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Geological Circular 82-3
SURFICIAL EVIDENCE OF TECTONIC ACTIVITY AND
EROSION RATES, PALESTINE, KEECHI, AND
OAKWOOD SALT DOMES, EAST TEXAS
by
Edward W. Collins
Prepared for the U.S. Department of Energy
Under Contract No. DE-AC97-80ET46617
(formerly DE-AC97-79ET44605)
Bureau of Economic Geology W. L. Fisher, Director
The University of Texas at Austin Austin, Texas 78712
1982
9303110355 930305 PDR WASTE 14l-11 PDR
/6ý5ý
CONTENTS
ABSTRACT . • ............
INTRODUCTION .............
REGIONAL SETTING
GEOMORPHIC SETTING
TRINITY RIVER TERRACES. . .......
Terrace ages . . •..........
Terraces as indicators of long-term regional uplilt
DOME GEOLOGY AND GEOMORPHOLOGY.
General stratigraphy
Palestine Dome ... .........
Keechi Dome.............
Oakwood Dome ........... ......
Morphologic mapping . . . . .
SEROSIONAL BREACHING OF DOMES
Denudation rates in East Texas
Entrenchment of the Trinity River
SUMMARY
ACKNOWLEDGMENTS ..... .........
REFERENCES
* 1
2
3
4
6
7
8 . . .71
. . .81
* 8
10
14
18
. . . 24
S. . 24
28
29
34
35
35
ILLUSTRATIONS
Figures
Location map of study area showing regional structural elements .
Location of topographic cross sections of terraces along the Trinity River...................
iii
1.
2.
3
5
3. Profile of terrace deposits of the Trinity River..... . . .
-4. Linear regression lines expressing the regional gradient for terrace levels T-2, T-lb, modern floodplain, and the contact between Trinity River alluvium and bedrock ............ .......
5. Stratigraphic column for study area . .....
6. Geologic map of Palestine Dome area .......... .....
7. Topographic map of Palestine Dome area ...... .......
8. North-south and east-west topographic profiles over Palestine Dome.
9. Topographic profiles of terrace surfaces on the western flank of Palestine Dome and adjacent to the dome . . .
10. Geologic map of Keechi Dome area. ... .
11. Topographic map of Keechi Dome area
12. North-south and east-west topographic profiles over Keechi Dome
13. Photograph of tension fracture at Keechi Dome .........
14. Geologic map of Oakwood Dome area .... ........ ..
15. Topographic map of Oakwood Dome area .... .........
16. North-south and east-west topographic profiles over Oakwood Dome.
17. Cross section G-G' of floodplain deposits above Oakwood Dome .
18. Morphologic map of Palestine Dome area .... ........
19. Morphologic map of Keechi Dome area
20. Morphologic map of Oakwood Dome area ........ ... .
21. Location of sampling stations for suspended-sediment-load data .
22. Location of reservoirs for sedimentation resurvey data ........
23. Profile showing Trinity River terraces and depth of incision into bedrock ............... ................
24. Topographic profile of Keechi Creek and its incision into bedrock.
Tables
1.
2.
Denudation rates determined from suspended-sediment load data . . . . 31
Denudation rates determined from sedimentation resurvey data . . . . 31
iv
6
8
9
*11
12
13
15
16
17
18
19
20
21
22
23
25
26
27
30
32
33
34
ABSTRACT
Surficial geologic investigations at Palestine, Keechi, and Oakwood salt domes
have provided information necessary for evaluating these domes as nuclear waste
repositories. Diapir growth uplifted sediments to form domes and created complex
radial faulting. Cretaceous rocks crop out at Palestine and Keechi Domes, whereas
only Eocene Claiborne sediments are exposed over Oakwood Dome. Annular drainage
patterns at Oakwood and Palestine Domes reflect the domal structure. Holocene
deposition is occurring over the center of all three domes in topographic depressions;
these topographic lows suggest that minor subsidence has occurred. At Palestine
Dome, recent sinkholes caused by abandoned brining operations indicate that the dome
is unsuitable as a repository site.
All three diapirs are located within the central Trinity River drainage basin.
Depths to salt at Palestine, Keechi, and Oakwood Domes are 37 m, 133 m, and 351 m,
respectively. Quaternary terraces of the Trinity River reveal no evidence of warping
caused by domal or regional uplift. The average denudation rate in East Texas is
calculated to be 8.85 cm/l,000 yr. Incision by the Trinity River into the bedrock is
S 15 m beneath the present floodplain near the domes. Geomorphic studies of
denudation and river entrenchment in the Trinity River drainage basin indicate that it
is unlikely that Oakwood or Keechi Domes would be breached by erosion during the life
of a potential repository.
INTRODUCTION
Detailed investigations involving both regional and site-specific geology and
geohydrology of the East Texas salt basin have provided information needed for
geologic evaluation of salt domes as potential nuclear waste repositories (Kreitler,
1979; Kreitler and others, 1980; Kreitler and others, 1981).
Investigations of East Texas domes are part of geologic studies of Gulf Coast
salt domes in Texas, Louisiana, and Mississippi sponsored by the U.S. Department of
Energy. Palestine, Keechi, and Oakwood Domes in East Texas were selected for
I
detailed investigations. Geomorphic and geologic studies investigated present and
IuLure %LabibiLy ol tic :,all doiin"-s, I lydrologic investigations of the Palestine Dome
area determined that the dome was unsuitable to be a nuclear waste repository. More
recently it has been determined that Keechi Dome is too small to be a repository.
Oakwood Dome is still being considered as a possible repository site, although it is less
suitable than other Gulf Coast salt domes.
Palestine, Keechi, and Oakwood Domes lie within the central Trinity River
drainage basin in Anderson, Freestone, and Leon Counties (fig. 1). These domes are
among 15 shallow domes within the East Texas salt basin. Depth to salt over these
shallow East Texas domes is between 37 m at Palestine Dome and 1,088 m at Brushy
Creek Dome. East Texas domes generally underwent maximum uplift during the early
Cretaceous, reduced growth in the Early Tertiary, and relative stability in the late
Tertiary and Quaternary (M.P.A. Jackson, personal communication, 1981).
