Abstract: Silicification of Calcium Phosphate in Carbonate Environment, San Andres Island, Colombia
M. J. Kocurko, D. J. Robertson
Modern soil derived from the weathering of limestones on San Andres Island, Colombia, is composed primarily of low-magnesium calcite and organic residue. Analyses of samples using an X-ray diffractometer and petrographic microscope indicate the presence of a significant diagenetic sequence between fresh soil cover and lithified soil remnants.
Solution cavities in limestones along the west coast of the island contain remnant soil material, which is subjected to periodic soaking by both fresh water and seawater in the vadose zone. Pisolitization of the remnant soil is evident together with subsequent cementation. Pore fluids within the soil deposits have an average pH of 7.7 and average temperature of 28°C.
During progression of the diagenetic sequence the calcium carbonate content of the soil decreases as the calcium phosphate and silica content increase. The most advanced diagenetic stage found on San Andres Island was represented by an oolitic silicified calcium phosphate.
AAPG Search and Discovery Article #90968©1977 AAPG-SEPM Annual Convention and Exhibition, Washington, DC