Biochronology and Evolution of Latest Cretaceous and Paleocene Nonmarine Mollusca of the Northern Great Plains

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Nonmarine molluscs are abundant animal macrofossils of uppermost Cretaceous and Paleocene continental strata in western North America. Their biochronologic potential, however, has yet to be realized due primarily to the lack of study focused on biostratigraphic ranges of taxa in thick sequences of strata temporally controlled by correlation with fossil mammals. The proposed study will construct a biostratigraphic and biochronologic zonation of Lancian (uppermost Cretaceous), Puercan, Torrejonian, and Tiffanian (lower, middle, upper Paleocene, respectively) strata in the northern Great Plains. The project will consist of the following parts: 1) Field work to stratigraphically organize known Lancian age localities in the Hell Creek Formation of the Williston Basin (Montana/North Dakota) and the Lance Formation in the Powder River Basin (Montana/Wyoming), 2) field work to discover Puercan and Torrejonian age mollusk localities in the lower portion of the Fort Union Group, which remain relatively uncommon, 3) general taxonomic study of the uppermost Cretaceous and Paleocene mollusks to provide a framework for taxon identification, and 4) detailed taxonomic study of selected taxa within families that appear to be particularly useful for purposes of biostratigraphy and biochronology in the northern Great Plains.//