Abstract

Data from about 5,000 gravity stations in northeastern Utah were used to construct simple Bouguer, free-air, and residual gravity anomaly maps. The area covered by the gravity maps includes the Uinta Mountains, the Uinta Basin, and the northern parts of the San Rafael Swell, Castle Valley, Paradox Basin, and Uncompahgre Uplift.

Four gravity profiles were used to construct two-dimensional models of the major geologic structures. These models indicate maximum basement surface depths of 27,000 ft below sea level for the Uinta Basin and 18,500 ft below sea level for the Green River Basin. The models show a zone of up-thrust faulting along the southern flank of the Uinta Mountains, where the sediments of the Uinta Basin continue northward under the southern edge of the surface structure of the Uinta Mountains. A zone of faulting with up to 6,000 ft of throw is upthrown to the southwest near the southwestern margin of the Uinta Basin. In the southern part of the study area, a model indicates about 13,000 ft of structural relief between Castle Valley and the San Rafael Swell, about 13,000 ft of structural relief between the san Rafael Swell and the Paradox Basin, and about 16,000 ft of structural relief between the Paradox Basin and the Uncompahgre Uplift.

The gravity maps and profiles indicate that the basement complex in northeastern Utah is heterogeneous, with many large density contrasts. A large eastward-trending anomaly in the east-central part of the Bouguer gravity map is one of the largest anomalies on the map, and appears to be caused by a density contrast within the basement. An apparent low density in the basement on the southwestern flank of the Uncompahgre Uplift makes the nature of the faulting on that side of the uplift difficult to determine from the available data.