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Upper Eocene impact horizon in east-central Georgia

¹ Department of Geology, University of Georgia, Athens, Georgia 30602-2501, USA
² J.M. Huber Corporation, Wrens, Georgia 30833, USA
³ Department of Space Sciences, Fernbank Science Center, Atlanta, Georgia 30307, USA

We report the discovery of shocked quartz grains in upper Eocene sediments from the Coastal Plain of east-central Georgia. The grains exhibit low refractive indices and contain one or more sets of planar deformation features formed during a hypervelocity impact. These grains were collected from a sand layer near the base of the Twiggs Clay Member of the Dry Branch Formation and most likely are ejecta from the Chesapeake Bay impact, which occurred between 35.7 and 36.0 Ma. In this layer, 1 in 250 quartz grains from the fine-sand size fraction and fewer medium-sand– sized grains show some evidence of shock metamorphism. This horizon could represent the source stratum for the Georgia tektites and potentially contains important evidence revealing the dynamics and environmental effects of the late Eocene cataclysm.

Key Words: impacts • shock metamorphism • Chesapeake Bay • ejecta • Atlantic Coastal Plain • tektites

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