Evidence for an impact origin of the Late Ordovician Bear Swamp structure in upstate New York, USA

Abstract

A 3D seismic survey has imaged a complex crater of possible impact origin in the Finger Lakes region of upstate New York near Bear Swamp State Forest. The Bear Swamp crater is uppermost Ordovician (∼444 Ma) in age and is completely buried in the subsurface at a depth of approximately 1220 m (4000 ft). The nearly circular crater is about 3.5 km (2.2 mi) in diameter and contains a central rebound structure with a diameter of about 1 km (0.6 mi). Two exploration wells were drilled into the crater and core and image-log data were obtained. The first well tested the central rebound which consisted of steeply dipping beds and heavily brecciated zones as seen on the image logs. The second well tested the flank of the central uplift in the roughly 300 m (1000 ft) thick annular basin. Thin sections taken from whole core recovered in the second well revealed planar deformation features (PDF) in quartz grains within the reworked crater fill sediments. Minor gas shows were encountered at the base of the crater fill section in the second well, and both wells encountered significant gas shows in the fractured target rock beneath the crater. Both macroscopic and microscopic evidence from the seismic and well data suggest this could have been the site of a meteor impact in a shallow marine to transition zone environment at the end of the Ordovician Period.