The role of sedimentary and tectonic brines in the Damara Orogen, Namibia

Along the southern margin of the Upper Proterozoic Damara Orogen, Namibia, an accumulation of extraordinarily large megacrystalline quartz-dolomite bodies occur. They were emplaced in tectonically controlled positions during an early deformational phase of the Damara Orogeny, where hot nappes were thrust over a fluvial-lacustrine and evaporitic metaplaya sequence (Kamtsas and Duruchaus Formations) which was deposited on the faulted EW-trending continental margin of the Kalahari craton. Individual occurrences of the quartz-dolomite bodies often cover several hundred square meters. Characteristic for the quartz-dolomite bodies is zoning with an outer shell of giant milky quartz crystals, some more than 15 m long along the c-axis, tightly intergrown or twinned (Brazilian twins) with a perfect cleavage parallel to the positive rhombohedral faces {1011}; there is an inner shell of crystalline dolomite and a central pipe of dolomitic breccia. Based on fluid inclusions studies the formation fluids of quartz-dolomite bodies can be related to the mobilization of interstitial fluids and to dehydration and leaching of evaporitic hydrate minerals of the metaplaya sequence. The fluids are characterized by extremely high salinities of up to 68 wt % total salt content. Minimum temperatures of formation, as determined in fluid inclusion studies, ranged from 150 to 250°C. At a later stage CO₂ derived from decarbonatization reactions was dissolved in the fluids. Changes in pressure and temperature led to effervescence and the formation of a quartz stockwork in the surrounding country rock. During the main phase of the progressive Damara Orogeny, the southward advancing accretionary nappe pile of the Khomas trough drove ahead large amounts of tectonometamorphic fluids, characterized by intermediate salinity and high CO₂ contents. When these fluids met with the previously established hypersaline fluid system, large amounts of CO₂ were released due to the mixing of the two fluids; if there is no mixing, each fluid then maintains its salinity and there is no CO₂ degassing. The CO₂ from this mixing is now present as secondary, high-density inclusions not only in the quartz-dolomite bodies but also in the surrounding country rock. Pressure estimations indicate at least 100–600 MPa as a minimum pressure of formation for these inclusions. The remaining aqueous fluid phase has produced local alterations and Cu, Pb, and Au mineralization.     

Geochemistry of Brines from Salt Ore Deposits in Western Tarim Basin

In the geological evolution of the Tarim Basin, many transgressions and relictions happened. So there have been plentiful sources of salt. Moreover, because of uttermost drought, a lot of salt has been deposited. It is possible to find potash salt in this area. In our fieldwork, we have found salt and brine in western Tarim Basin. Based on a geological survey and the characteristics of sedimentary facies and paleogeography, this paper deals with the geochemical parameters and discusses the possibility of formation of potash salt in terms of the chemical analyses of samples collected from western Tarim Basin. Results of brine analysis lead to some conclusions: most of these salt brines have eluviated from very thick halite beds, mainly chloridetype salt and this kind of halite does not reach the stage of potash deposition in all aspects; WKSL (Wukeshalu) occupies a noticeable place, and we should attach importance to this district because there have been some indicators of the occurrence of potash deposits as viewed from the contents of Br and K. Finally, low Br contents are recognized in the Tarim Basin as a result of salt aggradation, and this point of view has been proved by the results of this experiment and the data available. It cannot depend upon the index of Br to judge the evolution stage of halite. We must look for other facies of potash except marine facies.     

Seismic stratigraphy of sedimentary cover in the Podvodnikov Basin and North Chukchi trough

The multichannel seismic reflection data (MCS data) obtained in the Arktika-2014 expedition revealed the essential fact that must be taken into account by the tectonic model of the Central Arctic region. The Brookian, Lower Cretaceous, and Upper Jurassic unconformities are continuously traced from the North Chukchi offshore trough into the Podvodnikov Basin, indicating that the depocenter in the latter accumulated both Cretaceous sedimentary sequences and Early–Middle Mesozoic ones.     

