EVOLUTION OF THE NIGER DELTA MARGIN DURING THE LATE PLEISTOCENE-HOLOCENE: NEW PALYNOLOGICAL EVIDENCE

Deep sea and delta shelf sediments deposited along the Gulf of Guinea margin are vital records for characterising terrestrial and marine palaeoclimate signals. A multi-proxy approach (sedimentology, geochemistry, calcareous plankton and palynomorphs) was carried on three cores collected in the Niger sea delta to understand the land-ocean correlation as well as to detect abrupt climate variability in relation to the West African monsoonal system. Our data indicate that sea level was lower than present day during the Late Pleistocene (NN 19 = MIS 2) until the early Holocene (NN 20 = MIS 1), when sea level rose and humid conditions were established. The system stabilised around the Middle Holocene (NN 21 = MIS 1).

An increase in Ti/Zi ratio and Poaceae as well as the decrease in the Rhizophoraceae and Fe/S ratio suggests an open vegetation - grassland, strong erosional context and wind transported pollen source from the hinterland catchment area to the Niger Delta during NN19 = MIS 2. This assumption is in agreement with the dry climate, weak WAM, lowering of SSTs in the Gulf of Guinea and southward seasonal migration of ITCZ. Conversely, the sharp increase in the Rhizophoraceae and Fe/S ratio, and the sporadic drop - decrease in the Ti/Zi ratio and Poaceae during the last deglaciation - indicates an overall reduction in the erosion from the hinterland catchment. The resultant control in the expansion of the Rhizophoraceae is due to the increase of pyrite (FeS ) content, warm climate and sea level rise.

Additionally, our vegetation records show that the period of reduction in mangrove vegetation and some fresh water swamp vegetation is marked by an increase in sedimentation rate. The inferred hinterland vegetation shows arid / cold climate conditions during the Northern Hemisphere H1 and YD events, while a shift to the littoral vegetation indicate humid conditions during the African Humid Period.