Abstract Quaternary glacio-eustasy has traditionally been determined in part by the examination of fossil coral reefs on carbonate islands and coasts uplifted by tectonics. These studies do not properly account for dissolutional denudation, which is cumulative, making higher and therefore older terraces exist at elevations far below their assumed depositional elevation. Karst pedestals (karrentische) on Guam reveal the extent of the denudation ( c. 50 mm ka −1 ) and demonstrate that theoretical denudation models can be accurately applied to eogenetic carbonates in tropical settings. Aeolian calcarenite islands such as the Bahamas have been used as tectonically stable sea-level calibrations for other islands, which may not be correct. Flank margin caves, forming in the distal margin of the freshwater lens within a carbonate island, are excellent sea-level indicators. Analysis of flank margin cave elevations indicates that the Bahamas have had past sea-level highstands >6 m, perhaps up to 15 m or more, for which no fossil coral data exist. Denudational removal of these older corals has biased the record to younger events and only flank margin caves remain as viable terrestrial signatures of these older sea-level highstands.

Insights from previous karst studies of the relatively simple and stable carbonate islands of the Caribbean and Western Atlantic have been applied to develop the carbonate island karst model (CIKM), a general model with which we can interpret the karst of more complicated islands in the Western Pacific. This paper summarizes the karst of the five southernmost Mariana Islands in order of increasing complexity. All exhibit complicated histories of tectonic uplift and subsidence overprinted by glacio-eustasy. Each, however, is distinct and can be described in total or by subunit in terms of the four idealized carbonate island types defined in the CIKM: (1) simple carbonate island, (2) carbonate-cover island, (3) composite island, and (4) complex island. Aguijan is a simple carbonate island, but contains a probable phreatic-lift cave draining a confined aquifer. Tinian illustrates application of the CIKM to subunits: the northern lowland is a simple carbonate island area, while the southeastern ridge fits the carbonate-cover island category, and the central portion fits the composite island category. Rota is a composite island grading laterally from the volcanic core into a carbonate-cover island, thence to a simple carbonate island from the southwestern highland to the plains and terraces north and east. Northern Guam is a simple carbonate island ringing a carbonate-cover section, which contains a small composite island portion. Southern Guam exhibits composite and complex island features. Saipan is a complex island, where syndepositional volcaniclastic units interfingering with limestone are faulted to create isolated aquifers, including confined aquifers drained by phreatic-lift caves.