Kinematic history of a foreland uplift from Paleocene synorogenic conglomerate, Beartooth Range, Wyoming and Montana

An integrated structural, sedimentological, and provenance study of the upper Paleocene Beartooth Conglomerate along the eastern flank of the Beartooth Range yields new information about Laramide tectonics in the northern Rocky Mountain foreland and has implications for models of fault-propagation folding and the development of synorogenic basins in thrust-faulted terranes. By utilizing the results of provenance modelling and the orientations of the basal and intraformational angular unconformities, we have been able to retrodeform stepwise an area balanced cross section through the eastern Beartooth uplift. Retrodeformation of the cross section indicates that 3.8km of uplift occurred before deposition of the oldest part of the proximal Beartooth Conglomerate. Further uplift of ~1.7km and total horizontal shortening of ~3.7km accompanied ~1.3km of displacement on the Beartooth fault. Our data indicate that during the early stages of uplift by fault-propagation folding, sediment derived from the uplift bypassed the proximal realm and was deposited in distal settings. Bypassing occurred because the eventual footwall of the Beartooth fault was uplifted during fault-propagation folding. Viewed from this perspective, the early fine-grained fills of many Laramide basins may owe their existence to a combination of fine-grained source material and sediment bypassing during the early stages of Laramide uplifts. -from Authors