MICROFACIES, MINERALOGY, AND STABLE-ISOTOPE RECORD OF THE EAST BEACH LAGOON SEDIMENT, SAN SALVADOR ISLAND, BAHAMAS
The results of the XRD analysis of powdered off-reef, pure carbonate sediment (aragonite + calcite = 100%) indicates predominance of aragonite over calcite. Aragonite is the dominant mineralogy in 80% of the samples; in those samples aragonite content ranges from 54-73%. Where dominant, the calcite content ranges from 63-67%. Overall, the average aragonite to calcite ratio is 1.28. The studied calcite is high in magnesium, with values ranging from 14.3-16.4 mole% (mean 15.5 mole%). The frequency analysis of microfacies data indicates that the major sediment producer is Halimeda (20% of all grains), followed by red algae (11%), foraminifera (5%), bivalves (4%), gastropods (3%), and corals and echinoids (<1%). Non-skeletal grains comprise 56% of all grains, and are predominantly peloids. There appears to be a correlation between an increase in calcite content and abundance of bivalve fragments. Oxygen isotope values range from -0.28 to -2.29 ‰VPDB, with mean value of -0.99 ‰VPDB; carbon isotopes range from -0.73 to 3.18 ‰VPDB, with mean value of 2.27 ‰VPDB. The isotope values of the bulk sediment are clustered, while the individual skeletal grains exhibit greater ranges of values.