Paleohydrological Reconstruction from Late Holocene Records in Interdune Lakes (N'Guigmi, Northern Bank of the Lake Chad, Niger)

David Sebag (1, 2) , Alain Durand (1) , Zibo Garba (3) , E.P. Verrecchia (4)

1 M2C - Morphodynamique Continentale et Côtière
2 HSM - Hydrosciences Montpellier
3 UAM - Abdou Moumouni University of Niamey = Université Abdou Moumouni de Niamey
4 Institut de Géologie et Paléontologie

An old erg covers the northern part of the Lake Chad basin. This dune landform allowed the formation of many inter- dune 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 dis- tribution of their deposits. In the Manga, these interdune deposits represent the main sedimentary records of the Holo- cene 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 char- acters 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 autoch- thonous mineralization (i.e. amorphous silica, clays, calcium carbonates) can be interpreted using a straightforward hy- dro-sedimentary model. Established to explain the geochemical dynamics of Lake Chad, this model is based on a bio- geochemical 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 impor- tant paleohydrological informations about the regional aridification since ca 6500 14C BP.

Mots clés: Climate Change; Depositional Environments; Sahel; Lake Chad; Holocene; Mineralogy

Domaines: Hydrologie; Climatologie; Minéralogie

David Sebag, Alain Durand, Zibo Garba, E.P. Verrecchia. Paleohydrological Reconstruction from Late Holocene Records in Interdune Lakes (N'Guigmi, Northern Bank of the Lake Chad, Niger). Open Journal of Geology, 2013, 3 (2), pp.143-155. ⟨10.4236/ojg.2013.32018⟩. ⟨hal-00842661⟩