Geochemical Characteristics of Organic Matter-rich Sedimentary Strata in Lower Cambrian, Tarim Basin and Its Origins
Geochemical Characteristics of Organic Matter-rich Sedimentary Strata in Lower Cambrian, Tarim Basin and Its Origins
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发表时间：
2004
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通讯作者：
Sun Xing-li
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作者：
Sun Xing-li
塔里木盆地是中国西北部面积最大、勘探程度最低的含油气盆地。在塔里木盆地海相沉积地层中，下寒武统的尤尔图斯组已被证实是塔里木盆地的主要生油岩之一。于尔图斯组可分为两层，下层为黑色页岩、硅质岩、磷灰岩和少量石灰岩，黑色页岩夹杂硅质岩，上层为白云岩。硅质岩的Al(Al+Fe+Mn)比值和Si/(Si+Al+Fe)比值分别为0.0023~0.0046和0.965~0.98时，表明硅质岩形成于远离陆源区的海底热液喷发环境。在由黑色页岩、硅质岩、磷岩和少量石灰岩组成的富含有机质的沉积层中，As、Hg、铅、锌、铜、钴、P、V、Ba等微量元素含量丰富，其集中系数均大于1。硅质岩、页岩和石灰岩中的Ba/Sr比值远大于1，具有现代海底热水沉积的地球化学特征。Th/U和V/Sc比值分别在0.018~0.735和81.0~7800之间变化，表明它们形成于海洋缺氧事件。富含有机质沉积地层的地球化学特征表明，海洋缺氧的成因是火山作用的产物，并伴随着海底的热液喷发。
Tarim basin is the largest and the least explored petroliferous basin in the northwest of China. In marine sedimentary strata of Tarim basin, Yurtusi formation belongs to Lower Cambrian has been proved to be one of the main source rocks. Yurtusi formation can be divided into two horizons, i.e. lower horizons consist of black shale,chert, phosphorite and minor limestone, black shale intercalated with cherts and upper horizons are dolomite. Al(Al+Fe+Mn) ratio and Si/(Si+Al+Fe) ratio of cherts rangs from 0.0023 to 0.0046 and 0.965 to 0.98, respectively, it suggests that cherts formed in the submarine hydrothermal venting environments which is far away terrigenous area. Trace elements, such as As, Hg, Pb, Zn, Cu, Co, P, V, Ba, are abundant in organic matter rich sedimentary strata consisting of black shale,chert, phosphorite and minor limestone,and their concentrated factors are over 1. The Ba/Sr ratio are much more than 1 in cherts, shale and limestone, which has similar geochemical feature with modern sea-floor hydrothermal sediments. Th/U and V/Sc ratio range from 0.018 to 0.735 and 81.0 to 7800, respectively, indicating that they formed in ocean anoxia event. The geochemical characteristics of organic matter-rich sedimentary strata show that the cause of oceanic anoxia is resulted from volcanism and companied with hydrothermal venting in seafloor.