ML20148D765
| ML20148D765 | |
| Person / Time | |
|---|---|
| Issue date: | 11/02/1987 |
| From: | Warner J NRC OFFICE OF NUCLEAR MATERIAL SAFETY & SAFEGUARDS (NMSS) |
| To: | Ballard R NRC OFFICE OF NUCLEAR MATERIAL SAFETY & SAFEGUARDS (NMSS) |
| References | |
| REF-WM-16 HLWR, NUDOCS 8803240276 | |
| Download: ML20148D765 (15) | |
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OFFICIAL CONCURRENCE AND DISTRIBUTION RECORD
- MENORANDUM FOR
- Ronald Ballard, Branch Chief n Technical Review Branch Division of High-Level Waste Management THRU: Phil Justus, Section Leader Geology / Geophysics Section Technical Review Branch Division of High-Level Waste Management FROM: James Warner Geology / Geophysics Section Technical Review Branch Division of High-Level Waste Management
SUBJECT:
Trip Report on Symposium / Field Trip: Late Tertiary Ogallala
=ind Quaternary Blackwater Draw Formations; Lubbock, Texas 2 and Vicinity; 10/1-10/4/87 DAT5: 10/29/87 -
DISTRIBUTION 5 eHLim/SF- hMS.S RF RBrowning, HLWM MBell, HLWM JBunting, HLSE Youngblood, HLOS s RBallard, HLTR TCardone, HLTR FRoss, HLTR JWarner, HLTR ATescriero, HLTR DGillen, HLTR NTanious, HLTR CPeterson, HLTR PJustus, HLTR ,
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CONCURRENCES ORGANIZATION /CONCUREE INITIALS DATE CONCURPED l JWarner, HLTR /v 87/10/3 0 PJustus, HLTR () W fg 87/11/ g ( j V l
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.s MEMORANDUM FOR: Ron.Ballard, Branch Chie.f k Technical Review Branch Division of High-Level Waste Management THRU: Phil Justus, Section Leader Geoiogy/ Geophysics Section ,
Technical Review Branch Division of High-Level Was e Management FROM: James Warner Geology / Geophysics Section Technical Review Branch Division of High-Level Waste Management
SUBJECT:
Trip Report on Symposium / Field Trip: Late Tertiary ?gallala and Quaternary Blackwater Draw Formations; Lubbock, Texas and Vicinity; Oct. 1-4, 1987 l
INTRODUCTION During the time field trip (Oct. 3-4) period October 1-4, Itoattended coveringamany symposium aspects(Oct. 1-2) and
, which in addition of the l Cenozoic geology and hydrology of an area extending from the Texas Panhandle to central Nebraska, addretsed the Ogallala Formation, the Blackwater Draw Formation, the origin of playas, and dissolution of Permian salt in the Southern High Plains. This meeting was sponsored by the Texas Bureau of i Economic Geology (TBEG), University of Texas and The Institute For Quaternary 1 Studies, Univarsity of Nebrasba. Copies of the abstracts and the field guide l are on record in the NRC Docet Control Center. Dr. Thomas Gustavson (TBEG) was chairman of the symposium. A list of participants is appended to the end of this trip report (Appendix Al-A4).
INFORMATION RELEVANT TO EVALUATING THE DEAF SMITH COUNTY REPOSITORY SITE Many topics from a large geographic area were discussed during the symposium and on the field trip; however, only the information related to Cenozoic stratigraphy / tectonics and dissolution of Pennian salt in the Southern High Plains is summarized in this section. This information is subdivided by author (s) and especially relevant abstracts are included as appended material.
(1) Dr. Thomas Gustavsen (TBEG) presented a talk (Appendix B1-B2) on the effects of the dissolution of Permian salt on Cenozoic sedimentary and geomorphologic trends in the Texas Panhandle and eastern New Mexico. Dr.
Gustavson's talk, which is basically summarized in Gustavson (1986) and Gustavson and Budnik (1 AS), described two broad types of salt dissolution in the Southern High Plains.
