STABLE ISOTOPE RECORD OF SOIL CARBONATES FROM THE EOCENE-OLIGOCENE TRANSITION, BADLANDS NATIONAL PARK, SOUTH DAKOTA

The White River Group of the northern High Plains of the United States has produced a wealth of faunal and floral data across the Eocene -Oligocene transition. Sections in and around Badlands National Park in South Dakota are of particular interest as these have provided important paleontological data in defining the Chadronian and Orellan North American Land Mammal Ages (NALMAs). The Chadronian-Orellan boundary is considered to represent the Eocene-Oligocene boundary in the western interior of North America. Faunal and floral changes associated with Chadronian-Orellan interval have long been attributed to global climatic events associated with the Greenhouse-Icehouse transition of the Eocene-Oligocene. Additionally, a magnetostratigraphic timeline has been successfully applied to Badlands previously. This allows for direct comparison of the sediments and their fossil assemblages to geo-synchronous sections around the world, including marine sediments. The sections in the Badlands provide an opportunity to compare a response to global change in a temperate continental system with a response in a subtropical marine system (Gulf Coastal Plain, southeastern USA).

Stable isotopes were obtained from paleosol carbonates across the Eocene-Oligocene boundary in 4 sections in Badlands National Park, Custer County, South Dakota. Results indicate climate stability through the Chadronian with wide fluctuations of oxygen isotope records in the uppermost Chadronian and lower Orellan. Records of Carbon isotopes remain relatively stable through the studied interval, though a slight shift near the boundary is noted.

The results are consistent with changing climate associated with the Oi-1 glacial event in the early Oligocene but differ from Eocene-Oligocene patterns elsewhere. Oxygen isotope records across the Eocene-Oligocene boundary in the shallow marine record of the St. Stephens core of Alabama indicate a gradual cooling through the late Eocene with a sharp decrease in temperatures associated with the early Oligocene. While the signal of global climate change may be present in the Eocene-Oligocene strata of the Badlands, local climate conditions may be more important in controlling the record of stable isotopes in paleosol carbonates in the region.