Syntectonic sedimentation and Laramide basement thrusting, Cordilleran foreland; Timing of deformation
Richard A. Beck, Carl F. Vondra, Jeffrey E. Filkins, Jon D. Olander, 1988. "Syntectonic sedimentation and Laramide basement thrusting, Cordilleran foreland; Timing of deformation", Interaction of the Rocky Mountain Foreland and the Cordilleran Thrust Belt, Christopher J. Schmidt, William J. Perry, Jr.
Download citation file:
Recent seismic and drilling data from the Laramide-style basement-cored uplifts of the central Rocky Mountains suggest that thick-skinned basement thrusting due to horizontal compression, rather than block uplift due to vertical forces, is responsible for their origin. Interpretation of these structural uplifts as basement thrusts requires a new sedimentary-tectonic model for the region. Sedimentary facies associations within the Upper Cretaceous and lower Tertiary strata of Laramide-style intermontane basins are best understood as a response of sedimentation to thick-skinned basement-thrusting.
Laramide-style structural features of the central Rocky Mountains include asymmetric basins and arcuate, basement-cored thrust sheets. Sedimentary facies of the basins reflect a common history of asymmetric subsidence due to thrust loading and a consistent pattern of depositional environments. These facies have a depositional polarity similar to the structural asymmetry of their underlying basement. Characteristic syntectonic sedimentary facies of these basins include a narrow, coarse conglomerate facies adjacent to the thrust, a narrow to absent sandstone/mudstone/coal facies just basinward, a basinal thrustward-thickening mudstone/coal/carbonate/evaporite facies above the depositional axis, and finally, a wide distal sandstone/mudstone/coal facies. The wide distal sandstone/mudstone/coal facies depositionally thins above the shallowing basement opposite the impinging thrust or above the hanging wall of yet another thrust, as in the Wind River Basin.
Episodes of rapid Laramide-style basement thrusting caused rapid tectonically induced asymmetric basin subsidence that equaled or exceeded the rate of sedimentation. Major sediment sources were the gently dipping basin margins opposite each thrust. The frontal edges of the hanging walls of basement thrusts provided coarse but volumetrically minor quantities of clastic sediment during thrust movement. Areally extensive, thick, coarse-grained, fluvial clastic wedges derived from impinging basement thrusts developed only after thrusting had greatly slowed or ceased.