Sedimentary Environments in Cretaceous Dakota Sandstone in Northwestern Colorado

Depositional environments in the Dakota Sandstone between Rifle, Colorado, and the northern Front Range foothills have been identified through comparisons of primary structures in the Dakota and in Recent sediments, aided by gross lithologic character, organic content, and geometric configuration of sedimentary units. It is shown that the Dakota west of the Front Range contains a simple transgressive sequence which, from base to top, is: (1) fluvial and floodplain, (2) swamp—tidal flat—lagoon, (3) beach, and (4) surf zone and related shallow sub-littoral deposits. The study demonstrates the usefulness of primary structures in the identification of specific sedimentary environments.