--> --> Imaging Exhumed Impact Craters Using Resistivity and Magnetic Surveys, Sheep Mountain, Douglas, Wyoming, USA

AAPG Rocky Mountain Section Meeting

Datapages, Inc.Print this page

Imaging Exhumed Impact Craters Using Resistivity and Magnetic Surveys, Sheep Mountain, Douglas, Wyoming, USA

Abstract

Fifteen circular to ellipsoidal impact craters have been drone mapped and field verified on private property on the northeast facing flank of Sheep Mountain near Douglas, Wyoming, USA centered on 42° 39’ 03” N, 105° 26’ 58” W. The craters are exposed in the quartz-cemented sandstone top of the Pennsylvanian Casper Formation. Rim-to-rim crater diameters range from 10 meters to 63 meters in a strewn field covering approximately 2,600 meters in length and a minimum width of 275 meters. A previous study identified 40+ possible craters in the Douglas Impact Site with 10+ producing shocked-quartz planar deformation features (PDF) as evidence of impact related shock pressures. This study sampled each of the craters for documentation of shocked quartz. Satellite and drone imagery revealed crater shape, orientation, size, structure, fracture patterns, and possible ejecta field areas. The imagery data was acquired with DJI Phantom 4 drones while using ArcGIS Drone Deploy software for each crater, then ArcGIS Drone2Map software was used to create final maps. Length, width and depth of each crater were measured in the field. Detailed geologic data includes strikes and dips of bedding, multiphase episodes of fracturing and faulting, hardened quartzite surfaces, and impact breccia filled veins and surfaces. Based on the crater ellipsoid orientation and sizes, modeling of the possible impactor with these observed features suggest a minimum 15-meter diameter possible nickel-iron bolide fragmenting in the atmosphere with fragments impacting the Casper Formation sand or sandstone from either a southeast direction at a shallow angle of about 10 – 15 degrees and/or from a northeast direction. Since the craters are exhumed from beneath Permian redbeds (basal Opeche Shale of Goose Egg Formation) on a very resistant 20 degree northeast dipping surface, the exact age of impact is unknown but is inferred to be soon after Casper Formation deposition (~280Ma), because there is no crater filling with younger Pennsylvanian sandstone. Casper College students are undertaking classic geologic surface mapping, 3-D drone mapping, and other geophysical surveys (resistivity, magnetics, electromagnetics, and possibly seismic) within the next few years to better understand these ancient yet well preserved impact features.