EVIDENCE FOR EUSTASY AT THE KINDERHOOKIAN-OSAGEAN (MISSISSIPPIAN) BOUNDARY IN THE USA: RESPONSE TO LATE TOURNAISIAN GLACIATION?

Evidence for eustasy at the Kinderhookian-Osagean (K-O) boundary in the conterminous United States is presented by mapping the inferred positions of shorelines during the Kinderhookian Stage, K-O boundary interval, and early Osagean Stage based on stratigraphic data from the COSUNA charts. This analysis shows areas of extensive unconformity at the K-O boundary across the U.S. inferred to be the result of sea level fall and recovery during a period of approximately 2 m.y. Within the central Appalachian basin, coarse-grained, fluvial sandstones (Black Hand, Burgoon, Big Injun, Purslane) are associated with valley incision up to 60 m and a widespread sequence boundary (SB2) inferred to have resulted from a forced regression at the K-O boundary interval. Evidence for eustasy at the K-O boundary in the midcontinent is also reviewed. The K-O boundary is equivalent in age to the global Tn2-Tn3 boundary in the late Tournaisian. Evidence for global regression and eustasy at this boundary is also reviewed.

Recently reported middle to early late Tournaisian (Tn2a-Tn3b) diamictites in South America provide direct evidence for continental glaciation. Both oxygen and carbon isotope data for marine carbonates and fossils from other studies show strong positive anomalies suggestive of global cooling at the K-O/Tn2-Tn3 boundary. Combining the evidence on eustasy, diamictites, and carbon and oxygen isotope anomalies supports the hypothesis of continental glaciation in the late Tournaisian.