Southwest Montana Cenozoic Sequences, Paleosols, and Trace Fossils: Debbie Hanneman скачать в хорошем качестве

Southwest Montana Cenozoic Sequences, Paleosols, and Trace Fossils: Debbie Hanneman

This talk will encompass both long-term research on Cenozoic regional sequences and in-progress work on Paleogene and Neogene paleosols and trace fossils done with my colleagues Chuck Wideman, Don Lofgren, and Steve Hasiotis. Regional Cenozoic sequences are defined by unconformities that in southwest Montana occur at approximately 53 Ma, 42 Ma, 30 Ma, 16 Ma, and 4 Ma. The regional unconformities can be traced from the US Great Plains to the US Pacific Northwest. Age constraints provided by 30 newly acquired 40Ar/39Ar ages, derived primarily from ashfall tuffs, better refine timing of the regional unconformities. Southwest Montana Cenozoic tuff ages also enhance the biochronology of several Paleogene vertebrate faunal assemblages and provide additional calibration for the Wasatchian-Bridgerian and Duchesnean-Chadronian North American Land Mammal Age boundaries.