Early Jurassic anoxic conditions and organic accumulation in the eastern Tethys

The Bilong Co oil shale, located in the South Qiangtang depression, northern Tibet Plateau, may record the Early Jurassic anoxic event in the eastern Tethys. New geochemical data from the Bilong Co oil shale section are presented in order to determine the mechanism of organic accumulation and to evaluate Early Jurassic anoxia in the eastern Tethys. In organic-rich oil shales, many redox proxies including the relationship of Mo to total organic carbon (TOC), Re/Mo ratios, and pyrite framboid size distribution suggest deposition under euxinic conditions. However, the correlation between TOC and P and Mo contents indicates that organic matter accumulation was controlled mainly by primary productivity. The Sr/Al ratios and clastic influx proxies such as Si, Ti, Th, Zr, and Al concentrations suggest a continuous supply of fresh water from a nearby continent during oil shale deposition. This supply could have initiated stratification of the water so that the upper zone became favourable for marine life. Increased primary productivity could have led to formation of anoxic/sulphidic bottom waters, which enhanced the preservation of organic matter. Deposition of organic-rich oil shales terminated when primary productivity decreased, leading to more oxic bottom water conditions.     

North Atlantic climatic events recorded in Aptian Naskapi Member cores,Scotian Basin

Early Aptian black laminated organic mudstones, including the Selli Level, are recognized over large areas of Tethys and western European basins. This interval was investigated in a 75 m-thick continuously cored section of varicoloured shale in the lower Naskapi Member from the Panuke B-90 well in the Scotian Basin, offshore eastern Canada. This study complements the palaeogeographic range of correlatable Selli black shales and provides information on their relationship to sea-level change and palaeoclimate. Total organic carbon (TOC) was measured on 127 discrete samples, chemical environmental proxies (Th/K, Mn/Ti, K/Ti, Th/Ti, V/Ti) were measured with a portable X-ray fluorescence (pXRF) spectrometer, and colour parameters L*a*b* were measured by spectrophotometer. Several black shale levels are recognized and correlated with similar shales in Europe between the Barremian–Aptian boundary and the Selli Level. The Th/K ratio proxy for hinterland humid or arid climate conditions shows no systematic variation with black shale levels. Several sea-level lowstands are inferred from condensed sandy intervals with some brackish water biota and tidal sedimentary structures. Black shale intervals are found in highstand intervals, with no systematic relationship to inferred transgressions. The formation of black shales is related to palaeoceanographic changes that may be driven by conditions remote from the Scotian Basin.     

羌塘盆地中生界海相黑色泥页岩特征及页岩气远景区预测

青藏高原羌塘盆地中生界发育上三叠统肖茶卡组（T3x）、中侏罗统布曲组（J2b）和上侏罗统索瓦组（J3s）3套海相黑色泥页岩,形成于有机质比较丰富且易于保存的营养型还原性沉积环境,以台地相为主,其次为盆地相和三角洲相;厚度在41～474 m范围内,有机碳（TOC）含量平均值为0.25%～8.34%,有机质类型主要为Ⅱ型干酪根,镜质体反射率（Ro）平均值为1.21%～3.0%,处于高-过成熟生气阶段,脆性矿物以石英、长石为主,含量为65%～70%,页岩孔隙度约2%。与美国主要盆地产气页岩各项指标相比较,羌塘盆地中生界海相黑色泥页岩具有厚度大、有机质丰度低、热演化熟度高、脆性矿物种类多、石英含量较低、长石和粘土矿物含量较高及孔隙度低的特征,具备了形成页岩气基本地质条件,是我国海相页岩气勘探的沉积盆地之一,综合评价预测的页岩气远景区以上三叠统肖茶卡组（T3x）分布范围大,其次是布曲组（J2b）和索瓦组（J3s）。     

Characteristics of the Middle Jurassic marine source rocks and prediction of favorable source rock kitchens in the Qiangtang Basin of Tibet

