Tectono-thermal Evolution in the Bachu Uplift,Tarim Basin,China

The thermal evolution of source rocks in the Paleozoic has long been a problem to petroleum exploration in the Bachu uplift, Tarim basin, since the thermal history in the Paleozoic could not be rebuilt objectively due to lack of effective thermal indicators in the Lower Paleozoic successions. The apatite and zircon （U-Th）/He thermochronometry can be used as a new kind of technique to study the thermal history and tectonic uplift of sedimentary basins. Based on the measured apatite and zircon （U-Th）/He ages, apatite fission track data and equivalence vitrinite reflectance （%EVRo）, the tectonothermal histories in 5 wells of the Bachu uplift were modeled. The modeling results show that there was relatively high gradient at the Early Paleozoic in the Bachu uplift and it decreased gradually during the entire Paleozoic： 33-35℃/km in the Cambrian- Ordovician, 32-33℃/km in the Silurian-Devonian, 30-32℃/km at the end of Carboniferous and 27.5- 31℃/km at the end of Permian. Therefore, the thermal history can be modeled by combining multiple thermal indicators of AFT, （U-Th）/He ages and EVRo data. Especially, this provides a new method to rebuild the thermal history for the Low Paleozoic carbonate successions in the Tarim Basin.

Dual influence of the rejuvenation of Southern Tianshan and Western Kunlun orogen on the Cenozoic structure deformation of Tarim Basin,northwestern China:A superposition deformation model from Bachu Uplift

Based on new high-resolution seismic profiles and existing structural and sedimentary results,a superposition de-formation model for Cenozoic Bachu Uplift of northwestern Tarim Basin,northwestern China is proposed. The model presents the idea that the Bachu Uplift suffered structure superposition deformation under the dual influences of the Cenozoic uplifting of Southern Tianshan and Western Kunlun orogen,northwestern China. In the end of the Eocene (early Himalayan movement),Bachu Uplift started to be formed with the uplifting of Western Kunlun,and extended NNW into the interior of Kalpin Uplift. In the end of the Miocene (middle Himalayan movement),Bachu Uplift suffered not only the NNW structure deformation caused by the Western Kunlun uplifting,but also the NE structure deformation caused by the Southern Tianshan uplifting,and the thrust front fault of Kalpin thrust system related to the Southern Tianshan orogen intrudes southeastward into the hinterland of Bachu Uplift and extends NNE from well Pi1 to Xiaohaizi reservoir and Gudongshan mountain,which resulted in the strata folded and denuded strongly. In the end of the Pliocene (late Himalayan movement),the impact of Southern Tianshan orogen decreased because of the stress released with the breakthrough upward of Kalpin fault extending NE,and Bachu Uplift suffered mainly the structure deformation extending NW-NNW caused by the uplifting of Western Kunlun orogen.

Strike-Slip Faults and Their Control on Differential Hydrocarbon Enrichment in Carbonate Karst Reservoirs: A Case Study of Yingshan Formation on Northern Slope of Tazhong Uplift, Tarim Basin

Objective Oil and gas are abundant in the Ordovician Yingshan Formation carbonate karst reservoirs on the northern slope of Tazhong uplift in the Tarim Basin, and have extremely complicated oil-gas-water distribution, however. The difference in burial depth of the reservoirs between east and west sides is up to 1000 m. Water-bearing formations exist between oil- and gas-bearing formations vertically and water-producing wells are drilled between oil- and gas-producing wells. Macroscopically, oil and gas occur at low positions, while water occurs at high positiona on the northern slope of Tazhong uplift. The mechanism of differential hydrocarbon enrichment in heterogeneous reservoirs is by far not clarified, which has affected the efficient exploration and development of oil and gas fields in this area.

