depositos salinos

AUTHORS

Jennifer L. Aschoff Jackson School ofGeosciences, Department of Geological Sci-ences, University of Texas at Austin, Austin,Texas 78712; [email protected]

Jen Aschoff earned her B.S. degree in geologyfrom Montana State University in 2000 andher M.S. degree in geology from New MexicoState University (NMSU) in 2003. Researchpresented in this paper was derived from herM.S. work with the Institute of Tectonic Studiesat NMSU. Presently, Jen is pursuing a Ph.D. ingeology at the University of Texas at Austin.

Katherine A. Giles Institute for TectonicStudies, New Mexico State University, LasCruces, New Mexico 88003; [email protected]

Kate Giles graduated from the University ofWisconsin, Madison, the University of Iowa,and the University of Arizona. She worked atExxon Production Research and is currentlyan associate professor at New Mexico StateUniversity. She specializes in carbonate depo-sitional systems, sequence stratigraphy, andsedimentation as it relates to tectonics.

ACKNOWLEDGEMENTS

The authors gratefully acknowledge the La PopaBasin Joint Industry Consortium, AAPG Grants-in-Aid, and the New Mexico Geological Societyfor funding. Additionally, valuable technicalreviews by L. Krystinik, C. North, and R. Steelimproved the final manuscript. Discussions withD. Bowen, T. Lawton, G. Mack, M. Rowan, J.Schmitt, D. Shelley, and R. Steel contributedmany different perspectives on this researchand inspired new ideas. Insightful reviews andcriticisms of an early version of this manuscriptby D. Bowen and J. Schmitt are much appreci-ated. Finally, the first author thanks S. Furgal,M. Hughes, and D. Mercer for assistance inthe field.

Salt diapir-influenced,shallow-marine sedimentdispersal patterns: Insightsfrom outcrop analogsJennifer L. Aschoff and Katherine A. Giles

ABSTRACT

Unique outcrop exposures of two salt diapirs, a secondary salt

weld, and associated syndiapiric strata in northeast Mexico offer an

important perspective on salt-influenced petroleum reservoirs by

allowing recognition and description of salt-related sandstone de-

pocenters. Spectacular progressive unconformities and halokinetic

sequences, coupled with laterally continuous exposures, permit ac-

curate correlation and interpretation of syndiapiric units. Analysis

of the syndiapiric Upper Cretaceous, Delgado Sandstone Member

( Potrerillos Formation) delineates regional shoreline sediment dis-

persal locally impacted by diapiric relief and the distribution and

internal character of salt diapir-proximal sandstone depocenters.

Sequence-stratigraphic correlation defines striking relationships be-

tween highstand ( HST) and transgressive systems tracts (TST),

stratal thinning trends, and salt diapir relief. Transgressive systems

tract and highstand systems tract strata show thinning and litho-

facies shoaling trends toward diapirs; however, the latter is more

pronounced in the HST and occurs at a greater distance from salt

diapirs (within 12 km [0.61.2 mi]). Sandstone depocenters,

roughly 0.51.0 km (0.30.6 mi) wide and 0.50.2 km (0.30.1 mi)

thick, are present in both TST and HST strata and consist of sand-

ier, shallower water facies. However, depocenters are better de-

veloped in TST strata as thicker stratigraphic sections on updip

diapir margins. We propose that sandstone depocenters formed

by preferential sediment reworking and shelf ridge development

on landward diapir margins during marine transgression. Elevated

diapir relief and higher subsidence rates adjacent to salt diapirs

likely enhanced this process. Additionally, depocenters adjacent to

El Papalote diapir are smaller and contain deeper water facies than

AAPG Bulletin, v. 89, no. 4 (April 2005), pp. 447469 447

Copyright #2005. The American Association of Petroleum Geologists. All rights reserved.

Manuscript received February 10, 2004; provisional acceptance June 24, 2004; revised manuscriptreceived September 22, 2004; final acceptance October 26, 2004.

DOI:10.1306/10260404016

the age-equivalent depocenters adjacent to El Gordo

diapir, suggesting that it had higher, broader sea-floor

relief.

INTRODUCTION

Outcrop analog studies provide vital information to

better understand sedimentation in salt basins and are

crucial to reducing exploration risk and increasing pro-

duction efficiency from salt-related hydrocarbon reser-

voirs. Current understanding of the interplay between

salt diapirism and sedimentation is predominantly based

on subsurface geophysical data interpretation and mod-

els. Many of these data are below the resolution nec-

essary to thoroughly examination the internal fabric

and composition of sandstone bodies that comprise

salt-controlled depocenters. In many unexplored and

underexplored basins, the paucity of high-resolution

data combined with complex structural histories make

accurate reconstruction of sediment dispersal patterns

arduous (Ge et al., 1997; Volozh et al., 2003). Outcrop

description of syndiapiric strata that record sediment

dispersal patterns in ancient salt-influenced basins pro-

vides a unique view of paleodepositional processes, stra-

tal thickness trends, and lithofacies distribution, thereby

offering insight into the complex interplay between

salt diapirism, sedimentation, and petroleum plays.

Downbuilding of passive salt diapirs and marine

sedimentation comprise an intricate system that links

depositional loading adjacent to salt diapirs with pas-

sive salt diapir uplift ( Barton, 1933; Jackson and Talbot,

1991; Vendeville and Jackson, 1992a, b; Jackson and

Talbot, 1994; Ge et al., 1997; Rowan and Weimer, 1998;

Rowan et al., 2003). In these systems, diapir uplift

creates relief that can cause sedimentation patterns to

adjust to the new basin-floor topography. Sedimenta-

tion may respond to sea-floor relief by lateral shifting of

depositional loci and by adopting different modes of

sand deposition. In turn, the location and internal char-

acter of sandstone depocenters determine the location

of maximum sediment loading, thereby impacting

the uplift rate and style of salt diapirs. This complex,

salt-sediment interplay impacts sandstone reservoir

distribution, architecture, and quality, as well as the

type, size, and geometry of petroleum traps and seals

(Magoon and Dow, 1994; Morse, 1994; Apak and Moors,

1996; Rowan et al., 2003; Volozh et al., 2003).

