Carbonate Cementation in Quiet Water Environments: Role of Bacterial-Microalgal Films

小行星9315056 现代浅水海相碳酸盐岩沉积物中的胶结作用被认为局限于潮间带、高盐度的限制环境以及台地边缘的生物礁和砂滩。 在其他浅海环境中，微生物内岩的钻孔作用，导致泥晶化或颗粒的破坏，被认为是主要的成岩过程。 然而，不同工作人员发表的研究报告和调查人员的初步工作表明，大量水泥在低至中等能量的正常海洋潜水环境中沉淀，这一事实对碳酸盐在受保护环境中的循环和储存具有重要意义。 人们还普遍认为，海相胶结作用在很大程度上是一个物理化学过程，微生物在碳酸盐胶结作用中的作用仅限于通过改变孔隙沃茨的pH值和Eh值来诱导碳酸盐沉淀。 然而，沉积学家通常使用的样品采集和制备方法会降解或破坏有机结构，因此它们在胶结作用中的作用往往得不到承认。 拟议的工作将评估chasmolithic细菌，蓝细菌和微藻在胶结作用中的作用，通过使用旨在保持样品的微生物成分完整的技术，并将制定新的标准，在古代沉积物中的钙化chasmoliths的识别。 与高能、台地边缘环境相反，在低能海洋潜水环境中，砂岩的胶结物形成过程似乎主要是裂隙岩的钙化，而不是碳酸盐的物理化学沉淀。 在低能量环境中，不同亚环境之间的水泥类型和丰度似乎也存在差异。 建议的工作将描述水泥的类型和数量，以及它们在圣萨尔瓦多土地上的低能量泻湖、中等能量泻湖和高能量泻湖中与生物活性砂的分布。 巴哈马，并在这三个设置的环境因素，如海草覆盖，波和电流的能量，以及生物扰动程度的水泥的类型和分布。 胶结物类型及其分布与环境因素的关系的表征将为解释古浅海碳酸盐沉积物的早期成岩环境提供有用的标准。

9315056 Gaffey Cementation in modern shallow-water marine carbonate sediments is believed to be confined to the intertidal zone, restricted environments with high salinity, and reefs and sand shoals at platform margins. Boring by microbial endoliths, resulting in micritization or destruction of grains, is thought to be the dominant diagenetic process in other shallow marine environments. However, published studies by various workers, and preliminary work by the investigator, indicate that significant volumes of cement are precipitating in low to moderate energy, normal marine phreatic environments, a fact with important implications for cycling and storage of carbonate within protected settings. It is also widely believed that marine cementation is largely a physicochemical process, and that the role of microorganisms in carbonate cementation is restricted to inducing precipitation of carbonate by changing pH and Eh of pore waters. However, sample collection and preparation methods commonly used by sedimentologists degrade or destroy organic structures, so that their role in cementation often goes unrecognized. The proposed work will assess the role of chasmolithic bacteria, cyanobacteria, and microalgae in cementation by using techniques designed to preserve the microbial component of samples intact, and will develop new criteria for recognition of calcified chasmoliths in ancient sediments. In contrast with high energy, platform margin settings, calcification of chasmoliths rather than physicochemical precipitation of carbonate appears to be the dominant cement- forming process in sands from low energy marine phreatic environments. There also appear to be variations in cement types and abundance between different subenvironments within low energy settings. the proposed work will characterize the types and amounts of cements, and their distribution with bioclastic sands in a low, an intermediate, and a high energy lagoon on San Salvador Is land. Bahamas, and relate types and distributions of cements in these three settings to environmental factors such as sea grass cover, wave and current energy, and degree of bioturbation. Characterization of cement types and of their distributions in relation to environmental factors will provide useful criteria for interpreting early diagenetic environments of ancient shallow marine carbonate sediments.