HR: 11:20h
AN: U22A-05    [Abstracts]
TI: Chicxulub Crater Infilling and Yucatan Carbonate Platform Development: Implications for the Evolution of Large Terrestrial Impact Craters
AU: * Whalen, M T
EM: mtwhalen@gi.alaska.edu
AF: University of Alaska Fairbanks, Dept. of Geology and Geophysics 900 Yukon Dr., Fairbanks, AK 99775-5780, United States
AU: Pearson, Z F
EM: ftzfr@uaf.edu
AF: University of Alaska Fairbanks, Dept. of Geology and Geophysics 900 Yukon Dr., Fairbanks, AK 99775-5780, United States
AU: Gulick, S P
EM: sean@ig.utexas.edu
AF: Institute for Geophysics University of Texas at Austin, J.J. Pickle Research Campus 10100 Burnet Rd. (R2200), Austin, TX 78758-4445, United States
AU: Norris, R D
EM: RNorris@ucsd.edu
AF: Scripps Institution of Oceanography, 301 Vaughan Hall, MS-0244, La Jolla, CA 92093- 0244, United States
AB: Stratigraphic analysis of the Yaxcopoil-1 core and seismic analysis of offshore 2D seismic data provide insight into the Tertiary infilling history of the Chicxulub impact basin. High-resolution logging of the carbonate-dominated rocks in Yax-1 provides details of the litho- and bio-stratigraphy and permits a preliminary Tertiary sequence stratigraphic analysis of the basin. Seismic analysis provides a broader view of Tertiary basin infilling and the history of Yucatan carbonate platform development. We have identified 10 lithofacies and 5 lithostratigraphic units based on data from the core and examination of 150 thin sections. Lithofacies are categorized as either redeposited or background facies. Redeposited facies include a wide variety of coarse and finer-grained gravity flow deposits while fine-grained background facies were deposited mainly from suspension. Depositional environments range from a steep, bathyal slope inside the Chicxulub crater inner rim to a neritic, outer carbonate ramp setting once the YucatÃÆ' n platform prograded seaward. We have identified 5 depositional sequences based on preliminary sequence stratigraphic analysis of the Tertiary succession in the core. Equivocal biostratigraphic data indicate that sequences 1-3 range from Early Paleocene to Early Eocene in age. The bases of sequences 1-4 contain redeposited carbonates interpreted as lowstand deposits. Sequences 4 and 5 consist mainly of background and fine-grained redeposited facies. By the top of sequence 4 it appears that the Yucatan platform had prograded over the position of the Yax-1 core. Seismic analysis identified at least 6 seismic units, the lower 5 of which appear to roughly correlate with the 5 lithostratigraphic units in the Yax-1 core based on available P-wave velocity data. The seismic stratigraphic analysis shows two major patterns of post-impact deposition within the basin. The earlier one is controlled by the underlying crater morphology where major accumulation (units A and B) is on both sides of the peak ring and infilled the western and central parts of the basin first. Later sedimentation is potentially controlled by changes in sea level as suggested by the deposition of clinoforms (unit C) and regional unconformities (top units C, D, E). The timing of the switch from impact-dominated to sea level-dominated sedimentation occurs within seismic unit C. If Chicxulub is representative, large marine impacts in tectonically quiescent regions may dominate local depositional environments for millions to tens of millions of years before returning control to eustasy. These successions will likely record shoaling and reduction of slope as the instantaneously created impact basin is filled over geologic timescales. Remarkably, most of the topographic scar along the southern Chicxulub crater margin appears to have been annealed within 10-15 Ma after the impact.
DE: 3002 Continental shelf and slope processes (4219)
DE: 3022 Marine sediments: processes and transport
DE: 3025 Marine seismics (0935, 7294)
DE: 5420 Impact phenomena, cratering (6022, 8136)
SC: Union [U]
MN: 2007 Fall Meeting