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Synimpact-postimpact transition inside Chesapeake Bay crater

C. Wylie Poag
Synimpact-postimpact transition inside Chesapeake Bay crater
Geology (Boulder) (November 2002) 30 (11): 995-998


The transition from synimpact to postimpact sedimentation inside Chesapeake Bay impact crater began with accumulation of fallout debris, the final synimpact deposit. Evidence of a synimpact fallout layer at this site comes from the presence of unusual, millimeter- scale, pyrite microstructures at the top of the Exmore crater-fill breccia. The porous geometry of the pyrite microstructures indicates that they originally were part of a more extensive pyrite lattice that encompassed a layer of millimeter-scale glass microspherules--fallout melt particles produced by the bolide impact. Above this microspherule layer is the initial postimpact deposit, a laminated clay-silt-sand unit, 19 cm thick. This laminated unit is a dead zone, which contains abundant stratigraphically mixed and diagenetically altered or impact-altered microfossils (foraminifera, calcareous nannofossils, dinoflagellates, ostracodes), but no evidence of indigenous biota. By extrapolation of sediment- accumulation rates, I estimate that conditions unfavorable to microbiota persisted for as little as <1 k.y. to 10 k.y. after the bolide impact. Subsequently, an abrupt improvement of the late Eocene paleoenvironment allowed species-rich assemblages of foraminifera, ostracodes, dinoflagellates, radiolarians, and calcareous nannoplankton to quickly reoccupy the crater basin, as documented in the first sample of the Chickahominy Formation above the dead zone.

ISSN: 0091-7613
EISSN: 1943-2682
Serial Title: Geology (Boulder)
Serial Volume: 30
Serial Issue: 11
Title: Synimpact-postimpact transition inside Chesapeake Bay crater
Author(s): Poag, C. Wylie
Affiliation: U. S. Geological Survey, Woods Hole, MA, United States
Pages: 995-998
Published: 200211
Text Language: English
Publisher: Geological Society of America (GSA), Boulder, CO, United States
References: 28
Accession Number: 2002-079177
Categories: Stratigraphy
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. sketch maps
N37°00'00" - N37°45'00", W76°45'00" - W75°30'00"
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2019, American Geosciences Institute. Reference includes data supplied by the Geological Society of America, Boulder, CO, United States
Update Code: 200224
Program Name: USGSOPNon-USGS publications with USGS authors
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