Petroleum Exploration of Craton Basins in China

Craton basins are a significant petroliferous provenance. Having undergone multiple open- dose tectonic cycles and strong reworking of the late Cenozoic tectonic movement, the craton basins in China are highly broken. This has resulted in multi-source and multiphase hydrocarbon generation and later hydrocarbon accumulation so that a complicated spatial assemblage of primary, paraprimary and secondary oil-gas pools has been formed. The primary factors controlling hydrocarbon accumulation include hydrocarbon-generating depressions, paleouplifts, paleoslopes, unconformity surfaces, paleo-karst, faults and fissure systems as well as the later conservation conditions. In consequence, the strategy of exploration for China＇s craton basins is to identify the effective source rocks, pay attention to the different effects of paleohighs and late reworking, enhance studies of the secondary storage space, attach importance to the exploration of lithologic oil-gas reservoirs and natural gas pools, and approach consciously from the secondary oil pools to the targets near the source rocks. At the same time, a complete system of technologies and techniques must be built up.

Relationship Between Gas Carbon Isotope and Maturity in the Craton Basin, Tarim Basin

Carbon isotopes of natural gases are controlled not only by source and mature effect, but also by accumulating (leakage and mixing) effect. The gases, distributed in the three paleo\|uplifts, Tazhong, Tabei and Bachu in the Tarim Basin, are generated mainly from Cambrian and Lower Ordovician hydrocarbon\|source rocks. Being under good preservation conditions, gas pools in the Tazhong region experienced a long accumulation period, resulting in a successive gas accumulation region in this region. The gas carbon isotope values are more negative than those in other regions because of the strong accumulating effect. The Tabei and Mazhatage regions have poor preservation conditions, the gas pools are formed in a short accumulation period, and the gas carbon isotope values are more positive. This is called the transition\|stage gas accumulation region. Because of involvement of low mature gas, even biogenic gas from Upper\|Middle Ordovician, some gas in Ordovician reservoirs on the northern slope of the Tazhong uplift is characterized by much more negative \{δ\{\}\+\{13\}C\-1\}. The \{δ\{\}\+\{13\}C\-2\}\|\{δ\{\}\+\{13\}C\-1\} value is an effective index to measure the gas maturity of the main body in a gas pool. Combining \{δ\{\}\+\{13\}C\-2\}\|\{δ\{\}\+\{13\}C\-1\} with \{δ\{\}\+\{13\}C\-1\} and \{δ\{\}\+\{13\}C\-2\}, the effects described above can be explained very well. Results of our study show that the gas maturity for the Mazhatage region is the highest in the craton basin, followed by Tabei. Gases in the Tazhong area are high\|over mature gases though the gas carbon isotope values are highly negative.

Oil-gas microseapage and shallow hydrocarbon anomaly in craton basin

Although it has been accepted that oil and gas can migrate a long distance throughfaults, surface of unconformity and fractures in vertical and horizontal directions, it isuncertain whether deep oil-gas can reach the surface in stable craton basin in which faultsand fractures are poorly developed. The vertical changes of pyrolysis hydrocarbon,

Detrital zircon U-Pb geochronology of stromatolitic carbonates from the greenstone belts of Dharwar Craton and Cuddapah basin of Peninsular India

Oldest rocks are sparsely distributed within the Dharwar Craton and little is known about their involvement in the sedimentary sequences which are present in the Archean greenstone successions and the Proterozoic Cuddapah basin.Stromatolitic carbonates are well preserved in the Neoarchean greenstone belts of Dharwar Craton and Cuddapah Basin of Peninsular India displaying varied morphological and geochemical characteristics.In this study,we report results from U-Pb geochronology and trace element composition of the detrital zircons from stromatolitic carbonates present within the Dharwar Craton and Cuddapah basin to understand the provenance and time of accretion and deposition.The UPb ages of the detrital zircons from the Bhimasamudra and Marikanve stromatolites of the Chitradurga greenstone belt of Dharwar Craton display ages of 3426±26 Ma to 2650±38 Ma whereas the Sandur stromatolites gave an age of 3508±29 Ma to 2926±36 Ma suggesting Paleo-to Neoarchean provenance.The U-Pb detrital zircons of the Tadpatri stromatolites gave an age of 2761±31 Ma to1672±38 Ma suggesting Neoarchean to Mesoproterozoic provenance.The Rare Earth Element(REE)patterns of the studied detrital zircons from Archean Dharwar Craton and Proterozoic Cuddapah basin display depletion in light rare earth elements(LREE)and enrichment in heavy rare earth elements(HREE)with pronounced positive Ce and negative Eu anomalies,typical of magmatic zircons.The trace element composition and their relationship collectively indicate a mixed granitoid and mafic source for both the Dharwar and Cuddapah stromatolites.The 3508±29 Ma age of the detrital zircons support the existence of 3.5 Ga crust in the Western Dharwar Craton.The overall detrital zircon ages(3.5-2.7 Ga)obtained from the stromatolitic carbonates of Archean greenstone belts and Proterozoic Cuddapah basin(2.7-1.6 Ga)collectively reflect on^800-900 Ma duration for the Precambrian stromatolite deposition in the Dharwar Craton.

