【作者】 王国茹；

【导师】 陈洪德；

【作者基本信息】 成都理工大学 ， 沉积学， 2011， 博士

【摘要】 鄂尔多斯盆地是我国第二大含油气盆地,其上古生界地层分布广,含气层位丰富,天然气资源量大,具巨大潜力。近些年盆地北部苏里格地区、榆林地区、乌审旗地区和大牛地地区天然气勘探取得了重要成果,上古生界地层成为盆地天然气储量增产的主力层系,为盆地完成“西气东输”任务奠定了坚实基础。盆地北部油气勘探不断取得新突破离不开新认识、新理论、新思路及各种新技术、新方法的引入和使用,然而,由于区域面积较大,随着勘探程度的不断深入和发展,一系列新的地质问题开始困扰不同地区的油气勘探,如盆地北部沉积物源、沉积体系发育分布规律和差异性以及统一的层序地层格架等,这些科学问题要求对盆地北部甚至整个盆地开展系统、整体研究,对盆地北部相关问题取得全面认识。论文在前人研究基础上,采用多种物源分析技术综合分析盆地北部上古生界物源,通过野外剖面、钻井岩心、地震测井及地球化学等资料建立层序地层格架,分析层序格架内沉积体系特征,并以长期旋回为编图单元系统编制上古生界层序岩相古地理特征,揭示盆地北部晚古生代沉积体系发育分布规律和沉积演化过程,主要取得以下几点认识:(1)盆地北部上古生界砂岩碎屑组分显示研究区西部不同时期的沉积物质主要来自于盆地西北部,而研究区中部、东部的沉积物质则来自于盆地的北部和东北部,为阴山古陆西部和东部物源控制下的沉积产物,沉积物源均具再旋回造山带性质。(2)重矿物组合显示盆地北缘的阴山西段和盆地西北缘的狼山、贺兰山为研究区西部的物源区;盆地北缘中部的乌拉山和盆地东部的大青山西段是盆地中部的物源区;盆地北缘东部的大青山及研究区以外东北部的兴蒙造山带等地区为盆地东部物源区;ZTR指数从北向南逐渐递增,说明研究区的物源在其北方。(3)上古生界岩屑组合类型在本溪组、太原组、山2段、山1段、盒8下段、盒8上段、盒7段-盒5段、盒4段-盒1段等8个层段各有不同,每一层段岩屑组合类型平面上均可分为西、中、东三个区域,表明上古生界盆地北部不同地区受三个不同的物源控制。(4)研究区太原组-下石盒子组的石英在阴极发光主要呈棕色,其次为蓝色、蓝紫色,再次为紫红色,最后为不发光,说明其母岩分别为中-深变质岩或浅变质岩;深成岩、火山岩或接触变质岩和沉积岩,沉积物源来自盆地北部的寒武系的结晶变质基底,其构造背景具有混合特性。(5)常量元素地球化学特征表明太原期至上石盒子组物源区为同时具有沟-弧-盆体系的活动大陆边缘和具有碰撞造山带的被动大陆边缘的大地构造背景;太原期、山西期具有明显的大洋岛弧和大陆岛弧的性质,石盒子期逐渐转为单一的被动大陆边缘碰撞造山带环境。(6)微量元素地球化学特征表明盆地北部物源区为活动大陆边缘、被动大陆边缘和大陆岛弧等同时存在的复杂构造背景;盆地钻井与周缘古陆REE特征对比表明西部物源来自阿拉善古陆和阴山古陆西段、东部物源来自阴山古陆的东段、中部物源同时受到阿拉善古陆和阴山古陆的影响。(7)通过露头、钻井、测井及地震资料,根据盆地演化、区域构造及层序界面特征,结合前人研究成果,将鄂尔多斯盆地古生界划分为1个巨旋回层序3个超长期基准面旋回层序和20个长期基准面旋回层序,并建立了相应的层序地层格架。(8)根据沉积学、古生物学、地球物理学和地球化学标志,结合岩石组合、沉积组构、剖面序列特征在鄂尔多斯盆地北部上古生界划分出陆相、海陆过渡沉及海相3个沉积体系组,识别出冲积扇、河流、湖泊三角洲、湖泊、河控-潮控三角洲、有障壁海岸和碳酸盐岩台地7种沉积体系和8种相应的沉积相单元。(9)以长期旋回为编图单元,系统编制20张上古生界层序-岩相古地理图,揭示盆地北部晚古生代沉积体系发育分布差异性及沉积体系演化过程,表明盆地北部晚古生代以发育毯式三角洲为特征,不同时期沉积体系呈现出一定的差异性,其晚古生代沉积经历了海相—海陆过渡相—陆相的沉积演化过程,并建立相应沉积演化模式为上古生界岩性油气藏勘探提供地质依据。更多还原

