【作者】 陈安清；

【导师】 陈洪德；

【作者基本信息】 成都理工大学 ， 沉积学， 2010， 博士

【摘要】 中国海相油气勘探取得重大突破及潜在勘探区域主要集中在特提斯构造域的秦祁昆构造带两侧的四川盆地、塔里木盆地、鄂尔多斯盆地与羌塘盆地。其中,鄂尔多斯盆地的海相油气勘探尚未取得大的突破,是一个有很大希望的勘探区域。相对其上古生界和中生界而言,下古生界的海相层系的研究最为薄弱。因此,有必要进一步解决盆地和古隆起的形成演化、沉积物质聚集分布规律和盆地充填过程等基础地质问题。本论文在借鉴前人研究成果的基础上,以“构造控盆、盆控沉积、沉积控组合”为指导,运用沉积学、地层古生物学、层序地层学、地球化学、地球物理学等理论和技术方法,将鄂尔多斯盆地构造演化与全球构造背景相结合,以野外露头、测录井和地震资料为基础资料,研究了鄂尔多斯地块早古生代的沉积物质的聚集分布规律和盆地演化过程,主要内容和成果如下:(1)通过研究鄂尔多斯盆地下古生界的岩石地层、生物地层和年代地层,将野外剖面和钻井进行了系统的地层划分与对比。进行了层序界面类型和划分标志研究,识别出了7种层序界面,厘定了鄂尔多斯盆地下古生界的层序地层划分方案,将下古生界寒武系和奥陶系划分为5个超层序和27个三级层序,建立了层序地层格架。(2)通过野外剖面、岩心、测井和地震资料,研究了层序格架内的沉积体系发育特征,识别出了滨海沉积体系、陆棚沉积体系、碳酸盐缓坡沉积体系、碳酸盐台地沉积体系、大陆斜坡沉积体系、深海盆地沉积体系等六大沉积体系;深入分析了含磷建造、混合沉积、广布式鲕粒滩和竹叶滩、富硅质碳酸盐岩、蒸发岩、生物礁、深水沉积和磨拉石建造等八类特殊沉积体的特征、成因及其意义。(3)以超层序体系域为编图单元,系统编制了鄂尔多斯盆地下古生界的构造-层序岩相古地理图,揭示了不同时期的沉积物的聚集分布规律和沉积演化:寒武纪早期为含磷沉积和混合沉积阶段;寒武纪中、晚期为广布式台地鲕粒滩和竹叶滩沉积阶段;奥陶纪早期为富含硅质的碳酸盐缓坡沉积阶段;马家沟期为以局限环境为特征的碳酸盐台地阶段;晚奥陶纪为镶边台地和深水重力流发育阶段。(4)分析了有关Rodinia超大陆裂解、原特提斯洋和古亚洲洋形成演化、鄂尔多斯克拉通周缘的区域构造演化等盆地演化的动力背景,系统编制了华北陆块的构造-古地理格局图,深入分析了鄂尔多斯盆地5个超层序的沉积建造和层序结构的差异性,揭示了鄂尔多斯克拉通的盆地结构:北缘于早古生代发育伊盟“长寿”古陆,西南缘在寒武纪表现为被动大陆边缘背景下的“坡-隆-坪”结构,奥陶纪则转换为活动大陆边缘背景下的“坡-隆-坳”结构。(5)探讨了盆地形成机理,认为Rodinia超大陆裂解,原特提斯洋打开,在鄂尔多斯南缘形成的秦祁昆分支洋盆和克拉通内部的贺兰坳拉谷和晋陕坳拉谷是盆地形成的主要动力。寒武纪,虽然由于华北陆块向东纲瓦纳漂移而使北缘处于弱俯冲状态,但南缘原特提斯洋的扩张使盆地整体上仍以伸展作用为主,克拉通内部的缓慢沉降主要由热沉降和地壳均衡补偿所致;克拉通边缘盆地的沉降机制与伸展背景下的岩石圈减薄有关。寒武纪末和奥陶纪初华北陆块由伸展应力场向挤压应力场转换,导致克拉通内部沉降中止。马家沟期,由于南缘北祁连-北秦岭洋的俯冲作用,鄂尔多斯克拉通内部受南北对挤的远场应力,发生下坳沉降,压应力导致的岩石圈内粘度降低和下伏的前寒武纪晋陕坳拉谷造成的地壳不均一性对盆地沉降亦有重要影响;克拉通边缘盆地则与板块俯冲导致的岩石圈挠曲有关,导致沉积速率和沉积幅度远大于克拉通内部。平凉期-背锅山期,中加里东运动导致俯冲作用的增强,使整个华北克拉通区域快速上升到海平面之上,只西南缘发育裂谷盆地。奥陶纪末,北秦岭与鄂尔多斯地块发生明显的碰撞,鄂尔多斯南缘发生前陆挠曲,形成具有前陆性质的残留海盆地。(6)通过古构造图分析了古隆起的形态演化,认为前寒武纪基底地貌、板块聚敛作用、全球海平面变化和板块不同构造部位的差异沉降是古隆起形成的四大主控因素:辛集期-张夏期的隆起暴露(古陆)面积的逐渐缩小,是由于继承前寒武纪基底裂谷成因的隆-坳相间的地貌,以及低海平面背景下的海平面逐渐上升引起的;晚寒武世的中央古隆起雏形以及奥陶纪早期的整体隆起暴露,是由板块由伸展作用向聚敛作用转换、克拉通沉降中止和同时伴随的海平面下降所致;马家沟期的“L”型隆起是聚敛作用的远场应力和差异沉降形成的克拉通边缘隆起;并且最终由于板块碰撞作用,于晚奥陶世盆地构造反转,接受长期的风化剥蚀。(7)在大量的前人研究成果的基础上,综合分析了鄂尔多斯早古生代克拉通盆地的演化特征,揭示了海平面变化、盆地沉积充填过程、古隆起演化、构造事件、古气候等之间的耦合关系,恢复了不同演化阶段的盆地原型,创新性地探讨了盆地和古隆起的形态和形成机制:总体上鄂尔多斯盆地早古生代具有“北高南低,东缓西陡夹中隆”的构造-沉积格局,认为鄂尔多斯克拉通的演化受Rodinia超大陆裂解和Pangea泛大陆形成间的I级全球旋回的制约,具体表现为受北侧古亚洲洋动力体系和南侧原特提斯洋动力体系的联合控制;由于古亚洲洋的俯冲作用,在克拉通北缘发育“长寿古陆”;东缘则与华北克拉通相连;因此,西南缘的构造转化成为控制盆地结构的主要因素,在威尔逊构造旋回过程中,盆地总体上经历了“坡-隆-坪”(SS1~SS3)→“坡-隆-坳”(SS4)→“沟-弧-盆”(SS5)→前陆盆地(SS5末)→消亡的演化过程。更多还原

【Abstract】 China marine oil and gas exploration has achieved significant breakthrough in Sichuan Basin, Tarim Basin, Ordos Basin and Qiangtang Basin which concentrated along Qinling–Qilian- Kunlun- tectonic belt of Thetys tectonic area. But Ordos Basin have not yet achieved a major breakthrough. Compared lower Paleozoic marine strata’s to Upper Paleozoic and Mesozoic, which studied weakness. So it is necessary to resolve those basic geological problems, such as the evolution of Paleo-uplift and basin, the distribution and accumulation of sediments and the basin filling process et.al. Referring to the predecessors’s research, guiding by the academic ideology of "structural control basin, basin control sediment, sediment control combination" and theories of sedimentology, paleontology, sequence stratigraphy, geochemistry and geophysics, based on outcrops , logging and seismic data, the character of sediments accumulation ,distribution and basin evolution in the early Paleozoic Ordos continental block were researched. The main content and achievements as follows:First, according to lithostratigraphy, biostratigraphy and chronostratigraphy of the