ABSTRACT: Stratigraphy of Cretaceous Rocks in the Red Desert and Washakie Basins, Southwestern Wyoming

B. E. Law, J. Dolson, W. R. Hanson, V. L. Leighton

Cretaceous rocks in the Red Desert and Washakie basins of southwest Wyoming range in thickness from 2100 to 4200 m. The strata, composed predominantly of sandstone, siltstone, and shale, are mostly derived from source areas in western Wyoming and Idaho. Sediments were also derived from local uplifts in southwestern Wyoming during latest Cretaceous time. The Cretaceous rocks were deposited in marine and nonmarine environments that, in general, display more marine characteristics from west to east. Shorelines for most of the timestratigraphic units trend north to northeast. The stratigraphic sequences presented here are a composite of surface and subsurface data that are being studied as part of the ongoing Western Interior Cretaceous (WIK) Project of the Global Sedimentary Geology Program.

On the west sides of the Red Desert and Washakie basins, in the Rock Springs uplift area, the Cretaceous sequence includes the Aptian to Cenomanian (?) Dakota Group, the Cenomanian Mowry Shale, the Cenomanian to Coniacian Frontier Formation, the Coniacian to Campanian Baxter Shale, the Campanian and Maastrichtian Mesaverde Group, and the Maastrichtian Lewis Shale, Fox Hills Sandstone, and Lance Formation. On the east sides of the Red Desert and Washakie basins equivalent Cretaceous strata include the Aptian to Cenomanian (?) Dakota Group, the Cenomanian Mowry Shale, the Cenomanian to Coniacian Frontier Formation, the Coniacian Sage Breaks Shale, the Coniacian and Santonian Niobrara Formation, the Santonian and Campanian Steele Shale, the Campanian and Maastrichtian (?) Mesaverde Group and the Maastrichtian Lewis Shale, Fox Hills Sandstone, and Lance Formation. Within the Dakota and Mesaverde groups, correlation of stratigraphic units between the west and east sides of the basins are uncertain at this time. Regional unconformities associated with the Dakota, Thermopolis, Frontier, and the Ericson and Pine Ridge Sandstones of the Mesaverde Group, and marine transgressions and regressions associated with the Dakota, Mowry, Baxter/Steele, and Lewis reflect eustatic sea-level changes and/or tectonism.

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