Northern Guam geospatial information server
Argillaceous Member of Mariana Limestone
The uppermost limestone unit in the southern part of the northern Guam plateau (and also the unit flanking the east coast of southern Guam) was mapped as the Argillaceous Member of the Mariana Limestone by Tracey et al. (1964). These units lie adjacent to higher-standing volcanic terrain and are distinguished from the rest of the Mariana Limestone by their high clay content.
The terrain that develops on Mariana Limestone Argillaceous Member is characterized by a combination of mixed underground and surface drainage, and is a special type of karst known as fluviokarst (Taborosi & Jenson 2002). While common in continental karst, fluviokarst is uncharacteristic of carbonate islands. It exists on Guam due to argillaceous limestone's high clay content and proximity to non-carbonate terrain. The former reduces the rocks' matrix porosity and the latter promotes arrival of focused surface water flow to the limestone area.