THREE-DIMENSIONAL DEFORMATION ALONG THE ALTYN TAGH FAULT ZONE AND UPLIFT OF THE ALTYN MOUNTAIN, NORTHERN TIBET

he convergence between India and Eurasia is partly accommodated by motion of a few large blocks along strike\|slip faults. About 1800km long Altyn Tagh fault strikes in N60～80°E and allows the northeastward displacement of the Tibet plateau relative to the Tarim. The Altyn Tagh fault zone is a typical transpressional fault zone, characterized by blocks rotation and crustal shortening and vertical extrusion of blocks within the Altyn Tagh strike\|slip system. Differences of three\|dimensional deformation and configuration of the active structures are recognized at different segment of the Altyn Tagh fault zone.1\ Structural configuration of the Altyn Tagh fault zone\;In the Altyn Tagh strike\|slip fault zone, the assemblage pattern of the (active) faults is in the form of parallel plumes, especially in the eastern and the western segments of the Altyn Tagh fault zone. These plumes structures in the eastern segment are assembled by string\|like left lateral strike\|slip fault and broom\|like thrusting faults, and in the western segment by arc\|like left lateral strike\|slip faults along with thrusting faults and normal faults. In the middle segment of the Altyn Tagh fault zone, the structures are characterized by the string\|like left lateral strike\|slip faults in the center and reverse thrusting faults on the two sides.

Structural patterns of fault damage zones in carbonate rocks and their influences on petroleum accumulation in Tazhong Paleo-uplift, Tarim Basin, NW China

Based on the outcrop survey,3D seismic data interpretation,drilling data analysis,the structural patterns and distribution of fault damage zones in carbonate strata of Tazhong Paleo-uplift were established to reveal the oil and gas enrichment law in the fault damage zones.The following findings were reached:(1)Through the filed survey,the fault damage zone system consists of fault core,damage zone with branch fault and fracture network.Affected by the active nature of the major faults,the fault damage zones differ in planar pattern and scale along the major faults.(2)3D seismic profiles reveal that there are three types of fault damage zones in carbonate strata in Tazhong paleo-uplift,strike-slip fault damage zones,thrust fault damage zones and superimposed fault damage zones.Featuring3 flowers and 3 root belts in vertical,the strike-slip fault damage zone can be subdivided into linear type,oblique type,feather type and horsetail type in plane.Thrust fault damage zones can be further divided into fault anticline type,anticline type and slope type.As the superimposition result of the above two kinds of fault damage zones,superimposed fault damage zones appear in three patterns,intersect type,encompassment type and penetrating type.(3)Cores from wells and geochemical data show oil and gas may migrate along the major fault and laterally.The feather type in strike-slip fault system,fault anticline type in thrust fault damage zone and intersect type in superimposed fault damage zone are possible sites for high production and efficiency wells.

Characteristics of Fault Activity in the Taiyangshan Uplift Area in Hunan,China

Lying on the west edge of Dongting Lake,the Taiyangshan area in Hunan Province is part of a hilly region which has uplifted since the Late Cenozoic.According to field investigation of the six existing faults in the Taiyangshan area,we found that four of them are not active in the Quaternary,and that the Gangshi-Hefu fault is likely to have been active in the early Mid-Pleistocene.The geological evidence derived suggests that the Xiaowupu fault was active from the late Mid-Pleistocene to the early late-Pleistocene.It cut the stratum with a TL age of 123±10ka BP and has the property of thrusting.The research results are of great significance for understanding the seismogenic structure of the Changde earthquake with M6 3/4 in 1631.

Terraces and Tectonic Uplifts at Yandantu and Changcaogou on the Northern Margin Fault of Altun

