Time of initial thrusting in the Sevier orogenic belt, Idaho- Wyoming and Utah ( USA).

Abstract

Re-examination of the distribution of fossils found in the earliest preserved synorogenic conglomerates within the Sevier thrust belt suggests that initial thrust movement may be no older than Aptian age. A major episode of middle Cretaceous (Aptian-Cenomanian) subsidence is interpreted as recording the initiation of thrust loading deformation in the adjacent Sevier orogenic belt. An earlier subsidence event took place during Middle Jurassic time, >30Ma prior to the Cretaceous event, and may be the result of tectonic events to the W that are unrelated to thrust deformation in the Idaho-Wyoming and Utah thrust belts. We find no verifiable evidence to support previous interpretations that Sevier belt deformation and uplift began in Late Jurassic time.-from Authors