Mathematics – Logic
Scientific paper
May 2005
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005agusm.p11a..02m&link_type=abstract
American Geophysical Union, Spring Meeting 2005, abstract #P11A-02
Mathematics
Logic
5420 Impact Phenomena (Includes Cratering)
Scientific paper
The terrestrial record is the only source of 3-D ground truth observations on the lithological and structural character of natural impact structures. Of the three largest known impact craters on Earth, Chicxulub is the best preserved because of a slow burial on a tectonically quiet carbonate platform. Our proposal is to drill two wells that address fundamental issues about the structure of the Chicxulub impact crater and its environmental effects. CHICX-01A will focus on constraining the environmental effects of the impact. Current emphasis is on the potential effects of vapor species derived from shocked carbonates and sulfates. Chicx-01A will supply a complete litho-stratigraphic section of the offshore sedimentary portion of the target. Anhydrite is likely to be the most lethal component of the target rocks, but estimates of its constituent percentage range between 10 and 40 %. Half of the crater lies offshore, and seismic indicate that the Mesozoic section is > 1-km thicker offshore than onshore. The thicker the sedimentary layer, the greater the volume of potential pollutants released. If we drill Chicx-01A, we will be able to calibrate the marine reflection data, in terms of depth, strata and lithology, and be better able to convert travel-time to depth for the entire marine reflection dataset. Onshore drilling at Yaxcopoil-1 penetrated 600 m of late Cretaceous calcarenite, dolomite and anhydrite rocks. These data are of significant value in establishing the chemistry of the uppermost section of target rock, and will serve as a baseline for onshore-offshore comparisons if Chicx-01A is drilled. CHICX-02A is specifically designed to sample the peak ring and provide information to constrain formational processes. It is widely believed that peak rings form from hydrodynamic collapse in some form of extension of the structural uplift process that leads to central peaks in smaller complex craters. However, annular rings within terrestrial craters correspond to different morphological elements and this diversity, as well as a lack of common understanding as to what constitutes the planetary equivalent of a peak ring, means that there is currently no consensual agreement on the nature of a topographic peak ring. Drilling through the peak ring at Chicxulub will answer this fundamental cratering question. Geophysical property measurements on the core will be used to improve 3D structural models of the central crater. Of particular interest is the source of the short-wavelength magnetic anomalies that appear to track the peak ring, and may represent enhanced hydrothermal circulation. Our high-resolution 3-D seismic survey, shot in early 2005, will place the drill-hole in its correct structural context. Understanding the mechanism for peak-ring formation is fundamental to understanding cratering. When we can model crater formation in detail, we can better use craters as a diagnostic tool for understanding the surface evolution of the other terrestrial planets. Subtle differences in crater morphology between different planetary bodies provide clues to their near-surface rheology.
Barton Penny
Christeson Gail
Grieve Richard
Gulick S. S.
Melosh Jay
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