The formation of strath and strath terrace is closely related to tectonic uplift in the drainage basin. Based on the investigation of straths at Yandantu and Changcaogou on the eastern segment of the northern margin fault of Altun, and in combination with the paleoclimatic data, the tectonic uplift since late Epipleistocene as revealed by stream terraces at the two places is discussed. At Yandantu, three levels of stream terraces(T 1, T 2 and T 3)have developed since 16ka BP, where T 1, T 3 and T 2 are fill terraces and the buried major straths are exposed. The ages of three treads are dated to be about 16.1ka BP, 12.8ka BP and 6.2ka BP, respectively. The three terraces reflect three tectonic uplift events, while the ages of the treads represent the occurrence time of these events. The stream is still beveling the bedrock and widening the channel at present, and the modern strath is being generated. The uplift rate is 4.8～4.5mm/a since 16.1 ka BP in this area. From 12.8ka B.P to 6.2ka BP, The uplift rate was 6.4mm/a. The uplift rate is 3.1mm/a since 6.2ka BP. At Changcaogou, four levels of stream terraces(T 1, T 2, T 3 and T 1′)have developed since 7ka BP. All of them are fill terraces. There are buried straths under the deposits. The buried major strath is exposed on T 3 and T 2 and the minor strath on T 1′and T 1. The ages of treads of the three terraces (T 3, T 2 and T 1′) are 7 ka BP, 3 ka BP and 2.5 ka BP, respectively. The four terraces reflect two uplift events induced by tectonic activities. One occurred in about 7 ka BP, and the other in 3ka BP. The uplift rate is 5.9mm/a since 7.0 ka BP at Changcaogou. From 7ka BP to 3ka BP, the uplift rate was 7.0mm/a, and since 3ka BP till now, the uplift rate is 4.7 mm/a.

忻定盆地金山凸起东缘断裂展布及晚第四纪最新活动特征

通过野外地质地貌调查结合无人机航拍测量、地质雷达勘探及浅层地震勘探综合分析认为,金山凸起东缘断裂整体呈NE向展布,走向40°,北起忻口村一带,向SW经金山铺村西、前淤泥村西延伸至部落村以北,进而向SWS转折进入盆地区。经探槽开挖和年龄测试,该断裂段最新断错晚更新世早期地层。

塔里木盆地塔中隆起中北部地区断裂构造特征及演化

为系统揭示塔里木盆地塔中隆起中北部地区断裂构造特征及其成因演化,通过对该区大连片三维地震工区精细构造解析和相干体等分析,并结合区域动力背景,系统论述了该区的断裂构造类型、几何学特征、差异活动机制及其构造演化过程。研究结果表明,塔中隆起中北部发育了4类7期断裂构造,其中逆冲断裂和走滑断裂尤其发育。平面上北西向弧形逆冲断裂与北东向、北西向及南北向走滑断裂相互交切与耦合;垂向上断裂分层差异活动特征明显,下奥陶统及其以下地层,断裂发育数量多且以线形为主,中奥陶统-中下泥盆统多呈雁列式,上泥盆统-二叠系仅在塔中Ⅱ号断裂带、顺北5号断裂带西南端等地区发育少量断裂。研究区断裂活动受多期、多方向不同性质应力场所控制,经历了极其复杂的演化历史:加里东早期以塔中Ⅱ号断裂带等少量北倾正断层活动为主;加里东中期Ⅰ幕断裂活动强烈,表现为逆冲断裂与走滑断裂协同演化和相互耦合特征,走滑断裂对逆冲断裂的切割或限制作用明显;加里东中期Ⅲ幕断裂活动基本继承了加里东中期Ⅰ幕的构造格局,但在工区北部的顺北4号、5号等断裂带张扭性断裂活动特征显著;加里东晚期-海西早期,部分断裂发生继承性活动且张扭断裂发育范围进一步向南扩大;印支-燕山期,仅有少数断裂发生继承性活动;喜山期该区构造比较稳定,早期形成的复杂断裂构造进入深埋阶段。

