontium isotope

compositions from Hedge et al. (1967), Peterman et al. (1970), Crittenden and

Peterman (1975), Divis (1977), Peterman and Hildreth (1978), Zielinski et al.

(1981), Burke et al. (1982), Mueller et al. (1985), Meen and Eggler (1987),

Frost et al. (1998), Hiza (1999), Patel et al. (1999).

88 Bohacs, 1999). Climate during the final stages of Wilkins Peak deposition is interpreted to

have been subtropical, with a mean annual temperature of ~20 oC and annual rainfall of 80

cm (Wilf, 2000). Similar conditions may have existed during deposition of the Laney

Member, although paleoclimate data have not been reported for this interval. In the study

area, the Laney Member is composed of fluctuating lake marginal and profundal facies of the

LaClede Bed, overlain by the volcaniclastic deltaic facies of the Sand Butte Bed. The

LaClede Bed contains well-defined cycles of flooding and desiccation (Surdam and Stanley,

1979). A typical cycle begins with stromatolitic facies that are often associated with

dolomicritic intraclasts and oolitic and ostracode grainstones; these are overlain by profundal

facies dominated by laminated micrite (oil shales) that finally grade upward into shallow

dolomicrite that contains desiccation cracks and occasional displacive evaporite crystals.

The Sand Butte Bed of the Laney Member is characterized by coarsening-and-thickening-

upward volcaniclastic sandstone beds that were deposited by deltas which prograded from

the north-northwest (Surdam and Stanley, 1980).

Drainage to Lake Gosiute during deposition of the Laney Member was likely

delivered from several different source terranes. Drainage over the Precambrian-cored Uinta

Mountains, Sierra Madre, Granite Mountains, and Wind River Range provided local-sources

of runoff to the lake. Paleozoic and Mesozoic marine carbonate and siliciclastic strata are

widely exposed within the Sevier thrust belt to the west and also flank Precambrian-cored

uplifts (Figure 3.1). Finally, Surdam and Stanley (1980) interpreted a hydrologic connection

to the Wind River Basin, through which Lake Gosiute received drainage from the Tertiary

Absaroka volcanics (Figure 3.1).

89 3. EVOLUTION OF STRONTIUM ISOTOPE COMPOSITION IN LAKE CYCLES

Several lines of evidence indicate that the 87Sr/86Sr ratios reported in Table 3.1

represent either primary or penecontemporaneous lake-water values, rather than later

diagenetic fluids. The dominant sample lithology is relatively impermeable mudstone, which

appears to have limited the transport of diagenetic fluids. The preservation of a wide range

of strontium isotope ratios within individual lake cycles suggests that no pervasive diagenetic

alteration occurred. Wolfbauer and Surdam (1974) concluded that dolomite formed

penecontemporaneously on the mudflats of Lake Gosiute through evaporative pumping,

which explains its abundance near the top of each lake cycle. This model is consistent with

the occurrence of primary dolomite in a modern saline lake (Mason and Surdam, 1992). In

the present study, thin-section petrography was used to identify fabrics that may indicate

diagenetic modification, such as overgrowths or recrystallization. Nearshore stromatolite

facies containing ostracodes commonly contain evidence of such fabrics, whereas laminated

micrite and dolomicrite usually do not. Samples were visually inspected and microdrilled to

avoid possible diagenetic alteration.

The data from the sampled interval demonstrate a close relationship between

preserved strontium isotope compositions and lake facies (Table 3.1, Figure 3.2; WB1-562-

WB1-583, see Appendix A for UW samples numbers). 87Sr/86Sr ratios are relatively high in

stromatolite and dolomicritic intraclast facies near the base of each cycle, decrease toward

mid-cycle in laminated micrite facies, and increase again toward the top within the

dolomicrite. High 87Sr/86Sr ratios near the base of each cycle in part reflect physical

reworking of dolomicrite from the previous cycle as intraclasts. Note that the ostracodes and

90

Depth Sr Rb 87Rb/86Sr 87Sr/86Sri *87Sr/86Srm Lithology

(ft) ppm ppm

562 189.6 1.30 0.019 82 0.712 14 ± 2 0.712 15 Tuffaceous ss563 954.7 1.03 0.003 13 0.712 39 ± 1 0.712 39 Dolo. intraclast564 1 116.0 1.49 0.003 86 0.712 78 ± 1 0.712 78 dolomicrite565 974.2 1.44 0.004 29 0.712 09 ± 1 0.712 09 micrite566 902.2 1.42 0.004 54 0.711 99 ± 1 0.711 99 micrite567 1 081.0 1.58 0.004 23 0.712 21 ± 1 0.712 21 micrite568 816.8 5.39 0.019 09 0.712 68 ± 1 0.712 69 micrite569 1 430.0 0.99 0.002 00 0.713 31 ± 1 0.713 31 Dolo. intraclast570 1 595.0 0.16 0.000 28 0.712 97 ± 1 0.712 97 Dolo. intraclast571 805.4 1.57 0.005 70 0.712 51 ± 1 0.712 51 micrite572 755.0 2.51 0.009 63 0.712 41 ± 1 0.712 42 micrite573 899.1 1.29 0.004 17 0.712 05 ± 1 0.712 05 micrite574 626.7 1.63 0.007 55 0.712 24 ± 1 0.712 25 micrite575 649.6 1.55 0.006 89 0.712 61 ± 1 0.712 61 dolomicrite576 1 223.0 0.36 0.000 86 0.712 51 ± 1 0.712 51 micrite577 1 160.0 0.90 0.002 25 0.712 56 ± 1 0.712 56 micrite578 1 060.0 0.40 0.001 10 0.712 22 ± 1 0.712 22 Dolo. stromatolite579 661.8 5.12 0.022 38 0.712 22 ± 1 0.712 24 micrite580 891.9 1.56 0.005 07 0.712 22 ± 1 0.712 22 micrite581 1 085.0 1.92 0.005 13 0.712 50 ± 1 0.712 50 micrite582 1 276.0 1.10 0.002 50 0.712 66 ± 1 0.712 66 micrite583 609.1 1.24 0.005 89 0.712 68 ± 1 0.712 68 Dolo. intraclast

Note: Methods for strontium isotopic analysis of lacustrine carbonates are similar to those described by Winter et al. (1995). Samples were microsampled and leached with ammonium acetate to decrease contamination from clastic components. The carbonate fraction was dissolved in 1M acetic acid, spiked, and dried in 6M hydrochloric acid in preparation for ion-exchange chromatography. Mass analysis was done by thermal-ionization mass spectrometry using a multi-collector dynamic analysis with exponential normalization to 86Sr/88Sr = 0.1194; 162 analyses of the NBS-987 standard (March 2000 to April 2001) produced an average 87Sr/86Sr ratio of 0.710 262 ± 18 (2-SE). Errors are ± 2-SE and refer to the least significant digits. * Age for initial ratios is 50 Ma.

TABLE 3.1. Sr ISOTOPE COMPOSITIONS FOR ARCO WASHAKIE BASIN NO. 1 CORE SAMPLES

91

Figure 3.2. Lithologies, interpreted cyclicity, and strontium isotope

compositions for Arco Washakie Basin No.1 core (sec. 17, T. 14 N.,

R. 99 W.). See Table 3.1 regarding full documentation of methods

and data.

92 ooids in sample 578 have been recrystallized and may therefore record the strontium isotope

composition of diagenetic fluids rather than original lake water.

The range of variation in strontium isotope ratios within each cycle examined

increases upward through the sampled interval (Figure 3.2), possibly due to an increase in the

stratigraphic completeness of each successive cycle. For example, cycle 1 (Figure 3.2)

includes dolomicrite intraclasts and mudcracked micrite at its base, but lacks the dolomicrite

facies that occurs at the top of an idealized cycle. The range in 87Sr/86Sr ratios within this

incomplete cycle is relatively small. In contrast, cycle 4 represents a complete facies

succession and contains a wider range of 87Sr/86Sr ratios. The lowest 87Sr/86Sr ratio within

each successive cycle records a gradual shift toward less radiogenic strontium in profundal

laminated micrite facies (Figure 3.2).

We propose that these variations in 87Sr/86Sr ratios are due primarily to changes in the

relative proportion of water that drained highly radiogenic lithologies immediately adjacent

to Lake Gosiute compared to water that drained less-radiogenic rocks north and west of the

greater Green River Basin. Figure 3.3 illustrates a hypothetical three-stage lake-cycle

evolution of Lake Gosiute. During time 1 (expansion), the lake was confined to the center of

the basin, exposing a large lake plain incised by fluvial channels. Stromatolite, oolite, and

intraclast facies were deposited along a transgressive shoreline. Strontium input to the lake

was heavily influenced by internal drainage from highly radiogenic Precambrian-cored

uplifts, increasing the 87Sr/86Sr ratio that has been preserved in the lacustrine carbonates.

Fluvial incision of alluvial lake-plain mud may also have helped to increase the 87Sr/86Sr

ratio of lake water, through cation exchange with relatively radiogenic clay minerals. Time 2

(highstand) represents maximum expansion of the lake and corresponds to widespread

93

Figure 3.3. Idealized lake cycle and stratigraphic correlation from lake margin to

alluvial lake plain in Laney Member (lake cycle modified from Surdam

and Stanley, 1979). Data from cycle 4 of the Arco Washakie Basin No.1

core (WB1-564 to WB1-570, see Appendix A for UW sample numbers) is

plotted alongside generalized cycle according to facies.

94 deposition of laminated micrite. The influence of less-radiogenic drainage increased as

water spilled over from the Wind River Basin to the north and tapped inlet streams into a

larger area of marine carbonates, lowering the 87Sr/86Sr ratios preserved in profundal deposits

(Figure 3.1). Finally, during time 3 (contraction), the relative influence of highly radiogenic

internal drainage increased again, and regional streamflow and spillover decreased.

Dolomite and evaporite facies in the basin center initially maintained relatively low 87Sr/86Sr

ratios because strontium from the previous highstand was evaporatively concentrated, but Sr

isotope compositions gradually shift to more radiogenic compositions.

Climatically induced differential weathering of lithologies exposed within the

drainage basin may also have influenced the observed variations in 87Sr/86Sr ratios. A

number of studies have shown that increased weathering tends to decrease the 87Sr/86Sr ratio

in surface waters and increase the 87Sr/86Sr ratio in residual clays, compared to the

unweathered parent rock (e.g., Singer and Navrot, 1973; Brass, 1975; Andersson et al., 1994;

Bain and Bacon, 1994; Galy et al., 1999; White et al., 1999). Differential weathering within

the drainage basin of Lake Gosiute would therefore drive 87Sr/86Sr ratios for lake water lower

during wetter periods (lacustrine highstands) and higher during drier periods (lacustrine

lowstands). Although it is difficult to quantify the magnitude of the change in Sr isotope

compositions that occurred owing to differential weathering, the direction of change is

expected to be the same as for changes in the drainage-basin area proposed herein.

95 4. CONCLUSIONS

This study demonstrates for the first time that significant, systematic variation in the

87Sr/86Sr ratios occurs within pre-Quaternary lacustrine carbonate facies deposited during

expansion-contraction cycles. We have shown that lacustrine strata offer unique records of

past continental weathering and that variations in Sr isotope compositions may provide a new

approach to reconstructing the paleohydrologic histories of lacustrine systems. Climatic

variations are interpreted during the time-scale in which individual lacustrine expansion-

contraction cycles are deposited due to the direct correlation between lake facies and

87Sr/86Sr ratios. The slight shift toward lower 87Sr/86Sr ratios between cycles might reflect

larger-scale tectonic or magmatic changes; this is a focus of current investigations.

Additional future work, including mass-balance modeling of strontium fluxes, as well as

analysis of a broader stratigraphic sample set, will help to verify and expand on the

interpretations presented in this study.

96

Chapter Four

Strontium isotopic evidence for changes in the paleohydrology of Lake Gosiute during deposition of the

Laney Member, Green River Formation

97 ABSTRACT

The Sr isotope composition of lacustrine carbonates within the LaClede and Sand

Butte beds of the Laney Member, Green River Formation, varies significantly on several

scales. Sr isotopic analysis of alternating 1-cm beds of micritic and dolomicritic mudstone at

the base of the Sand Butte Bed reveals a range of 87Sr/86Sr ratios between 0.71172 and

0.71249 across 4-cm of strata. The 87Sr/86Sr ratios measured from individual expansion –

contraction cycles in the lower LaClede bed vary systematically with the relative abundance

of calcite and dolomite. Dolomicritic facies interpreted to have formed through evaporative

pumping on mudflats surrounding the lake are more radiogenic than calcite-rich facies. The

Sr isotope composition of lacustrine carbonate material from the profundal facies throughout

the LaClede Bed gradually shifts toward less radiogenic Sr (averaging 0.71231 for lower

LaClede; 0.71172 for upper LaClede).

The Sr isotopic composition of water samples collected from modern drainages in the

Green River Basin and Bighorn/Absaroka Basins were used to drive a mass balance model

composed of three stages; an incremental addition model to simulate the basin infilling with

water, a steady-state flux model to simulate changes in the Sr isotope composition when the

lake had a constant outlet, and an evaporation model adapted from assimilation and fractional

crystallization models. Model results indicate that the range in the 87Sr/86Sr ratio measured

from lacustrine expansion-contraction cycles can best be explained by a combination of

drainage from uplifts in the Green River Basin, groundwater from mudflat environments, and

less radiogenic drainage from the Absaroka Range during lake highstand. A long term shift

in Sr isotope composition toward the incorporation of less radiogenic drainage strengthens

the sequence stratigraphic interpretation of an overall paleohydrologic shift punctuated by a

98 temporary, but major hydrologic event in the basin recognized stratigraphically and

geochemically as the buff marker bed.

99 1. INTRODUCTION

Sediments within long-lived ancient lacustrine basins contain valuable records of

continental processes. Because lake basins are local catchments for a limited number of

drainages, they offer the opportunity to closely examine the weathering history of particular

orogenic plateaus and other areas of continental deformation. One approach to reading this

history is to analyze the Sr isotopic compositions preserved in lacustrine carbonate facies

(e.g., Stewart et al., 1993; Benson and Peterman, 1995; Bouchard et al., 1998; Pedone, 2000;

Pache et al., 2001; Rhodes et al., 2002). Given that there is no mass fractionation of Sr when

it is precipitated from fluids, the Sr isotope composition of lacustrine carbonate material

should reflect the flux-weighted compositional average of runoff and groundwater that

entered the lake (e.g., Faure, 1986; Palmer and Edmond, 1992; Capo et al., 1998; Singh et al.,

1998; White et al., 1999; English et al., 2000). This paper addresses the significance of Sr

isotopic variability within ancient lacustrine carbonates.

The Greater Green River Basin of southwestern Wyoming is an ideal location to

investigate the Sr isotopic variability of carbonates in an ancient lake system. First, the basin

contains the Eocene Green River Formation, one of the most studied ancient lacustrine

systems in the world (Bradley, 1964; Roehler, 1973). Second, during the evolution of Lake

Gosiute, the lake from which the Green River Formation was deposited, several

geochemically distinct terranes are documented to have drained into the basin (Surdam and

Stanley, 1979, 1980; Roehler, 1993; Sundell, 1993). Highly radiogenic Precambrian cored

Laramide style uplifts flanked by Paleozoic marine carbonates bound the basin, and the

presence of a deltaic sandstone unit derived from the Absaroka Range (Surdam and Stanley,

1980) supports a hydrologic connection to the young Eocene volcanic rocks. If the

100 hydrologic connection between the Absaroka Range and Lake Gosiute existed prior to the

progradation of deltaic sand across the basin, there should be a geochemical record of the

introduction of less radiogenic drainage from that region preserved in the lacustrine

carbonates.

Post-Eocene uplift and erosion of the Green River Basin has subsequently exposed

tens of kilometers of laterally continuous lacustrine strata. This paper represents the first

study of a pre-Quaternary system that is fully integrated within a well-known stratigraphic

framework. It begins to characterize the potential source of Sr to Lake Gosiute, summarizes

variations in the Sr isotopic composition preserved on several scales within the final saline to

freshwater deposits of the Laney Member of the Green River Formation, addresses Sr

isotopic variability with a mass balance model, and explores the value of Sr isotopic analysis

of lacustrine strata.

1.1. Geologic setting

Lake Gosiute was impounded in the subsiding Sevier foreland basin by Precambrian

cored Laramide-style uplifts in southwestern Wyoming during the late early to early middle

Eocene time (Figure 4.1). The lake evolved from freshwater to hypersaline to freshwater

successively depositing the Luman Tongue, Tipton, Wilkins Peak, and Laney members of the

Green River Formation during the warmest period of the Cenozoic (Roehler, 1993; Zachos et

al., 1994, Sloan and Rea, 1995).

The Laney Member is composed of micritic and dolomicritic mudstone of the

LaClede Bed, volcaniclastic sandstone of the Sand Butte Bed, and shallow, freshwater

101

Figure 4.1. Geologic map of the Green River Basin and basin bounding uplifts (modified

from Witkind and Grose, 1972). Arrows illustrate the probable introduction of

drainage to Lake Gosiute. References for 87Sr/86Sr ratios are in Table 4.1.

102 lacustrine deposits of the Hartt Cabin Bed (Roehler, 1973). The LaClede Bed is further

divided into lower and upper units by a dolomitic volcaniclastic bed informally known as the

“buff marker” (Roehler, 1973). The upper LaClede bed is laterally equivalent to the Sand

Butte Bed, a volcaniclastic deltaic sandstone unit derived from the Absaroka Range that

prograded across the basin from the north to the south marking the end of lacustrine

deposition in the basin (Surdam and Stanley, 1980). The Hartt Cabin Bed is laterally

equivalent to the Sand Butte Bed and limited in outcrop in the Green River Basin. Strata of

the Laney Member have been identified over an area of ~39,900 km2 across the entire

Greater Green River Basin and are interpreted to mark the maximum expansion of Lake

Gosiute (Roehler, 1992).

The drainage basin to Lake Gosiute during the deposition of the Laney Member likely

included the Precambrian cored uplifts immediately surrounding the basin (Uinta Mountains,

Sierra Madre, Laramie Range, Granite Mountains, and Wind River Mountains) as well as

strata within the Sevier Thrust Front. Drainage entering the basin from the north was from

the Absaroka volcanics and could have also originated in the Owl Creek and Beartooth

Mountains. Table 4.1. contains the Sr isotope composition and concentration weighted

averages for the lithologies in the vicinity of the Green River Basin. Figures 4.2a. and 4.2b.

are plots of the 87Sr/86Sr vs. 1/Sr that are reported in the literature for each uplift (see Table

4.1. for references). The plots indicate that a wide range in Sr isotope compositions exist in

and around the Green River Basin. Most of the data can be interpreted to fall into one of two

trends (Figure 4.2b.), one dominated by low 87Sr/86Sr characterized by volcanic lithologies of

the Absaroka volcanics and Stillwater Complex, and the other with a larger range in 87Sr/86Sr

as represented by the granitic Precambrian cored Laramide uplifts. The Sr isotope

103

Table 4.1.

