Uncompahgre fault geometry: a seismic, field, and gravity study near Nucla, Colorado, Paradox Basin, USA

Abstract

Seismic, well, field and gravity data are used to further understand the Uncompahgre fault near Nucla, Colorado, Paradox Basin, USA. The data help explain the complex sedimen- tary and structural history associated with faulting and salt flowage along 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 vis- ible 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 fault movement. In addition, along-strike variability of Uncompahgre fault is evident in the seismic data. Along- strike Uncompahgre fault structural variation has been a subject of scientific debate, and the data collection near Nucla, Colorado reveal two end member structural styles of the Uncompahgre fault. A gravity (Bouger Anomaly) study in the area shows an anomalous low-gravity zone to the northeast (hinterland) side of the Uncompahgre fault. These gravity data suggest the presence of an allochtonous block in the hanging wall of the Uncompahgre fault, overriding evaporitic (Her- mosa Group) sediments. Integrated, these data offer a more complete analysis of Uncompahgre fault character in southwest Colorado than previously documented.