GIS MODELING OF THE DETACHMENT AND COLLAPSE OF A CARBONATE PLATFORM FOLLOWING THE LATE DEVONIAN ALAMO IMPACT EVENT, LINCOLN COUNTY, NEVADA

The Alamo meteor impact event caused the detachment and collapse of 28,000km² of carbonate shelf which is draped by debris flow and tsunami breccias of the Guilmette Formation. A recent model for the Alamo impact has identified realms within the collapsed shelf that share similar impact-related features and predicts that (1) the detachment surface cuts platform rocks most deeply nearest the impact and most shallowly away from the impact, and that (2) the collapsed platform formed ring-shaped basins and ridges. The large geographic extent of the Alamo Breccia provides exceptional exposure to test these predictions, and is ideally suited for a GIS approach in resolving the geometries of the platform collapse, breccia deposition and platform recovery.

The Alamo Impact Database is in development to spatially relate the geological attributes of the Guilmette Formation, including stratigraphic thicknesses and facies, to develop 3D models of the impact region and to test predictions of the realm model. The current model uses stratigraphic thickness data from >40 locations in over a dozen ranges. Surface raster maps for each subunit of the Guilmette Formation are interpolated using conservative methods, and combined using raster math tools. From these compilations, thickness profiles were analyzed along E-W and N-S transects through the impact region.

Preliminary results show that the Alamo detachment surface is more complex than originally hypothesized. Although the detachment cuts platform rocks to a depth >100m in western Ring realm localities and shallows to 0m in the east, there are at least two areas where the depth of detachment varies by 50m over an E-W span of 5km. The topography modeled for the top of the collapsed platform blocks shows a similar scale of heterogeneity, with 40m of vertical relief over an E-W span of 2km. More localities are required to test if these thickness variations correspond to ring-shaped structures.