Location Area/lithology No. of analyses reported

Rb a

(ppm)Sr a

(ppm)

87Sr/86Sr b Reference

Absaroka Range andesite, trachybasalt, rhyodacite welded tuff, absarokite 14 109 1 032 0.706 16 Peterman et al., 1970Independence Volcano 19 161 577 0.705 81 Meen and Eggler, 1987average 27 86 972 0.705 06 Hiza, 1999

Beartooth Mountains Stillwater Complex 3 0 51 0.703 03 DePaolo and Wasserburg, 1979Stillwater Complex 5 2 96 0.704 08 Simmons and Lambert, 1982gneiss 21 70 273 0.728 54 Mueller et al., 1982migmatite 6 129 96 0.898 25 Mueller et al., 1982SE Archean granites, granodiorite, dioritic amphibolite, basaltic amphibolite, gneiss, aplitic dike 32 73 364 0.725 61 Wooden et al., 1982

Owl Creek Mountains Archean volcanics 18 61 169 0.743 82 Mueller et al., 1985Archean granite 20 192 190 0.939 92 Hedge et al., 1986

Granite Mountains granites 33 245 150 0.877 32 Peterman and Hildreth, 1978metamorphics 15 204 216 0.838 38 Peterman and Hildreth, 1978

Wind River Range banded gray gneiss, Native Lake gneiss, Bridger batholith, Louis Lake batholith, Bears Ears batholith, South Pass granites 39 82 445 0.724 51 Frost et al., 1998

Laramie Range Sherman Granite 4 164 137 0.774 40 Zielinski et al., 1981Cheyenne Belt 20 96 75 0.830 26 Patel et al., 1999

Sierra Madre quartz biotite gneiss, Baggot Rocks Granite, Encampment River Granodiorite, Green Mountain Formation, Big Creek Gneiss, Sierra Madre Granite, white quartz monzonite, North Park Granite 40 120 331 0.731 10 Divis, 1977

Uinta Mountains Uinta Mountain Group, Red Pine Shale 3 190 111 0.782 94 Critenden and Peterman, 1975

Uinta, Sevier Thrust Paleozoic marine clastics and carbonates

1000 - 10000 0.707-0.709 Burke et al., 1982

a Average ppm. b Concentration weighted average.

Reported strontium isotopic composition for Greater Green River Basin bounding uplifts

104

Figure 4.2. 1/Sr vs. 87Sr/86Sr for the uplifts within the drainage basin to Lake Gosiute. Both

graphs illustrate the same data, graph b) is an expanded view of graph a). Data are

from references listed in Table 4.1.

105 composition of carbonate material in the Laney Member is expected to be a mixture of these

compositions.

2. SAMPLING AND STRATIGRAPHIC FRAMEWORK

2.1. Water samples

To characterize the potential sources of Sr to Lake Gosiute, water samples were

collected from modern rivers that drain basin bounding uplifts upstream of the influence of

Tertiary sediments. Sampled rivers include Carter Creek, West Fork of Blacks Fork, and

East Fork of Blacks Fork which drain the Uinta Mountains, LaBarge Creek within the Sevier

Thrust Belt, the Green River and Big Sandy that originate in the Wind River Mountains,

Elkhead Creek and Little Snake River from the Sierra Madre, and Sweetwater Creek and

North Fork of the Shoshone River within the Absaroka Range (Figure 4.3. and Table 4.2. for

locations). Water samples were filtered through a 40 µm screen and acidified with 6M HCl

for storage in LDPE bottles.

2.2. Sampling within a stratigraphic framework

To begin to characterize variations in the Sr isotope composition of carbonate material

in the Laney Member, five stratigraphic sections (Trail Dugway, Sand Butte, Antelope

Creek, Delaney West, and North Barrel Springs) through the LaClede and Sand Butte beds of

the Laney Member were measured along the Delaney and Kinney Rims in the Washakie

Basin, and one from Firehole Canyon in the Green River Basin proper (Figure 4.4). Outcrop

gamma ray measurements at 50-cm intervals facilitated the correlation of stratigraphic

sections along the Delaney and Kinney Rims. In addition, two cores taken from less than

106

Figure 4.3. Location of water samples from the Green River and Bighorn Basins (see Table

4.2. in Results section for latitude and longitude). 1) Carter Creek, 2) Blacks Fork, 3)

LaBarge Creek, 4) Green River, 5) Big Sandy, 6) Elkhead Creek, 7) Little Snake

River, 8) Sweetwater Creek, 9) North Fork of the Shoshone River.

107

Figure 4.4. Location map for stratigraphic sections and cores. The line of section noted is

shown in Figure 4.5. FC = Firehole Canyon; TD = Trail Dugway; SB = Sand Butte;

AC = Antelope Creek; DW = Delaney West; NBS = North Barrel Springs.

108 1-km behind the Delaney and Kinney Rims (Arco Oil and Gas WB 1 and Arco Oil and Gas

2WB) that are housed in the USGS Core Repository in Denver, CO, were logged, sampled,

and correlated to outcrop sections (Figure 4.4). The samples were named first by location

and then by the meter in the section from which they were collected (ie. TD-34.25 is from

meter 34.25 in the Trail Dugway section). Core samples were taken from boxes containing 8

feet of core and were consequently sampled in feet.

Figure 4.5 illustrates the stratigraphic correlation and sequence stratigraphic

interpretation for the Laney Member across the study area. The lower LaClede bed is

divided into four thinning upward sequences capped by the major desiccation event that

marks the base of the buff marker bed (Rhodes and Carroll, 2002; see Chapter 2). These

sequences are composed of a fluctuating profundal facies association deposited in a balanced

fill basin (Carroll and Bohacs, 1999). The upper LaClede bed is comprised of a single

lacustrine sequence that contains within it the shift from fluctuating profundal to fluvial-

lacustrine facies associations, or strata characterizing the shift from balanced fill to overfilled

basin hydrologies (Carroll and Bohacs, 1999) recognized by initial progradation of the

deltaic sand of the Sand Butte Bed across the basin. The overall sequence stratigraphic

framework of the Laney Member is interpreted to represent the decrease in basin subsidence

and the increase in the amount of sediment and water delivered to the basin during the

waning stages of Laramide deformation and the initiation of Absaroka volcanism (Roehler,

1973; Sundell, 1993; Chapter 2).

To characterize variations in Sr isotope composition within the Laney Member of the

Green River Formation, strata were sampled and analyzed on 3 different scales (Figure 4.5

for sample locations). An outcrop sample from the Firehole Canyon section with centimeter-

109

110 scale lithologic changes was selected for analysis at the finest scale from which four sub-

samples were collected by microdrilling each visually identifiable cm-scale layer. The

sample is composed of alternating 1-cm beds of brown-red dolomicritic mudstone and tan

silty micritic mudstone, both with mm- to cm-scale rip up clasts (Figure 4.6). The lowermost

dolomicritic layer (D) is composed of ~4 fining upward successions with rip-up layers at the

base of each. The overlying silty micritic mudstone layer (C) is scoured into the lowermost

layer 1 to 2 mm, and fines upward toward the base of the next dolomicritic layer. The top of

this micritic layer appears to have relief and may represent a mudcracked surface.

Centimeter scale rip up clasts in the overlying dolomicritic mudstone (B) rest on the

mudcracked surface. Near the top of the second dolomicritic surface is a 1 mm thick,

laterally continuous orange layer that underlies the uppermost micritic layer. Water escape

features and/or bioturbation structures are present throughout all layers, and have reworked

the uppermost micritic layer (A) entirely. This sample is interpreted to represent a

fluctuating lake marginal mudflat deposit, indicating a drop in the lake level from which

underlying profundal facies were deposited. The Firehole Canyon section from which this

sample was collected contains within it the transition from profundal facies of the LaClede

Bed to the deltaic facies of the Sand Butte Bed. The sample selected marks the base of this

major shift in facies, laterally equivalent to the base of the buff marker bed, and above which

the toe of the Sand Butte delta appears.

Variation in the Sr isotope composition within lacustrine expansion – contraction

cycles was investigated by analyzing core samples at ~ 1 ft intervals across 4 cycles (see

Figure 4.5 for location). Rhodes et al. (2002) previously reported that the Sr isotope

composition measured from individual lake cycles in the lower LaClede bed varies

111

Figure 4.6. Outcrop sample from Firehole Canyon illustrating centimeter scale interbeds of

micritic and dolomicritic mudstone. Samples were microdrilled for Sr isotopic

analysis (sample FC-422.75; UW 1941/25.1).

112 significantly. In a typical lacustrine cycle composed of a basal stromatolite overlain by

laminated micritic and finally dolomicritic mudstone, the most profundal micritic mudstones

are consistently less radiogenic than the lake marginal dolomicrite and stromatolite facies.

This Sr isotopic variation was attributed to the expansion of drainage basin boundaries during

lake highstand to include drainage from less radiogenic terranes such as the Absaroka

volcanics to the north-northwest of the basin. For this study, the calcite/dolomite ratios were

measured from the same samples to compare the mineralogy to the Sr isotope composition

using semiquantitative x-ray diffraction techniques (methods follow).

Wolfbauer and Surdam (1974) interpreted the dolomite in the Laney Member to have

precipitated through evaporative pumping from the groundwater table. Evaporative

pumping, first defined by Hsu and Siegenthaler (1969), describes groundwater movement as

a result of a vertical hydraulic gradient created entirely by evaporation. In order to address

the contribution of a groundwater Sr component to Lake Gosiute, a tufa was collected from

the North Barrel Springs section, and analyzed for its Sr isotope composition (Benson, 1994;

Benson et al., 1995; Pache et al., 2001; Figure 4.5 for location, see Appendix A for UW

sample numbers). Tufas are documented to have developed along stable lake shorelines

where shallow Ca-rich groundwater intersects lake surface waters (King, 1978; Russell,

1885; Benson, 1994). The sample measured for this study is from an isolated tufa mound at

the margin of the lacustrine facies in the Green River Basin in the North Barrel Springs

section, and it is assumed to have formed as a result of the interaction of groundwater with

lake water.

Finally, given that the Sr isotope composition varies between lithofacies (Rhodes et

al., 2002), only micritic mudstone facies from the lower and upper LaClede beds were

113 sampled and analyzed from the Arco Oil and Gas WB 1 and 2WB cores to test for larger

scale variations in Sr isotope composition (Figure 4.5 for location). In addition, samples of

the buff marker bed and Sand Butte Bed were collected for comparative Sr isotopic analysis

over this thick (~ 75 meters) stratigraphic interval.

2.3. Description of microfacies

Descriptions and photomicrographs of eight Laney Member microfacies are provided

to help elucidate a relationship between the measured Sr isotope composition and carbonate

genesis. Microfacies include laminated micrite, bioturbated silty micrite, laminated

dolomicrite, massive dolomicrite, oolitic/ostracode/intraclast grainstone, algal laminations,

dolomitic and volcaniclastic siltstone, and volcaniclastic siltstone and sandstone (Figure 4.7).

Laminated micrite

Laminated micrite is the dominant facies in the LaClede Bed of the Laney Member,

and is composed primarily of ~10 to 40 µm scale laminae of micrite and organic matter, with

minor amounts of dolomite, quartz, and feldspar (Figure 4.7a). Fossil fish and ostracodes are

common in this facies. Buchheim (1994) described a vertical and horizontal gradation

between kerogen-rich (2-14% TOC) laminated micrite in the basin center and kerogen-poor

(~ 2% TOC) laminated micrite closer to the basin margins of Eocene Fossil Lake in the

Greater Green River Basin.

114 Bioturbated silty micrite

Bioturbated silty micrite is generally tan in color, and contains minor amounts of

dolomite. It is further characterized by numerous internal scour surfaces, water escape

structures, and mm-scale micritic rip-up clasts. Quartz silt is abundant in this facies and

often fills discrete burrows in weakly bedded sediments. This facies fines upward from rip-

ups at the base to micrite at the top of cm scale beds (see Figures 4.6 and 4.7b). At a

millimeter scale, this facies forms a complex, amalgamated package of scoured, quartz silt

infilled burrows topped by micro-ripples.

Laminated dolomicrite

Laminated dolomicrite is visually similar to laminated micrite. The major difference

between the two facies is that the laminated dolomicrite contains relatively more dolomite

than calcite. The dolomicritic laminae contain no visible dolomite rhombs, often appear

slightly crenulated, include abundant ostracodes, and variable amounts of organic matter

(Figure 4.7c).

Massive dolomicrite

Massive, tan dolomicrite is comprised of sub-micron to 20-30 micron scale dolomite

with the larger dolomite rhombs are located closer to pore spaces (Figure 4.7d and 4.7f).

Faint outlines of ostracodes are expressed as recrystallized dolomite. Quartz silt is a minor

component of this microfacies.

115 Oolitic/ostracode/intraclast grainstone

Oolitic, ostracode, and intraclast grainstones can contain any combination of the three

components as they were deposited in close association with each other. Ooids are typically

~ 1-mm, ostracodes range from 0.5 to 1.5 mm, and intraclasts, either algal, micritic, or

composed of oolites and ostracodes, are found up to 3-4 cm. Concentric laminations of algal

coatings are found around ostracodes and intraclasts. These lithic, organic, and inorganic

carbonate constituents can be weakly to strongly bedded in outcrop but appear massive in

thin section.

The constituents are grain supported and either have a micritic matrix (packstone) or

the matrix (or pore space) has been completely silicified or dolomitized (Figure 4.7e and

4.7g). Secondary porosity created by carbonate dissolution is common in oolites and

silicification and calcite precipitation is common between the valves of intact, but clearly

replaced ostracodes.

Algal laminated

Algal laminated facies are closely associated oolite, ostracode, and intraclast

grainstones. Algal laminations are expressed in thin section as a series of concave, sub-

parallel dark tan dolomicritic laminations separated by 1-2 millimeters of light tan

dolomicrite. In Figures 4.7g and 4.7h, ostracode-cored oolites are found along the

laminations. Quartz silt grains form thin veneers over some of the algal laminations.

116 Dolomitic and volcaniclastic siltstone

This facies characterizes the buff marker bed of the Laney Member and contains

abundant dolomite rhombs (10 to 200 µm) in a massive volcaniclastic mudstone and siltstone

matrix (Figure 4.7i). This buff colored facies also contains centimeter scale rip-up clasts.

Microscopic sedimentary structures are rare.

Volcaniclastic siltstone and sandstone

Volcaniclastic siltstone and sandstone characterizes the Sand Butte Bed of the Laney

Member. It is comprised of silt to medium sand sized quartz, feldspar, and volcanic lithic

fragments. There is a carbonate component in the matrix that otherwise appears to be a tan-

yellow glassy groundmass. In outcrop, volcaniclastic siltstone and sandstones are

interbedded with mudstone and have strongly progradational geometries disrupted by soft

sediment deformation, synsedimentary growth faults, and meter scale water escape

structures. In thin section the sediment appears to be massive to weakly interbedded silt and

sandstone (Figure 4.7j).

117

Figure 4.7. (see next page for caption).

118

Figure 4.7. (previous page) Photomicrographs of microfacies from the Laney Member. The

scale bar is 1 mm unless otherwise noted. A) laminated micrite (WB1-567;

UW1941/8.2); B) bioturbated silty micrite (FC-422.75; UW1941/25.2); C) laminated

dolomicrite (WB1-575; UW1941/16.2); D) massive dolomicrite (WB1-569;

UW1941/10.2); E) oolitic and intraclast grainstone (AC-55.95; UW1941/70); F)

massive dolomicrite (WB1-570; UW1941/11.2); G) ostracode-cored oolites within

algal laminations (WB1-578; UW1941/19.2); H) algal laminations (WB1-578;

UW1941/19.2); I) dolomitic and volcaniclastic siltstone (TD-34.25; UW1941/2.1); J)

volcaniclastic siltstone (FC-433; UW1941/28.2). See Figure 4.5 for sample locations.

119 3. ANALYTICAL PROCEDURES

3.1. Strontium isotopic analysis

Water samples were spiked, evaporated, and dissolved in 4.5 M HNO3 in preparation

for ion-exchange chromatography. Methods for strontium isotopic analysis of lacustrine

carbonates are similar to those described by Winter et al. (1995). Samples were inspected in

thin section to identify obvious diagenetic fabrics, microsampled, and leached with

ammonium acetate to decrease contamination from clastic components. The carbonate

fraction was dissolved in 1M acetic acid, spiked, and dried in 6M hydrochloric acid in

preparation for ion-exchange chromatography. For one sample from the buff marker bed and

two samples from the Sand Butte Bed, a partial dissolution in 1 M acetic acid was completed

from which the carbonate and clastic aliquots from the same sample, as well as for a whole

rock sample, were analyzed for their Sr isotope composition. Mass analysis was done by

thermal-ionization mass spectrometry using a multi-collector dynamic analysis with

exponential normalization to 86Sr/88Sr = 0.1194; 238 analyses of the NBS-987 standard

(March 2000 to June 2002) produced an average 87Sr/86Sr ratio of 0.710 263 ± 18 (2-SE).

Errors are ± 2-SE and refer to the least significant digits. All Sr isotope data is presented in

Appendix E.

3.2. X-ray diffraction

Samples reported in Rhodes et al. (2002) were analyzed on a Scintag Pad V X-ray

Diffractometer using a copper target. Voltage and current for the diffractometer were set at

35kV and 40mA and the slit combination used was 2, 3, 1, 0.5. Samples were microdrilled,

mixed with acetone, and dried on slides for analysis and scanned from 10 to 60 degrees at a

120 rate of 5 deg/min. DSM NT software was used to collect raw data and perform background

subtraction. Net intensity files were created and peaks were located using an estimated

standard deviation of 4 and a ripple multiplier of 1.5. Peaks were profile fit using a Pearson

VII curve to create peak files that include degrees (2�), d-spacing, absolute intensity, relative

intensity, and area under the peak. The dominant peak for calcite and dolomite was

identified and used as a proxy for abundance in each sample (Royse et al., 1971). All XRD

data is presented in Appendix D.

4. RESULTS

4.1. Sr isotope composition of modern drainage

Due to the process of differential weathering, the Sr isotopic compositions of modern

rivers in the Green River Basin are measured to be less radiogenic than the uplifts they drain

(Tables 4.1 and 4.2; Brass, 1975; Palmer and Edmond, 1992). Specifically, this is important

because radiogenic Sr (87Sr) comes from the beta decay of 87Rb, an element that replaces K

in minerals. Older, K-rich lithologies contain more 87Sr. Minerals that contain more Rb tend

to be more resistant to weathering than minerals that contain Sr (replacing Ca), therefore

relatively more Sr is chemically weathered from the drainage basin. This lowers the 87Sr/86Sr

ratio of the surface water relative to the 87Sr/86Sr of the uplifts drained, and consequently,

increases the Rb/Sr ratio of the weathered rock making it more radiogenic.

