Correspondance entre les couples erosion-sedimentation et pluvial-aride au Sahara nord-occidental

Abstract

Abstract A climato-sedimentologic cycle is proposed on the basis of Villafranchian deposits in the northwest Sahara. The relationship between the erosion-sedimentation cycle and the pluvial-arid cycle is shown. The stratigraphy and sedimentation of the material composing the terrace deposits show an evolution toward increasing aridity, beginning with gravel deposits of a fluvial character and progressing toward typically arid sediments. The proposed cycle begins with a period of maximum aridity during which massive dunes cover the ancient terraces and hamadas, and debris from gravity erosion accumulates in cones. In the arid-pluvial transition period, humidity gradually increases, causing erosion of the slopes and debris cones. Maximum erosion occurs in the pluvial period. In the pluvial-arid transition period, sedimentation is at first fluvial, involving coarse-grained material, then loamy, and finally eolian. Lacustrine levels, crust formations and secondary rhythms are also recognized and briefly described. This cycle is confirmed by the prehistoric civilizations from the Pebble Culture to the Neolithic.