Evaluating new fault-controlled hydrothermal dolomitization models: Insights from the Cambrian Dolomite,Western Canadian Sedimentary Basin

Fault-controlled hydrothermal dolomitization in tectonically complex basins can occur at any depth and from different fluid compositions, including ‘deep-seated’, ‘crustal’ or ‘basinal’ brines. Nevertheless, many studies have failed to identify the actual source of these fluids, resulting in a gap in our knowledge on the likely source of magnesium of hydrothermal dolomitization. With development of new concepts in hydrothermal dolomitization, the study aims in particular to test the hypothesis that dolomitizing fluids were sourced from either seawater, ultramafic carbonation or a mixture between the two by utilizing the Cambrian Mount Whyte Formation as an example. Here, the large-scale dolostone bodies are fabric-destructive with a range of crystal fabrics, including euhedral replacement (RD1) and anhedral replacement (RD2). Since dolomite is cross-cut by low amplitude stylolites, dolomitization is interpreted to have occurred shortly after deposition, at a very shallow depth (<1 km). At this time, there would have been sufficient porosity in the mudstones for extensive dolomitization to occur, and the necessary high heat flows and faulting associated with Cambrian rifting to transfer hot brines into the near surface. While the δ¹⁸O_water and ⁸⁷Sr/⁸⁶Sr ratios values of RD1 are comparable with Cambrian seawater, RD2 shows higher values in both parameters. Therefore, although aspects of the fluid geochemistry are consistent with dolomitization from seawater, very high fluid temperature and salinity could be suggestive of mixing with another, hydrothermal fluid. The very hot temperature, positive Eu anomaly, enriched metal concentrations, and cogenetic relation with quartz could indicate that hot brines were at least partially sourced from ultramafic rocks, potentially as a result of interaction between the underlying Proterozoic serpentinites and CO₂-rich fluids. This study highlights that large-scale hydrothermal dolostone bodies can form at shallow burial depths via mixing during fluid pulses, providing a potential explanation for the mass balance problem often associated with their genesis.     

Hydrogen isotopic compositions of individual alkanes as a new approach to petroleum correlation: case studies from the Western Canada Sedimentary Basin

Isotopic compositions of carbon-bound hydrogen in individual n-alkanes and acyclic isoprenoid alkanes, from a number of crude oil samples, were measured using gas chromatography-thermal conversion-isotope ratio mass spectrometry. The precision of this technique is better than 3‰ for most alkanes, compared to the large range of δD variation among the samples (up to 160‰). The oils were selected from major genetic oil families in the Western Canada Sedimentary Basin, with source rocks ranging in age from Ordovician (and possibly Cambrian) to Cretaceous. The hydrogen isotopic composition of alkanes in crude oils is controlled by three factors: isotopic compositions of biosynthetic precursors, source water δD values, and postdepositional processes. The inherited difference in the lipid's biosynthetic origins and/or pathways is reflected by a small hydrogen isotopic variability within n-alkanes, but much larger differences in the δD values between n-alkanes and pristane/phytane. The shift toward lighter hydrogen isotopic compositions from Paleozoic to Upper Cretaceous oils in the WCSB reflects a special depositional setting and/or a minor contribution of terrestrial organic matter. The strong influence of source water δD values is demonstrated by the distinctively lower δD values of lacustrine oils than marine oils, and also by the high values for oils with source rocks deposited in evaporative environments. Thermal maturation may alter the δD values of the alkanes in the oil to some extent, but secondary oil migration does not appear to have had any significant impact. The fact that oils derived from source rocks that could be of Cambrian age still retain a strong signature of the hydrogen isotopic compositions of source organic matter, and source water, indicates that δD values are very useful for oil-source correlation and for paleoenvironmental reconstructions.     

Petroleum systems modeling in tectonically complex areas — A 2D migration study from the Neuquen Basin, Argentina

A roughly 30 km 2D section across the Faja Plegada y Corrida del Agrio in the Neuquen Basin, Argentina, is the basis for a petroleum systems study, including structural restoration through time, deposition and erosion, pressure, temperature and migration modeling. Integrating tectonic and petroleum systems modeling proved critical to properly evaluate sub-thrust plays. Multi-dimensional modeling of dynamic processes allows accurate assessment and prediction of the potential of petroleum systems in tectonically complex areas such as the Neuquen Basin.     

