j•.,. jW2,•L/c•z•
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 /6ý5ý
9303110355 930305 PDR WASTE 14l-11 PDR CONTENTS
ABSTRACT . • ...... * 1
INTRODUCTION ...... 2 REGIONAL SETTING 3 GEOMORPHIC SETTING 4 TRINITY RIVER TERRACES...... 6 Terrace ages . . •...... 7 Terraces as indicators of long-term regional uplilt 8 DOME GEOLOGY AND GEOMORPHOLOGY. . . .71 * 8 General stratigraphy . . .81 10 Palestine Dome ...... 14 Keechi Dome...... 18 Oakwood Dome ...... 24 Morphologic mapping ...... S. . 24 SEROSIONAL BREACHING OF DOMES 28 Denudation rates in East Texas 29 Entrenchment of the Trinity River
SUMMARY 34 35 ACKNOWLEDGMENTS ...... 35 REFERENCES
ILLUSTRATIONS
Figures
1. Location map of study area showing regional structural elements . 3
2. Location of topographic cross sections of terraces along the Trinity River...... 5
iii 3. Profile of terrace deposits of the Trinity River...... 6
-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 ...... 8
5. Stratigraphic column for study area ...... 9
6. Geologic map of Palestine Dome area ...... *11
7. Topographic map of Palestine Dome area ...... 12
8. North-south and east-west topographic profiles over Palestine Dome. 13
9. Topographic profiles of terrace surfaces on the western flank of Palestine Dome and adjacent to the dome . . . 15
10. Geologic map of Keechi Dome area. ... . 16
11. Topographic map of Keechi Dome area 17
12. North-south and east-west topographic profiles over Keechi Dome 18
13. Photograph of tension fracture at Keechi Dome ...... 19
14. Geologic map of Oakwood Dome area ...... 20
15. Topographic map of Oakwood Dome area ...... 21
16. North-south and east-west topographic profiles over Oakwood Dome. 22
17. Cross section G-G' of floodplain deposits above Oakwood Dome . 23
18. Morphologic map of Palestine Dome area ...... 25
19. Morphologic map of Keechi Dome area 26
20. Morphologic map of Oakwood Dome area ...... 27
21. Location of sampling stations for suspended-sediment-load data . 30
22. Location of reservoirs for sedimentation resurvey data ...... 32
23. Profile showing Trinity River terraces and depth of incision into bedrock ...... 33
24. Topographic profile of Keechi Creek and its incision into bedrock. 34
Tables
1. Denudation rates determined from suspended-sediment load data . . . . 31
2. Denudation rates determined from sedimentation resurvey data . . . . 31
iv 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 is caused by domal or regional uplift. The average denudation rate in East Texas calculated to be 8.85 cm/l,000 yr. Incision by the Trinity River into the bedrock is of S 15 m beneath the present floodplain near the domes. Geomorphic studies 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 present and detailed investigations. Geomorphic and geologic studies investigated of the Palestine Dome IuLure %LabibiLy ol tic :,all doiin"-s, I lydrologic investigations waste repository. More area determined that the dome was unsuitable to be a nuclear to be a repository. recently it has been determined that Keechi Dome is too small site, although it is less Oakwood Dome is still being considered as a possible repository suitable than other Gulf Coast salt domes. Trinity River Palestine, Keechi, and Oakwood Domes lie within the central 1). These domes are drainage basin in Anderson, Freestone, and Leon Counties (fig. salt over these among 15 shallow domes within the East Texas salt basin. Depth to 1,088 m at Brushy shallow East Texas domes is between 37 m at Palestine Dome and during the early Creek Dome. East Texas domes generally underwent maximum uplift in the late Cretaceous, reduced growth in the Early Tertiary, and relative stability 1981). Tertiary and Quaternary (M.P.A. Jackson, personal communication, were Surficial studies concentrating on surface geology and geomorphology investiga conducted in conjunction with subsurface, remote-sensing, and hydrologic essential to reveal tions. Site-specific investigations of the three Texas domes are to dome uplift or fractures, warping, and drainage anomalies that might point Trinity River basin subsidence. Studies of denudation and stream entrenchment in the permit evaluation of the potential for erosional breaching of each dome.