Surficial studies concentrating on surface geology and geomorphology were
conducted in conjunction with subsurface, remote-sensing, and hydrologic investiga
tions. Site-specific investigations of the three Texas domes are essential to reveal
fractures, warping, and drainage anomalies that might point to dome uplift or
subsidence. Studies of denudation and stream entrenchment in the Trinity River basin
permit evaluation of the potential for erosional breaching of each dome.
REGIONAL SETTING
The East Texas salt basin is bounded by the Mexia-Talco fault zone in the north
and west, the Sabine Uplift in the east, and the Angelina Flexure in the south (fig. 1).
The Mexia-Talco fault zone originated in Middle Jurassic and may have been
associated with the early development of the Gulf of Mexico (Jackson and Wilson, in
press). Initial movement of the Sabine Uplift occurred in pre-Cenomanian (mid
Cretaceous) time, with subsequent rejuvenation continuing until post-Eocene time
(Eaton, 1956). The Angelina Flexure represents a hinge line that marks the southern
limit of the East Texas Basin.
The Mount Enterprise-Elkhart graben system occurs north of the Angelina
Flexure. It consists of contemporaneous down- and up-to-the-basin normal faults with
dips of 350 to 600 that steepen toward the surface. Initial movement on the Mount
Enterprise faults was during the Cretaceous; the most pronounced activity was during
2
OKLA
I ' , • /SABINE LA
" 0 /s 4' Tyler sUPLIFT
/ KeecI . esi W eons o"/ ok-ood, • ''ka:'
R'iOT' RIVER
EBA IN .
O 5Onsr
0O 80 km
EXPLANATION
-I, Fault
Sail dome
Figure 1. Location map of study area showing regional structural elements.
Eocene time (Eaton, 1956). Recent studies indicate that this fault system was active
duringthe Quaternary (Collins and others, 1980; Pennington and others, 1981).
Basement in the East Texas Basin is probably folded and faulted Paleozoic rocks
of Ordovician to Early Pennsylvanian age. Overlying Mesozoic and Cenozoic strata
record a series of transgressive to regressive depositional events (Nichols and others,
1968). A rapidly subsiding north-trending low, the Tyler Basin, received thick
accumulations of Mesozoic and Early Tertiary sediments. Post-Eocene sediments were
deposited beyond the southern basin margin in the younger part of the Gulf Basin.
GEOMORPHIC SETTING
The East Texas Basin underlies the Rolling Hills and Prairie physiographic
subprovince of the East Texas Timber Belt (Fenneman, 1938). Dense vegetation,
dominated by oak and pine forests, limits field studies in the region. Soils are
predominantly acidic sands or sandy loams of low organic content, and they are easily
eroded when vegetation is cleared. Normal annual precipitation varies eastward from
3
75 cm to more than 130 cm, and the average annual temperature ranges between 160
and 200 C (Orton, 1969).
East Texas is drained by the Trinity, Neches, and Sabine Rivers. Palestine,
< - Keechi, and Oakwood Domes are within the Trinity River drainage system, which
encompasses an area of about 48,000 km 2 (fig. 1). The river flows southeastward for
about 650 km from its headwaters north of Dallas to the Gulf of Mexico. Elevation at
the headwaters reaches 400 m above sea level, although in the study area elevation
ranges from 60 to 150 m above sea level. The northern part of the basin is a slightly
rolling area of treeless prairies and rolling, timbered hills. Heavily forested rolling
hills characterize the study area in the central part of the basin, whereas the southern
part of the basin is a relatively flat coastal prairie (Leifeste and Hughes, 1967).
Several terrace levels and a broad floodplain, commonly 8 km wide, are
developed along the Trinity River valley. Meanderbelts may be as wide as the
floodplain, and oxbow lakes are common. Along the upper Trinity River, five terrace
levels have been recognized by Slaughter and others (1962), although near the mouth of
the river on the Gulf Coastal Plain, Failing (1969) observed only four terrace levels. In
the study area four terrace levels exist, and poorly exposed remnants of gravel are
common at high elevations. These poorly exposed gravel deposits are designated
"upland gravels" and may represent older terraces (Stenzel, 1938). Terraces along the
Trinity River result from the river's response to base-level changes associated with
Pleistocene sea-level fluctuations and climatic variations.
TRINITY RIVER TERRACES
In the study area, four terrace levels are identified according to their heights
above the river floodplain (figs. 2 and 3):
T-3 27.5 to 36.5 m
T-2 15 to 21 m
T-lb 4.5 to 9 m
T-la 1 to 3 m
The lower terraces are normally better defined than the highest terrace, and outcrops
exposing terrace sediments are rare. The lithology within the terraces varies
considerably. In general, the upper two terrace levels, T-3 and T-2, have a similar
composition consisting of clay, sand, and subangular to rounded pebbles of vein quartz,
chert, quartzite, silicified wood, and ironstone; occurrence of bone is rare. Thurmond
4
A I
N
Tzý EXASI
0 20 40mi i I I 1 II 1 I1 1 I I
0 20 40 60 km
w E Elevation (
S1 60
0 4000ff
0 -1
Keechi Dome
• PALESTINE
>"-Rtlestine Dome
Ookwood Dome
w E9
Elevation ft f
400--- 2
300 90
200 70 T-2 T-to IT-lb T-3 A
0 f200.
0 4000ff
EFevofieo n r
200 60
40 100
F. loponTI T-fb Frneoon SAY
Figure 2. Location of topographic cross sections of terraces along the Trinity River. From Kreitler and others (1981).
-5
P
It A
+ IC
100t+ @ Mesquite and
300+ Forney North
-50 @ogLk - 7 8 and Oakwood EXPLANATION
oor Quadrangles x T-3 ST
T-lb
010Trinity River floodplain T-io
00 0 Libery 0 50M
Quadrangle +n T- I 0 80km
Figure 3. Profile of terrace deposits of the Trinity River. From Kreitler and others (1981).