桑托斯盆地盐下孤立碳酸盐台地沉积建造与深水大油田

针对桑托斯被动陆缘盆地深水盐下碳酸盐岩储层分布特征及大油田成藏规律不清的难题,综合利用地质、地震及岩心等数据资料,通过早白垩世原型盆地与岩相古地理恢复重建,提出盐下碳酸盐岩沉积建造受控于坳间断隆型和坳中断凸型两类孤立台地。坳间断隆型孤立台地分布于现今盐下坳间隆起带上,建造于早期陆内和陆间裂谷两个原型阶段继承性发育的单断式和双断式垒式断块上,早白垩世陆内裂谷晚期沉积的ITP组介壳灰岩和陆间裂谷早期沉积的BVE组微生物灰岩为连续建造;坳中断凸型孤立台地分布于现今盐下坳陷带中,建造于早期陆内裂谷原型阶段火山岩建隆所形成的凸起带上,发育BVE组微生物灰岩。两类孤立台地灰岩所形成礁滩体均具有储层厚度大、物性好的特点。结合盐下已发现大油田解剖,发现两类台地均可形成大型构造-岩性复合圈闭,周缘为优质湖相和潟湖相烃源岩环绕,上覆为巨厚的优质蒸发盐岩盖层高效封堵,形成了“下生中储上盖”式最佳生储盖组合关系,油气富集程度高。已发现大油田均为具有统一压力系统的底水块状油田,且均处于充满状态。未来勘探重点目标是西部隆起带和东部隆起带南段上的坳间断隆型孤立台地及中央坳陷带中的坳中断凸型孤立台地。该项研究成果为在桑托斯被动陆缘盆地超前选区选带、新项目评价及中标区块探区勘探部署提供了重要依据,也为今后在全球被动大陆边缘盆地深水勘探战略选区提供借鉴。

鲁中南典型地热区地热水氟分布特征及其驱动机制

山东省鲁中南典型地热区主要包括沂沭断裂带地热区和鲁中隆起地热区,为了探明研究区地热水氟分布特征及其富集规律,综合运用水化学图解、地球化学模拟和主成分分析等方法,分析沂沭断裂带地热区和鲁中隆起地热区地热水水化学数据。结果表明:研究区地热水以Na-Ca-Cl型、Na-Ca-SO_(4)-Cl型和Na-Cl^(-)SO 4型为主,基本为弱碱性水,优势阳离子为Na^(+),氟质量浓度在0.38~4.5 mg/L之间,富钠弱碱性环境有利于地热水中氟的富集。地热水中F-质量浓度与Na^(+)、Cl^(-)和总溶解固体(TDS)质量浓度呈显著正相关,而沂沭断裂带地热水样中F-质量浓度还与K^(+)、SO_(4)^(2-)质量浓度呈显著正相关,与Mg^(2+)和HCO_(3)质量浓度呈显著负相关;鲁中隆起地热区地热水中阳离子交换作用较沂沭断裂带地热区更为强烈,Na^(+)反应强度明显强于Mg^(2+)。鲁中隆起地热区和沂沭断裂带地热区均为裂隙型热储,热储岩性分别为石灰岩、灰岩热蚀变带和安山岩破碎带,水岩作用强烈。研究区地热水中氟离子的物质来源主要为萤石等含氟矿物的溶解沉淀,受控于阳离子交换等水岩相互作用影响,最终形成高氟地热水,其中高温和富钠对研究区地热水中氟离子富集影响较大。研究成果为地热资源开发利用提供了参考。

断层的地电响应特征及其在砂岩型铀矿地质解译中的作用——以巴楚隆起地区为例

砂岩型铀矿成矿理论认为,适宜的构造斜坡带可发展为有利的铀成矿区。斜坡带内受重力、挤压等因素形成的断裂对铀成矿和保矿都有非常重要的作用。北方沉积盆地内,利用大地电磁法进行断裂解译的精度不仅受沉积地层绝对电阻率的影响,也受地层间相对电阻率影响。为准确解译隐伏断裂,建立了不同电性差异下的正、逆断层地电模型,正反演模拟了不同电阻率差异及不同性质断层模型的一维、二维反演电阻率断面。正反演模拟结果表明:正、逆断层在反演地电断面上具有不同的特征,即正断层在断层斜面处呈倾斜形态,而逆断层在断层斜面处呈凹陷形态;一维反演结果对断裂的识别效果要优于二维反演结果。通过断层地电相应特征规律的总结,为巴楚隆起西部凹陷大地电磁剖面隐伏断裂的解译提供了依据与指导。