REGIONAL SETTING
in the north The East Texas salt basin is bounded by the Mexia-Talco fault zone the south (fig. 1). and west, the Sabine Uplift in the east, and the Angelina Flexure in may have been The Mexia-Talco fault zone originated in Middle Jurassic and and Wilson, in associated with the early development of the Gulf of Mexico (Jackson (mid press). Initial movement of the Sabine Uplift occurred in pre-Cenomanian post-Eocene time Cretaceous) time, with subsequent rejuvenation continuing until that marks the southern (Eaton, 1956). The Angelina Flexure represents a hinge line limit of the East Texas Basin. the Angelina The Mount Enterprise-Elkhart graben system occurs north of normal faults with Flexure. It consists of contemporaneous down- and up-to-the-basin Mount dips of 350 to 600 that steepen toward the surface. Initial movement on the was during Enterprise faults was during the Cretaceous; the most pronounced activity
2 OKLA
LA I' , • /SABINE " 0 /s 4' Tyler sUPLIFT
/ KeecI. esi
"/ ok-ood,W eons o • ''ka:'
R'iOT' RIVER
EBAIN .
O 5Onsr 0O 80 km
EXPLANATION
-I, Fault Sail dome
Figure 1. Location map of study area showing regional structural elements.
system was active Eocene time (Eaton, 1956). Recent studies indicate that this fault 1981). duringthe Quaternary (Collins and others, 1980; Pennington and others, rocks Basement in the East Texas Basin is probably folded and faulted Paleozoic Cenozoic strata of Ordovician to Early Pennsylvanian age. Overlying Mesozoic and (Nichols and others, record a series of transgressive to regressive depositional events received thick 1968). A rapidly subsiding north-trending low, the Tyler Basin, sediments were accumulations of Mesozoic and Early Tertiary sediments. Post-Eocene Basin. deposited beyond the southern basin margin in the younger part of the Gulf
GEOMORPHIC SETTING
physiographic The East Texas Basin underlies the Rolling Hills and Prairie vegetation, subprovince of the East Texas Timber Belt (Fenneman, 1938). Dense Soils are dominated by oak and pine forests, limits field studies in the region. and they are easily predominantly acidic sands or sandy loams of low organic content, eastward from eroded when vegetation is cleared. Normal annual precipitation varies
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 AI
w E Elevation (
S160
0 4000ff
0 -1
Dome N Keechi • PALESTINE
TzýEXASI >"-Rtlestine Dome
Ookwood Dome 0 20 40mi i I I 1 II 1 I11 I I 0 20 40 60 km
P
Elevation ftf 400--- 2
300 90
w E9 A 200 70 T-2 T-to IT-lb T-3 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 A AI It A
+ IC
0 1 0t+ @ Mesquite and
300+ Forney North
-50 @ogLk - 7 8 and Oakwood EXPLANATION T-3 oor Quadrangles x ST T-lb T-io 010Trinity River floodplain 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 Pleistocene Beaumont Formation, whereas the T-2 terrace level corresponds to the late Pleistocene or Formation. Terrace levels T-lb and T-la are related to the (T-2) and Deweyville Holocene Deweyville Formation (figs. 2 and 3). The Beaumont the Trinity River terraces (T-lb and T-la) are well developed along the section of flowing through East Texas. probably occurred Montgomery alluviation, related to the highest terrace, 1965, p. 146). Verte between 170,000 and 300,000 years B.P. (Bernard and LeBlanc, northern part of the brate and invertebrate fauna from a T-2 terrace located in the Age (Slaughter, Trinity River drainage basin have been determined to be of Sangamon 1969). The Sangamon Interglacial lasted from 128,000 to 73,000 years B.P. (Suggate, Pleistocene Beaumont 1974). Figure 2 shows that terrace T-2 correlates with the late interstadials; Formation, a widespread accumulation related to early Wisconsin B.P. (Bernard and Beaumont alluviation occurred from 70,000 to 100,000 years from Deweyville LeBlanc, 1965, p. 146). Radiocarbon age dates of wood fragments range from 17,000 terraces (T-lb and T-la) on the Trinity, Neches, and Sabine Rivers to more than 30,000 years B.P. (Bernard and LeBlanc, 1965).
