【作者】 梁积伟；

【导师】 李文厚；

【作者基本信息】 西北大学 ， 矿物学、岩石学、矿床学， 2007， 博士

【摘要】 鄂尔多斯盆地是位于华北地台西部的大型克拉通叠合盆地，含有丰富的油、气、煤、铀等多种能源矿产，研究这些能源矿产在盆地内时空的赋存分布特点，需要多个不同的学科，从不同的角度进行深入的研究。其中沉积学和层序地层学的研究是其中不可或缺的重要方面。应用适合于陆相坳陷盆地层序地层学的理论体系，对鄂尔多斯盆地侏罗系进行高分辨率层序地层划分，研究侏罗系长期、中期、短期旋回的构成及各自的特点，建立鄂尔多斯盆地侏罗系的层序地层格架，在层序地层格架内探讨沉积体系的构成及空间分布。煤、气、油、铀形成和富集总是和特定的层序部位或者特定的沉积体系相联系，而层序的形成受控于构造作用、沉积物供应、基准面变化和气候等多个方面。研究沉积体系和层序地层与某种矿种之间的联系，有助于从理论上阐明能源矿产的赋存分布规律。依据47个野外露头剖面，325口勘探井的测井资料对鄂尔多斯盆地侏罗系进行了层序地层划分，把鄂尔多斯盆地侏罗系层序地层划分为一个构造旋回，即印支期后到燕山中期构造运动所限定的地层，上下均为不整合面限定。内部可以划分为3个明显的超长期旋回，富县组和延安组构成第一个超长期旋回(SLSC1)，直罗组和安定组构成第二个超长期旋回(SLSC2)，芬芳河组构成第三个超长期旋回(SLSC3)。相邻两个超长期旋回之间都以不整合面为界。旋回内部具有从早期的构造活动期到晚期的构造平静期过渡的特点，富县组和延安组下部的延10代表了构造活动期的沉积，延安组的中上部则是相对平静期。直罗组下段代表了第二个构造活动期，直罗组上段和安定组是第二个构造平静期。芬芳河组代表了第三个构造活动期。依据高分辨率层序地层学的原理，考虑到构造运动，沉积物供应，气候和湖平面变化，侏罗系可以进一步划分为7个长期旋回和13个中期旋回。第一个长期旋回(LSC1)由1个中期旋回构成：富县组为MSC1。延安组有3个长期旋回构成，LSC2—LSC4，进一步划分为7个中期旋回MSC2—MSC8。直罗组和安定组分别代表一个长期旋回，即LSC5和LSC6，均有两个中期旋回，直罗组为MSC9—MSC10，安定组为MSC11—MSC12。芬芳河组由1个长期旋回，只能识别出1个中期旋回构成，即MSC13。每个中期旋回可划分出若干短期旋回，短期旋回在全盆地不具有可对比性，不同区域划分的短期旋回的数量和特征各不相同。通过盆地内多条连井对比剖面，建立了侏罗系层序地层格架。层序的对比既有界面对界面的对比和地层对地层的对比，同时也有地层对界面的对比。通过对沉积构造、测井资料垂向序列、岩矿特征和生物化石资料的综合分析，识别和划分侏罗系各组的沉积相及沉积体系。将研究区内的侏罗系沉积划分为冲积扇、河流、湖泊和三角洲沉积体系。冲积扇以干旱扇为主，特别指出延安组发育湿地扇沉积。河流沉积体系既有辫状河相，也有曲流河相。详细讨论了各种相、亚相、微相的特征及其空间展布，以及各种相在层序地层序列中的位置和控制机制。在构造活动期，即在基准面旋回的早期，沉积物堆积速率快，往往发育冲积扇或者辫状河沉积，但是其分布范围局限。在长期旋回的中期，随着构造活动进入相对稳定期，发育曲流河、三角洲和湖泊沉积。以中期旋回为单位对沉积体系进行平面制图，刻画了沉积体系的空间展布特征。对不同旋回沉积体系的对比研究，展示了鄂尔多斯侏罗纪沉积盆地充填、演化历程。研究侏罗系的层序地层和沉积体系，不能不探讨原型盆地的类型及规模。现今的鄂尔多斯盆地是经历了构造运动和剥蚀作用改造后的残留盆地，通过构造分析和利用盆地周边的沉积记录进行对比，恢复了鄂尔多斯侏罗纪的原型盆地。侏罗纪时，除了盆地的南界为印支期隆起的秦岭造山带外——该造山带一直是一个限定性的边界，其他西部、东部和北部边界都有不同程度变化。盆地现今的西界为西缘逆冲推覆带所限，而西缘逆冲推覆带主要形成于晚侏罗世一白垩纪。通过构造分析和沉积对比，认为盆地的西界在西缘逆冲推覆带之外，而且西界的南部和北部存在差异。盆地的东界并非现在的吕梁山，吕梁山隆起于晚侏罗世，在早中侏罗世不能起分割盆地的作用。同时，山西和河南等地的侏罗系残留地层与鄂尔多斯可以进行对比，可以推断，盆地的东界在吕梁山以东，而太行山在印支期已经隆起，所以盆地的东界最远只能达太行山。盆地的北界在侏罗纪虽然亦有活动，但是幅度小，可以认为与现今边界大致一致。在早中、侏罗世盆地的主体轮廓几乎是个正方形，随着燕山期东西向挤压应力场，盆地在东西方向收缩，南北方向变化弱，变成南北向的长方形盆地。鄂尔多斯盆地侏罗系富集了煤、气、油、铀多种能源矿产，沉积体系和层序地层的研究可以从一个方面揭示能源矿产的分布规律。煤层——尤其是区域性展布的厚煤层的形成需要特定的构造背景、沉积环境和物质基础。在平面上，煤主要分布于盆地的边缘，尤其以盆地北部和西部较为富集，向“三延地区”(延长、延安、延川)方向，煤层和厚度减小和尖灭。在垂向上，煤层位于基准面旋回上升半旋回的晚期。铀在延安组和直罗组均有产出，在平面上，铀分布于盆地周边地区，以盆地北部最为富集。在垂向上，铀赋存的层位属于基准面上升半旋回的早期，有利沉积相为河流相的河道砂体。侏罗系的油气具有下生上储的特点，有利油气富集的场所受沉积相控制，形成古地貌河道披覆油藏和岩性油藏。更多还原

【Abstract】 The Ordos Basin is a large-scale craton superimposed basin locating on the west of the North China platform, which is rich in oil, natural gas, coal, uranium and many other energy resources minerals. Many distinct subjects and points of view are needed in order to deeply study the characteristics of the occurrence and distribution of these energy resources in the basin. The studies of sedimentology and sequence stratigraphy are important indispensable aspects. The method system that is suitable for depression basin sequence stratigraphy of the continental facies is applied, in order to carry out the partition of high resolution sequence stratigraphy of Jurassic in Ordos basin and study the composition and characteristics of long-term, mid-term and short-term cyclic sequence. Which is measure up to set up the sequence stratigraphic framework of Ordos basin and discuss the composing and spatial distribution of sedimentary system in sequence stratigraphic framework. The formation and gathering of coal, gas, oil and uranium are always related to the given sequence position or sedimentary system. Moreover, the formation of sequences are controlled by tectonism, supply of sediments, transformation of base level and climate etc. It will give us great help to illustrate the gathering and distribution laws of energy resources in terms of theory if we study the relationships between sedimentary system, sequence