Christian KOEBERL

1
BOSUMTWI IMPACT CRATER, GHANA THE 2004 ICDP
DRILLING PROJECT
Christian KOEBERL Dept. Geological Sciences,
University of Vienna, Vienna, A-1090,
Austria with B. Milkereit, J.T. Overpeck, C.A.
Scholz (ICDP PIs) and J. Peck, J. King, W.U.
Reimold, A. Deutsch, H. Newsom, P. Claeys, N.
Schleifer, P. Amoako..
2
An example of a successful interdisciplinary and
multinational drilling project, predominantly
supported by ICDP
3
ICDP SCIENCE TOPICS
4
Bosumtwi Impact Structure Location Ghana, West
Africa centered at 06o30'N and 01o25'W) Diameter
10.5 km Age 1.07 Ma Source of Ivory Coast
tektites
5
Panoramic View of Bosumtwi from the North
6

• Importance of Bosumtwi
• Largest young impact structure known on Earth
• Extremely well preserved (and accessible)
• All pre-drilling, site surveys already finished
• One of only 4 craters with tektites
• Sediment trap important location for
  paleoenvironmental studies

7
Lake Bosumtwi Impact Crater Drilling
Project Three groups working on Bosumtwi 1)
Impact Studies from 1995 (Austria, South Africa,
Finland, UK, USA, Ghana) 2) Geophysics of Crater
from mid 1990s (Germany, Ghana) 3)
Paleoclimatology Geophysics, late 1990s (USA,
Ghana) Surface studies exhausted in early 2000s
pool efforts for drilling multinational and
multidisciplinary study Submitted to ICDP as a
preproposal in 2000 Workshop proposal submitted
January 2001 Workshop held successfully in
September 2001 Full proposal submitted to ICDP
January 2002, approved mid 2002 Logistical
preparations started late 2002 Drilling and
geophysics early July early October 2004
8

• The Drilling Project Motivation and Goals
• to obtain detailed information on the subsurface
  structure and crater fill of one of the best
  preserved large young impact structures, to
  correlate these data with the geophysical studies
  that were recently completed or are in progress,
  to determine the presence and composition of melt
  bodies in the crater fill, and to perform
  comparative geochemical (including isotopic) and
  petrographical studies of the crater fill
  breccias, possible melt rocks, basement rocks,
  and known ejecta.
• to obtain a complete paleoenvironmental record
  over the duration of one million years in an area
  for which so far only limited data exist e.g., a
  detailed understanding of long-term variations in
  the West African monsoon.

9
Three aspects to drilling strategy 1) Acquire
two long cores into the deep structure of the
crater through the central uplift, and through
the annular moat. 2) In the sediment section
conduct a drilling transect from 25 m water
depth into the deep basin center, in order to
reconstruct all the intermediate and deep low
lake stand events over the past 1 million
years. 3) Acquire several cores in sedimentary
section of the deep basin, in order to facilitate
stacking of the anticipated long varved record.
This will yield an unparalleled record of
seasonal and annual climate variation extending
hundreds of thousands of years.
10
Multichannel seismic reflection profile (top)
with interpretation (bottom), from Scholz et al.
(2002)
11
Locations of proposed drill cores
12
Locations of proposed drill cores
13

• Drilling program goals
• (Impact Cratering Studies)
• Crater Morphology and Geometry Studies
• Study of Crater Fill Breccias and Melts
• Geophysical Studies
• (Ground Truth for Seismic, Gravity, Magnetic..)
• Study Post-Impact Events
• Astrobiological implications
• Extreme environments and extremophiles
• Regional impact-induced destruction
• Local trauma to living systems
• Climatic influence from impact event

14

• Drilling program goals
• (Paleoenvironmental Studies)
• 1 M.yr. high-resolution record lake level
  change Sahara/Sahel dust transport
  geomagnetics cosmic ray flux
• Biological evolution within lake basin
• High-resolution record of seasonal variability
  over several time windows
• Sensitivity to climatic forcing
• Catchment hydrological modeling
• Environmental background to human occupation in
  West Africa

15

• DRILLING AT BOSUMTWI
• societal benefits, as it provides
• understanding of the natural lake limnology
• range of impacts humans can have on limnology
• improved ability to predict future climate change
  
• and resulting consequences
• improved understanding of broader regional to
  global
• climate dynamics needed for better climate
  prediction
• understanding of the formation and local and
  regional
• effects of medium-sized impact craters
• education of local technicians, researchers,
• and students
• assistance with designing exhibits for a museum
• on the Bosumtwi structure
• related benefits for tourism (museum etc.)

