Holocene climatic changes in an archaeological landscape: The case study of Wadi Tanezzuft and its drainage basin (SW Fezzan, Libyan Sahara)

Recharge of aquifers in the SW Fezzan dates back to the last millennia of the Late Pleistocene and to the very beginning of the Holocene, with a consistent delay between the mountain area (at the beginning) and the ergs. Since that period and up to the end of the fifth millennium BP, the whole area of the Wadi Tanezzuft and of its basin, including mountain ranges and low lands (ergs and pediments), consisted of a wet savannah, and in the low lands displayed a continuous belt of ponds and lakes. During this period, all the physiographic units of the landscape were exploited by hunters and collectors and later, much more intensively, by pastoral communities. Apart from two minor dry episodes, the whole area dried out around 5000 years BP. The wadi Tanezzuft was substantially reduced in discharge and size, but its main course was still fed with water for about three millennia, and during the third millennium BP it was a green oasis about one hundred kilometres long; and for this reason it was intensively settled by the Late Pastoral communities and later by the Garamantes. The different behaviour of the Tanezzuft valley in comparison with the surrounding areas is to be attributed to the fact that it is the main outlet of the Eastern Tassili hydrographic basin, whose water reserve was recharged during the wet Holocene and reduced, but not exhausted by the onset of aridity at 5000 years BP.During the first centuries AD the size of the oasis was strongly reduced as a consequence of the final depletion of water reservoirs. However strong wind erosion, which is the present dominant geomorphic process, began in the late medieval period.