stratigraphy and certain minerals.According to 47 outcrops sections, and log formations of 325 exploitation wells, the sequence stratigraphy of Jurassic in Ordos basin is devided into a tectonic cycle, which is the stratum constrained between post-Indo-Chinese epoch to mid-Yanshan epoch, and is limited by unconformities both up and down. The interior of the sequence can be divided into three clear super-long-period cyclic sequences. The first super-long-period cyclic sequence (SLSC1) is made up of Fuxian and Yan’an Formation, while Zhiluo and Anding Formation constitute the second super-long-period cyclic sequence (SLSC2), and Fenfanghe Formation forms the third super-long-period cyclic sequence (SLSC3). The adjacent two super-long-period cyclic sequences are separated by unconformities. The interior of the sequence has the characteristic that it transits from the early tectonic active stage to the late stable stage. Fuxian Formation and Yan 10, the under parts of Yan’an Formation, represent the sedimentation in tectonic active stage; while the middle and upper parts of Yan’an Formation are the relative stable stage. The under parts of Zhiluo Formation represent the second tectonic active stage, and the upper parts and Anding Formation are the second stable stage. Fenfanghe Formation represents the third active stage. According to the principle of high resolution sequence stratigraphy, and considering tectonic movement, supply of sediments, climate and changes of lake level, Jurassic can be further divided into7 long-term cyclic sequences and 13 mid-term cyclic sequences. The first long-term cyclic sequence is made up of 1 mid-term cyclic sequences: Fuxian Formation is MSC1.Yan’an Formation is made up of 3 long-term cyclic sequences: LSC2—LSC4 which are further divided into 7 mid-term cyclic sequences: MSC2—MSC8. the LSC5 and H LSC6 long-term cyclic sequences are partly represented by Zhiluo Formation and Anding Formation, which are all divided into 2 mid-term cyclic sequences. Zhiluo Formation is MSC9—MSC10, and Anding Formation is MSC11—MSC12. The third long-term cyclic sequence is made up of one mid-term cyclic sequence, which is the MSC13 that Fenfanghe Formation represents. Each mid-term cyclic sequence can be divided into several short-term cyclic sequences that do not have comparability in the whole basin. The amount and characteristics of the divided short-term cyclic sequences are different in distinct regions. The Jurassic sequence stratigraphic framework is set up through two or more well tie contrast sections in the basin. There are comparisons of both boundaries and sequences for the sequence’s comparison, as well as contrasting boundary with sequence.Through the multidisciplinary analyses of sedimentary structures, vertical secessions of log information, characteristics of rocks and minerals and fossils information, we can distinguish and measure off sedimentary facies and sedimentary systems of each formation in Jurassic. The Jurassic in study region can be divided into alluvial fan, river, lake and delta sedimentary systems. Arid fan takes the dominate place of alluvial fan,and particularize the humid fan developed in Yan’an Formation. River sedimentary system includes both braided stream facies and meandering river facies. Discuss the characteristics and interspace distribution of different kinds of facies, subfacies and microfacies in detail, as well as every facies’ position and control mechanism in sequence stratigraphic array. In tectonic active stage, the early period of base level cycle, sediments accumulated quickly, and alluvial fan or braided stream was always developed, but their