Mathematics – Logic
Scientific paper
Sep 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995metic..30r.562p&link_type=abstract
Meteoritics, vol. 30, no. 5, page 562
Mathematics
Logic
1
Crater, Chesapeake Bay, Oceanic, Tom Canyon, Impact Craters, Impacts, Late Eocene, Peak-Ring Crater, U.S. East Coast
Scientific paper
Two coeval(?) impacts produced craters on the middle late Eocene continental shelf of the United States at ~35 Ma. The smaller crater (1 5-20-km diameter) is buried beneath the New Jersey continental shelf, near Toms Canyon [1]; the larger crater (90-km diameter) lies beneath the floor of Chesapeake Bay, Virginia [2]. Both features are documented by seismic reflection profiles, bore-hole stratigraphy, and shock metamorphism. The Chesapeake Bay crater also is expressed by a distinctive bull's-eye gravity signature. The Toms Canyon crater exhibits atypical features attributable to an oblique impact into a water column 500-1000 m deep. Tektite-bearing sediment gravity flows, generated by the impact, have been cored 30 km southeast of the crater at Deep Sea Drilling Project Site 612 and Ocean Drilling Project Site 904 [3]. The Chesapeake Bay crater appears to be a typical peak-ring crater, as expressed on seismic profiles, but its gravity signature may indicate the presence of an irregular central peak, as well. Seismic profiles document the fault-bounded outer rim of the crater at four locations in the bay and two locations on the adjacent continental shelf, which constrains the position and geometry of two-thirds of the crater perimeter. Two seismic profiles show the presence of six secondary craters (1-5-km diameter) outside the crater rim. Depsite the large size of the Chesapeake Bay crater, there is no signal of global environmental distress or mass extinction associated with the impact. The postimpact strata immediately overlying the breccia lens, however, contain a record of local paleoenvironmental damage. A distinctive postimpact assemblage of agglutinated foraminifera is associated with a low-diversity, infaunal group of calcareous benthic foraminifera, plus abundant planktoninc foraminifera and radiolarians. This taphofacies reflects highly productive late Eocene surface waters (200-500 m deep), resulting in abundant organic matter and oxygen-poor conditions on the sea floor. Similar assemblages have been reported at some K-T boundary sites [4]. These primary and secondary craters are among the best preserved impact structures known on Earth and are relatively easily accessible to researchers. They should provide excellent future opportunities to improve our knowledge of both primary and secondary subaqueous craters and of the structural and sedimentological processes associated with their formation. References: [1] Poag C. W. and Poppe L. J. (1995) GSA Bull. [2] Poag C. W. et al. (1994) Geology, 22, 691-694. [3] Poag C. W. and Aubry M.-P. (1995) Palaios, 10, 1643. [4] Coccioni R. and Galeotti S. (1994) Geology, 22, 779-782.
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