Government Draw Bentonite Beds: A Newly Identified Stratigraphic Marker in the Virgin Creek Member of the Pierre Shale, Central South Dakota

A grouping of four bentonite beds, herein named the Government Draw Bentonite Beds, is identified as a stratigraphic marker within the Virgin Creek Member of the Pierre Shale. The beds are found west of Pierre, South Dakota, over an area of at least 130 mi/sup 2/ where no other markers within the Virgin Creek Member have been identified. In this area, the Government Draw is a potential tool needed to determine the stratigraphic and structural relationships within the upper part of the Pierre Shale, heretofore little known. A better understanding of structural elements found in the Pierre Shale is needed to unravel the Late Cretaceous and younger geologic history of the area. This is part of a study to characterize Cretaceous shales for subsurface engineering construction undertaken by the US Government to evaluate the feasibility of using shales as a medium for disposal of toxic waste.