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Press Release
Meteorite Crater Drilling
Provides Extensive Samples - and a
Mystery
Drillings made in the Bosumtwi crater in Ghana, one of the youngest meteorite
craters in the world, led to yet another mysterious finding - the rock
formation caused by the heat of the meteoric impact is only half as thick
as expected. This is the first result from a large international drilling
project, which will provide new information simultaneously to both the
earth and climate sciences as a result of detailed planning. The technically
very demanding drilling operations were carried out during the past weeks
by a multi-national team led by an Austrian scientist, partially funded
by the Austrian Science Fund (FWF) within the International Continental
Drilling Program (ICDP). Over 2.2 km of drill core have been retrieved
and that will provide important material for detailed analyses.
The Bosumtwi crater in Ghana (West Africa) is interesting in many respects.
First of all, at an age of one million years it is one of the youngest
and best preserved impact craters on earth. Second, along with only three
other of the total 170 known impact craters on earth, it is associated
with a special geological feature - during the impact the uppermost rock
layers were melted and formed glass (so-called tektites), which are scattered
over a distance of over 1000 kilometres.
Climatic Archive Under Water
However, it is the third aspect that makes the Bosumtwi crater particularly
interesting - an eight-kilometre wide lake that fills the 11-km-diameter
crater. The Austrian principal investigator, Prof. Christian Koeberl of
the Department of Geological Sciences, University of Vienna, explains
the significance of this lake: "Sediments have been deposited in
this lake for a million years. According to the season, the sediment input
is dominated by the Atlantic monsoon or by the dust from the Sahel and
Sahara. Thus, this sedimentary layer offers a comprehensive archive of
the climate of the last one million years in West Africa."
Based on Data
This sedimentary layer now overlies the rocks formed by the meteoritic
impact. A two-step approach was taken to study both the climate record
contained in the lake sediments and the rocks that formed during the meteorite
impact event. The research team comprising members of seven nations has
been drilling from June to October 2004. First, a U.S. led part of the
team extracted lake sediment cores. Fourteen cores from six locations
yielded a total of 1850 metres of core samples, spanning the whole million-year
climate history contained in the lake sediments.
The logistically very challenging drilling in the impact-derived rocks
began under Prof. Koeberl's management at the end of August. Prof. Koeberl
explained the difficult logistics, which were supported by the International
Continental Scientific Drilling Program (ICDP): "In order to satisfy
all the requirements of the project, our team comprised up to 10 drilling
engineers, 10 geophysicists and 11 people just for the scientific analysis
on site. Moreover, in such a remote area as the Bosumtwi crater, the efficient
coordination of such a technically demanding project presented special
scientific and logistical challenges. For example, to allow the launching
and loading our floating drilling platform, we had to construct part of
a road and a special pier."
However the effort proved worthwhile; within just five weeks the team
managed to drill at two locations through the sedimentary layer and into
the impact-derived rock to depths of 540 and 452 metres, respectively.
This yielded over 350 m of "hard rock" core. Preliminary studies
of the available cores resulted in a big surprise - the layer with "impact
melt rock", which formed by melting of country rock during the meteorite
impact, is not as thick as expected from previous geophysical studies.
But only the detailed analysis of all the samples in the 122 core boxes,
which are currently on their way to Europe, will hopefully deliver the
answer to the question - why?
Scientific contact
Prof. Christian Köberl
Department of Geological Sciences
University of Vienna
Althanstraße 14
1090 Vienna, Austria
Tel: +43 -1 - 4277-531-10
E-mail: christian.koeberl@univie.ac.at
Austrian Science Fund (FWF)
Mag. Stefan Bernhardt
Distributor
PR&D - Public Relations for Research & Development
Campus Vienna Biocenter 2
1030 Vienna, Austria
Tel : +43 - 1 - 505 70 44
E-mail: contact@prd.at
Vienna, October 18, 2004
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