Alluvial Holocene terraces in eastern Maghreb : climate and anthropogenica controls
Résumé
There are usually two Holocene terraces along the watercourses of the eastern Maghreb. Ther lower Prehistoric Holocene terrace is present from the humid part of the Mediterranean climate to the lower Saharan zone. This feature is equivalent to the 'remblaiement holocène principal' as found in the southern French Alps. This terrace formed during a climatic period of greater humidity which lasted from the beginning of the lower Holocene (Boreal - 8300 BP) to the end of the Climatic Opitum (Atlantic - 5000 BP), or even perhaps the beginning of the Subboreal (3700 BP). In the Maghreb, the Pleniglacial period was generally arid and was followed by an increase in humidity during the Late glacial. The lower Prehistoric Holocene terrace developped during more humid conditions following the Late glacial period.
The very low Historical Holocene terrace is not found in the Saharan part of the eastern Maghreb. Its sediments began to accumulate from the 2nd century AD and commonly ceased formation in about the 6th century (1470 to 1350 BP). The sedimentological characteristics of these terraced sediments indicate deposition under similar conditions to the modern fluvial environment. As a result of the nature of human settlement and land use, the rate at which aggradation and incision took place was generally greater at this time than during the development of the lower terrace. The evidence suggests that only slight climatic variation resulted in alluviation because of the slope instability created by human activity. A second very low terrace developped locally after the High Islamic era (600 BP). River terraces of similar age have been noted from several locations around the Mediterranean Basin, in particular in the Lower Provence region of France.
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