During the deposition of the Laney Member, the mean average temperature is

estimated to have been roughly 5˚ C higher than it is today and the mean annual precipitation

dropped from ~80 cm in the Eocene to ~25 cm today (Wilf, 2000). The increased

temperature and precipitation would have intensified the chemical weathering of all

121 Table 4.2.

Basin River Sr (ppm)

1/Sr 87Sr/86Sr

Green River Carter Creek a E. Uintas 40° 52.335' N 0.035 28.5714 0.71566 ± 1109° 41.592 W

W. Fork Blacks Fork above Madison ls. b W. Uintas 40° 51.718' N 0.016 62.5000 0.74318 ± 1

110° 39.901' W

below Madison ls. b W. Uintas 40° 55.660' N 0.033 30.3030 0.71949 ± 1110° 37.187' W

E. Fork Blacks Fork above Madison ls. b W. Uintas 40° 53.070' N 0.022 45.4545 0.74024 ± 1

110° 32.216' W

below Madison ls. b W. Uintas 40° 56.796' N 0.025 40.0000 0.73546 ± 1110° 34.617' W

LaBarge Creek c Sevier Thrust 42° 17.199' N 0.379 2.6385 0.70869 ± 1110° 25.835' W

Green River c NW Wind Rivers 43° 09.438' N 0.223 4.4843 0.70917 ± 1110° 02.045' W

Big Sandy c S. Wind Rivers 42° 33.379' N 0.031 32.2581 0.72560 ± 1109° 21.778' W

Elkhead Creek d Sierra Madre 40° 38.721' N 0.259 3.8610 0.70847 ± 1107° 16.594' W

Little Snake River d Sierra Madre 40° 59.811' N 0.104 9.6154 0.71004 ± 1107° 22.751' W

Absaroka / Sweetwater Creek e E. Absarokas 44° 28.037' N 0.05 20.0000 0.70484 ± 1Bighorn 109° 37.695' W

N. Fork Shoshone River e E. Absarokas 44° 28.039' N 0.01 100.0000 0.70535 ± 1109° 38.017' W

a Sampled on July 28, 2000 b Sampled on July 21, 2000 c Sampled on July 22, 2000 d Sampled on July 29, 2000 e Sampled on June 21, 2002

Strontium isotopic composition of modern river waters entering the Green River BasinLocation

Note : Water samples were collected from drainages above the modern extent of Tertiary sediments.

122 lithologies in the drainage basin. At higher temperatures, the Sr isotope composition of

drainage from granitic rocks around the basin is expected to have been less radiogenic than

for lower temperatures (White et al., 1999). This indicates that the composition of Sr from

waters draining the Precambrian cored uplifts surrounding the basin in the Eocene were

likely slightly less radiogenic than for modern drainages in the basin.

4.2. Small-scale variability in Sr isotope composition

The initial Sr isotope study of lacustrine carbonate material in the Laney Member was

designed to test for centimeter scale Sr isotopic variability and to address the possibility of

large scale diagenetic alteration of carbonate materials. Figure 4.8 illustrates the range in the

87Sr/86Sr ratio measured from the previously described Firehole Canyon sample. The results,

also listed in Table 4.3, show significant variation in the Sr isotope composition within 4-cm

of strata, ranging from 0.71172 ± 1 to 0.71249 ± 1. The less radiogenic ratios are associated

with the dolomicritic layers, and the uppermost micritic and dolomicritic layers are less

radiogenic than the lowermost micritic and dolomicritic layers respectively. The dolomicritic

layers have higher concentrations of Sr. The concentrations of Rb measured from the

carbonate fraction indicates significant silicate contamination of the sample.

Stratigraphic unit Sample name

Sr (ppm)

Rb (ppm)

87Rb/86Sr 87Sr/86Sr i a 87Sr/86Sr

m Lithology

LaClede Bed FC-422.75 A 55.85 5.20 0.269 60 0.712 34 ± 1 0.712 53 calc silty mudstoneFC-422.75 B 207.2 6.10 0.084 80 0.711 72 ± 1 0.711 78 dolo silty mudstoneFC-422.75 C 48.24 2.98 0.178 67 0.712 49 ± 1 0.712 62 calc silty mudstoneFC-422.75 D 256.5 3.70 0.041 74 0.712 06 ± 1 0.712 09 dolo silty mudstone

a Age for initial ratios is 50 Ma.

Centimeter scale variability in stronium isotope composition for Firehole Canyon Samples, Laney Member, Green River Formation

Table 4.3.

123

Figure 4.8. Stratigraphic section in Firehole Canyon from which sample for small scale

variation in Sr isotope composition was collected. A hand sample (FC-422.75;

UW1941/25.1) is pictured and layers A-D are labeled and annotated with their

respective 87Sr/86Sr ratios.

124 4.3. Cycle-scale variability in Sr isotope composition

Because the Sr isotope composition of lacustrine carbonate material in the Firehole

Canyon sample varied significantly within a very small stratigraphic interval and between

different lithologies, a systematic Sr isotopic and stratigraphic analysis was completed within

individual lake expansion-contraction cycles. Here, additional mineralogical data are

provided for the samples reported in Rhodes et al. (2002). Each sample was analyzed on an

x-ray diffractometer to compare the relative amounts of calcite and dolomite (Figure 4.9). In

general, the profundal mudstone facies has a greater proportion of calcite, and the lake

marginal facies are more dolomitic. Two samples, recognized by arrows, indicate analyses

from samples with visually identifiable diagenesis (see Figures 4.7f, g, and h).

Figure 4.10 illustrates thin sections and the Sr isotope and mineralogy data for seven

samples at 1 foot intervals from the uppermost cycle in Figure 4.9 (see Appendix A for UW

samples numbers). The expansion-contraction cycle begins with a massive dolomicritic

mudstone, composed primarily of microcrystalline dolomite (WB1-569) that has the most

radiogenic Sr isotope composition in the cycle. Sample WB1-568 through WB1-564

contains mm-scale laminations of alternating microcrystalline calcite and organic material.

Within these profundal mudstone samples, pyrite decreases upward, ostracodes and silt

increase upward, and the laminations appear to become slightly disrupted up-section. The

87Sr/86Sr ratio decreases to sample WB1-566 and then increases to sample WB1-564, and the

mineralogy trends toward increasing calcite. Stratigraphically above the last sample (WB1-

564) is a dolomicritic unit (not sampled) caps the cycle (see Figure 4.9 for stratigraphy).

125

Figure 4.9. Sr isotope composition and carbonate mineralogy for WB1 lacustrine expansion-

contraction cycles (modified from Rhodes et al., 2002; see Appendix A for UW

sample numbers). The light gray diamonds within the 87Sr/86Sr data highlight samples

that have visual evidence of carbonate diagenesis (see Figure 4.7).

126

Figure 4.10. Thin sections, XRD data, and Sr isotope composition for samples at 1 foot

intervals from the uppermost cycle in Figure 4.9 (Appendix A, UW sample numbers).

127 Table 4.4 contains the Sr isotope composition of a tufa measured from the North

Barrel Springs section. The Sr isotope composition of this tufa was considered to

approximate the Sr isotope composition of groundwater entering Lake Gosiute.

Table 4.4.

Stratigraphic unit Sample name

Sr (ppm)

Rb (ppm)

87Rb/86Sr 87Sr/86Sr i a 87Sr/86Sr

m Lithology

LaClede Bed NBS-Tufa 1 968 0.20 0.000 29 0.713 23 ± 1 0.713 23 tufaNBS-Tufa 2 1 591 0.27 0.000 49 0.713 31 ± 1 0.713 31 tufaNBS-Tufa 2 1 621 0.29 0.000 51 0.713 31 ± 1 0.713 31 tufa

Strontium isotope composition of a tufa within the Laney Member of the Green River Formation, Greater Green River Basin, SW Wyoming

a Age for initial ratios is 50 Ma.

4.4. Large-scale variability in Sr isotope composition

The cycle-scale variation in Sr isotope composition related to the expansion and

contraction of Lake Gosiute indicates a relationship between lithofacies and the 87Sr/86Sr

ratio measured. To detecting larger scale changes in paleohydrology, similar facies were

analyzed for throughout a stratigraphic section. Figure 4.11 illustrates the stratigraphic

framework from which the Sr isotopic ratios of micritic mudstone facies were analyzed

throughout the LaClede Bed (see Figure 4.5 and Chapter 2 for more detailed discussion of

stratigraphy).

The whole rock, clastic, and carbonate fractions of Sand Butte Bed samples collected

from Firehole Canyon in the Green River Basin and Antelope Creek in the Washakie Basin

were analyzed for their Sr isotope compositions to compare to those measured from micritic

mudstone (Table 4.5; see Appendix A for UW sample numbers).

128

129 Table 4.5.

Stratigraphic unit Sample name

Sr (ppm)

Rb (ppm)

87Rb/86Sr 87Sr/86Sr i a 87Sr/86Sr

m Lithology

Sand Butte Bed FC-433 595.3 82.10 0.399 27 0.711 44 ± 1 0.711 72 calc. volcaniclastic ssFC-433 4 877 5.59 0.003 32 0.710 48 ± 1 0.710 49 carbonateFC-433 395.8 113.64 0.831 35 0.712 74 ± 1 0.713 33 volcaniclastic sand

Sand Butte Bed AC-176.5 416.6 69.97 0.486 14 0.709 89 ± 1 0.710 24 calc. volcaniclastic ssAC-176.5 863.7 2.66 0.008 91 0.711 03 ± 1 0.711 04 carbonateAC-176.5 561.5 92.12 0.474 92 0.709 80 ± 1 0.710 14 volcaniclastic sand

a Age for initial ratios is 50 Ma.

Strontium isotope composition of samples from the Sand Butte Bed, Greater Green River Basin, SW Wyoming

The 87Sr/86Sr ratios for the carbonate fraction of micritic mudstone samples from the

Arco WB 1 and 2WB cores (Figures 4.11 and 4.12; Tables 4.6 and 4.7) trends toward less

radiogenic ratios in the upper LaClede bed, averaging 0.71231 in the lower LaClede and

0.71172 in the upper LaClede. The Sr isotopic composition of a sample from the buff marker

bed at Trail Dugway, separating the lower from the upper LaClede beds, is given in Table 4.8

(see Appendix A for UW samples numbers).Figure 4.12 contains Sr isotope data for the

carbonate fraction of micritic mudstone measured throughout the LaClede Bed. Figures

4.12a and 4.12b illustrate a trend with Sr and Rb concentrations relative to the amount of

carbonate removed from the sample. This is interpreted as a dilution trend, where samples

containing more carbonate material have relatively more Sr than Rb (a measure of clastic

contamination). Figure 4.12c shows that the 87Sr/86Sr ratio measured is not dependent on the

relative amount of carbonate in the sample and suggests that the 87Sr/86Sr of the clastic

contaminant is between 0.713 and 0.711. Figure 4.12d is a scatter diagram that shows the

difference in the 87Sr/86Sr vs. 1/Sr for the carbonates from the lower and upper LaClede beds.

The plot suggests that there was a change in the source of Sr to the lake from lower LaClede

to upper LaClede deposition.

130

Figure 4.12. Sr isotope data for micritic material from the Laney Member. A) and B)

illustrate a correlation between Sr and Rb concentrations and the amount of carbonate

material removed from the sample. C) illustrates the 87Sr/86Sr ratio of the carbonate

does not appear to be related to the percent carbonate removed. D) The Sr isotope

composition of the source of micritic material in the lower LaClede bed of the Laney

Member is different than for the upper LaClede Bed.

131 Table 4.6.

Stratigraphic unit Sample name

Sr (ppm)

Rb (ppm)

87Rb/86Sr 87Sr/86Sr i a 87Sr/86Sr

m Lithology

Upper LaClede Bed WB1-341 368.9 3.24 0.025 39 0.711 85 ± 1 0.711 87 micriteWB1-344 716.8 0.99 0.003 99 0.711 58 ± 1 0.711 58 micriteWB1-347 410.2 1.33 0.009 39 0.711 89 ± 1 0.711 90 micriteWB1-350 387.2 1.08 0.008 07 0.711 75 ± 1 0.711 76 micriteWB1-353 176.7 3.16 0.051 70 0.711 66 ± 1 0.711 70 micriteWB1-356 103.2 2.31 0.064 86 0.711 58 ± 2 0.711 63 micriteWB1-362 608.4 0.57 0.002 73 0.711 34 ± 1 0.711 34 micriteWB1-368 1 171 1.94 0.004 79 0.711 82 ± 1 0.711 82 micriteWB1-371 552.0 0.54 0.002 81 0.711 57 ± 1 0.711 58 micriteWB1-374 630.2 0.77 0.003 56 0.710 90 ± 1 0.710 91 micriteWB1-374 667.1 0.86 0.003 74 0.710 94 ± 1 0.710 94 micriteWB1-383 747.9 3.13 0.012 12 0.711 91 ± 1 0.711 92 micriteWB1-398 517.8 3.05 0.017 04 0.712 20 ± 1 0.712 21 micriteWB1-401 820.8 1.21 0.004 28 0.712 04 ± 1 0.712 04 micriteWB1-407 479.4 1.11 0.006 72 0.712 15 ± 1 0.712 16 micriteWB1-410 624.4 0.87 0.004 02 0.711 82 ± 1 0.711 82 micriteWB1-416 1 112 0.75 0.001 94 0.712 38 ± 1 0.712 38 micriteWB1-416 1 280 0.69 0.001 55 0.712 38 ± 1 0.712 39 micriteWB1-419 914.8 0.63 0.002 00 0.711 77 ± 1 0.711 78 micriteWB1-422 835.4 0.88 0.003 05 0.711 54 ± 1 0.711 54 micrite

Lower LaClede Bed WB1-499 818.5 2.10 0.007 43 0.712 69 ± 1 0.712 69 micriteWB1-518 521.7 0.82 0.004 65 0.711 75 ± 1 0.711 75 micriteWB1-527 749.7 0.69 0.002 67 0.712 37 ± 1 0.712 38 micriteWB1-556 823.2 1.31 0.004 62 0.712 63 ± 1 0.712 63 micriteWB1-565 974.2 1.44 0.004 28 0.712 09 ± 1 0.712 09 micriteWB1-566 902.2 1.42 0.004 56 0.711 99 ± 1 0.711 99 micriteWB1-567 1 081 1.58 0.004 23 0.712 21 ± 1 0.712 21 micriteWB1-568 816.8 5.39 0.019 10 0.712 68 ± 1 0.712 69 micriteWB1-571 805.4 1.57 0.005 64 0.712 51 ± 1 0.712 51 micriteWB1-572 755.0 2.51 0.009 63 0.712 41 ± 1 0.712 42 micriteWB1-573 899.1 1.29 0.004 15 0.712 05 ± 1 0.712 05 micriteWB1-574 626.7 1.63 0.007 53 0.712 24 ± 1 0.712 25 micriteWB1-576 1 223 0.36 0.000 85 0.712 51 ± 1 0.712 51 micriteWB1-577 1 160 0.90 0.002 25 0.712 56 ± 1 0.712 56 micriteWB1-579 661.8 5.12 0.022 40 0.712 22 ± 1 0.712 24 micriteWB1-579 675.7 1.57 0.006 74 0.712 23 ± 1 0.712 24 micriteWB1-580 891.9 1.56 0.005 06 0.712 22 ± 1 0.712 22 micriteWB1-581 1 085 1.92 0.005 13 0.712 50 ± 1 0.712 50 micriteWB1-582 1 378 0.83 0.001 75 0.712 64 ± 1 0.712 64 micriteWB1-582 1 276 1.10 0.002 50 0.712 66 ± 1 0.712 66 micriteWB1-583 609.1 1.24 0.005 89 0.712 68 ± 1 0.712 68 micriteWB1-587 921.1 1.04 0.003 27 0.712 26 ± 1 0.712 26 micriteWB1-589.4 672.5 6.48 0.027 89 0.712 98 ± 1 0.713 00 micriteWB1-593 816.7 1.42 0.005 02 0.712 44 ± 1 0.712 44 micrite

a Age for initial ratios is 50 Ma.

Strontium isotope composition of carbonate from micritic facies in the Arco Oil and Gas WB 1 core, Laney Member, Green River Formation

132

le 4.8.

Stratigraphic unit Sample name

Sr (ppm)

Rb (ppm)

87Rb/86Sr 87Sr/86Sr i a 87Sr/86Sr

m Lithology

buff marker bed TD-34.25 727.6 41.85 0.166 60 0.716 28 ± 1 0.716 40 dolo. volcaniclastic sandTD-34.25 121.3 88.79 2.123 36 0.728 13 ± 1 0.729 63 volcaniclastic sandTD-34.25 1 003 0.19 0.000 55 0.715 26 ± 1 0.715 26 dolomiteTD-34.25 1 304 0.60 0.001 33 0.715 27 ± 1 0.715 27 dolomiteTD-34.25 985.8 0.20 0.000 58 0.715 28 ± 1 0.715 28 dolomite

a Age for initial ratios is 50 Ma.

Strontium isotopic composition of the buff marker bed, Laney Member, Washakie Basin

Table 4.7.

Stratigraphic unit Sample name

Sr (ppm)

Rb (ppm)

87Rb/86Sr 87Sr/86Sr i a 87Sr/86Sr

m Lithology

Upper LaClede Bed 2WB-43.1 323.1 2.16 0.019 34 0.711 62 ± 1 0.711 63 micrite2WB-48 414.6 2.26 0.015 79 0.711 43 ± 1 0.711 44 micrite2WB-66 407.2 1.34 0.009 51 0.711 89 ± 1 0.711 90 micrite2WB-72 466.0 0.43 0.002 69 0.711 21 ± 1 0.711 21 micrite2WB-80.8 1 287 1.98 0.004 45 0.711 61 ± 1 0.711 61 micrite2WB-89.1 539.8 0.52 0.002 81 0.711 53 ± 1 0.711 54 micrite2WB-101 87.38 1.15 0.038 14 0.711 71 ± 1 0.711 74 micrite2WB-126.9 406.1 2.37 0.016 91 0.711 82 ± 1 0.711 83 micrite

Lower LaClede Bed 2WB-187 1 006 0.57 0.001 65 0.713 56 ± 1 0.713 56 dolomicrite2WB-188 1 074 2.21 0.005 95 0.712 44 ± 1 0.712 44 micrite2WB-189 806.9 2.43 0.008 71 0.712 27 ± 1 0.712 27 micrite2WB-190 513.4 2.25 0.012 66 0.712 25 ± 1 0.712 26 micrite2WB-191 1 311 1.01 0.002 23 0.711 74 ± 1 0.711 74 micrite2WB-192 1 722 0.90 0.001 52 0.711 60 ± 1 0.711 60 micrite2WB-192 1 586 0.80 0.001 46 0.711 59 ± 1 0.711 59 micrite2WB-193 1 307 0.85 0.001 89 0.711 85 ± 1 0.711 85 micrite2WB-194 720.7 1.82 0.007 32 0.712 23 ± 1 0.712 24 micrite

a Age for initial ratios is 50 Ma.

Strontium isotope composition of carbonate from micritic facies in Arco Oil and Gas 2 WB core, Laney Member, Green River Formation

Tab

133 5. MASS BALANCE MODEL APPROACH

structed and used to evaluate the

contrib he model

1

s).

0 years;

an assu

in,

the

Sr

from mudflats.

A simple Sr mass balance model was con

ution of Sr to Lake Gosiute from various drainages surrounding the basin. T

was designed to simulate changes in the range of 87Sr/86Sr ratios measured from lacustrine

carbonate material in lake expansion – contraction cycles. It is composed of 3 stages; stage

is an incremental addition model of the expansion of the lake, stage 2 is a steady state flux

model of the lake overflowing its sill during maximum expansion (eg. Hodell et al., 1989),

and stage 3 is an evaporation model adapted from the assimilation and fractional

crystallization model of DePaolo (1981) (see Table 4.9 for variables and equation

The model was run arbitrarily for a period of 21,000 years, each stage for 7,00

mption that the sedimentation rate and duration of each stage is the same and that

there are no sedimentary hiatuses. Other model assumptions include 1) a cone shaped bas

50 meters deep and capable of holding 700 cubic kilometers of water, and 2) the relative

contents of all Sr reservoirs are the same. The model is driven by changing the relative

contribution of Sr from groundwater (through and across mudflats), drainages internal to

Green River Basin, and extrabasinal drainage (from the Absaroka Range) to Lake Gosiute

during lake expansion and contraction. During lake expansion, the relative contribution of

to the lake from mudflats decreases in proportion to the increase in the relative contribution

of Sr from extrabasinal drainage, to simulate the shift from closed to open basin hydrologies.

