| Abstract: | 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. |
| Genre: | Article |
| ProdID: | 70024176 |
| Citation Author: | Poag, C. W. |
| Citation Contributing Office: | |
| Citation Datum: | |
| Citation Day: | |
| Citation Edition: | |
| Citation Editor: | |
| Citation End Page: | 998 |
| Citation Issue: | 11 |
| Citation Keywords: | |
| Citation Language: | English |
| Citation Larger Work Title: | Geology |
| Citation LatN: | |
| Citation LatS: | |
| Citation LonE: | |
| Citation LonW: | |
| Citation Month: | |
| Citation No Pagination: | |
| Citation Number Of Pages: | 4 |
| Citation Online Only Flag: | |
| Citation Phsyical Description: | |
| Citation Projection: | |
| Citation Public Comments: | |
| Citation Publisher: | |
| Citation Series: | |
| Citation Series Code: | |
| Citation Series Number: | |
| Citation Search Results Text: | Synimpact-postimpact transition inside Chesapeake Bay crater; 2002; Article; Journal; Geology; Poag, C. W. |
| Citation Start Page: | 995 |
| Citation Volume: | 30 |
| Citation Year: | 2002 |
| Type: | citation/reference |
| Text: | Synimpact-postimpact transition inside Chesapeake Bay crater; 2002; Article; Journal; Geology; Poag, C. W. |
| URL (THUMBNAIL): | http://pubs.er.usgs.gov/thumbnails/outside_thumb.jpg |
| URL (DIGITAL OBJECT IDENTIFIER): | http://dx.doi.org/10.1130/0091-7613(2002)030<0995:SPTICB>2.0.CO;2 |
| Date Other: | Tue, 1 Jan 2002 00:00 -0600 |
| Publisher: | |