La Popa basin, northeast Mexico, is an extraordi-

nary location to study salt-sediment interaction because

outcrops of several exhumed salt diapirs, growth strata,

and a continuously exposed succession of syndiapiric

strata (up to 5000 m [16,400 ft] thick) are present. In

this setting, outcrops of syndiapiric strata adjacent to

salt diapirs form discrete ridges that can be traced lat-

erally for many kilometers. Outcrop data collected in

La Popa basin from the laterally extensive syndiapiric,

Upper Cretaceous to lower Paleogene Delgado Sand-

stone Member ( Potrerillos Formation) contributes a

unique perspective that further illuminates enigmatic,

salt-sediment interaction. The specific goals of this paper

are to (1) reconstruct ancient sedimentation patterns re-

corded by the Delgado Sandstone Member in the La Popa

basin; (2) determine how sediment dispersal was influ-

enced by salt diapirism and withdrawal; and (3) assess the

nature and recurrence of spatial and temporal sediment

dispersal shifts. Detailed lithofacies analysis, sequence

stratigraphy, and sandstone provenance of strata from 36

detailed stratigraphic sections of the Delgado Sandstone

Member provided a database to achieve these goals.

GEOLOGIC SETTING OF LA POPA BASIN

La Popa basin is located in the northeastern margin of

the Hidalgoan foreland basin system, Nuevo Leon,

northeastern Mexico (Figure 1). The basin forms an

east-westoriented segment, approximately 60 km

(37 mi) wide, of a foreland basin that roughly parallels

the deformational front of the Sierra Madre Oriental

fold and thrust belt. The thick succession (as much

as 6500 m [21,300 ft]) of Mesozoic and Tertiary ma-

rine and nonmarine sedimentary rocks (Figure 2) ex-

posed in La Popa basin record a complex, three-phase

tectonic history. This history includes (1) thermal

subsidence following Jurassic rifting (Late Jurassic to

early Late Cretaceous); (2) salt diapirism and with-

drawal (early Late Cretaceous to middle Tertiary); and

(3) crustal shortening from the Late Cretaceous to Ter-

tiary (Murray et al., 1962; McBride et al., 1974; Gold-

hammer, 1999; Dickinson and Lawton, 2001; Lawton

et al., 2001; Druke and Giles, 2003). Previous studies

showed that crustal shortening related to the Sierra

Madre Oriental has controlled regional sedimentation

patterns in the foreland basin; however, intrabasinal

folding began as late as the latest Cretaceous to Paleo-

cene. Although poorly temporally constrained, intra-

basinal diapirism predates and postdates Sierra Madre

Oriental deformation (McBride et al., 1974; Vega and

Perrilliat, 1989; Ye, 1997; Hon, 2001; Lawton et al.,

2001; Shelley, 2001; Weislogel, 2001; Druke and Giles,

2003; Graff, 2003; Rowan et al., 2003).

448 Salt Diapir-Influenced, Shallow-Marine Sediment Dispersal Patterns

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Aschoff and Giles 449

Sierra Madre Oriental

The Sierra Madre Oriental orogenic belt is a southern

extension of the Late CretaceousEocene Cordilleran

fold and thrust belt of the western United States.

Structural styles present in the Sierra Madre include

north-vergent, east-west trending, steep-limbed,

thrust-bounded fold nappes as well as doubly plung-

ing, asymmetrical, and overturned folds that involve

Upper Triassic to Cretaceous rocks (McBride et al., 1974;

Goldhammer and Johnson, 2001). Locally, contractional

deformation in the fold-thrust belt is manifest as a

convex-eastward belt of folds south of La Popa basin

known as the Monterey Salient (Campa and Coney,

1983; Campa, 1985; De Cserna, 1989; Ye, 1997; Dick-

inson and Lawton, 2001).

Although most of the deformation associated

with the Sierra Madre Oriental is restricted to regions

south and west of La Popa basin, a series of broad

folds involve the Mesozoic and Cenozoic sedimen-

tary fill of La Popa basin. This deformation does not

structurally thicken strata in La Popa basin but for-

tuitously exposes Mesozoic and Cenozoic strata on

the erosional limbs of the folds, rendering superb, con-

tinuous exposure. The Sierra Madre Oriental com-

prised highlands that provided detritus to La Popa

basin; influx of this sediment contributed to diapir-

peripheral depositional loading, which sustained down-

building processes and uplift of passive salt stocks

(Hon, 2001; Shelley, 2001; Weislogel, 2001). The struc-

tural grain produced by the encroaching Sierra Madre

Oriental thrust belt coupled with its influence as a sig-

nificant sediment source suggest that uplift and basin-

ward propagation of Sierra Madre Oriental influenced

regional sediment dispersal in the adjacent La Popa

basin.

Figure 2. Generalized stratigraphy ofLa Popa basin showing the stratigraphicposition of the Delgado Sandstone Mem-ber and depositional environment inter-pretations for all stratigraphic units ex-posed in La Popa basin (Lawton et al.,2001).


Salt Diapirism and Withdrawal in La Popa Basin

Many salt-related structures are present in La Popa

basin, including several exhumed salt diapirs and a sec-

ondary salt weld, which are accompanied by adjacent

syndiapiric growth strata (progressive unconformities).

This study focuses on the influence of the two best ex-

posed diapirs, El Papalote and El Gordo diapirs, on sed-

iment dispersal in the basin (Figure 1). El Papalote and

El Gordo diapirs are composed of gypsum and anhy-

drite presumably derived from the underlying Juras-

sic Minas Viejas Formation. The diapirs intrude Lower

Cretaceous to Paleogene strata that belong to the Di-

funta Group (McBride et al., 1974; Laudon, 1984, 1996;

Dickinson and Lawton, 2001; Lawton et al., 2001; Giles

and Lawton, 2002). Diapir-flanking strata in the Di-

funta Group include sandstone and shale with localized

lenticular limestone units adjacent to diapirs. Stratal

stacking patterns, lithofacies distribution, local uncon-

formities, growth strata, halokinetic sequences (Giles

and Lawton, 2002), and structural relations in these

diapir-flanking strata record the episodic uplift, topog-

raphy, and development of the diapirs (Hon, 2001;

Shelley, 2001; Weislogel, 2001; Mercer, 2002; Aschoff,

2003; Rowan et al., 2003). Diapir uplift initiated as late

as the Albian, and uplift processes remained dominantly

passive throughout the Cretaceous, i.e., uplift processes

driven by sediment loading (Lawton et al., 2001). Our

use of the term passive diapirism is based on the model

of Rowan et al. (2003) in which passive diapirism in-

cludes cycles of small-scale, active diapirism (Rowan

et al., 2003).