巴彦浩特盆地石炭系物源及沉积相研究

通过岩石薄片分析和石英阴极发光特征,对巴彦浩特盆地石炭系进行物源分析.结果表明,该盆地石炭系存在北部阿拉善古陆、东南部陇西古陆、西部龙首山隆起及东部骡子山隆起4个物源方向,母岩分别为太古界及元古界变质岩、前石炭系沉积岩及加里东期岩浆岩.古物源与沉积体系具良好空间配置关系,通过野外剖面观察,结合物源和相标志,认为研究区石炭系早期主要受阿拉善古陆影响,发育障壁海岸和混积陆棚相,中晚期受多物源共同影响,发育障壁海岸、无障壁海岸、扇三角洲、曲流河三角洲和混积陆棚相.     

塔里木盆地玉北地区奥陶系沉积相与沉积演化模式

在塔里木盆地玉北地区奥陶系层序地层格架建立的基础上,通过对岩心、钻井、测井、地震及古生物等相关资料分析,以地震地层学和海相碳酸盐岩沉积模式为指导,对玉北地区奥陶系沉积相进行详细的研究,结果表明研究区奥陶系可划分为台地潮坪、局限台地、开阔台地、台地边缘、陆架内缘斜坡和陆棚等6种沉积相,并明确了研究区奥陶纪各期沉积相平面展布特征,总结了纵向上的沉积演化规律为:早奥陶世早期发育台地潮坪相;早奥陶世晚期随着海平面的持续缓慢上升,过渡为局限台地相;中奥陶世演化为开阔台地相;晚奥陶世早期演变为斜坡相,至晚奥陶世中晚期则发育陆棚相沉积体系。综合考虑古地理沉积环境、沉积相平面组合规律及控制因素,建立了玉北地区奥陶系沉积演化模式。     

鄂尔多斯盆地子洲地区上古生界沉积相及演化特征

在对大量钻井岩心观察分析的基础上, 结合鄂尔多斯盆地区域地质背景, 利用岩性、古生物、沉积构造、粒度分析、地球化学特征等鉴别沉积标志特征, 分析鄂尔多斯盆地子洲地区晚古生代各时期沉积相特征, 总结其演化规律.晚古生代研究区共发育5种沉积体系, 分别是障壁海岸沉积体系、浅海陆棚沉积体系、曲流河三角洲沉积体系、辫状河三角洲沉积体系以及湖泊沉积体系.研究区晚古生代沉积演化经历两大阶段.重点分析山西期与石盒子早期盒8期沉积环境, 子洲地区山西组沉积为水下还原环境, 受河流三角洲作用控制, 仅在山西组早期研究区南部受到短期海泛的影响; 石盒子早期研究区处于完全的淡水环境, 受辫状河三角洲作用控制.晚古生代沉积时气候特点体现出由温暖潮湿气候向半干旱—干旱气候转变, 沉积体系表现为由海相、海陆过渡相向陆相过渡转变的特点.     

汾渭盆地古近系—新近系沉积特征

汾渭盆地位于鄂尔多斯地块与秦岭造山带的衔接部位,地理位置十分特殊。作为一个新生代断陷盆地,在周缘及内部一系列断裂带控制下,具有边断、边陷、边沉积的特征,新生代地层厚度逾几千米。本文根据大量野外露头及相关钻井资料,综合岩石学、沉积构造、古生物化石、测井及区域地质资料,系统研究了汾渭盆地古近系—新近系各时期的沉积相特征。结果表明,新生代汾渭盆地发育冲积扇、河流、三角洲、湖泊及风成沉积5种沉积类型。盆地边缘及山前主要发育冲积扇沉积,向盆地中心逐渐过渡为河流、三角洲及湖泊沉积,风成堆积集中分布于盆地边缘。各次级盆地沉积演化具有差异性,除三门峡地区外,汾渭盆地主体自晚始新世开始沉积并持续至渐新世早期;渐新世晚期在经历隆升剥蚀作用后,中新世再次沉降,沉积范围逐渐扩大;至晚中新世,渭河盆地的西安凹陷、固市凹陷两大沉积区以及三门峡—芮城、运城—永济一线均为湖相分布区。上新世湖盆沉积范围达到最大,湖泊广泛分布,盆地边部则大量发育风成沉积。     

鄂尔多斯盆地丰富川油田西部探区延长组沉积演化特征研究

丰富川油田西部探区为多层系低渗透复合含油区,储层沉积类型复杂多样,沉积演化在很大程度上控制着油藏的富集。利用钻井、岩心、测井、生产动态等资料,深入分析了该区主要含油层系延长组长2、长4+5、长6沉积相标志、物源方向、沉积构造等特征,建立了多期沉积序列体系,并进行沉积演化特征分析。研究结果表明,延长组主要发育为三角洲沉积体系;沉积物主要通过分流河道由北东向南西输入湖盆,不同时期发育的河道展布继承性较好,充分阐明了该区延长组主要含油层段的沉积规模与沉积演化特征;在同一小层内部,河道展布的继承性较好,且组成的良好储盖组合,为油田下步勘探与寻找油藏富集有利区提供可靠保障。     

