The Sedimentary Record of Meteorite Impacts

Origin and emplacement of impactites in the Chesapeake Bay impact structure, Virginia, USA
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Published:January 01, 2007
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CiteCitation
J. Wright Horton, Jr., Gregory S. Gohn, David S. Powars, Lucy E. Edwards, 2007. "Origin and emplacement of impactites in the Chesapeake Bay impact structure, Virginia, USA", The Sedimentary Record of Meteorite Impacts, Kevin R. Evans, J. Wright Horton, Jr., David T. King, Jr., Jared R. Morrow
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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 acousticwave 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.
- acoustical waves
- Atlantic Ocean
- boreholes
- breccia
- Cenozoic
- Chesapeake Bay
- Chesapeake Bay impact structure
- cores
- ejecta
- Eocene
- erosion
- fluidization
- fragmentation
- impact breccia
- impact craters
- impact features
- impact melts
- impactites
- impacts
- liquefaction
- marine environment
- melts
- metamorphic rocks
- metamorphism
- Paleogene
- resurgence
- sedimentation
- shelf environment
- shock metamorphism
- suevite
- Tertiary
- United States
- upper Eocene
- Virginia
- Chickahominy Formation
- Exmore Beds
- annular trough