The 25-km (16-mi)-long, La Popa secondary salt

weld (Figure 1), originally described by Laudon (1984)

as a reverse fault, is one of the only outcrop examples of

a secondary salt weld in the world (Giles and Lawton,

1999). Time-equivalent strata exposed on either side of

the weld were once separated by an elongate evaporite

mass (salt wall) before complete closure of the weld;

hence, strata that presently flank the La Popa weld oc-

cupy space that was filled by salt prior to salt evacua-

tion. Differential displacement along the weld during

salt evacuation caused downdropping of strata on its

southwest side relative to strata on its northeast side,

resulting in a discontinuous outcrop belt northeast of

the La Popa weld. Delgado Sandstone Member strata

thin toward the salt weld, suggesting that salt-related

relief existed during the time of deposition, and that

salt evacuation and displacement postdated deposition.

Hence, the La Popa weld is herein treated as a syndepo-

sitional salt wall instead of a weld as it is preserved today.

STRATIGRAPHY

La Popa Basin Stratigraphy

Early geologic investigations and geologic mapping (i.e.,

Imlay, 1936; Murray et al., 1962; McBride et al., 1974;

Weidie and Murray, 1976) coupled with numerous re-

cent studies have refined La Popa basin stratigraphy (e.g.,

Giles and Lawton, 1999; Goldhammer, 1999; Goldham-

mer and Johnson, 2001; Lawton et al., 2001) (Figure 2).

The mixed stratigraphic assemblage of marine, marginal-

marine, and nonmarine siliciclastic rocks with diapir-

flanking, lenticular, carbonate platform rocks (i.e., lentils,

after McBride et al., 1974) is interpreted as a record of

multiple deltaic progradations and retrogradations in-

fluenced by regional and local salt tectonics (McBride

et al., 1974; Goldhammer and Johnson, 2001; Lawton

et al., 2001). Data collected from the Delgado Sand-

stone Member (Potrerillos Formation), a thin basinwide

marker bed, were used to reconstruct sedimentation

patterns in the basin (Figure 2).

Delgado Sandstone Member

The Upper Cretaceous to Paleogene Delgado Sand-

stone Member was defined by Lawton et al. (2001) as

a thin ( less than 100 m [330 ft]) member of the Po-

trerillos Formation (Difunta Group), forming a promi-

nent, sharp-based sandstone ridge at the top of the

Middle Siltstone Member (Figure 2). Basinwide facies

variation caused the basal and uppermost contacts to

be more commonly gradational with the underlying

Middle Siltstone Member and overlying Upper Mud-

stone Member, respectively (Figure 3). For the purpose

of this study, the base of the Delgado Sandstone Mem-

ber is placed at the base of the lowermost sandstone

bed thicker than 0.5 m (1.6 ft), and the top is placed at

the top of the uppermost sandstone bed thicker than

1.0 m (3.3 ft) (Figure 3).

LITHOFACIES ASSEMBLAGES OF THEDELGADO SANDSTONE MEMBER

The Delgado Sandstone Member contains 14 lithofa-

cies ranging from massive mudstone to chaotic bedded,

carbonate-rich polymictic, boulder conglomerate. Litho-

facies are grouped into three assemblages: (1) an open-

marine, outer-shelf assemblage, (2) wave-dominated

inner-shelf shoreface assemblage, and (3) conglomer-

atic event deposits.


Assemblage 1: Open-Marine Outer-Shelf Lithofacies

Lithofacies assemblage 1 consists of thick mudstone and

shale intervals with thin interbeds of sandy siltstone and

very fine-grained sandstone (Figure 4a). Table 1 contains

detailed descriptions and interpretations of lithofacies

present in this assemblage. Massive mudstone and shale

with pervasive bioturbation and relict horizontal lami-

nation suggest suspension deposition, followed by pro-

longed exposure and bioturbation. Poorly developed

Bouma sequences suggest deposition by episodic, storm-

induced turbidity currents (Bouma, 1962; Bouma et al.,

1985; Colquhoun, 1995). Abundant fine-grained pelagic

facies and sparse hummocky cross-stratified sandstone

beds, coupled with high-abundance, low-diversity,

trace fossil associations, suggest a low-energy, below-

fair-weather wavebase environment dominated by sus-

pension deposition punctuated by storm-wave events

(Hill, 1984; Pemberton et al., 1992; Colquhoun, 1995).

Offshore to distal lower shoreface regions of the shelf

environment are compatible with these processes.

Assemblage 1 occupies multiple (two to four) strati-

graphic intervals separating robust, ridge-forming sand-

stone beds (assemblage 2, described below). Strati-

graphically, this lithofacies assemblage dominantly

occupies the lowermost 20 m (66 ft) of the Delgado

Sandstone Member, is the most abundant assemblage

(by thickness and volume), and is omnipresent in the

southeastern regions of La Popa basin (Figure 3). Typ-

ically, mudstone and shale intervals coincide with the

base of shoaling-upward successions marking flood-

ing surfaces and the base of parasequences.

Assemblage 2: Wave-Dominated, Inner-ShelfShoreface Lithofacies

The wave-dominated, inner-shelf lithofacies assem-

blage constitutes nearly all sandstone lithofacies and

cliff-forming sandstone units in the Delgado Sand-

stone Member. Because sandstone depocenters exclu-

sively contain sandstone lithofacies of assemblage 2,

special attention is paid to its description (Table 2). This

assemblage consists of (1) 12-m (3.36.6-ft)-thick,

isolated, lenticular hummocky cross-stratified sand-

stone sets with subordinate ripple cross-lamination

and bioturbation (Ophiomorpha) interbedded with

210-m (6.633-ft)-thick massive mudstone and/or

shale successions; (2) thick, amalgamated hummocky

cross-stratified sandstone beds, up to 10 m (33 ft) thick;

(3) thinly bedded, wave-ripple cross-laminated, fine-

grained sandstone; (4) medium-bedded trough cross-

stratified, medium- to coarse-grained sandstone with

Gyrolithes trace fossils interbedded with horizontally

stratified, coarse-grained sandstone; and (5) massive, very

fine- to medium-grained bioturbated sandstone. Isolated

hummocky cross-stratified sandstone with interbedded

massive mudstone lithofacies is concentrated in either

the lowermost 1025 m (3382 ft) or the uppermost

510 m (1633 ft) of the Delgado Sandstone Member

(Figure 3). Many of these isolated hummocky cross-

stratified beds are broadly lenticular. The abundance,

thickness, and degree of amalgamation of hummocky

cross-stratified bed sets increase upsection with a corre-

sponding decrease in mudstone-rich lithofacies. Locally,

hummocky cross-stratified sandstone sets are completely

amalgamated and grade into interbedded trough cross-

stratified and horizontally stratified sandstone. Col-

lectively, both modes of hummocky cross-stratified

sandstone lithofacies (e.g., isolated and amalgamated)

dominate assemblage 2, whereas trough cross-stratified

and horizontally stratified lithofacies do not form a

significant volume ( less than 5%) of strata. Although

the latter is not abundant, its occurrence and lateral

distribution help delineate the sequence stratigraphy

and constrain basinwide sedimentation patterns.

