Geological Map of the Bosumtwi impact crater

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Description

This map presents one of the best preserved and best-studied young meteorite impact craters on Earth. It was compiled by Christian Koeberl (University of Vienna, Austria) and Wolf Uwe Reimold (University of the Witwatersrand, Johannesburg, South Africa) and published – with a 40 page full color explanation booklet – by the Austrian Geological Survey.

The Bosumtwi impact structure is located in the Ashanti Province, Ghana, and was formed in 2.1-2.2 Ga Precambrian metasedimentary and metavolcanic rocks. The location lies in the forest zone of southern Ghana (centered at 06o30’N and 01o25’W) in West Africa. Bosumtwi is a very well preserved, only 1.07 Ma old complex impact crater of ca. 10.5 km diameter. The crater displays a pronounced rim and is almost completely filled by the about 8.5-km-diameter Lake Bosumtwi, which is up to 78 m deep in its central part. Bosumtwi is one of only 19 currently confirmed African impact craters and is associated with one of only four tektite strewn fields (the Ivory Coast tektite field) known worldwide.

Lake Bosumtwi has several important characteristics that make it well suited to provide a detailed record of climate change in an equatorial region. The lake developed in a hydrologically closed basin, and the deep water is anoxic, which has led to the preservation of laminated sediment varves in the lake sediments, providing a means for high resolution (annual) paleoclimate reconstruction.

Because of its importance for impact geology and paleoclimatology, Bosumtwi was recently the subject of an interdisciplinary and international drilling effort of the International Continental Scientific Drilling Program (ICDP). From the mid 1990s, renewed interest in Bosumtwi led to geological, geophysical, petrological, geochemical, and sedimentological studies of the impact crater, the associated impact breccias and geological structure, and lake sediments by several multinational teams. Remote sensing and geophysical measurements (gravity, magnetics, reflection and refraction seismics) provided abundant new data on the crater and its subsurface.

However, the only comprehensive regional mapping around Bosumtwi dates to the 1960s, when the geology of the environs of the lake was recorded on two separate map sheets. The purpose of the present work is to present a unified geological map that also includes new and updated information and emphasizes impact-induced deformation and known distribution of impact breccias.

Scale: 1:50 000
Size of the map: 86 x 61 cm
Map supplied folded with explanatory notes
Published as part of the 2005 Year Report of the Geological Survey of Austria
©Geological Survey of Austria (2005)
Topography© 1972 Survey Department, Ministry of Lands and Mineral Resources of Ghana