BEAR SWAMP IMPACT STRUCTURE
by: Charles O’Dale
- Type: Simple
- Location: N 42° 43.187’ W 76° 16.637’
- Diameter: 3.5 Km
- Age Ma: ~444a – ORDOVICIAN
- Shock Metamorphism: planar deformation features (PDF) in quartz grains.
a minimum age at the end of the Ordovician period.
Possible Impact Origin for the Late Ordovician Bear Swamp Structure in the Finger Lakes Region of New York
Impact structures, or astroblemes, are one of rarest formations in the geologic record. Presently there are 176 confirmed impact structures on the planet with roughly two-thirds of them evident at the surface. A potential impact structure has been discovered in a 3D seismic survey in the Finger Lakes Region of upstate New York. The Bear Swamp crater is uppermost Ordovician (~444 Ma) in age and is situated within the fluvial-deltaic to shallow marine Queenston Formation. This nearly circular structure measures 3.5 km (2.2 mi) in diameter and is completely buried in the subsurface at a depth of approximately 1,220 m (4,000 ft).
This three-dimensional morphology resembles other complex craters of confirmed impact origin. Two exploration wells were drilled into the crater and image logs were run. The first well tested the central rebound which consists of steeply dipping beds and heavily brecciated zones. The second well was drilled in the annular basin which contains alternating sequences of chaotic zones and shallow dipping beds. Based on analogous impact structures, this crater fill is here interpreted as resurge breccias and turbidites which were the result of intense wave action in the moments after impact. Above these impact-related deposits lies a zone of very thin (~2cm) laminae which resemble varved sediments in lacustrine environments. A bioturbated zone overlies these thin laminae, which is in turn capped by the End Ordovician unconformity. Observations of both seismic and well data are consistent with a shallow marine to transition zone impact origin for the Bear Swamp crater.
- © 2012 by The Society of Exploration Geophysicists
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.
[see – METEORITE]