反射地震剖面揭示容城凸起基岩面和断裂结构及其对地热成因的启示

容城凸起是华北地区地热资源富集区域之一,探测容城凸起基岩面的精细结构、埋深和断裂,对理解该区地热资源的分布和富集以及地热资源的勘查与开发具有重要意义。本文基于中国地质科学院2018年在容城凸起采集的SN向反射地震剖面数据,通过对反射数据精细处理,获得容城凸起4 km以浅的高精度几何结构,经地热孔资料标定后开展解释。主要获得以下4点认识:容城凸起基岩面以上新生代沉积地层呈近水平层状分布,这些近水平地层对容城地热田起到保温盖层作用;容城凸起基岩面埋深在700~3000 m之间,其凸起中心部位变化相对平缓,向周边迅速加深到3000 m左右;牛南断裂和容东断裂在深部延伸交汇,与其他中、小型断裂组成的断裂系统为水和热的传导提供了通道和空间;基岩面凸起的几何结构有利于热流在凸起下方汇聚。

塔里木盆地东北缘吐格尔明背斜和阳北断裂带构造分析

吐格尔明背斜和阳北断裂位于塔里木盆地北缘,南天山山前库车褶皱冲断带的东段,两者均为基底卷入型构造。阳北断裂是一个反转构造,其变形历史可以追溯到侏罗纪—白垩纪的正断层;新生代构造反转,发生了多期冲断变形加速期,分别发生于白垩纪末—古近纪初、古近纪末—新近纪初、中新世早期、上新世和第四纪。吐格尔明背斜构造带是阳北断裂中新世早期及以后的冲断作用派生出来的一个次级基底卷入型构造变形带。它由吐格尔明背斜及其南、北两条呈背冲关系的逆冲断层组成。背斜核部元古宇变质岩出露地表;中、新生界直接不整合于变质岩之上,缺失全部古生界,说明研究区可能属于一个长期存在的古生代古隆起。

塔中凸起张扭走滑断裂带分段构造特征及生长机制

塔里木盆地奥陶系碳酸盐岩发育斜向挤压背景下的压扭走滑断裂,但塔中凸起发现了一系列张扭走滑断裂,并对油气富集具有重要的控制作用。基于塔中凸起西部地区三维地震资料,结合相干、曲率等属性,统计走滑断裂运动参数,运用走滑断裂构造解析方法,优选塔中凸起F_(Ⅱ)21走滑断裂带开展走滑断裂分段建模研究,并探讨其生长机制。结果表明,F_(Ⅱ)21走滑断裂带具有平面分段、垂向分层特征,奥陶系碳酸盐岩顶面发育线状构造、斜列构造、马尾构造、翼尾构造、辫状构造和叠覆构造。走滑断裂构造高差分布特征揭示了走滑断裂带的分段生长与尾端扩张生长机制,该断裂带为调节走滑断裂带两侧反向收缩变形的变换断裂,经历雁列断裂阶段、生长连接阶段及再激活雁列断裂阶段的演化过程。

