Sediment deposits along the South Kerala coast are helping scientists reconstruct the geological evolution of the region over the past 10,000 years and come up with adaptation strategies for climate change and sea level variation.
A case study of the coastal sediments in Kollam and adjoining areas by scientists at the Centre for Earth Science Studies (CESS) here indicates that the combined effects of sea level variation and climate change during the Holocene epoch representing the last 10,000 years of the earth’s geological history had influenced the evolution of coastal wetlands and associated landforms in South Kerala.
The study by D. Padmalal, K. Maya and S.Vishnu Mohan used sediment analysis as proxy evidence to decode the climate scenarios of the Holocene period. The findings of the study have been published by CESS in the form of a monograph.
According to the authors, the analysis of the sediments present in the coastal lowlands in Kerala not only throws light on the palaeoclimate and sea level changes of the area but also helps understand how ancient human civilization has responded to the geological events of the past. The data, they feel, could be used for future climate prediction systems and help planners design appropriate adaptation strategies.
Collaborative projectThe team analysed the sediment deposit in the South Kerala sedimentary basin and adjoining coastal lowlands to unlock the palaeoclimatic and environmental signatures.
Funded by the Kerala State Council for Science, Technology and Environment (KSCSTE), the collaborative project also involved scientists from the Agarkar Research Institute, Pune; Birbal Sahni Institute of Palaeobotany, Lucknow, and ZMT, Bremen, Germany.
The South Kerala sedimentary basin and adjoining coastal lowlands have a 50 to 60 m thick deposit of Late Quarternary (the past 0.5 to 1.0 million years) sediments including alluvial and sandy clays, peat and coastal sands. The sedimentary archives in the coastal lands between the Pallickal river in the north and Ayroor river in the south were chosen for the study.
According to the authors, the investigations revealed that the early and middle Holocene period was characterised by heavy rainfall and excessive sediment transport from inland areas into the coastal wetlands. It was inferred that sea level rise in the study area peaked about 5,000 to 6,000 years back in time.
Surface and subsurface sediment samples collected from wetlands, beaches, coastal plains, rivers and lakes were subjected to mineralogical and geochemical analysis. Sub fossil wood and sediments were radiocarbon dated at BSIP, Lucknow, while stable isotopic studies were carried out at ZMT, Bremen.
Extensive studiesSelected samples were also subjected to palynological studies to confirm the presence of plant pollen, spores and microscopic planktons, indicators of environmental conditions like freshwater, brackish or marine environment, mangrove vegetation, humidity, high rainfall, wet evergreen climate or agricultural practices. The analysis revealed that the early Holocene period was characterised by heavy rainfall and high erosion of terrestrial sediments, burying riparian vegetation.
The early-middle Holocene sediments were marked by the presence of the pollen of wet evergreen plants, indicating heavy rainfall. The middle Holocene sediments were found to contain marine nanoplanktons, dinoflagellates and sponge spicules, all evidence of sea level rise. Mangrove pollen was observed in certain areas, pointing to the prevalence of brackish water environment.
The study revealed that the climatic and sea level conditions in the early Holocene period led to the development of bay head deltas in the landward side of the estuarine basins.
The transport of alluvial sediments and riverine deposits was instrumental in the formation of wetlands like the Sasthamcotta lake and Chelupola and Chittumalachira in the Ashtamudi basin, Kotta kayal and Polachira in the Paravur basin and Poovankal wetland in the Nadayara basin.