lower Paleozoic in Ordos basin, the outcrops and drilling is carried out a systematic stratigraphic division and contrast. After research on the types of sequence boundary and classification standard, seven kinds of sequence boundaries are identified, sequence stratigraphy division plan of lower Paleozoic in Ordos basin is setted, the Cambrian and Ordovician can be divided into 5 Super sequences and 27 third-order sequences, and sequence stratigraphy framework was establishedSecond, by the outfield section, cores and well logging and seismic data, it is studied the sedimentary system development characteristics within the sequence framework. Six depositional systems are identified, they are the coastal sedimentary system, shelf depositional system, carbonate ramp depositional systems, carbonate platform depositional system, the continental slope depositional system and deep-sea basin depositional system; and it is analyzed in-depth the special sedimentary features, causes and significance of the eight categories, the phosphorus construction, mixed sediments, widespread oolitic shoal and wormkalk shoal, rich siliceous carbonate rocks, evaporites, reefs, deep water sediment and molassesThird, taking super sequence system tract as mapping unit, the tectonic sequence paleogeographic of lower Paleozoic in Ordos Basin were drew, which revealed the accumulation and distribution of sediments and the sedimentary evolution in different periods of early Cambrian, it was phosphorus deposition and mixed sedimentary stage during early Cambrian, in the late Cambrian was the stage of platform the widespread oolitic shoal deposits and wormkalk shoal; early Ordovician was the stage of the deposition of silica-rich carbonate ramp, Majiagou period was characterized by restricted carbonate platform environment, Late Ordovician was the rimmed platform and gravity flow developmental stage.Forth, after analysis on the dynamic background including the splitting of super continent Rodinia, paleo-Tethys Ocean, the formation and evolution of Paleo-Asian Ocean and the regional tectonic evolution of margin of Ordos Craton basin, the structure paleogeographic of North China continental block were drew systematic, the sediment construction and sequence structure diversity of 5 super sequences were analyzed deeply, which reveals the basin structure of Ordos Craton, everlasting Emeng ancient land developed in north edge early Paleozoic, southwest edge showed the structure of slop-upheaval-plat in background of passive continental margine during Cambrian, then it transformed into the structure of slop-upheaval-depression in background of active continental margin during Ordovician.Fifth, after discussion the mechanism of basin formation, it is brought forward that the splitting of supercontinent Rodinia and the open of Paleo-Tethys Ocean are the main forces of basin forming in Helan aulacogen and Jinshan aulacogen, which are they’re in Qinliankun branch ocean basin and Craton formed in south edge of Ordos. During Cambrian, the north edge is in the condition of weak subduction due to the drifting north china continental block to east Gondwana, but the expanding of south edge Paleo-Tethys Ocean made the basin showed the character of stretching entirely, the slow subsidence inside of Craton mainly caused by the thermal subsidence and crust equilibrium compensation, and the subsidence mechanism