Geology and Geomorphology

Abstract

Sri Lanka, formerly known as Ceylon, is a small tropical island located in the southern tip of the Indian peninsula, separated by narrow and shallow Palk Strait in the Indian Ocean. The island is a small landmass of the old Gondwana Supercontinent until the Cretaceous and detached and drifted northward with the Indian subcontinent. Then, the island was separated from the Indian subcontinent possibly in late Miocene. Although Sri Lanka is a small land block with 65,610 km2 land area, it is having variety of geological and geomorphological features. Geomorphologically the island is characterized with three erosional levelsErosional levels based on the elevationsElevation, known as lowlandsLowlands, uplandsUplands, and highlandsHighlands. The lowlandsLowlands are mostly flat and undulating while uplandUplands and highlandsHighlands are characterized with ridge and valley topographyTopography with variety of geomorphological features. The highest point of the country is at Pidurutalagala at 2,524 m above mean sea level. Since the uplandsUplands and highlandsHighlands are receiving much rainfallRainfall, most of the rivers are originated from this part and then radiated to the Indian Ocean. Geologically, over 90{\%} of the land is underlain by PrecambrianPrecambrian high-grade metamorphic rocksMetamorphic rocks, which divided into three main divisions as the Highland ComplexHighland complex, Vijayan ComplexVijayan complex, and Wanni ComplexWanni complex, based on the lithology, metamorphic grades and isotope characteristics. The remaining land is mainly covered with sedimentary sequences. Miocene limestoneMiocene limestone underlies in the northern and northwestern coastal stretch while JurassicJurassic beds are present in few isolated patches in the northwestern part of the island. Few scattered igneous intrusions can also be recognized within the PrecambrianPrecambrian complex.