The most obvious and widespread dissolution is occurring along the western, northern, and eastern margins of the Southern High Plains where the
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Permian evaporites are uplifted to relatively shallow depths and incision by th( Pecos and Canadian Rivers is occurring along major dissolution fronts (see l Gustavson, 1986). Evidence for Cenozoic salt dissolution includes collapse and subsidence features, missing or thin salt beds (not attributable to facies variation) in exploration wells, and high Na and Cl solute loads in streams draining the region. Of the three nargin dissolution fronts, dissolution of i salt along the northen margin of the Southern High Plains is the closest to the site (18.5 miles from the San Andres salt dissolution front to the site);
however, calculations of dissolution rates in this area (/ in./yr from the
! FEA) suggest this process will not jeopardize the repository during it's I operational lifetime.
Dr. Gustavson also discussed dissolution of Permian salt beneath large lake basins, playas, and along certain draws within the interior of the Palo Duro Basin / Southern High Plains. The example most proximal to the site is thought to be occurring beneath Tierra Blanco Creek and Frio Draw (approximately 25 miles southeast of the site). In this area, a series of paleo lacustrine basins overlies a zone of dissolution of the upper Seven Rivers Formation salt (see Gustavson and Budnik, 1985). The NE/SW orientation of this drainage system disobeys the regional SE dip of the Southern High Plains, which i supports the notion that these subsidence / drainage features are/were developed over NE-trending fractures or faults. At this location, the lower San Andres l Formation unit 4 salt occurs approximately 1200 feet below the dissolution zone and is undissolved. Intervening salt beds of the San Andres and lower Seven
! Rivers Formations are undissolved as well.
(2) Dr. Reeves (Texas Tech University) presented a classification of playas and models to account for the various types of playas on the Scathern High Plains I (Appendix B3). This classification recognizes three types of playa basins. Type I playa basins are small basins that originate in natural topographic lows and/or by hydrocompaction in Tertiary and Ovaternary sands. Fonding and infiltration beneath Type I playa basins leads to dissolution of Calcium Carbonate is Cenozoic sands, piping of detritus, and eluviation to produce deeper Type II playa basins. At certain locations (see abstract for specific locations), possibly where well-developed fractures exist in underlying Cretaceous and Triassic sediments, infiltration of groundwater has led to dissolution of Permian salt and subsidence to produce large (4-15 km2) Type III playa basins. With time, these basins may become tilled with lacustrine sediments, which diminishes their topographic expression to that of broad depressions.
Dr. Reeves previously published a paper (Reeves and Temple, 1986) that i discusses Type III playa basins that are located far (greater than 40 miles) to l
the south and southeast of the repository site. More recent work by Dr. Reeves has been focused on an advanced Type III basin (Anton Depretsion) that is located greater that 40 miles to the south of the repository site and a smaller playa (Dead Horse Playa) that is located in southern Deaf Smith County. Dr.
Reeves said that a preliminary (and presently inconclusive) study of water well logs in the vicinity of the Dead Horse Playa shows that the Triassic red beds
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1 define a topographic low beneath the playa. The origin of this depression has not been proven, although salt dissolution-related subsidence is a possibility.
The data from the Anton depression (see guide book pgs. 46-41), which was extensively drilled as a candidate site for the Superconducting Collider, is !
more complete. This 6 km2 depression is underlain by 27 m of lacustrine sediments, undifferentiated Ogallala and Blackwater Draw Formation sediments, a topograahically depressed (6 m) top of the Cretaceous Edwards Formation, topographically depressed tops of the Permian Rustler and Yates Formations, and 43 m of missing (probably dissolved) Rustler salt. This suggests that salt dissolution has been important to the development of the Anton Depression.
