A GEOCHEMICAL AND MINERALOGICAL ANALYSIS OF THE MUDS OF MOON POND, SAN SALVADOR ISLAND, BAHAMAS: ORGANIC OR INORGANIC?

Moon Pond is a hypersaline lake on San Salvador, Bahamas. Unlike the other ponds in the interior northern part of the island, which contain a primarily molluscan shell debris substrate and thus are very coarse-grained, Moon Pond contains a white carbonate mud which is primarily <63µm. Other researchers (Davis, 1990) have speculated that the mud in Moon Pond is inorganic. The result of meteoric dissolution of the surrounding rock and the mixing with the hypersaline waters of Moon Pond. This study is based on calculating Sr content within the aragonitic phase of the sediment in Moon Pond and comparing these values with the Sr content of calcareous algae and invertebrates, as well as the Sr signature of inorganically precipitated carbonate muds. The geochemical analysis was performed on an atomic absorption spectrophotometer and x-ray diffraction quantified the mineralogy of the samples. The muds of Moon Pond are >90% aragonite with Sr values close to 1.0%, which would indicate that they are mostly inorganically precipitated (Milliman, 1974; Loreau 1982). However, the Acetabularia of the pond (97% aragonite and approximately 0.9% Sr) could also significantly contribute to this size fraction. The silt and very fine sand of the pond has a slightly lower aragonite value and a much lower Sr value than the clay-size fraction indicating input from the molluscan assemblage of the pond, which is 100% aragonite but only 0.26% Sr. High Sr content of the aragonite within the fine fraction (<63µm) is consistent with an inorganically precipitated origin with some addition of copious amounts of the calcareous green alga Acetabularia, which is ubiquitous in the pond. The lower Sr content of the silt and fine sand would indicate that it is the breakdown product of shell material, primarily molluscan in origin.