When the lake entirely fills the basin, the mudflats are covered and there is no contribution of

Sr from water across and through the mudflats to the lake. During lake contraction, the Sr

contribution from extrabasinal drainage decreases in proportion to the increase in drainage

134

ake (incremental addition model)

Assumptions: A) fill a cone shaped basinB) relative Sr contents of all reservoirs are the same

Limits: Ru =

Table 4.9.Strontium mass balance model for Lake Gosiute.

STAGE 1: Fill the l

87Sr/86Sr input from intrabasin mountainsRa =

87Sr/86Sr input from extrabasinal Absaroka RangeRm =

87Sr/86Sr input from groundwater and runoff on mudflatsRi = input of 87Sr/86Sr into laker = radius of lakeR = maximum radius of lakeI = fraction of 87Sr/86Sr from intrabasinal sourcesE = fraction of 87Sr/86Sr from extrabasinal sourcesM = fraction of 87Sr/86Sr from mudflatsf ( r ) = fraction of total area covered by lakeVL = volume of lakeVi = volume of inputSr = Sr concentration of reservoir(I, E, M) water = percent of water from source(I, E, M) Sr = percent of Sr from source(I, E, M) ppm = water times concentration

When there is no lake, r = 0, thenRi = (I Sr * Ru) + (E Sr * Ra) + (M Sr * Rm)

When the lake is at its maximum extent, thenRi = (I Sr * Ru)+ (E Sr * Ra)

STAGE 2: Standard Flux model (e.g. Hodell et al., 1989)

Rlake (t) = Rn - [Rn-Ri] e^[(t-t0)/t]

t = residence time, ~10,000 yrs if a lot of Sr ppt ~5,000,000 yrs if a little Sr ppt

Rn =87Sr/86Sr from mountains, lake full, no mudflats

Rlake =87Sr/86Sr of lake at end of stage 1

STAGE 3: Assimilation and Fractionational Crystallization Model (adapted from DePaolo, 1981)

R = ratio assimilation/crystallization (DePaolo, 1981)rate input/ rate evaporation (this study)

D = crystal/liquid Kd (DePaolo, 1981)0 (no strontium evaporates)

Ra = assimilant isotope comp (DePaolo, 1981)input 87Sr/86Sr (this study)

Ci = concentration Sr initial

Ca = concentration Sr assimilant (input)

Ri = initial 87Sr/86Sr of lake

f ( r ) = fraction of liquid remaining = 1.0 when lake is fullF fraction of input from mountains

"Z" = (R+D-1)/(R-1) = 1"RZ" = R/((R-1)*Z) = R/(R-1)

87Sr/86Sr Lake = RZ*Ca(1-f( r )^(-Z))*Ra+Ci*f( r )^(-Z)*Ri

(RZ*Ca(1-f( r )^(-Z))+Ci*f( r )^(-Z))

135 5.1. Model Inputs

Model inputs include 87Sr/86Sr ratios and Sr concentrations for runoff inte

basin, drainage from extrabasinal sources (“spilled” from upstream basins), and groundwater

sourced from mudflat environments around the contracted lake. The initial contribution

(percentage) from each potential Sr source is also required to run to the model. Additional

inputs include Sr residence time for the steady-state stage of the model and the ratio of water

input to evaporation for the final stage of the model. An explanation of the data input to

drive the model follows.

The Sr isotopic compositions and concentration weighted averages of modern

drainage entering the Green River Basin and within the Absaroka Range (Table 4.2.) were

used to approximate the Sr isotopic compositions of internal and extrabasinal drainages in the

model (87Sr/86Sr ~ 0.7116, Sr ~ 0.113 ppm; ~0.7049, 0.050 ppm, respectively). The

contribution of Sr to the lake from groundwater is difficult to characterize. Fo

conditions, the 87Sr/86Sr ratio for groundwater entering the lake was considered to be sim

to the concentration weighted average for a tufa measured from the Laney Memb

4.4; 87Sr/86Sr of 0.7133). Alternatively, an 87Sr/86Sr ratio of ~0.7136 measured from

dolomitic carbonate within an expansion – contraction cycle in the 2WB core is s

radiogenic Sr isotope composition, possibly derived from groundwater (Wolfbauer and

Surdam, 1974; Table 4.7). However, groundwater filtering through radiog

have been significantly more radiogenic. Sr isotope compositions of 0.7200 and 0.7400 were

also input into the model to test the sensitivity of this source of Sr to the lake on m

conditions. The concentration of Sr in the groundwater, influenced by uplifts internal to the

basin as well as clastic and carbonate sediments in the basin, was initially estim

rnal to the

r initial model

ilar

er (Table

a

lightly more

enic clays could

odel

ated to be 1

136 ppm (cf. Lyons et al., 1995; Katz and Bullen, 1996; Johnson and DePaolo, 1997), and

evaluat

for

data

the

ts

om

ed at 0.100 ppm.

The residence time of Sr in the lake was considered to be similar to the residence time

of Sr in the ocean (~2 Ma). The residence time of Sr in the ocean is a function of Sr

concentration, the amount of Sr supplied to it (from rivers, mid ocean ridges, and

atmospheric fluxes), and the amount of Sr removed from the system. The sensitivity of this

parameter in a lacustrine system during the steady-state stage of the model was evaluated

shorter residence times.

Paleoclimate data was needed to drive the final stage of the model. Paleofloral

from Wilf (2000) suggest a mean annual precipitation of roughly ~ 80 cm during the final

stages of Lake Gosiute and Bradley (1963) estimated the evaporation to have been ~140

cm/year, making the input/evaporation ratio ~0.57.

5.2. Model Scenarios

Eight different model scenarios are documented in Table 4.10 and Figure 4.13. The

modeled curves are plotted with measured data from an expansion-contraction cycle in

WB1 core (see Table 4.6). Because the contribution of Sr from each source is unknown,

models 1 and 2 contain initial contributions of 50% runoff from Green River Basin uplif

and 50% drainage and groundwater from mudflats. The only variable between models 1 and

2 is the 87Sr/86Sr of water from the mudflats (0.7133 to 0.7136, both 1 ppm). Figures 4.13a

and 4.13b illustrate the effect of changing the Sr isotopic composition of groundwater fr

the mudflats in the model, the shape of the curve does not vary, but the range in 87Sr/86Sr

shifts toward slightly more radiogenic ratios. Both curves slightly underestimate the range in

137

138

Figure 4.13. Mass balance models and the measured 87Sr/86Sr ratios from expansion-

contraction cycles of Lake Gosiute. The red dotted line is measured data from an

expansion – contraction cycle from the WB1 core. Model parameters are documented

in Table 4.10. Models 1-6 include a component of extrabasinal drainage and Models

7-8 do not.

139 87Sr/86Sr, and model 2 more closely predicts the initial and final Sr compositions. Initial

contributions of 50% runoff, 50% groundwater is probably unrealistic for the tectonically

controlled Green River Basin. A more realistic initial relative contribution of water to the

basin from internal sources is attained by increasing the 87Sr/86Sr ratio from waters in the

mudflats to 0.7200 (Model 3, Figure 4.13c). In order to approach the range in the measured

data with a higher Sr isotope composition from the mudflats, the initial contribution to the

lake from the mudflats was reduced to 3.7% (see Table 4.10). The shape of the model curve

changed as a result of the increase in radiogenic Sr from this source. Stage 1 approaches the

measured data and the inflection in stage 3 is reduced. The absolute range in the measured

data is still not supported. Model 4 illustrates that the same model curve can be derived with

the addition of water from the mudflats with an 87Sr/86Sr ratio of 0.7400, consequently

decreasing the initial contribution from that source to 0.71% to approach measured ratios

(Table 4.10).

In order to increase the range in 87Sr/86Sr ratios modeled to include less radiogenic

ratios and to better approximate measured data, the concentration of the extrabasinal drainage

was increased from 0.050 to 0.150 ppm in Model 5 (Figure 4.13e). This is a reasonable

estimate for drainage from intermediate composition volcanic rocks in the Absaroka Range.

However, to honor the measured Sr isotope composition from drainage in the Absaroka

0.7200

as an i to

0.100

component of extrabasinal drainage and that the variation in Sr isotope composition within

Range, a similar result is attained in Model 6 by once again using an 87Sr/86Sr ratio of

nput for the drainage from mudflats and decreasing the concentration of that source

ppm (Table 4.10, Figure 4.13f).

Models 7 and 8 (Figures 4.13g and h) evaluate the possibility that there was no

140 an expansion – contraction cycle is a result of eliminating the source of Sr from the mudfl

by expanding the lake over them. Both models were run with a Sr input from groundwater

0.7200; Model 7 with a Sr concentration of 0.100 ppm; and Model 8 with a concentration o

1.0 ppm. The modeled curves do not support the range in the Sr isotope composition of th

measured data.

Figure 4.14 illustrates that the model is much more sensitive to a range in the water

balance of the basin (input to evaporation) than it is for reasonable variations in Sr residence

time in the lake. Stage 1 of the model is most influenced by the Sr isotopic composition of

sources and the initial contribution of Sr to the basin. Stage 2 is dependent upon the Sr

residence time. For long Sr residence times (0.5 to 2.0 Ma) the model does not shift

significantly. Shorter, and more unrealistic, residence times do shift the model significa

Stage 3 of the model is driven by the input/evaporation values. There are significant chang

in the range of

ats

of

f

e

ntly.

es

Sr/86Sr ratios predicted for low input/evaporation vs. high input/evaporation.

Figure he

e in

87

4.14 shows the approximate shift in the modeled curve for input/evap from 0.57 in t

model (dark blue), equal input/evap (1.0) for light blue line, and considerably more

evaporation (~0.34) in green. For a range of realistic values, this variable is very sensitiv

the model.

141

Figure 4.14. Model sensitivities for Sr residence time and input / evaporation values for

stages 2 and 3 of the model. The dark blue line indicates a representative model

condition. The red dotted line is measured data from WB 1 core. The shape

curve in Stage 1 is most influenced by the parameters set for the initial Sr

contri

of the

bution to the basin. The shape of the line for Stage 2 line is determined by the

Sr residence time. The modeled line (dark blue) is for a residence time of 2 Ma and

the green line indicates the approximate shift in its position for a Sr residence time of

50 Ka. Stage 3 is driven primarily by the input to evaporation to the basin. For lower

input/evaporation (1/3), the green line shifts toward a less variable and less radiogenic

Sr isotope composition, and for higher input/evaporation (1/1), the light blue line

indicates a more variable and more radiogenic 87Sr/86Sr.

142 5. DISCUSSION

The Sr isotope composition of lacustrine carbonate material in the Laney Member

varies significantly at a cm scale within different facies, within individual expansion –

contraction cycles as a function of facies and stratigraphic position, and unidirectionally

within micritic mudstone facies throughout the LaClede Bed. These results 1) are discussed

with respect to diagenesis; 2) considered with respect to mass balance modeling; 3) indicate

an increasing hydrologic connection to less radiogenic waters during lake expansion; and 4)

strengthen the sequence stratigraphic interpretation of a paleohydrologic shift punctuated by

a temporary, but major hydrologic event in the basin.

5.1. Diagenesis

It is important to recognize the effects of diagenesis because it can alter th primary

overgro re

observe s

and stro detectable

in relat

Our ini

imperm

ratios b

can be

diagene

measur . If a late diagenetic fluid

e

Sr isotope composition of carbonate materials. Diagenetic fabrics, such as dolomitic

wths, replacement, carbonate dissolution and recrystallization, and silicification a

d in many of the more porous lake marginal facies (ie. ostracode and ooid grainstone

matolites) of the Laney Member (Figure 4.7e, f, g, h), and are not visually

ively impermeable profundal lacustrine micritic mudstone facies (Figure 4.7a, b, c).

tial study, to test for small scale variations in Sr isotope composition within relatively

eable lake marginal facies, indicated that there are significant shifts in the 87Sr/86Sr

etween consecutive samples spaced 1-cm apart. The variable Sr isotope composition

interpreted to illustrate that the strata were unaffected by large scale, homogenous

tic alterations. However, it is possible that the carbonate Sr isotope composition

ed from this sample characterizes fine-grained diagenesis

143 passed through these strata, it altered the carbonate fraction of the various lithologies

differen

ata

WB 1 core for which the Sr isotope

composition was measured (samples WB1-570 and WB1-578; see Figure 4.9 for data).

located at the base of cycles 2 and 4 that are bound by impermeable

mudsto

tly. This might be resolved by measuring the Sr isotope composition of the clastic

fraction of this sample.

The calcite/dolomite ratios analyzed for the lacustrine expansion – contraction str

of Rhodes et al. (2002) illustrate that the Sr isotope composition is related to the carbonate

mineralogy of the strata, which is in turn related to stratigraphic position within an individual

cycle. This predictable trend in mineralogy and 87Sr/86Sr ratio within individual cycles is

interpreted to support the presence of primary carbonate. Figure 4.7 illustrates visually

identifiable diagenetic fabrics in samples from the Arco

These samples are

ne, placing the strata in a pathway vulnerable for the migration of diagenetic fluids.

In each case, the 87Sr/86Sr ratio is less radiogenic than measured for the sample

stratigraphically above it. Given the dominant trend in Sr isotopic composition with

stratigraphic position, it is possible that less radiogenic diagenetic fluids altered the primary

Sr isotopic composition of these strata.

Despite the trends in mineralogy and Sr isotope composition reported here, carbonate

diagenesis of the fine-grained micrite can not be ruled out entirely. To further address this

possibility, a systematic oxygen isotope and clay mineralogy study is necessary.

144 5.2. Mass Balance Modeling

Mass balance modUncertainties

els of the Sr isotope composition measured from carbonate

minera

e

ion of

e Sr to

ribution to Lake Gosiute.

e

e cyclicity

dicate that climate may not been the dominant influence on lake expansion and contraction

orrill et al., 2001). Nonetheless, climatic conditions could have changed significantly

uring a lacustrine expansion and contraction, and throughout the deposition of the Laney.

ls in lacustrine expansion – contraction cycles contain several uncertainties. The

model assumes a constant time component related to lacustrine expansion and contraction,

and that each stage of the model is represented stratigraphically. If the cycle is

stratigraphically incomplete, then the true range in 87Sr/86Sr in Lake Gosiute might not hav

been recorded. The duration of each individual lake stage with respect to the others

(expansion, steady-state, contraction) could have greatly influenced the variation in Sr

isotope composition of the water, especially for lake expansion and contraction.

The assumption that a groundwater component, or any water that may have been

influenced by radiogenic clays in the mudflat environment, had an influence on the Sr

isotope composition of the lake is another uncertainty. The Sr isotope composit

Eocene groundwater is difficult to characterize, but may have been an important sourc

the lake. Analysis of paleosol carbonates, spring deposits, and mudflat clay may help to

further characterize the groundwater cont

The climate conditions during the deposition of the Laney Member are estimated

based on the Leaf Margin Analysis (Wilf, 2000) of quarried floral assemblages from discret

stratigraphic intervals. Climate models created to test for orbitally driven lacustrin

in

(M

d

145 The current resolution of climatic data is too coarse to compare to cycle-scale variation in Sr

isotope composition.

ion, a model

sults

f

radiogenic,

extraba of

o

tion

igh stand, and

contrac

e

Interpretation of Model Results

Recognizing the uncertainties associated with some of the model conditions,

especially with respect to cycle duration and lake-stage stratigraphic representat

fit should be first evaluated by how appropriately it matches the range in Sr isotope

composition measured from the expansion and contraction of the lake. The model re

suggest that the range of Sr isotope composition measured from the carbonate fraction o

micritic mudstone in the Laney Member can be best explained by including a less

sinal component of drainage to the lake. Models 7 and 8 that contain only sources

Sr internal to the Green River Basin do not predict 87Sr/86Sr ratios that are low enough t

honor the measured data. This is a preliminary conclusion based on the current source

characterization of Sr to Lake Gosiute.

If the expansion – contraction cycle analyzed for its carbonate Sr isotope composi

was deposited during roughly equivalent periods of lake expansion, h

tion (stages 1-3), then the model does not accurately predict the geochemical

evolution of the lake within the cycle. For example, the model curves for stage 1 predict an

increasing rate of change with time, whereas the measured data trend toward a decreasing

rate of change upsection. Similarly, the steady-state model for stage 2 predicts a linear trend

with very little change in the Sr isotope composition with time. This is not observed in th

measured data.

146 However, assuming the model inputs are reasonable, the shape of the model curve for

each stage of the lake evolution can provide clues about the drivers for changing Sr isotopic

composition within an expansion – contraction cycle. For example, the shape of the 87Sr/86Sr

zed, and compared to models in Figure 4.13 could represent

a relati r period

are

he

icritic mudstone and lacks the well-developed

dolomi

e

from the region. The mass balance model indicates that the range in Sr

isotope composition measured from the micritic mudstone can be explained by including a

curve of the cycle sampled, analy

vely short period of sedimentation during lake expansion, followed by a longe

of sedimentation during lake contraction. If there was a steady-state, “overfilled” stage, then

it was recorded below the resolution of sampling in this interval. This interpretation

indicates that the net loss of the lake through evaporation is the dominant control on lake

level and the sources of Sr to the basin. For comparison, Figure 4.9. shows the Sr isotope

composition of the carbonate fraction of micritic mudstone throughout 4 lake expansion –

contraction cycles. The shape of the data from cycle 1 is similar to the general shape of

stages 1 and 2 of the model, indicating that the initial expansion and overflow of the lake

the dominant processes preserved in the sediments. This interpretation is supported by t

stratigraphy of this cycle; it is primarily m

critic mudstone that typifies lake contraction.

5.3. Long term shift in Sr isotope composition

A hydrologic connection between Lake Gosiute and the Absaroka Range was

documented by Surdam and Stanley (1980) during the final stages of Laney deposition. On

of the objectives of this study was to test for a hydrologic connection to the Absaroka Range

in the fine-grained micritic mudstone that is stratigraphically below the volcaniclastic

sandstone derived

147 compon

ured

r

d

ppm; 0.7118, 500 ppm). The range

of data from the upper LaClede bed overlaps the lower LaClede bed data, but is additionally

he lake (<~0.7105, 1600 ppm). The overall

trend is uence),

n.

ent of extrabasinal drainage (Figure 4.13). Whole rock, clastic, and carbonate Sr

isotopic analyses of the overlying Sand Butte Bed (Table 4.5; Figure 4.7j) support a

provenance that is less radiogenic than the surrounding Precambrian uplifts. Carbonate

cement sampled from the volcaniclastic sand derived from the Absaroka Range has Sr

isotopic ratios of 0.71048 (Green River Basin) and 0.71104 (Washakie Basin), less

radiogenic than the fine-grained carbonate within the mudstone, but more radiogenic than

either previously documented Sr isotope compositions of Absarokan rock or the meas

value for drainage in the region. A hydrologic connection to the Absarokas could be bette

delineated by characterizing the potential source of Sr from the larger drainage basin that

includes the Eocene volcanics, the Beartooth Mountains, and uplifts further northward.

