Quantifying early marine diagenesis in shallow-water carbonate sediments
Quantifying early marine diagenesis in shallow-water carbonate sediments
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DOI：
10.1016/j.gca.2018.02.042
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发表时间：
2018-09-01
影响因子：
5
通讯作者：
Higgins, John A.
中科院分区：
文献类型：
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作者：
Ahm, Anne-Sofie C.;Bjerrum, Christian J.;Higgins, John A.
浅水碳酸盐沉积物是地球表面演化最丰富、应用最广泛的档案之一。该档案的主要局限性之一是碳酸盐沉积物的化学性质对沉积后成岩作用的敏感性。在这里，我们建立了一个海洋碳酸盐成岩作用的数值模型，该模型跟踪了原生碳酸盐溶解和次生碳酸盐矿物再沉淀过程中钙、镁、碳、氧和锶的元素和同位素组成。该模型通过测量巴哈马平台及其附近的地球化学指标（Higgins et al., 2018）和富含有机物的深海蒙特雷组自生碳酸盐（Blattler et al., 2015）进行地面验证。从这些不同的沉积学和成岩环境中观察到，大块沉积物钙和镁同位素之间存在广泛的共变，这可以通过海水缓冲或沉积物缓冲条件下沉积物成岩作用程度的变化来解释。模型结果表明，钙和镁同位素的共变可以对早期海洋成岩作用的程度和类型（流体缓冲与沉积缓冲）提供半定量的估计。当应用于古碳酸盐岩的地球化学特征时，该模型可用于量化早期海相成岩作用对其他感兴趣的地球化学指标（如碳和氧同位素）的影响。人们越来越认识到早期海洋成岩作用是浅水碳酸盐沉积物中的一种重要现象，这使得这种方法对于从碳酸盐沉积物的化学和同位素组成中准确记录地球的化学和气候历史至关重要。(C) 2018 Elsevier Ltd.版权所有。
Shallow-water carbonate sediments constitute one of the most abundant and widely used archives of Earth's surface evolution. One of the main limitations of this archive is the susceptibility of the chemistry of carbonate sediments to post-depositional diagenesis. Here, we develop a numerical model of marine carbonate diagenesis that tracks the elemental and isotopic composition of calcium, magnesium, carbon, oxygen, and strontium, during dissolution of primary carbonates and re-precipitation of secondary carbonate minerals. The model is ground-truthed using measurements of geochemical proxies from sites on and adjacent to the Bahamas platform (Higgins et al., 2018) and authigenic carbonates in the organic-rich deep marine Monterey Formation (Blattler et al., 2015). Observations from these disparate sedimentological and diagenetic settings show broad covariation between bulk sediment calcium and magnesium isotopes that can be explained by varying the extent to which sediments undergo diagenesis in seawater-buffered or sediment-buffered conditions. Model results indicate that the covariation between calcium and magnesium isotopes can provide a semi-quantitative estimate of the extent and style (fluid-buffered vs. sediment-buffered) of early marine diagenesis. When applied to geochemical signatures in ancient carbonate rocks, the model can be used to quantify the impact of early marine diagenesis on other geochemical proxies of interest (e.g. carbon and oxygen isotopes). The increasing recognition of early marine diagenesis as an important phenomenon in shallow-water carbonate sediments makes this approach essential for developing accurate records of the chemical and climatic history of Earth from the chemical and isotopic composition of carbonate sediments. (C) 2018 Elsevier Ltd. All rights reserved.