# I 2 BUREAU OF ECONOiC GEOLOGY THE UNIVERSITY OF TEXAS AT AUSTIN W'M OCKET N0TROL lSt To78713-750-(512)471-1534or471-7721(jZE *87 JIN -9 A1O:26 June 1, 1987 WM RecorgFile WM Project / /WI Docket No. 13 Dr. Theodore J. Taylor Salt Repository Project Office )rLPDRt adI9 n _ __ ta_ . U. 3* Uepdriinent UT Energy Dii b.iO 110 North 25 Mile Avenue _ _______- Hereford, TX 79045 Reference: Contract No. DE-AC97-83WM466t M __ ______ Dear Dr. Taylor: Per a request from Susan Heston to Chris Lewis, the status of the open-file report entitled *Basin and Range-Age Reactiviation of Rocky Mountain Structures in the Texas Panhandle, (OF-WTWI-1986-3),m by R. Budnik, is as follows. Dr. Budnik left the Bureau in August, 1986. The manuscript was revised by Dr. Budnik to reflect comments from GSA reviewers and resubmitted to the Journal before DOE comments were received at the Bureau. The article was published in the February, 1987 issue of Geology. Please note the title of the article was changed, it is now entitled nLate Miocene Reactivation of Ancestral Rocky Mountain Structures in the Texas Panhandle: A Response to Basin and Range Extension." Three copies of the reprinted article are enclosed. Also, the above referenced article supersedes OF-WTWI-1986-3. If you have any questions, please do not hesitate to contact me. Sincerely, Asoc iat cto Associate Director DCR:CL:cl Enclosures cc: P. Archer (BPMD) S. Heston (SRPO) F. Brown C. Lewis T. Clareson (BPMD/GRC) J. Raney S. Doenges F. Ross (NRC) L. Drover (BPMD/TIC) E. Washer (S&W) J. Ellenberger (SRPO) J.3 Williams (SRPO) L. Harrell - QA Files R. Helgerson (BMI/ONWI) --- 88123035 IMProjecti UN-16 OM Record File: 106 LPIR w/encl 6712I00O2 870601 E FDR Owl PDR AT PDR (Return to UK, 623-SS) 1416 / 710 Late Miocene reactivation of-Ancestral Rocky Mountain structures in the Texas Panhandle: A response to Basin and Range extension 3. Roy T. Budnik* Bureau of Economic Geology. University of Texas University Station Box X, Austin, Texas 78713 ABSTRACT Structural and stratigraphic evidence from the Ogallala Formation (Neogene) documents late Miocene tectonic activity within the Great Plalns Field and mibsurface studies hi the Texas Panhandle Indicate that parts .f the Adulo uplift, amajor element of the Penn- __ sylvanian Ancestral Rocky Mountains, were elevated as much as 150 mduring Initial dep- osition of the Ogallala Formation. Beactiva- I. lion of these basement structures occurred In response to Basin and Range extension and opening of the Rio Grande rift hi central New Mexico and Colorado. INTRODUCTION Investigations in the Texas Panhandle docu- ment late Tertiary tectonism within the Great Plains, more than 300 km beyond the known limits of contemporary Basin and Range faulting in central New Mexico. Evidence of tectonic activity within the panhandle comes primarily from the Ogallala Formation, a vast alluvial apron that was shed eastward from mountains bordering the Rio Grande rift in central New Mexico and. Colorado during Neogene time (Fig 1). Previous work in the panhandle sug- gested that distribution of the Ogaflala was con- trolled primarily by preexisting topography and by subsidence related to the dissolution of under- :::v: 2 lying evaporites (Seni, £980-, Gustavson and - Budnlk, 1985). However, recent neotectonic studies, part of alarger program examining the 22 2: * . 22 :1 it ::: kasihihty of siting a high-level nuclear waste repository in the Texas Panhandle, has shown 222 222 322. thatatleastlocallytectonicprocessesalsoaf- fected the distribution and structural attitude of the Ogallala Formation. This paper reports on research conducted along the Amarillo uplift in the central panhandle about 75 km northeast of fhenw,,,Afiwtnvvtp .4 ICOhu 0A6062 FIgure 1. BasIn and Range province of western United Stat.. (lop) and distribution of Neogene sediments hi southern Rocky Mountains and western Great Plains (bottom). 'Present addrem RRl, Box 440.Aincnia, New Heavy fines In bottom figure are pm-Cenozoic faults. York 12501. GEOLOGY, v. 15,p. 163-166, Febnuy 1987 163 I STRUCTURAL GEOLOGY OF THE High Plains (SchulZ 1977). The overlying Co- can (Pliocene) lacustrine deposits (Schultz, AMARILLO UPL1F etas Formation contains a Clarendonian verte- 1977) to the south of the uplift. The Amarillo uplift isa narrow basement pos- brate fauna (Schultz, 1977). Paleoctologic and itive element that is part of a complex zone of isotopic data indicate that Ogallala deposition LATE TERTIARY DEFORMATION horsis and grabens extending west-northwest- ended during the Hemphillian Stage (late Ml- IN THE TEXAS PANHANDLE ward won the Texas Panhandle (Fig. 2). The ocene/early Pliocene) 4 to S Ma (Izett, 1975). Structures along the Amarillo uplift appear to Amarillo uplift and colinear Wichita uplift to The upper part of the OgalIala Formation is have been unaffected by the Laramide orogeny the southeast in Oklahoma form the southern undated in the vicinity of the uplift, but it is to the west, as