GEOLOGICAL FORMATION & PALEOENVIROMENT OF THE RAKWANA-PANNILA MOUNTAIN - SRI LANKA

GEOLOGICAL FORMATION & PALEOENVIROMENT OF THE RAKWANA-PANNILA MOUNTAIN - SRI LANKA

Sumanarathna. A.R^1,2,3,  Wijayathunga. W.A.L.K^1,2, Silva E.I.P⁴,  Hathalahawaththa D.K¹,  Fernando G.W.A.R.², Sewwnadi SL² , Silva.A.C²

1. South Asian Astrobiology & Palaeobiology Research Unit of Eco Astronomy Sri Lanka

2. Faculty of Natural Science, The Open University of Sri Lanka, PO Box 21, Nugegoda

3. Postgraduate Institute of Archaeology, University of Kelaniya

4. Faculty of Applied Sciences University of Sri Jayewardenepura,Nugegoda

The Rakwana mountain range, which is located in the margin of the northern side of Sinharaja,UNESCO world heritage site, is an area having rich bio–diversity,included unique geological formations such as limestone caves etc. Numerous fossils of  Elephants(Elephas spp.), Gaur(Bos gaurus), Sambar Deer (Rusa unicolor), Rhinoceros (Rhinoceros kangawena), Red dogs(Cuon sinhaleyus), Hippopotamus (Hexaprotodon sinhaleyus) & Tiger (Panthera tigris) dated to 17,000-13,000 ybp belongs to the Pleistocene Epoch, could be identified during the recent excavations of the alluvial deposits in Sabaragamu basin. Isolated living Elephants, Sambar Deer & Eel (Anguilliformes ssp.) are unique to this area. The detailed study of the limestone cavern at Pannila mountain revealed that it is of 750 meters in length. The height of the cave entrance is 300 cm (3.5 feets) of which 60 cm filled with water, where special cave characteristics are visible. Stalagmite and stalactites of  5 m height formed after re-crystallization of pre-existing limestones could also be observed at the core of the cave. The studied limestone cave popularly known as ‘Pannila Hunugala’ is a part of the basement marble bed in the Highland Complex of Sri Lanka belongs to the Precambrian age. It is postulated that the same marble bed is extended to the marble beds located at the Samanalawewa, Waulpane and Rakwana. The action of chemical weathering occurred in the recent times makes it secondary features like stalagmite and stalactite. It is interesting to study that the existence of animal fossils within and around the cave is an indication of the period of cave formation, which probably contemporaneously to the Pleistocene Epoch. It was reported in the literature that during the Pleistocene Epoch, the entire island  experienced heavy rain fall resultant the growing of thick rain forests, of  which Sinharaja is one of the best existing example (Deraniyagala 1958). These heavy showers created large lakes and marshes in the Sabaragamuwa basin providing habitats for a number of marsh-loving mammals and other animal species mentioned above that were once lived in Sri Lanka and have got extinct as a result of the Earth’s Precession change in the following period.

Fig 01 : Distribution of limestone (+ marble) formation in Sri lanka

A.Pannila Hunugala(Sinharaja heritage site)  , C. Cavity of  right bank at river level in Samanalawewa. , D . Handagiriya( Balangoda), B.Model  for action of chemical  weathering formations of  limestone cave.

Key Words:Sinharaja Forest, Crystalline Limestone, Paleontology, Pleistocene Geology, Sri Lanka

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