BGHMS: A Geohistory Modeling System for Cratonic Basins

The BGHMS system described in this paper was designed to model the geohistory for cratonic basins and written in turbo BASIC language with a user-friendly interface for data inputs and outputs on IBM PC-compatible computers. The major mathematical models in this system include the models of compaction correction. unconformity restoration. sea-level change and paleo-water-depth correction. and tectonic subsidence modeling. Two geological events of sediment compaction and erosion are considered in this system. It consists of three modules for data input, geohistory modeling and graph conversion and output. containing more than twenty subroutine programs, is an easy-to-use. menu-driven program system with many obvious advantages, and is a useful tool for hydrocarbon geologists to make quantitative studies on geohistory and to make exploration decisions in regional evaluation.

Meso-Cenozoic lithospheric thermal structure in the Bohai Bay Basin,eastern North China Craton

The Bohai Bay Basin is a region where part of the North China Craton has been thinned and destroyed. It has experienced two periods of crustal thinning that occurred during the Cretaceous and Paleogene, but investigations of its Mesozoic and Cenozoic lithospheric thermal structure are limited. Therefore, in this study,the distributions of mantle heat flow, crustal heat flow, and Moho temperatures during the Meso-Cenozoic are calculated based on analyses of the thermal history of the Bohai Bay Basin. The results indicate that the ratio of mantle heat flow to surface heat flow peaked during the late stages of the early Cretaceous and during the middle to late Paleogene. The corresponding mantle heat flow was more than 65% of the surface heat flow. Moho temperatures reached three peaks: 900-1100℃ in the late stages of the early Cretaceous;820-900℃ in the middle to late Paleogene; and(in the Linqing Depression, Cangxian Uplift, and Jizhong Depression) 770-810℃ during the early Neogene. These results reveal that the Bohai Bay Basin experienced significant geological change during the Cretaceous, including the transformation of lithospheric thermal structure from "cold mantle and hot crust" before the Cretaceous to "hot mantle and cold crust" after the Cretaceous. The results also indicate that the basin experienced two large-scale rifting events.Therefore, this work may provide the thermal parameters for further investigations of the geodynamic evolution of eastern China.

Characteristics of the crystalline basement beneath the Ordos Basin:Constraint from aeromagnetic data

Aeromagnetic anomaly zonation of the Ordos Basin and adjacent areas was obtained by processing high-precision and large-scale aeromagnetic anomalies with an approach of reduction to the pole upward continuation. Comparative study on aeromagnetic and seismic tomography suggests that aeromagnetic anomalies in this area are influenced by both the magnetic property of the rock and the burial depth of the Precambrian crystalline basement. Basement depth might be the fundamental control factor for aeromagnetic anomalies because the positive and negative anomalies on the reduction to the pole- upward-continuation anomaly maps roughly coincide with the uplifts and depressions of the crystalline basement in the basin. The results, together with the latest understanding of basement faults, SHRIMP U-Pb zircon dating of metamorphic rock and granite, drilling data, detrital zircon ages, and gravity data interpretation, suggest that the Ordos block is not an entirety of Archean.

