Studies of drill cores of the Bosumtwi impact crater, Ghana

This is a multidisciplinary proposal to study drill cores from the Bosumtwi impact structure in Ghana, West Africa, within the framework of an international drilling project, led by the Principal investigator of this proposal. The Bosumtwi impact crater in Ghana (centered at 0632`N and 0125`W) is almost completely filled by Lake Bosumtwi. The crater has a rim-to-rim diameter of about 10.5 km, while the lake has a diameter of about 8 km and maximum depth of about 80 m. The crater has an age of 1.07 Ma and was excavated in lower greenschist facies metasediments of the 2.1-2.2 Ga Birimian Supergroup. The Ivory Coast tektites and microtektites originated from this crater. Only recently, detailed geophysical studies were done, which provided all the background work necessary to characterize the subsurface structure of the Bosumtwi crater that are necessary to define the targets for the deep drilling program proposed here. Deep drilling 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. Bosumtwi is the largest and best preserved young crater of this size, and may have a crucial diameter at the changeover between a traditional "complex" crater with a central peak and a crater structure that has a central peak-ring system. Drilling will allow to correlate previous and borehole geophysical studies and will provide material for geochemical and petrographic correlation studies between basement rocks and crater fill in comparison with tektites and ejected material. To obtain the goals outlined in detail in this proposal, nine 50 m to 1 km long cores will be recovered; total core length: 3 km sediments, 1 km impact-related rocks. Drilling will be undertaken using the DOSECC/ICDP GLAD-800 lake drilling system. Goals for the impact cratering studies include: a) crater morphology and geometry studies; b) petrographic and geochemical study of crater fill breccias and melts; c) geophysical studies (ground truth for seismic, gravity, magnetic, etc. studies); d) study of post-impact events; and e) astrobiological implications (extreme environments, recovery, planetary comparisons). Laboratory studies in Vienna wll concentrate mainly on aspect (b), the geochemical and petrographic studies, but as the overall drilling project leader, the PI of the present proposal will collaborate with a team of international colleagues on studies of the other impact-related aspects as well.

This is a multidisciplinary proposal to study drill cores from the Bosumtwi impact structure in Ghana, West Africa, within the framework of an international drilling project, led by the Principal investigator of this proposal. The Bosumtwi impact crater in Ghana (centered at 0632`N and 0125`W) is almost completely filled by Lake Bosumtwi. The crater has a rim-to-rim diameter of about 10.5 km, while the lake has a diameter of about 8 km and maximum depth of about 80 m. The crater has an age of 1.07 Ma and was excavated in lower greenschist facies metasediments of the 2.1-2.2 Ga Birimian Supergroup. The Ivory Coast tektites and microtektites originated from this crater. Only recently, detailed geophysical studies were done, which provided all the background work necessary to characterize the subsurface structure of the Bosumtwi crater that are necessary to define the targets for the deep drilling program proposed here. Deep drilling 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. Bosumtwi is the largest and best preserved young crater of this size, and may have a crucial diameter at the changeover between a traditional "complex" crater with a central peak and a crater structure that has a central peak-ring system. Drilling will allow to correlate previous and borehole geophysical studies and will provide material for geochemical and petrographic correlation studies between basement rocks and crater fill in comparison with tektites and ejected material. To obtain the goals outlined in detail in this proposal, nine 50 m to 1 km long cores will be recovered; total core length: 3 km sediments, 1 km impact-related rocks. Drilling will be undertaken using the DOSECC/ICDP GLAD-800 lake drilling system. Goals for the impact cratering studies include: a) crater morphology and geometry studies; b) petrographic and geochemical study of crater fill breccias and melts; c) geophysical studies (ground truth for seismic, gravity, magnetic, etc. studies); d) study of post-impact events; and e) astrobiological implications (extreme environments, recovery, planetary comparisons). Laboratory studies in Vienna wll concentrate mainly on aspect (b), the geochemical and petrographic studies, but as the overall drilling project leader, the PI of the present proposal will collaborate with a team of international colleagues on studies of the other impact-related aspects as well.