We have evaluated the hydrocarbon-bearing potential of Middle Jurassic marine source rocks in the Qiangtang Basin, Tibet, through a comprehensive study of samples from a large number of surface outcrops in different structural units, and from the Qiang-D2 Well in the southern Qiangtang Depression. Data that were acquired, including the depositional environment, thickness of sedimentary units, and organic geochemistry, are used to identify the principal controlling factors and predict the location of favorable hydrocarbon kitchens. The source rocks are mainly platform limestone of the Middle Jurassic Buqu Formation. This formation comprises a suite of intra-platform sag marls, micrites, and black shales that were deposited in a deep-water and restricted depositional environment. The marls form hydrocarbon-rich source rocks with organic matter that is mainly type II and in the mature to highly mature stage. In the Dongco–Hulu Lake and Tupoco–Baitan Lake deep sags, limestone also forms a medium-level source rock. In the Qiangtang Basin, limestone is the favorable source rock kitchen and is more significant in this regard than mudstone. The results provide important constraints on evaluating the hydrocarbon potential of Jurassic marine source rocks and for locating petroleum resources in the Qiangtang Basin.     

Paleoclimate evolution and aridification mechanism of the eastern Tethys during the Callovian–Oxfordian: evidence from geochemical records of the Qiangtang Basin,Tibetan Plateau

Global climate during the Jurassic has been commonly described as a uniform greenhouse climate for a long time. However, the climate scenario of a cool episode during the Callovian–Oxfordian transition following by a warming trend during the Oxfordian (163.53 to 157.4 Ma) is documented in many localities of the western Tethys. It is still unclear if a correlatable climate scenario also occurred in the eastern Tethys during the same time interval. In this study, a detailed geochemical analysis on the 1060 m thick successions (the Xiali and Suowa formations) from the Yanshiping section of the Qiangtang Basin, located in the eastern Tethys margin during the Callovian–Oxfordian periods, was performed. To reveal the climate evolution of the basin, carbonate content and soluble salt concentrations (SO₄²⁻, Cl⁻) were chosen as climatic indices. The results show that the overall climate patterns during the deposition of the Xiali and Suowa formations can be divided into three stages: relatively humid (~ 164.0 to 160.9 Ma), dry (~ 160.9 to 159.6 Ma), semi-dry (~ 159.6 to 156.8 Ma). A similar warming climate scenario also occurred in eastern Tethys during the Callovian–Oxfordian transition (~ 160.9 to 159.6 Ma). Besides, we clarify that the Jurassic True polar wander (TPW), the motion of the lithosphere and mantle with respect to Earth’s spin axis, inducing climatic shifts were responsible for the aridification of the Qiangtang Basin during the Callovian–Oxfordian transition with a review of the paleolatitude of the Xiali formation (19.7 + 2.8/−2.6° N) and the Suowa formation (20.7 + 4.1/−3.7° N). It is because the TPW rotations shifted the East Asia blocks (the North and South China, Qiangtang, and Qaidam blocks) from the humid zone to the tropical/subtropical arid zone and triggered the remarkable aridification during the Middle-Late Jurassic (ca. 165–155 Ma).

     

