川渝地区下三叠统海相碳酸盐岩的碳氧同位素研究

发布时间：2018-07-29 12:17

【摘要】：地球与生命的起源、发展与演化一直是地球科学研究的热点领域,早三叠世处于古—中生代地质突变转折期,因晚二叠世生物大灭绝和早三叠世萧条的生态复苏而受到了人们广泛的关注。论文以四川盆地丰富的下三叠统碳酸盐岩为研究载体,在异常地质事件及异常沉积记录背景下,对四川盆地6条地表剖面碳酸盐岩样品进行了岩石学、元素和碳氧同位素分析,探讨了早三叠世海相碳酸盐岩碳同位素异常震荡的可能驱动机制及早三叠世白云石与伴生方解石的碳氧同位素组成差异。利用薄片观察、阴极发光、扫描电镜及能谱分析等多项研究手段对研究区样品进行了详细的岩石学特征研究,同时选择Mn/Sr比值和δ18O值来评估样品对海水地球化学信息的代表性。研究表明:泥微晶灰岩对海水信息有较好的代表性,绝大多数颗粒灰岩、过渡岩类和白云岩在很大程度上保存了古海水的信息,重结晶灰岩对古海水信息的代表性较差,而盐溶角砾岩-次生灰岩代表了表生环境的地球化学信息,其地球化学特征已经明显偏离了古海水的特征。在详细的成岩蚀变评估基础上建立了3条早三叠世海相碳酸盐岩碳同位素演化曲线,并进行了全球性与区域性对比,表明所建立的碳同位素演化曲线具有很好的全球和区域可对比性,显示碳酸盐岩碳同位素在晚二叠世-早三叠世经历了数次不同幅度的震荡,主要包括P/T界线附近急剧的负偏移,Denerian-Smithian、Smithian-Spathian、Spathian-Anisian界线处的三次正漂移,共同构成了早三叠世约5Myr的高频率、大幅度的异常碳循环演化型式。碳同位素演化曲线显示了δ~(13)C最小值约为-2‰,最大值约为6‰,震荡幅度高达8‰。研究区海相碳酸盐岩碳同位素演化曲线与大贵州滩关刀剖面建立的早三叠世碳酸盐岩碳同位素曲线具有良好的对比性,但也存在一定的差异。关刀剖面整个早三叠世碳酸盐岩碳同位素的峰值分布在Denerian-Smithian界线处,而我们建立的同期碳同位素曲线中2条剖面的峰值分布在Smithian-Spathian界线处,且峰值不及大贵州滩的峰值8‰。早三叠世碳循环的异常震荡说明了早三叠世生态环境的不稳定性和生物复苏过程的复杂性。利用碳同位素地层学原理对研究区地层进行了年代地层和岩石地层对比,表明飞仙关组可大致相当于Induan阶,嘉一段可大致相当于Smithian阶,嘉二段、嘉三段和嘉四段下部可大致相当于Spathian亚阶。在综合岩石学、地球化学信息的基础上探讨了早三叠世碳酸盐岩碳同位素大幅度波动的可能驱动机制,提出了单一的地质事件不足以造成晚二叠世-早三叠世海水碳同位素几乎对称式的正漂移和负漂移。晚二叠世西伯利亚暗色岩系向大气中输入的轻碳可能会造成碳同位素负漂移1‰左右,与我们观察到的碳酸盐岩碳同位素负漂移程度相差甚远,可能与火山喷发等地质事件触发的甲烷水合物释放有关。然而对于早三叠世海水碳同位素几乎对称式的正漂移和负漂移,甲烷水合物释放理论则难以解释这一波动型式。这种波动型式可能与有机碳和无机碳埋藏率的周期性变化有关,海水碳同位素正漂移可能和提高的有机碳埋藏率有关。在早三叠世白云岩比相邻地层灰岩有较高的碳同位素组成,我们在手标本尺度上定量研究了早三叠世沉积温压条件下的白云石与伴生方解石的碳同位素组成差异,认为白云石比伴生方解石的碳同位素偏正约2~2.6‰,这一结果与白云石化过程中的碳同位素分馏实验和理论计算结果一致。碳酸盐岩氧同位素易受成岩蚀变影响使得手标本天然样品中定量研究白云石和方解石的氧同位素差异没有实际意义,但是可以肯定的是沉积温压条件下白云石比伴生方解石具有较高的氧同位素组成。
[Abstract]:The origin, development and evolution of the earth and life have been a hot field in the research of earth science. The early three fold period was in the palaeo Mesozoic geological catastrophe period. People paid much attention to the Late Permian biological mass extinction and the ecological resuscitation of the early three fold depression. The paper took the rich lower three carbonate rocks in the Sichuan basin as research. Under the background of abnormal geological events and abnormal sedimentary records, the petrology, elements and carbon and oxygen isotopes of the 6 surface profile carbonate samples of the Sichuan basin were analyzed. The possible driving mechanism of carbon isotopes in the early three fold marine carbonate rocks and the carbon and oxygen of the early three Permian dolomites and associated calcites were discussed. A number of research methods such as thin film observation, cathodoluminescence, scanning electron microscopy and energy spectrum analysis have been used to study the petrological characteristics of the samples in the study area. At the same time, the Mn/Sr ratio and delta 18O value are selected to evaluate the representative of the samples on the geochemical information of the sea water. The research shows that the mud microcrystalline limestone is better for the sea water information. Most of the granular limestone, transitional rock and dolomite, to a great extent, preserved the information of the ancient sea water, and the recrystallized limestone is less representative of the information of the ancient sea water, while the salt dissolving breccia - Secondary limestone represents the geochemical information of the epigenetic environment, and its geochemical characteristics have obviously deviated from the characteristics of the ancient sea water. On the basis of detailed diagenetic alteration assessment, the carbon isotope evolution curves of 3 early three fold marine carbonate rocks have been established, and a global and regional comparison is carried out. It shows that the carbon isotope evolution curve has a good global and regional contrast, showing that carbon isotopes of carbonate rocks experienced a number of late Permian early three generations. The