ABSTRACT: Cretaceous Sedimentary Rocks, Uinta Basin, Utah

Thomas D. Fouch, C. M. Molenaar, K. J. Franczyk

Cretaceous strata range in thickness from near 3050 m at westernmost end of Uinta basin to about 1700 m near the Colorado-Utah state line. Rocks represent sediments accumulated in the depositional and structural foredeep (within 100 km of the western thrust belt), the eastern slowly subsiding parts of the sea floor, and Campanian-Maastrichtian intermontane basins resulting from tectonic breakup of the foreland.

Lower Cretaceous strata (Cedar Mountain, and Dakota of north side) consist of 75-100 m of nonmarine rock. Cenomanian to Santonian strata consist of 1500 m of rocks formed adjacent to thrusts (part of Indianola Group, Frontier Formation), 1750 m in the rapidly subsiding foredeep (parts of Indianola Group, Tununk, Ferron Sandstone, Emery Sandstone, and Bluegate Members of Mancos Shale, Mowry Shale, Frontier and Mesaverde formations), and about 840 m in the eastern part of the area (Juana Lopez, Emery Sandstone, and part of Bluegate Members of Mancos Shale, Frontier Formation, Mowry Shale, and informal Hatch Mesa, Woodside, and part of Mancos B units). Campanian strata consist of about 840 m of rocks formed near thrusts (part of Indianola Group, Castlegate, Mesaverde, and Price River for ations); 1070 m in the then-slowing subsiding structural foredeep (part of Indianola Group, Mancos Group tongues, and Blackhawk, Castlegate, Price River, and Mesaverde formations); and 670 m east of the foredeep (Mancos Group tongues, Castlegate, Rimrock and Sego Sandstones, and Price River, Neslen, Mesaverde, Tuscher, and Farrer formations. Locally, as much as 150 m of sediment accumulated in Campanian?-Maastrichtian intermontane sites (North Horn Formation).

Of at least seven regional unconformities, four extend east of the structural foredeep; of those four, two extend across the entire Uinta basin. Of the seven, one occurs in the Cenomanian, one each in the late Turonian/early Cenomanian?, Santonian, and Maastrichtian, and three in the Campanian. Tectonic activity most influenced distribution of facies and extent of unconformities west of foredeep. Unconformities also resulted from tectonic division of the foreland basin.

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