TITLE:
Paleohydrological Reconstruction from Late Holocene Records in Interdune Lakes (N’Guigmi, Northern Bank of the Lake Chad, Niger)
AUTHORS:
David Sebag, Alain Durand, Zibo Garba, Eric P. Verrecchia
KEYWORDS:
Sahel; Lake Chad; Holocene; Mineralogy; Depositional Environments; Climate Change
JOURNAL NAME:
Open Journal of Geology,
Vol.3 No.2,
April
30,
2013
ABSTRACT: An old erg covers the northern part of the
Lake Chad basin. This dune landform allowed the formation of many interdune
ponds of various sizes. Still present in certain zones where the groundwater
level is high (e.g. Kanem, southern Manga), these ponds formed in the past a
vast network of lacustrine microsystems, as shown by the nature and the distribution
of their deposits. In the Manga, these interdune deposits represent the main
sedimentary records of the Holocene environmental succession. Their paleobiological
(pollens, diatoms, ostracods) and geochemical (δ18O, δ13C, Sr/Ca)
contents are often the basis for paleoenvironmental reconstruction. On the
other hand, their sedimentological characters are rarely exploited. This study
of palustro-lacustrine deposits of the Holocene N’Guigmi lake (northern bank of
the Lake Chad; Niger) is based on the relationships between the
sedimentological features and the climato-hydrological fluctuations. The
mineralogical parameters (e.g. calcium carbonate content, clay mineralogy) and
the nature of autochthonous mineralization (i.e. amorphous silica, clays, calcium carbonates) can be interpreted using a
straightforward hydro-sedimentary model. Established to explain the geochemical
dynamics of Lake Chad, this model is based on a biogeochemical cycle of the main elements (i.e. silicium, calcium) directly controlled by the local
hydrological balance (i.e. rainfall/evaporation
ratio). All these results show that a detailed study of sedimentological
features can provide important paleohydrological informations about the regional
aridification since ca 6500 14C BP.