Lindsay 9526386 This project is for biostratigraphic and magnetostratigraphic study of the Panaca Formation in eastern Nevada. This dominantly lacustrine deposit is more than 300 meters thick, representing aggradation in basins formed by tectonic extension. both Hemphillian (latest Miocene-early Pliocene) and Blancan (middle-late Pliocene) mammals are known from the Panaca Fm.; our objective is to establish a sequence of magnetozones in the Panaca Fm. using both marker beds and magnetostratigraphy, and to assemble this data to resolve the boundary between Hemphillian and Blancan land mammal ages. North American sites with Blancan and Hemphillian mammals are probably more common than sites of any other pre-Pleistocene land mammal ages; superposition, however, of Blancan over Hemphillian mammal sites is rate. When superposition can be demonstrated, relative to Hemphillian and Blancan faunas, correlation and calibration of the boundary has never been securely established. The Panaca Fm. provides a combination of thick and well exposed sediments, diverse and locally abundant fossils, and strong, stable magnetic minerals. The combination of these factors in the Panaca Fm. promises to provide a robust data base for resolution of the Hemphillian/Blancan boundary. The geochron of the Panaca Fm., approximately 3 to 6 m.y., was an interval of dynamic mammal radiation. The early radiation of microtine rodents (e.g., voles and lemmings) in Holarctica, the appearance of hominids in Africa, and the Great American Interchange all occurred in that time span. It is interesting that here in North America, where mammal chronology is most securely established, the boundary between Hemphillian and Blancan land mammal ages is so poorly constrained. This project is designed to correct that weakness; when securely calibrated, the boundary between Hemphillian and Blancan land mammal ages will be a firm cornerstone for global correlation of biotic and geologic events during the late Cenozoic Era.
