华南P-Tr之交黏土矿物与地球化学特征及其气候环境演变意义

发布时间：2018-06-13 05:00

  本文选题：黏土矿物 + 化学风化指数(CIA)　； 参考：《中国地质大学》2017年博士论文

【摘要】：二叠纪末(~250Ma)发生了地史时期最具灾难性的集群灭绝事件,约90%的海洋生物种、70%的陆地脊椎动物及绝大数陆地植物在这次事件中消亡。尽管历经几十年的不懈努力,这次地史上最大生物灭绝事件的触发机制及灭绝机制至今未有最终定论。目前最广为接受的是以二叠纪末-三叠纪初强烈的火山活动为最终触发机制、其派生产物——气候环境恶化(包括全球变暖、海陆酸化等)为灭绝机制的假说。然而假说是否成立,仍需沉积记录的直接验证,其第一步即是全面系统地查明二叠纪-三叠纪之交全球气候变化、寻找海陆酸化的地质证据,然后才可能在精确的年龄框架内探讨气候环境与火山活动、生物灭绝之间的时间序列关系与因果关系。对于P-Tr之交古环境气候演变,目前最大的进展是生物成因氧同位素定量恢复古气温的研究,其结果证明了晚二叠世末全球气候变暖的事实。然而气候环境变化的其它方面,如气候变干还是变湿、化学风化作用增强还是减弱,是否存在酸化等问题还广受争议。因此本论文就针对以上问题,拟通过对华南4条海相剖面(扬子地台北缘:上寺、甘溪;扬子地台南缘:新民、东攀)和1条陆相剖面(扬子地台西缘滇东鲁贝)进行高分辨率黏土矿物及CIA等指标的综合分析研究,以期为探明华南P-Tr之交古气候环境演变提供证据支持。本文研究过程及取得结论如下:(1)通过对各研究剖面稳定主微量元素比值(如Al2O3/TiO_2、Zr/Hf,Zr/Sc、Nb/Ta、Th/Sc等)、稀土元素配分模式(和TOC)的纵向变化及对比得出:扬子北缘上寺、甘溪剖面物源成分及纵向变化相似,但自N.changxingensis带向上变化不显著;扬子南缘新民剖面和东攀剖面物源成分相差较大,前者更偏基性,后者偏酸性,且前者在P-Tr界线上下具有较为明显的物源变化,而后者几乎无变化;鲁贝剖面物源为峨眉山玄武质,纵向无变化,物源较稳定。(2)通过X射线粉晶衍射分析(XRD)、扫描电镜/透射电镜(SEM/TEM)观察以及岩石热解分析(Rock-eval)等手段综合判断华南黏土矿物组合特征及其影响因素。结果表明黏土矿物组合具有明显的地域性:扬子北缘P-Tr剖面黏土矿物组成以伊利石+伊蒙混层为主,绿泥石含量在二叠系顶部开始出现并向三叠系增加,上寺剖面界线附近另含蛭石矿物;扬子南缘P-Tr剖面黏土矿物组成复杂,以伊利石质+绿泥石质矿物为主,伊蒙、绿蒙、绿蛭等混层矿物发育,东攀剖面P-Tr界线及其之上含蛭石;滇东鲁贝剖面黏土矿物亦以伊利石质+绿泥石质矿物为主,含少量高岭石和蛭石;扬子南缘、滇东鲁贝剖面黏土矿物组成较扬子北缘富含绿泥石质矿物,其原因主要是物源富镁铁质,这与它们距离峨眉山玄武岩较近及晚二叠世末扬子南缘发育大量海相玄武岩有关。同时,综合各剖面岩石裂解分析、有机质镜质体反射率Ro、火山粘土岩伊蒙混层中伊利石层片含量(上寺最低:50-60%;东攀、鲁贝剖面中等:70-80%;甘溪、新民最高:90%)以及SEM/TEM观察,笔者认为各剖面黏土矿物明显受成岩作用影响,但影响程度各不相同:扬子北缘剖面以蒙脱石的伊利石化为主,上寺剖面转化程度最低,成岩作用程度最小,同时非混层矿物伊利石和绿泥石在扬子北缘不受成岩作用主导;扬子南缘剖面成岩作用则以蒙脱石的伊利石化和绿泥石化为主,且成岩转化在二叠系碳酸盐岩层位更高,东攀剖面是研究剖面中唯一仍含R0型伊蒙混层的剖面,其原因可能是该剖面缺乏蒙脱石转化所需的K+;滇东鲁贝剖面黏土矿物成岩作用亦以蒙脱石的绿泥石化和伊利石化为主,成岩转化在二叠系较为粗粒的层位及三叠系比较显著。(3)评估了成岩作用影响后,整体上华南P-Tr之交黏土矿物蕴含向上逐渐干旱化的气候趋势,但各区域表现形式不尽相同:扬子北缘剖面绿泥石在二叠系顶部出现并向三叠系逐渐增加、伊利石结晶度亦从二叠系向三叠系增加;扬子南缘东攀剖面R0型伊蒙混层、高岭石向上逐渐减少、伊利石结晶度反而略有略增加;滇东鲁贝剖面则表现在高岭石向上逐渐减少,并伴随煤层/线的向上减薄消失、好温喜湿Gingantopteris植物群被相对更适应干旱气候的Peltaspermum盾籽类为主体的植物面貌所代替。但总体上,气候在P-Tr附近的干旱化是循序渐进的,直至界线之上约0.08Ma才出现干旱化的快速加强。(4)为探究华南P-Tr之交化学风化强度变化,笔者计算了各剖面化学风化指数CIA,结果表明扬子北缘剖面CIA受碳酸盐含量影响很大,其值与CaO及方解石含量呈明显的此消彼长的变化关系,表明CIA在扬子北缘剖面应用受化学沉积影响大;而扬子南缘新民剖面除了碳酸钙含量影响CIA的应用外,过多的火山物质也是限制CIA应用的一大原因,因此也无法用来恢复化学风化强度变化。相比之下扬子南缘东攀剖面与滇东鲁贝剖面样品以细粒碎屑岩为主,生物化学碳酸盐组分极少,物源保持一致且后期成岩改造影响小,因此是较为合适的CIA应用剖面。结果显示,东攀剖面CIA值域在75-90之间,而鲁贝剖面CIA二叠系则近100,均有从二叠系到三叠系减小的趋势,但从二叠系至P-Tr界线附近减小程度微弱,表明化学风化作用虽有减弱,但不明显或基本无变化;而化学风化的快速减弱在P-Tr界线之上的三叠系底部(距P-Tr界线约0.08Ma),该变化在鲁贝剖面有记录,海相东攀剖面三叠系因采样地层较短样品较少,没有到达对比于鲁贝剖面CIA快速降低的层位,因此无此记录。(5)为验证黏土矿物得出的气候干旱化,本文还增加了鲁贝剖面环境磁学特征的实验,结果表明该剖面P-Tr界线之下磁性矿物以主要形成于温暖潮湿气候环境中的磁铁矿为主,三叠系中赤铁矿(和磁赤铁矿)等主要形成和保存于高温干旱、氧化环境中的磁性矿物取代磁铁矿的主导地位,与前人在海相上寺、峡口及东攀剖面进行的磁学实验得出相同的结论,结合黏土矿物及CIA数据变化,笔者认为至少在华南,三叠系红层应为高温干旱气候条件下的产物,其磁性矿物转变亦主要为沉积初期气候环境变化的产物,而不是有些学者认为的仅代表后期成岩作用中磁性矿物氧化的结果。(6)鲁贝剖面CIA在三叠系东川组并非完全处于低值,而间歇性的出现极高值,这些高值恰好对应更细粒的泥岩-粉砂岩同时相对于沉积的绝大部分细砂岩来说含有更多的磁铁矿、具有更高的磁化率。这些泥岩-粉砂岩层位表明在三叠纪高温干旱气候大背景下气候具有短暂间歇性的强降雨时期,具有明显的季风性气候特点。而在二叠系,无论CIA还是磁化率在二叠系均没有如此巨大的变化,因此季风性气候在三叠纪相对于二叠纪是明显加强的。这从华南各沉积剖面三叠系的岩性旋回性比二叠系更明显也可见一斑。(7)火山活动CO_2气体大量释放及高温能够促进硅酸盐矿物的化学分解,化学风化作用增强,因此目前地学界广泛“想当然地”认为在广泛且强烈的火山活动的大背景下,化学风化作用在P-Tr之交应是增强的;然而另一方面,P-Tr之交Pangea大陆特殊的分布格局使得季风性气候十分盛行,其特点是总体降水少、干旱,间歇有短期强降水,因此总体上是抑制化学风化作用的。因此,笔者认为,P-Tr之交及早三叠世气候湿润或干旱取决于火山活动影响与季风性气候两者之间的博弈。而就本论文研究结果显示,至少在当时的华南地区,气候总体是向干旱转变的,表明大陆联合引起的季风性气候可能略占上风。(8)本文提出了华南P-Tr剖面中可用于反映陆地酸化的指标——蛭石、HIM矿物。蛭石是一种膨胀性2:1型黏土矿物,在自然界中多形成于偏酸性的沉积环境中(pH范围一般在4-6),是弱酸性土壤中常见的黏土矿物类型。HIM矿物是一种膨胀性黏土矿物间层被“岛屿状”羟基铝/镁/铁等聚合物充填的特殊黏土矿物,其形成及稳定pH较蛭石偏低。在本论文上寺、东攀、鲁贝剖面中,蛭石(和HIM矿物)仅存在于跨越各剖面P-Tr界线附近层位,且与碳同位素负偏及陆源物质/炭屑大量输入具有很好的对应性。因此,笔者认为二者的出现可能指示了陆地生态系统崩溃、植被破坏,大量偏酸性土壤物质输入沉积盆地的现象。另外蛭石、HIM矿物的出现与碳同位素负偏较好的对应性,因此酸化很可能是P-Tr之交强烈的火山活动释放大量酸性气体的结果。(9)关于华南P-Tr之交气候环境变化与生物灭绝之间的关系,根据本文的研究结果,笔者认为气候干旱化在二叠纪末-早三叠世最早期是循序渐进且不显著的,直到界线之上才出现迅速加强,但植物灭绝层位附近广泛发育的森林野火可能是造成陆地植物灭绝及生态崩溃的一大原因。另一方面,灭绝界线附近的迅速升温则可能是导致海陆生物灭绝的主要原因。但更精细的研究仍在进行以期检验温度骤升是否真正为生物灭绝的主要原因。同时,就全球范围来看,酸化证据目前在不同地域、甚至不同剖面与灭绝层位关系也是不一致的,酸化是否是生物灭绝的直接原因还有待于进一步验证。