(1967) determined in terrace studies of the northern part of the Trinity River valley
that gravels of a terrace 28 to 37 m above the floodplain consist largely of exotic
sediments such as red quartzites, dark cherts, and vein quartz. Gravels of this
composition, however, are also abundant in the T-2 terrace and less common in the
T-lb terrace, although outcrops of T-lb are poor. No exposures of the T-la terrace
were accessible. Gravels of the T-3 and T-2 terraces, as well as the older upland
gravels, are commonly cemented by iron oxides. The upland gravels are also composed
mainly of cobble-size sediment.
Soils developed on the upper two terraces vary from a clayey loam to sand. Soils
on terrace T-lb are composed of clay to clayey loam, and soils on the T-la terrace
and the river floodplain are predominantly clay (Coffee, 1975). The lower rivet
terraces, T-lb and T-la, are characterized by oxbow lakes and scrolls.
Terrace Ages
Absolute ages of the Trinity River terraces have not been determined, but tý
terraces may correlate with Pleistocene formations of the Texas Gulf Coastal Plai
The upper terrace level, T-3, appears to be related to the Pleistocene Montgome
6
AIA
Formation, whereas the T-2 terrace level corresponds to the Pleistocene Beaumont
Formation. Terrace levels T-lb and T-la are related to the late Pleistocene or
Holocene Deweyville Formation (figs. 2 and 3). The Beaumont (T-2) and Deweyville
terraces (T-lb and T-la) are well developed along the section of the Trinity River
flowing through East Texas.
Montgomery alluviation, related to the highest terrace, probably occurred
between 170,000 and 300,000 years B.P. (Bernard and LeBlanc, 1965, p. 146). Verte
brate and invertebrate fauna from a T-2 terrace located in the northern part of the
Trinity River drainage basin have been determined to be of Sangamon Age (Slaughter,
1969). The Sangamon Interglacial lasted from 128,000 to 73,000 years B.P. (Suggate,
1974). Figure 2 shows that terrace T-2 correlates with the late Pleistocene Beaumont
Formation, a widespread accumulation related to early Wisconsin interstadials;
Beaumont alluviation occurred from 70,000 to 100,000 years B.P. (Bernard and
LeBlanc, 1965, p. 146). Radiocarbon age dates of wood fragments from Deweyville
terraces (T-lb and T-la) on the Trinity, Neches, and Sabine Rivers range from 17,000
to more than 30,000 years B.P. (Bernard and LeBlanc, 1965).
Terraces as Indicators of Long-Term Regional Uplift
Terrace level gradients from the headwaters of the Trinity River to the Gulf
Coastal Plain show that Pleistocene deposits have not been affected by major regional
or local uplift except at the Elkhart Graben where minor displacement was caused by
faulting (Collins and others, 1980). In analyses of Quaternary coastal plain elevations,
Bernard and LeBlanc (1965) showed that the landward part of the Texas Coastal Plain
was uplifted while the offshore zone subsided. This differential vertical movement
resulted from isostatic adjustment caused by sedimentary loading and by greater
compaction rates offshore. Gradients of Quaternary terraces updip of the Coastal
Plain do not reveal uplift, probably because of the distance from the hingeline
separating the uplifted coastal plain and the subsided offshore zone.
Figure 4 shows lines of linear regression for terrace levels T-2 and T-lb, the
present floodplain, and the base of incision into bedrock. These slopes are similar,
suggesting that no pronounced uplift has occurred. A terrace level near the Elkhart
Graben system (location 9, fig. 4) appears to vary slightly in elevation above the
floodplain, possibly due to displacements from faulting (Collins and others, 1980),
although terraces at other locations also display slight variations in elevation.
7
Elevohon
fl M +
400 120
0s
200 60 T-2,terrace BeG... .-Io 7
T- lb terrace ® ©
STrinity River floodplai s =slope 0 3 .0kin
all uviumn and bedrock
0 (D-lcotio (D 0 T @ SL@ @
Figure 4. Linear regression lines expressing the regional gradient for terrace levels
T-2 and T-lb, the modern floodplain, and the contact between Trinity River alluvium
and bedrock. The study area is the central Trinity River basin. Locations refer to
figure 2.
DOME GEOLOGY AND GEOMORPHOLOGY
Surface geology and geomorphology at Palestine, Keechi, and Oakwood Domes
document different strata and drainage patterns. Morphological and structural
elements of the three domes are similar, however.
General Stratigraphy
In the study area, sediments of the Claiborne Group crop out except where
overlain by Quaternary sediments deposited by local rivers and streams and where salt
diapirs have uplifted older rocks ranging from the Tertiary Wilcox Group to the
Cretaceous Washita Group. Outcrops of these older strata are typically very poor.
The oldest stratigraphic unit exposed at the surface of Palestine Dome is the
Cretaceous Buda Limestone (Hightower, 1958). At Keechi Dome the oldest units
8
exposed are the Cretaceous Taylor and Navarro Groups (Ebanks, 1965). Tertiary
Claiborne sediments crop out at Oakwood Dome. The stratigraphic succession in the
study area is shown in figure 5.
Figure 5. Stratigraphic column for study area.
The Buda Limestone is a medium- to massive-bedded, slightly glauconitic and
fossiliferous, microcrystalline limestone (Hightower, 1958). It is overlain by Woodbine
strata. The massive to poorly bedded, very fine to fine-grained quartz sands of the
Woodbine are overlain by the interbedded, very fine grained sandstones and shales of
the Eagle Ford Group. Overlying the Eagle Ford shales are glauconitic, fossiliferous,
chalky limestones of the Austin Group. Younger Taylor Group and Navarro Group
strata are undifferentiated at both Palestine and Keechi Domes. These groups
comprise sequences of massive to poorly bedded, fossiliferous marls, and clays
(Hightower, 1958).
