THE ROLE OF CONTINENTAL SCIENTIFIC DRILLING IN THE STUDY OF TERRESTRIAL IMPACT CRATERS

Currently ca. 170 impact craters are known on Earth; about one third of those structures are not exposed on the surface and can only be studied by geophysics or drilling. The impact origin of geological structures can only be confirmed by petrographic and geochemical studies; thus, it is of crucial importance to obtain samples of subsurface structures. In addition, also structures that have surface exposures often require drilling and drill cores, to obtain information of the subsurface structure, to provide ground-truth for geophysical studies, and to obtain samples of rock types not exposed at the surface. For many years drilling of impact craters was rarely done in dedicated projects, mainly due to the high cost involved. Structures were most often drilled for reasons unrelated to their impact origin. Only in the former Soviet Union a number of impact structures were drilled for scientific reasons, but in most of these cases the curation and proper care of the cores was not guaranteed. More recently by the International Continental Scientific Drilling Program (ICDP) has supported projects to study impact craters. ICDP has about a dozen member countries and supports a large variety of programs, including the study of impact craters. The first ICDP-supported study of an impact structure was the drilling into the subsurface Chicxulub impact crater, Mexico, between December 2001 and February 2002. The core retrieved from the borehole Yaxcopoil-1, 60 km SSW from the center of the structure, reached a depth of 1511 m and intersected 100 m of impact melt breccia and suevite, which has been studied by an international team. In the fall of 2004, the 10.5 km Bosumtwi crater, Ghana, is being drilled within an ICDP project. Drilling there is desirable for several reasons, including 1) to obtain a complete 1 million year paleoenvironmental record in an area for which so far only limited data exist; 2) to study the subsurface structure and crater fill of one of the best preserved large young impact structures. In late 2005 another ICDP-funded drilling project, at the 85-km-diameter Chesapeake Bay impact structure, eastern USA, will start; drilling to a depth of 2.5 km is anticipated. Later the El’gygytgyn structure (Russia) should be drilled. All these studies and international and interdisciplinary and provide important samples and data.