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Lake Bosumtwi Drilling Project

 

Description

Lake Bosumtwi
(Photo ©:Christian Koeberl)

The Bosumtwi impact crater in Ghana is almost completely filled by Lake Bosumtwi with a rim-to-rim diameter of about 11 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 age. The Ivory Coast tektites and microtektites originated from this crater.  

Recent detailed geophysical studies provided a detailed image of the crater structure. Several projects have dealt with land- and lake-based geophysical measurements and surface geological and geochemical investigations. A shallow drilling project studied the near-surface composition of impact rocks. High-resolution seismic studies led to the discovery of a sediment-covered central uplift. Some shallow cores of lake sediments were also recovered. The results from these studies provided all the background work necessary to define the targets for the deep drilling program. 

Deep drilling was desirable for several reasons, including

  • to obtain a complete 1 million year paleoenvironmental record and
  • to study the subsurface structure and crater fill of one of the best preserved large young impact structures.

Bosumtwi is in a perfect location to reconstruct and investigate interannual through orbital-scale variations in

  • the West African monsoon,
  • hydrologic variations of the Sahel,
  • dust export from SW Africa, and
  • sea-surface temperature variations in the tropical East Atlantic.

Bosumtwi is one of only two known young craters 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 us to correlate all the 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.


 

Location

Africa, Ghana, Ashanti, Lake Bosumtwi

 

Coordinates

6° 30' N, 1° 25' W (Please scroll down to end of page for more information.)

 

Project Start and End
  • Phase I: Sediment Coring
    • Begin of drilling July 8, 2004
    • End of drilling August 8, 2004
  • Phase II: Impact Rock Coring
    • Begin of drilling September 17, 2004
    • End of drilling October 5, 2004

 

Programs and Funding

 

Principal Investigators
  • Christian Koeberl, University of Vienna, Center for Earth Sciences, Department of Lithospheric Research
  • Bernd Milkereit, University of Toronto, Department of Physics
  • Jonathan T. Overpeck, University of Arizona, Department of Earth Science
  • Christopher A. Scholz, Syracuse University, Department of Earth Sciences

 

Partners and Contractors

 

Keywords

Africa, BOSUMTWI, Climate Change, Ghana, Global Environment, ICDP-2002/08, Impact Crater, Lake Drilling, Paleoclimatology

 

Current State

Completed

 

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