Palaeoclimate Change during Glacial Periods Evidence from Sri Lanka

Abstract

In the Earth's history, there were five major glaciations, namely, Huronian (2,300 Ma), Cryogenianor SturtianVarangian(850�635 Ma), AndeanSaharan (460�430 Ma, Karoo (360�260 Ma) and the Quaternary (2.58 Ma to Present) that occurred between 2,300 Ma and 0.0114 Ma. It is revealed that Gondwanaland emerged between the Huronian glaciation (2300�2100 Ma) in the Paleoproterozoic Era and the AndeanSaharan glaciation (460�420 Ma) in t he Early Paleozoic Era. During this time, most continental land masses were clustered in the southern hemisphere, and Sri Lanka was part of the Gondwanaland landmass comprising present day Africa, Madagascar, India and Antarctica. Within the Ordovician (485.4�445.2Ma) to Permian Periods (299. 0�254.2 Ma) there were signs of the breaking up of Gondwanaland resulting in the severing of India and Sri Lanka together and subsequently Sri Lanka from India. By end of the Permian Period (260 Ma) Karoo Glaciation had ended and the present Mannar Basin developed within a deep canyon (about 4�7 km deep) on the Precambrian basement. Although the island of Sri Lanka presently lies in the Indian Ocean between 5 o 52´N�9 o 54´N and 79 o 30´E�81 o 55´E, to the southwest of Bay of Bengal and southeast of Arabian Sea, it was positioned within 67 o S�65 o S and 34 o E�43 o E during the Lower and Middle Jurassic Era (201.3�1 66.1 Ma). Huge rocky blocks (erratic boulders) have been transported to different places by continental ice sheets due to climatic changes in the Permian, Triassic and Jurassic Periods, but erratic pebbles (2 to 8 cm or more in size) and streams fed deposits have been transported by glacifluvial processes. These glaciofluvial processes occurred on four occasions during the Jurassic Period and Eocene, Miocene and Pliocene Epochs on Sri Lankan landmass, which fallowed the climatic changes and sea level fluctuations that broke up the sedimentary beds, initiating establishment of the present topography and structural configuration. As a result, the earlier sedimentary deposits were obliterated from greater part of Sri Lanka. During the Quaternary Period the erosional rate increased and the resultant erratic boulders along with glaciofluvialdeposits can still be found on "Planated Surfaces"of Sri Lanka.