Thrust controlled sedimentation patterns of the earliest Cretaceous nonmarine sequence of the Montana-Idaho-Wyoming Sevier foreland basin

Recent research on the Upper Jurassic/Lower Cretaceous nonmarine deposits of the central Rocky Mountain Foreland indicate that the sedimentary-tectonic model developed for Laramide intermontane basins is valid for the Sevier foreland basin as well. Episodes of thin-skinned thrusting and tectonic stacking caused asymmetric subsidence of the foreland and the localization of its structural axis adjacent to the fold-thrust belt. A regional thrust-ward-dipping paleoslope formed cratonward of the structural axis of the foreland basin during thrust events as a result of rapid subsidence of the foredeep. However, during periods of tectonic quiescence, rates of sedimentation within the foredeep exceeded rates of subsidence with the result being a reversal of the regional paleoslope. During thrusting, low gradient fluvial, paludal, and lacustrine depositional environments were localized adjacent to the thrust tips. Early Cretaceous movement of the Paris thrust is recorded by the occurrence of thick lacustrine deposits of the Peterson and younger Draney limestones within the foredeep in western Montana and along the Idaho-Wyoming border. Coeval with the lacustrine environments were two major west to northwest flowing fluvial systems now preserved within the Lower Cretaceous Cloverly Formation of north-central Wyoming. Those fluvial systems are represented by a major channel complex within the Littlemore » Sheep Mudstone and the Himes Member. Paleocurrent analysis and isopach data indicate the influence of incipient Laramide structures on sedimentation both within the Sevier foredeep (DeCelles, 1984) and the more distal margins of the foreland basin.« less