UNCOMPAHGRE THRUST GEOMETRY: A SEISMIC, FIELD AND GRAVITY STUDY NEAR NUCLA, COLORADO, PARADOX BASIN, USA

Seismic, well, field and gravity data lend tools to further understand the Uncompahgre Thrust near Nucla, Colorado, Paradox Basin, USA. The data help explain the complex sedimentary and structural history associated with faulting and salt flowage in Post-Pennsylvanian strata of the eastern margin of the Paradox Basin. Near Nucla, Colorado, 2D seismic lines document several episodes of thrust tectonics, sedimentation, and salt flowage associated with the late Paleozoic-age Uncompahgre Thrust. Prominent unconformities and disconformities within the Permian Cutler Group are visible in the study area. Faults and unconformities seen on seismic data give an indication for the timing of salt flow caused by episodic sedimentation triggered by Uncompahgre Thrust fault movement. In addition, along-strike variability of Uncompahgre Thrust character is evident in the seismic data. Along-strike Uncompahgre Thrust structural variation has been a subject of scientific debate, and the data near Nucla, Colorado offer a glimpse of two end member structural styles of the Uncompahgre Thrust. A gravity (Bouger Anomaly) study in the same area shows an anomalous low-gravity zone to the northeast (hinterland) side of the Uncompahgre Thrust. These gravity data suggest the presence of an allochtonous block in the hanging wall of the Uncompahgre Fault, overriding evaporitic (Hermosa Group) sediments. Integrated, these data offer a more complete analysis of Uncompahgre Fault character in southwest Colorado than previously documented.