Seismic Reflection Imaging of Impact-Induced Faulting and Deformation at Upheaval Dome, Canyonlands National Park, Utah

This report describes a study in which seismic profiling was used to re-interpret the origin of Upheaval Dome, Utah, a geologic structure that was originally thought to be the results of a salt diapir, but which the authors believe may be the remains of an ancient impact structure. ABSTRACT: Seismic imaging techniques applied to a reflection survey show two phases of faulting and deformation beneath Upheaval Dome, Utah. Recent work suggests Upheaval Dome may be the largest impact structure on the Colorado Plateau, having a ring syncline ~3 km in diameter. To better describe the impact deformation of a brittle layer above a viscous layer, as exists at Upheaval Dome with the underlying Paradox Salt, four institutions conducted a NASA-funded seismic reflection survey in January 1995. We obtained a 5 km section extending radially from the Dome's central depression using a 320 kg weight-drop source and a 48-channel off-end receiver spread 0.5 km long. The data show clear reflections as deep as 1.5 km. Imaging of the reflection section with velocity filtering and 3-d prestack Kirchhoff migration techniques reveals the geometries of deformed stratigraphy from the surface to the top of the Paradox Formation at 1.2 km depth. Stratigraphic terminations and fault-plane images show the paths of listric faults. We tie our sections to two well logs, one in the ring syncline and one outside the zone of deformation. Deformation appears in two phases with respect to depth, with listric normal faults in the ring syncline and the megablock zone confined to the part of the section above the Hermosa Formation. Listric faults flatten and sole into the clastic formations above the calcareous layers of the Hermosa at 1.0 km depth. At the base of the Hermosa, on the axis of the ring syncline, the Paradox has forced the Hermosa 0.1 km up and broken it with thrust faults. Post-impact relaxation of the crater form may have driven this deeper uplift. These two modes of deformation, driven from above and below, leave the upper Hermosa as the least-deformed part of the structure