An Assessment of Geological Formation of The Rakwana-Pannila Mountain of Sri Lanka

The Rakwana mountain range, situated along the northern margin of the Sinharaja rainforest, a UNESCO World Heritage Site, represents a significant geodiversity hotspot. Recent excavations of alluvial deposits within the Sabaragamuwa Basin have led to the identification of cave systems within the crystalline limestone (marble)
formations of the Pannila Mountain region, locally referred to as ‘Pannila Hunugala.’ The primary cave structure extends approximately 550 meters in length with an entrance height of 350 cm, of which 60 cm is submerged in water. The cave exhibits distinct secondary mineralogical features, including stalagmites and stalactites reaching heights of 2.5 meters, which are hypothesized to have formed through the re-crystallization of pre- existing Precambrian basement rocks within the Highland Complex. Speleothem volumetric analysis was conducted to estimate the deposition rates of calcium carbonate. The speleogenetic processes within these caves are largely driven by chemical weathering of the crystalline limestone, wherein dissolution and precipitation cycles contribute to the formation of speleothems. Regional geological mapping suggests that this crystalline limestone sequence extends beyond Pannila Hunugala to other significant karstic formations, including Samanalawewa and Handagiriya caves. These findings enhance the understanding of the geochemical evolution of karst systems in the region and underscore the role of subterranean processes in the broader geomorphological framework of Sri Lanka.