The Ancestral Salt Flat Graben. Alternative Paleozoic History of the Sierra Diablo and Apache Mountains, Trans Pecos, West Texas. Robert C. Trentham CEED/Univ. Texas of the Permian Basin

“Thus, the present Sierra Diablo appears to have been a positive through much of its history.” P. B. King, 1942, p. 614

Acknowledgements  University of Texas of the Permian Basin  Bob Lindsay, Chevron – Consultant  Bob Ward  Al Smith  Hughes Family – Apache Ranch

After King (1965) West Texas Physiographic Features

After King (1965) Salt Flat Graben

An Ancestral Salt Flat Graben Can Explain:  The location of the western boundary of the Tobosa Basin  Wolfcampian and Leonardian shelf margins in the Sierra Diablo’s  A lack of Siliciclastics in the upper Guadalupian in the Apache Mountains  The location of the Ochoan “Western Marine Channel”  The presence of a separate Apache Platform

Issues  The Salt Flat Graben is not solely a Basin and Range Feature.  The eastern boundary faults of the Sierra Diablo, Beach, Carrizo and Van Horn Mountains have had a complex history and were active periodically during the Paleozoic.  The Ancestral Graben controlled regional deposition throughout the Paleozoic.

Lack of Evidence  The position of the Guadalupian Shelf Margin between the Guadalupe and Apache Mountains is unknown  The exact location of the Ochoan age western channel connecting the Delaware Basin and the Marfa Basin/Permian Ocean is unknown

Evidence  Western margin of the Tobosa Basin is coincident with the eastern boundary fault of the Sierra Diablo Uplift.  The eastern boundary fault of the Sierra Diablo Uplift was active during lower Hueco (l. Wolfcampian) as there is evidence of thick Powwow Conglomerate in the Basin  The Wolfcampian in the Sierra Diablo Range appears to have been composed of a series of isolated platforms which shed debris in the Basin  The location of the Leonardian shelf margins, at the north end of the Sierra Diablo Range, appears to have been controlled by the position of the Sierra Diablo Fault and Babb Flexure

Evidence  There is a lack of thick siliciclastics in the Guadalupian section in the Apache Mountains which needs to be explained.  The presence of Super Mature sand in the upper Munn in the Apache Mountains indicates the presence of a local Ordovician source  Fault trends in the Baylor Mountains are different than in the surrounding ranges

Lower Paleozoic of West Texas Trans Pecos Delaware Basin u. Mississippian Helms Fm. Miss. Lime Miss. Lime Barnett Fm. Miss Lime l. Mississippian Percha Shale Woodford Shale DevonianSiluro-Devonian Thirtyone Fm. u. Silurian Siluro-Devonian Wristen Fm. l. Silurian Fusselman Fm. u.Ordovician Montoya Fm. m. Ordovician [ Simpson Group ] Simpson Group l. Ordovician El Paso Group Ellenburger Group Cambro-Ord Bliss SS. Wilberns SS.

Tobosa Basin  Defined by the limits of Simpson Group sediments  125’ of Simpson Group sediments are present in the Baylor Mountains.  Simpson has been assumed to feather out between the Baylor and Beach Mountains. Galley (1956)

Tobosa Basin Margin  The Simpson is missing in the Beach and Sierra Diablo Mountains where Montoya overlies El Paso  There are facies changes in the Montoya from the Beach to the Baylor Mountains (King, 1965)  Tobosa Basin margin could be controlled by the Sierra Diablo Fault Zone. BEG, 1983

Upper Paleozoic Stratigraphy Apache / Sierra Diablo Delaware Basin OchoanCastileSalado/Castile u. Guadalupian m. Guadalupian TansillYates Seven Rivers Goat Seep u. Munn (Queen) l. Munn (Grayburg) Lamar Lime Bell Canyon Cherry Canyon l. Guadalupian San Andres Brushy Canyon u. Leonardian Cutoff Fm. Victorio Peak Fm. Cutoff Fm. Victorio Peak Fm. m. Leonardian Clear Fork Bone Springs l. Leonardian Abo Bone Springs u. Wolfcamp HuecoHueco PowwowPowwow

Powwow Conglomerate Thickness In outcrop and subsurface, the Powwow Conglomerate (lower Hueco) is nowhere thicker than 300’

Powwow Conglomerate  Except in the three wells which penetrate the Hueco in the Graben: McBay #1 Strasser Davis, Armour & West #1 Davis Gulf #1 Grisham in these wells, there are from 742 to >2450’ of debris.  Conclusion: The only three wells in the Graben indicate Permo-Penn movement on the Graben Margin

Wolfcampian – Leonardian Carbonate shelves  Recent work by the BEG has concluded that the Sierra Diablo's were a series of isolated platforms capped by carbonate banks shedding debris into an Ancestral Salt Flat Graben during Wolfcampian. The Kriz Lens is now believed to be composed of a series of carbonate debris flows.  Conclusion: The Graben existed during the lower Permian Wilde, 1995

Wolfcampian – Leonardian Carbonate shelves  The location of the Leonardian shelf margin, at the north end of the Sierra Diablo Range, appears to have been controlled by the position of the Sierra Diablo Fault and Babb Flexure Fitchen 2000

Sierra Diablo – A Low Relief Highland  There is evidence of a Sierra Diablo positive/Salt Flat Graben negative during middle and upper Ordovician, Wolfcampian and Leonardian  During the Guadalupian where was the shelf margin? The only Guadalupian in the range is “back reef” Goat Seep north of the Babb Flexure (King,1965). Was there ever any Guadalupian present in the Sierra Diablo's?  and Ochoan…

Guadalupian Siliciclastics  The thick sections of Grayburg and Queen siliciclastics, present in the Guadalupe Mountains, are missing in the Apache Mountains  Sands are assumed to be brought into the basin thru channels in the Guadalupe Mountains, the Salt flat area  It appears that some was deflected into the basin north of the Babb Flexure – Brushy Canyon channel directions  “Back Reef” Goat Seep is present north of Babb Flexure Beaubouef et. al. 1999

Simpson age sand grains in the lower Munn/Grayburg (upper Guadalupian)

Ochoan Evaporites  There was a western channel between the Delaware Basin and the Marfa Basin / Permian Ocean. However,  The location of the channel is conjectural Adams (1967)Hill (1999)

Western Ochoan Channel  If the Salt Flat graben system was active during Ochoan, the egress would most logically be to the south thru the Van Horn area with the Sierra Diablo – Beach – Van Horn Ranges as low relief highlands to the west and the Apache and Wylie Mountains to the east

A Separate Apache Platform  The lack of siliciclastics in Apache Mountains  Periodic rejuvenation of the eastern boundary faults of the Sierra Diablo – Beach – Van Horn Mountains and subsequent graben development  Ochoan outlet to Marfa Basin

Summary  Evidence of an Ancestral Salt Flat Graben is found throughout the Paleozoic in:  Simpson and Montoya age Tobosa Basin margin  Powwow Conglomerate  Wolfcamp and Leonard shelf margins  Guadalupian siliciclastics  Ochoan Channel

Thank You