渤海湾盆地惠民凹陷中央隆起带张扭性断裂演化的构造物理模拟研究

惠民凹陷位于渤海湾盆地济阳坳陷西部,新生代时期经历了南北向伸展,形成了典型的“北断南超”半地堑结构。平面上,惠民凹陷中央隆起带发育了NE至近EW向的张扭断裂体系;垂向上,中央隆起带断裂体系从深部到浅部呈现出由雁列式分段到逐渐连接贯通的特征。目前对惠民凹陷中央隆起带断裂体系的结构特征有了较好的刻画,但是对于该断裂体系形成的运动学过程及其控制因素仍然停留在描述阶段。文章设计了一组张扭构造物理模拟实验,以探究惠民中央隆起带断裂构造演化过程及其控制因素。实验再现了惠民凹陷中央隆起带断裂体系在平面上由早期孤立分段、侧向传播、最终贯通的三个阶段;在剖面上也很好对应了中央隆起带沿走向由共轭断裂系向阶梯式断裂的结构转变特征。基于粒子成像测速(PIV)的应变分析,文章构建了三阶段的应变—断层距离统计图,揭示了各分段断裂由早期无连接,经历侧向生长,从软连接到硬连接的构造演化过程。研究证实在南北向区域伸展作用下,盆地基底NEE向先存断裂的活化是惠民凹陷中央隆起带张扭构造形成的根本原因。文章利用砂箱构造物理模拟实验揭示了惠民凹陷中央隆起带断裂发育的机制,可为类似的张扭性断陷盆地的断裂演化与油气成藏研究提供有益的启示。

塔里木盆地阿克库勒凸起东南斜坡走滑断裂构造特征及油气地质意义

塔里木盆地阿克库勒凸起东南斜坡发育大量走滑断裂。走滑断裂的几何学、运动学特征对油气的运移和富集起到了重要控制作用。本文以东南斜坡S118-AT22-YUKE2断裂、S113-AT13-YUKE3断裂、AT20断裂、AT18-YUKE5断裂为研究对象,依据中小尺度走滑断裂精细解析技术,对走滑断裂在不同层系的变形特征、平面分段性、断裂体系活动强度、后期活动性、通源性、演化模式和成因机制开展精细解析,结合生产动态资料研究其油气地质意义。阿克库勒凸起东南斜坡走滑断裂在垂向上呈深层线性断裂与浅层雁列式断裂组合的变形结构。中—下奥陶统发育的走滑断裂在平面上具有明显分段特征。阿克库勒凸起东南斜坡走滑断裂相对活动强度西强东弱,由北向南呈强—弱—次强的特征;晚海西期—燕山期断裂活动性近SN—NE向断裂体系强于NNE—NNW向断裂体系;断裂通源性受控于早期裂谷,主干断裂通源性优于次级断裂,NNE—NNW向断裂体系的主干断裂通源性优于近SN—NE向断裂体系,但次级断裂通源性较差。NNE—NNW向和近SN—NE向断裂体系都形成于中加里东期,NEE向断裂形成于晚加里东期—早海西期,东南斜坡走滑断裂经历了中加里东期、晚加里东期—早海西期、中晚海西期、印支期—燕山期多期构造活动垂向叠加,NNE向和近SN向主干断裂滑移方向相反是由于破裂方式的不同。阿克库勒凸起东南斜坡烃源岩排烃期为晚海西期—喜马拉雅期,断裂活动期与排烃期的耦合有利于油气充注;断裂活动强度控制了通源性和储集体规模,进而控制了油气富集程度。后期活动明显、断裂活动强、通源性好的走滑断裂是下一步勘探的有利目标。

塔中隆起F_(Ⅱ)21断裂带油气成藏过程与多相态成因

针对塔中隆起F_(Ⅱ)21断裂带奥陶系油气藏相态分布复杂问题,基于构造解析、地球化学的综合分析认为,原油密度、天然气干燥系数及气油比等参数的平面分布趋势与走滑断裂分段构造密切相关,翼尾构造带北部发育凝析气藏,南部依次发育挥发性油藏与原油油藏。F_(Ⅱ)21断裂带与北部拗陷富满、顺北地区原油生源相同,主要来源于下寒武统烃源岩。原油成熟度沿断裂带由北至南依次降低,断裂带北部主要为原油裂解气,中部与南部主要为干酪根裂解气。F_(Ⅱ)21断裂带经历多期油气充注,翼尾地堑部位为油气有利充注点,喜马拉雅期盐下原油裂解气的强烈充注改造是北部凝析气藏形成的重要原因,受古构造影响,晚加里东期与晚海西期生成的原油资源主要于翼尾地堑构造南部鼻状隆起区域聚集成藏。