Investigation of plateau basin crustal structures and thickening mechanisms in the northeastern margin of the Tibetan plateau

This paper uses deep seismic sounding （DSS） data to contrast and analyze the crustal structures of three plateau basins （Songpan-Garze, Qaidam, Longzhong） in the northeastern margin of the Qinghai-Xizang （Tibetan） plateau, as well as two stable cratonic basins （Ordos, Sichuan） in its peripheral areas. Plateau basin crustal structures, lithological variations and crustal thickening mechanisms were investigated. The results show that, compared to the peripheral stable cratonic basins, the crystalline crusts of plateau basins in the northeastern margin are up to 10 15 km thicker, and the relative medium velocity difference is about 5% less. The medium velocity change in crustal layers of plateau basin indicates that the upper crust undergoes brittle deformation, whereas the lower crust deforms plastically with low velocity. The middle crust shows a brittle-to-plastic transition zone in this region. Thickening in the lower crust （about 5 10 km）, and rheological characteristics that show low- medium velocity （relatively reduced by 7%）, suggest that crustal thickening mainly takes place in lower crust in the northeastern margin of the Tibetan plateau. The crust along the northeastern margin shows evidence of wholesale block movement, and crustal shortening and thickening seem to be the main deformation features of this region. The GPS data show that the block motion modes and crustal thickening in the Tibetan plateau is closely related to the peripheral tectonic stress field and motion direction of the Indian plate. The Mani-Yushu- Xianshuihe fold belt along the boundary between the Qiangtang block and the Bayan Har block divides the different plateau thickening tectonic environments into the middle-western plateau, the northeastern margin and the southeastern plateau.

Decoding Provenance and Tectonothermal Events by Detrital Zircon Fission-Track and U-Pb Double Dating: A Case of the Southern Ordos Basin

Multi-dating on the same detrital grains allows for determining multiple different geo-thermochronological ages simultaneously and thus could provide more details about regional tectonics.In this paper,we carried out detrital zircon fission-track and U-Pb double dating on the Permian-Middle Triassic sediments from the southern Ordos Basin to decipher the tectonic information archived in the sediments of intracratonic basins.The detrital zircon U-Pb ages and fission-track ages,together with lag time analyses,indicate that the Permian-Middle Triassic sediments in the southern Ordos Basin are characterized by multiple provenances.The crystalline basement of the North China Craton(NCC)and recycled materials from pre-Permian sediments that were ultimately sourced from the basement of the NCC are the primary provenance,while the Permian magmatites in the northern margin of NCC and Early Paleozoic crystalline rocks in Qinling Orogenic Collage act as minor provenance.In addition,the detrital zircon fission-track age peaks reveal four major tectonothermal events,including the Late Triassic-Early Jurassic post-depositional tectonothermal event and three other tectonothermal events associated with source terrains.The Late Triassic-Early Jurassic(225–179 Ma)tectonothermal event was closely related to the upwelling of deep material and energy beneath the southwestern Ordos Basin due to the coeval northward subduction of the Yangze Block and the following collision of the Yangze Block and the NCC.The Mid-Late Permian(275–263 Ma)tectonothermal event was associated with coeval denudation in the northern part of the NCC and North Qinling terrane,resulting from the subduction of the Paleo-Asian Ocean and Tethys Ocean toward the NCC.The Late Devonian-early Late Carboniferous(348±33 Ma)tectonothermal event corresponded the long-term denudation in the hinterland and periphery of the NCC because of the arc-continent collisions in the northern and southern margins of the NCC.The Late Neoproterozoic(813–565 Ma)tectonothermal event was associated with formation of the Great Unconformity within the NCC and may be causally related to the Rodinia supercontinent breakup driven by a large-scale mantle upwelling.

鄂尔多斯盆地东南部黄龙背斜的构造几何学与运动学

研究克拉通内构造变形对于揭示克拉通的构造属性具有重要意义,对于油气勘探也具有重要的参考价值。本文应用钻井与高精度反射地震资料,剖析了鄂尔多斯盆地东南部黄龙背斜的构造几何学与运动学特征。研究表明,黄龙背斜发育在渭北隆起东端,是一长18 km、宽15 km的短轴状背斜,地层起伏幅度达200 ms;黄龙背斜自长城系往上至三叠系均具有相似的背斜形态;它是在燕山期基底断层复活而形成的断层传播褶皱背斜;黄龙背斜区内东西向与南北向剖面控制的缩短分别为70 m和90 m,缩短量较小,指示该部位处于燕山期冲断变形的前锋部位,变形即将终止。黄龙背斜响应于周缘构造边界挤压作用,是克拉通内部的基底正断层反转而在沉积盖层形成的褶皱背斜,因地层能干性差异发生了分层剪切。黄龙背斜是一个有利的天然气勘探目标。

