Sandbox Modeling of the Fault-increment Pattern in Extensional Basins

Three series of sandbox modeling experiments were performed to study the fault-increment pattern in extensional basins. Experimental results showed that the tectonic action mode of boundaries and the shape of major boundary faults control the formation and evolution of faults in extensional basins. In the process of extensional deformation, the increase in the number and length of faults was episodic, and every ＇episode＇ experienced three periods, strain-accumulation period, quick fault-increment period and strain-adjustment period. The more complex the shape of the boundary fault, the higher the strain increment each ＇episode＇ experienced. Different extensional modes resulted in different fault-increment patterns. The horizontal detachment extensional mode has the ＇linear＇ style of fault-increment pattern, while the extensional mode controlled by a listric fault has the ＇stepwise＇ style of fault-increment pattern, and the extensional mode controlled by a ramp-flat boundary fault has the ＇stepwise-linear＇ style of fault-increment pattern. These fault-increment patterns given above could provide a theoretical method of fault interpretation and fracture prediction in extensional basins.

Evolution of the Extensional Rifted Yunnan-Guizhou-Guangxi Oceanic Basin During the Late Hercynian to Middle Indosinian Stage

On the basis of exhaustive researches on the facies sequences and depositlonal evolutionary process of various depositional systems, the genetic stratigraphic framework of the extensional rifted oceanic basin, which has undergone strong structural destruction, has been reconstructed by means of dynamic genetic stratigraphic analysis. Five depositional episodes have been distinguished from various isochronous stratigraphic boundaries and stratigraphic sequences with the three-dimensional structure of each depositional episode analysed in detail. The tectonic paleogeographic environment corresponding to different stages of each depositional episode has been reconstructed for individual depositional system tracts. And the evolution history of this rifted basin has been divided into four stages' initial rifting and oceanization of continental crust, stretching and spreading of the basin, subduction and basin differentiation, and convergence and collision. A NNE-trending intracontinental soft collision suture was left after the closing of the basin.

Inversion of two-phase extensional basin systems during subduction of the Paleo-Pacific Plate in the SW Korean Peninsula:Implication for the Mesozoic “Laramide-style” orogeny along East Asian continental margin

During subduction, continental margins experience shortening along with inversion of extensional sedimentary basins. Here we explore a tectonic scenario for the inversion of two-phase extensional basin systems, where the Early-Middle Jurassic intra-arc volcano-sedimentary Oseosan Volcanic Complex was developed on top of the Late Triassic-Early Jurassic post-collisional sequences, namely the Chungnam Basin. The basin shortening was accommodated mostly by contractional faults and related folds. In the basement, regional high-angle reverse faults as well as low-angle thrusts accommodate the overall shortening, and are compatible with those preserved in the cover. This suggests that their spatial and temporal development is strongly dependent on the initial basin geometry and inherited structures.Changes in transport direction observed along the basement-sedimentary cover interface is a characteristic structural feature, reflecting sequential kinematic evolution during basin inversion. Propagation of basement faults also enhanced shortening of the overlying sedimentary cover sequences. We constrain timing of the Late Jurassic-Early Cretaceous(ca. 158-110 Ma) inversion from altered K-feldspar 40 Ar/39 Ar ages in stacked thrust sheets and K-Ar illite ages of fault gouges, along with previously reported geochronological data from the area. This "non-magmatic phase" of the Daebo Orogeny is contemporaneous with the timing of magmatic quiescence across the Korean Peninsula. We propose the role of flat/low-angle subduction of the Paleo-Pacific Plate for the development of the "Laramide-style" basement-involved orogenic event along East Asian continental margin.

