塔里木下寒武统富有机质沉积层段地球化学特征及意义

塔里木盆地寒武系下统玉尔吐斯组底部富有机质沉积层段分布广泛,层位稳定,其中的硅质岩发育,并伴有磷矿产出.硅质岩的Al(Al Fe Mn)和Si/(Si Al Fe)比值分别在0.0023～0.0046和0.965～0.98之间,表明其形成于海底热水沉积环境,远离陆源区.富有机质沉积层段明显富集As、Hg、Pb、Zn、Cu、Co、P、V、Ba等微量元素,富集系数F(N)远大于1.Ba/Sr比值远远大于1,与现代海底热水沉积物中的Ba/Sr比值相似,具有明显的海底热水沉积特征;Th/U和V/Sc比值显示其形成与海洋缺氧事件有关,而导致缺氧事件发生的主要原因则是海底火山作用及其与之相伴的海底热水流体活动.

Geochemical Characteristics of Organic Matter-rich Sedimentary Strata in Lower Cambrian, Tarim Basin and Its Origins

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.