Terraces as Indicators of Long-Term Regional Uplift
to the Gulf Terrace level gradients from the headwaters of the Trinity River major regional Coastal Plain show that Pleistocene deposits have not been affected by was caused by or local uplift except at the Elkhart Graben where minor displacement faulting (Collins and others, 1980). In analyses of Quaternary coastal plain elevations, Coastal Plain Bernard and LeBlanc (1965) showed that the landward part of the Texas movement was uplifted while the offshore zone subsided. This differential vertical and by greater resulted from isostatic adjustment caused by sedimentary loading of the Coastal compaction rates offshore. Gradients of Quaternary terraces updip from the hingeline Plain do not reveal uplift, probably because of the distance separating the uplifted coastal plain and the subsided offshore zone. and T-lb, the Figure 4 shows lines of linear regression for terrace levels T-2 present floodplain, and the base of incision into bedrock. These slopes are similar, near the Elkhart suggesting that no pronounced uplift has occurred. A terrace level elevation above the Graben system (location 9, fig. 4) appears to vary slightly in and others, 1980), floodplain, possibly due to displacements from faulting (Collins elevation. although terraces at other locations also display slight variations in
7 Elevohon + fl M
400 120
200 60 T-2,terrace BeG... .-Io 7
T- lb terrace ® © 0s
River floodplai s =slope STrinity 0 3 .0kin
all uviumnand bedrock
0 (D-lcotio(D 0 T @ SL@ @
regional gradient for terrace levels Figure 4. Linear regression lines expressing the between Trinity River alluvium T-2 and T-lb, the modern floodplain, and the contact River basin. Locations refer to and bedrock. The study area is the central Trinity figure 2.
DOME GEOLOGY AND GEOMORPHOLOGY
Keechi, and Oakwood Domes Surface geology and geomorphology at Palestine, Morphological and structural document different strata and drainage patterns. elements of the three domes are similar, however.
General Stratigraphy
Group crop out except where In the study area, sediments of the Claiborne local rivers and streams and where salt overlain by Quaternary sediments deposited by the Tertiary Wilcox Group to the diapirs have uplifted older rocks ranging from these older strata are typically very poor. Cretaceous Washita Group. Outcrops of the surface of Palestine Dome is the The oldest stratigraphic unit exposed at 1958). At Keechi Dome the oldest units Cretaceous Buda Limestone (Hightower,
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 I-
...... ------
CONTQUR ON TOP OF SALT
-75000FT.
......
......
EXPLANATION
>ElMODERN ALLUVIUM
z '1TRINITY RIVER TERRACE Ujfl DEPOSIT ...... CyL UPLAND TERRACE DEPO~ SIT ...... :QUEEN CITY FM ...... {REKLAW FM CARRIZO FM HWILCOX GROUP L .MIDWAY GROUP
...... UPS ...... E-AYLOR a NAVARRO GRO E AUSTIN CHALK I WOOD BIN E a EAGLE FOI RD GROUPS I ml BUDA LIMESTONE ...... 0 U/-D FAULT -- INFERRED OR 0 Ikm COVERED
Figure 6. Geologic map of Palestine Dome area. Modified from Hightower (1958).
11 .0,00• '.° • a° 0,, a'• 0
-' * o4o'o a 0
0 0o 0*• '~~ .°o0 ' ~0 0 ~...... o o a 'o ' 00*0oo .. % , * 0', . 0 I ao 0
3000
*oo a o o 30 • o0.000000o . 0 0 0 0 0 0 o o-o . o0 0 0 :oaa0,, o a 30 33 o 00 o0o 0 ~ 300000 aoo° 0~ 0a ,•0 ° °o~o0,o 0 'o 'o 30 o .. ~ ~
Elevation (above msl) • -350 ft 250-300ft 0 Imi (76- 92m) (>107m) F <250ft 0 1km 300-350ft Lake 4 Swamp (92- 107m) (<7Gm)76
on top 1000 ft contour F -17r00ofP 0 t i of Soal
eterndohs(91) map of Palestine Domeaa.ro Figure 7. Topographic
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 1km
Elevation ft m WE W 350- 1I00
300 90 Duggey's 80 j Lke
250 70 200-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 6 and 9). This suggests that no terrace surface north and south of the dome (figs. terrace deposits, although this dome growth has occurred since deposition of the surface has not been leveled by assumption is based on the idea that the terrace '. erosion.
