Studies of sedimentary environments in the Cretaceous Dakota Sandstone in northwestern Colorado

Abstract

The Cretaceous Dakota Sandstone is a land-derived, relatively unfossiliferous lithogenetic unit which occurs over a large part of the western interior of the United States and Canada. Its thickness over most of this area does not exceed 600 feet. In many places it disconformably overlies a former land surface comprised of a variety of formations and rock types, from Precambrian granites to Late Jurassic mudstones. Above the Dakota, and conformable with it, is a marine black shale whose name and age vary from place to place. Thus the Dakota records the passage of an ancient shoreline over a large part of the western interior of the North American continent, the last large-scale invasion of the craton by marine waters. The purpose of this study is the reconstruction of sedimentary environments and determination of geologic history from deposits of the Dakota Sandstone in northwestern Colorado. Close study should reveal the presence of several continental, marginal, and marine deposits within the unit.