龙门山北段晚侏罗世冲积扇沉积特征分析及意义

发布时间：2018-07-02 13:14

本文选题：龙门山 + 莲花口组　；参考：《成都理工大学》2015年硕士论文

【摘要】：青藏高原东缘龙门山中生代构造隆升是研究热点。针对龙门山幕次构造运动多次叠加的特殊性,龙门山山前冲积扇一直被看做是盆山耦合的研究重点。前人大多数研究仅集中在早期(晚三叠世-早侏罗世)和晚期(白垩纪-新生代)的冲积扇研究,而对形成于区域气候变化最显著、沉积岩相突变阶段的晚侏罗世莲花口组的冲积扇的研究却相对薄弱,究其主要原因可能是气候、构造作用的同时叠加导致了对盆山耦合演化认识的局限。本论文针对受气候和构造双重控制的龙门山北段晚侏罗世莲花口组冲积扇,对其进行细致的沉积相和沉积环境解析。首先在野外对剖面进行系统的岩相分析,然后识别砾石的不同成分,测量古水流方向,进而结合镜下对砂岩碎屑组分的统计和阴极发光对碎屑组分的识别,综合分析了莲花口组冲积扇沉积特征及物源。本次研究取得了如下认识:(1)运用岩相分析方法和沉积岩相组合模式,首先在莲花口组中识别出9种砾岩岩相:富砂质杂基砾岩Gmd,块状颗粒支撑砾岩Gcd,定向性粒序层理砾岩Gco,底冲刷正粒序砾岩Ghg,含砂质透镜体砾岩Gmg,槽状交错层理砾岩Gt,夹层状砂体砾岩Gst,斜层理砾岩Go,平行层理砾岩Ghi;5种砂岩岩相:槽状交错层理砂岩St,块状砂岩Sm,平行层理砂岩Sh,底冲刷沉积砂岩Ss,斜层理砂岩So;9种细粒沉积岩相:细纹层泥岩Fl,块状(板状)泥岩-粉砂岩Fm,水平层理泥岩-粉砂岩Fh,细粒纹层泥岩-粉砂岩Fg,生物扰动泥岩-粉砂岩Fb,灰绿色泥岩Ms,含钙化泥砾泥岩Cg,碳酸盐岩Cm,古土壤P;7种主要沉积建造:沉积物重力流(SG),辫状河道沉积(BF),河道冲刷充填沉积(CH),河漫滩-洪泛平原(OB),片流沉积(SF),天然堤(MF),浅湖泊相(LD)。在此基础上共划分出10类岩相组合:①-③复成分块状砾岩(PC):Ⅰ类、Ⅱ类、Ⅲ类;④砾岩和泥岩条带CM;⑤砾岩和砂岩CS;⑥砾岩、砂岩和泥岩CSM;⑦泥岩和复成分砾岩MC;⑧砂岩和泥岩SM;⑨泥岩和砂岩透镜体MS;⑩泥岩和泥灰岩MCa。最终将研究区的莲花口组的沉积环境划分为4种:冲积扇沉积环境,辫状河沉积环境,远端河流沉积环境,浅湖沉积环境。(2)初步查明莲花口组中砾石的古水流方向。对研究区的野外具古流向指示意义的沉积构造进行古水方向测定和统计,并对比了晚三叠世以来研究区的古流向特征,初步判断莲花口期古流向主要为SE向(140°~160°),并推断龙门山北段自晚三叠世至早白垩世的古水流向具有明显的整体继承性,以SE向(130°~170°)为主。(3)限定了莲花口组砾石与碎屑物质的成分及其物源区的岩性特征。利用系统的野外砾石成分统计、常规显微镜和阴极发光分析砂岩碎屑组分,砾石成分与砂岩碎屑组分具有一致性。砾石成分空间上存在明显区域差异:①广元金子山附近,砾石成分以石英岩和石英砂岩为主,石英质砾岩达67%~89%,灰岩砾石成分最高不超过30%,白云岩砾石零星出现;②安县附近,砾石成分以石英砂岩,灰岩和白云岩为主,灰岩砾石成分最高超过90%(平均52%),白云岩砾石成分比例明显较其他地方高,最高可达23%。同时根据岩石学、生物化石的特征初步推断了莲花口组中砾石的物源:①灰岩砾石主要来自龙门山地区的石炭系~二叠系(以二叠系为主);②石英砂岩砾石均为钙质石英砂岩,阴极发光光色特征表明部分钙质石英砂岩与泥盆系石英砂岩有较高的相似性。碎屑组分统计表明:①金子山剖面砂岩中石英含量一般30%(平均为20%~29%),长石含量为5.7%~16.3%,岩屑37.7%~74.4%,一般大于60%;②青林口地区砂岩中石英含量较稳定为23%~25%,长石2.3%~9%,岩屑含量为65.6%~72.6%;③安县地区砂岩中石英含量为26%~45%,长石含量为0.7%~2.8%,岩屑占53%~81.9%。基于砾岩成分、砂级碎屑组分、石英成因类型的差异性,以及古水流的继承性,综合表明冲积扇沉积物质展布受古河流水系控制,与源区为孤立式点状物源对应关系。(4)晚侏罗世四川盆地从“黑层”转变“红层”后,从细粒的遂宁组到粗粒的莲花口组,沉积物表现出相同气候背景下的岩相和沉积环境的突变,应为龙门山地区强烈构造运动所驱使。对比“黑层”阶段沉积的白田坝组冲积扇和“红层”阶段沉积的莲花口组冲积扇的沉积序列,表明在相似活动构造背景下,莲花口组的沉积序列旋回性明显受区域气候的控制。这表明在研究区陆相沉积体系研究中应重视构造和气候的双重因素,回避或忽略气候因素是不可取的。(5)龙门山北段莲花口期冲积扇的形成受构造-气候-古河流水系三重因素联合控制。莲花口组冲积扇是龙门山构造活动背景下,构造隆升驱动源区和沉积空间、古河流水系控制沉积物空间展布、持续干旱和充沛雨水补给交替气候变化影响沉积序列砾-泥旋回叠加,扇体砾石层重在垂向叠加,侧向延展较弱的多期次复合型扇体。
[Abstract]:The Mesozoic tectonic uplift of the Longmen mountain in the eastern margin of the Qinghai Tibet Plateau is the focus of research. In view of the particularity of the repeated superposition of the subtectonic movement of the Longmen mountain episodes, the alluvial fan in the Longmen mountains has been regarded as the focus of the study of the basin mountain coupling. Most of the previous studies of the predecessors were concentrated only on the alluvium of the early (late three fold - Early Jurassic) and late (Cretaceous - Cenozoic). Fan studies, however, are relatively weak in the study of alluvial fans in the late Jurassic Lianhua Group formed by the most significant regional climate change and the sedimentary facies mutation stage. The main reason may be the climate, the superposition of the tectonics and the limitation of the understanding of the coupling evolution of the basin and mountain. This paper is aimed at the Dragon controlled by climate and structure. The sedimentary facies and sedimentary environment of the late Jurassic Lianhua mouth group in the northern part of mendan are analyzed. First, systematic lithofacies analysis is carried out in the field, and then the different components of the gravel are identified and the direction of the paleo flow is