Three depositional processes are suggested by

the collection of sedimentary structures present in

lithofacies assemblage 2 (Table 2). Hummocky cross-

stratified sandstone associated with Ophiomorpha

(Figure 4b) indicate deposition by oscillatory or combined-

flow conditions resulting from surges of strong, mul-

tidirectional storm waves followed by colonization of

storm-generated sediments by brine shrimplike organ-

isms (Hamblin and Walker, 1979; Allen, 1982; Dott

and Bourgeois, 1982; DeCelles, 1987; DeCelles and

Cavazza, 1992). Stratigraphic successions dominated

by thick intervals of mudstone with isolated hum-

mocky cross-stratified sandstone are compatible with

fair-weather mud fallout truncated by episodic storm-

wave sand deposition. Conversely, stratal successions

Figure 3. Stratigraphic column of the Delgado Sandstone Member measured at the northeastern termination of the La Popa weld.Lithology, position of lower and upper member boundaries, thickness, sedimentary structures, lithofacies interpretation, parase-quence picks (17), significant surfaces, systems tracts, and sequences shown in this section represent an ideal section where alllithofacies assemblages are observed in the same section. Lithofacies symbols are the same as those listed in Tables 13.


containing thick intervals of amalgamated, higher angle

hummocky cross-stratified sandstone (Figure 4c) suggest

an environment dominated by more frequent storm-

wave deposition with minimal suspension-deposition

(Harms et al., 1982). The lower to middle shoreface of

the inner-shelf environment is consistent with storm-

wave and suspension sedimentary processes (Bour-

geois, 1980; Dott and Bourgeois, 1982).

Trough cross-stratified sandstone lithofacies

(Figure 4d) contain abundant angle-of-repose bedding

that suggests traction transport by strong currents as

three-dimensional dunes in a persistent, high-energy en-

vironment. The presence of this relatively high-energy

sedimentary structure (upper part of the lower flow

regime) in association with well-sorted texture and the

presence of Gyrolithes suggest deposition in the up-

per shoreface environment of the inner shelf (Clifton,

1976; Harms et al., 1982; Boggs, 1992; Pemberton et al.,

1992). Horizontally stratified sandstones are well sorted

and consist of rounded, coarser grains; these characteris-

tics suggest deposition in upper flow regime conditions,

above storm and fair-weather wave base in the foreshore

(swash zone) (Clifton, 1976; Komar, 1976; Burgeois,

1980; Dott and Bourgeois, 1982; Harms et al., 1982).

Collectively, these lithofacies represent upper shore-

face and foreshore environments, the shallowest water

deposits preserved in the Delgado Sandstone Member.

Spatially, lithofacies assemblage 2 is omnipresent

in the northeastern zone of La Popa basin, where sand-

stones are typically amalgamated and contain more,

shallower water lithofacies. To the southeast, it grades

into lithofacies assemblage 1 (outer shelf mudstone and

siltstone) and is truncated by a younger unconformity

in the northwest. Locally, shallower water facies, such

as amalgamated, hummocky cross-stratified sandstones

with interbedded trough and horizontally stratified

sandstones, are concentrated on the northwestern

flanks of both El Papalote and El Gordo diapirs and at

both terminations of the La Popa salt wall. Mudstone-

rich stratigraphic successions that contain more isolat-

ed, hummocky cross-stratified beds are more abundant

on the southeastern margins of salt diapirs. Sandstone

loci are clearly defined in the northeastern region and

near diapir margins.

Lithofacies Assemblage 3: AnomalousCoarse-Grained Deposits

Swale-Filling Deposits

Lithofacies assemblage 3 consists of a lower, swale-

filling, massive, pebble to boulder conglomerate with

a distinctive, disorganized motif interbedded with and

overlain by massive to low-angle, cross-stratified pebbly

sandstone, collectively marking an abrupt change in

Figure 4. Outcrop view of lithofacies assemblage 1 (a) exposed in the lower one third of the Delgado Sandstone Member southeast ofEl Papalote diapir showing interbedded shale (Fh), graded sandy siltstone (Fg), ripple cross-laminated sandy siltstone (Fr), and sub-ordinate, thin (less than 30 cm [12 in.]) hummocky cross-stratified beds (Shcs). (b) Hummocky cross-stratified, fine-grained sandstonetaken about 3 km (1.8 mi) northwest of El Papalote diapir near the top of the HST. (c) Amalgamated hummocky cross-stratified sandstonelithofacies in lithofacies assemblage 2 exposed in uppermost HST strata northwest of El Papalote diapir. (d) Well-developed trough cross-stratified, medium-grained sandstone in uppermost HST strata exposed northwest of El Gordo diapir.

Table 1. Lithofacies Assemblage 1: Open-Marine Outer-Shelf Facies

Lithofacies Description Interpretation (Process/Setting)

Graded siltstone and sandy

siltstone (Fg)

very thinly bedded, gray and brown

sandy siltstone with basal, sand-rich lamina

that comprise fining-upward successions

silty turbidity current/offshore

Shale (Fh) horizontally laminated, black and gray shale

with dark, organic lamina

undisturbed suspension

deposition/offshore

Massive mudstone and

siltstone (Fm)

massive, homogeneous, gray, and brown

mudstone

suspension deposition/lower

shoreface and offshore

Bioturbated mudstone and

siltstone (Fmb)

massive, bioturbated siltstone and mudstone

with Ophiomorpha trace fossils and burrow casts

bioturbated suspension

deposition/offshore

Ripple cross-laminated sandy

siltstone (Fr)

thinly bedded, oscillation-ripple cross-laminated,

tan and gray sandy siltstone with slightly

bioturbated tops

wave reworked, silty turbidity

currents/offshore grading into

lower shoreface


depositional character (Table 3). The conglomeratic

units of this assemblage occur only as fill in the deepest

part of localized swales (small channel forms approxi-

mately 10 m [33 ft] wide by 27 m [6.623 ft] deep)

