Mathematics – Logic
Scientific paper
Dec 2007
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007agufm.u22a..03g&link_type=abstract
American Geophysical Union, Fall Meeting 2007, abstract #U22A-03
Mathematics
Logic
1027 Composition Of The Planets, 1060 Planetary Geochemistry (5405, 5410, 5704, 5709, 6005, 6008), 3025 Marine Seismics (0935, 7294), 3036 Ocean Drilling, 5420 Impact Phenomena, Cratering (6022, 8136)
Scientific paper
Formation, release of volatiles, and subsequent collapse of the 65 Ma Chicxulub impact crater are of key interest due to the impact's role in the Cretaceous-Paleocene (K/P) mass extinctions. Seismic data acquired in 1996 and 2005 image the buried and surprisingly asymmetric final crater, and highlight key features that are the target of proposed IODP-ICDP drilling. Gravitational collapse of the transient crater created a terrace zone consisting of faulted slump blocks that reach the greatest depth in the northwest part of the crater. Lying above the terrace zone closer to the center of the crater is the topographic peak ring; a geometry that suggests interaction of the inward slumping terrace zone and the rebounding central uplift is important for the formation of the peak ring. The peak ring rises higher above the crater floor in the west and northwest relative to the east and northeast. A Cenozoic basin overlies the peak ring and crater floor within the inner rim in all imaged azimuths except north and northeast where the inner rim is absent. The K/P surface, defined based on mapped reflections that correlate with the base of the Cenozoic basin, shows significant pre-existing relief on the Cretaceous seafloor. This relief appears to correlate with the observed asymmetries in terrace zone depth, peak ring relief and lack of a crater rim to the north and northeast, and therefore suggests that target heterogeneities strongly influence final crater structure. Reflectivity is present beneath the topographic peak ring along all imaged azimuths that may represent a lithologic base of the peak ring material, or a marker for an extinct hydrothermal system. Asymmetry in the peak ring allows for sampling the lithologies beneath the topographic peak ring at relatively shallow depths in order to explain how the proposed deep crustal material can result in lower velocities and densities than the surrounding impact rocks. Bright, discontinuous reflections to the interior of the topographic peak ring may represent the top of the impact melt sheet that lies beneath potential re-surge deposits and is thought to cap the central uplift observed on seismic and gravity data. A proposed IODP-ICDP drilling transect plans to penetrate and sample the shallowest peak ring and underlying dipping reflectivity in the offshore and the Cenozoic sediments deposits, potential surge deposits, melt sheet, and if possible the central uplift onshore to calibrate existing models for impact crater formation and the mass extinction.
Barton Penny J.
Christeson G. C.
Gulick Sean P. S.
McDonald Michael
Mendoza-Cervantes K.
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