Lithostratigraphy and Paleoenvironments of Upper Paleozoic Continental Red Beds, North-Central Texas: Bowie (New) and Wichita (Revised) Groups

Approximately 2,200 ft (670 m) of principally continental and paralic rocks of late Virgilian, Wolfcampian, and early Leonardian age (late Pennsylvanian and early Permian) are exposed in an area of about 4,950 mi2 (12,800 km2) between the Brazos and Red Rivers in North-Central Texas. The stratigraphic complexity of these strata has impeded internal correlation and mapping ever since the rocks were first described by W. F. Cummins in the late 19th century. Precise correlation of this irregularly stratified fluvial sequence with well-defined, limestone-bounded fluvial-deltaic and marine formations to the south has been hampered because of (1) the gradational change in lithology that accompanies this facies transition, (2) a maximum shift in strike of approximately 65' that coincides with a change in facies tract, thus amplifying the stratigraphic complexity of the region, and (3) the generally poor exposure of the gently inclined strata.The continental sequence comprises approximately 30 major and numerous minor upward-fining, principally fluviogenic cycles. Sandstone units mark the bases of these cycles and occur as regionally persistent zones with multistory and multilateral geometry. These generally resistant cuesta-forming units interfinger with limestone-bearing strata or are laterally separated from them along strike by broad intervening zones of red mudstone. The fine-grained upper part of each cycle is predominantly concretionary red mudstone, although gray and variegated claystone and mudstone lenses, thin siltstone and sandstone beds, and lenticular and channel-fill conglomerates are common.Precise field and photogeologic mapping of continental sandstone units and their correlation with the northern terminations of persistent limestone marker beds have enabled a stratigraphic tie with the dominantly marine section exposed within the Colorado and Brazos River valleys. Continental and paralic rocks are divided into the Bowie (new) and Wichita (revised) Groups; equivalent marine and fluvial-deltaic strata are divided into the Cisco and Albany (revised) Groups, respectively. New formations of the continental sequence were defined to allow the maximum degree of correlation between groups of the continental and marine sections.The continental sequence is composed of facies assemblages that delimit a broad coastal zone peripheral to the northeastern margin of the Eastern Shelf of the Midland Basin. Channel deposits of sandy braided rivers and mixed-load meandering rivers are interstratified in the easternmost region of exposure of the Bowie and lower Wichita Groups and define a piedmont to upper coastal plain physiographic province. Mixed-load meandering rivers with moderate sinuosity were the principal sediment transport routes across the upper coastal plain and are associated with concretionary overbank mudstones, thin crevasse splay sandstones, and gray and variegated lenticular claystones of small floodbasin ponds or marshes (backswamps). Upper coastal plain deposits are represented in the Bowie and lower to middle Wichita Groups. High-sinuosity, mud-rich meanderbelts of the middle and upper Wichita Group typified the broad low-relief lower coastal plain. Small sandy and conglomeratic channel systems of ephemeral streams occurred throughout the coastal plain but were more common in the lower region. Desiccation-cracked beds of tidal mud flats containing fossiliferous storm-berm conglomerates and sand-filled tidal or distributary channels are interstratified with shallow-water marine limestones and carbonaceous shales and claystones of shoreline marshes and supratidal ponds in southwestern exposures of the middle and upper Wichita Group.
Tucker F. Hentz

Hentz, T. F., 1988, Lithostratigraphy and Paleoenvironments of Upper Paleozoic Continental Red Beds, North-Central Texas: Bowie (New) and Wichita (Revised) Groups: The University of Texas at Austin, Bureau of Economic Geology, Report of Investigations No. 170, 55 p.

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The University of Texas at Austin, Bureau of Economic Geology
Report of Investigation