[Abstract]:At the end of the Permian period (~250Ma), the most catastrophic mass extinction event occurred in the history of the earth, about 90% of the marine species, 70% of the terrestrial vertebrates and the great number of terrestrial plants died out in this event. Despite the unremitting efforts of decades of unremitting efforts, the triggering mechanism and extinction mechanism of the largest biological extinction event in the earth's history have not been the most. The most widely accepted theory is that the most widely accepted triggering mechanism is the volcanic activity of the early Permian Late Triassic, and its production, the hypothesis of the extinction mechanism of climate and environment (including global warming, sea and land acidification, etc.). However, whether the hypothesis is established or not, the direct verification of sedimentary records is still needed, and the first step is a comprehensive system. To find out the global climate change at the Permian Triassic period and find the geological evidence for the acidification of the sea and land, then it is possible to explore the time series relation and causality between the climate environment and the volcanic activity, the extinction of the organisms in the exact age frame. The biggest progress is the biogenic oxygen same at present in the evolution of the Paleoenvironment of P-Tr. The results of the quantitative restoration of the paleo temperature by the position element have proved the fact that the global climate warming at the end of the Late Permian. However, other aspects of the climate and environment change, such as the climate change or the wetting, the chemical weathering enhancement or weakening, and the existence of acidification are still widely disputed. 4 southern marine sections (the northern margin of the Yangtze Platform: Shangsi, Gan Xi, the southern margin of the Yangzi platform: Xinmin, East Panzhihua) and 1 continental facies profiles (the western margin of the Yangtze platform) in the comprehensive analysis of high resolution clay minerals and CIA, in order to provide evidence for the exploration of the evolution of the paleoclimate environment at the intersection of the Southern China P-Tr. The conclusions are as follows: (1) through the stability of the main trace elements ratio (such as Al2O3/TiO_2, Zr/Hf, Zr/Sc, Nb/Ta, Th/Sc, etc.) and the longitudinal variation and comparison of the distribution pattern of rare earth elements (and TOC), the source composition and longitudinal variation of the Gansu Creek profile are similar, but the upward variation of the N.changxingensis zone is not significant, and the south of the Yangtze is not significant. The source composition of the margin Xinmin section and the East Panzhihua section is quite different, the former is more basic and the latter is partial acid, and the former is more obvious in the P-Tr boundary, and the latter is almost unchanged. The source of the lube section is the basalt of Mount Emei, the longitudinal and the source is stable. (2) through the X ray powder diffraction analysis (XRD), scanning electricity Mirror / transmission electron microscopy (SEM/TEM) observation and rock pyrolysis analysis (Rock-eval) are used to synthetically determine the characteristics of Southern China clay mineral assemblage