Basinal brines and groundwaters as possible metal carriers in the formation of sandstone-hosted lead-zinc deposits

Features of the two best-documented worldclass sandstone-hosted Pb-Zn deposits (Laisvall, Sweden; Yava, Nova Scotia, Canada) and a few similar but smaller deposits (SE Missouri, Quebec Appalachians) are compared with the purpose of contributing to the debate on the problem of the aqueous medium of metal transport: basinal brines or groundwaters? For the dolostone-sandstone-hosted deposits in SE Missouri, it is concluded that basinal brines formed this medium in both host rocks. The paleotopographic control of these Missouri deposits is pronounced and leads to the conclusion that such control is insufficient evidence to establish the groundwater hypothesis for the Yava deposit. In the Quebec Appalachian deposits, basinal brines, expelled tectonically, were the most likely metal carriers; these deposits constitute an ore type that differs from other known sandstone-hosted lead deposits.     

Shale basins,sulfur-deficient ore brines and the formation of exhalative base metal deposits

The massive sulfide deposits of the Iberian Pyrite Belt are interbedded with felsic volcanic rocks and shale, and underlain by several thousand meters of siliciclastic sedimentary rocks known as the PQ Group. Isotope geochemistry and regional geology are both consistent with equilibration of the ore-forming fluids with the PQ Group, prior to ore deposition near the former seafloor. The average Cu:Zn:Pb ratio of the PQ Group rocks (ca. 26:55:19) is similar to the weighted average of all the massive sulfide orebodies combined (ca. 25:52:23).The genetic relationship between massive sulfide deposits and a siliciclastic sedimentary metal source is explained here by a thermodynamic model, proposing that mildly reducing redox conditions imposed by equilibration with the sedimentary rocks are most critical for the formation of an effective ore-forming fluid. Relatively metal-rich but organic-poor pyrite-bearing shale undergoing dewatering of saline pore fluids is an effective source for the generation of sulfur-deficient but relatively iron and base metal-rich brines. Thus, we propose that the giant deposits of the Iberian Pyrite Belt owe their existence not to exceptionally metal-enriched (e.g., magmatic) fluids, but to the existence of a fairly ordinary but large metal source in reactive siliciclastic sediments, combined with an underlying igneous heat source and a particularly efficient mechanism of sulfide precipitation by mixing with H₂S-rich fluids at or near the seafloor.Essentially similar mineral equilibria are imposed when saline fluids are buffered by typical continental basement rocks. Leaching of retrograde minerals and possibly residual salts from their magmatic or metamorphic prehistory is expected to generate similar, variably metal-rich but relatively sulfide-deficient fluids. Thus, the existence of mildly reducing rocks can be the dominant chemical control in the source of fluids generating many volcanogenic, Irish-type or sedex deposits, many of which are known to precipitate their metal load in response to biogenic sulfide addition at the ore deposition site.     

琼东南盆地陵水组层序地层与沉积相分析

利用高分辫率层序地层学方法,结合岩心?测井和地震资料,识别琼东南盆地陵水组各级层序界面,建立地层层序格架,探讨地层格架下沉积相类型?演化规律以及平面展布,并就有利沉积相带分布进行了讨论?结果表明:从测井资料看出,层序界面识别标志主要为岩性和颜色发生突变;将琼东南盆地陵水组划分为3 个三级层序(Els1?Els2和Els3);结合测井响应特征,对地震剖面进行精细刻画,在3 套三级层序中识别出辫状河三角洲?扇三角洲?滨海?陆棚?碳酸盐台地等5种沉积相?     

The role of dense brines in the formation of vent-distal sedimentary-exhalative (SEDEX) lead–zinc deposits: field and laboratory evidence

A majority of the world's sediment-hosted exhalative (SEDEX) lead-zinc deposits are vent-distal. They are not underlain by a discordant alteration zone or stockwork vent complex that would indicate the path by which ore fluids reached the seafloor. The absence of a vent complex, together with sulfide mineral replacement of host rock mineral assemblages has led several investigators to suggest that, in spite of the well-layered nature of these deposits, mineralization was formed by sub-seafloor lateral migration of ore fluids along permeable strata. Field observations, supported by simple laboratory experiments, however, suggest an alternative process for characterizing the genesis of vent-distal SEDEX deposits. Cool, saline brines (e.g., ~120 °C and >15 wt% NaCl equiv.) are denser than seawater and, upon discharging into the sea, would flow away from the discharge vent as bottom-hugging fluids, similar to the behavior of turbidity currents. Their high densities and velocities prevent them from mixing with overlying seawater, thereby precluding significant cooling and dilution of the ore fluid. Upon coming to rest in a seafloor depression, the addition of H₂S and/or dilution of the ore fluids to lower salinities result in the eventual precipitation of a vent-distal SEDEX deposit. Furthermore, the dense ore-forming fluid can sink into permeable sediments beneath the brine pool by displacing less dense pore water. The ore fluids are thus capable of effectively overprinting and/or replacing pre-existing minerals in the consolidating sediment pile.     

