Biochronology and Evolution of Early and Middle Paleocene Nonmarine Mollusca of the Northern Great Plains

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Nonmarine Mollusca are the most abundant animal macrofossil of 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 the determination of the biostratigraphic ranges of taxa in thick sequences of strata temporally-controlled by correlation with fossil mammals. This study will complete a biostratigraphic zonation of Puercan and Torrejonian Strata (early and middle Paleocene) in the Crazy Mountains Basin, Montana where the number of molluscan and mammalian localities are particularly numerous. This zonation will be biochronologically correlated with mollusk-and mammal-bearing strata of similar age in the Fort Peck area of Montana, and the Cypress Hills and Big Muddy areas of Saskatchewan. The Puercan, Torrejonian, and early Tiffanian age strata composite section will be temporally overlapped with the richly fossiliferous Tiffanian (upper Paleocene) strata of the Little Missouri River section in southwestern North Dakota. The composite section will provide the first overall nonmarine molluscan biochronology for the Paleocene of North America, and will specifically serve as a reference section for both mollusks and mammals in the northern Great Plains.