节点文献
弥渡地区上古生界沉积地球化学特征及古环境分析
【作者】 蔡稳；
【导师】 张世涛；
【作者基本信息】 昆明理工大学 ， 地球化学， 2010， 硕士
【摘要】 本文以中国地调局“弥渡、祥云地区1：5万区域地质矿产调查项目”为基础,通过野外地质调查,选取弥渡地区晚古生代泥盆纪—二叠纪地层为研究对象。研究区大面积发育着较为连续的晚古生代地层,这些地层各具有不同的岩石组合,形成于不同的沉积相。因此,本论文选取云南大理弥渡地区晚古生代两个代表性剖面,宏观方面从野外产状态、岩石组合以及沉积环境等方面对弥渡地区晚古生代泥盆纪—二叠纪地层做了比较系统的研究;微观方面开展了沉积岩常量元素、微量元素、稀土元素地球化学研究,试图用系统的地球化学方法来更进一步揭示研究区在地史上这段时期的沉积地球化学特征和古海洋环境及古气候的变迁。通过近两年野外地质调查及综合研究,研究结果表明：1.对云南省大理弥渡地区晚古生代泥盆纪—二叠纪地层的岩性组合特征进行了纵、横向的研究对比,并对各组岩性的空间展布做了一定的分析研究,这对综合研究该区岩相古地理具有一定的参考作用。2.在前人研究的基础上,结合各组地层岩性组合等特征认为泥盆系中统—二叠系下统各组均为海相沉积。区内泥盆系中统莲花曲组应为浅海陆棚相沉积；泥盆系中统—上统长育村组应为深海相—次深海相沉积,出现水体向上逐渐变浅的变化特征,沉积环境向台地相转变；石炭系下统横阱组属于低能的碳酸盐台地相沉积；石炭系上统—二叠系下统水长阱组仍为台地边缘浅滩相沉积；二叠系中统阳新组仍以开阔台地相-台后盆地相为主体,随水动力加强,逐步演化为高能的台地边缘浅滩环境。泥盆系中统—二叠系中统总体水深变化特征为：浅水→深水→次深水→浅水。3.本文对研究区晚古生代各个地层常量元素、微量元素、稀土元素的沉积地球化学特征进行分析、归纳、总结。分析结果表明：①泥盆系莲花曲组—二叠系阳新组地层绝大多数样品m值与B/Ga都属于海相沉积范畴,泥盆纪-二叠纪地层均为海相沉积；②Ni/Co比值是反应古氧相的良好地球化学指标。泥盆系莲花曲组Ni/Co比值大多数<5,平均值为4.9属于富氧环境；泥盆系长育村组Ni/Co比值总体>5,平均值为5.74属于贫氧环境；石炭系横阱组Ni/Co比多数>5,平均值为5.22仍属于贫氧环境；石炭二叠系横阱组Ni/Co比多数>5,平均值为5.22仍属于贫氧环境；石炭系水长阱组-二叠系阳新组Ni/Co绝大多数<5,平均值为3.79属于富氧环境；因此,泥盆纪—二叠纪古氧相变化规律总体呈现富氧→贫氧→次富氧的变化特征。③对各个地层进行了古海水盐度的计算,泥盆系莲花曲组古盐度变化范围在8.60‰～13.67‰之间,平均值为11.75‰,海水盐度为半咸水环境；泥盆系长育村组古盐度变化范围在2.50‰～8.29‰之间,大多数样品S>3%o,平均值为4.64‰,此时海水盐度整体上为半咸水环境；石炭系下统横阱组古盐度变化范围在0.46‰～3.12‰之间,平均值为1.67‰,S<3‰,早石炭世海水盐度较低。石炭—二叠系水长阱组—石炭系中统阳新组古盐度变化范围在0.03‰～4.46‰之间,大多数样品S<3%o,平均值为2.25%o,说明自晚石炭世—中二叠世古海水盐度一直维持在较低的水平,可能与大陆边缘河水注入有关。计算结果表明古海水盐度经历了半咸水环境海水盐度逐渐降低的变化过程。④对各个历史时期古环境的气候特征运用常量元素指标ω(MgO)/ω(CaO)进行判别,得出研究区晚古生代泥盆纪-二叠纪气候总体变化趋势是从干热气候变为温湿气候；4.研究区泥盆系长育村组发育有大量的灰色—黑色的薄层状硅质岩,硅质岩水平纹层发育。本文对硅质岩样品成因进行了探讨分析。研究区硅质岩样品常量元素具有Al/(Al+Fe+Mn)值为0.24～0.56,落在热水成因硅岩标准内,并且普遍具有高Si02低TiO2、MgO、Al2O3、和∑REE含量的特征,北美页岩标准化的稀土分配模式平坦,且具δCe<1负异常与δEu>1正异常,轻稀土元素富集。表明研究区硅质岩具有明显的热水沉积成因属性,同时有陆源组分的加入。5.研究区Al2O3/(Al2O3+Fe2O3)-Fe2O3/TiO2图解与Al2O3/(A12O3+Fe2O3)-La/Ce图解说明该地区的沉积岩形成于大洋盆地和大陆边缘之间的构造背景下,海底裂谷拉伸,硅质岩形成受到了海底热液的影响。
【Abstract】 This paper is based on the "Midu、Xiangyun 1:5 million regional geology and mineral resources survey project" of China Geological Survey Bureau, Through the field investigation, select Midu regional Paleozoic Devonian-Permian strata to study. In the study area the Late Paleozoic strata was relatively large and continuou developed, they all have different rock strata combined, formed in different sedimentary facies. Therefore, in this thesis, Choose two representative The Late Paleozoic sections of Dali Midu, the macro aspects conducted Systemaly researc on the production from the wild state, rock composition and depositional environment, of the Midu Late Paleozoic Devonian-Permian strata; micro aspects conducted sedimentary rocks geochemistry researc of Constant element、Trace Elements and REE elements, Trying to use the system geochemical method further that ancient sedimentary geochemistry、the marine environment and ancient climate changof the study area in this history period. After nearly two years, field investigation and comprehensive study, made the following understanding:1. We make vertical and horizontal comparison study of Late Paleozoic Devonian-Permian lithologic characteristics of Midu Dali, Yunnan Province.And each group spatial distribution of lithology has done some analysis, which comprehensive study of lithofacies