【Abstract】 Ordos Basin is the second largest petroleum basin in our country, the Upper Palaeozoic strata are widely distributed with rich gas-bearing and large natural gas resources whose potential is huge. In recent years, natural gas exploration has made important achievements in the north Sue’s area, Yulin region, Wushen banner region and Daniudi area. The upper palaeozoic strata have become the main formations of increasing the natural gas’production which lay a solid foundation for the West-East natural gas transmission. The new breakthrough in oil and gas exploration in the north part of the basin could not be achieved without new knowledge, new theories, new ideas, new technologies and the introducing and using of the new method. However, due to the large region, a series of new geological problems start bothering in different parts with the deepening and developing of the exploration, such as sediment sources in the northern basin, distribution and differences in depositional systems and unified layer sequence stratigraphic framework etc. In order to have a fully recognization about the related issues of the northern basin, these scientific problems require to carry out a systematic and holistic research about the northern basin or even the whole basin. The thesis reveals the distribution in the development of sedimentary system and sedimentary evolution process on the basis of the previous research. The following understands are mainly obtained:(1) The clastic compositions of Upper Palaeozoic in the northern basin show different periods of sediments in the west part of the research area are mainly from the northwest of the basin. While in the east and middle research area, the sediments are from the north and northeast of the basin which are under the control of the sources from the west and east ancient land in Yin Mountain. What is more, sediment sources have properties of recycled orogen.(2) The combination of heavy minerals show the western part of northern margin of the basin in Yin Mountain and northwestern margin of the basin in Lang Mountain and Helan Mountaim are the source areas in the Western study area. The Ural Mountain in the central of the northern margin and the western part of the Daqing Mountain in the eastern basin are the source areas of the central basin. ZTR index increased gradually from south to north which indicates the study area is in the north.(3) The debris combination types of Upper Palaeozoic in 8 formations are different from each other. These 8 formations are Benxi Formation, Taiyuan Formation, Shan2 Formation, Shan1 Formation, lower part of member 8 of Shihezi Formation (Lower H8 Formation), upper part of member 8 of Shihezi Formation (Upper H8 Formation), member 7- meber 5 of Shihezi Formation (H7-H5 Formation) and member 4- member 1 of Shihezi Formation (H4-H1 Formation). Each layer of debris combination types can be divided into three regions: the western, the central and the eastern part which indicate that different regions in the Upper Paleozoic northern basin are under the control of three different sources.(4) The cathode luminescence of quartz in Taiyuan Formation and Xiashihezi Formation are mainly brown then followed by blue, bluish violet, amaranth and nonluminous ultimately. It shows its parent rock is the mesomemetamorphic and the low- grade metamorphic rock. Plutonic, volcanic, contact metamorphic, sedimentary rock and sediment sources are from the crystallization metamorphic basement in the northern basin in Cambrian with mixed properties in its tectonic background.(5) The geochemistry characteristic of macroelement shows that the tectonic setting in source areas of Taiyuan Formation and Shangshihezi Formation is an active continental margin with trench-arc-basin systems and a passive continental margin with collisional belt. Taiyuan period, Shanxi period have an obvious nature of island arc and continerntal island, while Shihezi period turns to a single passive continental margin with collisional belt gradually.(6) The geochemistry characteristic of macroelement shows that source areas in northern basin have a complex tectonic setting background which exist at the same time. These are active continental margin, passive continental margin and continental island arc. Compared with basin drilling and REE characteristics of peripheral archicontinent, a conclusion is drawn that the material sources in the west are from Alashan archicontinent and the western archicontinernt in Yinshan, the material sources in the east are from the eastern archicontinent in Yinshan and the material sources in the middle is influenced by the Alashan archicontinent and Yinshan archicontinent. (7) According to the basin evolution, regional structure and sequence interfacial features, combined with previous studies, the Paleozoic of Ordos Basin is divided into one giant cyclical sequence, three super long base- level cyclic sequences and twenty long cyclic sequences and established corresponding sequence stratigraphic framework from outcrop, drilling, logging and seismic data.(8) According to the sedimentary, paleontology, geophysics and geochemical symbols, combined with rock assemblage, depositional fabric and profile sequence characteristics, the northern Upper Paleozoic Ordos Basin is divided into continental facies, paralic deposition and marine facies and recognized alluvial fan, rivers, lake delta, lakes, river control- tide dominated delta, a barrier coast and carbonate platform.(9) The system which makes long term cycles as the mapping unit compiled 20 pieces of the Upper Paleozoic- lithofacies palaeogeography maps. It reveals the differences of the northern basin’s development and distribution and the evolution process in the sedimentary systems. The development of Late Paleozoic basins in the north is characterized by carpet delta and depositional systems in different periods have some differences. The sediment in Late Paleozoic experienced marine facies, paralic facies and continental facies and established a corresponding sedimentary evolution mode. It provides geological basis for oil and gas exploration in the Upper Paleozoic.更多还原