and are concentrated southeast of El Papalote diapir

(Figure 5a). Hummocky cross-stratified sandstone stra-

ta are immediately below the swales and locally contain

large (13-m (3.310-ft)-high) soft sediment defor-

mation structures, as well as plastically deformed Ophio-

morpha trace fossils; no evidence of bioturbation is

observed in swale-filling deposits (Figure 5b). Internally,

swale-filling deposits consist of a lower, thick to massive-

bedded, massive, matrix-supported, polymictic, cobble

to boulder conglomerate with maximum particle size

of about 70 cm (28 in.). This lower unit is overlain by

medium- to thick-bedded, interbedded massive, matrix-

supported, normally and inverse coarse-tail graded cob-

ble to pebble conglomerate (Figure 5c). Conglomeratic

units are disorganized with outsized, randomly orient-

ed clasts, poorly sorted matrix and subordinate, plas-

tically deformed clasts, and localized, weakly devel-

oped imbrication. Superficially, deposits of assemblage

3 resemble incised-valley fills because they fill channel-

like features (swales); however, we do not interpret

these deposits as incised valleys based on the following

criteria: (1) minimal incision occurs at the base of

swales, suggesting that the underlying sediment was

wet, and preexisting sea-floor topography was ex-

ploited and initially filled with gravel; (2) the basal

channel contact exhibits none of the classic criteria

used to identify sequence boundaries (Van Wagoner

et al., 1990); and (3) parasequence stacking patterns

are invariable above and below the deposit (Aschoff

et al., 2001; Aschoff, 2003; Shipley et al., 2003).

Regionally Extensive Pebbly Sandstone Deposits

Southeast of El Papalote diapir, pebbly sandstone units

overlie swale-filling conglomeratic units and both on-

lap and overlap swale margins. Elsewhere, pebbly sand-

stone units pinch and swell in thickness but contain the

same distinctive grain and clast-type assemblage with

Table 2. Lithofacies Assemblage 2: Wave-Dominated, Inner-Shelf Shoreface Facies


Isolated hummocky cross-stratified

sandstone (Shcs)

thin- to medium-bedded, hummocky

cross-stratified, very fine- to medium-grained

sandstone with erosive basal contacts,

locally ripple cross-laminated tops and

abundant Ophiomorpha

infrequent episodic storm

deposition/distal lower shoreface

Amalgamated hummocky

cross-stratified sandstone (Shcs)

cliff-forming medium- to thick-bedded,

amalgamated, higher angle hummocky

cross-stratified, very fine- to medium-grained

sandstone with erosive basal contacts

and scarce Ophiomorpha

more frequent, episodic storm

deposition with little suspension

deposition/lower to middle shoreface

Wave-ripple cross-laminated

sandstone (Sr)

thin- to medium-bedded, oscillation-ripple

cross-laminated, very fine- to medium-grained

sandstone

wave oscillation deposition/lower

shoreface

Massive sandstone (Sm) massive, homogenous, very fine- to

medium-grained sandstone devoid of

sedimentary structures

reworked tempestite/lower

shoreface

Bioturbated sandstone (Smb) massive, bioturbated very fine- to

medium-grained sandstone with abundant

Ophiomorpha trace fossils

reworked tempestite/lower

shoreface

Trough cross-stratified sandstone (St) medium-bedded, trough cross-stratified,

fine- to coarse-grained sandstone with

sparse Gyrolithes

upper flow regime longshore

current and/or wave

deposition/upper shoreface

Horizontally stratified sandstone (Sh) medium- to thick-bedded, horizontally

stratified, medium- to coarse-grained

sandstone

upper flow regime wave

deposition/foreshore


local low-angle stratification (Figure 5d) and occupy

the same stratigraphic position as swale-filling units.

The unique, clast- and grain-type assemblage that links

the pebbly sandstone units to swale-filling conglomer-

ate matrix of assemblage 3 includes (1) bubbly, calcite

spherules, (2) micrite-coated bioclasts, (3) glass tek-

tites, (4) limestone lithics, and (5) micrite-filled bio-

clasts (Aschoff et al., 2001; Aschoff, 2003; Shipley et al.,

2003). The compositional similarity of swale-filling con-

glomerates to overlying sandstones and lack of uncon-

formities suggests that the two deposits are genetically

related. Disorganized internal fabric, massive-bedding,

poorly sorted matrix, randomly oriented clasts, and large

clast size of conglomeratic units suggest deposition

by subaqueous debris-flow processes (Hampton, 1979;

Lowe, 1979; Ghibaudo, 1992; Smit et al., 1996; Bralower

et al., 1998; Klaus et al., 2000; Soria et al., 2001). The

wide distribution (at least 20 km [12 mi]) and dis-

tinctive composition of the overlying pebbly sandstones

combined with lack of internal bioturbation, erosional

surfaces, and unvarying composition of assemblage 3

suggest a regionally extensive (shelfwide) rapid, mul-

tiphase sedimentation event, such as a tsunami wave.

We interpret the conglomeratic unit of assemblage 3 as

subaqueous debris flows and overlying pebbly sand-

stones as tsunami deposits.

Possible Relationship to the Chicxulub Impact

The presence of tektites, shocked minerals, and ac-

cretionary lapili in lithofacies 3 imply a connection

between this lithofacies and the Chicxulub impact

structure, located on the Yucatan Peninsula (approx-

imately 800 km [500 mi] southeast of La Popa ba-

sin) (Alvarez et al., 1980; Bourgeois et al., 1988; Glass

and Burns, 1988; Alvarez and Asaro, 1990; Glass,

1990; Alvarez, 1996; Bralower et al., 1998). The close

proximity and genetic relationship of the deposits to

the Chicxulub structure suggest that debris flows

and tsunamis may have ensued from the Chicxu-

lub bolide impact (Bourgeois et al., 1988; Glass and

Burns, 1988; Glass, 1990; Alvarez, 1996; Bralower

et al., 1998; Soria et al., 2001; Ward and Asphaug,

2002).

