The Traders’ Cave of Niah (NW Borneo): morphology and features as indicators of speleogenesis and karstification

Abstract

Relict caves which are isolated from regional groundwater flow are common in deeply dissected tropical tower karsts. Their passage morphology and the micro-morphology of their walls can provide valuable information on former karst processes and speleogenesis. The Traders’ Cave at Niah (Sarawak, Malaysia) was selected for a case study including comprehensive survey and observations to establish a model of the cave’s formation which can serve as a basis for comparison with other caves in the region. The research identified six levels of vadose alluvial notches showing evidence of relative water-level drop of at least 15 m during the main vadose phase of speleogenesis. During this phase, the passage reached its maximal dimensions, possibly over 90 m wide. The notches are associated with paragenetic ceiling anastomoses formed by upward or antigravitative erosion. The results indicate that point-recharge allogenic flow, i.e., sinking streams from non-karst terrains, and sediment transport and removal played a major role during cave formation. The position of limestone boulders within the cave suggests that cave-ceiling collapse and un-roofing contributed to erosion of a large part of the cave and formation of the steep-sided valley between adjacent karst towers. The collapse is linked to landscape rejuvenation associated with a significant relative water-level drop leading to the present situation in which the Traders’ Cave is isolated and relict. Most speleothems post-date the opening of the cave into the karst valley and are fed by epikarstic flow. Many speleothems are phototropic, indicating a biological influence.