Figure 4.15 is a plot of 87Sr/86Sr vs. 1/Sr that illustrates a shift in Sr isotope

composition from the lower LaClede bed to the upper LaClede bed of the Laney Member.

Data from the lower LaClede bed are marked by triangles and the upper LaClede bed marke

by squares. The Sr composition of the lower LaClede bed appears to be constrained by at

least 3 components (~0.7136, 1000 ppm; ~0.7116, 1600

constrained by a less radiogenic source of Sr to t

interpreted to indicate a mix of Sr from radiogenic groundwater (or clastic infl

Sr from uplifts internal to the Green River Basin, Sr from extrabasinal volcanics, and the

freshening of the lake during upper LaClede deposition.

The variation in the Sr isotope composition is interpreted to be a measure of the

geomorphic response to changes in tectonic and/or magmatic processes in the drainage basi

The long term measured hydrologic shift, superimposed by smaller scale fluctuations as

148

Figure 4.15. A scatter plot illustrating the shift in the Sr isotope composition of the carbon

fraction of the Laney Member from the lower LaClede bed to the upper LaClede bed.

The data suggest that the source water shifted toward a less radiogenic component,

and supports the freshening of the lake waters during the deposition of the upper

LaClede bed.

ate

149 described for the individual lake cycles, indicates the continued incorporation of less

radiogenic through time. This may be due to the fill and spill of upstream drainages to Lake

Gosiute, as represented by the Sand Butte Bed.

5.4. Sequence stratigraphy, hydrology, and Sr isotope composition

The lacustrine sequence stratigraphic stacking patterns of the Laney Member are

interpreted to indicate a decrease in basin subsidence and increase in the sediment and water

supplied to the basin (Chapter 2, Rhodes and Carroll, 2002). The Sr isotopic composition of

lacustrine carbonate material throughout the Laney Member strengthens the sequence

stratigraphic interpretation by highlighting a paleohydrologic shift, uniting chemical

evolution of lakewater with its record of lacustrine sedimentation. A review of the possible

hydrologic evolution in response to interpreted tectonic, magmatic, and geomorphic

processes recorded in Laney strata follows.

the infi

perhaps ce

upstrea er

while i rd the basin (Sundell, 1993). Volcanoes within the drainage basin

reated new topographic highs in pre-existing basins, perhaps capturing more precipitation.

hether or not the amount of water increased to the basin, the potential sediment supply

creased with the evolution of the volcanic terrane. Although there are no coarse-grained

olcaniclastic deposits from the Absaroka Range in the lower LaClede bed, the shift in Sr

A decrease in the basin subsidence as Laramide deformation came to an end initiated

ll of the balanced fill Green River Basin beginning in lower LaClede time (and

earlier). This changed regional base level and allowed drainage networks to coales

m, gradually increasing the component of runoff from the Absaroka volcanic cent

t migrated towa

c

W

in

v

150 isotope composition can be modeled to support a hydrologic connection during this tim

The volcaniclastic sediments could have been trapped in upstream basins during this time.

The stratigraphic relations and Sr isotope

e.

composition of the buff marker bed (whole

rock, dolomite, and clastic fractions, Table 4.7) indicate that a drastic change in

tion of less radiogenic

drainag dal

m

he

d the

The dolomite rhombs in the buff marker bed

(Figure

Sr

paleohydrology occurred within an overall shift toward the incorpora

e to the basin. The buff marker bed overlies a major desiccation surface in profun

mudstone facies of the lower LaClede bed, and contains sedimentary features indicative of

rapid sedimentation (Rhodes et al., in review; Chapter 5 for details). The desiccation event

and subsequent deposition of the buff marker bed is interpreted to represent the upstrea

damming of a major drainage to the basin, the contraction of the lake, desiccation of t

basin, and the reintroduction of drainage to the basin (Chapter 5). Dolomitic facies in the

unit are more radiogenic than for any carbonate facies below or above it (0.71527) an

clastic fraction is very radiogenic (0.72813).

4.7i) are interpreted to have formed during desiccation of the lower LaClede bed

when temporary playa conditions prevailed after the lake was eliminated from the basin

(Wolfbauer and Surdam, 1974). The Sr isotope composition of the dolomite rhombs may

reflect cation exchange with the radiogenic clastic fraction (Johnson and DePaolo, 1997).

The expanding lake ripped up and re-deposited the evaporative crust that formed over the

desiccated lower LaClede bed, analogous to the deposition of lake marginal transgressive

units within individual lake cycles of the lower LaClede. Importantly, the shift in overall

isotope composition across the buff marker bed indicates that the deposit was only a

temporary perturbation in the long-term paleohydrologic evolution of the basin.

151 Following the deposition of the buff marker bed, the lake attained its sill level once

again, and the volcaniclastic deltas of the Sand Butte Bed prograded into the overfilled lake

basin.

e Creek and

al

ate

ge

rates

n. Figure

4.16. contains a plot of 87Sr/86Sr vs. 1/Sr for the modern drainages entering the basin, and a

The appearance of volcaniclastic sandstone in the basin signified the fill of upstream

basins and the “spill” into the Green River Basin, and eventually into the Piceanc

Uinta Basins to the south (Surdam and Stanley, 1980). Sedimentation outpaced subsidence

and could have been accentuated by regional tilt associated with the migration of magmatic

activity toward the basin. Nonetheless, it is true that the presence of Lake Gosiute depended

upon the existence of relative accommodation space that was no longer being created fast

enough near the end of Laney time.

5.4. Future work

Though I have suggested what might have driven variations in the Sr isotope

composition of lacustrine carbonates in the Laney Member of the Green River Formation,

additional data are needed to quantitatively resolve the relative importance of different

sources of Sr to the basin. The Sr isotopic composition of Eocene groundwater, a potenti

lever on the Sr mass balance of Lake Gosiute, is very difficult to quantify. Primary carbon

materials from paleosol concretions and tufa deposits will help to directly measure the Sr

contribution from groundwater input to the lake. In addition, the systematic geochemical

analysis of the clastic fraction of micritic mudstone will provide data regarding ion exchan

with carbonates and possible mudrock diagenesis. A better estimate of the relative

contribution of Sr to Lake Gosiute can be modeled by understanding stream discharge

and the relative proportion of component lithologies crossed in each drainage basi

152 probable Sr isotope composition for Lake Gosiute water. The Sr isotope composition of

modern drainage can be utilized to better constrain the relative Sr contents of each potential

source area, and to therefore improve attempts at mass balance modeling the Sr flux to Lake

Gosiute.

153

Figure 4.16. The Sr isotopic composition for modern drainages in the Green River Basin.

he end members are drainage from the Uinta Mountains (primarily Precambrian

ged) and drainage from the Sevier Thrust Belt (Paleozoic carbonates and Mesozoic

arbonates and clastics).

T

a

c

154 6. CONCLUSIONS

1) The Sr isotope composition of lacustrine carbonates from the Laney Member

varies significantly between different lithologies on a cm scale.

2) Permeable, lake marginal carbonate facies contain visually recognizable

diagenetic fabrics, whereas impermeable, profundal facies do not. Significant

variation in the Sr isotope composition on a cm scale and throughout

lacustrine expansion contraction cycles is interpreted as evidence that there

has been no pervasive diagenesis of fine-grained lacustrine carbonates,

although diagenesis has not been investigated thoroughly.

3) The Sr isotope composition of lacustrine carbonates from individual

expansion – contraction cycles in the Laney Member varies with carbonate

mineralogy. Calcite-rich micrite from expanded lacustrine intervals are less

radiogenic than dolomicrites from contracted lake periods.

ic

best explained by a hydrologic connection to less

radiogenic extrabasinal drainage from the Absaroka Range.

5) The shape of the curve generated in the Sr mass balance models of the

incremental expansion, steady-state highstand, and evaporation of Lake

Gosiute are potentially useful to interpret the particular hydrologic processes

recorded in fine-grained micritic mudstone.

4) The long term trend in Sr isotope composition from profundal lacustrine

carbonates indicates the increasing influence of drainage from less radiogen

source. Preliminary mass balance models predict that the range in Sr isotope

composition can be

155 6) The shift in paleohydrology interpreted by the unidirectional trend in Sr

aleohydrology

7) y

asin,

of Laramide

isotope composition of fine-grained lacustrine carbonates toward less

radiogenic 87Sr/86Sr ratios can be traced across a major shift in p

recognized by a desiccation event at the base of the buff marker bed, and

within the Sr isotopic record of the buff marker bed.

The trends in Sr isotope composition of the carbonates within the Lane

Member strengthen the sequence stratigraphic interpretation of a gradual

decrease in basin subsidence and increase in sediment and water to the b

interpreted to reflect the geomorphic response to the waning

deformation.

156

Chapter Five

Sudden desiccation of Lake Gosiute at 49 Ma: A downstream effect of Heart Mountain faulting?

157 Rhodes, Meredith K., Malone, David H., and C rroll, Alan R., in review, Sudden desiccation

of Lake Gosiute at 49 Ma: a downstream effect of Heart Mountain faulting?,

submitted to Geology.

ABSTRACT

Mudcracks that were originally more than 3 m deep are directly superimposed on

profundal lacustrine mudstone of the lower LaClede Bed of the Green River Formation in the

Washakie basin, recording sudden and intense siccation of Eocene Lake Gosiute. We

propose that emplacement of the upper plate of the Heart Mountain Detachment caused this

desiccation, through blockage of debris avalanche. Stratified

epiclastic volcanic sediments in the Absaroka basin may represent the deposits of a short-

lived lake sin,

dolomitic mudstone to sandstone (known as th “buff marker bed”) was deposited above the

mudcrack horizon. These fluvial deposits mark the first appearance of volcaniclastic

sediments in the Green River Formation, and t lacustrine mudstone

record the reestablishment of regional drainages after the debris avalanche. Sudden

desiccation of Lake Gosiute contradicts model hat require slow emplacement of the upper

plate of the Heart Mountain Detachment, and highlights the importance of lacustrine strata as

archives of continental tectonics and paleogeom

a

de

south-flowing rivers by a giant

that was impounded upstream of this debris-flow dam. In the Washakie ba

e

ogether with overlying

s t

orphology.

158 1. INTRODUCTION

It is becoming increasingly apparent that the tectonic and magmatic history of lake

basins exerts a first-order control on the character of their deposits (Carroll and Bohacs,

1999). Major changes in lacustrine sedimentary facies associations may be induced by subtle

ructural influences on regional drainage organization (e.g., Kowalewska and Cohen, 1998;

Sáez et al., 1999; Pietras et al., in press), by spillover from upstream basins (e.g., Surdam and

Stanley, 1980), or volcanic activity (Bouchard et al., 1998). It is generally believed that

tectonic influences on lacustrine sedimentation tend to act relatively slowly, whereas higher-

frequency changes are usually attributed to periodic climate variability. However, this

presumption has seldom been directly tested. Sudden tectonic events might indeed be

capable of producing abrupt stratal discontinuities.

The Heart Mountain Detachment (HMD) has been one of the most enigmatic and

controversial features in North American structural geology for more than a century (c.f.,

Hauge, 1993). It is an important part of an ongoing debate over the significance and

processes of low-angle faulting and large-scale landsliding. Several aspects of the HMD are

in dispute, the most notable of which is the rate at which the upper plate was emplaced.

Emplacement was broadly contemporaneous with widespread igneous activity within the

18,000 km Absaroka Volcanic Province (Sundell, 1990; Hiza, 1999; Figure 5.1), and

occurred within a 2 million year window during the early middle Eocene (49.5-47.5 million

years ago; Pierce, 1973, 1987; Torres and Gingerich, 1983). Pierce (1973, 1987) argued for

atastrophic emplacement as numerous independently moving sliding blocks. In this

“tectonic denudation” model, overlying and adjacent Eocene volcanic rocks were interpreted

to largely post-date faulting. Malone (1995, 1996, 1997) also argued for rapid emplacement,

st

2

c

159

Figure 5.1. Regional geologic map with Eocene paleocurrent patterns,

present known extent of the Deer Creek Member, approximate

location of the buried paleo-valley, outline of Eocene Lake

Gosiute, and the field localities for buff marker bed correlation.

160 but interpreted Eocene volcanic rocks in the distal areas of the HMD as a gigantic debris

avalanche derived from the gravitational failure of a pre-existing volcanic edifice. In

contrast, Hauge (1985, 1990) envisioned a single, continuous allochthon that was gradually

deformed over a period of one million years or more, with synchronous Eocene volcanism.

Beutner and Craven (1996) advanced a model that was geometrically and kinematically

similar to Hauge’s continuous allochthon model, but that invoked the injection of volcanic

gases to trigger catastrophic movement along the detachment. Unfortunately, present

geochronologic contraints from the area of the HMD are insufficient to exclude any of these

hypotheses.

Eocene Lake Gosiute was impounded to the south and downstream of the HMD

(Surdam and Stanley, 1980; Smith et al., 2001; Pietras et al., in press), and was therefore

ideally situated to record the effects of emplacement of the upper plate on regional drainage

patterns. The deposits of the Green River Formation provide a higher-resolution record than

is available in the area of the HMD, and recent advances in age-dating of Green River

Formation tephras allow the timing of upstream events to be determined at a high level of

precision and accuracy. Conversely, recognition of the downstream effects of the HMD on

sedimentation in Lake Gosiute would greatly expand our general understanding of the

genesis of lacustrine stratigraphic sequences. In this paper we propose a causal relationship

placement of the upper plate of the HMD as a debris avalanche, and the

occurre osits of the

Laney Membe

between the em

nce of a major desiccation surface and subsequent fluvial-lacustrine dep

r of the Green River Formation.

161 2. DEER CREEK MEMBER OF THE WAPITI FORMATION, ABSAROKA BASI

The Deer Creek Member (DCM) of the Wapiti Formation consists of blocks

(individually as large as several km

N

se

,

d

e Wapiti Formation because it is within the type section of that unit as defined

by Nels s of

ody

e DCM is overlain by a stratified succession

of light colored, epiclastic volcanic sediments (the “upper stratified” unit of Figure 5.2a).

2 in area) of vent-medial-facies lava flows, breccia, and

sandstone, all within a thin, heterogeneous matrix of boulder to sand-sized volcaniclastic

material. It is interpreted as the deposit of a large debris avalanche, formed by the collap

of a large stratovolcano within the Absaroka Range during the early middle Eocene (Malone

1995, 1996). It was deposited into the adjacent Absaroka basin, with an areal extent an

volume of proximal facies totaling ~450 km2 and ~100 km3, respectively. The DCM was

assigned to th

on and Pierce (1968). Further work by Malone (1997) indicates that a distal facie

the unit also occurs throughout the upper South Fork Shoshone River valley. Malone and

Sundell (2000) broadened the interpretation of the DCM to include spatially and temporally

associated allochthonous Paleozoic rocks in the distal areas of the HMD. Thus allochthonous

Eocene volcanic and Paleozoic carbonate units together comprise the DCM.

The DCM rests upon a paleotopographic surface with at least 1000 m of relief. A

major early Eocene paleo-valley, more than 300 m deep and 10 km wide, was infilled and

preserved beneath the DCM along the eastern margin of the Absaroka Basin near the C

Arch (Sundell, 1990, Figure 5.2). The paleo-valley floor is within Cretaceous Cody Shale,

and the western paleo-valley wall is cut into the early Eocene Willwood Formation (the

eastern paleo-valley wall has been removed by erosion).

About 5 km west of this paleo-valley, th

162

Figure 5.2. The Deer Creek Member (DCM) of the Wapiti Formation along the North Fork

of the Shoshone River valley. West is to the left. The west edge of the large paleo-

valley is marked with an arrow. Also shown are: Kc = Cody Shale, Twl = Willwood

Formation; Twd = Deer Creek Member of Wapiti Formation; Mm = allocthonous

block of Madison limestone within the Heart Mountain allocthon; Twus = ‘upper

stratified’ post Deer Creek epiclastic volcanic sediments; Twlb = lower breccias of

Wapiti Formation; Twj = Jim Mountain Member of Wapiti Formation; Twub = upper

breccias of the Wapiti Formation.

163 This succession consists of alternating beds of mudstone, sandstone, conglomerate, and tuff,

and ranges in thickness from 0-150 m. It is thickest where it fills topographic lows on the

underly tructurally, texturally, and compositionally different

from overlying Wapiti Formation rocks and have a general appearance that is similar to older

Wapiti and Aycross Formation lithologies present further to the south (Malone, 1997;

Sundell, 1990). The overlying Wapiti Formation rocks consist of massive, dark-colored

breccias and lava flows that reflect the onset of the next cycle of volcanic activity in this part

of the Absaroka Range (see Figure 5.2).

3. LANEY MEMBER OF THE GREEN RIVER FORMATION

The Laney Member of the Green River Formation (Figure 5.1) records the final saline

to freshwater stage of Eocene Lake Gosiute (Bradley, 1964; Roehler, 1993). Maximum

expansion of the lake is represented by profundal facies of the lower LaClede Bed, which is

characterized by stacked, 1-3 meter cycles of stromatolite, laminated organic-rich micritic

mudstone (oil shale), and dolomicritic mudstone. These cycles have been previously

interpreted to represent episodes of relatively rapid deepening, followed by gradual

shallowing of the lake (e.g., Rhodes et al., 2002).

The lower LaClede Bed is capped by a horizon of deep mudcracks that extend ~2

meters downward (compacted length; Figures 5.3, 5.4, and 5.5). The cracks are generally

spaced 15 to 20 meters apart and are filled with dolomitic, volcaniclastic fine-grained sand

and intraclasts. The mudcrack horizon is present from the Delaney West section to the Sand

Butte section (Figures 5.1, 5.3). Similar giant desiccation cracks, comparable to the size

ing DCM. These rocks are s

164

Figure 5.3. Stratigraphic correlation through the buff marker bed along the Delaney and

Kinney Rims in the Washakie Basin.

165

Figure 5.4. Photomosaic of the section at Sand Butte illustrating the lower LaClede,

desiccated surface, buff marker bed, oil shale interval, and upper LaClede beds.

166

Figure 5.5. Mudcrack at the base of the buff marker

bed from the section at Sand Butte.

167 documented here, have been documented within modern playas of the Great Basin (Neal et

l., 1968) and the Black Rock and Smoke Creek Deserts (Willden and Mabey, 1961). In

contrast to the lesser mudcracks that often occur near the top of individual shallowing-

upward cycles of the lower LaClede Bed, the deep mudcrack horizon is directly

superimposed on laminated profundal mudstone. We interpret this horizon to record a period

of sudden and profound desiccation of Lake Gosiute that was anomalous and apparently

unique.

