The Arkoma is a structural-sedimentary basin covering much of eastern Oklahoma and western Arkansas, and extending south to the Choctaw fault. (This report covers only the Oklahoma part of the basin). In general the basin deepens and thickens toward the south, a pattern which was well developed by Simpson time (early Middle Ordovician), but which was sharply interrupted during Middle Ordovician (late Bromide) and not resumed until after Early Devonian. During this interregnum the sediments are represented largely by a succession of thin but widespread carbonate units separated by diastems and unconformities. This period began with an intertidal environment which extended over most of the basin (late Bromide; Fite), followed by a succession of widespread, shallow carbonate seas, generally with prolific faunas including many representatives of the sessile benthos, separated by times of uplift of varying intensity and duration. The only significant departure from this pattern is the Upper Ordovician Sylvan Shale, a calcareous mudstone and shale representing an environment which inhibited almost all of the sessile benthos, the only persistent organisms being graptolites and chitinozoans. Carbonate sedimentation was resumed following this shale episode, continuing to the end of the Early Devonian. This depositional model produced a body of sediments whose total thickness does not exceed 500 ft (152 m), and which neither individually nor collectively shows any directional thickening. Early Devonian deposition was followed by a prolonged period of uplift accompa ied by extensive erosion and truncation. The region was then submerged by the advancing Chattanooga (Woodford) sea, and the pattern of southward subsidence and thickening again resumed.

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