New data on the unresolved paradox of the Tibesti crater paleolakes (Central Sahara, North Chad)

Abstract:

Recent field work in the volcanic Tibesti Mountains opens a new chapter in the reconstruction of the last climatic cycles in the central Sahara and their lacustrine environments. For the first time, complete lacustrine sections were sampled in the 900 m deep crater of Trou au Natron at Pic Toussidé (3,315 m a.s.l.), and in 800 m deep Era Kohor, the major sub-caldera of Emi Koussi, the Sahara’s 3,445 m high peak (photo). The probed diatomites are located 360 and 125 m above the present-day bottom of the calderas. Studies in the 1960s suggested that lake levels in the Trou au Natron were 300-500 m high at 12,400-14,970 uncal. yrs BP. Such lake depths and resulting water volumes, however, are hardly conceivable in view of the limited intake area and precipitation-evaporation ratios which would have required local rainfall by far surpassing estimates for latitudes 19-21°N from the full-Holocene record of Lake Yoa situated 460 or 220 km southeast, and 1,550 or 2,450 m lower. The presentation will examine whether differences in altitude may explain unparalleled lake depths and postglacial humid conditions 4,000-7,000 years earlier than in the surrounding lowlands, and present alternative hypotheses of lake formation in this Saharan key region.