敦煌盆地五墩凹陷中间沟组下段泥页岩地球化学特征及沉积模式

分析泥页岩形成的沉积环境对页岩气储层评价和甜点区优选具有重要意义。为深入探讨敦煌盆地五墩凹陷中间沟组下段富有机质泥页岩的形成环境和有机质聚集机制,以DY1井为研究对象,开展了总有机碳(TOC)含量、显微组成、碳同位素、主量元素、微量元素和稀土元素等测试。结果表明,五墩凹陷中间沟组下段岩性为灰黑色炭质泥页岩、粉砂质泥页岩夹薄煤层等,泥页岩具有较高的TOC含量,质量分数介于0.53%~25.25%,均值为8.18%,成熟度R_ran介于0.74%~1.21%。Mo含量、P/Ti值和有机质显微组成表明,中间沟组下段沉积水体具有较低的初级生产力,高丰度有机质主要来自于陆源高等植物,反映了研究区浅水三角洲–半深湖环境下泥页岩的古生产力不是有机质聚集的关键控制因素;V/(V+Ni)、Ce_anom、Th/U和U_EF-Mo_EF协变模式等揭示中间沟组下段泥页岩形成于缺氧环境;Sr/Cu、Rb/Sr和气候指数C等指标反映了温暖–半干旱的古气候条件;Sr/Ba、Ba/Ga、Ca/(Fe+Ca)和Al₂O₃/MgO等特征指示古水体为淡水–微咸水;Zr/Al、Rb/K和MnO 含量等指标反映了沉积水体为浅水–半深水。依据DY1井沉积环境参数与有机质聚集的关系,建立了中间沟组下段富有机质泥页岩的沉积模式,自下至上经历2个旋回4种沉积模式,沉积水体由浅水三角洲–半深湖沉积–浅水三角洲–半深湖沉积演变,富有机质泥页岩形成于低初级生产力、高等植物陆源输入为主以及缺氧的半深湖环境,缺氧条件是中间沟组下段泥页岩有机质聚集保存的关键控制因素。该研究为敦煌盆地侏罗系页岩气成藏机理、资源潜力评价和有利区优选提供了理论支持。      

羌塘盆地那底岗日地区上侏罗统—下白垩统碳酸盐岩稀土元素地球化学与古气候

通过对羌塘盆地那底岗日地区上侏罗统—下白垩统索瓦组碳酸盐岩稀土元素丰度、分布模式及稀土总量(ΣREE)的分析,结合总有机碳(TOC)含量、EFMn、Sr/Cu的变化特征,探讨了稀土元素纵向变化与气候环境之间的关系。结果表明:那底岗日地区碳酸盐岩中稀土元素总丰度值平均为45.3μg/g(不包括Y)。稀土元素与总有机碳(TOC)之间存在较好的相关性,与EFMn和Sr/Cu值的变化呈反向对应关系。ΣREE的高值段代表相对湿润的气候环境,ΣREE的低值段代表干热的气候环境。根据稀土元素分布与沉积环境的关系,推断晚侏罗世—早白垩世那底岗日地区经历了干热和相对温湿频繁交替变更的气候演化过程。     

四川盆地中部中侏罗统沙溪庙组沉积期古环境与古气候演化——以永浅1井为例

四川盆地中部中侏罗统沙溪庙组沉积期古环境与古气候研究对揭示该时期盆内的沉积格局、重建古地理及油气形成与演化具有重要的理论和实践意义。本文以四川盆地中部永浅1井的47件泥岩样品为研究对象,通过主微量元素的变化特征恢复研究区沙溪庙组沉积期的古环境与古气候演化过程。研究结果表明,Sr/Ba比值、Rb/K2O比值、Ca/Mg比值和Ca/(Ca+Fe)比值指示川中地区中侏罗统沙溪庙组沉积期整体为淡水环境,但在沙溪庙组一段沉积中、晚期出现了短暂的水体盐度升高;V/(V+Ni)比值、U/Th值、V/Cr比值与Ni/Co比值指示沙溪庙组沉积期整体为间歇暴露的浅水氧化环境,局部为弱氧化或还原环境;C值、CIA值和Rb/Sr比值等指标显示,沙溪庙组沉积期古气候总体为温暖湿润的气候环境,但期间发生波动性干旱,在温暖湿润和半干旱—半湿润之间频繁波动。多元地球化学参数为川中地区中侏罗统沙溪庙组沉积期的古气候演化和区域性古气候对比提供了新的证据。     

淮南煤田山西组泥页岩微量元素地球化学特征及其意义

泥页岩中微量元素特征对反演泥页岩形成时的沉积和古地理气候条件具有重要意义。采集淮南煤田山西组泥页岩样品,利用ICP-MS对泥页岩中微量元素进行了测试分析,探讨了研究区山西组泥页岩中微量元素的地球化学特征及其意义。结果表明,B、Cr、U、Ga、Li、Sn、Pb、Mo、Th、W等元素富集,Cd、Co、Cu、Ti、Zn、Sc、Ba、Mn、Ni、Sr等元素亏损;揭示淮南煤田山西组形成于温暖湿润和半咸水-高咸水的沉积环境中,沉积体系为开放型,体系内为弱氧化-还原环境,其中以弱还原-还原环境为主,且表现出从早期弱氧化到中后期的还原环境的演化特征;依据U/Th、Ni/Co、Sr/Cu、B/Ga、Sr/Ba、TOC等地球化学参数结果推测,盐度和氧化还原条件受到多种因素的影响,有机质的原始堆积量是影响山西组泥页岩中有机质含量的主要因素,而盐度和氧化还原条件影响有机质中各显微组分含量。研究区温暖湿润的气候和较为还原的环境为有机质的堆积和保存提供了有利条件,为页岩气的成藏提供了物质基础。      

