On the Origin of Sedimentary Aragonite Needles of the Great Bahama Bank

Abstract

Field evidence on the origin of sedimentary aragonite needles indicates that the needles may be derived from certain algal carbonates. Determinations were made of the relative $$O^{18}$$/$$O^{16}$$ and $$C^{13}$$/C$$^12$$ ratios of various aragonitic carbonates, including needle-secreting algae, oölites, grapestones, and sedimentary aragonite needles from the Great Bahama Bank area. The range of isotopic ratios of the needle-secreting algae was different from that of the oolites and grapestones. The isotope ratios for both carbon and oxygen of the sedimentary aragonite needles lie in the median range of the algal carbonates and outside the range of that of the oolites and grapestones. This would indicate that the sedimentary needles are primarily of organic origin. The possibility that the isotope data for sedimentary needles are compatible with their being of inorganic origin is evaluated.