Contrasting intensity of aragonite dissolution and dolomite cementation in glacial versus interglacial intervals of a subtropical carbonate succession
Contrasting intensity of aragonite dissolution and dolomite cementation in glacial versus interglacial intervals of a subtropical carbonate succession
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亚热带碳酸盐岩序列冰期与间冰期区间文石溶解和白云石胶结强度对比
DOI：
10.1111/sed.12985
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发表时间：
2022
期刊：
影响因子：
3.5
通讯作者：
Bassetti Maria‐Angela
中科院分区：
文献类型：
--
作者：
Reuning Lars;Deik Hanaa;Petrick Benjamin;Auer Gerald;Takayanagi Hideko;Iryu Yasufumi;Courtillat Margot;Bassetti Maria‐Angela
文石和高镁方解石在现代浅海碳酸盐系统中很丰富，但在化石中几乎不存在。这些亚稳矿物相的溶解通常不会在沉积记录中留下任何可见的痕迹，从而影响了从岩石记录中获取古环境信息。综合大洋钻探计划（IODP）位于西澳大利亚大陆架外斜坡的U1460站点的上部25米进行了调查，以研究有机碳贫乏沉积物中的浅埋（数十米）海洋成岩作用，使用显微镜，总有机碳，生物标志物和矿物学分析，结合孔隙水地球化学。文石的溶解在海底可以忽略不计，但在5米以下会加剧，即使大量孔隙水对文石来说是过饱和的。这种明显的矛盾可能是由于溶解在不饱和的微环境。与冰期相比，间冰期中5至6米以下的文石溶解平均更为强烈。浸染状framboidal黄铁矿和孔隙水结果的存在表明，轻微的硫酸盐还原是活跃在IODP站点U1460。硫酸盐还原可能是有限的有机质含量低（钙0.2%）。从文献中众所周知，初始硫酸盐还原可导致pH值下降，从而导致碳酸盐溶解。因此，据推测，在间冰期的有机质浓度略高，允许增加的文石溶解硫酸盐还原过程中相比，冰川床。少量的白云石胶结物（<15%）开始在同一深度（5至6米）形成，因为文石溶解加剧。白云岩的形成和文石的溶解也显示出在5至6米以下的米尺度上的协方差，表明低碳酸盐饱和状态可能会促进白云岩的形成。这种机制提供了白云石形成，文石溶解和轨道周期之间的间接联系。因此，这项研究的结果，有助于更好地了解差异成岩作用在海相碳酸盐岩。
Aragonite and high‐Mg calcite are abundant in modern, neritic carbonate systems but almost absent in their fossil counterparts. Dissolution of these metastable mineral phases commonly leaves no visible trace in the sedimentary record, compromising the derivation of palaeoenvironmental information from the rock record. The upper 25 m of Integrated Ocean Drilling Program (IODP) Site U1460 on the outer ramp of the western Australian Shelf were investigated to study shallow burial (tens of metres) marine diagenesis in organic‐carbon poor sediments using microscopic, total organic carbon, biomarkers and mineralogical analysis in combination with porewater geochemistry. Aragonite dissolution is negligible at the seafloor but intensifiesca5 m below, even though bulk porewaters are supersaturated for aragonite. This apparent contradiction likely results from dissolution in undersaturated microenvironments. Aragonite dissolution below 5 to 6 m is on average more intense in interglacial compared to glacial intervals. The presence of disseminated framboidal pyrite and porewater results indicate that minor sulphate reduction is active at IODP Site U1460. Sulphate reduction is probably limited by the low organic matter content (ca0.2%). It is well‐known from the literature that incipient sulphate reduction can lead to a drop in pH and consequently to carbonate dissolution. It is therefore assumed that the slightly higher concentration of organic matter in the interglacial intervals allowed increased aragonite dissolution during sulphate reduction compared to glacial beds. Low amounts of dolomite cement (<15%) start to form at the same depth (5 to 6 m) as aragonite dissolution intensifies. Dolomite formation and aragonite dissolution also show covariance on a metre‐scale below 5 to 6 m, indicating that a low carbonate saturation state might enhance dolomite formation. This mechanism provides an indirect link between dolomite formation, aragonite dissolution and orbital cycles. The outcome of this study, therefore, contributes to a better understanding of differential diagenesis in marine carbonates.