Palaeoecological studies of quaternary sediments from the University of Lagos, Nigeria

Abstract

The knowledge of changes in past ecological conditions during the Quaternary period of Nigeria is still incipient. This necessitated a palaeoecological investigation through drilled sediments of a 45 m borehole in a swampy area at the University of Lagos, in order to ascertain possible changes in the past ecological conditions of the study area over time. Sixteen sediment samples were collected at intervals of 3 m between the depth of 0.00 m and 45.00 m and subjected to palynological, lithological, pH and salinity analyses. In the palynological study, pollen of open forest types: Alchornea cordifolia, Elaeis guineensis, Asteraceae, among others were recovered, indicating human influence over time. Pollen of Rhizophora sp., Combretaceae/Melastomataceae, Poaceae, Ceratopteris sp., Cyclosorus afer, amongst others; were also represented. Spores of Pteris sp., Nephrolepis sp. and Acrostichum sp., charred Poaceae cuticles, epidermal cells and fungal spores were also recovered. From the lithological analysis of the samples, a considerable number of lithological types were recognized, which varied in grain-size, grain sorting and grain-texture. The pH and salinity values of the sediment samples also varied considerably at different depths. However, vegetation changes during this period could be attributed to an interplay between fluctuations in the wet-dry climatic phases and anthropogenic activities. The data obtained from lithological, pH and salinity analyses reveal a mosaic of sedimentary depositional environment in which the recovered palynomorphs were preserved. Parent plants of the recovered fossil palynomorphs are still found as extant plants till today, despite the ever increasing human activities at the study area. Absolute ages were extrapolated and these revealed the period at which paleoecological changes occurred but limited to some intervals.

Keywords: palynomorphs, Quaternary period, climatic phases, anthropogenic, sediments