塔里木盆地超深层走滑断控油气藏研究进展与趋势

在塔里木盆地开辟了超深层走滑断控油气藏勘探开发领域,但断控油气藏极为复杂,难以效益开发,亟需加强油气藏基础地质研究。走滑断控油气藏具有非均质性强、储集层与流体分布复杂、油气产量变化大及采收率低的共性,不同地区走滑断控油气藏的断裂、储集层、成藏与流体存在较大的差异,面临一系列勘探开发难题。建立了差异成因的走滑断裂破碎带及其控储模型,揭示了沿走滑断裂带“相-断-溶”三元复合控储、连片差异规模发育的成储机制;构建了“源-断-储-盖”四元耦合成藏、“小藏大田”的走滑断控油藏模型,揭示了超深层走滑断控油藏的形成与保存机理。突破了克拉通盆地弱走滑断裂难以形成走滑断控大规模储集层与大油气田的理论认识局限,明确了克拉通盆地走滑断裂系统大规模发育的成因机制、走滑断裂破碎带差异成储成藏机理与油气富集规律。

鄂尔多斯盆地东部上石炭统铝土岩系储集层特征及形成模式

基于岩心观察、岩石薄片、X射线衍射、扫描电镜、低温气体吸附和等温吸附等实验,分析鄂尔多斯盆地东部上石炭统铝土岩系岩性和孔隙特征,以揭示铝土岩系储集层形成演化过程。研究表明:(1)提出以铝的氢氧化物、铁矿物和黏土矿物三单元的铝土岩系岩石学命名分类方案;(2)铝质泥岩产状主要为致密块状和碎屑状,(泥质)铝土岩多呈致密块状、豆状、鲕状、多孔土状和碎屑状,溶蚀孔、晶间孔和微裂缝是主要储气空间,孔隙度一般小于10%,以介孔为主;(3)华北地区铝土岩系纵向上总体上可分为5段,即铁岩(山西式铁矿,A段)、铝质泥岩(B段)、铝土岩(C段)、铝质泥岩(含碎屑)(D段)和暗色泥岩-煤岩段(E段);(4)在岩溶平台、缓坡和洼地分别发育潜穴/漏斗状、透镜状、层状/块状铝土岩沉积,岩溶平台及缓坡处有利于地表水淋滤,岩溶改造作用强,孔隙发育,储集层厚度大且物性好,但连贯性差,低洼处物性较差但储集层相对连续稳定。铝土岩天然气富集受源岩-储集层-裂缝综合控制,相关认识可为该层段和类似铝土岩系天然气勘探开发提供地质依据。

鄂尔多斯盆地及周缘岩相古地理与沉积演化

鄂尔多斯盆地的沉积演化起始于中元古代,发育陆缘裂谷和陆内拗拉槽,沉积滨海相碎屑岩和潮坪相碳酸盐岩,新元古代盆地性质为大陆边缘地堑型坳陷,沉积滞留海盆碎屑岩、冰水沉积物组合及陆棚碎屑岩;早古生代寒武纪和奥陶纪的克拉通盆地主要沉积浅海碳酸盐岩,在西南缘发育沟-弧-盆体系;经过加里东运动抬升剥蚀后,开始了华北克拉通坳陷盆地的沉积演化过程,晚石炭世和早二叠世发育了陆表海沉积,早二叠世晚期—中三叠世形成了近岸碎屑湖盆沉积;中晚三叠世延长期至早白垩世,鄂尔多斯盆地最终形成,进入大型内陆差异沉积盆地的形成和发展时期,上三叠统、侏罗系和下白垩统是在鄂尔多斯盆地缓慢沉降过程中堆积的以河流-三角洲-湖泊相为特征的陆源碎屑岩系;新生代进入周边断陷发育阶段,先后发育河流-湖泊及风成沉积。这一系列沉积演化过程揭示了鄂尔多斯盆地复杂的地质历史和多样的沉积环境。