and its influencing factors. The results show that the clay mineral assemblage has a distinct regionality: the clay minerals in the P-Tr section of the northern margin of the Yangtze River are mainly illite + imimon, and the content of chlorite in the top of the Permian system. The P-Tr section of the southern margin of the Yangtze River is complex with a complex mineral composition of clay minerals in the southern margin of the Yangtze, with illite and green muddy minerals as the main mineral, imimon, green Mongolia and green leech, and the P-Tr boundary and the vermiculite in the East Panzhihua section. The main green and muddy mineral mineral contains a small amount of kaolinite and vermiculite, and the southern margin of the Yangtze River, the clay mineral composition of the Lubei section in the east of Yunnan is rich in green mudstone minerals in the northern margin of the Yangtze, mainly due to its MgO rich source, which is related to their close proximity to the Mount Emei basalt and the development of a large number of marine basalts at the southern margin of the Late Permian Yangtze. The analysis of rock cracking in each section, the reflectance of the organic vitrinite Ro, the illite content in the illite layer of the volcanic clay rock (the lowest: the upper Temple: 50-60%; the East climbing, the Lubei section medium: 70-80%; Gan Xi, the Xinmin highest: 90%) and the SEM/TEM observation, the author thinks that the clay minerals in each section are obviously influenced by the diagenesis, but the influence degree is different: Yang The northern margin of the sub section is dominated by illite in montmorillonite, with the lowest transformation degree in the Shangsi section and the smallest diagenesis. At the same time, the illite and chlorite are not dominated by the diagenesis in the northern margin of the Yangtze, and the diagenesis of the southern margin of the Yangtze River is mainly montmorillonite illite and green mud petrifaction, and the diagenesis is converted to Permian carbon. The strata of the acid salt rock are higher, and the East Panzhihua section is the only section of the R0 immont mixed layer in the study section. The reason may be that the section lacks the K+ required for the transformation of montmorillonite, and the clay mineral diagenesis of the eastern Yunnan Rubei section is mainly of the montmorillonite's Greenstone and illite petrochemistry, and the diagenesis is converted to the coarse-grained layers of the Permian and three fold. (3) (3) after evaluating the influence of diagenesis, the climate trend of the clay minerals in Southern China on the whole is gradually arid, but the forms in each region are different: the chlorite in the northern margin of the Yangtze River appears at the top of the Permian and gradually increases to the Triassic, and the illite crystallinity is also increased from the Permian to the Triassic. In the East Panzhihua section of the southern margin of the Yangtze River, the R0 imimon mixed layer, the kaolinite gradually decreases, and the illite crystallinity slightly increases; in the east of Yunnan, the profile of the kaolinite decreases gradually, with the upward thinning of the coal seam / line, and the good temperature and humid Gingantopteris plants are relatively adaptable to the Peltaspermum shield seed of the drought climate. On the whole, the drought of the climate in the vicinity of P-Tr is gradual, and the rapid strengthening of the droughts on the boundary is about 0.08Ma. (4) in