Paleo-environment and reservoir evolution of the Middle Ordovician Kelimoli Formation in the northern Tianhuan area,Ordos Basin,China: implications for high-quality reservoir development

The Middle Ordovician Kelimoli Formation carbonate reservoirs in the northern Tianhuan area, Ordos Basin, China are main exploration targets. Subsurface core samples, logging, drilling and production data from the area were used to characterise the carbonate reservoir and to construct a genetic model for exploration. The sedimentary facies identified include trough–continental rise, upper–lower slope, platform margin reef-shoal, open platform and evaporation-restricted platform. The slope and platform margin facies are potential zones for high-quality reservoirs. Porosity in the study area comprises intergrain, intercrystal, intragrain and intracrystal pores, fractures and vughs. The Sr/Ba (0.40–4.87) and V/(V + Ni) (0.64–0.97) ratios indicate deposition in a brackish water-dominated environment under reducing conditions, associated with sea-level fluctuations during the deposition of the Kelimoli Formation. The Sr/Ba, V/(V + Ni), ⁸⁷Sr/⁸⁶Sr ratios, δ¹⁸O values and crystal texture of dolomite samples suggest that meteoric water was involved in the diagenetic fluid in the near-surface depositional environment. Isotopes (δ¹³C and δ¹⁸O) and trace elements (Fe and Mn) allowed the identification of seepage-reflux and mixed-water dolomitisation. The crystal textures of the samples consist of micritic, bioclastic and reefal limestones, and dolomite with gypsum, which were easily dissolved during the early diagenetic stage. The epidiagenetic stage was the key period for the development of high-quality reservoirs because of large-scale bedding-parallel karstification from meteoric water. The reservoir zones, dominated by partially filled and unfilled vughs, and fractures, are favourable exploration targets in the northern Tianhuan area.     

川东北地区中侏罗世新田沟期古气候波动的地球化学响应

四川盆地中侏罗统新田沟组作为侏罗纪大面积红层之下的重要岩石地层单元,见证了盆地由潮湿向干旱转变的整个过程。然而,以往的研究主要集中在古气候类型方面,缺乏系统深入的气候变化研究。本文以川东北地区宣汉七里乡塔坝剖面为对象,系统分析了泥岩的主微量元素地球化学特征,结果表明:化学蚀变指数(CIA)、C值、Sr/Cu、Sr/Ba、Rb/Ti、Cs/Ti、Rb/K等7种古气候替代指标综合显示新田沟期气候存在从炎热潮湿逐渐向干旱转变的趋势,整体以半干旱-半潮湿气候为主。且该时期气候变化过程并不稳定,存在多个短期的湿热与干旱的气候波动。在新田沟组沉积末期,气候条件变得极端干燥。川东北地区中侏罗世的元素地球化学特征记录了区域内重大地质转折期将至时的气候变化,在侏罗纪大面积红层发生之前,气候条件已经开始响应。在中侏罗世早期,四川盆地与欧洲地区并不处于同一个气候带内。     

