Coastal Karst Development in Carbonate Rocks

Coastal karst cave development globally is biased towards the tropics and subtropics, where carbonate deposition is ongoing, and therefore carbonate coasts are common. The Carbonate Island Karst Model (CIKM) delineates the unique conditions that separate coastal karst from traditional karst areas of continental interiors. In these warm-water carbonate islands, diagenetically immature, or eogenetic carbonate rocks are host to a fresh-water lens that creates flank margin caves in a diffuse flow environment. Diagenetically mature, or telogenetic carbonates, can also host flank margin caves. Flank margin caves can form rapidly, as carbonate sediment is deposited, to produce syndepositional caves called banana holes. Flank margin caves can survive as open voids for millions of years, and as infilled diagnostic features for tens of millions of years. Vadose fast flow routes called pit caves form as a result of surface micritization to provide point recharge to the fresh-water lens. The presence of non-carbonate rocks can perch vadose flow, creating stream caves that terminate in the fresh-water lens. When sea level falls to create large exposed carbonate platforms, phreatic conduit flow develops to carry recharge to the platform periphery. Collapse of these conduits, as well as bank margin fracture, account for the majority of blue holes in carbonate platforms. Closed depressions in eogenetic carbonate islands are commonly constructional, relicts from variable carbonate deposition. The most common sinkhole type is the cave-collapse sinkhole. Morphometric analysis of flank margin caves supports cave origin as the amalgamation of individual chambers, provides evidence of denudation rates, and can differentiate flank margin caves from some pseudokarst cave types