The Paleocene Midway Group consists dominantly of calcareous to non-calcare
ous marine shales interbedded with sandstones in the upper part. Overlying the
Midway Group are sandstones and mudstones of the Paleocene-Eocene Wilcox Group
9
that formed by fluvial-deltaic deposition (Fisher and McGowen, 1967). Cyclic
deposition continued in the Eocene with deposition of the Eocene Claiborne Carrizo,
Reklaw, and Queen City Formations. These Claiborne units are exposed throughout
the entire domal area. Sands in the lower part of the Carrizo Formation are
interpreted to be stream deposits of either coarse-grained meanderbelt (McGowen and
Garner, 1970) or braided alluvial origin, whereas the finer grained upper part reflects a
lower alluvial plain environment having extensive floodbasins. The Newby Member of
the overlying Reklaw Formation contains abundant glauconite and an open shelf fauna,
although a trace fossil assemblage is prevalent in shallow water. The Marquez
Member of the Reklaw Formation represents restricted marginal marine conditions.
Crevasse splays and small bayhead deltas were sites of coarser grained clastic
sedimentation (Collins, 1980). The Queen City Formation comprises upward
coarsening, shoal-water, delta sequences and polymodally cross-bedded marginal
marine sand shoals (Hobday and others, 1979).
Quaternary terrace deposits of the Trinity River also occur in the study area.
Four terrace levels and an additional gravel unit that occurs at higher elevations,
termed "upland gravels" by Stenzel (1938), have been identified.
Palestine Dome
Strata cropping out over Palestine Dome range from the Cretaceous Washita
Group to Pleistocene terrace deposits (fig. 6). Cretaceous and Tertiary units have
been uplifted to develop a typical domal outcrop having dips up to 50°. Pleistocene
sediments unconformably overlie older stratigraphic units on the western flank of the
dome. Patches of terrace sediments may occur as erosional remnants in other areas
over the dome, although this is difficult to determine. Well-developed radial faults
were mapped by Hightower (1958). The depths to salt and cap rock are 37 m and
36.5 m, respectively (Halbouty, 1980).
The unique topography at Palestine Dome was first recognized in early studies by
Hopkins (1917) and Powers (1926). A man-made lake fills a central depression over the
dome, and is enclosed by a ring of hills (figs. 7 and 8). The dome is encircled by
annular drainage, and intermittent streams in a centripetal pattern flow into the lake
in the central topographic depression over the dome. Powers (1926) observed gas
seeps, mud springs, mud volcanoes, and "craters" or collapse holes that have resulted
from early salt brining operations. In recent studies, 15 of these collapse features
were mapped by Fogg (in Kreitler and others, 1980, p. 46-54). Because of the
... .... ... - - - - - -
CONTQUR ON TOP OF SALT
-75000FT.
... .........
............. ............ ...
................. ..... ..............
.................
..........
... ........... .................
0 ............
I-
II ml
0 Ikm
EXPLANATION
>ElMODERN ALLUVIUM
z '1TRINITY RIVER TERRACE Ujfl DEPOSIT
CyL UPLAND TERRACE DEPO~ { :QUEEN CITY FM REKLAW FM
CARRIZO FM
HWILCOX GROUP
L .MIDWAY GROUP
E- AYLOR a NAVARRO GRO
E AUSTIN CHALK WOOD BIN E a EAGLE FOI
GROUPS B UDA LIMESTONE
U/-D FAULT -- INFERRED OR
SIT
UPS
COVERED
Figure 6. Geologic map of Palestine Dome area. Modified from Hightower (1958).
11
RD
0 '~~ ~ .........~ ' 0 0
.0,00• '.° • a° 0,, a'• 0
I ao 0
* o4o 0 'o -' a
3000
o o a 'o ' 0 % , * 0', . 0
000*0oo .. 0o *• .°o
o o o *oo a
o 0 0 o o- o ... 0 0 0 0 0 30 • o0.000000
o a 30 33 0 0 :oaa0,,
300000 aoo° o0o 0 ~ o 00
° °o~o0,o 00a ,•0 0~
'o 'o 30 o .. ~ ~
0 Imi
0 1 kmLake
4 Swamp
Elevation (above msl) • -350 ft 250-300ft
(>107m) (76- 92m)
300-350ft F <250ft
(92- 107m) 76 (<7Gm)
-1 0 1000 ft contour on top F 7r00ofP t i of Soal
Figure 7. Topographic map of Palestine Domeaa.ro eterndohs(91)
12
Elevation ft m
400- N $
-110 1350
100
300 90 Duggey's Lake
80 250
70
200- < 0 2000ft Salt at-IO00 ft (-305 rn) l- I
0 1 km
Elevation ft m WE
350- 1 W I00
300 90 Duggey's 80 j Lke
25070
200-I 0 2000ft
I • •Salt at -100ft (-305 m) 0 Ikm
Figure 8. North-south and east-west topographic profiles over Palestine Dome. Width of dome at the -305-m contour of salt is shown below the profile. From Kreitler and others (1981).
potential for additional collapses caused by inactive brining operations and the
uncertainty of long-term hydrologic stability at the dome, Palestine Dome was
eliminated as a potential site for a nuclear waste repository (Kreitler and others, 1980,
p. 46-54).
Palestine Dome is one of the few salt domes in East Texas that is overlain by
well-developed Quaternary terrace deposits. The stability of East Texas salt domes
during the Quaternary is an important criterion when evaluating domes as nuclear
waste repository sites. Topographic profiles of the terrace surface over and near the
dome do not indicate warping of Quaternary deposits. At Palestine Dome, the T-3
terrace level overlies the western flank of the dome (fig. 6). A topographic profile of
the T-3 terrace surface on the west flank of the dome matches profiles of the same
13
terrace surface north and south of the dome (figs. 6 and 9). This suggests that no
dome growth has occurred since deposition of the terrace deposits, although this
assumption is based on the idea that the terrace surface has not been leveled by
' . erosion.
Keechi Dome
Strata cropping out at Keechi Dome are of Cretaceous, Tertiary, and Quaternary
age (fig. 10). Rocks within the Taylor and Navarro Groups are the oldest sediments
exposed. Strata exhibit dips up to 450, and radial faults exist (Ebanks, 1965).
