上扬子板块陡山沱组黑色页岩硒的地球化学

发布时间：2018-02-23 19:39

本文关键词： 埃迪卡拉纪陡山沱组硒的富集古海洋环境 Mo-U关系硒同位素　出处：《贵州大学》2016年硕士论文　论文类型：学位论文

【摘要】：新元古代-早寒武世发生了地质历史上第二次大氧化事件,沉积岩中的氧化还原敏感元素在这一时期出现富集。分散元素硒是典型的氧化还原敏感元素,沉积岩中硒的富集可以指示海洋氧化环境的变化。为了讨论这一时期海洋氧化还原条件及硒的富集条件,本文所取上扬子地区6条陡山沱组剖面,白果园剖面、九龙湾剖面、陈家院子剖面、五河剖面、南皋剖面和三都剖面,对第四段黑色页岩的总硒含量,主量元素,微量元素及硒同位素的系统分析研究,初步的认识包括:(1)总硒含量测试测结果显示所测六个剖面黑色页岩Se均远高于Se的地壳丰度(0.05ppm),形成了不同程度的富集。硒的富集随剖面深度的增加而减弱。在白果园剖面、九龙湾剖面、陈家院子剖面、五河剖面,其黑色页岩的Se含量主要来自陆源风化物质的输入;而南皋剖面和三都剖面的黑色页岩中的Se可能来自陆源物质输入和热水(氧化性流体)物质。陡山沱组第四段黑色页岩Se元素的富集与Co、Ag、V等氧化还原敏感元素都有不同程度的相关性,反映了不同剖面Se的地球化学行为的区别。Se含量与Co含量的相关性反映了Se的富集与生物作用的关系;Se含量与Ag含量、Se含量与V含量的关系则暗示了Se(-Ⅱ)与Ag、V的结合物并形成共同富集。(2)结合Mo-U体系指示了这一时期上扬子板块不同程度的缺氧环境,对Se富集的影响进行探究:白果园剖面位于浅海相,主要为缺氧环境,陆源物质最为丰富,Se的富集程度最高;九龙湾剖面可能处于更深的稳定硫化水体位置,有较为稳定的缺氧(硫化)环境,Se被充分转化为还原态并与Ag、V结合形成富集;陈家园子剖面可能处于硫化水体的下缘,海洋环境的缺氧程度存在波动,富集程度略低于九龙湾剖面;贵州黔东南五河剖面处于斜坡相,硫化水体间歇出现,为较稳定的缺氧环境,Se的富集程度与陈家园子剖面相似;贵州黔东南南皋剖面处于斜坡相,生物作用较为薄弱,Se的富集程度低;贵州黔东南三都剖面处于斜坡相向深海相过渡的地带,为铁化海水环境,Se的富集程度最低。(3)结合实测的硒同位素数据和同时代前人数据对比,对海洋中硒同位素分馏的分层情况做了简单分析。浅海相陈家园子剖面陡山沱组第四段黑色页岩δ82/76Se的变化范围为0.30‰~1.65‰,平均值为0.73‰,偏向重的硒同位素组成。Srtandmann等(2015)对陡山沱斜坡相(斜坡相)的黑色页岩测试δ82/76Se值范围为-0.84~0.48‰,平均值为指示所处古海洋环境可能为厌氧和富铁的海水环境,轻的硒同位素分馏潜在的指示了其缺氧铁化的海洋环境。(4)综合前人数据,海洋中的无机态硒Se(Ⅳ)和Se(Ⅵ)在含氧环境中无机态硒可以通过吸附作用部分进入深海沉积物中,而在缺氧或静海环境中可以部分转化为Se(0)或形成Se(-II)进入沉积物。在低氧至缺氧/静海环境中,在沉积物中Se(Ⅳ)和Se(Ⅵ)也可以转化为Se(0)或Se(-II)。上扬子板块埃迪卡拉纪陡山沱组第四段黑色页岩硒的富集作用跟海平面上升、生物作用、硫化楔、铁化水体和不稳定的缺氧海洋环境有关,不同剖面的区域因素也造成了富集程度的差异。
[Abstract]:The Neoproterozoic Early Cambrian happened second times in the geological history of the great oxidation event, the oxidation of sedimentary rocks in the reduction of sensitive elements in this period. Enrichment of dispersed elements selenium is typical of redox sensitive elements in sedimentary rocks, selenium enrichment can indicate marine oxidation changes in the environment. In order to discuss the enrichment conditions during the period of oceanic redox conditions and selenium, the upper Yangtze region 6 Doushantuo Formation section, Baiguoyuan section, Jiulongwan section, Chen courtyard section, Wuhe section, South Gao profile and Sandu section, the total selenium content of fourth black shale, major elements, trace analysis system the elements and selenium isotopes, preliminary understanding include: (1) test total selenium content measurement results show that the crustal abundance measured by the six sections of the black shale Se was much higher than that of Se (0.05ppm), forming a different degree of enrichment of selenium enrichment with cesarean section. The increase of the surface depth decreases. In the orchard white section, the Jiulongwan section, Chen courtyard section, five profile, Se contents of the black shale mainly from terrigenous weathered material input; and the south bank section and Sandu section in the black shale Se may come from terrigenous input and hot water (oxidizing fluid) material. Enriched with Co, Doushantuo Formation fourth black shale Se elements Ag, V and other redox sensitive elements have different degree of correlation, reflect the correlation