TOURNAISIAN-VISEAN BOUNDARY CONODONT SUCCESSION FROM THE WESTERN FLANKS OF THE OZARK UPLIFT

The Tournaisian-Visean boundary is currently placed at a pronounced unconformity separating the Burlington Limestone from the overlying Keokuk Limestone in the Mississippi Valley region of North America. This level coincides with the boundary of the latest Visean Polygnathus mehli conodont zone and the early Visean Gnathodus texanus-Taphrognathus varians conodont zone. An intervening Gnathodus bulbosus conodont zone is recognized in the southern and western flanks of the Ozark Uplift in the top of the Pierson Formation and basal Reeds Spring Formation in a more basinward position on the depositional shelf. This zone is apparently missing to erosion or non-deposition in the Mississippi Valley where it was evidently deposited in a more high energy shallow shelf depositional setting.

The current research program is based on analysis of two complete stratigraphic successions that span the Tournaisian-Visean boundary. The first of these localities is at Roaring River State Park , Missouri and the second near Jane, Missouri. Both of these localities reveal a continuous conodont succession across the Tournaisian-Visean boundary without any apparent depositional break. The upper Tournaisian conodont succession include the following conodont zones in ascending order : Polygnathus communis carinus Zone, Pseudopolygnathus multistriatus Zone, Scaliognathus anchoralis-Doliognathus latus Zone, Bactrognathus distortus lanei Zone, Polygnathus mehli Zone, Gnathodus bulbosus Zone and the Gnathodus linguliformis Zone. Significantly, the Roaring River Section is the type section for Scaliognathus anchoralis, Doliognathus latus, Polygnathus mehli, and Gnathodus bulbosus. These two localities perhaps provide the most complete stratigraphic succession across the Tournaisian-Visean boundary interval in North America. Small foraminiferans are yet to be sampled and analyzed from these two localities.