四川盆地环开江——梁平海槽长兴组——飞仙关组沉积模式

在综合分析的基础上确定了环开江--梁平海槽长兴组--飞仙关组的层序划分方案,长兴组和飞仙关组均可划分出两个三级层序.在层序格架内进行了岩相古地理的编图及演化分析,认为在台地边缘不同地区具有不同的岩相古地理特征,发育不同类型的台地边缘.结合地震资料及钻井资料建立了台地边缘的三种沉积模式:(1)以剑阁地区为代表的"进积型台...     

四川盆地西部中二叠统茅口组油气地质条件及勘探潜力

四川盆地西部中二叠统茅口组为碳酸盐岩浅水缓坡相沉积,高能浅滩亚相颗粒岩发育。茅口组沉积末期,研究区古表生岩溶作用强烈,有利于岩溶储层发育。中二叠统发育栖霞组和茅口组碳酸盐岩、梁山组泥质岩等多套烃源岩,烃源岩厚度大,品质较好;各套烃源岩从中三叠世末起相继达到生烃高峰,资源潜力大。茅口组中上部发育两类储层:裂缝-孔洞型(或裂缝型)储层和白云岩孔隙型储层。钻井及露头剖面揭示茅口组含气性好。高能滩相沉积区与岩溶斜坡带叠合区是茅口组储层发育的有利地区。茅口组之上的区域盖层发育,保存条件好。认为川西地区茅口组具有良好的天然气勘探前景。     

Thermochemical sulphate reduction in the Upper Devonian Cairn Formation of the Fairholme carbonate complex (South-West Alberta, Canadian Rockies): evidence from fluid inclusions and isotopic data

The Fairholme carbonate complex is part of the extensively dolomitized Upper Devonian carbonate reefs in west-central Alberta. The studied formations contain moulds (up to 10 cm in diameter), which are filled partially with (saddle) dolomite, quartz and calcite cements. These cements precipitated from a mixture of brines that acquired high salinity by dissolution of halite and brines derived from evaporated sea water. The fluids were warm (homogenization temperature of primary fluid inclusions of 76 to 200 °C) and saline (20 to 25 wt% NaCl equivalent) and testify to thermochemical sulphate reduction processes. The latter is deduced from S in solid inclusions, CO₂ and H₂S in volatile-rich aqueous inclusions and depleted δ¹³C values down to −26‰ Vienna Pee Dee Belemnite. High ⁸⁷Sr/⁸⁶Sr values (0·7094 to 0·7110) of the cements also indicate interaction of the fluids with siliciclastic sequences. The thermochemical sulphate reduction-related cements probably formed during early Laramide burial. Another (younger) calcite phase, characterized by depleted δ¹⁸O values (−23·9‰ to −13·9‰ Vienna Pee Dee Belemnite), low Na (27 to 37 p.p.m.) and Sr (39 to 150 p.p.m.) concentrations and non-saline (∼0 wt% NaCl equivalent) fluid inclusions, is attributed to post-Laramide meteoric water.     

川西北部泥盆系观雾山组沉积相新认识——以大木垭剖面与何家梁剖面为例

川西泥盆系观雾山组沉积相研究缺乏横向对比,沉积模式还存在争议。根据川西北部白家乡大木垭剖面与何家梁剖面实测成果,对中泥盆统观雾山组沉积相进行了分析,认为:大木垭剖面与何家梁剖面观雾山组为碳酸盐镶边台地沉积,期间发生短暂的碳酸盐缓坡化;桂溪剖面观雾山组同属碳酸盐台地边缘,观雾山组中段发育开阔台地深水沉积,并不是前人认为的潟湖沉积。研究区碳酸盐镶边台地包括台地边缘和前缘斜坡两种亚相,前缘斜坡亚相发育于何家梁剖面,以塌积岩沉积为标志。碳酸盐缓坡包括深水缓坡和浅水缓坡两种亚相。随着海平面变化,观雾山组碳酸盐岩发育三个沉积旋回,第一、第三沉积旋回为镶边台地沉积,第二沉积旋回为碳酸盐缓坡沉积。观雾山组沉积微相对储层的分布起控制作用:生物碎屑滩和上斜坡微相为有利储层发育相带;生物礁中在油气运移之前形成的溶蚀孔洞已被白云石和方解石充填,滩间微相泥质(泥晶)白云岩不利于溶蚀孔洞形成,这二者均不是有利储层发育相带。     