order to explore the changes in the chemical weathering intensity of the Southern China P-Tr, the author calculated the chemical weathering index CIA of each section, and the result indicates that the CIA in the northern margin of the Yangtze is carbonated. Salt content has a great influence on the variation of the value of CaO and calcite content, which indicates that the application of CIA in the northern margin of the Yangtze River is greatly influenced by chemical deposition, and in addition to the application of calcium carbonate content in the Xinmin section of the southern margin of the Yangtze, excessive volcanic material is also a major reason for limiting the application of CIA, so it can not be used. To restore the change of chemical weathering intensity, the East Panzhihua section of the southern margin of the Yangtze River and the Lubei section in the southern margin of the Yangtze River are mainly fine grained clastic rocks, with few biochemical carbonate components, consistent source and late diagenetic transformation, so it is a more suitable CIA application section. The CIA Permian in the Lubei section is nearly 100, which decreases from Permian to Triassic, but decreases slightly from the Permian to the P-Tr boundary, indicating that chemical weathering has weakened, but not obvious or basically unchanged, and that the chemical weathering weakens at the bottom of the Triassic system above the P-Tr boundary (P-Tr boundary is about 0.08Ma). There is a record in the Lubei section, and the Triassic in the East Panzhihua section of the marine facies is less than the sample of short samples, and there is no comparison to the rapid reduction of CIA in the lube section. Therefore, there is no such record. (5) in order to verify the climate droughts obtained from clay minerals, this paper also increased the experiment of the environmental magnetic characteristics of lube's surface, and the results show that the section P-Tr The magnetic minerals under the boundary line are mainly magnetite formed in the warm and humid climate, and the Triassic hematite (and magnetite) is mainly formed and preserved in the high temperature and drought, and the magnetic minerals in the oxidizing environment replace the magnetite, and the magnetic experiments carried out with the predecessors in the upper monastery, the channel and the East Panzhihua section With the same conclusion, combined with clay minerals and CIA data changes, I think the red layer of the Triassic should be a product of high temperature and drought climate at least in Southern China, and its magnetic mineral transformation is also the product of the climate change at the early stage of the deposition, but not some scholars believe that the magnetic mineral oxidation in the late diagenesis is only a result of the formation of magnetic mineral oxidation. (6) the CIA section of the Ru Bei section is not completely at low value in the Triassic Dongchuan formation, but has a high value intermittently. These high values just correspond to more fine grained mudstone and siltstone with more magnetite and higher magnetization ratio relative to most of the fine sandstones. These mudstone siltstone layers indicate that the Triassic period was in the Triassic period. Under the high temperature and drought climate, the climate has a short period of intermittent strong rainfall and has a distinct monsoon climate characteristics. In the Permian, no matter the CIA or the susceptibility of the Permian in the