Keechi Dome
Tertiary, and Quaternary Strata cropping out at Keechi Dome are of Cretaceous, Groups are the oldest sediments age (fig. 10). Rocks within the Taylor and Navarro radial faults exist (Ebanks, 1965). exposed. Strata exhibit dips up to 450, and area, but exposures are poor. Brief Quaternary terrace deposits occur in the domal no evidence of warping or investigations of these Quaternary deposits indicate respectively (Halbouty, faulting. The depths to salt and cap rock are 133 m and 38 m, 1980). as conspicuous as at other The topographic expression at Keechi Dome is not the dome, interior salt domes. However, Keechi Creek flows north-south across of the dome (figs. II and 12). The through a slight topographic low over the center relief of about 30 m occurs between drainage pattern in the area is subdendritic, and and surrounding peripheral hills. the central topographic low occupied by Keechi Creek at the surface is a small salt lick Powers (1926) reported that the only evidence of salt located on the Keechi Creek floodplain. at Keechi Dome in Two unusual cracks or fissures (fig. 13) were observed reported that the cracks November, 1979 (Kreitler and others, 1981). A landowner 1980 the cracks had been filled by were first discovered in the spring of 1978. By May of N. 70 E. and N. 670 W. and slumping and soil erosion. These fractures display trends fault mapped near the dome are located along a southeastern extension of an inferred fractures to the inferred fault is center by Ebanks (1965) (fig. 10). The relation of the these fractores appeared to be speculative. When first observed in November 1979, larger fracture was 3.5 cm wide. nearly vertical and were 30 m and 12 m long. The of the larger crack was deeper than Exact depth of the cracks is unknown, but the base spring of 1978, I m. An approximate depth of 4 m was measured by landowners in the soil cover is composed of 50 cm but this has not been documented. The upper meter of mottled clay and 30 cm of silty of slightly clayey sand above 20 cm of red to yellow fractures is unknown, the fractures clay. Although the mechanism that produced the because they were dilated and appear to be tensional rather than shear fractures because no offset was observed.
14 ( ( (
ELEV It m 350 - I00
300 -90 • _ ~T-3
-80 250 -70 ft ELEVm CLAIBORNE GROUP 400- 120 8 200 60
ELEV 350 ft m 350 -00 I00 300 90 300 90 B -80 T-3 -80 250 250" _70 7 CLAIBORNE GROUP
200 -60
-50 150
-0SALT AT ELEV IOOTMt ft m 350 -I0 0 C 300 -9C C / C-8 T-3 250 -7C T-I / CLAIBORNE GROUP 200 -6 0 "'2 I ni -5( 0 "2 1 km 150i
adjacent to the dome. Figure 9. Topographic profiles of terrace surfaces on the western flank of Palestine Dome and From Kreitler and others (1981)...... 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 . .. ,...... ::
CRETACEOUS QUATERNARY TERTIARY ya V Io I
Midway Taylor a Navarro "Upland gravel" Queen City Reklaw Corrizo Wilcox Modern Group Group Groups (undiff.) alluvium terrace Formation Formation Formation Contour on lop of m Location of tension 0 Fault, dashed where /4 Strike and dip "•-5Oo,./. salt I fractures "t -covered or inferred
(1965). Figure 10. Geologic map of Keechi Dome area. Modif ied from Ebanks
16 Elevation (above mslO 0 I mi 375 -400fl 50Oft (114-122m) Lake 0 km ~( ::,- 152m) 350 -375 ft - 500 ft N =475 (107- 114m) Swamp 0145 -152 m)
.150-4175f I 325 - 350f.i -•1000 - I( conlour M337- 145m I (99 -107 m) on top of salt -/oooft '•• 4 25 - 4 50 f t 300-325ft (130-137m') t 92-99m) Z 300 ft r7- 400-425ft -9 2 m)
Figure 11. Topographic map of Keechi Dome area. From Kreitler and others (1981).
