Conodonts and the Devonian-Carboniferous boundary in the upper Woodford Shale, Arbuckle Mountains, south-central Oklahoma

The Woodford Shales was deposited in an offshore, quiet-water, oxygen-poor setting on the southern margin of North America in association with other dark organic-rich shales of the Upper-Devonian-Lower Carboniferous black-shale facies. The basal Woodford was deposited unconformably over lower Paleozoic carbonate strata as a south-to-north transgressive unit during the Frasnian and early Famennian. Black shales and cherts lie directly above the basal beds. Phosphatic shales in the upper Woodford contain a conodont succession characterized by three distinct environmentally controlled faunas. The middle fauna, which spans the Devonian-Carboniferous (D/C) boundary, is characterized by Polygnathus communis communis and species of Protognathodus. On the Lawrence uplift the D/C boundary is disconformable, as indicated by the absence of Protognathodus kockeli before the first occurrence of Siphonodella sulcata. Light-colored phosphate laminae and beds, indicative of erosion and nondeposition, and a change in biofacies from an offshore palmatolepid-bispathodid fauna to a more nearshore, palmatolepid-polygnathid-protognathodid fauna indicate higher energy conditions and a lowering of sea level associated with the boundary interval. In the eastern Arbuckle Mountains the D/C boundary is apparently conformable, marked by a green shale interval containing a Protognathodus fauna. -from Author