The proposed work will investigate the sequences, rates, timing, and environmental controls of diagenetic changes in two types of mineral controlled alteration: 1. Preneomorphic mineralogical and compositional changes in biogenic aragonites, 2. The stabilization of biogenic high Mg calcites to low Mg calcites. Materials for the work will be obtained from San Salvador Island, the Bahamas, where Holocene and Pleistocene sediments of reef, shallow subtidal, tidal delta, lagoonal, beach and dune facies exist in close proximity to modern analogs occupied by the same genera and species of organisms. Prior and ongoing work by others on the stratigraphy and depositional and diagenetic histories of these sediments, and age dates determined by a variety of techniques, provide and excellent framework for the proposed study. Tools (reflectance and nuclear magnetic resonance spectroscopy) and techniques are now available for non-destructive characterization of H20-, OH- and organic-containing phase in skeletons. Because abundances of these unstable phases in skeletons are taxonomically controlled, work will focus on a small number of important sediment-producing taxa. Comparisons of modern skeletons with suites of fossil skeletal material of the same genera and species whose ages and diagenetic histories are well-known, and whose mineralogy, chemical composition, and micro- and ultrastructure are thoroughly characterized will clarify the roles of several important mineral and compositional phases in the early diagenetic alteration carbonate skeletons.
