THE DESERT LOESS RECORD OF CLIMATE AND HUMAN IMPACT - EXAMPLES FROM SINAI PENINSULA AND LANZAROTE (CANARY ISLANDS)

Desert loess or loess-like silt in desert environments is increasingly recognised as a record of paleoecology and paleoclimate in lower latitudes. Dating of these deposits has so far been rare mainly due to the lack of datable organic material.

Luminescence (TL, IRSL) dating has been applied to thick sequences of silt-paleosol sequences in the Wadi Feiran (Sinai Peninsula) and Lanzarote (Canary Islands). In both areas past shifts to slightly more humid conditions are witnessed by paleosols and mineralogical and geochemical data. In the Wadi Feiran, the sedimentation of up to 55 m thick silt took place during MIS 2, and intercalated paleosols are only weakly developed humic horizons. In Lanzarote both, very weakly and very intensively developed paleosols are found. The sequences dated so far range between ca. 200 and ca. 5 ka. Intensive soil formation occurred during MIS 3 and, apparently, during MIS 7. Weaker cambic soils developed during the lower and middle Holocene and apparently during MIS 5. Periods of stronger desert loess accumulation apparently started shortly after the maximum of an interglacial, but the strongest desert loess input coincides with the "Erg Ogolien" arid phase (late MIS 2) in North Africa.

The arrival of man to Lanzarote during a lower or middle Holocene moister period between 10 and 5 ka is deduced from numerous finds of ovicaprid bones. The first human occupation occurred thus much earlier than proved from the archaeological record so far. It resulted in disastrous soil erosion and land degradation long before the colonial age. The early onset of soil erosion affecting a very sensitive semi-arid ecosystem could have been enhanced by more arid conditions since ca. 5 ka. More closely spaced luminescence dating will improve our understanding of the paleoecology and man-environment interaction.