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首页> 外文期刊>Earth and Planetary Science Letters: A Letter Journal Devoted to the Development in Time of the Earth and Planetary System >Organic matter and trace element rich sapropels and black shales: a geochemical comparison
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Organic matter and trace element rich sapropels and black shales: a geochemical comparison

机译：有机物和富含微量元素的腐殖质和黑色页岩：地球化学比较

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摘要

A distinct Pliocene eastern Mediterranean sapropel (i-282), recovered from three Ocean Drilling Program (ODP) Leg 160 Sites, has been investigated for its organic and inorganic composition. This sapropel is characterized by high organic carbon (C_(org)) and trace element contents, and the presence of isorenieratene derivatives. The latter suggests that the base of the photic zone was sulphidic during formation of the sapropel. Combined with evidence of bottom water anoxia (preservation of laminae, high redox-sensitive trace element contents, and the abundance and isotopic composition of pyrite) this leads to the tentative conclusion that almost the entire water column may have been anoxic. This anoxia resulted from high productivity and not from stagnation, because an approximation of the trace element budget during sapropel formation shows that water exchange with the western Mediterranean is needed. Entire water column anoxia has been suggested earlier for several black shales. With regard to the depositional environment and the C_(org) content, however, only the Cenomanian/Turonian Boundary Event (CTBE) black shales appear to be comparable to this sapropel. The proposed trace element removal mechanism of scavenging and (co-)precipitation in an anoxic water column, is thought to be similar for both types of deposits. The ultimate trace element source for the sapropel, however, is seawater, whereas it is hydrothermal and fluvial input for CTBE black shales (because they have a larger temporal and spatial distribution). Nonetheless, the C_(org)-rich eastern Mediterranean Pliocene sapropel discussed here may be considered to be a younger analogue of CTBE black shales.
机译：从三个海洋钻探计划（ODP）Leg 160站点回收的独特的上新世东地中海腐石（i-282），已对其有机和无机成分进行了研究。该腐烂植物的特征是有机碳含量高（C_（org））和痕量元素含量高，并且存在异烯戊二烯衍生物。后者表明，在腐草素形成过程中，光合带的底部是硫化的。结合底部缺氧的证据（层流的保存，对氧化还原敏感的痕量元素的高含量以及黄铁矿的丰度和同位素组成），得出了一个结论，即几乎整个水柱可能都是缺氧的。这种缺氧的原因是生产力高而不是停滞，因为在腐殖质形成过程中微量元素收支的近似值表明需要与地中海西部进行水交换。早先已建议对几种黑色页岩进行全水柱缺氧。但是，关于沉积环境和C_（org）含量，只有塞诺曼尼亚/土伦边界事件（CTBE）黑色页岩似乎可以与该腐泥相媲美。对于两种类型的沉积物，拟议的在缺氧水柱中清除和（共）沉淀的微量元素去除机理被认为是相似的。然而，腐殖质的最终微量元素来源是海水，而CTBE黑色页岩则是水热和河流输入（因为它们的时空分布较大）。但是，这里讨论的富含C_（org）的东地中海上新世腐殖土可能被认为是CTBE黑色页岩的年轻类似物。

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