Paleoseismic ruptures and evolution of a small triangular pull-apart basin on the Zemuhe fault

Trenching is a primary technique on paleoseismology to reveal evidence of surface deformation produced by large earthquakes.A good trenching site requires completeness of geologic recording on paleoseismic events and corresponding reliable dating from radiocarbon samples.Based on three-dimension trenching,we show a structure of a small triangular pull-apart basin at the Daqingliangzi section on the Zemuhe fault,then explore interrelation between paleoseismic surface rupturing and evolution of the pull-apart basin,and give a corresponding identification model.Sedimentary boundary of the pull-apart basin is tightly bounded by two branch faults,which produced multiple paleoseismic events with deformation of some large fissures in sequence.Strata are thinner at north of the pull-apart basin,however thicker at south.These above characteristics show that evolution of the pull-apart basin is a continuous sedimentation process accompanying extensional deformation produced by multiple paleoseismic events.Small pull-apart basins are favorable sites for trenching and paleoseismic study on active strike-slip faults.

Analysis of a Pull-Apart Basin and Its Associated Fractures in the Woodford Shale, Central Oklahoma

Pull-apart basins are faulting and folding zones with high intensity of fractures that strongly affect the production in unconventional shale gas. While most observations of pull-apart basins were from surface mapping or laboratory experiments, we investigated a nascent pull-apart basin in the subsurface. We characterized a nascent pull-apart basin along the strike-slip fault within the Woodford Shale by using seismic attributes analyses, including coherence, dip-azimuth, and curvature. The results indicate a 32 km long, N-S striking strike-slip fault that displays a distinct but young pull-apart basin, which is ~1.6 km by 3.2 km in size and is bounded by two quasi-circular faults. The curvature attribute map reveals two quasi-circular folds, which depart from the main strike-slip fault at ~25°, resulting in an elliptical basin. Inside the basin, a series of echelon quasi-circular normal faults step into the bottom of the basin with ~80 m of total subsidence. We propose that the controls of the shape of pull-apart basin are the brittleness of the shale, and we suggest proper seismic attributes as a useful tool for investigating high fracture intensity in the subsurface for hydrofracturing and horizontal drilling within the shale.

The formation and evolution of the Qiaojia pull-apart basin,North Xiaojiang Fault Zone,Southwest China

Sedimentary sequences with drastic thickening over short distances have been observed in Qiaojia County,Yunnan Province,Southwest China.These are related to a pull-apart basin controlled by the Xiaojiang strike-slip fault.Our field investigations include determining the surface characteristics of the Qiaojia basin which consists of three terrace sequences and a series of alluvial fans.Several drill holes were used to reveal the internal structure of the basin.The results suggest that the basinal sediments are over 300 m thick.From bottom to top,they can be classified into five different units.We inferred that the units of lacustrine sediments are deposited in a paleolake which was formed by a paleo-landslide.Accelerator mass spectrometry radiocarbon dating(AMS ^(14)C dating) was used to estimate the ages of the terrace and lacustrine sediments.We use the results to infer that the paleo-lake has existed about 15,000 years and that the Qiaojia basin was uplifted at an average rate of 3.3 mm/a.Furthermore,we then model the evolution process of the basin and interpreted 6 phases of development.

Pull-apart Basins and the Total Lateral Displacement Along the Haiyuan Fault Zone in Cenozoic

Pull-apart basins of three scales were found along the Haiyuan fault zone. The largest one is more than 50km long, named Laolongwan basin developed in Miocene. A model was built to calculate the amount of pull-apart of an extensional basin. Parameters used in calculation include thickness and length of deposition and depth of detachment. The results of calculation show that the amount of pull-apart of the Laolongwan Basin is about 30 km. Based on previous studies and calculating by using the average slip rate method, amount of pull-apart of the other two smaller basins are 22 km and 8 km, respectively. Thus, the total displacement of strike-slip along the Haiyuan fault zone is about 60 km, which is close to the offset of the Yellow River from Jingtai to Jingyuan.

