First chronostratigraphical data ofthe upper pleistocene deposits from the bandiagara cliff (mali, West Africa)

摘要

Pleistocene deposits at the base of the Bandiagara cliff (Dogon country, Mali) have never been accurately dated. This "glint", developed in Precambrian conglomeratic sandstones unconformably overlying the birrimian substratum, constitutes a major topographic obstacle. It was favorable to the deposition of aeolian sediments that were reworked during subsequent rainy seasons. Geomor-phological investigations along with prehistoric research helped to highlight both the stratigraphic and archaeological potentials of sandy sediments, which required an chronological framework established by OSL dating. The stratigraphic framework of Songona is compared with the Yame valley sediments (Ounjougou site) and, as hypothesis, with quaternary global palaeoclimatic curves. During marine isotope stages (MIS) 4 and 3 (between 85 and 30 ka), formations F2 and F3 buried the indurated sandy formation F1 (before 90 ka). Deposits from F2 and F3 formations testify to palaeoenvironmental conditions favorable to both aeolian sand deposition and to their local reworking. No deposit is recognized for period 30-7 ka. This sedimentary hiatus corresponds to the last dryness maximum. Archaeological data are also placed into the regional context. These data become integrated into the regional MSA knowledge acquired recently on the Ounjougou site(Yame valley).