16
Drilling Operations

• Permits 2003/4
• Shipping of equipment 3-6/2004
• Pier and road construction 5-6/2004
• GLAD-800 assembly 6-7/2004
• Sediment drilling 7.7. 29.8.2004
• Hard rock drilling ( geophysics)
  1.9. 2.10.2004
• Shipping of cores 10-11/2004

17
Sediment Sites Hard Rock Sites
18
1
2
Drilling Locations for Hard Rock (Impactite)
Aspects of Bosumtwi Drilling Program
19
(No Transcript)
20
(No Transcript)
21
(No Transcript)
22
GLAD-800 on Lake Bosumtwi
23
(No Transcript)
24
(No Transcript)
25
GLAD-800 on Lake Bosumtwi (C. Koeberl, 2004)
26
GLAD-800 on Lake Bosumtwi (C. Koeberl, 2004)
27
GLAD-800 on Lake Bosumtwi (C. Koeberl, 2004)
28
First impact melt breccia recovered, Bosumtwi
drilling project (C. Koeberl, 2004)
29
One of the impactite core boxes, Lake Bosumtwi
(C. Koeberl, 2004)
30
(No Transcript)
31
(No Transcript)
32
(No Transcript)
33
(No Transcript)
34
Bosumtwi Line 1
13
Stratigraphy of two central deep coreholes,
Bosumtwi drilling project (B. Milkereit, T.
Karp, and C. Koeberl, 2004)
35
Downhole logging
36
Preparation of airgun for VSP
37

• FIRST RESULTS FROM DRILLING AT BOSUMTWI
• 16 cores at 8 locations
• Depth record for GLAD800 at 540 m
• 2.2 km of lake sediment cores
• 350 m impactite/hard rock cores
• Layered/varved sediments to the bottom of
  sediment record potential to get 1 Ma climate
  record with annual resolution
• Found impact melt rock/breccia (magnetic anomaly)
  and suevites
• Thickness of impactites much less than expected
• Provides important ground truth for geophysics
• VSP measurements successful
• Scanning/logging from late November 2004
• Sampling party late January 2005
• First results in fall-winter of 2005

38
Processing sediment cores
Fish fossil at section break located at 240 m blf
Laminated (and most likely varved) lake sediments
from Bosumtwi core
39
Scanning in December 2004 at ICDP/GFZ Potsdam
40
Scanning in December 2004 at ICDP/GFZ Potsdam
Problem with moisture and cardboard boxes
41
Sampling party Jan. 24, 2005 Potsdam (Germany)
(hard rocks)
Core Scanning 12/2004
42
The Sediment Drilling Team
Group photo of sediment drilling team at Lake
Bosumtwi. Back row (l-r) Donald Bagley, James
Addo, Sylvester Blay, Dave Altman, Kevin
Loveland, Chris Walters (far back), Doug
Schnurrenberger, Adam Carey, Tim Shanahan Middle
row (l-r) Jannadi Lapukenu, Daniel Somuah, Eric
Boahen, Bernard Worlanyo, Anna Henderson,
Anthony, Kofi Front row (l-r) Jack Greenberg,
Chip Heil, Ailwasi Opoku, Kwame. Not Shown (on
shore) Phil Fox, Brad Hubney, Chris Delahunty.
(Photo J. Peck).
43
Bernd Milkereit
44
And thanks to many people on the hard
rock/geophysics team
Alex Deutsch
45
Philippe Claeys
Dona Jalufka
46
Horton Newsom and Paul Buchanan
47
Sylvester Danuor
Kwaku Atta Ntim
Daniel Boamah and Forson Karikari
48
Chris Delahunty, DOSECC On-site manager
Donald Bagley, Driller Helper
49
Egon Zech, Driller
Jack Greenberg, Kilindi Captain
50
Elizabeth LHeureux
Toby Karp
Refilwe Shelembe
51
And of course.
Uwe Reimold
52
AND MANY OTHERS!!
53
New Geological Map 150,000 With explanatory
booklet Compiled by C. Koeberl W.U.
Reimold Based on the original geological maps
(162,500) of the mid 1960s, with new geological
observations 1990-2004 In preparation to be
published summer 2005 by the Austrian Geological
Survey, Vienna
54
(No Transcript)
55
Geological Survey Department