Sedimentary Basins in the Western White Nile, Sudan, as Indicated by a Gravity Survey

An academic geophysical research as a regional gravity survey was made during1994 in the Western White Nile to infer the shallow crustal structures in the area. The result ofthe survey was compiled as a Bouguer anomaly map with a contour interval of 2 X 10^(-5)m/s^2. It isfound that the negative residual anomalies are related to the Upper Cretaceous sediments (NubianSandstone Formation) filling all depressions in the Basement complex surface while the positiveresidual anomalies are attributed to the relatively shallow or outcropping Basement rocks and thesteep gravity gradients are resulting from the sharp contacts between the sedimentary infill and theBasement rocks. To define the geological structures in the area, 9 profiles were studied. For eachof the profiles, measured and computed Bouguer gravity anomalies, crustal density model, subsurfacegeology evaluation were performed. A G-model computer program was applied in the gravity modeling,which is based on the line-integral method of gravity computation. A geological/structural map wasproposed showing inferred sedimentary basins, faulting troughs and uplifted Basement block andtectonic trends. The basins are believed to be fault-controlled which developed by extensionaltectonics (pull-apart mechanism). As for the mechanism and cause of faulting, the area is consideredas a part of the Central Sudan rift system which had been subjected to several tectonic eventssince Early Cambrian to Tertiary times which resulted in the formation of several fracture systemsassociated with block subsidence, rifting and basin formation.

汉中盆地地下水水化学特征及其成因研究

为研究汉中盆地地下水的水化学特征及成因,在丰水期共采集56件潜水样品,综合运用数理统计、相关性分析、Piper三线图、Gibbs模型和离子比等方法,分析了汉中盆地地下水的水文地球化学特征、各化学参数的空间变化规律、主要离子的控制因素及来源。结果表明,汉中盆地地下水阳离子以Ca^(2+)为主,阴离子以HCO_(3)-为主。从离子空间变化规律上来看,K^(+)波动最为剧烈,且从中下游开始逐渐降低,Cl^(-)和Na^(+)变化规律一致,呈波动变化;HCO_(3)-、Ca^(2+)、Mg^(2+)以及SO_(4)^(2-)的从中上游至中下游含量逐步降低,至下游含量增加;TDS值为128.5~590 mg/L,平均值为282.67 mg/L,在中下游含量明显增加;pH平均值为7.17,为弱碱性,在中上游波动剧烈,至下游逐渐降低。地下水水化学类型以HCO_(3)-Ca和HCO_(3)-Ca·Mg型为主,受碳酸盐岩和硅酸盐岩的溶解共同控制,阳离子交替吸附作用较弱,Na^(+)和K^(+)主要来源于钾长石、钠长石等硅铝酸盐矿物的溶解和部分盐岩的风化溶解,Ca^(2+)除来自碳酸盐岩的溶解外,还有大量硅酸盐岩的溶解;方解石及少量白云石等碳酸盐岩的风化溶解对Mg^(2+)和HCO_(3)-贡献较大。查明汉中盆地地下水水化学特征及成因机制,可为汉中地区地下水饮水安全提供有力科学依据。

Sedimentary and tectonic evolution of the Banquan pull-apart basin and implications for late Cenozoic dextral strike-slip movement of the Tanlu Fault Zone

The Banquan Basin is a pull-apart basin with the largest scale and the most prominent structure due to dextral slip of the Tanlu Fault Zone(TLFZ) in late Cenozoic. The depositional history of the basin records the start time and evolution of the right-lateral strike-slip movement of the TLFZ. This paper studies the sedimentary and tectonic evolution of the Banquan Basin by seismic reflection exploration, borehole detection and cosmogenic nuclide chronology. We analyze the coupling relationship between the pull-apart basin and the strike-slip fault and discuss the start time and tectonic significance of the right-lateral strikeslip of the TLFZ. Our study indicates that the Banquan Basin has undergone three evolutionary stages: weak rifting during the pre-pull-apart period, strong extension during the syn-pull-apart period and subsidence during the post-pull-apart period. This implies that the TLFZ, which controls the evolution of the basin, experienced an evolutionary process of weak activity,intensified activity and migration of activity toward the central basin. The sedimentary filling of the basin has strong response to the episodic pull-apart and extension of the basin. Lying upon the basement of the basin, a thin layer of Miocene mudstone slowly accumulated due to local rifting before the strong pull-apart event. Along with the dextral slipping and pull-apart process, the basin was filled with alluvial fan facies, fluvial facies and floodplain facies strata from bottom to top. The latest tectonic movement of the TLFZ in the North China Block in late Cenozoic was dominated by episodic dextral strike-slip motion, and this deformation pattern started at 4.01±1.27 Ma. The latest tectonic deformation in North China since late Cenozoic was governed by eastward extrusion and tectonic orogenesis of the eastern margin of the Qinghai-Xizang Plateau since late Miocene. The eastward thrusting of the Liupanshan fault zone and sinistral shearing of the Qinling fault zone led to the anticlockwise rotation and pushing of secondary blocks in North China, resulting in a planar bookshelf faulting and rotation pattern. This unique deformation pattern transferred eastwards to the North China Plain at ~4.01 Ma and the process continues to the present time.This planar bookshelf rotation, accompanied with regional sinistral strike-slip movement of the ~EW-trending boundary fault zones to the north and south of the North China Block and dextral strike-slip motion of the NNE-trending boundary faults between secondary blocks, is likely to be the long-range effect of the strong extrusion of the eastern margin of the QinghaiXizang Plateau.