Immediately overlying the mudcrack surface is a dolomitic, volcaniclastic siltstone to

sandstone deposit informally known as the “buff marker bed” (Roehler, 1973). The buff

marker bed thickens to the southwest and is roughly 12.5 meters thick at its best exposure in

the Trail Dugway section, where it is composed of dolomite, silt to medium-grained

micaceous sand, and volcaniclastic detritus interbedded with mudstone. The beds near the

bottom of the unit at this location are composed of siltstone to fine-grained sandstone, are

medium bedded, and contain parallel to sub-parallel wavy mudstone lamination. The beds

coarsen and thicken upward in the middle of the unit, where they are composed of fine- to

edium-grained sand that is either ripple cross-laminated, trough cross-laminated, or

massive and disco d thin upward and

are composed of thin bedd s clasts 3-4-cm in length, and

tercalated mudstone.

We interpret the stratigraphy of the buff marker bed to represent a period of alluvial

rogradation followed by retrogradation. The buff marker is overlain by a ~1.5 m bed of

olomitic oil shale. The overlying upper LaClede bed is characterized by 1 to 2 cycles

approximately 5 m thick, that each consist of a of a vertical succession of stromatolite,

a

m

ntinuous. In the upper part of the unit, the beds fine an

ed dolomitic siltstone with intraclast

in

p

d

168 micritic mudstone, and dolomicritic mudstone. These cycles are in turn overlain by 30 to 50

meters of relatively massive micritic and dolomicritic mudstone.

4. DISCUSSION AND CONCLUSIONS

Throughout the Green River Formation there is evidence that major drainage systems

entered the basin from the north. Early rivers flowing across the parts of the present Win

River Ra

d

nge and adjacent areas carried arkosic detritus that was deposited as southward-

prograd

r

r

ke

timing of emplacement of the upper plate of the HMD is consistent

with th

ed

f age

ing deltas of the Farson Sandstone (Roehler, 1993, Pietras et al., in press). Pietras et

al., (in press) argued that these drainages were subsequently diverted away from the greate

Green River Basin by renewed uplift of the Wind River range, resulting in a shift toward

evaporitic conditions in Lake Gosiute. Surdam and Stanley (1980) documented a late

northward expansion of drainage basin boundaries late in the history of Lake Gosiute, after

deposition of the LaClede Bed, when a series of deltas preserved as the Sand Butte Bed

prograded southward, eventually spilling into the Piceance Creek to the south.

It is therefore likely that major structural modifications of the landscape north of La

Gosiute could have significantly impacted lacustrine sedimentation. In particular, the

emplacement of debris-avalanche deposits has been shown in other cases to produce vast

changes in basin hydrology, due to the infill of stream channels (Reneau and Dethier, 1996;

Waythomas, 2001). The

e development of the giant mudcracks described above and with deposition of the

overlying buff marker. Radioisotopic dating of a tuff bed 7 m above the buff marker yield

a preliminary age of 49.02 ± 0.15 Ma (Smith et al., 2001), well within the lower bound o

constraints for the HMD. The size and orientation of the paleo-valley described above

169 suggests that it (and perhaps other similar features) could have been an important conduit for

water flowing south to the lake. Blockage of this paleo-valley would have at least

temporarily impounded or diverted these waters, and may have formed an upstream lake into

ents that post-date the DCM were deposited.

ay

ing

buff

mite

le on the lake

plain, a

loor.

hin

gh

which the stratified epiclastic volcanic sedim

We propose that catastrophic emplacement of the DCM was responsible for the

sudden desiccation of Lake Gosiute, and that the buff marker records the gradual

reestablishment of southward drainage following this event. The diversion of drainage aw

from the greater Green River Basin shifted the overall hydrologic balance of Lake Gosiute

toward evaporation, causing the lake to dry up, groundwater levels to drop, and giant

mudcracks to form. Shortly thereafter southward flow was gradually restored by overtopp

of the debris avalanche dam, breaching by outlet streams, or by headward erosion. The

marker bed first records rapid progradation of alluvial fine-grained dolomitic and siliciclastic

detritus into Lake Gosiute as regional drainage was reestablished. We infer that the dolo

was derived from reworking of efflourescent crusts formed above the water tab

s proposed by Wolfbauer and Surdam (1974). Depending on the duration of

basinwide desiccation, such crusts may also have formed on parts of the exposed lake f

The siliciclastic detritus is compositionally similar to volcaniclastic material contained wit

the Wapiti Formation, and marks the first known influx of such detritus into the greater

Green River Basin. Micaceous sand in the buff marker bed may also have been derived in

part from metamorphic basement uplifts. As inflow to Lake Gosiute increased, lake level

rose and shorelines transgressed back over the exposed basin floor. The oil shale bed that

immediately overlies the buff marker bed records the return of deep lacustrine conditions.

Reintegration of regional drainage networks was probably complete by this time, althou

170 the overall character of deposits above the buff marker bed suggests a continuing shift toward

increased inflow relative to evaporation.

The above scenario is consistent with catastrophic emplacement of an intact upper

plate of the HMD. The actual time required to form the giant mudcracks and buff marker

bed is u

eau and

ectonic

acement

of

,

nknown, but based on comparison with modern analogues, a period of years to

centuries seems most likely (c.f., Willden and Mabey; 1961; Neal et al., 1968; Ren

Dethier, 1996; Waythomas, 2001). The debris-avalanche model provides a convenient

mechanism for the sudden transfer of preexisting volcanic rocks from paleo-highs into

adjacent paleo-valleys. In contrast, the post-movement volcanism envisioned in the “t

denudation” model might be expected to mantle the pre-existing topography more uniformly,

and thus would have produced less sudden drainage modifications. Additional work in the

area of the HMD is needed to provide better geochronologic constraints, and to look for

debris-dammed lake deposits, deposits from outburst floods, or other sedimentologic

evidence of sudden drainage modifications. Rapid desiccation of Lake Gosiute and

subsequent deposition of the buff marker bed are not consistent with the slower empl

of a continuous allocthon. If this did in fact occur, then it has not left a clearly discernible

downstream record in the Green River Formation.

More broadly, this study shows that regional tectonic and magmatic events may

profoundly alter the character of lake deposits over very short timescales. A single event of

large magnitude may exert a disproportionate influence on the deposition and preservation

lacustrine facies, as has been previously proposed for other depositional settings (e.g., Dott

1983). The results of this study also demonstrate that lacustrine strata can provide an

171 important and unique perspective on the tectonic evolution of the continents that so far has

been underutilized.

172 REFERENCES

Albarede, F., and Michard, A., 1987, Evidence for slowly changing 87Sr/86Sr in runoff from

eshwater limestones of France, Chemical Geology, v. 64, p. 55-65.

Anderm ormational history of a portion of the north flank of the

inta Mountains in the vicinity of Manila, Utah, Wyoming Geological Association

Guidebook, 10th Annual Field Conference, p. 130-134.

Andersson, P.S., Wasserburg, G.J., Ingri, J., and Stordal, M.C., 1994, Strontium, dissolved

ticulate loads in fresh and brackish waters: The Baltic Sea and Mississippi

elta, Earth and Planetary Science Letters, v. 124, p. 195-210.

Axelrod, D.I., 1968, Tertiary floras and topographic history of the Snake River Basin, Idaho,

merica Bulletin, v. 79, p. 713-734.

Bain, D.C., and Bacon, J.R., 1994, Strontium isotopes as indicators of mineral weathering in

catchments, Catena, v. 22, no. 3, p. 201-214.

Baker, P.A., and Kastner, M., 1981, Constraints on the formation of sedimentary dolomite,

cience, v., 213, p. 214-216.

Barazangi, M., and Isacks, B.L., 1976, Spatial distribution of earthquakes and subduction of

the Nazca plate beneath South America, Geology, v. 4, p. 686-692.

Bartels, W.S., and Zonnenfeld, J.P., 1997, Lithofacies associations and sequence

stratigraphic framework of the Eocene Wasatch, Green River, and Bridger

ormations, western Green River basin, Wyoming: Geological Society of America,

bstracts with Programs, v. 29, no. 6, p. 272.

fr

an, G.G., 1955, Tertiary def

U

and par

D

Geological Society of A

S

F

A

173 Bell, W.G., 1954, Stratigraphy and geologic history of Paleocene rocks in the vicinity of

09, p. 55-87.

y, Palaeoecology, v.

Beutne and the Heart Mountain

Bohacs ositional sequences in mudrocks from

ttgart, Schweizerbart’sche Verlagsbuchhandlung, p. 33-

Bohacs asin type, source

Boucha uade, J., 1998, Quaternary history of

the Thatcher Basin, Idaho, reconstructed from the 87Sr/86Sr and amino acid

composition of lacustrine fossils: implications for the diversion of the Bear River into

Bison Basin, Wyoming, Geological Society of America Bulletin, v. 65, Part II, p.

1371.

Benson, L., 1994, Carbonate deposition, Pyramid Lake subbasin, Nevada: Sequence of

formation and elevational distribution of carbonate deposits (tufas),

Palaeogeography, Palaeoclimatology, Palaeoecology, 1

Benson, L., and Peterman, Z., 1995, Carbonate deposition, Pyramid Lake subbasin, Nevada:

3, The use of 87Sr values in carbonate deposits (tufas) to determine the hydrologic

state of paleolake systems, Palaeogeography, Palaeoclimatolog

119, p. 201-213.

r, E.C., and Craven, A.E., 1996, Volcanic fluidization

detachment, WY, Geology, v. 24, p. 595-598.

, K.M., 1998, Contrasting expressions of dep

marine to nonmarine environs, In: J. Schieber, W. Zimmerlie, and P. Sethi, (eds.),

Shales and mudstones I.: Stu

78.

, K.M., Carroll, A.R., Neal, J.E., Mankiewicz, P.J., 2000, Lake-b

potential, and hydrocarbon character: an integrated-sequence-stratigraphic-

geochemical framework, In: E.H. Gierlowski-Kordesch and K.R. Kelts, (eds.), Lake

basins through space and time: AAPG Studies in Geology 46, p. 3-34.

rd, D.P., Kaufman, D.S., Hochberg, A., and Q

174 the Bonneville Basin, Palaeogeography, Palaeoclimatology, Palaeoecology, v. 141,

p. 95-114.

, W.HBradley ., 1929, The varves and climate of the Green River epoch, United States

Bradley

aper 168, 58 p.

Bradley ster, H.P., 1969, Geochemistry and paleolimnology of the trona

ofessional Paper 496-B, 71 p.

Brauna

s tongue of the Wasatch Formation (Eocene), Wyoming, Journal of Sedimentary

Brown

an Association

Geological Survey Professional Paper 158-E, 110 p.

, W.H., 1931, Origin and microfossils of the oil shale of the Green River Formation,

of Colorado and Utah, United States Geological Survey Professional P

Bradley, W.H., 1964, The geology of the Green River Formation and associated Eocene

rocks in southwestern Wyoming and adjacent parts of Colorado and Utah, United

States Geological Survey Professional Paper 496-A, 86 p.

, W.H., and Eug

deposits and associated authigenic minerals of the Green River Formation of

Wyoming, United States Geological Survey Pr

Brass, G.W., 1975, The effect of weathering on the distribution of strontium isotopes in

weathering profiles, Geochimica et Cosmochimica Acta, v. 39, p. 1647-1653.

gel, L.H., and Stanley, K.O., 1977, Origin of variegated redbeds in the Cathedral

Bluff

Petrology, v. 47, no. 3, p. 1201-1219.

, L.F., and Fisher, W.L., 1977, Seismic-stratigraphic interpretation of depositional

systems: examples from Brazil rift and pull-apart basins, In: C.E. Payton, (ed.),

Seismic stratigraphy-applications to hydrocarbon exploration, Americ

of Petroleum Geologists Memoir 26, p. 213-248.

175 Brown,

s to general geology, United States Geological Survey Professional Paper

Brown, een River flora, United States

Buchhe

Buchhe

(eds Sedimentology and

Buchhe ment of

Buchhe mation,

Buchhe

g, In: J.K. Pitman and A.R. Carroll (eds.):

Burke,

hout Phanerozoic time, Geology, v.

10, p. 516-519.

R.W., 1928, Additions to the flora of the Green River Formation, in Shorter

contribution

154, p. 279-292.

R.W., 1934, The recognizable species of the Gr

Geological Survey Professional Paper 185-C, p. 45-77.

im, H.P., 1978, Paleolimnology of the Laney Member of the Eocene Green River

Formation, Ph.D. thesis, University of Wyoming, Laramie, Wyoming, 101p.

im, H.P., 1994, Eocene Fossil Lake, Green River Formation, Wyoming: A history of

fluctuating salinity, In: R.W. Renaut and W.M. Last,

Geochemistry of Modern and Ancient Saline Lakes, SEPM Special Publication No.

50, p. 239-247.

im, H.P. and Surdam, R.C., 1977, Fossil catfish and the depositional environ

the Green River Formation, Wyoming, Geology, v. 5, p. 196-198.

im, H.P., and Surdam, R.C., 1978, Carbonate cycles in Green River For

Wyoming, American Association of Petroleum Geologists Bulletin, v. 62, p. 881-882.

im, H.P., and Eugster, H.P., 1998, Eocene Fossil Lake: The Green River Formation of

Fossil Basin, southwestern Wyomin

Modern and Ancient Lake Systems, Utah Geological Association Guidebook 26, p.

191-207.

W.H., Denison, R.E., Hetherington, E.A., Koepnick, R.B, Nelson, H.F., and Otto,

J.B., 1982, Variation of seawater 87Sr/86Sr throug

176 Capo, R.C., Stewart, B.W., and Chadwick, O.A., 1998, Strontium isotopes as tracers of

ecosystem processes: Theory and methods, Geoderma, v. 82, p. 197-225.

Carroll, A.R., and Bohacs, K.M., 1999, Stratigraphic classification of ancient lakes:

Casano hydrological history of Lake

Clyde, ld, J-P., Stamatakos, J., Gunnell, G.F., and Bartels, W.S., 1997,

g, The Journal of

Cohen,

Critten

Dake, C.L., 1918, The Hart Mountain overthrust and associated structures in Park County,

Dam, G

regressions of the Rhaetian-Sinemurian Kap Stewart Formation,

Jameson Land, East Greenland, In: Steel, R.J. et al., (eds.), Sequence Stratigraphy of

Balancing tectonic and climatic controls, Geology, v. 27, no. 2, p. 99-102.

va, J., and Hillaire-Marcel, C., 1992, Late Holocene

Tanganyika, East Africa, from isotopic data on fossil stromatolites, Palaeogeography,

Palaeoclimatology, and Palaeoecology, v. 91, p. 35-48.

Cerveny, P.F., and Steidtmann, J.R., 1993, Fission track thermochronology of the Wind

River Range, Wyoming; evidence for timing and magnitude of Laramide exhumation,

Tectonics, v. 12, p. 77-92.

W.C., Zonneve

Magnetostratigraphy across the Wasatchian/Bridgerian NAMLA Boundary (Early to

Middle Eocene) in the Western Green River Basin, Wyomin

Geology, v. 105, p. 657-669.

A.S., and Thouin, C., 1987, Nearshore carbonate deposits in Lake Tanganyika,

Geology, v. 15, p. 414-418.

den, M.D., and Peterman, Z.E., 1975, Provisional Rb/Sr age of the Precambrian Uinta

Mountain Group, northeastern Utah, Utah Geology, v. 2, p. 75-77.

Wyoming, Journal of Geology, p. 45-55.

., Surlyk, F., Mathiesen, A., and Christiansen, F.G., 1995, Exploration significance of

lacustrine forced

177 the Northwest European Margin: Norwegian Petroleum Society Special Publication 5,

p. 511-527.

DeCelles, P.G., 1994, Late Cretaceous-Paleocene synorogenic sedimentation and kinematic

history of the Sevier thrust belt, northeast Utah and southwest Wyoming, Geological

DePaol

osmochimica Acta, v. 43, p.

DePaol

n, Earth and Planetary Science Letters, v. 53, p. 189-202.

Dickinson, W.R., 1979, Cenozoic plate tectonic setting of the Cordilleran region in the

estern United States, Pacific Coast Paleogeography

Dickins ide Orogeny, In:

of America Memoir 151, p. 355-366.

Society of American Bulletin, v. 106, p. 32-56.

o, D.J., and Wasserburg, G.J., 1979, Sm-Nd age of the Stillwater Complex and the

mantle evolution curve for neodymium, Geochimica et C

999-1008.

o, D.J., 1981, Trace element and isotopic effects of combined wallrock assimilation

and fractional crystallizatio

Desborough, G.A., 1978, A biogenic-chemical stratified lake model for the origin of oil shale

of the Green River Formation: An alternative to the playa-lake model, Geological

Society of American Bulletin, v. 89, p. 961-971.

United States, In: J.M. Armentrout, M.R. Cole, and J. TerBest, Jr., (eds.), Cenozoic

paleogeography of the w

Symposium, v. 3., p. 1-13.

on, W.R., and Snyder, W.S, 1978, Plate tectonics of the Laram

Matthews, V., III (ed.), Laramide folding associated with basement faulting in the

western United States, Geological Society

Divis, A.F., 1977, Isotopic studies on a Precambiran geochronologic boundary, Sierra Madre

Mountains, Wyoming, Geological Society of America Bulletin, v. 88, p. 96-100.

178 Donnel

acustrine unit from northern Australia, Sedimentary Geology, v. 58, p.

Dorr, J

Hoback Basin, Wyoming, Geological

Dott, R

er?, Journal of Sedimentary Petrology, v. 53, p. 5-23.

English

Rivers, Nepal, Geochimica et

Eugster

Eugster, H.P., 1969, Inorganic bedded cherts from the Magadi area, Contributions to

Eugster

erica

Explora eter

GR-320 Users Manual, software version 3V02, 73 p.

ly, T.H., and Jackson, M.J., 1988, Sedimentology and geochemistry of a mid-

Proterozoic l

145-169.

.A., Spearing, D.R., and Steidtmann, J.R., 1977, Deformation and deposition between

a foreland uplift and an impinging thrust belt:

Society of America Special Paper 177, 82 p.

.H., Jr., 1983, Episodic sedimentation; how normal is average? How rare is rare?

Does it matt

Eggleston, J.R., and Dean, W.E., 1976, Freshwater stromatolitic bioherms in Green Lake,

New York, In: M.R. Walter, (ed.), Stromatolites : Amsterdam, Elsevier Science

Publishing, p. 479-488.

, N.B., Quade, J., DeCelles, P.G., and Garzione, C.N., 2000, Geologic control of Sr

and major element chemistry in Himalayan

Cosmochimica Acta, v. 64, p. 2549-2566.

, H.P., 1967, Hydrous sodium silicates from Lake Magadi, Kenya; precursors of

bedded chert, Science, v. 157, p. 1177-1180.

Mineralogy and Petrology, v. 22, p. 2-31.

, H.P., and Surdam, R.C., 1973, Depositional Environment of the Green River

Formation of Wyoming: A Preliminary Report, Geological Society of Am

Bulletin, v. 84, p. 1115-1120.

nium Radiation Detection Systems, April 1998, Portable Gamma Ray Spectrom

179 Faure, G., 1986, Principles of isotope geology (2nd edition): New York, John Wiley & Sons,

589 p.

G., 1991Faure, , Principles and applications of inorganic geochemistry, Macmillan

Faure G

Transactarctic Mountains, Journal of

Fisher, ox Group of Texas

Frost, C and Hulsebosch, T.P., 1998, The Late Archean

Galy, A 1999, The strontium isotopic budget of

ntary Petrology, v. 39, no. 1, p. 49-69.

gists, Denver, CO, p. 9-32.

Publishing Company: New York, 626 p.

