Depositional systems in the Pennsylvanian Canyon Group of North-Central Texas



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The Canyon Group (Missourian Series) is a sequence of westward-dipping, genetically related carbonate and terrigenous clastic facies that crop out in a northeast-southwest belt across North-Central Texas. The section includes stratigraphic units between the base of the Palo Pinto Limestone and the top of the Home Creek Limestone. Surface and subsurface studies within thirteen counties indicate that terrigenous clastic rocks are principally component facies of high-constructive delta systems. The Perrin delta system repeatedly prograded westward and northwestward from source areas in the Ouachita Fold Belt. Algal-crinoid banks flanked the Perrin delta system on the northeast and southwest. A typical vertical deltaic sequence includes (upward) (a) organic rich, prodelta mudstone, devoid of invertebrate fossils; (b) thin, distal delta-front sandstone and mudstone, displaying graded beds, sole marks, and flow rolls; (c) thicker proximal delta-front sandstone, exhibiting contorted beds, flow rolls, and contemporaneous faults; (d) locally contorted distributary-mouth bar sandstone; and (e) distributary channel sandstone, containing abundant trough cross stratification and local clay-chip conglomerate. Thin, coal-bearing delta-plain deposits occur locally on top of deltaic sequences. All delta facies are rich in plant debris. During delta abandonment and destruction, shallow bay-lagoon environments developed. Destructional facies include bioturbated sandy mudstone, burrowed sandstone and thin, platy argillaceous limestone with abundant invertebrate fossils. Fossiliferous mudstone units grade upward into transgressive shelf carbonate units commonly composed of phylloid algal-crinoid biomicrudite and local intraclastic biosparite shoal facies. Shelf carbonate includes onlapping sheetlike deposits; thick elongate bank deposits, which stood above the sea floor with slight bathymetric relief; massive platform carbonate; and shelf edge reef-bank accumulations. The Henrietta fan-delta system, occurring exclusively in the subsurface of Montague, Clay, Wichita, Archer and Baylor counties, is composed of thick wedges of feldspathic sandstone and conglomerate that were deposited by high-gradient fluvial systems, which built southwestward into northern Texas from source areas in the Wichita-Arbuckle Mountains of southern Oklahoma.