Permian, the monsoon climate is obviously strengthened in the Triassic period relative to the Permian period. This is three overlapping sections in Southern China. The lithologic cyclicity of the system is more obvious than that of the Permian. (7) the mass release of CO_2 gas and the high temperature can promote the chemical decomposition of silicate minerals and enhance the chemical weathering. Therefore, the chemical weathering effect of chemical weathering in P-Tr is now widely considered in the field of extensive and intense fire mountain activities. On the other hand, on the other hand, the special distribution pattern of the Pangea continent at the turn of P-Tr makes the monsoon climate very prevalent, which is characterized by less overall precipitation, drought and short-term strong precipitation, which is therefore generally inhibited by chemical weathering. Therefore, the author considers that the early three fold climate wetness or drought depends on the early three fold climate or drought. A game between volcanic activity and monsoon climate, and the results of this study show that at least in the Southern China region at that time, the climate changed to drought in general, indicating that the monsoon climate caused by the continental union may have a slight upper wind. (8) this paper presents the indicators that can be used to reflect the acidification of the land in the Southern China P-Tr section. Vermiculite, HIM mineral. Vermiculite is an expansive 2:1 clay mineral, which is mostly formed in acidic sedimentary environment (pH range is generally in 4-6). It is a common clay mineral type in weak acid soil,.HIM mineral is a special clay filled clay mineral interlayer filled with "island" hydroxy aluminum / magnesium / iron and other polymers. Mineral, its formation and stability pH is lower than vermiculite. In this paper, the vermiculite (and HIM minerals) in the temple, East Panzhihua and Lubei sections in this paper only exist near the horizon of the P-Tr boundary across various sections, and have good correspondence with the negative carbon isotope bias and the heavy input of the terrestrial matter / carbon chips. The system collapse, vegetation destruction, a large amount of acidic soil material into the sedimentary basin. In addition, the vermiculite, HIM mineral appears to be in good correspondence with carbon isotopes, so acidification is likely to be the result of the release of a large number of acidic gases from the strong volcanic activity of P-Tr. (9) the climate change and biological extinction at the Southern China P-Tr According to the results of this study, the author believes that the early stage of climate droughts is gradual and not significant at the early stage of the Late Permian to the early three fold, and it is not very significant until the boundary, but the widespread forest wildfires near the plant extinction horizon may be a major cause of the extinction of the terrestrial plants and the ecological collapse. On the other hand, rapid warming near the extinction boundary may be the main cause of the extinction of the sea and sea, but more elaborate studies are still being carried out to test whether the sudden rise in temperature is the main cause of extinction. It is also inconsistent. Whether acidification is the direct cause of extinction is still to be further verified.
【学位授予单位】：中国地质大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：P532;P59
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本文编号：2012816