HR: 10:35h
AN: U22A-02    [Abstracts]
TI: Is the Chicxulub Crater Asymmetry due to Target Asymmetry or Oblique Impact? Insight From Numerical Modeling
AU: * Collins, G S
EM: g.collins@imperial.ac.uk
AF: Dept. Earth Science and Eng., Imperial College London, South Kensington Campus, London, SW7 2AZ, United Kingdom
AU: Morgan, J V
AF: Dept. Earth Science and Eng., Imperial College London, South Kensington Campus, London, SW7 2AZ, United Kingdom
AU: Wunnemann, K
AF: Museum fur Naturkunde, Humbolt University, Berlin, 10115, Germany
AU: Elbeshausen, D
AF: Museum fur Naturkunde, Humbolt University, Berlin, 10115, Germany
AU: Gulick, S
AF: Institute for Geophysics, University of Texas at Austin, Austin, TX 78758-4445, United States
AU: Christeson, G
AF: Institute for Geophysics, University of Texas at Austin, Austin, TX 78758-4445, United States
AU: Barton, P
AF: Dept. Earth Sciences, University of Cambridge, Cambridge, CB3 0EZ, United Kingdom
AB: We combine numerical modeling with seismic data interpretation to understand the formation of the Chicxulub impact crater, and, ultimately, the impact's role in the K/P mass extinction. Seismic data across the Chicxulub impact crater reveal that the crater structure varies around the offshore portion of the crater. The most striking azimuthal variation is in the position of the Cretaceous sediments that step down in a terrace from the crater rim to beneath the topographic peak ring (megablock zone). In the NW the megablock zone extends from 78-km to 42-km radius, with an average slope of 10 degrees; at its innermost point it is 9 km below the peak ring. In the NE the megablock zone is narrower (from 58-km to 42-km radius), and shallower (6.5 km below the peak ring) than in the NW. There also appears to be no crater rim in the NE quadrant. The azimuthal variation in crater structure may be a consequence of oblique impact, target asymmetry, or both. An oblique impact at Chicxulub might have released 2-10 times more volatiles into the atmosphere than a near vertical impact, due to focusing of high shock-pressures in near-surface rocks, with drastic consequences for global climate. However, the seismic data also reveal asymmetry in pre-existing geologic features of the target that correlate with the asymmetries in the final crater, which suggests a strong influence of the target on crater formation. In the NW, the broader terrace zone is associated with shallow Cretaceous bathymetry and a sediment thickness of 3-km, while in the NE the narrower terrace zone is associated with a deep, water-filled basin, overlying a thicker layer of sediments at the time of impact. We use 2D and 3D numerical impact models to examine whether impact angle or the observed pre-impact target asymmetry can explain the asymmetries in final crater structure. Our results suggest that the major asymmetries in the rim and megablock zone are a direct consequence of the sediment and water layer thickening from west to east.
DE: 5420 Impact phenomena, cratering (6022, 8136)
SC: Union [U]
MN: 2007 Fall Meeting