Onema Adojoh1, Fabienne Marret1, Robert Duller1, and Peter Osterloff2
1School of Environmental Sciences, University of Liverpool, Liverpool, L69 7ZT, UK
2Shell UK Limited, Aberdeen, AB12 3FY, UK
Evolutionary history of deltas are particularly sensitive to climate and sea level change, which can be expressed with change in the shelf morphology and the associated terrestrial components. However, the evolutionary history of the Niger delta over the last 20, 000 years based on the timing of the land-sea interaction has been a thing of debate due to poor understanding on the influence of West African Monsoon (WAM) circulation.
Our study describes the sedimentary records of the three gravity cores (GC) approximately 3m in length. The lithology shows dominant mudstones facies variations which could have been triggered by the mid to Early Holocene transgression (middle to the topmost part of the three GC) during the interglacial period supporting the assumption of a strengthened WAM, subsequent delta retrogradation and Nouakchottian transgression in Senegal.
During the Late Pleistocene regression, the bottom of the sequences shows medium sand interactions during the main late glacial period supporting the assumption of a weakened WAM. Integration of the grain-size analysis, Ti/Zr and foraminiferal ratios with the lithological sequences suggest a transition from delta plain to pro-delta environment at different intervals during sea-level rise and fall coinciding with the strengthened and weakened WAM circulation.
The integrated multi proxies also revealed the sediment provenance from the hinterland to be driven by the fluvial discharge to the Niger Delta during the southern migration of the intertropical convergence zone (ITCZ). This period could also be linked to the episode of “Congo palaeodischarge and Ogolian regression”, periods of sea level fall associated with the formation of Congo fans, Senegal and Mauritania sand dunes respectively.
Understanding the potential variability of ancient deltaic sequences where we do not have the control prominent in the Quaternary could help in decoding the past signals more thoroughly. Thus, the result permit a re-evaluation of the debate role of the sea level and sediment supply on the evolution of the Niger Delta.
Keywords:
Sea-level variability, Gulf of Guinea, palaeo-discharge, chemostratigraphic ratios, benthonic and planktonic ratios, sedimentary environments