Lake sediments on the Adamawa Plateau (Central Cameroon) as archives of climate change and the Bantu impact during the last 4000 years BP

This study investigates Late Holocene environmental changes in Central Cameroon induced by the combined effects of climate and human impact. For this purpose, sediments from lakes Dang, Massote, Fonjak and Ngaoundaba were studied through lithologic analysis including mineralogical composition and organic geochemistry combined with radiocarbon dates. From these analyses, the sediments at the base of lakes Massote and Dang cores are respectively dated to 4680–3530 and 4220–3580 cal yr BP, whereas the sediments of lakes Fonjak and Ngaoundaba seem to be younger, respectively dated to 3210–3000 and 1870–1740 cal yr BP. Lake sedimentation is dominated by organic matter (OM) poor deposits (OM < 3%) in the lower sections and OM-rich deposits (OM: 5–54%) in the upper sections. This shift from OM-poor to OM-rich sedimentation induced by climate variations occurred at 2800–2400 cal yr BP. The mineral assemblage is predominantly composed of kaolinite with minor contributions from chlorite, smectite, chlorite/smectite, illite/smectite, quartz, K-feldspar, gibbsite, plagioclase, siderite, hematite and goethite. These sediments are clastic, except for Lake Fonjak core sediments which correspond to peat intercalated with carbonate clay and clastic deposits. Age-depth models suggest that the sedimentation rate was 0.2 mm yr-1 for lakes Dang and Massote before 690–560 cal yr BP and 660–470 cal yr BP, respectively. Thereafter, it increased to 0.8 mm yr-1 in Lake Dang and 0.7 mm yr-1 in Lake Massote. Finally, Late Holocene environment changes in Central Cameroon consisted of the shift of open water lakes to marshy fringes with abundant vegetation induced by human activities and facilitated by increasing seasonality.