The Lake CHAd Deep DRILLing project (CHADRILL) – targeting ∼ 10 million years of environmental and climate change in Africa
At present, Lake Chad (∼ 13∘′ N, ∼ 14∘ E) is a shallow freshwater lake located in the Sahel/Sahara region of central northern Africa. The lake is primarily fed by the Chari–Logone river system draining a ∼ 600 000 km2 watershed in tropical Africa. Discharge is strongly controlled by the annual passa...
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Veröffentlicht in: | Scientific drilling (Hokkaido, Japan) Japan), 2018-10, Vol.24, p.71-78 |
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Zusammenfassung: | At present, Lake Chad (∼ 13∘′ N, ∼ 14∘ E) is
a shallow freshwater lake located in the Sahel/Sahara region of central
northern Africa. The lake is primarily fed by the Chari–Logone river system
draining a ∼ 600 000 km2 watershed in tropical Africa. Discharge
is strongly controlled by the annual passage of the intertropical convergence
zone (ITCZ) and monsoon circulation leading to a peak in rainfall during
boreal summer. During recent decades, a large number of studies have been
carried out in the Lake Chad Basin (LCB). They have mostly focused on a
patchwork of exposed lake sediments and outcrops once inhabited by early
hominids. A dataset generated from a 673 m long geotechnical borehole
drilled in 1973, along with outcrop and seismic reflection studies, reveal
several hundred metres of Miocene–Pleistocene lacustrine
deposits. CHADRILL aims to recover a sedimentary core spanning the Miocene–Pleistocene
sediment succession of Lake Chad through deep drilling. This record will
provide significant insights into the modulation of orbitally forced changes
in northern African hydroclimate under different climate boundary conditions
such as high CO2 and absence of Northern Hemisphere ice sheets. These
investigations will also help unravel both the age and the origin of the lake
and its current desert surrounding. The LCB is very rich in early hominid
fossils (Australopithecus bahrelghazali; Sahelanthropus tchadensis) of Late Miocene age. Thus, retrieving a sediment core from this
basin will provide the most continuous climatic and environmental record with
which to compare hominid migrations across northern Africa and has major
implications for understanding human evolution. Furthermore, due to its
dramatic and episodically changing water levels and associated depositional
modes, Lake Chad's sediments resemble maybe an analogue for lake systems that
were once present on Mars. Consequently, the study of the subsurface
biosphere contained in these sediments has the potential to shed light on
microbial biodiversity present in this type of depositional environment. We propose to drill a total of ∼ 1800 m of poorly to semi-consolidated
lacustrine, fluvial, and eolian sediments down to bedrock at a single
on-shore site close to the shoreline of present-day Lake Chad. We propose to
locate our drilling operations on-shore close to the site where the
geotechnical Bol borehole (13∘28′ N, 14∘44′ E) was
drilled in 1973. This is for two main reasons: (1) nowhere else in the C |
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ISSN: | 1816-3459 1816-8957 1816-3459 |
DOI: | 10.5194/sd-24-71-2018 |