Carboniferous stratigraphy of the Hall area, San Saba County, Texas



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Detailed mapping of Carboniferous rocks westward from areas mapped by Bogardus and Oden shows that rock units within the Marble Falls formation are traceable across "Cavern Ridge" a "barrier" invented by Plummer and referred to by others. The Ives breccia, Chappel limestone, Barnett formation, and Lower member of the Marble Falls formation formed as a transgressive depositional sequence. A thin zone of bypassing separates the Barnett and Marble Falls, but a hiatus between them in the Hall area cannot be demonstrated. A small-scale disconformity exists between the Lower and Middle members of the Marble Falls. Local faulting during deposition of the Marble Falls produced the Gibbons conglomerate, influenced the accumulation of Middle Marble Falls shale, and elevated the "Hall Uplift." Some lithosomes in the Upper member of the Marble Falls pinch out near the "Hall Uplift." Sandstone and mudstone of the Strawn formation abut against the carbonate mass of the Marble Falls to the north, but whether a period of erosion intervened between the deposition of the two is not known. Analysis of seven species of corals, twenty-three of brachiopods, two of pelecypods, five of gastropods, two of cephalopods, two of trilobites, and fourteen of conodonts suggests that the Chappel, Barnett, and Marble Falls faunal assemblages most closely resemble those of the Chouteau formation, Caney formation, and Morrow group respectively. In the Hall area no part of the Marble Falls should be correlated with the Atoka series.