【作者】 邱欣卫；

【导师】 刘池阳；

【作者基本信息】 西北大学 ， 矿产普查与勘探， 2011， 博士

【摘要】 鄂尔多斯盆地处于我国东西南北四大不同构造域活动影响的复合部位,西跨南北构造带。不同构造域和多种地球动力学环境的复合、叠加及其与时彼此消长变化,形成了极为复杂的盆地演化-改造历史。盆地中南部中晚三叠世延长期富烃凹陷的形成与秦岭碰撞造山过程在时间上彼此呼应,空间上毗邻共存,对该凹陷发育环境和沉积特征的深入研究,可进一步探索该区的盆山耦合关系,揭示富烃凹陷形成的动力学环境。本文以沉积盆地“整体、动态、综合”的研究思路为指导,在大量野外剖面考察和岩芯观察、多种岩矿、地球化学测试分析和地球物理等第一性资料研究的基础上,综合沉积学、构造地质学、油气地质与勘探等研究成果和资料,对富烃凹陷湖盆底形特征、优质烃源岩和与其伴生的多种事件沉积岩和生物化石等进行深入研究,探讨鄂尔多斯盆地中晚三叠世延长期富烃凹陷主要特征及其形成的动力学环境。大量岩石矿物学和地球化学分析表明,鄂尔多斯盆地延长组长7优质烃源岩富含黄铁矿,形成于深湖-半深湖相还原环境。优质烃源岩具有两个显著特征,其一是铀元素富集。富铀烃源岩平面上呈北西-南东向展布;缺氧的沉积环境、丰富的铀源、高含量的有机质及胶磷矿等共同促使了铀元素的富集;丰富的铀元素可能主要来自于火山灰、深部热液物质。优质烃源岩另一重要特征是与多层火山灰沉积物互层。延长组火山灰沉积物包括有空降型和水携型两种成因机制,平面上表现为整体呈北西-南东向展布,由南西至北东方向火山灰沉积物厚度逐渐变薄、层数逐渐表少、粒度逐渐变细;大地构造环境判识图解说明其可能源于火山弧钙碱性岩浆源区;盆地外西南方向西秦岭天水地区印支期流纹岩可能是火山灰沉积物的源区之一;火山灰带来大量营养物质可能导致了藻类勃发,提高了湖盆原始生产力,有利于形成富有机质层,对延长期富烃凹陷的形成有重要贡献。在众多野外剖面考察和岩芯观察的基础上,综合最新沉积相研究资料,分析了延长期湖岸线和深湖区演化特征,指出受秦岭造山过程的影响,延长期存在两次重要的沉积中心迁移。通过氧化-还原环境判识指标U/Th值及与GR关系,计算了优质烃源岩形成期的古水深,最大深度为100m左右,位于华池-白豹附近。恢复了长7优质烃源岩发育期湖盆底形结构,结果表明湖盆整体为北东缓、西南陡,呈北西-南东向展布,并向南东方向开口的特征。湖盆充填类型分析表明,长7₃深湖相亚组合发育的优质烃源岩有机质丰度最高,除与构造沉降幅度大导致可容空间较大以外,还可能与火山灰沉积和深部热液物质的输入关系密切。在富烃凹陷内的露头剖面和岩芯中发现有众多延长期同沉积变形构造及其活动遗迹。通过详细分析震积岩、浊积岩和软沉积局部变形的特征、分布和形成机制,指出富烃凹陷发育期构造活动明显,并总体受秦岭造山过程制约。优质烃源岩、火山灰沉积物、震积岩、浊积岩纵、横向和平面上耦合共存,相互影响,形成于统一的动力学背景。众多与优质烃源岩互层或共存的岩石矿物学、元素地球化学、同位素地球化学、铂族元素以及石油微量元素分析表明,富烃凹陷存在众多深部热流体活动的证据。这与该区受秦岭造山过程影响,基底断裂发生裂开-闭合的间歇式往复活动有关。盆地中南部富烃凹陷沉降幅度大,为较深-深湖区,且与盆地的热异常区、壳内高导层发育区分布相一致,在发育时间和分布位置上与秦岭造山过程有明显的耦合响应关系。深部作用活跃区主要分布于盆地中部38°N构造带和凹陷沉降幅度最大且存在热异常区,说明延长期富烃凹陷形成于深部作用活跃的背景。通过详细的野外考察,综合沉积学、岩石矿物学、元素-同位素地球化学分析,并结合区域地质构造研究表明,构造活动性明显、深部作用活跃可能是子洲双壳类动物勃发并集群死亡的主要原因。这对揭示延长期富烃凹陷的形成环境有重要启迪。综合磁异常和深部岩石圈结构资料,结合延长期富烃凹陷保留的众多特殊地质现象,依据延长期原始盆地面貌和盆山耦合关系,认为素以稳定著称的延长期富烃凹陷形成于受秦岭造山过程深、浅部耦合控制,构造活动性明显,深部作用活跃的动力学背景。更多还原