辽西金羊盆地髫髻山组火山岩锆石U-Pb年龄、Hf同位素组成及岩石地球化学特征

[研究目的]辽西地区侏罗系髫髻山组火山岩不仅代表了燕山期大规模火山喷发的开始,也与华北克拉通破坏减薄的时限、范围及机制研究密切相关。近年来,针对髫髻山组火山岩的成因研究取得了很多新认识,但其构造背景、岩浆源区尚存在争议。[研究方法]本文选取羊D1井连续钻井岩心样品为研究对象,开展锆石U-Pb测年、Hf同位素组成及岩石地球化学特征分析。[研究结果]锆石U-Pb测年结果表明,髫髻山组下部粗面岩锆石U-Pb年龄为162.8±1.7 Ma,结合羊D1井土城子组底部凝灰岩153.8±1.7 Ma的U-Pb年龄,认为髫髻山组火山岩形成于晚侏罗世。另外,髫髻山组下部粗面岩Eu负异常不明显,具有轻稀土富集、重稀土亏损以及低Sr、Yb型岩浆岩等特征,表明髫髻山组粗面岩是由壳源岩浆在较高的压力下,经历部分熔融作用产生,并伴随有不显著的结晶分异作用;其锆石的εHf(t)值为-22.1~-15.4,二阶段模式年龄(TDMC)为2.182~2.604 Ga,表明髫髻山组火山岩的岩浆源区主要来源于晚太古代,揭示其是在太平洋板块向欧亚大陆俯冲背景下,由晚太古代下地壳基性岩石的部分熔融所形成,为后期岩石圈地幔拆离即华北克拉通减薄准备了条件。[结论]该研究成果,明确了髫髻山组火山岩的形成时代及岩浆源区,对探讨燕山造山带中生代岩浆演化和区域构造演化研究提供了科学依据。

鄂尔多斯盆地及邻区中—晚二叠世构造-沉积环境与原型盆地演化

根据钻井、测井、野外露头及地球化学资料,参考盆地周缘构造环境、盆地构造沉降特征及沉积相展布,恢复了鄂尔多斯盆地中—晚二叠世不同时期构造-沉积环境,探讨了盆地性质及演化过程。研究结果表明:①中—晚二叠世鄂尔多斯盆地南缘和北缘经历了洋盆俯冲消减过程,以强烈的挤压构造环境为特征,上二叠统石千峰组沉积期盆地北缘古亚洲洋闭合进入陆陆碰撞阶段,盆地内构造沉降速度缓慢。②中—晚二叠世鄂尔多斯盆地为大型的克拉通内坳陷盆地,中二叠统石盒子组沉积期基准面呈下降趋势,盆地主体延续山西组沉积期南北高、中部低的古地理格局,南华北地区地势相对更低;周缘隆起区快速抬升且范围逐渐扩大,为坳陷盆地内提供物源,盆地内发育冲积扇、冲积平原、三角洲和浅湖相,向南发育残存潮坪—潟湖,呈南北向展布;晚二叠世基准面趋于稳定,湖相范围扩大,主要发育于盆地南部,潮坪—潟湖环境向南缩小。③研究区油气成藏受控于沉积环境,中二叠世发育的陆相三角洲沉积体系有利于形成储集层和盖层,且和下部煤系地层组成中二叠统良好的生-储-盖组合;上二叠统为氧化干旱的古气候,沉积水体较浅,形成的泥岩厚度小,生烃潜力有限,无法形成大规模气藏。

鄂尔多斯盆地东缘晋西挠褶带中段构造特征及演化

现今晋西挠褶带作为鄂尔多斯盆地的残余东部边界存在,近年来在上古生界石炭系—二叠系中发现有煤层气、致密气等丰富的油气资源,是一个重要的勘探领域。本文基于野外露头、钻井、地震资料等,明确其地层发育分布特征,结合浅表露头构建区域地质剖面,并利用2D-move软件对其进行反演分析与正演模拟,同时对其构造变形进行定量分析,研究表明:1)鄂尔多斯东缘晋西挠褶带中段主要在燕山期受东西向的挤压应力以及深部构造楔活动影响发生陆内构造变形,并遭受强烈的差异风化剥蚀作用,形成现今构造格局。2)研究区剖面现今长度约为114.96 km,以寒武系为标志层,燕山期地层缩短约4.06 km,地层抬升约6.12 km,地层缩短率为3.41%。3)晋西挠褶带中段形成原因为受到多方向的挤压构造应力作用,主要动力来源为古太平洋板块的西向低角度俯冲挤压。晋西挠褶带中段是重要构造单元,具深刻的动力来源。本文可为之后鄂尔多斯盆地东缘的陆内构造变形、演化特征研究以及油气勘探方向提供参考依据。