北羌塘盆地油页岩形成环境及其油气地质意义

最近在北羌塘长蛇山地区新发现了晚侏罗世—早白垩世大套油页岩及巨厚膏盐层,该油页岩与近年来作者在胜利河、长梁山地区发现的多处油页岩连成一片,构成了目前我国规模最大的中生代海相油页岩带—北羌塘油页岩带。沉积岩相、古地理研究表明,晚侏罗世—早白垩世时期,北羌塘盆地总体上为一个向北西开口的相对闭塞的巨大海湾,发育了河流-三角洲、海湾(潮坪-潟湖)和浅海-陆棚等沉积相组合。古气候、古环境研究表明,油页岩(段)沉积期,胜利河地区处于潮湿的热带-亚热带环境,大量淡水的注入以及高的生产力等综合因素,控制了油页岩的形成,其分布主要位于局限海湾-潟湖的边缘带;膏盐层(段)沉积则发育于相对干旱、炎热气候条件下的闭塞环境。北羌塘晚侏罗世—早白垩世油页岩及其上覆膏盐层是重要的烃源岩和区域性封盖层。油页岩及含膏盐层沉积组合的发现,对于重新认识羌塘盆地生烃条件及保存条件,具有十分重要的意义。     

Depositional Environment and Lithofacies Analyses of Eocene Lacustrine Shale in the Bohai Bay Basin: Insights from Mineralogy and Elemental Geochemistry

The effect of various depositional parameters including paleoclimate, paleosalinity and provenance, on the depositional mechanism of lacustrine shale is very important in reconstructing the depositional environment. The classification of shale lithofacies and the interpretation of shale depositional environment are key features used in shale oil and gas exploration and development activity. The lower 3^rd member of the Eocene Shahejie Formation(Es₃^x shale) was sel...     

鄂尔多斯盆地早侏罗世富县期沉积演化: 大洋缺氧事件前后陆地气候变化的响应*

托阿尔期早期早侏罗世大洋缺氧事件(T-OAE,~183.8 Ma)是一次全球性的地质事件,鄂尔多斯盆地下侏罗统富县组记录了此次地质事件的陆地响应过程。主要基于盆地东缘野外地质调查、扫描电镜及薄片分析,本次研究描述了盆地东北部富县组岩性、颜色和沉积序列,利用前人研究成果总结了富县期岩相古地理变化规律及沉积模式,认为富县期经历了由干旱到湿润的古气候变化: 富县组下部含植物化石较为丰富的白色砂砾岩及黑色、灰色泥页岩沉积于湿润气候时期,对应着盆地下切河谷发育期和填平补齐期; 而上覆的罕见植物化石的杂色、红色泥页岩为(富县期晚期)相对平坦地形条件下的沉积,对应着早、中侏罗世湿润气候背景下的一次干旱气候脉动,为托阿尔期大洋缺氧事件在陆相环境的气候响应,可由此进行富县组区域等时性对比。研究认为“粗富县”为下切谷内河流充填沉积, “细富县”形成于湖泊环境或河漫环境, “黑富县”和“白富县”是湿润气候条件下沉积产物,而“红富县”和“杂富县”为T-OAE期后干旱条件下形成。     

Jurassic Black Shales Facies from Qiangtang Basin (Northern Tibet):Rare Earth and Trace Elements for Paleoceanographic Implications

The Biluo Co and Amdo 114 station, northern Tibet, cropping out the Early Toarcian and Middle-Late Tithonian (Jurassic) organic-rich black shales, have been a focus to petroleum geologists in discussing their oil-producing potential. This paper first reports the trace elements and rare earth elements to discuss the paleoenvironments, redox conditions and sedimentary mechanisms of those black shales. Both sections exhibit variation in trace element abundances with concentrations <0.1 ppm to 760 ppm, mostly enriched in V, Cr, Ni, Cu, Zn, Mo, Ba and U. Element ratios of Ni/Co, V/Cr, U/Th and V/(V+Ni) plus U were used to identify redox conditions. The shale-normalized rare earth element (REE) patterns are characterized by the flat-shale type with instable Ce anomalies and very weekly positive Eu anomalies. Positive Ceanom values are significant with values varying between –0.064 and 0.029 in Biluo Co, which may be interpreted as release of REE and input of riverine terrestrial matter with rich Ce (resulting in pH change) during the anoxic conditions. In the middle parts of Amdo 114 station, distinct negative Ceanom values are observed (?0.238 to ?0.111) and associated surface water warming were interpreted as being related to a major sea level rise. In contrast, the formation of the black shales in the lower and upper part of the studied succession took place during a cooler (Ceanom values >–0.10), lower surface water productivity, and lower sea-level stage. Thus, we emphasize the role of different factors that control the formation of local and regional black shales. The most important factors are sea-level fluctuations and increasing productivity.     