17 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 (-305m) 0 1km Salt at -l00ft 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
::: : :: : : : : : : :: : : : : : : : :: : : : : : : : : : ..==...... •: ii~...... 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 • aoeh~ 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...... rc uf •dslc ...he ..m n ano eetrl ic utd h t a d.a.o.ae.-1 m a d 1 sa •r ...... sp c i e y ...... The...... h v a w o o e i h rctrz d b ...... o t -e.b ta depression....suro.de ..... etr,_1rsetsapdrdeao14h oten n eastern~~ ~ ~ ~ is.15ad~ ~~~~~_ 6.Tta ...... eie vrth oeis75m...... su d ndZi ove the o5te d me h ra .en.ea n lrdria e presen.we.r...asen5a k. oo...... e e •lo pani l ...... tdi h topograph...... deresi..boe.hedoe
20 Elevation (above MSL} 0 I mi 0050Oft Fý-350-400ft 0 lkm N)Lake (>152m) Lj (107- 122m)
N ' 300-350f, Swamp (137 - 152 m) (92 - I07m)
• .• ,j.-1000 ft contour S400-450ftI < 3500 ft (122-137m) (ý- 92m ) on top of salt
Figure 15. Topographic map of Oakwood Dome area. From Kreitler and others (1981).
21 •- Elevation S N ft1 m
-- SaIt at - i000 ft (-305 m)-A
0 6000 ft 0 2 km
Elevation W E ft, m
-150
-130
400
I--Salt at -Q000 ft (-:305 m)---- 300
O 6000 it
0 I 2km
profiles over Oakwood Dome. Figure 16. North-south and east-west topographic is shown below the profile. From Width of dome at the -305-m contour of salt Kreitler and others (1981).
22 20
Q. INCISION INTO BEDROCK GI NF"P(")AI T IC}N
50 -. X...... :i:iii!!::i:::.... 0(4O OK .20 201OK OK10 IOO0f 202O OK ...... S V E. = 2 = I ......
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 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 Stream 0-20 " .... '" Intermittent stream W 2-5o Swamp 5-15o Pond Slopes resulting from depositional processes
I0-2 " -/o00 --- Contour on top of salt (- 305m)
Figure 18. Morphologic map of Palestine Dome area. From Kreitler and others (1981).
25 . 0 1.
Streom erosional processes Slopes resulting from stream S0-2° ' Intermittent Swamp 2-5° •5-15' "Pond
Contour on top o0 salt depositional processes Slopes resulting from 5m ) r30 CF7 71 0 -2 - oDf
and others (1981). area. From Kreitier map of Keechi Dome Figure 19. Morphologic
26 Slopes resulting from erosional processes S- Stream 0O-2o "- Intermittent stream W. w2-5 Swamp M 5-155 Pond Slopes resulting from depositional processes 0Contour on top of salt 0-2o M (-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+BSA+-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 t
STATIONS
I Rosser 2 Corsicana 3 Crockell 4 Romayor To/edo 5 Diboll 6 Nacogdoches 7 Rockland 8 Zovalla 9 Tatum 10 Loganspor t, La.
0 50 mi.
0 80 km.
data. From Figure 21. Location of sampling stations for suspended-sediment-load Kreitler and others (1981).
30 /r determ• , East Texas from suspended-sediment-load data.a ( Table 1. Denudation rates (i
6 Derived from Stout and others (1961); Adey and Cook (1964): Cook (1970); Mirabal (1974); Dougherty (1979) From 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 ,' U EDALLAS2CI • TYLER KEECH I / S•c•.•T
OAKWOOD DOME
I Wolf Creek 2 Grand Saline 3 Dam B 4 Lake Cherokee
Kreitier and sedimentation resurvey data. From Figure 22. Location of reservoirs for others (198.1).
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 0
-00100 20 1i Confluence with TrirnityRiver ---. -- - - -..------KEECHIE C ID DOME M -50 (schematic) Cop rcrock atl3 38 m - - ncision into bedrock -ORIZONTALSCALE below surface, Ic0i bedrmock Sit solt at 133 m 0*00 i- Data point for incision into bedrock hi below surboce
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
DE This research was funded by the U.S. Department of Energy, Contract No. was reviewed by AC97-80ET46617 (formerly DE-AC97-79ET44605). The manuscript and D. A. Smith. C. W. T. C. Gustavson, M. P. A. Jackson, S. J. Seni, L. F. Brown, Jr., studies, also Kreitler, principal investigator for the East Texas Waste Isolation 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, Byron P. Holbert, Jeffrey Thomas M. Byrd, Micheline R. Davis, Margaret Evans, Dan F. Scranton. Cover Horowitz, and Jamie McClelland, under the supervision of design and text layout and assembly were by Micheline Davis.
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39