of the geochemical behavior of different profiles of Se difference between.Se content and Co content reflects the relationship between the enrichment and the biological effect of Se Se content and Ag content; and the relationship between Se content and V content, suggesting that Se (II) and Ag, V conjugates and the formation of common enrichment. (2) combined with the Mo-U system indicates that this period of the Yangtze plate in different hypoxia environment, to explore the effects of Se enrichment: Baiguoyuan section located in neritic facies, mainly for anoxic environment, the most abundant terrestrial material, Se enrichment degree is the highest; the Jiulongwan section may be in a stable position of deeper water curing, oxygen stable (vulcanization) environment, Se is fully transformed into reduced and Ag, V combined with the formation of enrichment; the lower edge of Chen home section may be in sub water curing, the degree of hypoxia of the marine environment fluctuates and enrichment degree is slightly lower than the Jiulongwan section; Guizhou Qiandongnan Wuhe section in slope facies, sulfide water intermittent, anoxic environment is stable, the degree of Se enrichment and Chen home sub section is similar to Guizhou Qiandongnan south bank section; in the slope. The biological effect is relatively weak, the enrichment degree of Se low profile in Guizhou; Qiandongnan Sandu slope transition zone to deep sea facies, marine environment for iron, Se enrichment degree (3) with the lowest. Selenium isotopic data measured and previous data at the same time of contrast, layered selenium isotope fractionation in the sea to do a simple analysis. The variation range of the neritic sub section of Chen Jia Yuan Doushantuo Formation fourth black shale delta 0.30 82/76Se% ~1.65%, the average value was 0.73 per thousand, selenium isotope composition of.Srtandmann heavy bias and (2015) of the Doushantuo slope (slope) of the black shale test 82/76Se values in the range of -0.84~0.48%, the average value is indicative of ancient marine environment for anaerobic and iron rich seawater, light selenium isotope fractionation potential indicates the hypoxia iron environment. (4 based on previous data), inorganic selenium in oceanic Se (IV) and Se (VI) in oxygen environment in inorganic selenium by adsorption into the deep-sea sediments, while in hypoxia or the environment in Jinghai can be partially converted into Se (0) or Se (- form II) into the sediments. In hypoxia to hypoxia / environment in Jinghai, in the sediment Se (IV) and Se (VI) can also be converted to Se (0) or Se (-II) on the Yangtze plate. Eddie from the Doushantuo Formation of fourth black shale selenium enrichment with sea-level rise, biological effect wedge iron, sulfide, water and unstable anoxic marine environment, regional factors of different sections also caused different degrees of enrichment.

【学位授予单位】：贵州大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：P595

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