thumbnail

Origin and emplacement of impactites in the Chesapeake Bay impact structure, Virginia, USA

Special Paper of the Geological Society of America

By:
, , ,
DOI: 10.1130/2008.2437(06)

Links

Abstract

The late Eocene Chesapeake Bay impact structure, located on the Atlantic margin of Virginia, may be Earth's best-preserved large impact structure formed in a shallow marine, siliciclastic, continental-shelf environment. It has the form of an inverted sombrero in which a central crater ???40 km in diameter is surrounded by a shallower brim, the annular trough, that extends the diameter to ???85 km. The annular trough is interpreted to have formed largely by the collapse and mobilization of weak sediments. Crystalline-clast suevite, found only in the central crater, contains clasts and blocks of shocked gneiss that likely were derived from the fragmentation of the central-uplift basement. The suevite and entrained megablocks are interpreted to have formed from impact-melt particles and crystalline-rock debris that never left the central crater, rather than as a fallback deposit. Impact-modified sediments in the annular trough include megablocks of Cretaceous nonmarine sediment disrupted by faults, fluidized sands, fractured clays, and mixed-sediment intercalations. These impact-modified sediments could have formed by a combination of processes, including ejection into and mixing of sediments in the water column, rarefaction-induced fragmentation and clastic injection, liquefaction and fluidization of sand in response to acoustic-wave vibrations, gravitational collapse, and inward lateral spreading. The Exmore beds, which blanket the entire crater and nearby areas, consist of a lower diamicton member overlain by an upper stratified member. They are interpreted as unstratified ocean-resurge deposits, having depositional cycles that may represent stages of inward resurge or outward anti-resurge flow, overlain by stratified fallout of suspended sediment from the water column. ?? 2008 The Geological Society of America. All rights reserved.

Additional Publication Details

Publication type:
Article
Publication Subtype:
Journal Article
Title:
Origin and emplacement of impactites in the Chesapeake Bay impact structure, Virginia, USA
Series title:
Special Paper of the Geological Society of America
DOI:
10.1130/2008.2437(06)
Issue:
437
Year Published:
2007
Language:
English
Larger Work Type:
Article
Larger Work Subtype:
Journal Article
Larger Work Title:
Special Paper of the Geological Society of America
First page:
73
Last page:
97
Number of Pages:
25