South Park, Colorado: The interplay of tectonics and sedimentation creates one of Colorado’s crown jewels

Recent mapping efforts and hydrocarbon exploration in the South Park Basin have brought to light the magnitude in complexity of a structural basin already recognized for its unique sedimentary and tectonic setting. This fi eld trip to one of Colorado’s scenic gems will examine how Paleozoic, Mesozoic, and Cenozoic strata record the tectonic signatures of at least three orogenic episodes. We will cross the Elkhorn–Williams Range thrust system into the structural block caught between Laramide uplifts, and preserving synorogenic sediments from the Pennsylvanian– Permian ancestral Rocky Mountain tectonic episode in juxtaposition with synorogenic sediments from the subsequent Laramide tectonic episode. Late Cretaceous marine sediments from the Western Interior Seaway caught up in complex fold-fault structures between Laramide uplifts create targets for petroleum exploration. Evidence of evaporitic tectonism originating from Pennsylvanian evaporite deposits and hinting at structural complexity dots the landscape. The trip will also explore a postLaramide surface preserved in a graben developed in the hanging wall of the Elkhorn fault system and view post-Laramide volcanic features. Glacier-carved ranges held up by Precambrian crystalline basement and Paleozoic sediments hardened by contact metamorphism from Paleogene stocks and sills rim the basin. Pleistocene glaciofl uvial deposits fan out from the high ranges to blanket the highly deformed basin, masking many of the primary structural features.