Oscillations of lake chad over the past 50,000 years: New data and new hypothesis

A recent sedimentological study of the Chari deltas area allowed an evaluation of the oscillations of palaeolake Chad over the past 50,000 years. Three maximum lake levels at circa 38,000, 22,000 and between 12,000 and 8000 years B.P. have been described. The levels reached by these large lakes were never very high, and there has not been any major variation over the last 8000 years. The hypothesis regarding a huge palaeolake Chad of 320,000 km2 reaching the 320-m level at circa 6000 years B.P. (instead of the present 279.5–282 m and approximatively 20,000 km2), is discussed and discarded on basis of stratigraphical, sedimentological, geomorphological, hydrological and geophysical arguments. Taking into account geophysical data and the deep structures of the basin, a new interpretation is proposed for the “perilacustrine dune ridge” which was considered to run along the shoreline of the 320-m level.