A slow environmental transition derived from changes in sedimentology and pollen assemblages in the Senegal River Delta about 6000 yrs BP

Palynological and mineralogical data from sections located in the N'Diael region, (Senegal River Delta) and exhibiting a peaty lever overlain by reddish sands, are presented. First they give the opportunity to confirm the radiocarbon dated sedimentological transition of peat mangrove facies to elastic continental beds at ca. 6600-6400 yrs BP. Secondly, because the pollen assemblage of the sandy sediments overlying the mangrove peat level is characterized by a high percentage of Poaceae and the absence of marine palynomorphs a dry, continental environment appears to have replaced the coastal tidal lagoon one; moreover, the clay mineral association of sandy levels points to a elastic origin by reworking of the surrounding ferralitic cover. The overall data allow to conclude to the gradual setting in of continental conditions and aridification of the studied area that seems to have begun soon after 6400 yrs BP and have reached a maximum ca. 5000 yrs BP.