Orogenesis vs. diagenesis: Can we use organic-rich shales to interpret the tectonic evolution of a depositional basin?

Black shales from the southern Appalachian Basin and the southwest Welsh Basin have anomalous U–Pb and Nd model ages suggesting syn- and post-depositional resetting of the Sm–Nd and U–Pb isotopic systems. This alteration to the primary detrital signature of these two shale sequences is indicative of black shale diagenetic/depositional processes that obscure paleo-environmental and provenance information recorded prior to and during deposition. The trace element and isotopic signatures of these two shale sequences reveal a syn-/post-depositional history that is de-coupled from the coeval orogenic history of the region making it difficult to reconstruct the tectonic and oceanographic conditions present at the time of deposition.Both the Ordovivian Welsh Basin and the Devonian Appalachian Basin sequences host REE- and U-bearing diagenetic phosphate minerals that play a critical role in the whole rock REE and U budgets. In the Welsh Basin shales, early diagenetic apatite and a later monazite phase dominate the REE budget and cause the redistribution of REE early in the basin's history (ca. 460 Ma). This redistribution is recorded by the Sm–Nd system (450 ± 90 Ma) and the Nd model ages that are anomalously old by as much as 20% (T_DM > 2.0 Ga). This early history is complicated by a Permo-Triassic fluid event affecting the whole rock U-budget and resetting the U–Pb isotopic system at 193 ± 45 Ma. The Appalachian Basin sequence appears to have a much less complicated history yet still records a significant disturbance in both the Sm–Nd isotopic system (392 ± 76 Ma) and the Pb isotopic system (340 ± 50 Ma) at about the time of deposition (ca. 365 Ma).These two sequences suggest a pattern of diagenetic disturbance common to black shales. These processes are unique to black shales and must be considered when interpreting provenance and paleo-environmental information from the black shale sequences. Although these rocks are susceptible to alteration, the alteration may provide extensive information on the post-depositional history of the basin while still retaining some primary depositional information. If black shale processes are considered during the interpretation of isotopic and trace element signatures from organic-rich shales, it may be possible to recover an extensive basin history.     

Middle and late Cenomanian oceanic anoxic events in shallow and deeper shelf environments of western Morocco

The response of shallow‐water sequences to oceanic anoxic event 2 and mid‐Cenomanian events 1a and 1b was investigated along the west African margin of Morocco north of Agadir (Azazoul) and correlated with the deep‐water sequence of the Tarfaya Basin (Mohammed Beach) based on biostratigraphy, mineralogy, phosphorus and stable isotopes. In the deeper Mohammed Beach section results show double peaks in δ¹³C_org for mid‐Cenomanian events 1a and 1b (Rotalipora reicheli biozone, lower CC10a biozone), the characteristic oceanic anoxic event 2 δ¹³C excursion (Rotalipora cushmani extinction, top of CC10a biozone) and laminated (anoxic) black shale. In the shallow environment north of Agadir, a fluctuating sea‐level associated with dysoxic, brackish and mesotrophic conditions prevailed during the middle to late Cenomanian, as indicated by oyster biostromes, nannofossils, planktonic and benthonic foraminiferal assemblages. Anoxic conditions characteristic of oceanic anoxic event 2 (for example, laminated black shales) did not reach into shallow‐water environments until the maximum transgression of the early Turonian. Climate conditions decoupled along the western margin of Morocco between mid‐Cenomanian event 1b and the Cenomanian–Turonian boundary, as also observed in eastern Tethys. North of Agadir alternating humid and dry seasonal conditions prevailed, whereas in the Tarfaya Basin the climate was dry and seasonal. This climatic decoupling can be attributed to variations in the Intertropical Convergence Zone and in the intensity of the north‐east trade winds in tropical areas.     

