A Lithostratigraphic Examination of the K-T boundary in northwestern South Dakota

Testin, Jason

The Hell Creek Formation has been described and to a great extent studied near the type section in eastern Montana and also extensively in southwestern North Dakota. Little work, however, has been done to characterize the Hell Creek deposits in northwestern South Dakota. As the last terrestrial rock unit of the Cretaceous period in northwestern South Dakota, the Hell Creek Formation represents the sediments below the Cretaceous-Tertiary (K-T) boundary. This boundary represents a period of time when a large number of Earth's organism went extinct; the debate over the biotic effects of the K-T boundary endures between both scientists and lay people, with some questioning the existence of a major K-T extinction of terrestrial biota. The Ludlow Formation is the basal formation of the Fort Union Group, the oldest Tertiary sedimentary unit in the region, representing the strata above the K-T contact in northwestern South Dakota. To date, although a K-T "contact" has tentatively been identified above marine units in the White River Badlands of southwestern South Dakota, its terrestrial equivalent is yet un-described in South Dakota.

This research examines the Hell Creek and Ludlow formations and the boundary between, as they outcrop in northwestern South Dakota. Outcrops were studied stratigraphically, sedimentologically and, to a limited extent, paleobotanically. By including an examination of the fossil flora, we gain a measurement of the scale of the K-T extinction and a method to infer paleoclimate. The lithostratigraphy of the Hell Creek Formation in South Dakota is in need of further study so that it can be compared to Hell Creek outcrops across the extent of the entire deposit, from eastern Montana to southwestern North Dakota. It is hoped that this study will help to provide a more complete picture of the late Cretaceous terrestrial environment of western North America.

AAPG Search and Discovery Article #90163©2013AAPG 2013 Annual Convention and Exhibition, Pittsburgh, Pennsylvania, May 19-22, 2013