HR: 17:50h
AN: U34A-07    [Abstracts]
TI: The Chicxulub Impact Crater and Oblique Impact
AU: * McDonald, M
EM: mmcdon17@uwyo.edu
AF: University of Wyoming, Department of Geology and Geophysics, Department # 3006, 1000 University Ave., Laramie, WY 82071, United States
AU: Gulick, S
EM: sean@ig.utexas.edu
AF: The University of Texas, Institute for Geophysics, 10100 Burnet Rd. (R2200), Austin, TX 78758, United States
AU: Melosh, H
EM: jmelosh@lpl.arizona.edu
AF: The University of Arizona, Lunar and Planetary Laboratory, Tucson, AZ 85721, United States
AU: Christeson, G
EM: gail@ig.ig.utexas.edu
AF: The University of Texas, Institute for Geophysics, 10100 Burnet Rd. (R2200), Austin, TX 78758, United States
AB: Determining whether or not the Chicxulub impact was oblique (<45 degrees) will aid in our understanding of the environmental consequences 65 Ma. Planetary impact events, and impact simulations in the laboratory, show that oblique impacts have clear asymmetric ejecta distributions. However, the subsurface structures of the resultant craters are not well understood. In 2005, we acquired 1822 km of seismic reflection data onboard the R/V Maurice Ewing imaging the massive (200+ km) Chicxulub impact crater. The seismic profiles show that pre- crater stratigraphy outside the central basin of the Chicxulub impact crater is offset downward into the crater marking the post-impact slumping and formation of the terrace zone. The inward collapse of the Chicxulub terrace zone coincides with the outward collapse of the central uplift to form the peak ring. Chicxulub's peak ring is offset to the southeast, away from the deepest terrace zone mapped in the seismic data, suggesting that its peak ring was offset toward a more gradual wall of the transient cavity. Peak ring offsets, relative to crater center, of Venusian craters from radar images in the Magellan data set allow us to determine whether there are systematic variations in peak ring offset due to oblique impact. Ten pristine Venusian peak ring craters formed by oblique impact show that peak rings are offset both uprange and downrange, suggesting that peak ring position, and related subsurface asymmetries in the terrace zone, do not provide information about impact obliquity. This analysis supports the idea that Chicxulub's peak ring offset is a consequence of target properties and pre-impact structure and independent of impact trajectory.
DE: 5420 Impact phenomena, cratering (6022, 8136)
SC: Union [U]
MN: 2007 Joint Assembly