Effects of Compositional Differences on Early Diagenetic Pathways of Carbonate Biominerals

这项工作将研究两类矿物控制蚀变中成岩变化的序列、速率、时间和环境控制：1.生物成因文石的原生矿物学和成分变化；2.生物成因高镁方解石对低镁方解石的稳定。这项工作的材料将从巴哈马的圣萨尔瓦多岛获得，在那里，珊瑚礁相、浅潮下相、潮汐三角洲相、泻湖相、海滩相和沙丘相的全新世和更新世沉积非常接近现代类似物，属于相同的生物属和物种。其他人以前和正在进行的关于这些沉积物的地层学、沉积和成岩历史以及由各种技术确定的年龄的工作，为拟议的研究提供了良好的框架。现已有工具(反射和核磁共振光谱学)和技术可用于对骨架中的H20-、OH-和有机相进行无损表征。由于骨骼中这些不稳定相的丰度受到分类学的控制，因此工作将集中在少数重要的产生沉积物的类群上。现代骨骼与同属同种化石骨骼材料的对比，其时代和成岩历史是众所周知的，其矿物学、化学成分、显微和超微结构得到了全面的表征，这将阐明几个重要的矿物和组成阶段在早期成岩蚀变碳酸盐骨架中的作用。

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.