oscillations at the different amplitude mainly include the sharp negative migration near the P/T boundary, the three positive drift of the Denerian-Smithian, Smithian-Spathian and Spathian-Anisian boundaries, which together constitute the high frequency of the early three superposition of about 5Myr and the large anomalous carbon cycle evolution pattern. The carbon isotope evolution curve shows that the minimum value of delta ~ (13) C is about -2 per thousand. The maximum value is about 6 per thousand and the amplitude of the oscillation is up to 8 per thousand. The carbon isotope evolution curve of the marine carbonate rock in the study area is well contrasted with the carbon isotope curves of the early three superposition carbonate rocks in the Guizhou beach cutting section, but there are some differences. The peak distribution of carbon isotopes of the early three carbonate rocks in the section of the Guan Dao section is in D At the enerian-Smithian boundary, the peak of 2 sections in the carbon isotope curve we set up in the same period is distributed at the Smithian-Spathian boundary, and the peak value is less than 8 per 1000 in the big Guizhou beach. The abnormal oscillation of the early three fold carbon cycle shows the instability of the early three fold ecological environment and the complexity of the biological resuscitation process. The principle of geostratigraphic stratigraphy has compared the stratigraphic and chronostratigraphy to the strata of the study area. It shows that the Feixianguan formation can be roughly equivalent to the Induan order. The Jijia section can be roughly equivalent to the Smithian order, the Jia two section, the Jijia three and the Jiayan four segments are roughly equivalent to the suborder of the Spathian. The possible driving mechanism of the large amplitude fluctuation of carbon isotopes in the three world carbonate rocks suggests that a single geological event is not sufficient to cause the positive drift and negative drift of the carbon isotopes of the Late Permian early three fold world. The light carbon input to the atmosphere in the Late Permian Siberia dark rock system may cause a negative carbon isotope drift of 1. The negative drift degree of carbon isotopes we observed in carbonate rocks is very far from that of the carbonate rocks we observed, which may be related to the release of methane hydrate triggered by volcanic eruptions. However, the theory of methane hydrate release is difficult to explain this wave pattern for the positive drift and negative drift of the early three superposition of the carbon isotopes of the sea water. This wave pattern may be related to the periodic changes of organic carbon and inorganic carbon burial rates. The positive drift of carbon isotopes in sea water may be related to the increase of organic carbon burial rates. In the early three fold dolomites, there was a higher carbon isotope composition than the adjacent stratigraphic limestone. We quantitatively studied the early three stack sedimentary warm pressure strips on the hand specimen size. The carbon isotope composition of dolomite and associated calcite is different from that of associated calcite, and it is believed that the carbon isotope of dolomite is about 2~2.6 per thousand than that of associated calcite. This result is consistent with the carbon isotope fractionation experiment and theoretical calculation in dolomitization. There is no practical significance for the quantitative study of oxygen isotope differences between dolomite and calcite, but it is certain that dolomite has a higher oxygen isotope composition than associated calcite under the condition of sedimentary temperature and pressure.
【学位授予单位】：成都理工大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：P588.245

【参考文献】