【作者】 林良彪；

【导师】 陈洪德；

【作者基本信息】 成都理工大学 ， 沉积学， 2008， 博士

【摘要】 华南板块在海西构造阶段以板内运动为主，处于拉张伸展构造环境下，发育了一系列具有拉张或左行拉分性质的裂陷盆地，特别是在二叠纪，拉张活动剧烈（即峨眉地裂运动），并已延伸到盆地内部，在板块上的不同部位形成了一些深水盆地，整体形成了台盆相间、台中有盆、盆中有台的古地理格局，而台盆边缘发育的礁滩恰恰是油气的有利储集体，如“普光”气田、“龙岗”气田等，因而对华南板块二叠纪层序充填与沉积物分布规律的研究具有十分重要的理论意义和现实意义。本论文以四川盆地东部（即川东地区）二叠系为研究对象，以野外露头剖面为研究重点，充分利用已有的钻井资料及地震资料，以沉积学、层序地层学、地球化学、古生物学、地球物理学和构造地质学等原理为指导，利用多种分析手段，深入研究二叠系硅质岩的岩石学特征、地球化学特征，以揭示硅质岩的成因类型，挖掘隐藏在硅质岩背后的地质背景信息；分析二叠系的沉积体系、层序充填特征，结合硅质岩研究成果、区域构造背景，以三级层序或三级层序体系域为编图单元，编制具有精确性、等时性、成因连续性等优点的岩相古地理图，揭示研究区的沉积物分布规律，进而分析整个沉积盆地的性质及演化特征，揭示上扬子板块的演化特征。通过研究，得出以下几点成果认识：（1）对重庆石柱冷水溪中二叠统茅口组和上二叠统吴家坪组层状硅质岩进行岩石学、主量元素、微量元素、稀土元素及硅氧同位素研究，表明它们都为热水硅质岩，形成于台盆环境中，但茅口组热水硅质岩的特征明显于吴家坪组。①茅口组和吴家坪组硅质岩化学成分均以SiO₂为主，含量分别为80．09％～97．91％和65．52％～97．76％，其Al／（Al+Fe+Mn）平均值分别为0．30和0．4599。Al-Fe-Mn判别图解、SiO₂-Al₂O₃图、SiO₂-Fe₂O₃图、Fe-Mn-（Cu+Co+Ni）三角图解、U-Th图解均表明茅口组和吴家坪组硅质岩绝大部分为热水硅质岩，少部分为非热水硅质岩。②茅口组和吴家坪组硅质岩稀土元素总量都较低，平均值分别为7．509×10^-6和38．540×10^-6，重稀土元素中度富集；Ce中度异常，北美页岩标准化配分模式图略为向左倾斜或平整，Eu无明显正负异常，这些特征表明两组硅质岩成分以热水沉积为主，并有部分非热水成因的物质混入。③茅口组和吴家坪组硅质岩δ³⁰Si的值总体上都位于热水成因硅质岩区域内，根据δ¹⁸O值计算得出茅口组和吴家坪组硅质岩形成时，古海水温度变化范围分别为34．45～80．77℃和43．28～93．61℃。④茅口组和吴家坪组硅质岩结构构造表明，该组硅质岩形成于水体较深的环境，这些为滑塌变形构造、灰岩砾石、菊石化石、放射虫、海绵骨针以及薄壳腕足等所证明：MnO/TiO₂值、Al₂O₃／（Al₂O₃+Fe₂O₃）值、δCe值和δ³⁰Si值也均表明茅口组和吴家坪组硅质岩形成于台盆环境。（2）二叠纪的沉积过程中，同生断裂活动频繁而强烈，并伴随有火山活动。区内茅口组和吴家坪组热水硅质岩的形成主要取决于以下两个条件：①板内沿断裂拉张，地壳具有可渗透性，海水向下渗透并在一定深度内发生循环，然后上涌。②剖面位于七曜山断裂的附近，该断裂提供了深部热液。下渗的海水与岩浆热液混合，海水被加温后，溶解了大量SiO₂及其他有关元素，并以热泉形式通过断裂喷出，使附近海水中SiO₂含量极大提高并沉淀；同时又促使放射虫和海绵等硅质生物繁殖，形成生物硅质岩。（3）川东地区二叠系发育了滨岸-潮坪、碳酸盐缓坡、碳酸盐台地、台盆4种沉积体系，研究认为随着生物岩隆的快速发展，晚二叠世吴家坪期的碳酸盐缓坡至长兴期转化为碳酸盐台地。（4）识别出6种层序界面的表现形式：古风化壳、古喀斯特作用面、火山事件作用面、最大海泛面、岩性、岩相转换面和底流冲刷侵蚀面，4类与盆地构造演化有关的成因类型：造山侵蚀层序不整合界面、升隆侵蚀层序不整合界面、海侵上超层序不整合界面和暴露层序不整合界面。以此为基础，将研究区二叠系划分出12个三级层序，详细讨论了各层序在不同相区内的特征及其变化，进行了区域对比，并建立了川东二叠纪的层序充填模型。认为层序充填主要受控于构造运动、全球海平面升降、沉积作用和气候四大因素。（5）以三级层序体系域或三级层序为编图单元对研究区进行岩相古地理编图研究，共编制了14张层序岩相古地理图（PSQ1、PSQ2、PSQ3、PSQ4、PSQ5、PSQ6、PSQ7、PSQ8LST、PSQ8TST、PSQ8HST、PSQ9、PSQ10、PSQ11和PSQ12），揭示了区域沉积物分布规律及演化规律。表明：早二叠世梁山期（PSQ1）发育了滨岸沼泽的细粉砂岩、泥页岩夹煤线：中二叠世（PSQ2～PSQ6）海平面升高，发育了开阔台地相的生物碎屑灰岩、含生物碎屑泥晶灰岩等，并常夹有燧石条带、页岩或含有燧石结核，局部地区有生物碎屑滩发育；PSQ7，在石柱地区发育了一硅质岩台盆，区内其它地区仍为开阔台地相沉积；吴家坪早期（PSQ8LST）普遍为一套滨岸相的页岩、铝土质页岩、褐黄色粉砂岩、泥质粉砂岩夹煤线沉积，在研究区北部（梁平）地区以发育玄武岩和辉绿岩为特征。吴家坪中晚期（PSQ8TST～PSQ10）为碳酸盐缓坡沉积，但在PSQ9～PSQ12，石柱冷水溪地区有硅质岩台盆存在；长兴期（PSQ11、PSQ12）为碳酸盐台地沉积，在研究区北部和南部分别存在“开江-梁平”和“石柱”两个泥质灰岩台盆。（6）峨眉山玄武岩喷发过程就是大陆裂谷形成演化过程，它始于茅口期，于晚二叠世早期喷出地表，结束于晚二叠世中期，分为以下5个阶段：①茅口早期（PSQ5、PSQ6）深部岩浆开始活动，使上覆地壳处于微上拱状态，海底地形略有起伏，海底未完全固结的沉积物在以上多种因素影响下较易发生塑性滑动，沉积了茅口组瘤状灰岩。富含SiO₂的热液进入海底，混迹于沉积物中，成岩过程中发生分异形成燧石结核或燧石条带。②茅口晚期（PSQ7）岩浆上拱，使上覆地壳形成穹窿，穹隆中心地区容易发生张性裂开，形成一些断陷盆地，盆地中沉积了硅质岩，本区如茅口期石柱台盆。③茅口未期，玄武岩即将喷出地表，岩浆上拱作用使四川盆地全面快速隆升形成穹窿，穹窿全面位于海平面上，形成了中上二叠统之间的平行不整合接触，即为东吴运动。④吴家坪早期（PSQ8LST）峨眉山玄武岩全面喷出地表，穹窿中心为陆相喷发，玄武岩中发育丰富的柱状节理；周边海域为水下喷发，玄武岩中有枕状构造。因地下岩浆大规模流出地表，周边地区基底下沉来弥补岩浆房的空间，在此背景下形成了石柱台盆，沉积了吴家坪组的硅质岩。⑤长兴期火山活动结束，四川盆地整体拉张下沉，大部分地区演变为沉积区，“开江-梁平”泥质灰岩台盆开始演化形成，与“石柱”台盆同时存在。更多还原