An integrated north–south paleo-Dadu-Anning River: New insights from bulk major and trace element analyses of the Xigeda Formation

The Xianshuihe-Anninghe fault extends SE–S and constitutes the southeastern margin of the Tibetan Plateau.However,the Dadu River which is associated with the fault does not flow following the path,but makes a 90ºturn within a distance of 1 km at Shimian,heading east,and joins the Yangtze River,finally flowing into the East China Sea.Adjacent to the abrupt turn,a low and wide pass near the Daqiao reservoir at Mianning separates the N–S course of the Dadu River from the headwater of the Anning River which then flows south into the Yunnan Province along the Anninghe fault.Therefore,many previous studies assumed southward flow of the paleo-Dadu River from the Shimian to the Anning River.However,evidences for the capture of the integrated N–S paleo-Dadu-Anning River,its timing,and causes are still insufficient.This study explored the paleo-drainage pattern of the Dadu and Anning Rivers based on bulk mineral and geochemical analyses of the large quantities of fluvial/lacustrine sediments along the trunk of the Dadu and Anning Rivers.Similar with sands in the modern Dadu River,the Xigeda sediments also exhibit a granitoid affinity with the bulk major mineral compositions of quartz(>50%),anorthite(about 10%),orthoclase(about 5%),muscovite(about 5%),and clinochlore(about 4%).Correspondingly,bulk major elements show high SiO_(2),with all samples>60%,and some of them>70%,low TiO_(2)(≤0.75%),P_(2)O_(5)(≤0.55%),FeO*(≤5%),and relatively high CaO(1.02%–8.51%),Na_(2)O(1.60%–2.52%),and K_(2)O(2.17%–2.71%),with a uniform REE patterns.Therefore,synthesizing all these results indicate that these lacustrine sediments have similar material sources,which are mainly derived from its course in the Songpan-Ganzi flysch block,implying that the paleo-Dadu originally flowed southward into the Anning River and provided materials to the Xigeda ancient lake.The rearrangement of the paleo-Dadu River appears to be closely related to the locally focused uplift driven by strong activities of the XianshuiheXiaojiang fault system.

Structural characteristics and tectonic division of the Zambezi Delta basin in the offshore East Africa:evidences from gravity and seismic data

The Zambezi Delta basin is a passive marginal basin located on the East African coast that has good oil and gas exploration potential.Due to the special geological evolutionary background of the Beira High in the Zambezi Delta basin,it has a low gravity anomaly,and the existing seismic survey lines do not cover the whole basin;therefore,it is difficult to interpret the structural characteristics of the whole basin based solely on gravity or seismic data.Based on satellite altimetry gravity anomaly data,this study infers the distribution characteristics of faults in the Zambezi Delta basin by using the normalized vertical derivative of the total horizontal derivative(NVDR-THDR)technique.Then,constrained by seismic data,the gravity anomaly at the Moho interface is extracted by using the fast forward method of the double-interface model of the gravity anomaly,and this anomaly is then removed from the Bouguer gravity anomaly to obtain the sedimentary layer gravity anomaly.The thickness of the sedimentary strata is obtained by inversing the sedimentary basement depth of the whole basin.Then,uplifts and depressions are divided based on a sedimentary layer thickness of 3 km.This research demonstrates that the Zambezi Delta basin mainly features nearly SN-trending and NE-trending faults and that these faults exhibit east-west partitioning.The nearly SN-trending strike-slip faults controlled the sedimentary development of the basin,and the NE-trending tensile faults may have acted as migration channels for oil,gas and magma.The“overcompensation”effect of the Moho interface gravity anomaly on the gravity anomaly of the sedimentary layer is caused by the depression of the Moho interface beneath the Beira High,which results in a low gravity anomaly value for the Beira High.The pattern of uplifts and depressions trends NE and has the structural characteristics of east-west blocks.