准噶尔盆地东北部逆冲推覆构造特征

准噶尔盆地东北部乌伦古坳陷内的断裂主要发育在坳陷周缘和中部,平面上以北西-南东向、北北西向和近东西向逆冲-走滑断层为主,地震剖面上显示为基底卷入型断层。存在坡坪式、叠瓦式、双重式、背冲式、对冲式等多种逆冲推覆构造样式。研究区内断裂的生长指数揭示主要断裂以及断裂体系其中生代活动强度具有横向和纵向的迁移规律:横向上,东早西晚,有自东向西的拓展演化规律;纵向上,主控断裂随时间由红盆断裂依次向红盆南断裂、喀拉萨依断裂转变,断裂活动中心由北东到南西迁移。西北部变形较东南部变形弱,受力方向来自北东和南东方向。     

塔北-塔中盆地三叠纪陆相层序地层划分及沉积演化

塔里木盆地的三叠纪除早三叠世有短暂的海侵外,其余时间均表现为典型的内陆盆地,发育扇-扇三角洲-湖泊沉积体系。三叠纪的塔里木盆地被北部的沙雅隆起剥蚀区和中、西部的塔中剥蚀区分割成南天山前的库车盆地,昆仑山前的塔西南盆地,阿尔金山前的塔东南盆地和中央的塔北-塔中盆地。前三个盆地的三叠系的残留面积不大,其石油地质意义仅表现在生烃方面。而塔北-塔中盆地的三叠系的残留面积大,构成了塔里木盆地三叠系分布的主体,也成为塔里木盆地油气勘探的主要目的层之一。
塔北-塔中盆地的三叠系包含了长周期、中周期和短周期三个级别的基准旋回,其包含有由不整合限定Ⅰ、Ⅱ两个长周期,长周期Ⅰ中可识别一个中周期(Ⅰ₁);长周期Ⅱ中可识别出三个中周期(Ⅱ₁,Ⅱ₂,Ⅱ₃)。塔北-塔中盆地三叠系-侏罗系的有利储集相带与中周期低水位体系域关系密切。盆地中三叠系的3套重要含油气储层Ⅲ油组(T₂a),Ⅱ油组(T₂a)和Ⅰ油组(T₃h),分别对应三个中周期的Ⅱ₁,Ⅱ₂和Ⅱ₃。     

若尔盖盆地黄河第一湾河岸沉积地层序列及其成因研究

经过在若尔盖盆地进行全面野外考察,在黄河第一弯岸边发现了沉积序列清晰的、具有代表性的完整沉积地层剖面。通过沉积学和地层学特征和沉积相的观测分析,结合实验室粒度分析、数据处理和测年断代,其结果表明：该剖面底部蓝灰色古湖相沉积层反映出盆地内部在OSL年龄35 ka之前为较深的湖泊。其上覆盖的风沙与泥炭互层,反映出在该区域湖水消失之后,在30 ka之前古湖底出现泥炭沼泽,同时风沙作用盛行。而浊黄橙色古洪水沉积层（OFD1）则反映出在30~27 ka之间,曾经有来自于黄河源区流域的规模巨大的洪水进入若尔盖盆地,在古湖底泛滥并且将其携带的分选良好的细沙与粉沙质泥沙堆积下来。该剖面中部厚度达5~7 m的河漫滩-风沙层,沿着河岸追索,则可见其表现为高低起伏的古沙丘。这表明在末次冰期盛期和冰消期,气候干旱寒冷,黄河已经下切形成其河槽,其河漫滩沉积物被强劲的风力吹扬,形成连绵起伏的沙丘。该层之上所覆盖的浊黄橙色古洪水沉积层（OFD2）,则反映出在全新世初期9.86~8.28 ka之间,来自于黄河源区流域的大洪水再次进入盆地,在黄河第一湾两岸的古湖底沉积了分选良好的细沙质与粉沙质的泥沙。到了全新世中期后,若尔盖盆地风沙作用依然盛行,黄河河槽深切,第一湾两岸接受沙尘暴沉积。在全新世中期的相对温暖湿润气候条件之下,沙尘暴沉积物被改造为亚高山草甸黑土类土壤,成熟度极高。到了全新世晚期以来,风沙作用与沙尘暴沉积过程持续,沙尘暴沉积物也被改造为亚高山草甸黑土层。本文研究对于深入理解黄河源区末次冰期以来环境变化与地表过程演变,以及晚更新世以来的气候水文变化规律具有重要的科学意义。     