., and Barret, P.J., 1973, Strontium isotope composition of non-marine carbonate

rocks from the Beacon Supergroup of the

Sedimentary Geology, v. 43, p. 447-457.

W.L., and McGowen, J.H., 1967, Depositional systems in the Wilc

and their relationship to occurrence of oil and gas, Transactions of the Gulf Coast

Association of Geological Societies, v. 17, p. 105-125.

.D., Frost, B.R., Chamberlain, K.R.,

history of the Wyoming province as recorded by granitic magmatism in the Wind

River Range, Wyoming, Precambrian Research, v. 89, p. 145-173.

., France-Lanord, C., and Derry, L.A.,

Himalayan rivers in Nepal and Bangladesh, Geochimica et Cosmochimica Acta, v.

63, p. 1905-1925.

Gebelein, C.D., 1969, Distribution, morphology, and accretion rate of recent subtidal algal

stromatolites, Bermuda, Journal of Sedime

Gries, R., 1983, North-south compression of the Rocky Mountain foreland structures, In:

Lowell, J.D. (ed.), Rocky Mountain foreland basins and uplifts, Guidebook, Rocky

Mountain Association of Geolo

Hail, W.J., 1965, Geology of the northwestern North Park, Colorado, United States

Geological Survey Bulletin, v. 1188, 133 p.

180 Halley, R.B., 1976, Textural variation within Great Salt Lake algal mounds, In:

Stromatolites, M.R. Walter, (ed.), Elsevier Sci. Publ. Co. Amsterdam, Netherlands, p.

Hanley nd biostratigraphy of nonmarine Mollusca

Hauge, untain allochthon, Geological

Hauge,

eds.), Geology of

Hedge,

ism in the northern Front Range, Colorado, Geological Society of

Hedge, ean

435-445.

, J.H., 1974, Systematics, paleoecology, a

from the Green River and Wasatch Formations (Eocene), southwestern Wyoming and

northwestern Colorado, University of Wyoming, Laramie, Unpublished Ph.D. thesis.

285 p.

Hauge, T.A, 1985, Gravity-spreading origin of the Heart Mountain Allochthon, northwestern

Wyoming, Geological Society of America Bulletin, v. 96, p. 1440-1456.

T.A., 1990, Kinematic model of a continuous Heart Mo

Society of America Bulletin, v. 102, p. 1174-1188.

T.A., 1993, The Heart Mountain detachment, northwestern Wyoming: 100 years of

controversy, In: A.W. Snoke, J.R. Steidtman, and, S.M. Roberts, (

Wyoming: Geological Survey Memoir #5, p. 530-571.

C.E., Peterman, Z.E., and Braddock, W.A., 1967, Age of the major Precambrian

regional metamorph

America Bulletin, v. 78, p. 551-558.

C.E., Simmons, K.R., and Stuckless, J.S., 1986, Geochronology of an Arch

granite, Owl Creek Mountains, Wyoming, Chemical and isotopic studies of granitic

Archean rocks, Owl Creek Mountains, United States Geological Survey Professional

Paper, p. 23-33.

181 Hiza, M.M., 1999, The geochemistry and geochronology of the Eocene Absaroka volcanic

province, northern Wyoming and southern Montana, USA [Ph.D. thesis]: Corvallis,

Oregon State University, 243 p.

Hsu, K Siegenthaler, C., 1969, Preliminary experiments on hydrodynamic movement

United States, Palaeogeography,

Johnso

12-829.

Katz, B

he hydrochemical interaction between groundwater and lakewater

in mantled karst, Geochimica et Cosmochimica Acta, v. 60, p. 5075-5087.

Hodell, D.A., Mueller, P.A., McKenzie, J.A., and, Mead, G.A., 1989, Strontium isotope

stratigraphy and geochemistry of the late Neogene ocean, Earth and Planetary

Science Letters, v. 92, p. 165-178.

.J., and

induced by evaporation and their bearing on the dolomite problem, Sedimentology, v.

12, p. 11-25.

Hutchison, J.H., 1982, Turtle, crocodilian and champsosaur diversity changes in the

Cenozoic of the north-central region of western

Palaeoclimatology, Palaeoecology., v. 37, p. 149-164.

n, T.C., Wells, J.D., and Scholz, C.A., 1995, Deltaic sedimentation in a modern rift

lake, Geological Society of America Bulletin, v. 107, p. 8

Johnson, T.M., and DePaolo, D.J., 1997, Rapid exchange effects on isotope ratios in

groundwater systems; 2, Flow investigation using Sr isotope ratios, Water Resources

Research, v. 33, p. 197-209.

Jones, L.M., and Faure, G., 1972, Strontium isotope geochemistry of Great Salt Lake, Utah,

Geological Society of America Bulletin, v. 83, p. 1875-1879.

.G., and Bullen, T.D., 1996, The combined use of 87Sr/86Sr and carbon and water

isotopes to study t

182 Keefer, W.R., 1965, Stratigraphy and geological history of the uppermost Cretaceous,

Paleocene and lower Eocene rocks on the Wind River Basin, Wyoming, United States

Geological Survey Professional Paper 495-A.

ociety Special Paper 40, p. 3-26.

King, C., 1878, Systematic geology of the Fortieth Parallel, U.S. Explor. Fortieth Parallel, v

Krishta

llegraven, J.A., 1987, Eocene

eochronology and

Korneg

and its relationship to Wyoming, In: Stratigraphy of

Kelts, K., 1988, Environments of deposition of lacustrine petroleum source rocks: an

introduction, In: A.J. Fleet, K. Kelts, and M.R. Talbot (eds.), Lacustrine Petroleum

Source Rocks, Oxford, Geological S

Kelts, K., and Hsü, K.J., 1978, Freshwater carbonate sedimentation, In: Lakes: Chemistry,

Geology, and Physics, A. Lerman, (ed.), p. 295-323, Springer-Verlag, Berlin.

1. p. 504-529.

lka, L., West, R.M., Black, C.C., Dawson, M.R., Flynn, J.J., Turnbull, W.D., Stucky,

R.K., McKenna, M.C., Bown, T.M., Golz, D.J., and Li

(Wasatchian and Duchesnian) biochronology of North America, In: M.O.

Woodburne, (ed.), Cenozoic mammals of North America: G

Biostratigraphy: Berkeley, California, University of California Press, p. 77-117.

ay, G.L., and Surdam, R.C., 1980, The Laney Member of the Green River Formation,

Sand Wash Basin, Colorado,

Wyoming, S. Hollis, (ed.), Wyoming Geological Association Guidebook, v. 31, p.

191-204.

183 Kowalewska, A., and Cohen, A.S., 1998, Reconstruction of paleoenvironments of the Great

Salt Lake basin during the late Cenozoic, Journal of Paleolimnology, v. 20, p. 381-

407.

Kutzbach, J.E., 1980, Estimates of past climate at paleolake Chad, North Africa, based on a

hydrological and energy-balance model, Quaternary Research, v. 14, p. 210-233.

s, D.R., and Chan, M.A., 1999, Facies architecture and sequence stratLemon igraphy of fine-

troleum

Lent, R.M., Gaudette, H.E., and Lyons, W.B., 1997, Strontium isotopic geochemistry of the

Leopol

Ludlam

and Oceanography, v. 14, p. 848-857.

Lyons, W.B., Tyler, S.W., Gaudette, H.E., and Long, D.T., 1995, The use of strontium

isotopes in determining groundwater mixing and brine fingering in a playa spring

zone, Lake Tyrrell, Australia, Journal of Hydrology, v. 167, p. 225-239.

grained lacustrine deltas along the eastern margin of late Pleistocene Lake

Bonneville, northern Utah and southern Idaho, American Association of Pe

Geologists Bulletin, v. 83, p. 635-665.

Devils Lake drainage system, North Dakota: a preliminary study and potential

paleoclimatic implications, Journal of Paleolimnology, v. 17, p. 147-154.

d, E.B., and MacGinitie, H.D., 1972, Development and Affinities of Tertiary Floras in

the Rocky Mountains, In: A. Graham (ed.), Floristics and Paleofloristics of Asia and

Eastern North America, Elsevier Publishing Company, 278 p.

Love, J.D., 1970, Cenozoic geology of the Granite Mountains area, central Wyoming, United

States Geological Survey Professional Paper 495-C.

, S.D., 1969, Fayetteville Green Lake, New York; 3. The laminated sediments,

Limnology

184 MacGinitie, H.D., 1969, The Eocene Green River flora of northwestern Colorado and

northeastern Utah, Berkeley and Los Angeles, California, University of California

Press, 203 p.

Malone Eocene Volcanic Rocks in the Lower North

Malone of the Deer

Malone ide/Debris Avalanche

MacLeod, M.L., 1981, The Pacific Creek anticline: buckling above a basement thrust fault,

Wyoming University Contributions to Geology, v. 19, p. 143-160.

Malone, D.H., 1995, A very large debris-avalanche deposit within the Eocene volcanic

succession of the Northeastern Absaroka Range, Wyoming, Geology, v. 23, p. 661-

664.

, D. H., 1996, Revised Stratigraphy of

and South Fork Shoshone River Valleys, Wyoming, Wyoming Geological Association

Annual Field Conference Guidebook, v. 47, p. 109-138.

, D.H., 1997, Recognition of a Distal Facies Greatly Extends the Domain

Creek Debris-Avalanche Deposit (Eocene), Absaroka Range, Wyoming, Wyoming

Geological Association Annual Field Conference Guidebook, v. 48, p. 1-9.

, D.H., and Sundell, K.A., 2000, Gigantic Eocene Landsl

Deposits of Wyoming’s Eastern Absaroka Range, Geological Society of America

Abstracts with Programs, v. 32, p. 79.

Markwick, P.J., 1994, “Equability”, continentality, and Tertiary “climate”; the crocodilian

prespective, Geology, v. 22, p. 613-616.

Marshak, S., 1999, Is Laramide (and ancestral Rockies) deformation, Western USA, a

consequence of rift inversion in the cratonic platform, Geological Society of America,

Abstracts with Programs, v. 31, p. 238.

185 Mason, G.M., and Surdam, R.C., 1992, Carbonate mineral distribution and isotope

fractionation: An approach to depositional environment interpretation, Green River

Formation, Wyoming, USA, Chemical Geology, v. 101, p. 311-321.

Meen, J.K., and Eggler, D.G., 1987, Petrology and geochemistry of the Cretaceous

Miller, synthesis,

Milliga

tocene climate at the eastern margin of Lake

continental rocks: Society of Sedimentary

Mitchu

onal sequence as a basic unit for stratigraphic

Maxson, J.A., and Tikoff, B., 1996, Hit and run collision model for the Laramide Orogeny,

Western United States, Geology, v. 24, p. 968-972.

McCulloch, M.T., and DeDeckker, P., 1989, Sr isotope constraints on the Mediterranean

environment at the end of the Messinian salinity crisis, Nature, v. 342, p. 62-65.

Independence volcanic suite, Absaroka Mountains, Montana: Clues to the

composition of the Archean sub-Montanan mantle, Geological Society of America

Bulletin, v. 98, p. 238-247.

Megard, F., and Philip, H., 1976, Plio-Quaternary tectono-magmatic zonation and plate

tectonics in the central Andes, Earth and Planetary Science Letters, v. 33, p. 231-238.

K.G., Fairbanks, R.G., and Mountain, G.S., 1987, Tertiary oxygen isotope

sea level history and continental margin erosion, Paleoceanography, v. 2, p. 1-19.

n, M.R., and Chan, M.A., 1998, Coarse-grained Gilbert deltas; facies, sequence

stratigraphy and relationships to Pleis

Bonneville, Northern Utah, In: K.W. Shanley, and P.J. McCabe, (eds.), Relative role

of eustasy, climate, and tectonism in

Geology Special Publication 59, p. 177-189.

m, R.M., Vail, P.R., and Thompson, S., III., 1977, Seismic stratigraphy and global

changes of sea level, Part 2: the depositi

186 analysis, In: C.E. Payton (ed.), Seismic stratigraphy applications to hydrocarbon

exploration, American Association of Petroleum Geologists Memoir 26, p. 53-62.

, C., Small, E.E., and Sloan, L.C., 2001, Modeling orbital forcinMorrill g of lake level

2, p.

Muelle

. and Wooden, J.L., eds., Precambrian Geology of the

Neal, J

n, v. 79, p. 69-90.

271-282.

change; Lake Gosiute (Eocene), North America, Global and Planetary Change, v. 29,

p. 57-76.

Morrill, C., and Koch, P.L., 2002, Elevation or alteration? Evaluation of isotopic constraints

on paleoaltitudes surrounding the Eocene Green River Basin, Geology, v. 30, no.

151-154.

r, P.A., Wooden, J.L., Odom, A.L., Bowes, D.R., 1982, Geochemistry of the Archean

rocks of the Quad Creek and Hellroaring Plateau areas of the eastern Beartooth

Moutains, In: Mueller, P.A

Beartooth Mountains, Montana and Wyoming: Montana Bureau of Mines and

Geology Special Publication 84, p. 69-82.

Mueller, P.A., Peterman, Z.E., and Granath, J.W., 1985, A bimodal Archean volcanic series,

Owl Creek Mountains, Wyoming, Journal of Geology, v. 93, p. 701-712.

Neal, J.E., Bohacs, K.M., Reynolds, D.J., and Scholz, C.A., 1997, Sequence stratigraphy of

lacustrine rift basins: critical linkage of changing lake level, sediment supply, and

tectonics, Abstracts with Programs, Geological Society of America, v. 29, p. 73.

.T., Langer, A.M., and Kerr, P.F., 1968, Giant desiccation polygons of Great Basin

Playas, Geological Society of America Bulleti

Neat, P.L., Faure, G., Pegram, W.J., 1979, The isotopic composition of strontium in non-

marine carbonate rocks: the Flagstaff Formation of Utah, Sedimentology, v. 26, p.

187 Nelson

ll.

ntains, Geology, v. 24, no. 5, p. 403-406.

l Society of America Bulletin, v. 108, p. 40-77.

Pache,

strine spring in a soda lake (Wallerstein

Palmer position of

Patel, S

al of

Pedone ntium isotope ratio in

, W. H., and Pierce, W. G., 1968, Wapiti Formation and Trout Peak trachyandesite,

northwestern Wyoming, United States Geological Survey Bulletin, 1254-H, p. Hl-H

Norris, R.D., Jones, L.S., Corfield, R.M., and Cartlidge, J.E., 1996, Skiing in the Eocene

Uinta Mountains? Isotopic evidence in the Green River Formation for snow melt and

large mou

Olsen, P.E., Kent, D.V., Cornet, B., Witte, W.K., and Schlische, R.W., 1996, High resolution

stratigraphy of the Newark rift basin (early Mesozoic, eastern North America),

Geologica

Oviatt, C.G., McCoy, W.D., and Nash, W.P., 1994, Sequence stratigraphy of lacustrine

deposits: a Quaternary example from the Bonneville basin, Utah, Geological Society

of America Bulletin, v. 106, p. 133-144.

M., Reitner, J., and Arp, G., 2001, Geochemical evidence for the formation of a large

Miocene “Travertine” mound at a sublacu

Castle Rock, Nördlinger, Ries, Germany), Facies, v. 45, p. 211-230.

, M.R., and Edmond, J.M., 1992, Controls over the strontium isotope com

river water, Geochimica et Cosmochimica Acta, v. 56, p. 2099-2111.

.C., Frost, C.D., and Frost, B.R., 1999, Contrasting responses of Rb-Sr systematics to

regional and contact metamorphism, Laramie Mountains, Wyoming, USA, Journ

Metamorphic Geology, v. 17, p. 259-269.

, V.A., 2000, Negative covariance between lake volume and stro

Great Salt Lake, Utah, Geological Society of America Abstracts with Programs, v. 32,

no. 7, p. 389.

188 Peterman, Z.E., Doe, B.R., and Prostka, H.J., 1970, Lead and Strontium Isotopes in Rocks of

the Absaroka Volcanic Field, Wyoming, Contributions to Mineralogy and Petrology,

v. 27, p. 121-130.

an, Z.E., and Hildreth, R.A., 1978, Reconnaissance geology and geochronology of the

Precambrian of the Granite Mountains, Wyoming,

Peterm

United States Geological Survey

Pierce,

John Wiley & Sons, New

Pierce,

Bulletin, v. 99, p. 552-568.

gical Society of

Pietras, ce stratigraphy:

Pietras, 1, Tectonostratigraphy of the Wilkins Peak

Pietras, M.E., Carroll, A.R., and Singer, B, 2002, Direct measurement of

depositional cyclicity using 40Ar/39Ar dating: A 430 thousand year record from

Professional Paper 1055, 22 p.

W.G., 1973, Principal features of the Heart Mountain fault and the mechanism

problem, In: Gravity and Tectonics, K. DeJong, (ed.),

York, p. 457-471.

W.G., 1987, The case for tectonic denudation by the Heart Mountain Fault; a

response, Geological Society of America

Pietras, J.T., Rhodes, M.K., Wartes, M.A., Carroll, A.R., Beard, B.L., and Johnson, C.M.,

1999, Strontium isotopes in provenance studies of large ancient lacustrine basins; an

example from the Junggar-Turpan-Hami basins, NW China, Geolo

America, Abstracts with Programs, v. 31, no 7, p. A298.

J.T., Carroll, A.R., and Rhodes, M.K., 2000, Lacustrine sequen

example from the Green River Formation of southwestern Wyoming, American

Association of Petroleum Geologists Annual Meeting, v. 9, p. A116.

J.T., Carroll, A.R., and Johnson, R.C., 200

Member of the Green River Formation, southwestern Wyoming, American

Association of Petroleum Geologists National Meeting, Abstracts, v. 10, p. A158.

J.T., Smith,

189 Eocene Lake Gosiute, Geological Society of America Abstracts with Programs, v. 34,

no. 6.

Pietras, J.T., Carroll, A.R., and Rhodes, M.K., in press, Lake basin response to tectonic

Pitman nd diagenetic carbonates in the lacustrine Green River

Platt, N .P., 1991, Lacustrine carbonates: facies models, facies distributions

Association of

Powell

Poyato eléndiz, N., and Wenz, S.,

drainage diversion: Eocene Green River Formation, Wyoming, Journal of

Paleolimnology.

, J.K., 1996, Origin of primary a

Formation (Eocene), Colorado and Utah, United States Geological Survey Bulletin

2157, 17 p.

.H., and Wright, V

and hydrocarbon aspects, In: Lacustrine Facies Analysis, P. Anadón, L. Cabrera, and

K. Kelts, (eds.), Special Publication of the International

Sedimentologists, p. 57-74.

, T.G., 1986, Petroleum geochemistry and depositional setting of lacustrine rocks,

Marine and Petroleum Geology, v. 3, p. 200-219.

-Ariza, F.J., Talbot, M.R., Fregenal-Martínez, M.A., M

1998, First isotopic and multidisciplinary evidence for nonmarine caecolanths and

pyncdontiform fishes: palaeoenvironmental implications, Palaeogeography,

Palaeoclimatology, Palaeoecology, v. 144, p. 65-84.

Ramos., A., Sopena, A., and Perez-Arlucea, M., 1986, Evolution of Buntsandstein fluvial

sedimentation in the Northwest Iberian Ranges (Central Spain), Journal of

Sedimentary Petrology, v. 56, p. 862-875.

