Paleogeography of Uncompahgre Uplift during Early-Medial Pennsylvanian Revealed by Progression of Siliciclastic Wedges in the Paradox Basin, Colorado and Utah

Rasmussen, Donald L.¹ (1) Paradox Basin Data, Longmont, CO

Pennsylvanian Hermosa strata in the Uncompahgre Trough (UT) along the SW margin of the Uncompahgre Uplift (UU) are cyclic, with each cycle containing mappable transgressive organic-rich shales, high-stand carbonates, low-stand evaporites, and wedges of arkosic siliciclastics. Arkosic siliciclastics in the Morrowan through Medial Desmoinesian cycles were from exposures of Precambrian basement in the early stages of UU in southern Colorado and northern New Mexico. Evaporites and carbonates within the same cycles in the deep UT abut against the thrusted SW margin of UU (late Penn. and Permian thrusting) but are not at their depositional limits which were beyond the thrusted margin. The UU adjacent to the deep UT was not positive when these evaporites and carbonates were deposited and the interstratified siliciclastics wedges had a distant source (carried to UT by rivers and turbidity currents). These wedges slowly prograded to the NW during Medial Pennsylvanian. During Late Desmoinesian through the Permian Wolfcampian, multiple siliciclastic wedges prograded out into the UT, with each successive wedge overlapping the one in the previous cycle. These wedges are arkosic and mapping indicates their source was unquestionably the nearby tectonically active UU. The UU reached its highest relief and erosion during the Permian Leonardian as seen by the very thick wedges of Cutler-Organ Rock strata in the UT.