Evolution morphologique des basses vallées de l'Atlas atlantique Marocain

Abstract

During a great part of the Quaternary period (from the Moghrebian = Plio-Pleistocene to the Ouljian = last Inter-glacial), the stages of cutting prevailed over those of accumulation in the low valleys of the Atlantic Atlas. It is rather difficult to join here continental deposits with the raised ancient sea-shore benches that are found, on the contrary, in many points. By means of those marine terraces, it is however possible to show the stages of uplift of that country : neotec-tonics explained the quickness of cutting in the valleys. After the Ouljian transgression, the correlations between alluvial and marine deposits allow to propose a relative chronology, rather precise. Some continental sediments extend more or less : the dunes (chiefly at the late Ouljian and at the early Holocene), the pink silts (at the late Wiirm) or the coarse alluvial deposits. Their succession cannot be explained by a single climatic or glacio-eustatic cycle. The possible causes of these successions of deposits are discussed and some interpretations and correlations presented here are tentative. difficult to join here continental deposits with the raised ancient sea-shore benches that are found, on the contrary, in many points. By means of those marine terraces, it is however possible to show the stages of uplift of that country : neotec-tonics explained the quickness of cutting in the valleys. After the Ouljian transgression, the correlations between alluvial and marine deposits allow to propose a relative chrono¬ logy, rather precise. Some continental sediments extend more or less : the dunes (chiefly at the late Ouljian and at the early Holocene), the pink silts (at the late Wiirm) or the coarse alluvial deposits. Their succession cannot be explained by a single climatic or glacio-eustatic cycle. The possible causes of these successions of deposits are discussed and some interpre¬ tations and correlations presented here are tentative.