190 Ratterm

he Green River Formation, Wyoming, Clays and Clay Minerals, v. 29, p.

Reneau

ite Rock Canyon, New Mexico, Geological Society of America

Rhodes

ember, Eocene Green River Formation, Washakie Basin, Wyoming,

Rhodes

gy, v. 30, p. 167-170.

e Eocene Green River Formation,

Rhodes

E1-E28.

Roehler, H.W., 1991, Correlation and oil-shale assays of measured sections of the LaClede

Bed of the Laney Member of the Green River Formation in outcrops along the

an, N.G., and Surdam, R.C., 1981, Zeolite mineral reactions in a tuff in the Laney

Member of t

365-377.

, S.L., and Dethier, D.P., 1996, Late Pleistocene landslide-dammed lakes along the

Rio Grande, Wh

Bulletin, v. 108, p. 1492-1507.

, M.K., and Carroll, A.R., 2001, Nonmarine sequence stratigraphic interpretation of

the Laney M

American Association of Petroleum Geologists Annual Meeting, v. 10, p. A167.

, M.K., Carroll, A.R., Pietras, J.T., Beard, B.L., and Johnson, C.M., 2002, Strontium

isotope record of paleohydrology and continental weathering, Eocene Green River

Formation, Wyoming, Geolo

Rhodes, M.K., and Carroll, A.R., 2002, Lacustrine sequence stratigraphic expression within

the balanced fill to overfilled Laney Member of th

Geological Society of America Abstracts with Programs, v.

, M.K., Malone, D.H., and Carroll, A.R., in review, Sudden desiccation of Lake

Gosiute at ~49 Ma: A downstream record of Heart Mountain faulting?, submitted to

Geology.

Roehler, H.W., 1973, Stratigraphic divisions and geologic history of the Laney Member of

the Green River Formation in the Washakie Basin in southwestern Wyoming, United

States Geological Survey Bulletin 1372-E,

191 western margins of Washakie Basin, Wyoming, and Sand Wash Basin, Colorado,

United States Geological Society, Miscellaneous Investigations Series, Map 2211.

r, H.W., 1Roehle 992, Correlation, composition, areal distribution, and thickness of Eocene

Roehle s, depositional environments, and geography, greater

Rosent rnary

Russell ary Lake of northwestern

Sáez, A

graphy in the Quillagua-Llamara Basin, central Andean fore-arc (northern

Scholz

etroleum Geologists Bulletin, v.

stratigraphic units, Greater Green River Basin, Wyoming, Utah, and Colorado, United

States Geological Survey Professional Paper No. 1506-E, 49 p.

r, H. W., 1993, Eocene climate

Green River basin, Wyoming, Utah, and Colorado, United States Geological Survey

Professional Paper No. 1506-F.

hal, Y., Karz, A., and Tchernov, E., 1989, The reconstruction of Quate

freshwater lakes from the chemical and isotopic composition of the gastropod shells:

the Dead Sea rift, Israel, Palaeogeography, Palaeoclimatology, Palaeoecology, v. 74,

p. 241-253.

Royse, C.F., Jr., Wadell, J.S., and Petersen, L.E., 1971, X-ray determination of calcite-

dolomite: and evaluation, Journal of Sedimentary Petrology, v. 41, no. 2, p. 483-488.

, I.C., 1885, Geologic history of Lake Lahontan, a Quatern

Nevada, US Geological Survey Monograph no. 11, 287 p.

., Cabrera, L., Jensen, A., and Chong, G., 1999, Late Neogene lacustrine record and

palaeogeo

Chile), Palaeogeography, Palaeoclimatology, Palaeoecology, v. 151, p.5-37.

, C.A., 1995, Deltas of the Lake Malawi rift, east Africa: seismic expression and

exploration implications, American Association of P

79, p. 1679-1697.

192 Scholz,

the East African and

Shanley, K.W., and McCabe, P.J., 1994, Perspectives on the sequence stratigraphy of

Simmo

preliminary evaluation using REE data for whole rocks and cumulate

Singer, eathering cycle in the Lake

Singh,

Lesser

C.A., and Finney, B.P., 1995, Late Quaternary sequence stratigraphy of Lake Malawi

(Nyasa), Africa, Sedimentology, v. 41, p. 163-179.

Scholz, C.A, Moore, T.C. Jr., Hutchinson, D.R., Golmshtok, A. Ja., Klitgord, K.D., and

Kurotchkin, A.G., 1998, Comparative sequence stratigraphy of low-latitude versus

high-latitude lacustrine rift basins; seismic data examples from

Baikal rifts, Palaeogeography, Palaeoclimatology, Palaeoecology, v. 140, p. 401-

420.

continental strata, American Association of Petroleum Geologists Bulletin, v. 78, p.

544-568.

ns, E.C. and Lambert, D.D., 1982, Magma evolution in the Stillwater Complex,

Montana: A

feldspars, In: Mueller, P.A. and Wooden, J.L., eds., Precambrian Geology of the

Beartooth Mountains, Montana and Wyoming: Montana Bureau of Mines and

Geology Special Publication 84, p. 91-106.

A., and Navrot, J., 1973, Some aspects of the Ca and Sr w

Kinneret (Lake Tiberias) drainage basin, Chemical Geology, v. 12, p. 209-218.

S.K., Trivedi, J.R., Pande, K., Ramesh, R., and Krishnaswami, S., 1998, Chemical and

strontium, oxygen, and carbon isotopic compositions of carbonates from the

Himalaya: Implications to the strontium isotope composition of the source waters of

the Ganga, Ghaghara, and the Indus Rivers, Geochimica et Cosmochimica Acta, v.

62, p. 743-755.

193 Sloan, L. C., 1994, Equable climates during the early Eocene; significance of regional

paleogeography for North American climate, Geology, v. 22, no. 10, p. 881-884.

Sloan,

l circulation modeling sensitivity study, Palaeogeography, Palaeoclimatology,

Smith,

logy of the Green River Formation, Wyoming: Geological Society of

Smith, ne

Smoot, s Peak

ene), Wyoming, USA, Sedimentology, v.

Smoot, sozoic

Soregh

ake Tanganyika; the effect of asymmetric basin structure on

Sloan, L.C. and Barron, E.J., 1992, A comparison of Eocene climate model results to

quantified paleoclimatic interpretations, Palaeogeography, Palaeoclimatology,

Palaeoecology, v. 93, p. 183-202.

L.C., and Rea, D.K., 1995, Atmospheric carbon dioxide and early Eocene climate: A

genera

Palaeoecology, v. 119, p. 275-292.

M.E., Singer, B., and Carroll, A.R., 2001, Precise 40Ar/39Ar laser fusion

geochrono

America, Abstracts with Programs, v. 33, p. 79.

M.E., Singer, B., and Carroll, A.R., in review, 40Ar/39Ar geochronology of the Eoce

Green River Formation, Wyoming, Geological Society of America Bulletin.

J.P., 1983, Depositional subenvironments in an arid closed basin; the Wilkin

Member of the Green River Formation (Eoc

30, p. 801-827.

J.P., 1991, Sedimentary facies and depositional environments of early Me

Newark Supergroup basins, eastern North American, In: A.R. Chivas, P. DeDeckker,

(eds.), Paleoenvironments of salt lakes, Palaeogeography, Palaeoclimatology,

Palaeoecology, v. 84, p. 369-423.

an, M.J., and Cohen, A.S., 1996, Textural and compositional variability across littoral

segments of L

194 sedimentation in large rift lakes, American Association of Petroleum Geologists

Bulletin, v. 80, p. 382-409.

Spencer, J.E., and Patchett, P.J., 1997, Sr isotope evidence for a lacustrine origin for the

upper Miocene to Pliocene Bouse Formation lower Colorado River trough, and

implications for timing of Colorado Plateau uplift, Geological Society of America

Stanley

Journal of Sedimentary Petrology, v. 48, p. 557-

Steidtm

e, Wyoming, In: J.D. Lowell, (ed.),

long the southern margin of the Wind River Range, Wyoming, In:

Steidtm 991, Fault chronology and uplift history of the

v. 103, p. 472-485.

Bulletin, v. 109, p. 767-778.

, R.C., and Surdam, K.O., 1978, Sedimentation of the front of Eocene Gilbert-type

deltas, Washakie Basin, Wyoming,

573.

ann, J.R., McGee, L.C., and Middleton, L.T., 1983, Laramide sedimentation, folding,

and faulting in the southern Wind River Rang

Rocky Mountain foreland basins and uplifts, Guidebook, Rocky Mountain

Association of Geologists, Denver, CO, p. 161-167.

Steidtmann, J.R, Middleton, L.T., Bottjer, R.J., Jackson, K.E., McGee, L.C., Southwell, E.H.,

and Lieblang, S., 1986, Geometry, distribution, and provenance of tectogenic

conglomerates a

J.A. Peterson, (ed.), Paleotectonics and sedimentation in the Rocky Mountains

Region, United States, American Association of Petroleum Geologists Memoir 41, p.

321-332.

ann, J.R., and Middleton, L.T., 1

southern Wind River Range, Wyoming: Implications for Laramide and post-Laramide

deformation in the Rocky Mountain foreland, Geological Society of America Bulletin,

195 Stein, M

al, and sedimentological evidence for the evolution of

Stewar

asin; radiogenic isotope results from the Owens River

Stewar

es in Plio-Pleistocene lacustrine evaporative deposits, Death Valley, California,

Sulliva

Sundel Absaroka Basin of northwestern

Sundel

Surdam gster, H.P., and Mariner, R.H., 1972, Magadi-Type Chert in Jurassic and

., Starinsky, A., Katz, A., Goldstein, S.L., Machlus, M., and Schramm, A., 1997,

Strontium isotopic, chemic

Lake Lisam and the Dead Sea, Geochimica et Cosmochimica Acta, v. 61, p. 3975-

3992.

t, B.W., 1998, Quaternary weathering processes and climate change in the Sierra

Nevada and western Great B

system, Geological Society of America Abstracts with Programs, v. 30, no. 7, p. 66.

t, B.W., Hsieh, J.C.C., and Murray, B.C., 1993, Strontium isotope record of cation

sourc

Geological Society of America Abstracts with Programs, v. 25, no. 6, p. 455-456.

n, R., 1985, Origin of lacustrine rocks of Wilkins Peak Member, Wyoming, American

Association of Petroleum Geologists Bulletin, v. 69, p. 913-922.

l, K.A., 1990, Sedimentation and tectonics of the

Wyoming, Wyoming Geological Association, 41st Annual Field Conference

Guidebook, p. 105-122.

l, K.A., 1993, A geologic overview of the Absaroka volcanic province, In: A.W.

Snoke, J.R. Steidtmann, and S.M. Roberts (eds.), Geology of Wyoming: Geological

Survey of Wyoming Memoir No. 5, p. 480-506.

, R.C., Eu

Eocene to Pleistocene Rocks, Wyoming, Geological Society of America Bulletin, v.

83, no. 8, p. 2261-2265.

196 Surdam, R.C., and Stanley, K.O., 1979, Lacustrine sedimentation during the culminating

phase of Eocene Lake Gosiute, Wyoming (Green River Formation), Geological

Society of America Bulletin, v. 90, no. 1, p. 93-110.

, R.C.,Surdam and Stanley, K.O., 1980, Effects of changes in drainage-basin boundaries on

Surdam e

Talbot,

ted

Talbot, otope evidence for a

Tiercel Cohen, A.S., Lezzar, K.E., Bouroullec, J.L., 1992,

-111.

4th Annual Field Conference Guidebook, p. 205-208.

sedimentation in Eocene Lakes Gosiute and Uinta of Wyoming, Utah and Colorado,

Geology, v. 8, no, 3, p. 135-139.

, R.C., and Wolfbauer, C.A., 1975, Green River Formation, Wyoming: A playa-lak

complex, Geological Society of America Bulletin, v. 86, p. 335-345.

M.R., and Allen, P.A., 1996, Lakes, 3; In: Sedimentary Environments; processes,

facies, and stratigraphy, H.G. Reading, (ed.), Blackwell Science, Oxford: Uni

Kingdom, p. 83-124.

M.R., Williams, M.A.J., and Adamson, D.A., 2000, Strontium is

late Pleistocene reestablishment of an integrated Nile drainage network, Geology, v.

28, p. 343-346.

in J.J., Soreghan, M.,

Sedimentation in rift lakes; example from the middle Pleistocene; modern deposits of

the Tanganyika Trough, East African Rift system, Bulletin des Centres de Recherches

Exploration Production Elf Aquitaine, v. 16, p. 83

Torres, V., and Gingerich, P.D., 1983, Summary of Eocene stratigraphy at the base of Jim

Mountain, North Fork of the Shoshone River, Northwestern Wyoming, Wyoming

Geological Association, 3

197 Ullman, W.J., and Collerson, K.D., 1994, The Sr-isotopic record of late Quaternary

hydrologic changes around Lake Frome, South Australia, Australian Journal of Earth

Sciences, v. 41, p. 37-45.

Vakarcs, G., Vail, P.R., Pogacsas, G., Mattick, R.E., and Szabo, A., 1994, Third-order

middle Miocene-early Pliocene depositional sequences in the prograding delta

complex of the Pannonian Basin, Tectonophysics, v. 240, p. 81-106.

. 91-92.

l., (eds.), Sea level changes: an integrated approach, SEPM

Van W

ence Stratigraphy in Well Logs, Cores, and Outcrops: Concepts for

von de

p. 283-285.

Van Wagoner, J.C., 1985, Reservoir facies distribution as controlled by sea-level change,

abstract, SEPM mid-year meeting, Golden, Colorado, August 11-14, p

Van Wagoner, J.C., Posamentier, H.W., Mitchum, R.M., Vail, P.R., Sarg, J.F., Loutit, T.S.,

and Hardenbol, J., 1988, An overview of sequence stratigraphy and key definitions,

In: C.W. Wilgus et a

Special Publication 42, p. 39-45.

agoner, J.C., Mitchum, R.M., Campion, K.M., and Rahmanian, V.D., 1990,

Siliciclastic Sequ

High-Resolution Correlation of Time and Facies, American Association of Petroleum

Geologists Methods in Exploration Series, no. 7, 55 p.

r Borch, C.C., Lock, D.E., Schwebel, D., 1975, Ground-water formation of dolomite

in the Coorong region of South Australia, Geology, v. 3,

Vonhof, H.B., Wesselingh, F.P., and Ganssen, G.M., 1998, Reconstruction of the Miocene

western Amazonian aquatic system using molluscan isotopic signatures,

Palaeogeography, Palaeoclimatology, Palaeoecology, v. 141, p. 85-93.

198 Waythomas, C.F., 2001, Formation and failure of volcanic debris dams in the Chakachatna

River valley associated with eruptions of the Spurr volcanic complex, Alaska,

Geomorphology, v. 39, p. 111-129.

White, k, J., 1999, The

Wilf, P

al Society of America Bulletin, v. 112, p. 292-307.

Wilson

ogia Plantarum, v. 83, p. 225-

Wing, d? Evidence for

Winland, H.D., and Matthews, R.K., 1974, Origin and significance of grapestone, Bahama

Islands, Journal of Sedimentary Petrology, v. 44, p. 921-927.

Webb, L.J., 1968, Environmental relationships of the structural types of Australian rain forest

vegetation, Ecology, v. 49, p. 296-311.

A.F., Blum, A.E., Bullen, T.D., Vivit, D.V., Schulz, M., and Fitzpatric

effect of temperature on experimental and natural chemical weathering rates of

granitoid rocks, Geochimica et Cosmochimica Acta, v. 63, p. 3277-3291.

Wilf, P., 1997, When are leaves good thermometers? A new case for Leaf Margin Analysis,

Paleobiology, v. 23, no. 3, p. 373-390.

., 2000, Late Paleocene-early Eocene climate changes in southwestern Wyoming:

Paleobotanical analysis, Geologic

Willden, R., and Mabey, D.R., 1961, Giant desiccation fissures on the Black Rock and

Smoke Creek Deserts, Nevada, Science, v. 133, p. 1359-1360.

, T.P., Canny, M.J., and McCully, M.E., 1991, Leaf teeth, transpiration and the

retrieval of apoplastic solutes in balsam poplar, Physiol

232.

S.L., Bao, H., and Koch, P.L., 1999, An early Eocene cool perio

continental cooling during the warmest part of the Cenozoic: In: B.T. Huber, K.

MacLeod, and S.L. Wing, (eds.), Warm climates in Earth history: Cambridge,

Cambridge University Press.

199 Winter, B.L., Johnson, C.M., Simo, J.A., and Valley, J.W., 1995, Paleozoic fluid history of

the Michigan Basin: Evidence from dolomite geochemistry in the Middle Ordovician

St. Peter Sandstone, Journal of Sedimentary Research, v. 65, p. 306-320.

sts, p. 34.

p. 1-71.

,

Wolfe, nd Greenwood, C.L.,

Wooden, J.L., Mueller, P.A., Hunt, D.K., and Bowes, D.R., 1982, Geochemistry and Rb-Sr

Special Publication 84, p. 45-55.

YN Formations in the

Witkind, I.J., and Grose, L.T., 1972, Geologic atlas of the Rocky Mountain region: Denver,

Rocky Mountain Association of Geologi

Wolfbauer, C.A., and Surdam, R.C., 1974, Origin of nonmarine dolomite in Eocene Lake

Gosiute, Green River Basin, Wyoming, Geological Society of America Bulletin, v. 85,

p. 1733-1740.

Wolfe, J.A., 1993, A method of obtaining climatic parameters from leaf assemblages, United

States Geological Survey Bulletin 2040,

Wolfe, J.A., 1998, Paleobotanical evidence of Eocene and Oligocene paleoaltitudes in

midlatitude western North America, Geological Society of America Bulletin, v. 110

p. 664-678.

J.A., Uemura, K., Wilf, P., Wing, S.L., Greenwood, D.R., a

1999, Using fossil leaves as paleoprecipitation indicators: An Eocene example:

Comment and Reply, Geology, v. 27, p. 91-92.

geochronology of Archean rocks from the interior of the southeastern Beartooth

Mountains, Montana and Wyoming, In: Mueller, P.A. and Wooden, J.L., eds.,

Precambrian Geology of the Beartooth Mountains, Montana and Wyoming: Montana

Bureau of Mines and Geology

Xue, L., and Galloway, W.E., 1993, Genetic sequence stratigraphic framework, depositional

style, and hydrocarbon occurrence of the Upper Cretaceous Q

200 Songliao lacustrine basin, northeastern China, American Association of Petroleum

Geologists Bulletin, v. 77, p. 1792-1808.

, J.C., Stott, L.D., and Lohmann, K.C., 1994, Evolution of early CenozZachos oic marine

Zachos Oligocene icesheet expansion on

Zielins n, Z.E., Stuckless, J.S., Rosholt, J.N., and Nkomo, I.T., 1981, The

alogy and Petrology, v. 78, p. 209-

temperatures, Paleoceanography, v. 9, p. 353-387.

, J.C., Breza, J., and Wise, S.W., 1992, Early

Antarctica, sedimentological and isotopic evidence from Kerguelen Plateau, Geology,

v. 20, p. 569-573.

ki, A., Peterma

chemical and isotopic record of rock-water interaction in the Sherman Granite,

Wyoming and Colorado, Contributions to Miner

219.