【Abstract】 Ordos basin locate at the overlapping part influenced by activities of various large structural domains consisting of the peri-Pacific, Siberia, Qinling-Qilian and Tethys, and spans in the west the famous N-S trending structural belt of China. The complicated evolution-reformation history is formed as a result of the combination, superposition and continuous changes different structural domain and multiple geodynamic setting. The spatio-temporal relationship of forming middle-late Triassic Yanchang period hydrocarbon -rich depression in middle-southern Ordos basin and the process of Qinling orogenic evolution are intimately related. Formational environment and sedimentary records of hydrocarbon-rich depression in depth study could explore the coupling relationship of orogenic belt and reveal the formational dynamic settings of hydrocarbon-rich depression.The thesis hold the three principles that research thinking“Integrity, Dynamics and Synthesis”of basin analysis as guidance. Based on lots of field profiles investigation, core observation, rock-minerals analysis, geochemical and geophysical data, synthesis research results and data of sedimentology, structural geology, oil-gas geology and exploring, reconstructing the bottom palaeo-topography framework of hydrocarbon-rich depression, analysis distribution characteristics and formational mechanism of excellent hydrocarbon source rocks, accompanies event deposits and fossil beds, then disscuss the major characteristics and formational dynamic settings of middle-late Triassic Yanchang period hydrocarbon-rich depression in Ordos basin.Many analyses of lithology-minerlogy and geochemistry indicate that Yanchang formation Chang7 excellent hydrocarbon source rocks containing much pyrite and forming reduction environment of deep lacustrine to semi-deep lacustrine facies in Ordos basin. The excellent hydrocarbon source rocks present two remarkbly characteristics, the first one is enriching uranium element. The uranium-rich source rock distribute in the center of hydrocarbon-rich depression with NW-SE trending. Uranium concentration induced by the action together with anoxia environment, abundant uranium element, high content organic matter and collophane. The uranium may be mainly from the volcanic ash sediments and deep hydrothermal liquid substances. The second distinguished characteristic of excellent hydrocarbon source rocks is interlay with much volcanic ash sediments. Water and air transport approches are the primary formational mechanism of volcanic ash sediment which depositing in NW-SE trending with the tendency that being gradually thinner, less and smaller from SW to NE. From the discrimination diagram of tectonic environment, we conclude that it came from calc-alkali magma area, the rhyolite of Tianshui area in western Qinling Mountain is one of original areas of volcanic ash sediments. The nutritive substance brought by volcanic ash may lead to blooming of alga and raised the primary productive of the palaeo-lake. It is benefit for building the organic-rich beds and it is important for the development of hydrocarbon-rich depression in Yanchang period.Based on lots of field profiles investigation, core observation, inegrate the latest sedimentary facies data, analysis the evolution characteristics of lake strandlines and deep lake zones, showing twice important depocenter migration in Yanchang period due to the orogenic process of Qinling. Using the relationship of U/Th value which is redox discrimination index and GR valute of log curve, caculated the palaeobathymetric, the deepest region loacating in Huachi-Baibao areas reached at 100m, and recovering the lacustrine basin bottom palaeo-topography frameworks indicate the lacustrine basin with flatter and steep slope in Northeastern and Southwestern, respectively. Express NW-SE trending distribution and opening to the east. Basin filling types analysis indicates that Chang73 deep lacustine sub-assemblage filling type develop excellent hydrocarbon source rocks which have the highest abundance organic matter. It may be closely relating with volcanic ash deposit and deep hydrothermal substance input except the bigger accommodation space due to the bigger amplitude of tectonic subsidence.Many syndepositional deformation structures and their activity imprints in outcrop area and core at hydrocarbon-rich depression can be observed. Through detail analysis on characteristics, distributions, formational mechanisms of seismites, turbidite and soft -sediment deformation sturtures, we conclude that the tectonic setting is obvious activities during the formation of hydrocarbon-rich depression periods, which are controlled by the Qinling orogeny belt. The spatio-temporal distrutbion of excellent hydrocarbon source rocks, volcanic ash sediments, seismites, turbidite are consistent and interactional, and forming the uniform dynamic setting. Combining with the petrological and mineralogical, elements geochemistry, isotopes geochemistry, platinum group elements of interbeds or existence with excellent hydrocarbon source rocks and trace elements in petroleum demonstrate the hydrocarbon-rich depression keeping many evidences about deep hydrothermal fluids activity, which are influenced by the process of Qinling orogeny belt and related with the intermittence rupture-close activity of fundamental faults. The subsidence amplitude is very large of hydrocarbon-rich depression, lacating in deep lake area, and consistenting with abnormal thermal and crust high conductivity area, which are closely related coupling with the the process of Qinling orogeny on spatio-tempal relationship. The deep hydrothermal fluids active areas distribute in 38°N structural zone and the biggest subsidence amplitude with anomalous thermal area in the basin, which shows that the hydrocarbon-rich depression developed in the background of active deep processes. Throngh detail investigation of outcrop, integrating a large number analysis of geochemistry, lithology-mineralogy and sedimentology, combining regional geological characteristics, which indicate that structural action is obvious and active deeply dynamic background settings are the mainly reasons of bivales blooming and death, which is benefit for revealing the formational settings of hydrocarbon-rich depression.After analyzing abnormal magnetic field and lithosperic data, combining many special geological appearances preserved in Yanchang period hydrocarbon-rich depression. So based on the analysis of prototype basin visage and basin-mountain coupling relationship in Yanchang period, the author believe that although its famous for stable, Yanchang period hydrocarbon-rich depression formed in the setting of structural action is obvious and actively dynamic background which response to the process of Qinling orogenic form deep to shallow.更多还原