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Abstract:

Two cores were recovered from deposits of the crater lake at Malha, in NW Sudan. One core was taken in the center of the lake (Core B), the other from a more marginal area (Core Y). In both cores, two main units are distinguished, each comprising the sediments of three distinct lacustrine phases. The first three lake stages (Periods I, II and III), all ending with lowstands or phases of complete dryness, are characterized by the deposition of mainly laminated sediments in a meromictic lake. During Periods IV, V and VI, the lake was holomictic and hyper- to mesosaline.

Mineral magnetic data for the cores allow us to trace several correlatable horizons that coincide with boundaries between the main lacustrine phases. Most peaks in magnetic susceptibility (χ) and saturation isothermal remanent magnetization (SIRM) are accompanied by shifts of the reverse field ratios to more negative values. These features indicate an increased supply of coarser grained detrital material to the coring sites, and correspond to periods when lake levels were either fluctuating or very low.

Only two radiocarbon dates are available for the entire Malha record: 8,290 ± 155 l4C years BP for 921-cm depth in Core Y, and 2,940 ± 70 l4C years BP for 643-cm depth in Core B. These two dates imply that the first lake desiccation, at the end of Period I, took place at ~7,000 years BP, and that the second lake desiccation, marking the boundary between Periods III and IV, occurred at ~2,200–2,300 years BP.

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