TAPHONOMY AND SEDIMENTOLOGY OF THE MIOCENE (BARSTOVIAN) TVOR FOSSIL SITE CLUSTER ON FORT POLK, LOUISIANA

The terrestrial mammalian faunas in the Miocene Fleming Formation deposits on Fort Polk, Louisiana, fill a geographic gap in the Gulf Coast paleontological framework and yield details on the local marine-terrestrial transition, but the provenance of the fossils, nature of the depositional environments, and relationships between the sites, especially in the TVOR site cluster, is still under study. TVOR SE has a mixture of marine and terrestrial vertebrates in association with a partly dissolved, in situ bed of articulated oyster shells, which stands in contrast to the fully terrestrial and freshwater assemblage at TVOR, and the indeterminate site TVOR S. Limited outcrops result in small assemblages and obscure site relationships.

Taphonomic and geologic data were integrated to create a more complete picture of the stratigraphic relationships between the sites and the paleoenvironmental factors contributing to the formation of the TVOR fossil sites. Magnetic susceptibility (MS) work on cores from each site allowed correlation between the TVOR S and TVOR SE sites, and possible correlation between TVOR S and TVOR. MS data indicated marine influence at all three sites, including TVOR, which previously had been considered fully terrestrial. Identified, curated fossils from the sites were assigned to bone dispersal groups to assess the degree of sorting in the fossil assemblages, and it was discovered that the vast majority of both macro- and micro-vertebrate fossils fall into Groups I and II, indicating that the fossil assemblages are the result of transport into the sites rather than attrition of local biota.

Although relative sea level was falling at the time these sites were formed, the subtle changes observed in the cored intervals from the TVOR site cluster as well as local alternation of terrestrial and marine influenced members of the Fleming Formation suggests that their deposition was more closely related to localized changes in depositional regimes than glacioeustatic sea level. Gulf Coast fluvial systems were changing rapidly during the Middle to Late Miocene, and the deposition of the Castor Creek Member and the Fort Polk fossil sites could be related to the waning influence and sediment supply of the Red River as the ancestral Mississippi River drainage system matured in the Late Miocene.