Quaternary terrace deposits occur in the domal area, but exposures are poor. Brief
investigations of these Quaternary deposits indicate no evidence of warping or
faulting. The depths to salt and cap rock are 133 m and 38 m, respectively (Halbouty,
1980).
The topographic expression at Keechi Dome is not as conspicuous as at other
interior salt domes. However, Keechi Creek flows north-south across the dome,
through a slight topographic low over the center of the dome (figs. II and 12). The
drainage pattern in the area is subdendritic, and relief of about 30 m occurs between
the central topographic low occupied by Keechi Creek and surrounding peripheral hills.
Powers (1926) reported that the only evidence of salt at the surface is a small salt lick
located on the Keechi Creek floodplain.
Two unusual cracks or fissures (fig. 13) were observed at Keechi Dome in
November, 1979 (Kreitler and others, 1981). A landowner reported that the cracks
were first discovered in the spring of 1978. By May 1980 the cracks had been filled by
slumping and soil erosion. These fractures display trends of N. 70 E. and N. 670 W. and
are located along a southeastern extension of an inferred fault mapped near the dome
center by Ebanks (1965) (fig. 10). The relation of the fractures to the inferred fault is
speculative. When first observed in November 1979, these fractores appeared to be
nearly vertical and were 30 m and 12 m long. The larger fracture was 3.5 cm wide.
Exact depth of the cracks is unknown, but the base of the larger crack was deeper than
I m. An approximate depth of 4 m was measured by landowners in the spring of 1978,
but this has not been documented. The upper meter of soil cover is composed of 50 cm
of slightly clayey sand above 20 cm of red to yellow mottled clay and 30 cm of silty
clay. Although the mechanism that produced the fractures is unknown, the fractures
appear to be tensional rather than shear fractures because they were dilated and
because no offset was observed.
14
(
ELEV It m
350- I00
300 -90
-80
250 -70
200 60
ELEV ft m
350
I00
300 90
-80
250" _70
200 -60
-50
150
T-3
7 CLAIBORNE GROUP
(
ELEV ft m 400- 120
350 -00
300 90
-80 250
-0SALT AT IOOTMt
0C
C /
T-3
T-I / CLAIBORNE GROUP
0 "'2 I ni
0 "2 1 km
Figure 9. Topographic profiles of terrace surfaces on the western flank of Palestine Dome and adjacent to the dome.
From Kreitler and others (1981).
(
8
B
ELEV ft m
350
-I0
300 -9C
C-8
250-7C
200 -6
-5(
150i
• _ ~T-3
CLAIBORNE GROUP
QUATERNARY TERTIARY CRETACEOUS
V Io I ya
Modern "Upland gravel" Queen City Reklaw Corrizo Wilcox Midway Taylor a Navarro
alluvium terrace Formation Formation Formation Group Group Groups (undiff.)
0 Fault, dashed where /4 Strike and dip "•-5Oo,./. Contour on lop of m Location of tension
"t -covered or inferred salt I fractures
Figure 10. Geologic map of Keechi Dome area. Modif ied from Ebanks (1965).
16
.. ... ... ... ..........! : • ............ ..i i ... .... . .... :..-.-.
. . . . . . . . .. . . . . . .... . . ...
::. \... .. ... ..... : . .......
...............................
~~~~~. . .'." " ...": : : ' • : " " " . . . . . . W
~~~~. . . . .. . . . . . .. .. . . .* ° " Q
S..... .... ... .. ..... . •.. .. !i..... .... ii ~~. . . . ....... . . . . .
~~~~~~~~~.. . ..........i~ i~ i~ i ii i i ii i~ i i
(• ; m .i ii~ i ii~ i iiii i~ ii ii~ i iii. .A.E . .. ,...... ...... ::
I mi
km Lake
Swamp
-•1000 - I( conlour
-/oooft '•• on top of salt
Elevation (above mslO
50Oft ~( ::,- 152m)
=475 - 500 ft
0145 -152 m)
.150 -4175f I
M337- 145m I
4 25 - 4 50 f t
(130-137m')
r7- 400-425ft
375 -400fl (114-122m)
350 -375 ft
(107- 114m)
325 - 350f.i
(99 -107 m)
300-325ft
t 92-99m)
Z 300 ft
-9 2 m)
Figure 11. Topographic map of Keechi Dome area. From Kreitler and others (1981).
17
0
0
N
Elevation ft m
550 160 N S
500--150
-140 450
-130
4005 1020
-110 350
-100
300 -90 Salt at -1000 ft (-305m) -80 0 km
250 1 , , _ -70 0 200Oft
Elevation
ft m 550
160 W E
500 150
-140 450
_130
400- 120
-110 350 _ too- oII 300-90 I
0 1km Salt at -l00ft (-305m) S i I I
0 2000 ft
Figure 12. North-south and east-west topographic profiles over Keechi Dome. Width of dome at the -305-m contour of salt is shown below the profile. From Kreitler and others (1981).
Oakwood Dome
Eocene Claiborne strata crop out in domal configuration over Oakwood Dome
(fig. 14) (Collins and others, 1981). Claiborne strata compose the Carrizo, Reklaw, and
Queen City Formations. These stratigraphic units dip up to 200. Quaternary terrace
18
Figure 13. Photograph of tension fracture at Keechi Dome. Scale is in 10-cm increments. Width of fracture is 3.5 cm. Photograph was taken in November 1979.
deposits exist over the southern half of Oakwood Dome and appear unaffected by
domal uplift and faults. Four normal faults visible in outcrop cut only Claiborne strata
downthrown away from the dome. Additional fracture zones are common, and a
lineament pattern visible on aerial photographs is probably fault-controlled. None of
the faults can be shown to displace Quaternary strata, but because of poor exposures
19
........................ .............: .............................................................: .............ii i i i i i
: : : : : : : : : : : : : : : :: : : : : : : : : : : : : : : : : : : : : .. ...... ... ... ..= = •: i i~ i~
. .. . ....... ... . . .... . . . . Q . . . . . . . . . . . . .: : : : . . . . . .. .. . .. .. . .. .. . .. . . .. ...R . . . . . . . . . . . . . . . . . . . . . . . . .. . .... .