STRATIGRAPHIC FRAMEWORK OF THEDELGADO SANDSTONE

The sequence-stratigraphic framework of the Del-

gado Sandstone Member was constructed using cor-

relation of key surfaces and parasequence stacking

pattern. Surfaces that were key components of sequence-

stratigraphic correlation include (1) regionally continuous

Table 3. Lithofacies Assemblage 3: Anomalous, Carbonate-Rich, Coarse-Grained Deposits


Massive pebble to boulder

conglomerate (Gm2)

gray, medium- to thick-bedded, massive, normal,

and normal coarse-tail graded pebble to boulder

conglomerate; clast/grain type assemblage:

(1) bubbly, calcite spherules, (2) micrite-coated

bioclasts, (3) glass tektites, (4) limestone lithics,

(5) micrite-filled bioclasts (oysters, rudists,

high-spired gastropods), (6) diapir-derived

metabasite, and (7) chert; bioclasts are commonly

articulated and with little evidence of abrasion

shelfal debris flow/catastrophic event

Carbonate-rich pebbly

sandstone (Gm2)

massive-bedded, unstratified to low-angle

cross-stratified pebbly sandstone with subordinate,

outsized carbonate cobbles; grain- and clast-type

assemblage: (1) bubbly, calcite spherules,

(2) micrite-coated bioclasts, (3) glass tektites,

(4) limestone lithics, (5) micrite-filled bioclasts

(oysters, rudists, high-spired gastropods),

(6) diapir-derived metabasite, and (7) chert;

bioclasts are commonly abraded and disarticulated

in this unit

shelfal tsunami wave pulse(s) roughly

coeval with debris flows/catastrophic event


unconformities (sequence boundaries), (2) transgressive

surface, (3) maximum flooding surface, and (4) the top

of event deposits (lithofacies 3). The top of event

deposits is a useful datum and timeline because it is

easily recognized in nearly all measured sections and

represents an event. Sequence boundaries and flooding

surfaces were identified using the criteria outlined by

Van Wagoner et al. (1990).

Parasequence Types

Two parasequence types are present in the Delgado

Sandstone Member, namely, wave-dominated inner-shelf

and outer-shelf parasequence types (Figure 6a, b). Wave-

dominated parasequences show shoaling-upward trends

defined by a progressive decrease in muddy lithofacies

(assemblage 1), an overall increase in sandy lithofacies

Figure 5. (a) Lithofacies assemblage 3 showing conglomeratic units filling broad, swale forms. Meter-scale soft sediment deformationstructures and injection dikes are present at the base of the swale, denoted by the large white arrow. Conglomeratic units areconcentrated in the lowermost part of the swale (unit 1), whereas pebbly sandstone with outsized cobbles composes the stratified,middle portion of the outcrop (unit 2). This succession is overlain by thick-bedded, hummocky cross-stratified sandstone that representsthe normal sedimentation mode (unit 3). (b) Close-up outcrop view of a cobble-dominated conglomeratic unit. (c) Outcrop of a boulder-dominated part of the conglomeratic unit of lithofacies assemblage 3. (d) Close-up view of the distinctive, unifying clast-type assemblageof lithofacies 3.


and increase in sandstone bed amalgamation upsection.

The sandy nature and overall abundance of storm-generated

facies suggest a generally shallower environment such as

the inner shelf. Conversely, outer-shelf parasequences are

rich in offshore facies, namely, lithofacies assemblage 1,

that shoal upsection into lower shoreface lithofacies of

assemblage 2 (Figure 6b). The marked abundance of off-

shore facies in these parasequence types suggests an overall

deeper water environment (i.e., outer shelf ). Spatially

wave-dominated inner-shelf parasequence types are om-

nipresent in the northwestern region of La Popa basin

(Figures 3, 6a), whereas offshore parasequences are con-

centrated in the southeast. This facies distribution sug-

gests a southeast-dipping shelf margin where diapirs

occur near the lower shoreface-offshore depositional

break.

Parasequence Stacking Patterns and Systems Tracts

Regionally consistent parasequence stacking patterns

permit accurate correlation across lateral facies tran-

sitions and salt structures. Parasequences are generally

515 m (1649 ft) thick and stack in two distinctive

patterns. Stacking patterns in the Delgado Sandstone

Member include a lower progradational pattern and

an upper, aggradational to retrogradational pattern.

The upper and lower parasequence sets are separated

by a sharp erosional surface mantled by a polymictic

lag (Figure 3) (Aschoff, 2003). Two to four parase-

quences form the lower, progradational parasequence

set, and two to four parasequences form the overly-

ing retrogradational to aggradational parasequence

set (Figure 7a, b).

The lowermost progradational parasequence set

forms a relatively thick (2030-m; 66100-ft) por-

tion, the highstand systems tract (HST) of sequence 1,

which begins in the underlying Middle Siltstone Mem-

ber (Figure 3). The HST is truncated and partially

eroded by a sequence boundary, termed the Delgado

sequence boundary (DSB). This sequence boundary is

marked by (1) a polymictic lag primarily consisting of

hinterland-derived chert, ancillary carbonate clasts, and

vertebrate fossil teeth; (2) an abrupt, non-Waltherian,

basinward shift in facies; and (3) a sharp, laterally con-

tinuous, erosive contact (Figure 7a, b). The presence of

Figure 6. Two general parasequence types occur in the Delgado Sandstone Member, including (a) an inner-shelf parasequencetype that is composed of offshore mudstone, lower shoreface, middle shoreface, upper shoreface, and foreshore lithofacies and (b) anouter-shelf parasequence type composed of offshore shale and mudstone and lower shoreface.


far-traveled, hinterland-derived detritus unique to the

lag supports a significant base-level lowering; however,

lowstand systems tract strata are absent.

The transgressive surface is amalgamated with the

DSB and is overlain by a distinct retrogradational para-

sequence stacking pattern (Figure 3). This retrograda-

tional parasequence set comprises the lowermost stra-

ta of the overlying transgressive systems tract (TST) of

sequence 2 (Figures 7a, b; 8). Event deposits (litho-

facies assemblage 3) occur in the TST. Figures 2 and 3

show the maximum flooding surface in a thick (hun-

dreds of meters), monotonous section of mudstone

and shale comprising the Upper Mudstone Member

(Potrerillos Formation), well above the upper bound-

ary of the Delgado Sandstone Member.

Stratigraphic Variation Adjacent to Salt Diapirs

Although this stratigraphic framework is generally

consistent, there is local deviation adjacent to both

El Gordo and El Papalote diapirs. Figures 7b and 8 show

four laterally discontinuous parasequences comprising

the TST sandstones on the updip (northwest) margin

of El Gordo diapir (e.g., sections 25, 26, 27, and 29).

A similar but less pronounced trend is observed on

the updip flank of El Papalote diapir (e.g., sections 3

and 4), where two parasequences comprise the TST

(Figures 7a, b; 8). Basinward sections (i.e., those in

the southeast and downdepositional dip of salt stocks)

contain only a monotonous succession of mudstone

and shale above the DSB and transgressive surface. No

sandy parasequences are observed. The thicker TST

observed on the updip margins of the diapirs suggests

that sediment ponding occurred on the updip flanks of

salt diapirs during marine transgression.