measured. Then, the statistics of the debris components in the sandstone and the identification of the debris components by the cathodic luminescence under the mirror are combined. The characteristics and source of the alluvial fan in Lianhua mouth formation are analyzed. (1) 9 kinds of conglomerate facies are identified in Lianhua Kou formation by lithofacies analysis and sedimentary facies combination model: Gmd, massive granular conglomerate Gcd, directional granular bedding conglomerate Gco, and bottom scour Rock Ghg, sandy lenticular conglomerate Gmg, grooved staggered conglomerate Gt, sandwich conglomerate Gst, diagonal conglomerate Go, parallel bedding conglomerate Ghi; 5 sandstone facies: trough staggered bedding sandstone St, massive sandstone Sm, parallel bedding sandstone Sh, bottom scour sedimentary sandstone Ss, diagonal bedding sandstone So; 9 fine grain sedimentary facies: fine striate Fl, block like (fine grain mudstone Fl, massive (")" Mudstone siltstone Fm, horizontal bedding mudstone - siltstone Fh, fine grain layer mudstone - siltstone Fg, bioturbate mudstone, siltstone Fb, gray green mudstone Ms, calcified mudstone Cg, carbonate Cm, paleosol P, 7 main sedimentary formations: sediment gravity flow (SG), braided channel deposition (BF), river scour filling deposition (CH), river flood Flood flood. Plain plain (OB), SF, natural dike (MF) and shallow lacustrine facies (LD). On this basis, 10 types of lithofacies assemblages are divided: (1) (3) complex block conglomerate (PC): class I, class II, class III; (4) conglomerate and mudstone strip CM; (5) conglomerate and sandstone CS; conglomerate and CS; conglomerate, sandstone and mudstone CSM; (7) mudstone and complex conglomerate MC; sandstone and mudstone SM; mudstone The sedimentary environment of Lianhua Group in the study area is divided into 4 types: alluvial fan sedimentary environment, braided river sedimentary environment, distal river sedimentary environment and shallow lake sedimentary environment. (2) preliminary identification of the direction of the paleo flow of gravel in Lianhua mouth group is preliminarily identified by the sedimentary environment of the Lianhua group in the study area. (2) the direction of the paleo direction of the study area is indicative of the direction of the paleo direction in the study area. The sedimentary structure carries out the measurement and statistics of the direction of the paleo water, and compares the characteristics of the paleo direction of the study area since the late three fold. It is preliminarily judged that the paleo flow of the lotus estuary was mainly SE (140 ~160), and that the paleo water flow from the late three to the early Cretaceous in the northern section of the Longmen mountain had obvious overall inheritance and was dominated by (130 [degree ~170]). (3). The composition of gravel and debris in Lianhua mouth group and the lithologic characteristics of its source area are determined. Using the statistics of the field gravel composition of the system, conventional and cathodoluminescence analysis of sandstone debris components, the conglomerate composition is consistent with the sandstone fragments. There are obvious regional differences in the space of the gravel composition: (1) near the gold mountain in Guangyuan, gravel. Quartzite and quartzite are the main stones, the quartzite conglomerate