. ._ _ , ,, ,.o . ,, ..... .,......... ........... ......~i~ i ! ! !i i ' :: ! ! ;i ! !~ i : i.. .... . ...... .. . . . . . . . . . . . . . . . . . . ~~~~~~~~~~~~~~:: : : ............ii i i i i i~ ii i i i ii i i i !!i i ;; i i• " . . . .. . . .
....... ...................
oK ,o • ao eh~ ei : •: : : : : : : : S .. .. .. .. . . . . . . .. . . . . . .. .. .. . . .. . . .. .... .. . .
. . . . .. .. .. .. ..... . .... . . . .. ..k .. . ..-.. . . ......00 l( 05 )c no ¢ ntpo s l . . .. • . •. :: : : : :
Figure......... ... Ge l.cma..aw odD m.r..F o olisa dohes( 1...
......... erosion .. .he ..rc uf •dslc m n ano eetrl ic utd h ............ .......... sa t a d.a.o.ae.-1 m a d 1 •r sp c i e y
The....... ........h .b v a w o o e i h rctrz d b o t -e ta depression.... suro.de ..... _1rsetsapdrdeao14h etr, oten n
eastern~ ~ ~ ~ ~ ~ ~~~~~_ ....... ........is.15ad 6.Tta eie vrth oeis75m .......... ....... su d ndZi ove the .en.e o5te d me h ra a n lrdria e
presen. ....... ...... we.r...asen5a k. oo e e •lo pani l tdi h topograph...... deresi..boe.hedoe
20
0
0 lkm
N
I mi
N)Lake ' Swamp
• .• ,j.-1000 ft contour
on top of salt
Elevation
00 50Oft (>152m)
(137 - 152 m)
S400-450ftI
(122-137m)
(above MSL}
Fý-350-400ft
Lj (107- 122m)
300-350f, (92 - I07m)
< 3500 ft (ý- 92m )
Figure 15. Topographic map of Oakwood Dome area. From Kreitler and others (1981).
21
•- Elevation
ft1 m
Elevation
ft, m
SN
-- SaIt at - i000 ft (-305 m)-A
0 6000 ft
0 2 km
W
-150
-130
400
300I--Salt at -Q000 ft (-:305 m)----
O 6000 it
0 I 2km
Figure 16. North-south and east-west topographic profiles over Oakwood Dome.
Width of dome at the -305-m contour of salt is shown below the profile. From
Kreitler and others (1981).
22
E
INCISION INTO BEDROCK GI Q.
20
50 -. X. . :i:iii!!::i:::.... .. .....
OK 0(4O
201 OK OK10 IOO0f 202 OK O
S V E . = 2 = I . ... ... ..... . . . .
.20
DOME CENTER SOUTHERN MARGIN OF SALT
"• MODERN ALLUVIUM- Ranges from fine to coarse :17 CLAIBORNE GROUP - Ranges from fine sand
sand, clayey fine sand, and silty clay to and inlerloyered clayey sand to
pebble-sized ironstone gravel silly cloy, burrowed, corbonaceous
QUATERNARY TERTIARY
Figure 17. Cross section G-G' of floodplain deposits above Oakwood Dome. Location
of section G-G' shown on figure 14. From Collins and others (1981).
Ten shallow boreholes were drilled into floodplain deposits to determine and
compare the thickness variations of these Holocene deposits over and adjacent to the
dome (fig. 17). Floodplain deposits consist of a persistent basal gravel (10 to 40 cm)
composed of subrounded to subangular ironstone pebbles and coarse- to medium
grained sand. Medium- to fine-grained sand and silty clay overlie the gravel. Over the
dome these Holocene floodplain deposits are consistently 8 to I I m thick, but flanking
the dome they thin to 4 m (fig. 17). At the center of the dome, 200 m north of the
well-developed floodplain, the intermittent streams are incising bedrock. Variations in
the thickness of Holocene deposits suggest that subsidence may have occurred before
or during deposition of the floodplain deposits, resulting in accumulation of thicker
sediment above the dome (Collins and others, 1981).
Evidence of subsidence has been noticed at other salt domes. Natural collapse
has been reported I km west of Butler Dome's center, where Lake Port is now (Powers,
1926). Significant post-Pleistocene dissolution and subsidence with contemporary
Holocene deposition were confirmed at Jefferson Island salt dome in Louisiana. After
man-induced collapse of a salt mine drained Lake Peigneur, several hundred feet of
soft lake sediment were identified over the dome. The lake had previously filled a
central depression over the dome (Martinez and others, 1981). Subsidence may result
23
NF"P(")AI T IC}N
from volume loss created by salt dissolution, or cap rock dissolution, or by ground
water, although this has not yet been established at Oakwood Dome.
Morphologic Mapping
Morphologic mapping of Palestine, Keechi, and Oakwood Domes (figs. 18, 19,
and 20) shows that hillside slopes at Oakwood are steeper than at the other domes. All
three domes display central topographic depressions in which modern sediments are
being deposited. Morphologic maps of the domes distinguish between slopes formed by
erosional processes and slopes formed by depositional processes. U.S. Geological
Survey topographic maps (scale 1:24,000) were used to determine degree of slope over
the domes.
Erosional slopes at Oakwood Dome are steeper than slopes at Keechi and
Palestine Domes. At Oakwood Dome approximately 50 percent of the surface has
slopes from 5 to 15 , whereas over Keechi Dome greater than 95 percent of the area has slopes from 00 to 50. Over Palestine Dome, hillsides having gradients from 0 to 50 comprise approximately 65 percent of the area. Above Oakwood and Palestine
Domes (but not at Keechi), erosional slopes are steeper than those near the dome.
