THE LATE HOLOCENE PALEOENVIRONMENT IN THE LAKE-NJUPI AREA, WEST CAMEROON - IMPLICATIONS REGARDING THE HISTORY OF LAKE-NYOS

Lake Njupi, 1 km east of Lake Nyos, on the Cameroon Volcanic Line, was formed by the damming of a local crustal depression. Two cores from L ake Nyos were analysed which penetrated sediments at the margin of the lake. The older deposits give an age of 3400 years BP and this date i s proposed as a minimum age for Lake Njupi. Sedimentological, palynolo gical and geochemical studies of a 2 m section provide an opportunity to reconstruct the Late Holocene environmental history. It is an organ ic-rich deposit (organic carbon up to 30%) with an abundant Silicospon gia spicules fraction. An obvious sedimentary homogeneity is interrupt ed by 5 fine to coarse layers with sandy quartz and lignitic remains. Such inputs were denoted by carbohydrate maxima or sometimes by phenol ic compounds. This study confirms the evidence of an arid period culmi nating between 2500 and 2000 yrs BP. This crisis began around 3000 yrs BP in the rain forest area of West Cameroon and also further to the s outh in Congo. Lake Njupi, situated today in a mostly grassland savann a environment known as the ''Grass Fields'', provides evidence for env ironmental changes from a mosaic of forest and savanna before 2500 yea rs BP to a savanna characterised by high grass pollen contents (75 to 85%), with small islands of forest. The mountain vegetation characteri sed by Podocarpus and Olea capensis retreated around 2300 years BP at the time Elaeis guineensis (the Oil Palm) began its extension as a pio neer tree, later providing opportunities for its domestication by man. (C) 1997 Elsevier Science Limited.