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.