Beschreibung
The birth of the Chicxulub multiring impact basin approximately 65 million years ago represents one of the most dramatic events in Earth's history since the onset of the Phanerozoic. Because Chicxulub is relatively young and because it formed in an area of active deposition, its interior morphology has been shielded from the effects of erosion and tectonics. Study of this basin, therefore, offers us a unique opportunity to gather new and important constraints on the nature of such large multiring impact basins and how their formation affects geological and biological evolution. We propose to drill a 2.5 km deep core hole into the southern part of the crater, located approximately 60-70 km radius from the basin center and between Pemex drill holes Ticul 1 and Y6. The primary coring goal of CSDP is to recover a complete sequence of impact-generated rocks overlying the downfaulted Mesozoic target rocks from within the crater. This would provide the first complete section through the sequence of melt-rocks and breccias at any large (>50 km) impact crater. Scientific evaluation of these core samples as well as complementary studies will help to:(1) test the link between the Chicxulub crater and the global K/T boundary layer and to unravel Chicxulub's role in the K/T boundary mass extinction event, and (2) to study the Chicxulub cratering event, as an unique example of the formation of a large impact crater on Earth, with important implications for large-scale cratering processes and ejecta distribution on Earth and other planetary bodies. Another important goal is to recover a continuous section through the Tertiary cover rocks above the impactites, from which information about post-impact faunal recovery and long-term modification of the crater can be gleaned. Finally, we hope to penetrate into the upper part of the disturbed Cretaceous platform rocks below, in order to provide additional constraints on target-rock compositions and deformation styles characteristic of the regions flanking the collapsed central excavation cavity of the impact basin. The administration of the project is defined by a joint research venture between UNAM on behalf of the PI's and GFZ-Potsdam on behalf of ICDP. Responsibility for the scientific success of the project lies with six PI's (List names and affiliations). They will be assisted by a science team consisting of approximately 70 scientists from around the world. This team will study the samples collected, as well as conduct experiments and do field work both at the borehole and in surrounding regions. Based on the research proposals submitted by the science team, the science has been grouped into six working areas, each with an assigned team leader: 1) Geophysics (J. Morgan, Imperial College, U.K.); 2) Regional geology, stratigraphy, and field geology (P. Claeys, University of Bruxelles, Belgium); 3)Paleontology and sedimentology (F. Vega Vera, UNAM, Mexico), 4) Structural geology and numerical modeling of crater formation and environmental effects (B. Ivanov, Russian Academy, Moscow); 5) Petrography, mineralogy and geochemistry of impact related rocks (C. Koeberl (University of Vienna, Austria)/U. Reimold (University of Witwatersrand, South Africa); and 6) Isotope geochemistry and age-dating (P. Layer, Univ. of Alaska, USA). It is anticipated that the hole will be drilled during September-October, 2001. A drilling contractor in Mexico has been retained for the actual drilling and site preparation, and several options for top-drive core recovery systems are being considered with core diameters of 8-10 cm. The hole will be continuously cored beginning at approximately 400 m depth. Standard wireline logging will be carried out by GFZ-Potsdam. Cores will be housed for study and archiving at UNAM, Mexico City. The estimated cost of the drilling is approximately $1.5 million (US). Prior to the drilling a workshop will be organized in Mexico City to orient all interested parties in the drilling operations, plus core handling and core descriptions.