However, the disparity between the structural subsidence of the Cretaceous (6 m) and the thickness of the lacustrine fill (27 m) suggests that salt dissolution is only one of several mechanisms that is acting to produce this feature. ,
(3) Field trip stops 3A and 38 (Guidebook pgs. 53-61) were to see evidence related to the development of the Gentry Playa, which is located approximately 5 miles north of Lubbock, Texas. Dr. Osterkamp (USGS-Denver) presented evidence, which is summarized in detail in Osterkamp and Wood (1986) and Wood and Osterkamp (1986), for the development of many Southern High Plains playas (including the Gentry Playa) by dissolution of Calcium Carbonate in the Ogallala and eolian and Blackwater deflatia. Draw Formations, Dr. Holliday (Universityeluviation, piping)of of Wisconsin fine detritus, discussed evidence for the development of the Gentry Playa by eclian deflation of the Blackwater 1 Draw Formation. I l
(4) Greg Wilson (0 asis Resources) presented a talk (Appendix B4) concerning the John Ray Dome portion of the Amarillo Uplift, deposition of the Ogallala l Formation in the vicinity of the Canadian River, and Cenozoic dissolution of Permian salt. This work, which will be published as a West Texas State 1 University Master's thesis, suggests pre / syn / post-0gallala time collapse basins )
in Potter County are a result of dissolution of Permian salt along the Potter County Fault. According the Greg Wilson, the Potter County Fault was active primarily during the Pennsylvanian development of the Palo Duro Basin Greg also feels the fault's significance during the Cenozoir, has been as a conduit for downward percolating groundwater to produce salt aissolution in thic area, rather than as an active tectonic feature.
(5) Warren Wood (USGS-Reston) presented geochemical evidence for the derivation of high salinity water in saline lakes of the Southern High Plains from the partial evaporation of High Plains aquifer fresh water (Appendix B5). This is in contrast to the view that the high salinity of these lakes is a result of the input of brine or dissolved salt from the underlying Persicn avaporite sequence.
CONCLUSIONS ;
The most valuable information that was presented during this meeting i relates to dissolution of Permain salt in and around the Southern High Plains, j l
The information to date suggests that dissolution along the margins of the I Southern High Plains /Palo Ouro Basin is occurring at a slow enough rate so as 3 to not threaten the repository; however, this process warrants furtrar study to accurately determine present and possible future rates of the dissolution j fronts' advances. Dissolution of salt in the interior of the Southern 1.1gh Plains, although much less widespread, could potentially occur /be occurr:ng in the immediate area of the repository site. Recent work by several authors suggests that playas and closed depressions in the Southern High Plains form by differential compaction, eluviation, piping of fine detritus, dissolution of calcium carbonate in Cenozoic sands, eolian deflation, and dissolution of Permian salt. Due to the spectrum of processes that may act individually or in conjunction with others, the origin of playas cannot be generalized and each area of suspected dissolution of Permian salt requires individual study.
Possible structurally-controlled dissolution of salt within the Southern High Plains has been identified (see (1) above) and is expected to be addressed during the Deaf Smith site characterization, i
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REFERENCES Gustavson, T.G., 1986. Geomorphic Development of the Canadian River Valley, Texas Panhandle: An Example of Regional Salt Dissolution and Subsidence, 0F-WTWI-1985-7.
Gustavson, T.G. and Budnik, R.T.,1985. Structural Influences on Geomorphic Processes and Physiographic Teatures, Texas Panhandle: Technical Issues in Siting a Nuclear Waste Repository, Geology, Vol. 13, pp. 173-176, March 1985.
Osterkamp, W.R. and Wood, W.W., 1987. Playa-lake Basins on the Southern High Plains of Texas and New Mexico: Part I. Hydrologic, Geomorphic, and Geologic Evidence for Their Development, Geological Society of America Bulletin, Vol. 99, pp. 215-223, August 1987.
Reeves, C.C. and Temple, J.M., 1986. Permian Salt Dissolution, Alkaline Lake Basins, and Nuclear Waste Storage, Southern High Plains, Texas and New Mexico, Geology, Vol .14, pp. 939-942, November 1986.
Wood, W.W. and Osterkamp, W.R., 1987. Playa-lake Basins on the Southern High Plains of Texas and New Mexico: Part II. A Hydrologic Model and Mass-Balance Arguments for their Development, Geological Society of America Bulletin, Vol. 99, pp. 224-230, August 1987.
Ai ATTENDEES AND SPEAKERS OGALLALA AND BLACKWATER DRAW FORMATIONS SYMPOSIUM OCTOBER 1 4. 1987 LUBBOCK. TEXAS Dr. Ronit' Nativ Dr. Joseph R. Thomasson Bureau of Economic Geology Fort Hayes State University The University of Texas at Austin Division of Biological Sciences Austin. TX 78713 Hayes. Kansas 67601-4099 Dr. Joe C. Yelderman Jr. Sabine Bock Department of Geology Kansas Geological Survey Baylor University 1930 Constant Ave.
