Paleoenvironmental Reconstructions using Organic Source Indicators: A Summary of Examples from Sri Lanka

Abstract

The qualitative and quantitative analysis of sedimentary organic matter (i.e., the residue of past biota) provides integrated histories of marine and continental past life and paleoenvironmental /paleoclimatic changes. Organic geochemical investigations are possible by combining (i) bulk properties such as elemental compositions, stable isotope ratios, and Rock-Eval pyrolysis data, and (ii) biomarker molecular compositions such as n-alkanes, sterol, and polycyclic aromatic hydrocarbons compositions. The analytical approaches described in this overview illustrate the published examples of lacustrine and marine organic geochemical studies in Sri Lanka. In summary, the Jurassic Andigama and Tabbowa Basins provide different sources of organic matter, followed by availability of nutrient for algal growth and the amount of land runoff to the basins. Rock-Eval analysis of the Cretaceous to Paleogene sedimentary rocks in the offshore Mannar Basin reveal the presence of gas-prone land-plant organic matter mainly and minor oil-prone algal organic matter. The amounts and types of organic matter variations in Bolgoda Lake sediments indicate changes in Holocene sea-level, coastal geomorphology, and continental climates during the last 7,000 years. In future directions, applications of novel organic geochemical proxies and understanding of original biologically synthesized materials in tropics would improve interpretations of paleoenvironmental changes. Besides, local and regional paleoclimatic proxy and model studies would refine future paleoenvironmental reconstructions in Sri Lanka.