Sequence and Timing of Structural Development in Wyoming-Idaho-Utah Thrust Belt: What Do Provenance Studies of Foredeep Basin Conglomerates Indicate?: ABSTRACT

Abstract

Studies of Late Jurassic through Eocene conglomerates deposited in the Sevier foredeep basin adjacent to the Wyoming-Idaho-Utah thrust belt typically attempt to relate conglomerate genesis to motion along particular thrusts on the basis of areal grain-size variation and/or clast compositions tied uniquely to one thrust. However, sedimentologic and provenance investigations for many of these units frequently are lacking in detail and at best provide only circumstantial or equivocal evidence of motion along a particular thrust. Additionally, most conglomerates thought to be related to periods of motion on major thrusts crop out in geographically restricted areas, making interpretation of major structural events based on their provenance applicable only on a local scale. In the absence of definitive cross-cutting structural or overlapping stratigraphic relationships, correlations of conglomerates with episodes of motion along particular major thrusts are extremely tenuous. Recent studies of structural development in the hinderland of the Sevier orogenic belt show that major Jurassic through Cretaceous low-angle faults are common. Other structural investigations in west-central Idaho document the importance of terrane accretion during Mesozoic time.