New views on late Paleozoic climate and tectonics in the Ancestral Rocky Mountains

Abstract

Recent research in Pennsylvanian-Permian strata of the Fountain Formation adjacent to the Front Range uplift and the Cutler Formation adjacent to the Uncompahgre uplift (Colorado) has resulted in new hypotheses about the climate and tectonics of the Ancestral Rocky Mountains. The Fountain and the Cutler formations are iconic deposits; the thick and coarse-grained nature of these units has been cited for nearly a century as documenting the Ancestral Rockies. Long considered the products of alluvial fan deposition in warm climates, new data support the hypothesis of proglacial deposition for these units, and thus glaciation of the Ancestral Rocky highlands. This bears on our understanding of Late Paleozoic climate in western equatorial Pangaea, as well as global climate at this time. Furthermore, new mapping in the Uncompahgre region indicates substantial onlap and possible burial of Precambrian highlands by Permian strata. The argument for Permian subsidence of the uplift emanates from the hypothesis that Unaweep Canyon, which bisects the Uncompahgre Plateau (paleo Uncompahgre uplift) originated as a Permian paleolandscape. This trip will include visits to (1) the Fountain and Cutler formations to discuss and debate the sedimentologic origin(s) of these deposits, and (2) Unaweep Canyon to examine evidence for both a possible Paleozoic age and glacial origin for this canyon, and its late Cenozoic history as a former stream course of the ancestral Gunnison River.