赣东北早中侏罗世层序地层、沉积体系及陆盆演化

在赣东北１／５万地质填图及上饶县清水乡缪源村下中侏罗统实测剖面基础上,提出林山组、罗坳组层序地层划分方案,分析了沉积体系的４种类型（冲积扇辫状河体系,辫状三角洲体系,湖泊三角洲与湖沼体系,曲流河体系）,编制了赣东北地区早侏罗世古地理略图,总结了侏罗纪陆盆演化的５个发展阶段。     

Mudstone lithogeochemistry and formation conditions of Vendian deposits in the Shkapovo-Shikhan Basin

Variation of geochemical modules and indices in mudstones from the Upper Vendian Kairovo and Shkapovo groups of the Shkapovo-Shikhan Basin provides the comprehensive information on changes in maturity of the fine aluminosiliciclastic material delivered in the basin, characterizes the redox environment in bottom water, and makes it possible to reconstruct the rock composition in provenance and its evolution through time. The generally moderate maturity of the fine terrigenous clastic material suggests that a nearly semiarid-semihumid climate dominated in paleodrainage area throughout the Late Vendian. It has been established that reducing environment did not exist in bottom water of the central Shkapovo-Shikhan Basin throughout the Late Vendian. Intermediate rocks prevailed in the paleodrainage area. More silicic rocks could occur only in the early Staropetrovo and late Salikhovo times. Data points of mudstones from the Kairovo and Shkapovo Groups plotted on the Cr-Ni, Co-V, Co/Hf-Ce/Cr, La-Th, and La/Sm-Sc/Th diagrams indicate that both Archean and more mature Paleoproterozoic crustal blocks existed in different proportions in the Late Vendian within source areas.     

Early Miocene lacustrine deposits and sequence stratigraphy of the Ermenek Basin,Central Taurides,Turkey

The lacustrine Ermenek Basin evolved as a SE-trending intramontane graben affected by strike–slip deformation, with the initial two lakes merging into one and receiving sediment mainly through fan deltas sourced from the basin's southern margin. The northern margin was a high-relief rocky coast with a wave-dominated shoreline. The Early Miocene lacustrine sedimentation was terminated by a late Burdigalian marine invasion that drowned the basin and its surroundings. The lacustrine basin-fill succession is up to 300 m thick and best exposed along the southern margin, where it consists of four sequences bounded by surfaces of forced regression. The offshore architecture of each sequence shows a thin lowstand tract of shoreface sandstones overlain by a thick transgressive systems tract of mudstones interbedded with sandy tempestites and delta-derived turbidites, which form a set of coarsening-upward parasequences representing minor normal regressions. The corresponding nearshore sequence architecture includes a thick lowstand tract of alluvial-fan deposits overlain by either a well-developed transgressive systems tract (backstepping parasequence set or single fan-deltaic parasequence) and poorly preserved highstand tract; or a thin transgressive tract (commonly limited to flooding surface) and a well-developed highstand tract (thick fan-deltaic parasequence). The sequences are poorly recognizable along the northern margin, where steep shoreline trajectory rendered the nearshore system little responsive to lake-level changes. The resolution of local stratigraphic record thus depends strongly upon coastal morphology and the character of the depositional systems involved.The sequential organization of the basin-fill succession reflects syndepositional tectonics and climate fluctuations, whereas the lateral variation in sequence architecture is due to the localized sediment supply (deltaic vs. nondeltaic shoreline), varied coastal topography and differential subsidence. The study points to important differences in the sequence stratigraphy of lacustrine and marine basins, related to the controlling factors. A crucial role in lacustrine basin is played by climate, which controls both the lake water volume and the catchment sediment yield. Consequently, the effects of tectonics and the dynamics of changes in accommodation and sediment supply in a lacustrine basin are different than in marine basins.     