【Abstract】 The South China Plate was under an extensional tectonic setting and was mainly characterized by intraplate movements during the Hercynian stage. A series of extensional rift basins or sinistral pull-apart rift basins were developed in it. Especially in Permian, an intenser extension was developed and extended to inner part of the basin, called Emei Taphrogenesis, which led to the formation of some deep-water basins in different places in the South China Plate. So the paleogeographic pattern presented as basins alternated with platforms, basins in platforms, and platforms in basins. As we know, reefs developed on the margin of platform-basins are good reservoirs of oil and gas, such as Puguang Gas Field and Longgang Gas field. Therefore, it is very meaningful to study the sequence filling and sediment distribution of Permian in the South China Plate.This dissertation was primarily focused on the Permian in eastern Sichuan basin. Base on the field outcrops and a large of logging data, and seismic materials, this paper studied the Permian cherts and their implications with multiple methods. The principle of Sedimentology, Sequence Stratigraphy, Geochemistry, Paleontology, Geophysics and Tectonics and some other traditional geology theories were used as the instructions of this paper. Besides, the characters of deposition system, sequence filling, and regional tectonic setting were analyzed. With regarding sequence or sequence systems tract, we drew the sequence-based lithofacies paleogeography map more scientifically, isochronously, continuously, and precisely. At the same time, we described and inferred the sediment distribution, and the characteristics and evolution of Permian sedimentary basin in eastern Sichuan basin as well as the evolution of the Permian Upper Yangtze Plate. According to the results, we obtained the findings as following:（1） The petrology, and distribution of major and minor elements, REE, and SiandO-isotopic geochemistry indicated that the Middle Permian Maokou Formation and the Upper Permian Wujiaping Formation consist of hydrothermal silicates in Lengshui Stream of Shizhu, Chongqing and they were deposited in inter-platform basins.①The contents of SiO₂ in the Maokou and Wujiaping Formation are relatively high, and the value is 80.09%-97.91% and 65.52%-97.76% respectively. The ratio of Al/（Al+Fe+Mn） is regarded as a helpful criterion for identifying hydrothermal silicates from other silicates. The average ratios are 0.30 and 0.4599 in the Maokou and Wujiaping Formation. In addition, along with the projection in Fe-Mn- （Cu+Co+Ni） ternary diagram, SiO₂-Al₂O₃, SiO₂-Fe₂O₃, and U-Th relative diagram, most of the Maokou and Wujiaping Formations’ silicate samples fall into the hydrothermal field. Only a few of them were not originated from hydrothermal.②In the Maokou and Wujiaping Formation, the REE contents of silicate are low (7.509×10^-6 and 38.540×10^-6), with mid enrichment of HREE and negative anomaly of Ce. Eu has not evident anomaly. These features suggest that the silicates are hydrothermal genetic.③The Silicon (δ³⁰Si) and Oxygen (δ¹⁸O) isotope compositions are similar to hydrothermal origin. Based on the Oxygen isotope fractionation equation of chert and water, the paleotemperatures of the silicates in the Formations are 34.45-80.77℃and 43.28-93.61℃.