鄂尔多斯盆地南部下奥陶统马家沟组沉积特征

依据鄂尔多斯盆地南部早奥陶世古构造、古地理、古水动力以及古气候背景,结合单井、野外露头沉积相分析等认为,秦岭海槽和中央古隆起的存在和演化控制盆地南部马家沟组沉积特征及演化。(1)平面上根据中央古隆起的障壁作用将其分为两大沉积区,西南区和东北区。西南区发育盆地—斜坡—台地边缘相,东北区为障壁潟湖沉积环境;(2)东北区马家沟组由"三云三灰"六段组成,马一、马三、马五段为白云岩、石膏和石盐组成的蒸发岩系,马二、马四、马六段为石灰岩夹白云岩的碳酸盐岩序列,在纵向上构成蒸发岩与碳酸盐岩间互的旋回性沉积。在此基础上进一步建立了马家沟组障壁潟湖沉积模式,该模式具有两个主要特征:(1)中央古隆起作为障壁控制秦岭海与潟湖之间的海水沟通;(2)依据海平面升降旋回将该模式动态地分为三个阶段,即与海侵期相对应的以石灰岩沉积为主的障壁潟湖沉积阶段(阶段Ⅰ)、与海退期相对应的以石灰岩夹蒸发岩沉积为主的障壁咸化潟湖沉积阶段(阶段Ⅱ)和与低海平面期对应的以膏盐岩沉积为主的障壁膏盐湖沉积阶段(阶段Ⅲ)。     

沉积盆地波动过程分析方法与应用 --以四川盆地东北部为例

介绍了沉积盆地波动过程分析的基本概念、发展过程、方法原理、研究步骤与应用范围,并应用此研究方法对四川盆地东北部波动过程进行了分析。通过划分波动单元、建立地层格架、恢复原始沉积厚度、计算沉积速率等步骤,建立反映盆地沉积—剥蚀过程的波动方程。应用此方程分析盆地的主要演化周期,总结沉积中心迁移规律,识别不整合面并计算剥蚀量,划分成藏旋回,识别波动转换带。此方法在中国南方海相沉积盆地可有较好的应用前景。     

柴达木盆地西部地区新生代沉积与构造演化

［摘要］新生代柴西地区南北变形具有很好的对称性,盆地边缘发育高角度逆冲断层,古近纪时期库木库里和苏干湖盆地与柴达木盆地相连,据此认为柴西地区是地壳纵弯褶皱的机制下形成的新生代向斜沉降区。其构造演化经历了古新世~渐新世早期纵弯褶皱形成、晚渐新世~中新世纵弯褶皱发展和晚期盆内断褶构造强烈活动三个阶段,控制了相应时期的沉积边界和沉积相分布。古近纪时期库木库里盆地和苏干湖盆地是柴达木盆地的一部分,新近纪以来,由于盆缘逆冲断层的活动,库木库里和苏干湖盆地逐步与柴达木盆地分割开来。据此认为盆地中部一里坪地区和盆地边缘的油气勘探有较大潜力。     

Research on Paleoecology of Middle Permian-Middle Triassic in the Western Sichuan Basin

The research area is located in the western part of Sichuan basin as a Yangtze ecotope of Cathaysian Tethyan area. It is dominated by benthic fauna, including brachiopods, Fusulinids, corals, bivalves, foraminifers, ammonites, bryozoans,Crinoids and pleopods which are less common with traces of trilobites, stromatoporas, nautilus and sporopollens seen in one or two areas,which are obviously controlled by sedimentary environments and in accordance with sedimentary facies.Through the analysis of fossils and research on burial characteristics from middle Permian middleTriassic, based on the combination of the feature of fossils in time and space, seventeen communities are recognized, the coposition, construction and palaeoenvironment of each community are expounded. Study shows that different ecological type biocoenose are distributed in different locations, which are mainly represented by sessile benthic community in the main research area, composed of Mianzhu, Mianyang, Deyang and Santai and nektonic community in marginal areas in the research area subdivided into two parts: Areas around Guangyuan-Nanjiang-Tongjiang, located at the margins in the northeast of the research area, and areas around Wenchuan-Maoxian-Dayidafeishui situated at the western borders of the research area. According to the combination of communities with sedimentary characteristics,six kinds of biofacies have been recognized and described in the study area and biofacies pattern are established. Category,ecotype, typical community and sedimentary facies of each biofacies are elucidated in this paper. The subdivision and analysis of community are meaningful for the studies of paleoenvironment ,paleogeography and their evolutions,The research of biaofacies is important for the recovery of paleobiogeography and paleoplate tectonic characteristics.     

