Post-speleogenetic biogenic modification of Gomantong Caves, Sabah, Borneo

Abstract

The Gomantong cave system of eastern Sabah, Malaysia, is well-known as an important site for the harvesting of edible bird's-nests and, more recently, as a tourist attraction. Although the biology of the Gomantong system has been repeatedly studied, very little work has been done of the geomorphology. Here we report on the impact of geobiological modification in the development of the modern aspect of the cave, an important but little recognized feature of tropical caves. Basic modelling of the metabolic outputs from bats and birds (CO 2 , H 2 O, heat) reveals that post-speleogenetic biogenic corrosion can erode bedrock by between ~3.0 mm/ka (1 m/~300 ka) and ~4.6 mm/ka (1 m/~200 ka). Modelling at high bat densities yields corrosion rates of ~34 mm/ka (or 1 m/~30 ka). Sub-aerial corrosion creates a previously undescribed speleological feature, the apse-flute, semicircular in cross-section, ~80 cm wide, vertical regardless of rock properties, developing in parallel but apparently completely independently, and often unbroken from roof to floor. They end at a blind hemi-spherical top with no extraneous water source. Half-dome ceiling conch pockets are remnants of previous apse-fluting. Sub-cutaneous corrosion creates the floor-level guano notch formed by organic acid dissolution of bedrock in contact with guano. Speleogenetic assessment suggests that as much as 70-95% of the total volume of the modern cave may have been opened by direct subaerial biogenic dissolution and biogenically-induced collapse, and by subcutaneous removal of limestone, over a timescale of 1-2 Ma.

Geomorphometric analysis of cave ceiling channels mapped with 3-D terrestrial laser scanning

“…Terrestrial laser scanning (TLS) is especially suitable since it uses its own source of electromagnetic energy, which makes it capable of mapping the surface with a high resolution in the darkness of the underground world (Buchroithner, 2015). Simpler methods exploiting laser distance measurers were used for capturing ceiling morphology (Lundberg and McFarlane, 2012), but the level of detail recorded does not reach the capabilities of TLS.…”

Characterization of Macro- and Micro-Geomorphology of Cave Channel from High-Resolution 3D Laser Scanning Survey: Case Study of Gomantong Cave in Sabah, Malaysia

“…So, building on the foundation of Ref. [7], this study experiments virtual geomorphological analysis with laser-scanning data collected in the less-accessible Simud Putih. The aim is to generate multi-scale resolution 3D models.…”

“…In terms of speleogenesis, the cave is believed to have started immediately after the uplift, compression and folding of the rock during the early Pliocene which was followed by dissolution of soluble rocks along bedding planes and joints [7,9]. Gomantong cave system consists of two major passages, one above the other [10].…”

“…Swiftlet birds and bats contribute significantly to ecosystem engineering, tourism and economy of the state of Sabah [13]. However, there are indications of threat of potential collapse of the cave due to natural and anthropogenic causes [7].…”

“…All these, in addition to natural geologic processes, weaken the structure and thereby accelerate the rate of deformation in the cave. Since the last six centuries, the cave has been one of the focal references to edible bird-nest (EBN) harvesting in southeast Asia [7]. While the business flourishes, enriching the economy of the state and her indigenous residents, the survival of the cave itself for life-long production of this lucrative commodity has been largely neglected, though unintentionally [4], despite the vicious impact of biologically induced alteration of the cave passage.…”