2010—2019年南盘江流域水资源空间均衡状况分析

为分析南盘江流域2010—2019年水资源空间均衡状况,基于南盘江流域的社会经济指标、水资源禀赋及开发利用数据,运用水资源负载指数、水土资源匹配系数、水资源效益指数及其基尼系数,分析了流域水资源利用状况和流域水资源空间均衡状况;建立社会经济-水资源开发利用-水资源禀赋的三角系统模型,描述了流域水资源空间均衡的稳定性及可持续性。分析结果表明:南盘江流域的水资源负载等级较高且空间分布不均,流域的水土资源匹配水平低且空间均衡性不高,用水效益虽有逐年升高趋势但整体水平依然不高。三角系统模型分析结果表明:南盘江流域整体上的水资源系统稳定性较好,但从流域套8个地级市区域来看,有一半地市水资源系统不能构成三角形系统,部分地区水资源系统空间失衡。

小型拉分盆地的生长与走滑断层的位移速率--以青藏高原东南缘则木河断裂带为例

活动断层滑动速率可以用来定量比较不同断裂带或同一断裂带不同时段的活动性,同时还是地震危险性评价的重要参数,合理评估活动断层的滑动速率主要受限于两个参数的可靠性,即断层的累积位移量和相应的活动时间。传统上较理想的用于评估走滑断层滑动速率的地貌体一般为阶地、冲洪积扇、冲沟等的位错测量和相应活动累积时间的确定,文中则尝试通过青藏高原东南缘则木河断裂带大箐梁子段三维组合探槽揭示的小型三角状拉分盆地的生长模式来约束断层的水平位移速率,基于野外详细的调查、拉分盆地底部14C测年以及实时差分GPS精确测量,约束了则木河断裂带全新世以来的断层平均左旋滑动速率为(2.4±0.2)～3.6mm/a,这比前人给出的滑动速率偏小,但却与古地震资料及GPS观测结果吻合得较好。

塔里木盆地西南缘山前带逆冲推覆构造特征

塔里木盆地西南缘山前带是西昆仑逆冲推覆构造在前陆形成的冲断带,主要由断层相关褶皱、双重构造、叠瓦状构造、三角带等构造组成。通过地表构造剖面、地震与非震资料的综合解释与研究,结合平衡剖面的正演方法,对该冲断带进行了几何学、运动学与动力学研究,对冲断带断层的扩展方式以及冲断时代进行了讨论。研究认为塔西南逆冲推覆构造具有"南北分带、东西分段以及垂向结构变异"的特点。自南向北分为逆冲推覆的根带、中带、锋带和反冲断裂带,由西向东可以划分为帕米尔弧形构造段、齐姆根弧形构造段、甫沙-克里阳三角带构造段与和田南逆冲推覆体构造段。冲断带在垂向结构上由三套区域性滑脱层划分为浅构造层次的外来系统断坡背斜、中构造层次的准原地系统双重构造、三角带构造以及深构造层次的原地系统弱变形带三层结构。冲断席内断层的扩展方式为前展式,而不同冲断席间则为后展式模式。冲断带自中新世中期开始形成,中新世末发生位移推覆,上新世—早更新世定型,中更新世—全新世隆升均衡调整。

