Pyrite and organic matter in Phanerozoic normal marine shales
Pyrite and organic matter in Phanerozoic normal marine shales
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DOI：
10.1016/0016-7037(86)90252-8
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发表时间：
1986-09
影响因子：
5
通讯作者：
R. Raiswell;R. Berner
中科院分区：
文献类型：
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作者：
R. Raiswell;R. Berner
从我们自己的化学分析和文献中获得了600多个寒武纪到现代正常海相页岩样品中有机碳（C）和黄铁矿硫（S）浓度的数据。（正常海洋是指含氧底层水中的沉积物，其证据是存在底栖化石和/或生物扰动迹象）。选择所有样品以使1最小化。(1)C和/或S因露头风化而损失（通过强调使用岩心材料）2. (2)分析误差和非成岩效应（避免C或S含量低的沉积物，如砂岩）3. (3)黄铁矿形成的铁限制（通过避免石灰岩，硅质岩和富氧页岩）4。(4)C相对于S的变质损失（通过避免岩石明显受到变质，即使是低级变质）。我们的结果表明：（1）对于所有年龄的正常海相页岩，有机碳和黄铁矿S之间通常存在良好的正线性相关性;（2）正常海相页岩的平均C S比随时间而变化。泥盆纪至第三纪页岩的平均C S重量比（1.8±0.5）略低于第四纪沉积物（平均C S= 2.8）。我们认为，这是由于优先C损失（相对于S）在生物甲烷加上成岩加热。寒武系和奥陶系的平均C/S值明显较低（0.5±0.1），不能仅仅用成岩C损失来解释，而是必须代表低的原始比率。我们认为，低的原始比率主要是由于当时河流向海洋环境中添加的细菌难降解有机物的缺乏，因为这种物质的主要来源，维管陆地植物，尚未进化。这一点，沿着可能较低程度的生物扰动，有助于增强黄铁矿的形成和保存，因此，较低的早古生代C S比。
Data have been obtained, from our own chemical analyses and from the literature, for the concentrations of organic carbon (C) and pyrite sulfur (S) in over 600 samples of Cambrian to recent normal marine shales.(Normal marine refers to deposition in oxygenated bottom water as evidenced by the presence of benthic fossils and/or indicators of bioturbation). All samples were selected to minimize 1.(1) loss of C and/or S due to weathering at the outcrop (by emphasizing the use of drill core material) 2.(2) analytical errors and non-diagenetic effects (by avoiding sediments low in C or S content such as sandstones) 3.(3) Fe limitation of pyrite formation (by avoiding limestones, cherts, and euxinic shales) 4.(4) metamorphic loss of C, relative to S (by avoiding rocks obviously subjected to, even low-grade, metamorphism). Our results indicate that (1) there is generally a good positive linear correlation between organic C and pyrite S for normal marine shales of all ages and (2) the mean C S ratio for normal marine shales has varied over time. Devonian to Tertiary shales exhibit mean C S weight ratios (1.8±0.5) somewhat lower than Quaternary sediments (mean C S= 2.8). This we believe is due to preferential C loss (relative to S) during biogenic methanogenesis plus diagenetic heating. Distinctly lower mean C/S values for the Cambrian and Ordovician (0.5±0.1) cannot be explained solely in terms of diagenetic C loss and, instead, must represent low original ratios. The low original ratios, we suggest, were due mainly to the absence of bacterially refractory organic matter added to the marine environment by rivers at that time, because the major source of such material, vascular land plants, had not yet evolved. This, along with a possibly lower degree of bioturbation, contributed to enhanced pyrite formation and preservation and, thus, lower early Paleozoic C S ratios.