Abstract

Airborne LIDAR data have previously been utilized to determine the relative ages of many of the depositional, erosional and fault features on the surface of the Prairie Allogroup near Lafayette, Louisiana, by their cross-cutting relationships. The overbank deposits of a Pleistocene Mississippi River meander have been interpreted to overlay and obscure the topography of a fault where the fault trends toward the meander scar. The fault is elsewhere well imaged in the LIDAR data.

The surface expression of the fault in question is difficult to trace accurately in the field because of its low relief. In 3D virtual reality we have created a technique which involves georegistering and intersecting a planar satellite image of the region with the 3D LIDAR data. As the elevation of the satellite data image is increased the intersection of the two images moves up the topography of the 3D LIDAR data image. The intersection of the fault scarp within the satellite data precisely establishes the location of the fault scarp. With this knowledge of the geographic location of the fault scarp we surveyed several topographic and gravity profiles across the fault. These profiles characterize the topographic and gravity signatures of the exposed portion of the fault. Further gravity profiles across the proposed extension of the fault beneath the meander deposits establish that the fault does extend beneath the deposits. Therefore, the faulting is strictly older than the Mississippi River meander. In fact, in this region we have no evidence that there has been discernible creation of surface topography by faulting since about 85,000 years ago.