EQUATORIAL EXTENSION OF THE YOUNGER DRYAS EVENT - ROCK MAGNETIC EVIDENCE FROM LAKE MAGADI (KENYA)

Magnetic parameters measurements (magnetic susceptibility chi and Isot hermal Remanent Magnetizations (IRMs) and sedimentological analyses ha ve been performed on Late Pleistocene/Holocene laminated deposits from Lakes Natron and Magadi (Kenya). Accelerator Mass Spectrometry (AMS) C-14 dating on the Total Organic Matter (TOM) locates a continuous lam inated sequence in the 12-10 ka B.P. time interval. The results show t he occurrence of a two-stepped lacustrine optimum. A first humid perio d, resulting in a high-stand above a 635 m altitude geographical barri er, reached its maximum between 12 and 11 ka B.P. Between 11 and 10.7 ka B.P., the lake level dropped below the 635 m altitude barrier, whic h resulted in the separation of Lake Natron and Lake Magadi. A second maximal high stand period occurred from ca. 10 ka B.P., at the beginni ng of Holocene times. The 11-10 ka arid event recorded in Lake Magadi confirms previous studies which suggested an equatorial extension of t he Younger Dryas event. Magnetic parameters and microfacies analyses s uggest that this event was produced by a progressive and general weake ning of monsoonal rainfall in East Africa.