④The well preserved remains of radiolarians, thin-shell brachiopoda, ammonites, and spongy spicules were recorded in the silicates. Moreover, slumps and limestone gravels were found in the silicates. These petrology characters indicate that the Maokou and Wujiaping Formations’ silicates were deposited in inter-platform basins. This conclusion was supported by the geochemical data of the silicates, whch are the values of MnO/TiO₂, Al₂O₃/（Al₂O₃+Fe₂O₃）, 8Ce andδ³⁰Si.（2） There were many syndepositional faults and volcanisms of Permian in eastern Sichuan basin. And the heat source responsible for hydrothermal convection is presented in study area. Two factors constrained the formation of hydrothermal silicates in the Maokou Formation and Wujiaping Formation:①Extensions along with the faults of the interior plate which lead to the crust being permeable, thus the sea water leaked into deep crust and was heated; Therefore, the circulation occurred and hot fluid upwelled.②Studied section is located near the Qiyaoshan fault, which could be the pass of hot liquid from deep crust. At that time, sea water encountered and was heated with magmatic liquid, and then dissolved much SiO₂ and other elements. Final, the warmer sea water with dissolved SiO₂ sprayed out from the faults, which made sea water be near the fault and contain much more SiO₂. At the same time, biota of radiolarian and sponge which enrich in SiO₂ grew much better and led to biogenic silicate deposition.（3） Four types of depositional system of the Permian developed in eastern Sichuan basin, which are coast-tidal flat depositional system, carbonate ramp depositional system, carbonate platform depositional system, and inter-platform basins depositional system. Because of the rapid development of reef-building, the paleoenvironment of the study area was changed from carbonate ramp depositional system to carbonate platform depositional system during Changxing.（4）In the strata, 6 kinds of sequence boundary characters were recognized, which are weathering crust, action surface of ancient karst, action surface of volcano event, flooding transgressive surface, transition surface of rock character and facies, erosion surface of turbidity flow in basin. Four kinds of contributing factor related to basin evolution are identified: orogenic erosional unconformity, uplift erosional sequence unconformity, transgressive onlap sequence unconformity, exposed sequence unconformity. Base on these, the Permian were divided into 12 third-order sequences in the study area, and different characters in different facies was discussed and correlated regionally in detail. Meanwhile, sequence stratigraphy filling models from PSQ1 to PSQ12 were establish in eastern Sichuan basin as well. In general, every sequence was dominantly controlled by the tectonic movements, global sea level change, sediments supply and paleoclimate.