Diagnostic Features of Hypogenic Karst: Is Confined Ascending Flow Necessary?

The term hypogenic cave, originally introduced by Arthur Palmer in 1991 to explain cave development de-coupled from surface hydrology, was recently refined by Alexander Klimchouk to be solely the result of ascending flow across semi-confined carbonate aquifers. A key aspect of the ascending-flow argument is the existence of diagnostic bedrock dissolutional forms such as, among others, rising wall channels, ear-like or dome orifices, point and rift floor infeeders, ceiling channels, cupolas, and thin bedrock partitions. The existence of such features in continental epigenic caves is argued to represent inheritance from an earlier confined stage, with an epigenic overprint. The key question is whether confined flow is essential in producing these diagnostic bedrock morphologies.

Because of inheritance and overprinting arguments, the bedrock morphology question can only be addressed by examining caves where confined conditions never existed. Caves developed on carbonate coasts and islands in very young limestones, free of tectonic influence, have never been subjected to confined conditions. These caves contain bedrock dissolutional morphologies remarkably similar or identical to those reported to be solely the result of confined flow. Therefore such bedrock morphologies cannot be true diagnostic indicators of confined conditions. The key factor in developing these bedrock morphologies is not confined flow, but low-velocity flow. Mixing dissolution in coastal carbonates occurs in a low-velocity flow system. In epigenic cave systems, stagnant ponding from certain flood conditions may also allow low-velocity flow to repeatedly participate in the bedrock dissolutional processes. This flooding could create an overprint on epigenic dissolution, instead of the other way around as the hypogenic cave model postulates. Confined caves are one category of hypogenic cave, and suffer from the same lack of explorational and scientific reporting common to all hypogenic caves, and as a result deserve more study by the karst community.