Abstract

Thick sequences of Late Cretaceous to early Tertiary quartzite conglomerate were deposited in the Sevier foreland basin of northwestern Wyoming. Included are the Late Cretaceous Harebell Formation and Late Cretaceous to Paleocene Pinyon Conglomerate.

Several hypotheses have been suggested to explain the origin of these thick quartzite-bearing conglomeratic sequences. These include: 1) erosion of the Targhee uplift, a now-buried basement-cored uplift, 2) progressive recycling through multiple episodes of fluvial transport during uplift on successive thrust plates, and 3) direct transport from an active thrust plate. Each of these hypotheses have limitations to their potential validity as sources for quartzite debris in the foreland basin.

Consideration of the styles and mechanisms of uplift in thrust belts, combined with knowledge of sediment provenance and dispersal in eroding thrusted terranes, leads to the proposal of passive thrust plate uplift as a viable mechanism for generating large volumes of quartzite debris. This hypothesis is compatible with observations elsewhere in the Cordilleran thrust belt and alleviates many of the inconsistencies of other models.