（5）According to the division of third-order sequences or third-order sequence systems, fourteen sequence-based lithofacies-paleogeography maps were figured out （PSQ1, PSQ2, PSQ3, PSQ4, PSQ5,PSQ6, PSQ7,PSQ8LST, PSQ8TST,PSQ8HST,0 PSQ9,PSQ10, PSQ11 and PSQ12）. These maps revealed the features of sediment distribution and basin evolution. The reconstructed paleogeography showed that: 1) fine siltstones and shales with coal-line of coast deposited in the Liangshan period （PSQ1）; 2) With sea-level rising, bioclastic limestones and bioclastic micrites intercalated with chert belts, shales or chert concretions were deposited on open platform in the Middle Permian Qixia Formaiton and Maokou Formation （PSQ2-PSQ6）; 3) An inter-platform basin was developed in Shizhu area in PSQ7, although the other areas were still open platform; 4) In PSQ8LST, the sediments were characterized by shales, bauxitic shales, brown siltstones, and argillaceous siltstones with coal-line of coast environment. But basalts were developed in Liangping in the north of study area; 5) In PSQ8TST-PSQ12, sediments of carbonate ramps were accumulated in the study area. However, there was an inter-platform basin with silicates in PSQ9-PSQ12 in Shizhu, Chongqing; 6) The paleoenvironments of the study area were changed from carbonate ramp depositional system to carbonate platform depositional system during PSQ11-PSQ12. Two inter-platform basins with argillaceous limestone were developed in Liangping and Shizhu.（6） The eruption of Emei basalt was a process of continental rift evolution, which started in Maokou period in the early of Late Permian, and ended in Changxin period. The eructation of Emei basalt could be divided into five phases:①In the early of Maokou Period（PSQ5, PSQ6）, magma in mantle started to be active, which made overlain crust updoming and made sea floor be fluctuated slightly. Under the influence of a variety of above factors, slides of incomplete consolidated marine sediments happened, therefore, the Maokou Formation nodular limestone deposited. Hydrothermal fluid enriched in SiO₂ went into sea floor and permeated into the marine sediments, which deposited as chert nodules or bands in diagenesis.②In the late of Maokou period （PSQ7）, the upwelling of magma made overlain crust become dome. Extensional faulting could be easily happened in the center of the dome, which led to the formation of rift basins, in which silicates deposited, such as Shizhu inter-platform basin of the Maokou period.③In the latest Maokou period, when the basalt wast close to eruption, the crust of Sichuan basin rose rapidly because of the upwelling of magma, which resulted in the domes being above the sea level. Therefore, a parallel unconformity developed between the Middle and Upper Permian named the Dongwu Movement.④In the early of Wujiaping period （PSQ8LST）, Emei basalt erupted out of the ground comprehensively. In the center of the dome, eruption was continental and abundant basaltic cleavages were developed in the basalt. Eruptions occurred in the surrounding sea too, and the pillow structures were found in the basal. Because magma effused out of ground on a large scale, basement of adjacent area subsided to fill up the magma chamber. Shizhu inter-platform basin was developed under this background and led to the accumulation of the Wujiaping Formation’s silicates.⑤Volcanism finished in Changxing period. Sichuan basin overall was extensional and subsided. Most part of the basin evolved to depositional area. "Kaijiang-Liangping" inter-platform basin with argillaceous limestones began to form along with "Shizhu" inter-platform basin.更多还原