ABSTRACT: Cretaceous Stratigraphy of Eastern Green River Basin, Wyoming and Utah

Dean P. Stilwell, Ramsey Bentley, Allen Smith

The Cretaceous strata in the Green River Basin, east of the Moxa arch, represent a series of alternating transgressive and regressive sequences. From Aptian through Santonian time, marine sedimentation dominated. Beginning in Campanian and through Maestrichtian time, nonmarine deposition was predominant. The strata described were studied as part of the Western Interior Cretaceous Project.

The dominantly marine sequence of Cretaceous strata includes marine and nonmarine Aptian to Albian age sediments known commonly as the Dakota Sandstone, the marine Albian Mowry Shale, the marine and transitional marine Cenomanian to Lower Coniacian Frontier Formation, and the marine Coniacian Hilliard Shale. Possible unconformities have been recognized at the Jurassic-Cretaceous boundary and in two intervals within the Dakota Sandstone. Another unconformity occurs at the base of the Frontier in the southern part of the basin.

The dominantly nonmarine sequence of Cretaceous strata includes the Campanian Mesaverde Group (Blair, Rock Springs, Ericson, and Almond formations), the Maestrichtian Lewis Shale and Fox Hills Sandstone (only deposited on the northwest flank of the Rock Springs Uplift), and the nonmarine Late Maestrichtian Lance Formation. Unconformities are recognized at the base of the Ericson Formation and on an irregular erosional surface at the Cretaceous-Tertiary boundary. The Cretaceous may be as much as 10,000 ft thick in the middle of the basin but no drilling has confirmed this estimate.

AAPG Search and Discovery Article #91002©1990 AAPG Rocky Mountain Section Meeting, Denver, Colorado, September 16-19, 1990