of Craton basin edge connected with the lithosphere reduction in the background of stretch. In the end of Cambrian and the beginning of Ordovician, the sedimentation inside of Craton ceased due to the transforming of stretch field to stress field in north China continental block. During Majiagou period, the subsidence sedimentation took place inside Ordos Craton due to the remote stress of extruding both from south and north, further caused by the subduction of north Qilian Mountain and north Qinling Ocean, the sedimentation was significantly affected by the viscosity decrease of lithosphere and the crust nonuniformity of underlying pre-Cambrian Jinsha aulacogen, which was caused by pressure. The edge of Craton connected with the lithosphere flexure caused by plate subduction, which caused the sediments rate highly exceed the one of Craton interior. And during Pingliang to Beiguoshan period, middle caledonian movement improved the subduction and made north China Craton region rose quickly above the sea level, the rift basin only developed in southwest edge. In the end of Ordovician, north Qinling Mountain collided Ordos continental block obviously. Foreland flexure happened in south edge of Ordos, and there formed a relict sea with the character of foreland.Sixth, based on paleo-structure map , this paper analysized the forming evolution of paleohigh, found that paleohigh development controlled by four factors ,they were the base physiognomy of pre-Cambrian, plate physiognomy, global sea level change and diversity settlement of different structure part of plate. The reason why the area of upheaval reduce in Xinji to Zhangxia period were the upheaval-depression physiognomy inherited from pre-Cambrian base rift valley and the sea level rise in the low sea level background. The central upheaval rudiment late Cambrian and the entirely rise expose early Ordovician are caused by the transform stretch to convergence, sedimentation cease and sea level drop. The L shape upheaval is the Craton edge upheaval formed by the remote stress of convergence and diversity sediment. Finally, due to the plate colliding, basin inverted structuredly in late Ordovician and began to receive weathering and denudation for a long term.Seventh, based on predecessors’achievements, this paper integrated analyzed the evolution characters of Ordos Craton basin during early Paleozoic, revealed the coupling relationship among sea level change, basin sediment filling process, paleo-uplift evolution , tectonic event and paleo-climate, and constructed the basin prototype of different evolution stage. The structure-sediment pattern of Ordos Craton basin during early Paleozoic which was high in north and low in south, gentle in east and steep in west , upheaval in middle, were controlled by the splitting of supper continent Rodinia and first level global cycles during the forming of Pangea, and concretely controlled both by force system of north Paleo-Asian Ocean and south Paleo-Tethys Ocean. Everlasting Emeng ancient land developed in north edge of Craton due to the weak subduction of Paleo-Asian Ocean. So, the structure evolution in southwest edge were the main controlled factors of basin structure change, it experienced the developing process of slope-upheaval- flat in SS1-SS3,slope-upheaval-depression in SS4, gutter-arc-basin in SS5 and foreland basin in SS5 in Wilson structure cycle.更多还原