SEDIMENTATION PATTERNS

Spatial and temporal thickness trends and lithofacies

distribution delineate a twofold sediment dispersal

pattern. This consists of southeast-directed, relatively

concordant regional sediment dispersal that is locally

complicated by diapirism. Downdip-oriented strati-

graphic cross sections across El Papalote and El Gordo

diapirs (Figure 7a, b) in association with a fence dia-

gram (Figure 8) illustrate (1) a systematic increase in

deeper water lithofacies toward the southeast (down-

dip) and (2) a local impact of diapirism on the stratig-

raphy. The spatial distribution of lithofacies (Figure 8)

is relatively concordant and consists of gradual, basin-

scale facies changes. However, locally (within approx-

imately 12 km [0.61.2 mi] of salt diapirs), strata

become sandier, and parasequences incorporate a slight-

ly higher percentage of shallower water lithofacies on

updip (landward) diapir margins (Figure 7a, b). Per-

cent sandstone data (Figure 9) from the Delgado Sand-

stone Member complement these lithofacies trends,

showing (1) a regional, systematic increase in sandstone-

to-mudstone ratio (percent sandstone) toward the north-

west; (2) a broad, elongate, northeast-trending belt of

50% or greater sandstone facies in the center of the

basin; (3) localized increases in percent sandstone from

3050 to 7090% within 13 km (0.61.8 mi) of salt

stocks; and (4) directly adjacent to diapirs (within 0.5 km

[0.3 mi]), percent sandstone increases to 100% on

the updip margins of El Papalote and El Gordo dia-

pirs. Additionally, lithofacies become sandier at a greater

distance from El Gordo diapir than El Papalote diapir

(Figure 9).

Stratal Thickness and Sandstone Depocenters

Spatial trends in stratal thickness emulate spatial litho-

facies distributions and corroborate the interpretation of

regionally concordant sedimentation locally disrupted

by diapirism. Stratigraphic cross sections (Figure 7a, b)

show relatively uniform stratal thickness punctuated

by distinct, asymmetric stratal thinning adjacent to

salt diapirs. Stratal thinning initiates 1.8 km (1.1 mi)

northwest (updip) and 0.5 km (0.3 mi) southeast (down-

dip) of El Papalote diapir (Figure 7a). Similarly, stratal

thinning initiates 2.3 km (1.4 mi) northwest (updip)

and 1.8 km (1.1 mi) southeast (downdip) of El Gordo

diapir. Thinning begins at a greater distance on the up-

dip flank of both diapirs; however, thinning initiates at

Figure 7. Stratigraphic cross sections (a) across El Papalote diapir and (b) across El Gordo diapir showing (1) downdip facieschange from a sand-dominated inner shelf to a mud-dominated outer shelf; (2) a more expanded, mud-rich section toward thesoutheast; (3) sandstone depocenters concentrated on the northwest (updip) margin of salt diapirs; and (4) stratal thinning onlywithin several kilometers of salt diapirs and downdip because of facies changes. Symbols used: EG = El Gordo diapir; EP = El Papalotediapir; HST = highstand systems tract; TST = transgressive systems tract; S1 = sequence 1; S2 = sequence 2; DSB = Delgado sequenceboundary; TS = transgressive surface (coincident with DSB). Measured sections are numbered above each column.


a greater distance from El Gordo diapir than El Papalote

diapir.

Thickness trends displayed in isopach maps of to-

tal (Figure 10), HST (Figure 11a), and TST (Figure 11b)

strata echo trends displayed in stratigraphic cross sec-

tions (Figure 7a, b) and the fence diagram (Figure 8).

The isopach map of combined HST and TST (total)

strata shows a broad northeast-southwesttrending,

Figure 8. Stratigraphic fence diagram of the Delgado Sandstone Member showing the basinwide distribution of sandstone bodiesand relative thickness. Inset map shows the location of cross section panels and measured sections. Symbols used: EG = El Gordo diapir;EP = El Papalote diapir; HST = highstand systems tract; TST = transgressive systems tract; S1 = sequence 1; S2 = sequence 2; DSB =Delgado sequence boundary; TS = transgressive surface (coincident with DSB). Measured sections are numbered in white circles aboveeach column.


regional-scale depocenter, a local depocenter between

El Papalote and El Gordo diapirs, and very local, minor

stratal thickening followed by abrupt thinning in about

2 km (1.2 mi) of updip diapir flanks (Figure 10). Spa-

tial thickness trends illustrated by the HST isopach

map (Figure 11a) include (1) a southern belt of thick

strata outlining a region of expanded sections (e.g.,

thick shale successions separated by thin sandstone

beds); (2) a northeast-southwestelongated, 3050-m

(100160-ft) depositional thick in the central part of

La Popa basin; (3) two poorly defined, isolated sand-

stone depocenters on the updip flanks of El Gordo and

El Papalote diapirs; and (4) a thick depocenter between

El Papalote and El Gordo diapirs. Consistent with this,

the TST isopach map (Figure 11b) shows (1) a southeast-

ern belt of thin strata outlining the basinal extent of

deposition; (2) a northeast-southwesttrending belt of

thick strata (>30 m; >100 ft); (3) two well-defined de-

pocenters on the northwest (updip) flanks of El Gordo

and El Papalote diapirs; and (4) a small, elongate depo-

center located between the diapirs and at the southern

termination of La Popa weld. The TST isopach map

highlights the presence of distinct, small depocenters on

the northwest (updip) flanks of both diapirs; the larger

depocenter is located on the northwest (updip) flank

of El Gordo diapir. In addition, comparison of HST

and TST isopach maps shows a northwest-westward

translation of the broad, northeast-southwestoriented

depocenter corresponding to marine transgression from

the HST to the TST. Collectively, isopach maps de-

pict uniform, regional thickness trends interrupted

by diapir-proximal (within 2.5 km [1.6 mi]) stratal

thinning and a broad northeast-southwestoriented

depocenter.

Figure 9. Percent sandstone lithofaciesmap of the Delgado Sandstone Memberconstructed using the stratigraphic ratioof sandstone to mudstone. Note that(1) major sandstone depocenters arecentered about salt diapirs; (2) the re-gion of sand deposition northwest ofEl Gordo diapir is slightly larger thanEl Papalote; and (3) sediment shadowzones occur downdip of salt diapirs.