Waco. TX 76798 Lawrence. KS 66046 Dr. Eileen Johnson Dr. Richard J. Zakrewski The Museum Department of Earth Sciences Texas Tech University Fort Hays State University Lubbock. Texas 70409 Hays. KS 67601 t Dr. Stephen A. Hall Dr. Raymond R. Neck Department of Geography Texas Parks and Wildlife Dept.
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University of Texas 4200 Smith School Road Austin. Texas 78712 Austin. TX 7874A l Dr. C. Reid Ferring Dr. Thomas M. Lehman Institute of Applied Sciences Department of Geosciences North Texas State University Texn Tech University P. O. Box 13078 Lubbock. TX 79409 Denton. TX 76203 Dr. Vance T. Holliday Mr. J. T. Webb Department of Geography P.O. Box 478 S(bnce Hall Miami. TX 79059 The University of Wisconsin Madison WI 53706 Dr. C. C. Reeves Jr. ,
Department of Geosciences Dr. M. R. Voorhies Texas Tech Unniversity University of Nebraska State Museum Lubbock. TX 79/09 W436 Nebraska Hall Lincoln NE 68588-0514 Paul N. Dolliver Geomap Company _Kenneth L. Doe 1100 Geomap Lane 925 El Avado Avenue Plano. Texas 75074 Lincoln. NE 68504 Dr. R. F. Diffendal, Jr. Althea P. Smith 113 Nebraska Hall % R. S. U. Smith University of Nebraska 44 Hillcrest Dr.
Lincoln, NE 68588 Ponca City. OK 74604 or 98 Arnold Road. R.F.D. 2 Dr. William J. Stone Amherst. MA 01002 N.M. Bureau of Mines Campus Station Socorro. NM 87801
A2 Jim Warner Gregory A. Wilson U.S.N.R C. Oasis Resources. Inc.
Mail Stop 623SS 2108 67th Street Washington. D.C. 20555 Lubbock. Texas 79412 Richard Bowen Dr. John W. Hawley Box 8152 New Mexico Bureau of Mines and University of Southern Mississippi Mineral Resources Hattiesburg Mississippi 39406 New Mexico Institute of Mining & Technology Socorro. New Mexico 87801 Mark Gabel Division of Science and Math. Jayne N Salisbury Black Hills State College 77.
Spearfish. SD 57783 Dr. Neil Salisbury Department of Geography Jack Sullma Unive sity of Oklahoma Battelle Memorial Institute Norman. Oklahoma 73019 r2 05 King Avenue Columbus. Ohio 43201 R. Canon Clements Clements Corporation John Byrnes 1500 Broadway. Ste 850 Battelle Memorial Institute Lubbock. TX 79401 505 King Avenue Columbus, Ohio 43201 John H. Peck Stone and Webster Engineering Corp.
Howard O'Connor P.O. Box 829 l Kansas Geological Survey Amarillo. TX 79105 ,
1930 Constant Avenue i Lawrence. KS 66046 Delbert Devlin Nuclear Waste Task Force. Inc.. l Cynthia A. Gestes 218 E. Bedford Dennis R. Sensenbrenner Dimmitt. TX 79027 Don McReynolds i 1
Mike Risinger R. A. Rappmund Jerry Funck Bureau of Reclaimation Kenneth Carver 714 South Tyler High Plains Underground Water Dist. No.1 Amarillo. TX 79101 2930 Avenue O Lubbock. Texas 79405 Margaret Hart 1 Texas Water Commission Dr. Jay Raney P.O. Box 13087 Bureau of Economic Geology Austin TX 78711 !
University of Texas Austin, TX 78713 l Forrest P. Lyford l Battelle Memorial Institute Dr. Steve Martel 505 King Avenue <
Bureau of Economic Geology Columbus. OH 43201 The University of Texas '
Austin. TX 78713 S. Christopher Caran Bureau of Economic Geology Bernt Richter The University of Texas at Austin Bureau of Economic Geology Austin. TX 78713 University of Texas Austin, TX 78713
M Dr. James B. Swinehart Dr. Carolyn G. Olson University of Nebraska 11725 Indian Ridge Rd.
