Ooid grains, a type of precipitated sand, are typically composed of calcium carbonate and are rounded in agitated water. Most ooids are composed of either aragonite or low-Mg calcite (Algeo and Waston, 1995). The minerals precipitated in ooids reflect a complex array of environmental and possibly even microbial processes, so a better understanding of the kinds of calcium carbonate minerals within ooids will help us constrain their depositional setting. The samples that I imaged in previous semesters appear to have bimineral cortices. The modern ooids from Shark Bay, Western Australia, have distinct Mg-rich rings surrounded by layers of aragonite. Sources from the literature have proposed various conditions for the precipitation of high-Mg calcite over aragonite or low-Mg calcite (Burton and Walter, 1987; Diaz and Eberli, 2019). These authors propose that the dominant controls are temperature and water saturation state. Studying these conditions will contribute to the understanding of ooid formation and its relationship with ocean chemistry.
A poster deriving from Special studies with Sara Pruss, Professor of Geosciences.