palaeogeography of the area has some reference.2. Based on previous studies, combined with the lithology combination group characteristics, We believe that the stratum between Mid-Devonian and Early-Permian was Marine deposit. The lianhuaqu stratum group of Mid-Devonian was Shallow shelf sediments; The changyucun stratum group of Middle to late Devonian was deep-sea sediments and the water lever gradually shallowed. Sedimentary environment transformed to Platform facies. The hengjing stratum group of ealy-Carboniferous was Carbonate Platform facie. Later stratum kept Platform margin shoal facies until shuichangjing stratum,which is belong to ealy Permian. Then the yangxin stratum of mid-Permian was Open platform and Basin facies yet. As the dynamic of water enhanced, it became high-energy platform margin shoal environment, From Mid-Devonian to Mid-Permian,the Water depth characteristics: shallow water→deep water→sub-shallow water→shallow water. 3. We analysis and summarized the various strata of Late Paleozoic and trace elements, REE geochemical characteristics of sedimentary. The results show that:①The lianhuaqu Group Devonian-Permian formation in most samples Sr/Ba ratio of the overall performance of the marine sedimentary environment;②Ni/Co ratio is the reaction of oxygen with a good old geochemical indicators. Most of the lianhuaqu Group of Devonian Ni/Co ratio are under 5, an average of 4.9 are oxygen-rich environment;The changyuchun Devonian Ni/Co ratio of the overall >5, an average of 5.74 are poor oxygen environment; Carboniferous Horizontal Well Unit Ni/Co than most> 5, an average of 5.22 is still a poor oxygen environment; Carboniferous-Permian horizontal wells group Ni/Co ratio of the majority of> 5, the average is 5.③Each stratum of the ancient sea water salinity calculated results show that the ancient sea water salinity brackish water environment through the process of change→salt water environment;④On the various historical periods of ancient climatic characteristics of the environment indicators using constant elementω(MgO)/ω(CaO) to discriminate, that the study of the Late Paleozoic, the general trend of climate is dry and hot climate becomes warm and humid climate;4. The changyuchun Devonian in the study area developed a large number of gray-like thin black chert, siliceous rock level laminar development. In this paper, cherts discussed the origin of the sample. Siliceous rocks in the study area has a constant element of Al/(Al+Fe+Mn) value of 0.24-0.56, fall within the standard hydrothermal chert, and generally have high SiO2 low TiO2, MgO, Al2O3, andΣREE content features, the North American shale standard flat rare earth distribution patterns, and possessedδCe<1 negative anomalies and 8Eu> a positive anomaly, LREE enrichment. Suggesting that the chert has obvious hydrothermal sedimentation properties, while a terrestrial component of the accession.5. We use the Al2O3/(Al2O3+Fe2O3)-Fe2O3/TiO2 diagram and Al2O3/(Al2O3+ Fe2O3)-La/Ce diagram to explain the study eara structure,which is formed between sea basin to the land border when the bottom of the sea drawing. Also the siliceous rock was impacted by the submarine hydrothermal.