Despite the variations in erosional slope at the different domes, all three domes
display depositional slopes commonly in a central topographic depression. In the
central area over Palestine Dome a man-made lake is surrounded by a ring of hills
(fig. 18). At Keechi Dome the floodplain of Keechi Creek in the central dome area is
approximately three times as wide as the floodplain upstream and downstream
marginal to the dome (fig. 19). In the south-central part of Oakwood Dome, a
relatively large floodplain has developed (fig. 20). Drilling at Oakwood has revealed
that the modern floodplain alluvium is twice as thick over the dome as in adjacent
areas. Topographic lows are also prominent above Louisiana salt domes (Kolb, 1976),
which may indicate subsidence over domes, possibly due to dissolution of cap rock or
salt by ground water.
EROSIONAL BREACHING OF DOMES
A critical factor in evaluating a salt dome as a nuclear waste repository is the
possibility of breaching of the dome by erosion. Not only could erosion cause actual
exposure of a repository, but salt dome breachment could also reactivate dome
24
km Imi
Slopes resulting from erosional processes
0-20
W 2-5o
5-15o
Slopes resulting from depositional processes
I0-2
Stream
" .... '" Intermittent stream
Swamp
Pond
" -/o00 --- Contour on top of salt (- 305m)
Figure 18. Morphologic map of Palestine Dome area. From Kreitler and others (1981).
25
0 1. .
Slopes resulting from erosional processes Streom
S0-2° ' Intermittent stream
2-5°
Swamp
• 5-15' "Pond
Slopes resulting from depositional processes Contour on top o0 salt
CF7 71 0 -2 - oDf r30 5 m )
Figure 19. Morphologic map of Keechi Dome area. From Kreitier and others (1981).
26
Slopes resulting from erosional processes
0O-2o
W. w2-5
M 5-155
Slopes resulting from depositional processes
M 0-2o
S- Stream
"- Intermittent stream
Swamp
Pond
0 Contour on top of salt (-305mJ
Figure 20. Morphologic map of Oakwood Dome area. From Kreitler and others (1981).
27
growth. Erosional breaching could also release radionuclides into the biosphere.
Growth history studies of Hainesville Dome in East Texas show that a significant
amount of salt was extruded through the eroded top of the salt pillow (Loocke, 1978).
To evaluate the potential for erosion and exhumation of an East Texas salt dome, two
studies were made to estimate the regional denudation rates in the East Texas salt
basin and to examine the previous incision of the Trinity River.
Denudation Rates in East Texas
Recent denudation rates appear low enough to pose no threat of breaching the
East Texas salt domes. The East Texas salt basin receives an average rainfall of 100
to 130 cm and is drained by the Trinity, Neches, and Sabine Rivers and their
tributaries. The region is characterized by heavy vegetation, and land cover varies
from cropland and pastureland to dense forested areas. Oakwood and Keechi salt
domes both underlie the Trinity River drainage basin.
In East Texas, sediment is removed from drainage basins primarily by rivers or
streams. Rates of denudation were computed using suspended-sediment-load data of
rivers (fig. 21 and table i) and data from sedimentation resurveys of East Texas
reservoirs (fig. 22 and table 2). The equations used for these computations are as
follows:
(1) Denudation from suspended-sediment-load data: S+B SA+-B sDs + Dc = DT
where A = net drainage area
S = suspended-sediment-load data (average per yr)
B = bed load (estimate per yr)
Ds = denudation from suspended-sediment (per yr) Dc chemical denudation (per yr)
D = total denudation (per yr)
(2) Denudation from sedimentation resurvey data:
d A = DT
where A = net drainage area
d = average annual deposition (per yr)
DT = total denudation (per yr)
Using suspended-sediment-load data, an average denudation rate for East Texas
is estimated to be 8.85 cm/l,000 yr. Rates computed for the Trinity, Neches, and
28
Sabine River basins are 11.45, 8.16, and 6.95 cm/l,000 yr, respectively (fig. 21 and
table 1). Computations of the modern denudation rates are probably relatively
accurate even though bed-load and dissolved-load values were estimated. Suspended
sediment-load data were collected for periods ranging from 7 to 36 yr at 10 recording
stations maintained by the Texas Department of Water Resources. Bed-load values
were calculated to be 10 percent of the suspended load (Fisk and others, 1954), and the
chemical denudation for the western Gulf region is estimated at 0.037 mm/yr
(Livingstone, 1963). Sedimentation resurvey data from four reservoirs in East Texas
were used to compute an average denudation rate of 16.8 cm/1,000 yr (fig. 22 and
table 2). This value is close to denudation rates computed using suspended-load data
and helps to verify the accuracy of the modern denudation values.
Extrapolation of recent denudation rates to the future is uncertain. Winker
(1979), however, calculated Pleistocene rates of denudation along the Texas Gulf
Coast that compare relatively well with the modern values. He determined that late
Pleistocene denudation rates ranged from 3 to 10 cm/l,000 yr. Recent denudation
rates in East Texas appear low enough to prevent erosional breaching of the salt
domes; however, to predict possible breaching of a dome requires consideration of
future climatic conditions.
Entrenchment of the Trinity River
Another factor in evaluating the possible breaching of salt domes is the response
of rivers to climatic and associated sea-level fluctuations. During a glacial stage,
river incision and sediment aggradation will occur because of changes in base level
created by fall and rise of sea level, respectively. With each fall in sea level the
nickpoint moves farther upstream because of the rapid removal of unconsolidated
alluvium of the preceding aggradational episode. This investigation concerns previous
incision of the Trinity River during sea-level fluctuations and suggests that potential
breaching of Oakwood, Keechi, and Palestine Domes is not of major concern. To evaluate possible breaching of the salt domes, it is necessary to understand
the relation between glacial cycles and river incision and formation of terrace levels.
The Trinity River terraces and terrace ages have been discussed. During glacial
cycles, river incision and sediment aggradation occur with the lowering and rising of
sea level, respectively. The gradient of the Gulf Coast continental shelf is considered
important because it decreases from the headwaters of the Trinity River onto the
continental shelf. Thus, as sea level falls, the maximum depth of river incision will be
much less than the sea-level drop. Estimates of the maximum fall of sea level during
29
To/edo
tSTATIONS
I Rosser 2 Corsicana 3 Crockell 4 Romayor 5 Diboll 6 Nacogdoches 7 Rockland 8 Zovalla 9 Tatum 10 Loganspor t, La.
