地球科学と気候変動ジャーナル

抽象的な

Depositional History of Coastal Plain Sediments, Southern Kerala, South West India

Varghese TI, Prakash TN* and Nagendra R

A 15.5 m long undisturbed sediment core were collected from the coastal plain of southern Kerala, India to study the micro-textural analysis of quartz grains to understand the fluvio-marine depositional environment. The down core variation of sediment between 0 m and 7 m shows medium to fine sand, 7 m to 10 m has sand-silt-clay, 10 m to 11 m clay which is hard and desiccated, and 11 m to 15.5 m contains silty clay rich in organic matter. The quartz surface micro-textural features shows conchoidal fractures, fracture plates, abrasion features and pits infers that the sediments undergone short period transportation and rapid deposition through mechanical processes in a fluvial regime under moderate to high-energy condition. Further, down the core the angularity of grains are reduced to become subrounded grains attributing to the recycled process with subaqueous solution activity. These processes can also lead to the development of linear branching-centipede solution features and oriented etch patterns. The sediments 11 m and 15.5 m depth exhibits corroded grain with solution pits and solutions crevasses indicating marine intervention followed by pressure solution, silica pellicle, silica plastering and dissolution etching features revealing prolonged digenesis deciphering the chemical processes under marine condition. Radiocarbon dating reveals that this coastal plain has undergone transgression-regression events during the last 40 kyrs BP depicting distinct textural characteristics of mechanical and chemical features reflecting the fluvio-marine depositional environment.