Conservation and Survey Division Reston. VA 22091 113 Nebraska Hall Lincoln, Nebraska 68588-0517 Steve Stadleman 5702 50th St. No. 95 Dr. Robert Hunt Lubbock. TX 79414 Departmerit of Geology 214 Bessey Hall Constantine D. Tsoris University of Nebraska 109 N. 28th St. No. 49 Lincoln. NE 68588-0340 Canyon. TX 79015 Owen Swanson J. Scott Harris Office of Nuclear Waste Isolation P.O. Box 143 Battelle Memorial Institute Canyon. TX 79015 505 King Avenue Columbus, OH 43201 Michael Blum 390.1 A Jefferson Dr. Thomas C. Gustavson Austhi. TX 78731 Bureau of Economic Geology Box X. University Station Doug Pierce The University of Texas Stone and Webster Engineering Corp.
Austin. TX 78713 Summer St Boston. MA Dr. Dale Winkler '
Shaler Museum of Paleontology Barry J. Solomon Southern Methodist University Battelle 33 Heroy St. P.O. Box 2360 :
Dallas. TX 75275 Hereford. TX Dr. Warren Wood Daryl E. Mergen U.S. Geological Survey Mail Stop 431. National Center 313 South Main ,
Lead. SD 57754 i Reston. VA 22092 '
I Stephen J. Seni Dr. Waite Osterkamp Bureau of Economic Geology )
U.S. Geological Survey University of Texas i
Mail Stop 413. Denver Federal Center i Austin. TX 78713 Denver. CO 80225 Bill Mullican Dr. Deborah Bennett Bureau of Economic Geology Smithsonian institution University of Texas NHB W. 77A Austin TX 78713 Washington DC 20560 Bridget R. Scanlon Dr. B. L. Allen Bureau of Economic Geology l
Department of Soil Sciences University of Texz:
Texas Tech University Austin TX 78713 Lubbock. TX 79409 Dr. C. Bertrand Schultz Dr. G. E. Schultz Department of Geology Department of Geology and University of Nebraska Anthropology Lincoln, Nebraska 68588 West Texas State University Canyon. TX 79016
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1 Marian R. Schultz Dr. Ted Taylor l TER-QUA U.S. Department of Energy Lincoln. Nebraska 68588 Salt Repository Project Office 110 North 25 Mile Ave.
J. A. " Tony" Fallin Hereford. TX 79045 Texas Water Development Board ;
P.O. Box 13231 W. E. Wadkins Capitol Station 804 North 14th Austin. TX 78711 Lamesa. TX 79331 John B. Ashworth Dr. Wayne Wendland Texas Water Development Board Illinois State Geological Survey P.O. Box 13231 2204 Griffith Drive '
Capitol Station Champaign. lilinois 61820 Austin. TX 78711 Jim Goeke 721 W. 4th Street North Platte. NB 69101 Sean Wilson 3712 101 St. - !
Lubbock. TX 79423 <
l Dr. Bonnie Jacobs 'i Shuler Museum of Paleontology '
Southern Methodist University i
Dallas. TX 75275 Dr. George Coleman Nebraska Wesleyan University Lincoln, NE 68510 Ron Ralph Texas Parks and Wildlife Commission Austin. TX Warren Rehfeldt CER Corproation
% U.S. DOE /SRPO 110 North 25 Mule Ave. '
Hereford. TX 79045 Sherie Harding :
Roy F. Weston. Inc.
955 L' Enfant Plaza SW 8th Floor e Washington, DC. 20024 ft David Stephens 2108 67th St. !
Lubbock. TX 79412 ;
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81 EFFECTS OF DISSOLUTION OF PERMIAN SALT ON LATE TERTIARY AND QUATERNARY LANDSCAPE AND SEDIMENTATION.
TEXAS PANHANDLE AND EASTERN NEW MEXICO Thomas C Gustavson
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Bureau of Economic Geology The University of Texas at Austin
j Subsidence that resulted from dissolution of Permian bedded salt (halite) l controlled the development of the Pecos and Canadian River valleys, the eastern I Caprock Escarpment. most large lake basins on the Southern High Plains, at least a 1
few playas. and segments of certain draws. Dissolution during the late Tertiary and Quaternary affected parts of the Upper Permian Salado. Seven Rivers. San Andres, 7
d Glorieta, and upper Clear Fork Formations. The thickness of salt lost to dissolution exceeds 150 m along the western northern. and eastern margins of the Palo Duro Basin. Extensive dissolution of the salts of the Salado and Seven Rivers Formations has also occurred beneath the Southern High Plains. Dissolution, which is active beneath the Pecos and Canadian River valleys and the Rolling Plains. results in Na' and CI' solute le,ds in streams draining these areas that collectively exceed 1.250.000
- ons per year.
