Asymmetric Structure of the Chicxulub Impact Crater: Possible Causes of Heterogeneity and Targets for Drilling
Abstract
Formation and subsequent collapse of the 65 Ma Chicxulub impact crater are of key interest due to the impact's role in the K-T mass extinctions and Chicxulub being the only preserved large impact crater currently accessible in the solar system. Seismic reflection profiles acquired in 1996 and 2005 image the buried, asymmetric structure of the crater and highlight key features that are the target of proposed IODP-ICDP drilling. The impact crater consists of a series of arcuate, listric faults that roughly cluster into exterior ring(s) (radii 117-144 km), outer ring(s) (97-123 km), and inner ring(s) (67-98 km). At depth, the rings in the western part of the crater sole into one or two mid-crustal detachment surfaces overlying reflective lower crust while in the eastern part the rings are all deep rooted and nest inside each other like bowls. The inner ring of the crater forms the crater rim in all azimuths except the north and northeast. The deep crater floor inside the rim allowed for the accumulation of a Cenozoic basin in the center of the crater subsequent to impact. Gravitational collapse of the initial crater (known as a transient crater) created a terrace zone consisting of 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 peak ring, which rises higher above the crater floor in the west and northwest relative to the east and northeast. Dipping reflectivity is present beneath the topographic peak ring along all imaged azimuths defining the thickness of the peak ring material. This material, which is likely some combination of breccia and melt, is significantly thicker in the west and northwest and thinner in the east and northeast. In all azimuths the terrace zone reflectors underlie and are truncated by the dipping reflectivity at the base of the peak ring suggesting a causal relationship. One primary drilling target is to determine the nature of the peak ring material and the processes of its formation by sampling the entire section down to the dipping reflectivity. Mapping of the K/P surface yields insights into the bathymetric variation at the time of impact allowing for the suggestion that heterogeneities in the target resulted in many of the asymmetries in the rings, terrace zone, and peak ring. Links with the extinction event require investigation into content of the ejecta and vapor plume, which may have included higher water content than previously suspected, and into the total energy of the event; the latter is a goal of the onshore drill site.
- Publication:
-
AGU Spring Meeting Abstracts
- Pub Date:
- May 2007
- Bibcode:
- 2007AGUSM.U34A..03G
- Keywords:
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- 1817 Extreme events;
- 3025 Marine seismics (0935;
- 7294);
- 5420 Impact phenomena;
- cratering (6022;
- 8136);
- 5470 Surface materials and properties;
- 8136 Impact phenomena (5420;
- 6022)