Changes in Sedimentation Patterns Related to SystemsTracts and Salt Diapirs

Temporal variation in lithofacies and stratal thickness

trends were discerned using the sequence-stratigraph-

ic framework (Figures 7a, b; 8) in conjunction with

isopach maps (Figure 11a, b). Regionally, there is a

landward shift in facies from the HST to the TST dur-

ing marine transgression; no other regional variations

occur (Figures 7a, b; 8). Temporal variation in sedi-

mentation is most pronounced locally, adjacent to salt

diapirs where correlations between sandstone depocen-

ter development and systems tracts exist. Stratigraphic

cross sections and a fence diagram illustrate abundant

shallower water lithofacies in HST strata that show

a strong correlation between lithofacies and distance

to salt diapirs (Figure 7a, b). Stratal successions con-

sisting of lower shoreface sandstone bodies become

sandier and more amalgamated, and progressively in-

corporate more middle and upper shoreface litho-

facies with increasing proximity to salt diapirs. No dis-

crete diapir-proximal depocenters are defined in HST

strata (Figure 12a). Conversely, TST strata show a weaker

correlation between lithofacies and salt diapir prox-

imity. Transgressive systems tract strata contain sev-

eral successions of lower shoreface sandstone and pe-

lagic mudstone that become sandier toward salt diapirs

but do not become more amalgamated or incorporate

Figure 10. Isopach map of total sand-stone thickness of the Delgado SandstoneMember. Note that expanded sectionsoccupy the darkest regions, sandstonesthin within 2 km (1.2 mi) of diapirs, andthe thinning halo about El Gordo diapiris larger than that of El Papalote.


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shallower water facies (Figures 7a, b; 8). A strong cor-

relation between thickness and salt diapir proximity

occurs in TST strata reflected by the presence of dis-

tinct sandstone depocenters on updip diapir margins

(Figure 11b). Sandstone depocenters in TST strata are

more restricted at El Papalote diapir than El Gordo

diapir. The depocenters occur at a maximum distance

of 2.3 km (1.4 mi) from salt diapirs and are roughly

0.52 km (0.31.2 mi) wide by 0.10.5 km (0.06

0.3 mi) thick.

DISCUSSION AND CONCLUSIONS

Regional lithofacies trends combined with thickness

and percent sandstone trends suggest sand deposition

in a geometrically complex, southwest-northeast

oriented shoreline system. The progressive southeast-

ward deepening of facies and decrease in percent

sandstone support a southeast-dipping slope and

southwest-northeastoriented shoreline. Previous

provenance studies are consistent with this shoreline

orientation, indicating a sediment source to the west

in the highlands of the Sierra Madre Oriental (Aschoff,

2003). Sand was likely transported from highlands

(west) to the shoreline (east) by river and delta sys-

tems, where it was reworked and redistributed by

wave and longshore current processes in a southwest-

northeast direction.

Regional sediment dispersal patterns remained rel-

atively uniform at distances greater than approximately

2.3 km (1.4 mi) from salt diapirs; diapiric influence

was very localized. Within 1.82.3 km (1.11.4 mi)

of El Gordo diapir and 0.51.8 km (0.31.1 mi) of

El Papalote, diapir-proximal variations overprint re-

gional trends. Diapir-related variations include shal-

lower water facies, stratal thinning, and increased per-

cent sandstone (Figure 12). Lithofacies adjacent to

El Gordo diapir represent shallower water environ-

ments than those adjacent to El Papalote. Consistent

with this, stratal thinning initiates at a greater distance

from El Gordo than El Papalote diapir, suggesting

that El Gordo diapir had higher sea-floor relief, cor-

roborating the conclusions of Rowan et al. (2003).

Diapir-related sandstone depocenters occur at a

maximum distance of 2.3 km (1.4 mi) from salt bodies

and are roughly 0.52 km (0.31.2 mi) wide by 0.1

0.5 km (0.060.3 mi) thick. These depocenters con-

tain stratal assemblages that are significantly sandier

(7090% sand) than diapir-distal assemblages and con-

tain a higher percentage of shallow-water facies (upper

shoreface and foreshore). Although HST strata show

the strongest correlation between diapir proximity and

lateral lithofacies shoaling, depocenters in the HST are

poorly developed. This suggests that diapir relief lo-

cally (in 2.3 km [1.4 mi]) influenced the mode of de-

position but did not cause regional lateral shifting or

focusing of sediment dispersal patterns. Conversely, TST

strata contain well-developed sandstone depocenters.

We propose that depocenters result from preferential

reworking of regressive sand during marine transgres-

sion. Storm and longshore processes deposited these

sands in the form of shelf ridges adjacent to salt dia-

pirs. Increased diapir-proximal subsidence and elevated

diapir relief likely contributed to the formation and

preservation of sandstone depocenters.

Figure 12. Block diagram of lithofacies summarizing sedimentation patterns in La Popa basin, including the regional trend of andinternal variation in the Delgado depositional system along with pronounced localized shoaling trends on the updip margin diapirs.Symbols used: FS = foreshore lithosome; USF = upper shoreface lithosome; LSF = lower shoreface lithosome; OS = offshorelithosome; EGD = El Gordo diapir; EPD = El Papalote diapir; EGA = El Gordo anticline (Rowan et al. 2003).


APPLICATION TO PETROLEUM EXPLORATION

Some of the most prolific petroleum reservoirs in the

world occur in salt-influenced basins such as west Af-

rica, the North Sea, and the Gulf of Mexico. Abundant

exploration opportunities exist in these basins because

of the diverse, complex assemblage of salt-related pe-

troleum reservoirs, traps, and seals coupled with the

intrinsically higher thermal conductivity of salt. The

extreme heterogeneity of these petroleum systems

requires outcrop analogs to build predictive models. In

addition to delineating basinwide sediment dispersal

patterns, we have identified and described potential

petroleum reservoirs present directly adjacent to salt

diapirs. These include sandstone depocenters on updip

diapir margins that develop in TSTs. Consequently,

depocenters coincide with the multiple trapping and

sealing opportunities that exist on diapir margins as a

result of faulting and halokinetic sequence develop-

ment. This investigation provides a conceptual frame-

work for petroleum explorationists deciphering salt-

related data sets in the subsurface.

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Allen, J. R. L., 1982, Sedimentary structures: Their character andphysical basis: Amsterdam, Elsevier, v. 2, 663 p.

Alvarez, L. W., W. Alvarez, F. Asaro, and H. V. Michel, 1980,Extraterrestrial cause for the CretaceousTertiary extinction:Science, v. 208, no. 4448, p. 10951108.

Alvarez, W., 1996, Trajectories of ballistic ejecta from theChicxulub Crater, in G. Ryder, D. Fastovsky, and S. Gartner,eds., The CretaceousTertiary event and other catastrophes inEarth history: Geological Society of America Special Paper 307,p. 141150.

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