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 levels based on the elevations, known as lowlands, uplands, and highlands. The lowlands are mostly flat and undulating while upland and highlands are characterized with ridge and valley topography with variety of geomorphological features. The highest point of the country is at Pidurutalagala at 2,524 m above mean sea level. Since the uplands and highlands are receiving much rainfall, 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 Precambrian high-grade metamorphic rocks, which divided into three main divisions as the Highland Complex, Vijayan Complex, and Wanni Complex, based on the lithology, metamorphic grades and isotope characteristics. The remaining land is mainly covered with sedimentary sequences. Miocene limestone underlies in the northern and northwestern coastal stretch while Jurassic beds are present in few isolated patches in the northwestern part of the island. Few scattered igneous intrusions can also be recognized within the Precambrian complex.