Mechanism of crustal extension in the Laxmi Basin,Arabian Sea

Continental rifting and magmatism has been extensively studied worldwide as it is believed that continental rifting, break up of continents and associated magmatism lead to genesis of new oceanic crust. However, various regions of the world show that these processes may lead to genesis of other types of crust than the oceanic crust. Laxmi Basin in the western continental margin of the India is one such region with an enigmatic crust.Due to its extreme strategic significance for the palaeogeographic reconstruction of continents during Cretaceous continental breakup of India, this basin has attracted various workers for more than two decades. However, still the issue of nature of crust in the basin remains controversial. In this contribution, in order to identify nature of crust, mechanism of continental extension in the Laxmi Basin has been studied for the first time through newly acquired seismic data from the basin. Here, we propose a plausible mechanism of crustal extension in the Laxmi Basin which eventually constrains the nature of crust of the Laxmi Basin. We have demonstrated that the crust in the Laxmi Basin can be categorised in two zones of stretched and transitional crust. In the stretched zone several fault bounded horst and graben structures are identified which preserve syn- and post-rift sediments along with different periods of hiatus in sedimentations as unconformities. These faults are identified as listric faults in the upper crust which sole out in the detachment faults.Detachment faults decouples the upper brittle and lower ductile crust. The transitional crust is identified as heavily intruded by sills and basaltic volcanic which were emplaced due to melting of subcontinental mantle（SCM） after hyper-stretching of crust and serpentinisation of the SCM. Panikkar Ridge is proposed to be one such basaltic volcanic body derived from melting of lower part of the SCM.

Extensional tectonics and sedimentary response of the Early—Middle Cambrian passive continental margin,Tarim Basin,Northwest China

The fact that several half-grabens and normal faults developed in the Lower--Middle Cambrian of Tazhong （central Tarim Basin） and Bachu areas in Tarim Basin, northwest China, indicates that Tarim Basin was under extensional tectonic setting at this time. The half-grabens occur within a linear zone and the normal faults are arranged in en echelon patterns with gradually increasing displacement eastward. Extensional tectonics resulted in the formation of a passive continental margin in the southwest and a cratonic margin depression in the east, and most importantly, influenced the development of a three- pronged rift in the northeast margin of the Tarim Basin. The fault system controlled the development of platform -- slope -- bathyal facies sedimentation of mainly limestone-dolomite-gypsum rock-saline rock-red beds in the half-grabens. The NW-SE trending half-grabens reflect the distribution of buried basement faults.

Brittle deformation in the Afikpo Basin (Southeast Nigeria): Evidence for a terminal Cretaceous extensional regime in the Lower Benue Trough, Nigeria

This paper deals with the regional and structural framework of the Cretaceous rocks in the Afikpo Basin located in the southeastern part of the Lower Benue Trough. Results from regional tectonics are presented together with those of the microtectonic analysis of microfaults in the Owutu-Afikpo-Adadama area in the basin. The Owutu-Afikpo-Adadama ridge at the north-central part of the basin marks the boundary between the Late Cenomanian-Turonian-Conianian sediments and the Campanian-Maastrichtian sandstones. This ridge trends N45oE on average and is faulted in three main directions, namely: (1) N-S normal faults; (2) NE-SW strike-slip faults; and (3) NW-SE strike-slip faults. The faulted rocks along these brittle discontinuities are mainly cataclastics with internal fracture cleavage and sigmoidal quartz mosaics that are reminiscent of extensional deformation. The cataclasites often bear slickenside striations. The NE-SW and NW-SE strike-slip faults are the results of the youngest brittle events on the Owutu-Afikpo-Adadama ridge. These faults were reactivated after deposition of the Campanian-Maastrichtain sediments (post-depositional faults) and, therefore, are post-Maastrichtain. Microfault analysis of these fault trends suggests an extensional regime that prevailed in the Lower Benue Trough. These results are of significance because this event is least poorly understood and less documented in contrast to the Cenomanian and Santonian events that affected the older Cretaceous strata in this region.

A Quantitative Analysis System for Continental Extensional Basin

Continental extensional basin is one of the most important oil and ga s bearing basin types in the world and is main basin type in east China. The qu antitative analysis for this kind of basins has important significance for oil a nd gas exploration and development in east China. Sedimentary basin is a geodyna mic system including sedimentary basin itself, the crust and the mantle under it . Basin evolution is affected by regional structure stress field geophysical sta tus in the deep of the earth and outer condition, such as climate changes, water supplying etc. Based on the concept of basin dynamic system, the authors develo ped a geological process modeling and analyzing system-Continental Extensional B asin Quantitative Analysis System (CEBQAS). The system consists of basin geodyna mic modeling, structural modeling, sedimentary modeling, geologic analysis, data base and display subsystem. The system can reappear structural and sedimentary e volution history to an extent and provide basin geodynamic information as well a s retrieving parameter for modeling from original data such as logging, core an d seismic data .