鄂尔多斯西南缘前陆盆地沉积物物源分析及其构造意义

前陆盆地充填沉积物中岩屑的分散形式和砂岩成分研究对确定物源区的逆冲事件、构造背景和与沉积物对应的物源层十分有效。通过对鄂尔多斯西南缘安口地区上三叠统沉积剖面系统采样测定发现，沉积物物源为一套变质碎屑岩和变质火山岩，为东祁连褶皱逆冲带中的陈家河组（Ｏ３ｃｈ）和葫芦河组（Ｚ－Ｏ２ｈｌ）。而西南缘千阳县上侏罗统砾岩物源为陇山群（Ｐｔ２ｌｎ）。上三叠统地层的物源分散形式为混合型，而上三叠统和上侏罗统两套地层统一的分散型式为倒序型，它是两期逆冲活动的沉积响应。根据鄂尔多斯西南缘安口地区上三叠统沉积物的ＱｍＦＬｔ端元成分作砂岩三角投影图，确定晚三叠世鄂尔多斯西南缘盆地性质为发育于碰撞造山带之前陆的前陆盆地。

准噶尔盆地南缘地区中新生代物源分析

准噶尔盆地南缘地区中新生界沉积物源研究中,通过薄片鉴定、碎屑岩类法、沉积学法及碎屑骨架三角图等方法,对研究区各层段砂岩中石英、长石和岩屑百分含量及各种碎屑成分进行统计,直接获得了物源证据,确定了物源区物质形成时期、范围及组成,为后期盆地储层性质、沉积相分析及勘探提供了依据。

太湖流域典型调水试验水质污染风险研究

跨区域跨流域调水是我国水资源优化配置的重要组成部分之一。太湖流域内水流缓慢,环境容量低,引水清污成为太湖流域改善水环境质量的手段之一。在污染源难以得到有效治理的条件下,引水使得江河原水中污染物发生二次迁移,对流域水环境质量产生污染风险。基于三角模糊数原理以及a-截集技术,选取氨氮关键水质参数,评估太湖流域典型调水试验受水区水质污染风险程度,从而为太湖流域水利工程的科学调度提供理论依据。

基于GIS技术的地表构造特征研究——以塔里木盆地库车前陆褶皱-冲断带为例

利用GIS技术研究了库车地区的地表构造特征及其与地下构造的相关性 ,认为地表构造的南北分带性和东西分段性主要受地下主断裂的分布状况控制 ,库车河地区是东西分段的一个转换带 .秋立塔克构造带受左旋断层的作用被分为东西两段 ,控制西段南部背斜生长的断层连续性较好 ,而控制北部背斜生长的断层连续性较差 ,大致可分为三段 ,呈左阶排列 .库车地区的主要水系基本上都表现出与山体走向斜交的特点 。

Tectonic Landform of Quaternary Lakes and Its Implications for Deformation in the Northern Qinghai-Tibet Plateau

The Hohxil region in the northern Qinghai-Tibet Plateau is occupied by numerous plateau lakes, which have long been inferred as being tectonic products. However, so far little evidence has been found to support this tentative inference. Field survey and morphotectonic analysis of TM satellite images in the eastern segment of the Hohxil region revealed that Kusai Lake and Yelusu Lake are S- shaped pull-apart basins, which were dominated by left strike-slip master faults trending WNW-ESE. The pull-apart distances of the two lakes are analyzed to be 〈15-20 km and 15 km respectively. Based on studies of the faulting rate, the initiation ages of the pull-apart basins are suggested to be approximately in the Early Pleistocene. The pull-apart basin tectonics is further regarded as a common mechanism for the widely distributed large lake basins in the northern Qinghai-Tibet Plateau. Regional distribution of these pull-apart basins and their substantial intra-block slip suggest that a sinistral shear stress, which is independent of the distinguished strike-slip faults, has been imposed on across the northern Qinghai-Tibet Plateau. Thus, the intra-block slip may be an important expression of the eastward extrusion of the Plateau crustal material in accommodating the ongoing continent-continent convergence between India and Eurasia. The revelation of pull-apart tectonics within the Plateau hinterland provides field evidence and a possible style of deformation for the newly proposed continuous deformation by the global positioning system （GPS） measurement across the northern Qinghai-Tibet Plateau. A model, with respect to systematic tectonic landform development, for pull- apart basins is finally proposed.

Seismo-tectonic divisions of strong earthquakes with M_s≥7.0 and their tectonic geomorphology along Xianshuihe-Xiaojiang fault zone

Seismo-tectonic areas of historical strong earthquakes with MS(7 along Xianshuihe-Xiaojiang fault zone are divided, and their individual fault-pattern and tectonic geomorphology are analyzed. Those strong-earthquake areas are located in some special parts of the fault zone, where the major branch-faults of the fault zone form left stepping, parallel, and fork-like patterns. In the strong-earthquake areas structurally complicated basins are developed, such as pull-apart basins in fork-like area, in double stepping area, and in stepping and fork-like areas.