indicated by parallelism of bed- margin of the Anadarko basin and are pert of lithologicafly similar to and in the same strati- ding in the lower part of the Ogallala Formation the Pennsylvanian Ancestral Rocky Mountain graphic position as the Dridwell Formation and underlying units. However, Permian, Tries- erogenic belt that extends from Oklahoma to (Evans, 1949) to the south, which is Hemphill- sic, and lower Ogallala strata dip as much as 1? Utah (ver Wiebe, 1930). Left-lateral motion of un in age (Winkler, 1985). Isotopic ages rang- off the southwest flank of the John Ray dome, as much as 120 km during the Pennsylvanian is ing from 4.5 to 6.6 Ma were obtained from ash documenting reactivation of the older structures indicated by the offset of lower Paleozoic strata beds near the top ofthe Ogallala Formation in after initiation of Ogallala deposition. An angu- seross the uplift (Budnlh, 1986). Hemphill County, just north of the uplift (Izett, hr unconformity lies between the Tertiary and Several thousand metres of structural relief 1975). The Ogallala islocally overlain by BIan- older units higher on the dome, and the Ogallala developed between the Amariflo uplift and ad- jacent basins to the northeast (Anadarko) and southwest (Whittenburg trough; Fig. 2) during the Pennsylvanian and Early Permian Reactiva- tion of Pennsylvanian structures since the Pa- leozoic is indicated by faulting of the Triassic Dockum Group against Permian strata won the Potter County fault, which separates the Wbittenburg trough from the Amarillo uplift. In addition, middle and Upper Permian and Tries- sic strata have been folded over en echelon basement horats (for example, the Exell and John Ray domes; Fig. 2) along the upthrown side of the fault. The Ogaflala Formation also has been folded this suggests that at least some of the deformation occurred in the Cenozoic. 5 4 n .I FCIUII. boll wadownllwown sade LATE TERTIARY SYNTECTONIC DEPOSITION IN THE TEXAS Saa,.es, conto interval 1000 ft. 10000 ft Anodorl.o Basin PANHANDLE Along the Amarillo uplift, basal Ogaflala sands and gravels (called the Potter Formation; Patton, 923) include well-rounded siliceous clasts as large as 30 omin diameter transported from mountains along the eastern margin of the Rio Grande rift (Schultz, 1977). as well as blocks of dolomite and red mudstoce up to 45 cm in diameter derived from underlying Permian strata. The Potter Formation is more than 100 m thick within the Whittenburg trough, but thins abruptly onto the Amarillo up. lift woes the Potter County fault (Fig. 3). The unit is conformably overlain within the trough by finely laminated calcareous slltstone and mudstone (Coetas Formation; Patton, 1923). Undifferentiated upper Ogallala sand, silt, and W14T1ENBt.UG caliche blanket the entire area, including the ThcuG folds a4jacent to the Potter County fault. Toflay Ogollolo Fomaat.on EJ P,ftO1 lip Wallunirci Vertebrate fossil data from the Texas Pan- handle indicate onset of deposition of the Ogal- as tiassec Ooctwm Group meP.nruon strata . Fault lala Formation during the Clarendonian (late J Permian vaonles L Pcterczoac basement Miocene), about 10 Ma (Schultz, 1977; earn Winkler, 1985). The Potter Formation appar- FIgure 2. Structure contour map on top of basement (lop) and cross section of Amarillo uplift ently has no indigenous fauna preserved, but (bottom). BrO -Bravo dome; BuD - Bush dome; CB - Carson basin; JRO -John Ray dome; LFB Lefora basin; WDG - White Deer graben; WT - Whlttenburg trough; XLD - Exell dome. Uplift of worn Gryphaea (Early Cretaceous) fragments Exell dome occurred prior to deposition of upper part of Ogallala Formation. Evidence to east are common in itand other basal Ogallala (Qar- (see Fig. 3) suggests that deformation took place during deposition @1lower Ogallala units endonian) deposits throughout the southern (Potter and Coetas Formations). which are not present along this En. of section. 164GEOLOGY. Febnuiy 1987 I%.% / fls sucusszvdy on the Dockum Group, or Extension across the Rio Grande rift wasac- proposed many years ago (ver Webe, 1930) 7erniian Strata, and Emily cc eroded Permiar commodated in part by reactivation of preexist- and termed variously the Wichita lineansent mcntheapexeicrure(Fig.3).k ing fault zones (Eaton, 1979; Tweto, 1979; (Sales, 1968), the Wichita megashear (Walper, 8ddition, the Ogaflala appears to lap onto thr Cordefi, 1982; Baldridge et a!, 1984). Faults 1970; Budnlk, 1986). the Olympic-Wichita Un- * dome so that the Potter Formation rests on thr associated with the north-northwest-trending Lament (Baars, 1976), and the Oklahoma-New Dockum Group within the Whitzenburg trough * Use-Gore fault system (Tweto, 1980) influenced Mexico-Colorado-Utah tectonic zone ([arson whereas the upper unit of the Ogalala rests di* the location of small, discontinuous rift basins in at aL, 1985). The use-Gore and Apishapa fault reedy on Perniian strata on the apex of the Johr central and northern Colorado (Fig.