ESCALATION OF PENNSYLVANIAN-PERMIAN UNCOMPAHGRE UPLIFT REVEALED BY PROGRESSION OF SILICICLASTIC WEDGES IN THE PARADOX BASIN, COLORADO AND UTAH

Pennsylvanian (Morrowan through medial Desmoinesian) Hermosa strata in the Paradox Basin's Uncompahgre Trough (UT) along the southwest margin of the Uncompahgre Uplift (UU) contain multiple local wedges of arkosic- and mica-bearing siliciclastics. The source of these siliciclastics is probably related to exposures of the Precambrian basement in the early stages of the UU in southwestern Colorado (and San Luis Uplift in adjacent northern New Mexico) and possibly to basement exposures in the slightly more distant Sawatch Uplift in west-central Colorado. Interbeds of evaporites and carbonates within these same strata abut against the thrusted southwest margin of the UU (late Penn. and Permian thrusting) but are not at their depositional limits, suggesting that the UU was not present when they were deposited and that the siliciclastics indeed had a distant source and were carried to the area by rivers. Siliciclastic wedges during the late Desmoinesian through the Permian Wolfcampian prograde out into the basin, with each successive wedge overlapping the previous one. These siliciclastics are dominantly arkosic and their source was unquestionably the nearby tectonically active UU. During the Permian Leonardian, the UU reached its highest relief and erosion as seen by the monstrously thick Cutler Organ Rock siliciclastics in the UT, and by the time of Moenkopi and Chinle deposition in the Triassic the UU was of low relief and no longer tectonically active.