克拉通内盆地走滑断层地震判识的若干陷阱

克拉通盆地内走滑断层位移量小、变形微弱且构造复杂,深层地震低分辨率识别走滑断层困难且受诸多假象影响。通过剖析塔里木和四川盆地克拉通内走滑断层的典型地震现象,结合地质因素综合分析辨别走滑断层是否发育,总结了典型的地震假象并建立三大类陷阱模式,主要包括:①基底陡崖、阶梯状断裂与断垒结构可能误判为“花状构造”,基底盖层垂向发育的相似褶皱也可能成为走滑构造假象;②喷发岩、蒸发岩厚度、岩性的横向变化,可能造成地震层速度横向突变,导致下伏岩体在地震剖面上产生似走滑断层的高陡假象;③垂向规模发育的沟谷地形、岩溶地貌、岩相相变等地质现象可能出现似走滑断层的地震响应。为避免这些地震解释陷阱,在提高走滑断层地震分辨率的基础上,排除蒸发岩和火成岩的速度影响,剔除地形地貌与岩相变化的影响,并基于以地震平面属性为主的典型走滑构造识别,排除地震走滑断层的假象,建立合理的走滑断层地震地质解释模式。

华北早白垩世古地貌动态演变及热河生物群东迁

早白垩世期间,华北地区东北部分布着极其重要的生物群——热河生物群,其繁盛期对应着华北克拉通破坏峰值时期(125 Ma)。华北克拉通破坏导致的古地貌和古气候等环境变化,可能是引起热河生物群分布时空发生变迁的重要外部驱动因素之一。然而,目前缺少对华北地区早白垩世古地貌动态演变过程的定量描述。因此,本研究主要通过构建古土壤风化指标(PWI、CFX_(Na))、碳酸盐同位素等数据库,重建了华北地区晚侏罗世—早白垩世之交(145 Ma)的古地形;并结合磷灰石/锆石裂变径迹、剥蚀厚度恢复、海平面变化等数据,利用Badlands软件定量化动态模拟了华北地区早白垩世古地貌演变过程。模拟结果表明,早白垩世期间,受控于古太平洋板块俯冲后撤的影响,华北克拉通经历了由“东高西低”变为“西高东低”的地形翘变和破坏过程,并伴随着自西向东的断陷盆地的迁移;大规模火山喷发与断陷盆地的出现共同控制了热河生物群的向东迁移,热河生物群在燕山地区的山间盆地兴起。

华北克拉通中部造山带中条山地区古元古代盆地演化

对华北克拉通中部造山带南部中条山地区古元古代中条群和担山石群岩石组合及地层详细调查研究,认为中条群为一套由粗碎屑岩-泥质岩-碳酸盐岩组成的多旋回沉积岩,变质砂岩地球化学特征显示,中条群经历了早期相对稳定到后期较活跃的转变。结合前人碎屑锆石年龄、源区特征和火山岩夹层年龄得出,中条群形成于2.1 Ga左右的活动大陆边缘弧后盆地。担山石群为一套砾岩-砂岩组成的磨拉石建造,碎屑锆石年龄显示,担山石群形成于1.85 Ga左右的碰撞造山阶段的前陆盆地内。结合前人研究,认为中条山地区古元古代盆地演化模式为,约2.1 Ga开始,西部陆块的前导洋向东部陆块活动大陆边缘之下持续俯冲,东部陆块西缘活动大陆边缘弧后盆地沉积了中条群,约1.85 Ga开始,东部陆块与西部陆块之间的大洋闭合,陆陆碰撞开始,中条群发生挤压褶皱变形,陆壳加厚及随后的快速抬升和剥蚀形成前陆盆地的担山石群磨拉石。中条山地区古元古代弧后盆地向前陆盆地的转化支持华北克拉通最初西部陆块向东俯冲,经历了约1.85 Ga的东、西陆块碰撞并最终克拉通化的演化模式。

鄂尔多斯盆地北部断裂分析

长期以来 ,多数研究者认为鄂尔多斯盆地为稳定的克拉通盆地 ,盆地内部不发育断裂。但近年在新采集、处理的地震剖面上陆续发现了盆地北部存在着断距约 40～ 2 40m的断层 ,总体上看 ,从天环向斜北部到苏里格庙、乌审召、东胜一带为北东向断裂多发带。这些断层以断开奥陶系风化壳、太原组和山西组煤层等地震反射层波组为主 ,通常组成单向逆冲断层、对冲断凹型、背冲断垒型和先逆后正反转型等几种断层类型。这些断层是鄂尔多斯盆地在燕山运动中、晚期受到周边构造单元强烈挤压所形成的 ,也是由克拉通盆地向前陆盆地转化的伴生产物。图 1参