Subsidence and, indirectly, salt dissolution have strongly influenced the j physiographic development of this region throughout Tertiary and Quaternary time.
I Consequently. these same processes have also strongly influenced the sedimentary facies of most of the Tertiary and Quaternary strata of the Southern High Plains.
For example. streams that deposited lower Ogallala fluvial sediments were apparently diverted by subsidence along the western and northern margins of the Palo Duro Basin to form the Pecos and Canadian Rivers. These events drastically curtailed fluvial sedirnentation in the Southern High Plains region during the late Miocene and early Pliocene. The floodplains and valley walls of the newly-formed Pecos and Canadian Rivers became the probable sources of late Tertiary and Quaternary eolian sediments. Lacustrine basins containing the Pliocene Rita Blanca Formation. the Quaternary Tule Formation. and Pliocene and Pleistocene lacustrine strata preserved along Tierra Blanca Creek resulted in part from dissolution-induced subsidence. Tierra Blanca Creek and Frio Draw. which connect a series of former lacustrine basins.
overlie and parallel a zone of accelerated dissolution in the Seven Rivers Formation.
Two playa lake basins overlie structural basins and areas of accelerated dissolution of San Andres salt in Gray County.
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62 This work was supported by the Department of Energy Salt Repository Project Office. The conclusions of the author are not necessarily approved or endorsed by the Department of Energy.
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1 EVIDENCE FOR SEQUENTIAL DEVELOPMENT OF PLAYA LAKE BASINS. SOUTHERN HIGH PLAINS. TEXAS AND NEW MEXICO C. C. Reeves. Jr.
Department of Geosciences Texas Tech University Lubbock. Texas 79409 Several recent studies. instigated by the Department of Energy's proposal to locate a high-level nuclear waste repository in northwest Texas and by test drilling for a possible site for the Superconducting Super Collider. revealed substantive evidence regarding the origin and progressive development of lake basins on the Southern High Plains of West Texas and eastern New Mexico.
Most small (~ playa") lake basins (Type 1) apparently originated (and are now '
forming) from natural depositional lows over 1.000-year periods or hydrocompaction in uppermost Tertiary and Quaternary aeolian sands or both. Infiltration of intermittently ponded water over 10.000 year periods causes dissolution of calcium carbonate in the l underlying sands. followed by piping and eluviation to enlarge and deepen the original ;
topographic lows to mature Type ll basins. However, in select areas of the Southern I High Plains. probably where fractures are unusually well developed in underlying Triassic and Cretaceous sediments, long-term (over 100.000-year periods).1,ocal 1 infiltration of Ogallala and/or Triassic (aquifer) water has caused point-source <
dissolution of deeply buried Permian salt beds beneath propitiously located Type 11 ;
basins. The resulting collapse of overlying strata, long after the overlying Type il j i basins have achieved their maximum normal development. undoubtedly accentuated '
fracturing. further enhanced infiltration of ground water and dissolution of the Permian salt. and thus reactivated. enlarged, and deepened the overlying Type 11 lake basins 2
. into large (~4 to 15 km ) subsidence basins (Type Ill).
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! The youngest of the large Type !!' subsidence basins are characterized by a more or less round to rectangular shape (for example Whalen. Shafter. Gooch basins),
whereas older basins (for example Yellowhouse. Brownfield basins) are elongate owing to Pleistocene fluvial drainage and perhaps fracture control. In time. the large subsidence basins fill with lacustrine and colluvial debris, becoming nothing more than broad, slightly depressed areas (Anton. Brownfield. Shallowater. Lazy S. Front basins) that commonly contain small (Type 1) lake basins.
