[meteorite-list] Meteorite Crater Drilling in Ghana Provides Extensive Samples -- and a Mystery

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Wed Oct 20 19:57:45 2004
Message-ID: <200410202352.QAA11082_at_zagami.jpl.nasa.gov>

Austrian Science Fund (FWF)
Wien, Austria

Scientific contact:

Prof. Christian K?berl
Department of Geological Sciences
University of Vienna
Althanstra?e 14
1090 Vienna, Austria
Tel: +43 -1 - 4277-531-10
E-mail: christian.koeberl_at_univie.ac.at

The Austrian Science Fund (FWF)
Stefan Bernhardt M. A.
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1040 Vienna, Austria
Tel: +43 - 1 - 505 67 40-36
E-mail: bernhardt_at_fwf.ac.at

Distributor
PR&D - Public Relations for Research & Development
Campus Vienna Biocenter 2
1030 Vienna, Austria
Tel : +43 - 1 - 505 70 44
E-mail: contact_at_prd.at

October 18, 2004

Meteorite Crater Drilling Provides Extensive Samples -- and a Mystery

Vienna -- 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?

IMAGE CAPTION:
[http://www.fwf.ac.at/de/press/Images/pa1004.jpg (925KB)]
Satellite photos of the Bosumtwi crater in Ghana, West Africa
Received on Wed 20 Oct 2004 07:52:31 PM PDT