四川盆地东南缘河坝MVT铅锌矿与古油气藏的成生关系

MVT铅锌矿与(古)油气藏在空间上的密切共生/伴生关系,说明成矿与成藏具有密切的成因联系。四川盆地东南缘的河坝铅锌矿产于震旦系灯影组古油气藏中,虽然二者在空间上密切共生,但铅锌矿的规模远较古油气藏的规模小。形成铅锌矿的流体具有较高的盐度(w(NaCl)=21.33%~23.83%)并富含有机质,成矿流体的峰温为122~134 ℃。与闪锌矿共生萤石的Rb Sr和Sm Nd同位素年龄显示成矿发生于128~130 Ma。研究区的古油气藏先后经历了多期成藏与破坏。奥陶纪-中志留世时期第一次成藏,加里东期末被破坏;二叠纪-中三叠世时期二次生烃形成油藏,晚三叠世-侏罗纪时期随着埋藏深度增加,石油发生热裂解形成古气藏,燕山期古气藏被破坏。铅锌矿的成矿仅与石油的热裂解和古气藏的破坏密切相关。石油热裂解形成硫化氢,热裂解过程中的超压使硫化氢溶于水为铅锌矿成矿提供硫源,构造隆升造成古气藏破坏,含硫化氢的油田卤水与成矿流体混合成矿。     

沉积物演化与某些层控矿床的形成

产于沉积建造包括火山沉积建造中的许多层控金属矿床,往往是沉积盆地内沉积物在沉积期后不同演化阶段上的派生产物。弥满在沉积物中的地层水,在沉积建造所经历的沉积、成岩、后生直至变质的不同演化阶段,水温和水质也随之发生变异,从而对分散在沉积物中的不同金属成矿物质具有不同淋滤萃取能力,使它们有先有后地发生迁移,而后在地球化学障壁部位尤其是在不同水质的混合带附近发生沉淀,形成不同矿化特色的矿床。每一个汇水-径流-排泄单元,就是一个成矿地质单元。这些矿床的控矿地质因素,很大程度上就是控制沉积物形成和演化的因素,尤其是控制地层水水温水质演他和活动规律的古水文地质因素,与油气藏的形成既有相似之处也有差别。     

塔河油田石炭系卡拉沙依组层序地层及沉积相研究

石炭系卡拉沙依组作为塔河油田碎屑岩领域主要产层之一,其沉积相类型及分布一直存在争议。本文通过井震结合,建立了该区的高精度层序地层格架。通过岩心观察,利用地震、测井、分析化验等资料,确定了沉积体系的类型,并开展了沉积相类型和展布的研究。研究表明,卡拉沙依组可划分为两个三级层序,其中层序CKLSQ1可划分为3个体系域,分别为低位体系域、海侵体系域和高位体系域;层序CKLSQ2可划分为两个体系域,分别为海侵体系域和高位体系域。沉积相为三角洲和潮坪相交互沉积,其中北部以三角洲相为主,南部盐上区以潮坪相为主,中部的盐边区为两者的过渡带。该认识为目的层段窄薄砂体的预测和精确刻画提供了地质依据。     

四川盆地南部下寒武统筇竹寺组页岩沉积微相研究

页岩气是我国未来一个重要的且比较现实的非常规油气资源,加强该领域的基础研究对页岩气油气成藏理论创新、页岩气开采技术运用和资源量的准确计算都非常必要.因此,本文运用野外露头资料、钻取岩芯和测井资料,以及页岩有机地球化学分析化验结果等大量第一手资料,通过详细分析四川盆地南部下寒武统筇竹寺组页岩沉积微相特征及其含气性特征,并结合研究区沉积相标志和测井相特征,明确指出泥质深水陆棚微相是四川盆地南部下寒武统筇竹寺组优质页岩最有利沉积微相带.     

鄂尔多斯盆地东缘保德地区上古生界层序地层与沉积相特征*

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