Abstract

Detailed geologic mapping and structural analysis along the northeast margin of the Wyoming overthrust belt indicates a complex timing history between the thrust belt and foreland faults and folds. Palynologic dates and structural overprinting provide the primary age control for the timing sequence. The timing of these events from oldest to youngest is: I) late Cretaceous to early Paleocene motion on the east-directed Granite Creek thrust, 2) middle to late Paleocene movement on the east-directed Granite Creek blind thrust and the genetically related west-directed Game Hill thrust, 3) possible early to late Paleocene motion on the foreland Cache Creek fault system on the Cache Creek "blind" fault, 4) late Paleocene to early Eocene motion on the out-of-sequence, east-directed Prospect thrust system, 5) early Eocene motion on the foreland Cache Creek subfault and Cache Creek fault of the Cache Creek fault system, and 6) late normal faulting which truncates the above structures. Thrusts within the out-of-sequence Prospect thrust system include the westward-younging Cliff Creek, Little Granite Creek, Bull Creek, Game Creek and Bear thrusts from east to west. The evolving Gros Ventre foreland uplift provided a buttress against further eastward thrusting, thus primarily causing this westward-younging thrust sequence.