Extensional Tectonic System of Erlian Fault Basin Groupand Its Deep Background

The Erlian fault basin group, a typical Basin and Range type fault basin group, was formed during Late Jurassic to Early Cretaceous, in which there are rich coal, oil and gas resources. In the present paper the abundant geological and petroleum information accumulated in process of industry oil and gas exploration and development of the Erlian basin group is comprehensively analyzed, the structures related to formation of basin are systematically studied, and the complete extensional tectonic system of this basin under conditions of wide rift setting and low extensional ratio is revealed by contrasting study with Basin and Range Province of the western America. Based on the above studies and achievements of the former workers, the deep background of the basin development is treated.

The Earlier Spreading of South China Sea Basin due to the Late Mesozoic to Early Cenozoic Extension of South China Block: Structural Styles and Chronological Evidence from the Dulong-Song Chay Metamorphic Dome, Southwest China

To understand the forming and tectonic evolution of the South China Sea basin, new data of the structural styles and geochronology were obtained from the Dulong-Song Chay dome, southeastern Yunnan and northern Vietnam. The structural styles were acquired through field investigation and geo-chronological dating was carried out using zircon SHRIMP Ⅱ U-P and argon isotopic analyses. The South China Sea basin extension occurred firstly at Late Mesozoic to Early Cenozoic, and then at Late Oligocene to Middle Miocene （32-17 Ma）. The second stage of extension formed immediately after the first stage, and both extensions have a consistent forming mechanism. New structural analysis and geo-chronological data do not support the models of ＂backarc spreading＂ and ＂strike-slip faults producing the extension＂. Then what mechanism resulted in the extension of South China Sea basin？ The data indicate that at least two episodes of major extensional tectonics, i.e. , the D1 deformation at 237-228 Ma resulted in the rising and exhumation of the dome, and D2 deformation at 86-78 Ma overprinted and redeformed the dome. Of them, the D2 shows a consistent forming time, extensional direction and tectonic regime among Dulong-Song Chay dome, South China block and the northern margin of the South China Sea basin. Regional geology has proved that the northern margin of the South China Sea basin belongs to the South China block, therefore, we interpreted that the Late Mesozoic to Early Cenozoic extensional tectonics occurred in the northern margin of the South China Sea basin due to the intraplate deformation of the South China block, while the Ailaoshan-Red River sinistral slip strengthened the Cenozoic extension in the South China Sea basin.

Subsidence History of the Eastern Depression in the North Yellow Sea Basin

Using a back-stripping method, our paper simulated the subsidence history of the eastern depression in the North Yellow Sea Basin. The subsidence history curve pattern and the subsidence chorisogram during every subsiding period were exposed. Combining with the regional geologic background and the distribution features of the subsiding centers in every period, a contrasting study of the pattern and the classical subsidence history curves shows the subsi- dence history is made up of Mesozoic (J3-K1) and Cenozoic (E2-Q) subsiding cycles. The two subsiding cycles are separated by the late Cretaceous and Paleocene (K2-E1) uplift denudation. Both subsiding cycles have the characteristics of an extension basin. The rapid subsidence during the late Jurassic and Eocene is equivalent to the initial subsiding phases in both cycles.. The slow subsidence of both, the early Cretaceous and Neogene, can be regarded as thermal sub-sidence phases .