基于三角模糊数的高阶煤层气压裂井产能影响评价模型——以鄂尔多斯柳林区块为例

基于储层物性、压裂施工和排采工艺为出发点,首次将三角模糊数的评价方法运用到高阶煤层气产能评价中,通过建立的层次关系,将影响高阶煤层气产能的复杂因素简单化,得到了各个参数对该区块产能影响的权重,并基于现场大量数据建立了隶属函数,将现场所测的不同参数值标准化,首次系统地建立了一套高阶煤层气压裂井产能影响评价模型。研究结果表明:压裂液黏度、井底流压和储层渗透率的大小是影响鄂尔多斯柳林地区高阶煤层气压裂井产能的主要因素。

Characterization of Alluvial Gold Bearing Sediments of Betare Oya District-East Cameroon, Implication for Gold Exploration and Recovery

Field studies (location Au pits, sampling of different layers of sedimentary sequences filling the pits, panning of sediments), litho-stratigraphic investigations, grain size analysis and outlining of depositional conditions revealed a characteristic fining upward sequence in all the sections of 08 Au-pits within the Betare Oya basin. A typical profile is 2.5 to 4.5 m thick and is composed of a 30 to 50 cm organic topsoil layer, underlain by a 1.5 m thick reddish brownish gold free saprolite, which is underlain by 1.5 m sandy section. From litho-stratigraphic investigations and grain size analysis results a quartz dominated gravelly 1.4 m thick layer consisting in boulders (275 mm), cobbles (2-−0.0148x2 + 1.2187x + 2.0344, R2 = 0.6929 (sandy layer);2) y = 0.0617x2 + 1.0849x + 0.8097, R2 = 0.8694 (gravelly layer);and y > R2 is satisfied in both cases. This implies that Au recovery from these layers could be effective through gravity separation using sieves mounted on classifiers of 7 cm (sandy layer) and 10 cm (gravelly layer) diameter.

Application of Interferometric Spaceborne Synthetic Aperture Radar to Morphotectonic Research in the Bengcuo Area of Tibet

Using ELLS-1/2 radar satellite data, we generated a Digital Elevation Model by Interferometric Synthetic Aperture Radar, and the ERS-1/2 DEM that we generated is obviously superior to both the 1/25 ten thousand-scale DEM of the National Fundamental Geographic Information System of China and the 90-m spatial resolution＇s SRTM DEM that America published in 2004 when it showed the characteristics of tiny structure relief. By analyzing the relief characteristics of the Bengcuo fault zone based on ERS-1/2 DEM, we find that the relief on the connection location of the Bengcuo and Pengcuo fault zones has complex characteristics. A structure relief that is similar to the Pengcuo fault zone crosses through the Dazi-Dasha fault on the the Bengcuo fault zone, while the Dazi-Dasha fault crosses through a gully at this place. This indicates that the Dazi-Dasha fault has been active at this place recently. At the same time, the Naka-Naduiduo fault is severed by the gully which was cut through by the Dazi-Dasha fault. Therefore, the Naka-Naduiduo fault was formed earlier than the Dazi-Dasha fault.

Evolution of a confined gravelly river to a braided-meandering river in the Late Cretaceous Khasi group,southern Shillong plateau,NE India

This paper intends to unravel the depositional condition of the Basal Conglomerate/Jadukata Formation and the Lower Mahadek Formation in southern Shillong Plateau,NE India deposited during the Late Cretaceous period.The studied succession is entirely siliciclastics in composition and was built up on the Precambrian basement rocks.State-of-art facies analysis and palaeocurrent evidence helped us to reconstruct the palaeogeography and palaeoenvironment.The facies tracts reveal that frequent hyperconcentrated mass flow deposits dominated the proximal part of the river channels.Gradually,the river evolved to a sandy braided and finally mud-dominated,meandering system.The river channel changed its pattern through onlapping and progressive elimination of the accommodation space created by the tectonic subsidence/upliftment.Major shifts in palaeocurrent direction at different stages of the river evolution confirm the role of tectonics on the river channel evolution.QFL detrital modes of the sandstones reflecting lithic wacke composition and the recycled orogeny corroborate the interpretation.Rapid lateral and vertical facies transition suggests a pull-apart type basin due to ongoing rifting.Geochemical analyses also show signatures of the overlapping tectonic conditions supporting the pull-apart basin model.