Abstract: Early Cretaceous Sedimentation and Lithospheric Deformation in the Foreland of the Sevier Thrust Belt, UT

W. M. Aubrey

A new stratigraphic model more clearly defines an Early Cretaceous flexural basin in the foreland of the Sevier thrustbelt in central Utah and leads to a better understanding of the timing and mode of deformation, both in the thrust belt and the foreland. Paleontologic data indicate that foreland basin subsidence began in Barremian to middle Albian time and ceased at the end of the Albian. The youngest rocks occur in the proximal part of the basin, indicating the basin narrowed as thrusting proceeded. This narrowing suggests that the lithosphere behaved viscoelastically during thrust loading. An unconformity between the Lower Cretaceous terrestrial foreland basin deposits and overlying Upper Cretaceous paralic transgressive rocks represents a period of quiescence in thrusting. The tra sgressive rocks onlap a paleoslope that dips away from the thrust belt. This east-dipping paleoslope was probably produced by flexural rebound of the basin during quiescence. Conglomerate derived from the thrust belt during the Early Cretaceous thrusting episode is primarily restricted to the proximal part of the basin in central Utah, where subsidence was most rapid. Conglomerate in the Buckhorn Conglomerate Member of the Cedar Mountain Formation and lower part of the Burro Canyon Formation, which is widespread across eastern Utah and western Colorado, is probably Late Jurassic rather than Early Cretaceous in age, as was previously thought, and is unrelated to the Sevier Orogeny.

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994