is 67%~89%, the composition of the limestone is not more than 30%, and the dolomite gravel occurs sporadically. In the vicinity of Anxian, the conglomerate is mainly composed of quartz sandstone, limestone and dolomite, and the highest composition of limestone is over 90% (average 52%), and the proportion of the dolomite gravel is obviously higher than that of other places. According to the characteristics of petrology and biological fossils, the source of the 23%. is preliminarily deduced from the characteristics of petrology and biological fossils: (1) the limestone gravel mainly comes from the Carboniferous Permian in the Longmen mountain area (mainly Permian), and the quartz sandstone gravel is calcareous quartz sandstone, and the glowing color characteristics of the Yin pole show that some calcareous quartz sandstone and mud are found. The quartz sandstone of the basin system has high similarity. The statistics of debris composition show that the quartz content in the sandstone of the Jin Zi Shan section is generally 30% (average 20%~29%), the feldspar content is 5.7%~16.3%, and the debris 37.7%~74.4% is more than 60%, and the quartz content in the sandstone of the Qinghai Province is more stable than that of 23%~25%, the feldspar 2.3%~9%, and the content of the cuttings is 65.6%~72.6%; 3. The quartz content in the sandstone in the county area is 26%~45%, the feldspar content is 0.7%~2.8%, the cuttings account for the 53%~81.9%. based on the conglomerate composition, the sand grade debris component, the quartz origin type difference and the inheritance of the paleo flow, which shows that the alluvial fan sedimentary material distribution is controlled by the ancient river water system and corresponds to the source area as the isolated point source. (4) late The Jurassic Sichuan basin has changed from the "black layer" to the "red layer" from the fine grain Suining group to the coarse-grained lotus flower mouth group. The sediment shows the abrupt change of the lithofacies and sedimentary environments in the same climate background. It should be driven by the strong tectonic movement of the Longmen mountain area. The depositional sequence of the alluvial fan in the Lianhua mouth group, which is deposited in the section, indicates that the cyclicity of the sedimentary sequence of the Lianhua mouth group is obviously controlled by the regional climate under the similar active tectonic setting. This indicates that the dual factors of structure and climate should be paid attention to in the study of the continental sedimentary system in the study area. It is not advisable to avoid or ignore the climatic factors. (5) the north of Longmen. The formation of the alluvial fan in the lotus flower mouth period is controlled jointly by three factors. The alluvial fan of Lianhua mouth formation is the source area and sedimentary space of the tectonic uplift in Longmen mountain. The ancient river flow system controls the spatial distribution of the sediment, and the continuous drought and the abundant rainwater supply alternate climate change influence the sedimentary sequence. The gravel layer is superimposed, and the fan gravel layer is vertically superimposed and the lateral extension is weak.
【学位授予单位】：成都理工大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：P534.52;P512.2

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