蒸发岩序列中氯化物盐的氯同位素分馏效应及应用——兼论塔里木盆地、柴达木盆地古代岩盐的沉积阶段

卤水蒸发析盐到晚期阶段,才有可能析出溶解度极大的钾盐类矿物,因此在一个成盐盆地要找到钾盐矿床,除判断物源特征外,还必须找到最晚沉积阶段的区域和层位。本文通过对实验室配制溶液和盐湖卤水蒸发析出的不同氯化物矿物、钾盐矿床沉积序列不同阶段盐类矿物对比分析,讨论了氯同位素的分馏规律。结果表明,不同蒸发浓缩阶段的氯化物盐,氯同位素发生显著分馏。一般钾盐沉积层位的石盐δ³⁷Cl值小于0,钾石盐及其以后沉积的氯化物δ³⁷Cl值小于-0.5‰,特别是钾石盐以后析出的氯化物更为偏负,光卤石一般小于-1.00‰,而钾盐沉积阶段之前早期沉积石盐的δ³⁷Cl值显著偏正。因此,δ³⁷Cl值是判断岩盐沉积阶段的有效指标。基于此,对塔里木库车盆地第三纪、莎车盆地白垩-第三纪部分代表性盐矿点以及柴达木盆地西部不同构造单元、不同层位第三纪岩盐沉积做了氯同位素分析。初步结果表明塔里木莎车盆地晚白垩世岩盐的沉积阶段明显晚于库车盆地第三纪沉积,特别是莎车盆地喀什次级凹陷δ³⁷Cl值最低,大部分样品小于-0.5‰,推测该区成盐古卤水已浓缩到晚期或接近晚期钾盐沉积阶段,应是今后一重点开展钾盐找矿的区域。柴达木盆地油墩子、南翼山地区中新统、上新统蒸发岩沉积序列δ³⁷Cl值普遍偏正,推测当时卤水浓缩演化可能只达到石盐沉积阶段,浓缩到后期阶段的富K⁺、Mg²⁺盐溶液随西部隆起迁移到柴达木盆地南部地区,因此认为第三纪地层虽然石盐沉积层位多,厚度大,但找到大规模钾盐矿床的可能性不大。     

鄂尔多斯盆地及周缘地区晚古生代沉积演化

基于笔者多年对鄂尔多斯盆地及周缘地区晚古生代研究成果,结合野外剖面实测、钻井资料分析、地层学与层序地层学、地球化学、年代学等研究结果,从岩性特征、地层厚度、地层接触关系、物源分析、沉积相类型多方面进行对比研究,认为鄂尔多斯盆地及周缘地区上古生界是华北地台的一部分,因此,其沉积充填及沉积演化研究必须置于晚古生代大华北盆地之中。在此研究基础上绘制了晚古生代各组鄂尔多斯盆地及周缘沉积相平面展布图,亮点是向东部和南部进行了扩张,并详述了晚古生代沉积演化过程,为该时期华北地台原始沉积面貌的恢复提供了新的依据。     

Fluid-dynamics driving saline water in the North East German Basin

In several areas of the North German Basin, saline water comes close to, or even reaches the surface. Available data from wells indicate that brine stratification is under unstable conditions in the deeper underground. In order to analyse the possible transport mechanisms, 3D thermohaline simulations have been carried out for two different scenarios. The 3D regional model (230×330 km) indicates that salty water is driven to the surface by hydrostatical forces from the surrounding highlands. In addition, a smaller scale model (10×10 km) has been constructed with a grid resolution accounting for possible convective flow. The results indicate that convective flow may play a dominant role in areas with minor topography. In summary, the complex pattern of near surface occurrences of saline water probably results from the interaction of hydrostatic and thermal forces.     

Muglad盆地Unity凹陷及邻区AG2段沉积相与沉积模式分析

通过研究沉积相与沉积模式,明确有利砂体展布特征对岩性—地层油气藏勘探具有重要意义。Muglad盆地Unity凹陷Abu Gabra组2段（简称AG2,下同）沉积特征及平面展布尚不明确,制约着岩性—地层油气藏的勘探工作。本文针对该问题,综合利用测井、录井、地震等资料,运用经典层序地层学理论以及构造演化分析,揭示了Unity凹陷AG2段沉积特征并建立了辫状河三角洲—湖泊沉积模式。研究结果表明：研究区AG2段的物源区为东部Toor凸起,凹陷内主要发育三角洲相及湖泊相,凹陷东部边缘发育冲积扇相;三角洲相、冲积扇相发育区均可成为有利的岩性地层油气藏勘探区。研究成果可为Unity凹陷岩性—地层油气藏有利区带优选提供科学依据。