松桃地区大塘坡组地球化学特征与古海洋化学状态研究

发布时间：2018-11-15 17:51

【摘要】：我国华南地区新元古代晚期到寒武纪早期地层发育完整,保存完好,该地区的各项重大研究发现成果引起了国内外地质学者的的高度关注,使得华南地区成为进行生命早期演化研究的国际经典地区。南华系海洋的化学状态的研究对于认识新元古代时期的生物的演化以及成矿规律具有重要意义。本文在前人研究基础上,通过野外地质剖面及钻井岩心的系统采样,借助XRD、扫描电子显微镜和X射线荧光光谱仪等测试手段,分析松桃地区大塘坡组的岩石学特征,主、微量地球化学特征及岩石中铁组分、硫同位素特征,分析古海洋环境的化学状态。华南松桃南华系大塘坡组为一套海相沉积的岩石类型,主要岩石类型为碳质页岩、含锰碳质页岩、硅质岩等。大塘坡组第二、三段主要岩石类型有页岩、粉砂质页岩、砂质页岩。研究区岩石样品中含量最高的矿物为石英和粘土矿物。华南松桃大塘坡组的锰矿石样品的n(Al_2O_3)/n(Al_2O_3+Fe_2O_3)等比值反映了远洋深海沉积特征,而围岩具明显的大陆边缘沉积特征;n(SiO_2)/n(Al_2O_3)等比值都反映了南华系大塘坡组沉积物源以陆源为主,并伴随着一定的热水作用,且锰矿石的形成受热水作用影响比较大;Sr/Ba指标反映了大塘坡组岩系形成于深水环境中,大塘坡组二、三段岩石形成的水体深度相对较浅,为浅海陆棚到台地边缘斜坡过渡的环境;Rb/Sr等比值都反映了锰矿石形成于热的气候环境,而围岩则形成于干燥的气候环境,且气候变化的波动明显;U、V、Mo等氧化还原指标的研究显示,大塘坡组第一段形成环境为较强的缺氧环境,而矿层和二、三段为弱缺氧-还原环境。华南松桃大塘坡组铁组分及硫同位素数据表明,大塘坡组第一段中锰矿石形成于缺氧铁化的环境,而第一段围岩形成于缺氧硫化的环境,第二、三段的沉积环境中几乎无硫化水体的发展,开始出现氧化的水体。综合南华系大塘坡组地球化学特征、铁组分及硫同位素数据以及沉积环境等得出,松桃地区南华系大塘坡组的古海洋化学状态总的来说大致符合晚新元古代华南盆地的三明治‖海洋化学模型,即表层为氧化水体,深部为缺氧铁化的状态,而在二者之间浅海局部区域出现动态的硫化的水体。
[Abstract]:The late Neoproterozoic to early Cambrian strata in South China are well developed and well preserved. It makes South China become the international classical area for the study of early life evolution. The study of the chemical state of the South China ocean is of great significance in understanding the evolution and metallogenic regularity of organisms in the Neoproterozoic period. On the basis of previous studies, this paper analyzes the petrological characteristics of Datangpo formation in Songtao area by means of systematic sampling of field geological profiles and drilling cores, and by means of XRD, scanning electron microscope and X-ray fluorescence spectrometer. The trace geochemical characteristics, iron composition and sulfur isotopic characteristics of the rocks are used to analyze the chemical state of the paleo-marine environment. The Datangpo formation of the South China Series of Songtao in South China is a set of marine sedimentary rock types, the main rock types are carbonaceous shale, manganese carbonaceous shale, siliceous rock and so on. The main rock types of the second and third member of Datangpo formation are shale, silty shale and sandy shale. Quartz and clay minerals are the most abundant minerals in rock samples in the study area. The ratios of n (Al_2O_3) / n (Al_2O_3 Fe_2O_3) of manganese ore samples of Songtao Datangpo formation in South China reflect the deep-sea sedimentary characteristics, while the surrounding rocks have obvious continental margin sedimentary characteristics. The ratios of n (SiO_2) / n (Al_2O_3) all reflect that the sediment source of Datangpo formation of South China series is mainly continental and accompanied by certain hot water, and the formation of manganese ore is greatly influenced by hot water. The Sr/Ba index reflects that the rock series of the Datangpo formation was formed in the deep water environment, and the water depth of the second and third sections of the Datangpo formation is relatively shallow, which is the environment of the transition from the shallow sea shelf to the platform margin slope. The ratios of Rb/Sr and so on reflect that manganese ore is formed in the hot climate environment, while the surrounding rock is formed in the dry climate environment, and the fluctuation of climate change is obvious. The study of redox indexes such as U _ (V) Mo shows that the formation environment of the first member of the Datangpo formation is a strong anoxic environment, while the ore-bed and the second and third stages are weak anoxia-reduction environment. The iron composition and sulfur isotopic data of Datangpo formation in Songtao, South China show that the manganese ores in the first member of the Datangpo formation were formed in anoxic iron-forming environment, while the surrounding rocks in the first section were formed in the environment of anoxic sulfidation. The depositional environment of the third member almost has no sulphide water development, and the oxidized water body begins to appear. Based on the geochemical characteristics of the Datangpo formation of the South China series, the data of iron and sulfur isotopes, and the sedimentary environment, etc., The paleo-marine chemical state of the Datangpo formation of the South China series in Songtao area is generally consistent with the marine chemistry model of the late Neoproterozoic South China basin, I. E. the surface layer is oxidized water body and the deep layer is anoxic iron. Dynamic sulfided water appeared in the local area of shallow water between them.
【学位授予单位】：中国矿业大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：P596

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