KARST DEVELOPMENT ON TINIAN, COMMONWEALTH OF THE NORTHERN MARIANA ISLANDS: CONTROLS ON DISSOLUTION IN RELATION TO THE CARBONATE ISLAND KARST MODEL

Abstract

Tinian, located in the western Pacific Ocean, is an Eocene volcanic edifice mantled by younger algal and coralline limestones. Carbonate rocks are eogenetic, producing an island karst terrane as predicted by the Carbonate Island Karst Model. Surface karst features include epikarst, closed depressions, and freshwater discharge sites. Subsurface karst features include three morphologically distinct cave types: mixing zone, fissure, and contact. Controls on cave development inferred from morphology are supported by non-parametric statistical analyses. Mixing zone cave development is controlled by freshwater lens position, fissure cave development is controlled by structural deformation, and contact cave development is controlled by lithologic boundaries. Horizons of mixing zone caves preserve at least three previous sea level positions, but differential rates of uplift between fault blocks prevent correlation of horizons across the entire island. Tinian karst development demonstrates the functionality of the Carbonate Island Karst Model and illustrates how portions of individual islands may exhibit each of the ideal island categories to some extent.