北康盆地基底构造特征及其对南海南部构造演化的启示

南海南部是研究东南亚地区构造演化的关键场所,以构造相对简单的北康盆地为基础探讨其构造演化过程。为了确定研究区的构造特征,进行了地震综合解释、主控断层的定性、定量分析和盆地之下的岩石圈伸展因子分析。通过构造分析,发现北康盆地15.5 Ma界面(MMU)之下发育了多条大规模、低角度的拆离断层,界面之下的原型盆地为裂陷盆地,并且局部可表现为拆离盆地,符合被动大陆边缘细颈化带内的构造特征。对北康盆地构造演化过程进行分析并将其与曾母盆地进行对比,发现2个盆地的构造演化特征迥然不同,据此重新将南海南部挤出-逃逸构造区和古南海俯冲-拖曳构造区之间的分界线确定为西巴拉姆线。结合南海南、北部的陆缘盆地基底卷入构造的发育特征发现,南海陆缘岩石圈在发生破裂后,应变的集中主要体现在靠近洋壳的细颈化带和远端带部位,远离洋壳地区的应变受海底扩张的影响较小,这一特征可能与被动陆缘岩石圈的近端和远端在拉伸过程中的解耦相关。

Tectonic and Geodynamic Setting of Oil and Gas Basins in China

About 26 sedimentary basins bearing oil and gas are developed in China. They can be classified into two main types . extensional basins and foreland basins . The former are chiefly distributed in the eastern part and the latter in the central and northwestern parts of the country . The present paper discusses the structural characteristics of these basins . including subsidence history , thermal history and structural style and kinematics . Combined with tectonic setting analysis of geophysical data and eruptive rocks , the geodynamic setting of the basins is established , and the formation mechanism of the basins is deduced to have been related to the subduction of the Izanagi and west Pacific plates and the closing of the Tethys ocean .

西秦岭北缘渐新世砾岩沉积特征及沉积环境——渐新世—中新世盆地构造环境约束

西秦岭北缘漳县—武山地区沿漳河两岸出露一套厚度近300 m的渐新统红色砾岩、砂砾岩夹粗砂岩组成的砾岩组合。这套砾岩角度不整合在古生代、中生代不同时代地层之上或以断层与前新生代地层相接触,其在孙家峡一带出露典型,层序完整,故称其为孙家峡砾岩。这套砾岩向上逐渐过渡为红色或灰色泥岩、粉砂质泥岩、钙质泥岩等湖相沉积,构成了一个下粗上细正旋回沉积组合。这套沉积组合是漳县渐新世—中新世含盐盆地最下部的一个沉积旋回,其沉积旋回、沉积环境及其沉积的构造背景研究对于漳县渐新世—中新世含盐盆地的构造属性确定和认识印度—欧亚板块碰撞汇聚动力学的远程地质响应等具有重要意义。通过对孙家峡砾岩的沉积旋回、沉积构造、砾石特征、古流向等详细研究,结合控制这套砾岩组合的边界断层多期变形资料和区域上同时代相应沉积地层的对比,取得了如下认识:(1)孙家峡砾岩沉积旋回、沉积构造和砾石分选、磨圆、排列等特征指示了其除底部为冲洪积扇和扇上河道沉积外,主体为山区辫状河道相、曲流河道相夹洪泛相沉积为主的河流加积沉积;砾石成分和古流向指示了F1断层之南的志留纪—三叠纪造山带地层虽对其物源有一定贡献,但其主要物源区更可能是来自西部祁连地块;(2)依据孙家峡砾岩及上覆湖相沉积共同构成的具有断陷盆地的正旋回沉积特征和控制盆地沉积的F1断层早期伸展正断层作用,证实这套砾岩组合为伸展断陷河谷盆地沉积,砾岩之上的湖相沉积是持续快速伸展断陷而形成的湖相沉积;(3)西秦岭北缘渐新世断陷盆地性质确认,澄清了地学界长期持有的压陷盆地或前陆挠曲盆地的模糊认识,也指示了西秦岭北缘渐新世—中新世盆地发育初期无疑是处于伸展拉张状态,这与印度—欧亚碰撞汇聚向北扩展的挤压缩短构造相悖。因此,推测渐新世印度—欧亚碰撞汇聚的动力学效应尚未波及到该区域。