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Q4 i STRATIGRAPHY AND STRUCTURE OF THE OGALLALA FORMATION CANADIAN RIVER VALLEY. POTTER COUNTY, TEXAS Gregory A. Wilson Oasis Resources 2108 67th Street Lubbock. Texas 79412 The Canadian River valley north of Amarillo. Texas. exhibits extensive outcrops of Miocene-age sediments of the lower Ogallala Formation. The Lower Ogallala sediments were deposited in a pre-Ogallala valley system that was influenced by the surface structure of the John Ray Dome, by the scar developed at the erosional limit of Triassic strata, and by subsidence induced by dissolution of Permian bedded salts.
The Ogallala Formation is represented by a lower section that contains a Clarendonian-age fauna and is subdivided into the basal Potter Member (0 to 150 ft),
a braided stream channel complex: the middle LX Member (0 to 100 ft), an eolian silty sand sheet: and the Coetas Member (0 to 60 ft), an upper facustrian deposit.
The Coetas Member is highly eroded, and the upper undifferentiated Ogallala Formation sediments lie on the erosional unconformity.
Deposition of the Potter. LX. and Coetas Members was restricted to a narrow palecerosional valley along the southwest flank of the John Ray Dome where the maximum combined thickness of the members is 300 ft. Along the depositional strike of the Potter Member to the east of the John Ray Dome, the paleovalley widens where the Potter stream flowed into the Carson County collapse basin. The thickness of th: lower Ogallala sediments in the collapse basin exceeds 500 ft. and the total Ogallala Formation thickness exceeds 800 ft. The Ogallala Formation above the Triassic paleo-scarp to the south is from 100 to 200 ft thick and is represented only by the upper undifferentiated Ogallala sediments. The lower Ogallala Formation i i
sediments are only present in the paleovalley system and in localized pre-Ogallala j collapse structures, whereas the upper Ogallala sediments, although varying in thickness, are present across the Texas Panhandle.
Several postdepositional collapse structures are evident along the Canadian River where the lower Ogallala Formation sediments can be seen to dip as much as 20 degrees into the collapse basins. Pre-Ogallala collapse structures are evident, but the major collapse itructures on the south side of the John Ray Dome occurred after the deposition of the Coetes Member. Some collapse basins contain thickened upper Ogallala Formation sediments lying horizontally: in other basins upper Ogallala strata
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are dipping and indicate that subsidence continued after deposition. Major collapse basins are also underlain by subsurface structural lows and parallel large subsurface faults.
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- ORIGIN OF SOLUTES IN SALINE LAKES ON THE SOUTHERN HIGH PLAINS AND THEIR EFFECT ON GROUND WATER IN THE SURROUNDING AQUlFER Warren W. Wood Mail Stop 431. National Center U.S. Geological Survey Reston. Virginia 22092 Approximately 40 large saline lakes having solute concentrations of as high as 320.000 milligrams per liter lie within the fresh water High Plains aquifer. Solutes in these lakes have generally been assumed to be from deep-basin brines originating in the Paleozoic gypsun -halite sequence that underlies these lakes, or from connate water within Cretaceous-age rocks in the wrea. However, recent analysis of hydraulic heads and solute chemistry have demonstrated that the solutes are most probably derived from runoff and water from the High flains aquifer. both of which are low in dissolved solids, and then concentrated by evaporation. Chloride-bromide ratios, which are believed to be unaffected by chemical processes in this system. average 160 in saline lakes, close to that of the average High Plains aquifer (140) and significantly different from that of deep-basin brines (270). Other ionic ratios also are consistent with the concept that solutes are derived from the High Plains aquifer rather than from the deep-basin brines. Because of increased density, a higher total hydraulic 1 head exists in the lakes than in the surrounding ground-water divide even though the I water levels suggest hydrologically closed basins. Thus, even though closed ground-
, water contours surround the lake. ground water down gradient from the lake contains i
a plume of very high dissolved solids, making it in many places unsuitable for some ;
domestic or agriculturale uses. Because of the high hydraulic head of the sahne lakes, ground water mounds as it attempts to enter the lakes. mixes with the lake j water, and forms brackish springs on the flank of many of these basins. This mixing i of lake and ground water in the brackish springs is documented by stable isotopes of hydrogen and oxygen that exhibit the isotopically heavy signature associated with 1
evaporation in the saline lakes.
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