Print this pageCarbonate Ramp Sands of the San Blas Islands, Panama, and the Effects of Meteoric Diagenesis
SARE, VICKEY P. and JOHN D. HUMPHREY
The San Blas carbonate ramp represents a new depositional and diagenetic model which will aid in the interpretation of ancient carbonate reservoirs. This ramp-top platform extends along the Caribbean coast of Panama for 200 kilometers, and ranges from 5 to 20 kilometers wide. Nearly 300 carbonate islands are scattered along the ramp culmination. Extensive shallow patch reefs dominate the marine environment; however, no barrier reef platform rim is present. Sediment deposited in the shallow marine and island environments of this platform is dominated by reef-associated skeletal sands with high primary porosity and permeability. The climate is tropical with more than 200 centimeters of rainfall per year. Consequently, year-round fresh water lenses are present in even the smallest islands.
The observed effects of early meteoric diagenesis in the San Blas islands include dissolution of allochems, creation of intraparticle and moldic porosity, rapid mineralogic stabilization, and precipitation of stable calcite cements in the upper fresh water lens and vadose zone. Reaction path chemical models suggest that the entire sediment package could be stabilized with less than 1% porosity occlusion. Relative sea-level fall equivalent to the Last Glacial Maximum could expose the entire platform complex to meteoric diagenesis and produce high quality carbonate reservoir rock over an area of more than 2000 square kilometers.