珠江口盆地白云东区古近纪挤压-伸展变形模式及勘探意义

珠江口盆地白云东区是白云凹陷2个有利成藏区之一,目前勘探正面临转向古近系深层的阶段,急需重新认识深层洼陷结构构造。为了解决珠江口盆地白云东区古近系深层缓坡带砂岩变少,与伸展型半地堑储层发育模式矛盾的问题,利用改善深层成像的重处理三维深度域地震资料及钻井数据进行综合解释,开展了白云东区古近系及基底之下滑脱面全三维构造解析。研究结果表明:按动力学机制对盆地演化阶段进行了重新划分,构造层序由一个被动裂陷旋回,修改为被动裂陷-主动裂陷-被动裂陷3个旋回;构造幕由3分细化为6个幕次,即由断陷幕-断坳转换幕-坳陷幕细化为裂陷两幕-褶皱两幕-裂陷萎缩幕-漂移幕,细分方案更好地反映了地层变形规律。地层变形方式表现为基底呈东西向挤压构造,盖层为南北向伸展构造。伸展构造发育过程中,主动裂陷旋回参与的基底盖层脱耦变形的新模式协调了白云东区古近纪构造-沉积响应,补充了主动裂陷阶段盆地充填富泥旋回的认识,挤压-伸展同步变形模式丰富了南海盆地空间演化模式,支持了白云凹陷深层新领域的勘探。

珠江口盆地开平凹陷构造单元划分与平面复原

盆地构造单元划分与平面复原是构造地质研究的基础问题,也是盆地普查和区域详查阶段的主要任务,对揭示研究区构造演化过程及动力学机制、促进油气勘探具有重要意义。以开平凹陷最新2D/3D地震和钻井资料为基础,根据控凹断裂及地层尖灭线展布、断陷期各反射层T_(0)构造图和△T_(0)厚度图,重新厘定了开平凹陷构造单元分布,将其划分为西洼、北洼、西南洼、主洼、东洼和①号、②号、③号、④号、⑤号背斜带共10个三级构造单元。在此基础上,结合平衡剖面分析,将开平凹陷断陷期文昌组构造演化划分为断陷Ⅰ幕的下文昌组下段、中段和断陷Ⅱ幕的下文昌组上段,上文昌组下段、中段、上段共6个阶段。其中,断陷Ⅰ幕以“南断北超”为特征,断陷Ⅱ幕转变为“北断南超”,早期彼此孤立的洼陷开始逐渐扩张连片。边界断层周期性活动控制着地层发育和展布,凹陷构造活动具有向西南迁移的趋势,沉积中心由主洼逐渐向西南洼和西洼迁移。凹陷中部的主洼和北洼伸展率最大,西南洼、东洼次之,西洼最小。本研究的构造单元划分方案,可通过平面复原进行动态验证,合理性更强,为开平凹陷动力学演化研究、生烃中心和砂体展布刻画提供了新的科学依据。

江汉盆地西北部构造变形特征与油气勘探

针对江汉盆地西北侧宜昌斜坡页岩气的接替勘探领域尚不明确的问题,开展江汉盆地西北部页岩气成藏地质条件研究。对江汉盆地西北部最新的地震剖面进行了解释,分析了区域构造变形模式,探讨了晚侏罗世南、北向挤压和白垩纪伸展作用对盆地的改造过程。结果表明,在晚侏罗世挤压变形期,雪峰陆内变形系统前缘的构造变形以基底物质堆叠引起的地层倾伏为主要特征,秦岭-大别造山带前缘的变形叠加于雪峰陆内变形系统的变形之上,以形成上冲断裂和褶皱变形为主要特征;白垩纪江汉盆地西北部的伸展变形具有不连续性,在早白垩世晚期晚阶段、晚白垩世早期晚阶段、晚白垩世晚期晚阶段发生了伸展变形的停滞和构造反转。沿江汉盆地西北缘延伸至雪峰陆内变形系统前缘的广大区域,具有受构造变形影响小且连续分布的志留系泥页岩层,具有页岩气勘探的潜力。

