DISTRIBUTION AND CHARACTERIZATION OF OOLITIC SAND IN PIGEON CREEK, SAN SALVADOR ISLAND, THE BAHAMAS

Ooids, small spherical to ellipsoidal coated grains characterized by concentric layers of calcium carbonate, are among the most prevalent components of carbonate sediments known from the geological record. Ooids tend to form in agitated shallow, carbonate environments, and despite the prevalence of ooids in the geologic past, there are not many sites where ooids are actively forming today. Oolitic sand was discovered in subtidal and beach settings along the Pigeon Creek Delta on San Salvador Island, The Bahamas. Three samples of subtidal sand were taken in the tidal channel at different locations to determine where ooids were most abundant. Individual samples were analyzed by separating sand into >231μm and 231–177μm size fractions and characterizing .05 g of the grains from each fraction. Generally, superficial ooids, ooids, and grapestones were the most abundant identifiable grains. Unidentifiable grains, grains with indistinct shapes or those that were abraded, comprised much of the samples (61.4% to 83.6%), which is a disadvantage of quantifying sand without examining internal grain fabrics. To complement this analysis, bulk sand samples were embedded in epoxy and thin sectioned to perform a petrographic analysis of the samples. Preliminary analysis of a 3mm by 3mm area in each thin section suggests that ooids and superficial ooids are present, but make up a small percentage of the total grains (~20% of all sand). Similarly, ooids are not the dominant grain in the sieved sand samples but make up 13.8%–27.5% of the >231μm fraction and 10.4%–29.2% of the 231μm–177μm fraction. In addition, superficial ooids make up 8.1%–11.5% of the >231μm fraction and 6.9%–20.6% of the 231μm–177μm fraction, and grapestones make up 0.6%–9.8% of the >231μm fraction and 2.4%–5.2% of the 231μm–177μm fraction. Our work suggests that ooids and other coated grains are an important component of subtidal sand samples in Pigeon Creek Delta on San Salvador Island, a previously undocumented site of ooid formation, and these grains likely formed as a result of tidal flow in this area. Future work will focus on more detailed sampling of oolitic sand in Pigeon Creek and additional quantitative petrographic analyses of existing samples.