中、下扬子地区下寒武统黑色页岩微量元素富集特征

中国南方扬子地区下寒武统黑色页岩分布广泛,主要由黑色页岩、黑色白云质页岩,黑色粉砂质页岩和黑色硅质页岩等组成;并伴生有较厚的磷块岩矿床、钒矿床和镍、钼多元素硫化物矿床。对黑色页岩岩石学特征、元素地球化学特征进行系统研究,并详细分析微量元素的富集成因,结果表明：黑色页岩主要形成于静水还原的浅海-半深海缓坡环境,层状元素富集带为沉积成因,海底热流体提供了丰富物质来源。总体上,Co、Be、Mn、Ga等元素含量较低;Cu、V、Ni、Mo等元素的含量较高,多数超过北美页岩平均值;以Ni、Mo为主的多元素富集层通常位于磷块岩之上,以黑色页岩、黑色白云质页岩中的硫化物和硫酸盐矿物为主要载体,其中有机碳（TOC）含量可达12.2%以上,远高于其他元素富集层,随着页岩内硅质成分增加,Ni、Mo、Fe、Co等元素含量明显降低;以V为主的多元素主要赋存于黑色硅质页岩中的水云母,与页岩内硅质成分具有较好的正相关关系;黑色页岩中稀土元素含量为(76.22~290.67)×10-6,轻重稀土比值LREE/HREE介于1.21~4.22,说明轻稀土更为富集,Sr/Ba值为0.04~0.34,δEu正异常,且北美页岩标准化配分曲线呈现平缓左倾,为沉积过程中存在海底热水流体提供了进一步证据。     

塔里木盆地北部下寒武统底部黑色页岩形成的次氧化条件

富有机质黑色页岩的形成长期以来被认为是缺氧沉积环境的证据,并被作为全球缺氧事件的标志。塔里木盆地下寒武统底部黑色页岩的岩石学特征说明其沉积在受陆源有一定影响的陆棚环境中。矿物学研究表明,硫均以硫酸盐状态存在,没有见到黄铁矿,说明其形成在硫酸盐还原带以上。黑色页岩中结核状氟磷灰石的存在以及剖面底部结核状磷块岩的出现,表明了一种与现代热带太平洋东海岸和阿拉伯海相类似的广泛发育上升洋流的大陆边缘沉积环境。黑色页岩的地球化学特征中,Re和Mo的高度富集、高的Re/Mo比以及含有一定量的Mn,Cd和U的相对富集以及低的Cd/U比等,这些特点均支持了黑色页岩沉积于次氧化条件的认识。     

西藏羌塘盆地东部中生代构造古地理特征及演化

在大量的区域地质调研和野外露头观测资料基础上,详细研究了西藏羌塘盆地东部中生代不同构造单元的沉积充填序列、地层发育特征与接触关系、构造界面性质、沉积体系配置和沉积相分布等,阐述了盆地沉积与周缘构造带演化之间的耦合关系,重建了研究区中生代不同时期的构造古地理面貌。研究表明,羌塘盆地是一个大型叠复式盆地,盆地东部中生代有海相、海陆过渡相和陆相3个沉积体系组、9个沉积体系和多个沉积（亚）相。盆地内部包括南羌塘坳陷、北羌塘坳陷、唐古拉山隆起带,以及不同时期的次级凸起与断凹等构造单元。其中,多玛断凹是以前石炭纪构造片岩为基底的侏罗纪-早白垩世早期被动大陆边缘陆表海盆地,早白垩世晚期转换为前陆盆地,晚白垩世以来与索县-左贡断凹联合为一体,在陆内造山过程中经历了压陷型盆地充填演化阶段。索县-左贡断凹是在晚三叠世班公湖-怒江沟-弧-盆体系基础上发展起来的前陆盆地。北羌塘坳陷是以华力西期开心岭-杂多隆起带为基底,经过晚三叠世昌都前陆盆地沉积、早侏罗世断陷盆地火山-沉积作用之后,于中侏罗世与索县-左贡断凹联合为一体,形成北羌塘-昌都巨型坳陷型盆地。白垩纪北羌塘陆块和昌都陆块处于隆升剥蚀状态。