乌石凹陷东洼伸展滑脱断裂演化特征及识别

滑脱断裂在断陷盆地中普遍发育,对油气成藏具有重要控制作用。通过对乌石凹陷海底电缆地震资料的精细解释,在乌石凹陷东洼首次识别出伸展滑脱断裂体系,流二段厚层泥岩、高角度斜坡和渐新世强烈拉张作用分别是其发育的重要物质条件、几何学条件和动力学条件。基于平衡剖面分析将其形成过程划分为3个阶段:高角度正断层形成阶段、高角度正断层向低角度正断层递变阶段、低角度正断层上覆地层滑动阶段。基于伸展滑脱断裂在地震剖面上的几何学和运动学特征,建立了伸展滑脱断裂断距不协调、非三角形减薄以及非沉积超覆等3种典型识别标志,并总结了伸展滑脱断裂旋转型、非旋转型、叠瓦状构造型、双重构造型等4种构造样式。该研究对乌石凹陷油气勘探具有重要理论和指导意义。

华北克拉通东部早白垩世伸展盆地的发育过程及其对克拉通破坏的指示

在晚侏罗世华北克拉通东部破坏之初出现了区域性隆起,全区缺失上侏罗统沉积。在早白垩世早期,出现了区域性的伸展活动,断陷盆地形成,克拉通南、北缘伸展活动最强,北部燕山构造带以出现变质核杂岩为特征,南部出现宽裂谷型盆地。早白垩世中期华北克拉通东部普遍出现了火山活动与岩浆侵入。早白垩世晚期克拉通上以出现窄裂谷型盆地为特征,沿北北东走向的郯庐断裂带断陷活动最强。这些断陷盆地的演化过程揭示,经历地表抬升后,克拉通破坏之初的岩石圈热而弱,从而形成变质核杂岩或宽裂谷型盆地。这期间的破坏强度在空间上具有不均匀分布的特征,受控于早期岩石圈地幔的结构。经过早白垩世中期的大量岩浆活动之后,早白垩世晚期克拉通岩石圈温度降低、强度变大,从而利用早期大型断裂构造形成窄裂谷型盆地。这些现象支持华北克拉通东部晚中生代的岩石圈减薄是以逐渐拆沉机制为主。

伸展构造盆地的平衡剖面及其构造意义——以松辽盆地南部为例

挤压构造的平衡地质剖面分析已经广泛应用于造山带构造分析 ,但伸展构造区的平衡地质剖面分析实例仍然很少 .运用盆地分析的技术与方法 ,分层序或阶段将地质构造依次恢复、地层逐层回剥 ,并通过在松辽盆地南部吉林两井油田扶余油层 4条剖面的实践 ,复原出不同时代盆地构造与地层发育的连续剖面 ,揭示出松辽盆地南部主要构造样式是以浅表构造层次的负花状构造及深层剥离断层发育为特征 ;断层生长指数、盆地的伸展史和伸展量等参数显示 ,晚白垩世是构造转型的重要阶段 ,此前主要为走滑构造样式形成阶段 ,此后则主要为伸展滑脱构造发育阶段 .在此基础上 ,提出松辽盆地具有伸展 -走滑双重力学构造性质 ,可能是一个弧后构造盆地 .

华北板块东部新生代断裂构造特征与盆地成因

华北板块东部新生代的构造特征及动力学演化主要受左行郯庐断裂带和右行兰考—聊城—台安—大洼—法哈牛断裂带的控制。这两条断裂都是新生代岩石圈断裂。在兰考—聊城—台安—大洼—法哈牛断裂带以西,新生代伸展盆地为NNE走向的铲形正断层控制的箕状断陷;两断裂之间为北断南超的NWW走向的断陷盆地;郯庐断裂以东的北黄海盆地为南断北超的NWW走向的断陷盆地。这些构造特征继承了该区中生代的构造格局,但其构造性质发生了根本变化,在这两条走滑方向相反的断裂带控制下,这两条断裂带内古近纪以张扭作用下的裂陷为主,随后以伸展断陷为主,第四纪沿两断裂带局部发生挤压,而鲁西地块和渤海湾盆地区仍然为伸展正断。渤海湾盆地及邻区这些新生代复杂的断块或断裂构造格局受控于应力—应变—基底格局3个基本要素。