distribution area was limited. In the middle period of long-term cyclic sequence, as tectonic movement went into the relative stable stage, meandering river, delta and lake deposit developed. Draw plans to the sedimentary system measured in mid-term cyclic sequence, and depict the interspace distribution characteristics of sedimentary system. The contrastive study on different cyclic sedimentary systems set out the Ordos sedimentary basin’s filling and evolvement history in Jurassic.We have to discuss the type and size of prototype basin in order to study the sequence stratigraphy and sedimentary system of Jurassic. The Ordos basin now is the relict basin having undergone tectonic movement and denudation. Resume Ordos prototype basin in Jurassic, through tectonic analyze and using sedimentary track record comparison around the basin. In Jurassic, the western, eastern and northern boundary of the basin had changed in varying degrees, except the south- Qinling orogenic belt rising in Indo-Chinese epoch, which is an always limited boundary. The western of the basin is limited by west-edge thrust nappe belt which formed in early and mid Jurassic. According to structural analysis and sediment comparison ,we judge the western of the basin is outside of west-edge thrust nappe belt .At the same time , the western of the basin is different in the north and south. Therefore in the early and mid Jurassic the western boundary was 40km west than today. The eastern boundary of the basin was not the Luliang Mountain now;and Luliang Mountain rose in late Jurassic, so it couldn’t be effective in dividing the basin in early and mid Jurassic. Meanwhile, the relict stratum of Jurassic in Shanxi and He’nan Province can compare with the stratum in Ordos. So we can inferred from that the eastern boundary of the basin is on the east of Luliang Mountain. However, Taihang Mountain has already risen in Indo-Chinese epoch,so the farthest place of the east boundary can only be Taihang Mountain. Though the northern boundary of the basin had activities, but the range was small. We can consider it to be the same with today. The basin’s main figure was nearly a square in early and mid Jurassic, but with latitudinal direction compression stress field in Yanshan epoch, the basin shrinked on latitudinal direction, and had little change on the north-south direction. So the basin turned to be oriented north-south rectangle.The Ordos basin has gathered coal, gas, oil,uranium and many other energy resources in Jurassic. The study of sedimentary system and sequence stratigraphy can post the distribution laws of energy resources from one side. The coal bed, especially the thick coal bed pertaining to a region, needs given particular structural setting, sedimentary environment and material basis. On the tabular surface, coal distributes mainly on the edge of the basin, especially gathering in the north and west of the basin. The thicknesses of coal bed minish or annihilate to the direction of "three Yan district"(Yanchang,Yan’an,Yanchuan). In the vertical section, coal bed locates on the late rising half cycle of base level cycle. Uranium outputs in both Yan’an and Zhiluo formation. On tabular surface, uranium distributes around the basin, and gathers most in north basin. In the vertical section, uranium locates on the early rising half cycle of base level cycle, and the avail sedimentary facies is river way sands. The oil has the characteristic of formation upside and save underside in Jurassic,which is favour of the gas and oil banking arena being controlled by sedimentary context, so as to form palaeogeomorphology channel draping oil deposit.更多还原