Palaeoclimatic Evidences from the Quaternary Coastal Deposits, Southwestern, Nigeria

Abstract

The studies on some samples retrieved from the coastal sediment deposit have been carried out. The palynological and geochemical indices were evaluated with the view of determining their chronology, palaeoclimatic conditions that prevailed during the time of their emplacement and also to re-asses the palaeoenvironment of the Lagos coastal deposit in Dahomey Basin. The identification of diagnostic species age entails the palynological analysis while the geochemical analysis determines the provenance of these Quaternary sediments. The occurrences of Laevigatosporites sp., Zonocostites ramonae, Acrostichum aureum in abundance along with few long ranging forms suggest that the vegetation development was under a humid climate and that the sediments were deposited during cooler and wetter conditions. The presence and high abundance of Crassoretitriletes vanraadshooveni, Zonocostites ramonae, Canthiumidites sp., Sapotaceoidaepollenites sp. and Pachydermitesdiederixi palynomorphs indicate an age range of late Pliocene (Gelasian) to early Pleistocene (Calabrian) (2.588 - 1.806 Ma). This age range is known to correspond to the 3.7 - 3.8 depositional cycles of relative change of coastal On-lap. The geochemical appraisal showed that the ratios of organic carbon-nitrogen (C/N) indicate that the sediments were sourced from aquatic, protein-rich and cellulose-poor milieu. The wetter climatic period has enhanced algae productivity as a consequence of greater wash-in of soil nutrients, and these periods are recorded as increased rate of organic carbon mass accumulation. Conversely, the dominance of a mangrove habitat, Zonocostites ramonae suggests a mangrove swamp environment which was the most prevalent environment of the Lagos lagoon in the Pleistocene.