0 50 mi.
0 80 km.
Figure 21. Location of sampling stations for suspended-sediment-load data. From
Kreitler and others (1981).
30
( /r determ• , East Texas from suspended-sediment-load data.a
Derived from Stout and others (1961); Adey and Cook (1964): Cook (1970); Mirabal (1974); Dougherty (1979) 6From Fisk and others (1954)
cFrom Livingstone (1963)
Table 2. Denudation rates determined from sedimentation resurvey data.a
Average
Date and annual
duration Drainage deposition Denudation Denudation
Reservoir Stream of survey area (km2) (mi) (cm/yr) (cm/1.000 yr)
Wolf Creek Wolf Creek 1919 to 66 1 446xtO' 2 19x10' 21 9 Apr. 1939
20 yr
Grand Saline Simons Branch Feb. 1925 to 55 2.143x10' 3.89xt0 2 38.9 Apr. 1938 13.25 yr
Dam B Neches River 1951 to 19.614 2 39x10' 1 18910 ' 1.18
(Steinhagen) Feb. 1960 8.83 yr
Lake Cherokee Sabine River Oct 1948 to 440 2 87x0l' 528xtO 5.28
Apr. 1960 11 5 yr
aEvans and Bramblett, 1960: U. S. Army Corps of Engineers. 1960: Sedimentation Committee of Water Resources Council. 1975; from Kreimier and others. 1981
Table 1. Denudation rates(i
,' U EDALLAS 2CI
• TYLER
S•c•.•T KEECH I /
OAKWOOD DOME
I Wolf Creek 2 Grand Saline 3 Dam B 4 Lake Cherokee
Figure 22. others (198.
Location of reservoirs for sedimentation resurvey data. From Kreitier and
1).
32
fl
600 0--1
500- -50
".~- ~ 400--fod li
_100A
300
200-EXLNTO
- 0 3
100 T-o
0 Caelod be•leta T-lty Rive
TrTO/ 0 -00 -1 004,0C
0 8Or
Figure 23. Profile showing Trinity River terraces and depth of incision into bedrock. Depths of incision into bedrock are determined from borehole data obtained from Texas Highway Department files, Dowell and Petty (1973), Rehkemper (1969), and the U.S. Army Corps of Engineers (1962). Locations 1, 10, and 16 are Liberty Quadrangle, Long Lake and Oakwood Quadrangles, and Mesquite and Forney North Quadrangles, respectively (see fig. 2 for locations).
Pleistocene glacial intervals vary from 80 to 140 m (Bloom, 1978). Sea-level estimates
for the Wisconsin glaciation indicate that sea level was between 100 and 135 m below
the present level (Andrews, 1975). Since cycles of incision followed by aggradation
occur with the fall and subsequent rise of sea level, maximum incision should occur
during the greatest fall in sea level, and incision to a greater depth should not occur
unless uplift of the area creates renewed incision.
Along the Trinity River, borehole data provided by the Texas Highway Depart
ment and the Texas Department of Water Resources were used to establish the depth
of river incision into bedrock (fig. 23). Figure 23 shows in the study area an average
alluvium thickness of 15 m from the modern floodplain to the contact between the
alluvium and bedrock. Because of the gradual headward retreat of nickpoints and
incision, actual incision of the streams over the domes is much less than the
entrenchment by the Trinity River. Less than 5 m of incision by Keechi Creek into
bedrock has occurred over Keechi Dome (fig. 24). Consequently, erosional breaching
of the domes is of only minor concern.
33
Si-, eecr Come Keechi Creek floodplain•
uu0 iUt• , V It'
0 t'r
20 1i Confluence with Trirnity River ---. ..-- -- - - - - - -- - - - - - E C ID M -00100 KEECHI DOME (schematic) rock at 38 m -50 Cop rc l3
- - ncision into bedrock -ORIZONTAL SCALE below surface, Ic0i Sit bedrmock solt at 133 m 0*00 i- Data point for incision into bedrock hi below surboce
0
0
Figure 24. Topographic profile of Keechi Creek and its incision into bedrock. Depths of incision into bedrock are determined from borehole data obtained from the Texas Highway Department files.
SUMMARY
Palestine, Keechi, and Oakwood Domes are located in the Trinity River drainage
basin. Four terrace levels have been identified along the Trinity River valley in the
central part of the drainage basin where the domes occur. The regional gradient of
these terraces provides no indication of significant regional or domal uplift. Quatern
ary terrace deposits at Palestine Dome show no indication of warping due to dome
uplift.
Although Palestine, Keechi, and Oakwood Domes display different types of
drainage patterns, central topographic depressions share similar characteristics over
all three domes. Deposition occurs within these central depressions. Thickness
variations of floodplain deposits over Oakwood Dome may indicate that subsidence has
occurred over the dome.
For evaluation of possible breaching of a salt dome, the regional denudation rate
in East Texas and the effects of future climatic conditions are also major factors.
Average denudation rates computed from suspended-sediment-load data and sedimen
tation resurvey data are 8.85 cm/I,000 yr and 16.8 cm/l,000 yr, respectively. Incision
by the Trinity River into bedrock is 15 m beneath the middle of the present floodplain
of the Trinity River valley in the vicinity of the domes.
34
ACKNOWLEDGMENTS
This research was funded by the U.S. Department of Energy, Contract No. DE
AC97-80ET46617 (formerly DE-AC97-79ET44605). The manuscript was reviewed by
T. C. Gustavson, M. P. A. Jackson, S. J. Seni, L. F. Brown, Jr., and D. A. Smith. C. W.
Kreitler, principal investigator for the East Texas Waste Isolation studies, also
provided constructive comments. The text was word processed by Charlotte J. Frere,
and edited by Amanda R. Masterson. Figures were drafted by John T. Ames,
Thomas M. Byrd, Micheline R. Davis, Margaret Evans, Byron P. Holbert, Jeffrey
Horowitz, and Jamie McClelland, under the supervision of Dan F. Scranton. Cover
design and text layout and assembly were by Micheline Davis.
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