Stratigraphy of the upper Pierre Shale and Fox Hills Formation (Campanian and Maastrichtian; Late Cretaceous) in the Badlands National Park region, South Dakota: Implications for eustatic changes in sea level, tectonism, and marine paleoecology of the wes

This research focuses on the upper Pierre Shale and Fox Hills Formation (Late Cretaceous, Late Campanian and Maastrichtian) in a study area extending from eastern Wyoming to the Missouri River valley in South Dakota, with an emphasis on the region encompassing Badlands National Park. Named stratigraphic units in eastern Wyoming include the Lower Unnamed Shale Member, the Kara Bentonitic Member, and the Upper Unnamed Shale Member of the Pierre Shale, and the Fox Hills Formation (oldest to youngest). The equivalent lithostratigraphic sequence in the Missouri River Valley is the Verendrye, Virgin Creek, Mobridge, and Elk Butte members of the Pierre Shale, and the Trail City and Timber Lake members of the Fox Hills Formation (oldest to youngest).;Evaluation of the sequence stratigraphy indicates that both eustatic changes in sea level and tectonism influenced depositional patterns in the Badlands National Park region. A fall in sea level during latest Campanian time (Baculites reesidei) resulted in the development of an unconformity encompassing the Campanian/Maastrichtian boundary in the park area. Sea level rose in early Maastrichtian time with a highstand during Baculites grandis time. Regression followed in Baculites clinolobatus time. Sea level rose and fell during deposition of the Fox Hills Fm.;Evaluations of sediment characteristics, outcrop features, and the general distribution of shell fauna and trace fossil assemblages provide insight into the paleoenvironmental conditions of the seaway. The generally uniform composition the sediment throughout the section and across the region suggests that marine circulation patterns thoroughly mixed the sediment. The characteristics of sedimentary facies are a function of water depth. The influence of episodic storms on sedimentation is suggested by storm-generated bedforms and the record of rapid kill events of marine fauna. Progradation of clinoform mudbanks from the south during Campanian time, and from the north during Maastrichtian time, suggest that early Laramide uplift in the Black Hills region influenced marine circulation and sediment transport in tbe seaway. Equivalent stratigraphic units in the Badlands National Park region are thinner by more than half by comparison to the Wyoming and Missouri River sections.