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Abstract: Facies Architecture and Parasequence Stratigraphy of the Upper Cretaceous Star Point Sandstone and Blackhawk Formation, Southern Wasatch Plateau, Central Utah

DUBIEL, RUSSELL F., and MARK A. KIRSCHBAUM, U.S. Geological Survey

Lower Campanian strata in the southern Wasatch Plateau, from 1-70 north to the town of Huntington, historically have been assigned to the Star Point Sandstone and overlying Blackhawk Formation. The Star Point Sandstone, which includes the Panther Tongue and Storrs Member farther north, consists of progradationally stacked marine-shoreface sandstones that interfinger with the marine Mancos Shale to the east and with the continental to marginal-marine Blackhawk to the west. Measured outcrop sections, photomosaics, and well-log cross sections depict the depositional facies and parasequence architecture of the Star Point Sandstone. Marine parts of individual parasequences shallow and coarsen upward from offshore through shoreface to foreshore facies, whereas the non-marine parts consist of vertical successions of estuarine to continental deposits, including fluvial channels and thin to thick coals. Parasequences amalgamate as forward-stepping parasequence sets, and thin coals associated with parasequence pinchouts coalesce in a landward direction directly over shoreface units.

Despite its formation rank, the Star Point is composed of parasequence sets similar in scale and depositional pattern to those reported for shoreface sandstones of the overlying Spring Canyon, Aberdeen, Kenilworth, Sunnyside, Grassy, and Desert Members of the Blackhawk in the northern Wasatch Plateau and the Book Cliffs. The Star Point outcrops display at least five progradationally stacked parasequence sets, each separated by a major marine flooding surface (parasequence set boundary). Thick coals developed 10 to 20 in stratigraphically above the lowermost shoreface sandstones and 10-20 km west of landward pinchouts of the subsequent parasequence sets in response to aggradation and accommodation space created during major flooding events. Modeling of the parasequence stratigraphy aids in the projection of coal trends and sandstone geometries into areas of subsurface exploration and evaluation.

AAPG Search and Discovery Article #90937©1998 AAPG Annual Convention and Exhibition, Salt Lake City, Utah