REVISITING THE CARBONATE ISLAND KARST MODEL

The Carbonate Island Karst Model [CIKM] has proved to be useful to visualize karst development in carbonate islands and coasts. Its main aspects are: 1) The fresh water - salt water boundary creates mixing dissolution, and produces organic-trapping horizons at the boundaries of the fresh-water lens. 2) Glacioeustasy has moved the fresh-water lens up and down through a vertical range of over 100 m in the Quateranry. 3) The karst is eogenetic, i.e., it has developed in carbonate rocks that are young and have never been buried below the range of meteoric diagenesis. 4) Carbonate islands can be divided into four categories based on basement/sea level relationships: A) Simple carbonate islands (no non-carbonate rocks), B) Carbonate cover islands (non-carbonate rocks beneath a carbonate veneer), C) Composite islands (carbonate and non-carbonate rocks exposed on the surface). D) Complex islands (faulting and facies interfingering create complex carbonate/non-carbonate relationships. 5) Local tectonics can overprint the glacio-eustatic sea level events, adding complexity to the record. The CIKM has direct application to location and extraction of useful fresh water resources, as well as prediction of the result of point and non-point contamination of the karst aquifer. The utility of caves and their contents to interpretation of sea level and climatic history of carbonate islands depends on understanding the spatial and chronologic boundary conditions established by the CIKM. The CIKM operates in a triple porosity environment of matrix porosity, vugular porosity, and conduit porosity, where the contribution of each of the three porosity types varies according to sea level position, island size, carbonate rock age, and carbonate rock position relative to non-carbonate rocks.