Pennsylvanian and Early Permian paleogeography of the Uinta-Piceance Basin region, northwestern Colorado and northeastern Utah

Abstract

The Uinta-Piceance basin region of northwestern Colorado and northeastern Utah includes parts of four major sedimentary provinces that were active during the late Paleozoic ancestral Rocky Mountain orogeny: the Eagle basin, the northern part of the Paradox basin, the southern Wyoming shelf, and the southeastern part of the Oquirrh basin. Depositional patterns in these sedimentary provinces were controlled to varying degrees by eustatic and climatic fluctuations (forced by expansion and contraction of late Paleozoic continental ice sheets), tectonism, and sediment supply. Four sets of paleogeographic maps illustrate the major changes in paleogeography and depositional patterns associated with repetitive transgressions and regressions. In general, clastic deposition (mostly sandstone in fluvial, deltaic, and eolian systems) dominated during regressions, whereas deposition of marine limestone and clastic rocks characterized transgressions. The most arid climates are correlated with regressions. Morrowan and lower Atokan strata throughout most of the Uinta-Piceance basin region consist of fine-grained clastic rocks (regressive deposits) and more abundant limestone (transgressive deposits). Significant Morrowan and early Atokan tectonic uplifts include the Front Range and Sawatch uplifts. The late Atokan to Desmoinesian history of the region is characterized by unroofing of the Front Range and Sawatch