Hydrothermal Venting on the Seafloor and Formation of Organic-rich Sediments--Evidence from the Neoproterozoic Xiamaling Formation, North China
Hydrothermal Venting on the Seafloor and Formation of Organic-rich Sediments--Evidence from the Neoproterozoic Xiamaling Formation, North China
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发表时间：
2003
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通讯作者：
Wang Darui
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作者：
Wang Darui
松辽坳陷新元古代下马岭组主要由黑灰色页岩、黄绿色页岩、粉砂质泥岩和硅质岩组成。在黑灰色页岩中，广泛分布着层状和薄层状硅质岩。利用X射线荧光光谱和热解分析（Rock-Eval）仪对北京下马岭剖面和河北下花园剖面的样品进行了系统的分析。结果表明，富有机质层中SiO2含量为69。63%到91。有机质含量与总有机碳（TOC）含量成正比，与TiO 2含量成反比，TiO 2是典型的陆源组分。Pb、Zn、P、Co、Ni、V等与海底热液喷发有关的元素在富有机质沉积物中富集，并与TOC成正比。富有机质沉积物中Ba/Sr的比值为5。6到31 8，这表明海底的热液喷口很强。在下马岭剖面，页岩中的层状和薄层硅质岩从Qb 1x 3向上逐渐增加，沿着TOC含量迅速增加。地质和地球化学研究表明，下马岭组富有机质沉积物形成时，盆地处于强烈的拉张和坳陷状态，热液喷发伴随着构造运动。海底热液的排出可以为热水区的嗜热微生物提供营养，并导致底层水缺氧，有利于有机质的保存。
The Neoproterozoic Xiamaling Formation in the Yanliao depression consists mainly of black-gray shale, yellowish green shale, silty mudstone and cherts. In the black-gray shale, laminar and thin-bedded cherts are widely distributed. Samples systemically collected from the Xiamaling section in Beijing and Xiahuayuan section in Hebei Province are analyzed with the X-ray fluorescence spectrum and analysis of pyrolysis (Rock-Eval) instrument. The results shows that the content of SiO2 in the organic -rich layers ranges from 69. 63% to 91. 09%, higher than in the normal mudstone, and is in direct proportion to the total organic carbon (TOC), but in inverse proportion to the contents of TiO2, which is typical of terrigenous component. The elements of Pb, Zn, P, Co, Ni and V, which are related to hydrothermal venting on the seafloor, and are rich in the organic-rich sediments,and in direct proportion to TOC. The ratio of Ba/Sr in the organic-rich sediments ranges from 5. 6 to 31. 8, which suggests that hydrothermal venting on the seafloor was strong. In the Xiamaling section, laminar and thin-bedded cherts in shale increase in volume gradually from Qb1x3 to upper strata, along with a rapid increase in the content of TOC. The geology and geochemistry indicate that the basin was in strong extension and depression during the formation of the organic-rich sediments of the Xiamaling formation and hydrothermal venting followed with tectonism. Hydrothermal venting on the seafloor can supply nutrition for thermophile microorganism blooming in the area of hot water, and result in the formation of anoxia in bottom water beneficial for the preservation of organic matter.