西藏色林错及邻区古近纪沉积凹陷对地壳增厚的响应

青藏高原中部古近纪发育伦坡拉盆地、色林错盆地、尼玛盆地,组成伦坡拉-色林错-尼玛沉积凹陷,总体呈近东西走向,长超过250km,宽30~50km;凹陷中心古近系河湖相沉积地层厚度达5~6km,下部为古新统-始新统牛堡组砾岩、砂岩、泥岩、泥灰岩,上部为渐新统丁青湖组泥岩、页岩、粉砂岩夹油页岩,顶部被新近系河湖相沉积不整合覆盖。凹陷南部发育尼玛-色林错逆冲推覆构造,凹陷北侧发育赛布错-扎加藏布逆冲推覆构造,伦坡拉盆地北部发育薄皮推覆构造,伴有不同规模的褶皱变形。地壳深部不同深度发育多重逆冲推覆构造,羌塘地块南部自北向南逆冲推覆,拉萨地块北部自南向北逆冲推覆;两者对冲部位地壳厚度发生显著变化,地表形成古近纪沉积凹陷。根据深地震反射及构造解释,结合Airy均衡分析,表明不同深度逆冲推覆及对冲构造运动导致地壳缩短增厚,增厚地壳均衡隆升及密度差异对古近纪沉积凹陷及盆地演化具有重要控制作用。色林错凹陷及邻区古近纪沉积记录对青藏高原地壳增厚与隆升过程具有重要指示意义。     

青藏高原中部色林错—伦坡拉逆冲推覆构造系统

通过野外地质观测结合地震反射剖面综合构造解释,在青藏高原中部色林错—伦坡拉古近纪沉积凹陷及邻区厘定3条较大规模的逆冲推覆构造,由逆冲断层、逆冲岩席、飞来峰、构造窗及伴生褶皱组成。沿班公—怒江缝合带发育赛布错—扎加藏布逆冲推覆构造,伦坡拉盆地北部发育双重推覆构造,拉萨地块北缘发育色林错—吴如错逆冲推覆构造,估算推覆距离分别为38~50 km。羌塘地块南缘自北向南逆冲推覆,拉萨地块北缘自南向北逆冲推覆,两者对冲导致色林错古近纪盆地及沉积地层发生比较强烈的褶皱变形,形成宽约20 km大型向斜构造。色林错—伦坡拉逆冲推覆构造运动开始时间为晚白垩世晚期,古近纪不同时期均发育逆冲断层,前锋逆冲断层和底部拆离滑脱构造主要形成时期为古近纪晚期—中新世早期。古近纪逆冲推覆构造对伦坡拉和色林错河湖相沉积盆地、烃源岩形成演化、油气成藏及保存条件具有显著控制作用。     

西藏中部尼玛—荣玛地区逆冲推覆构造特征

尼玛—荣玛地区位于羌塘盆地中段,发育大量的逆冲推覆构造体系。尼玛以北主要发育自北向南运动的逆冲推覆构造体系,导致中央隆起带和班公—怒江构造带的岩石地层组合、三叠系和侏罗系地层逆冲在红层之上,其中北羌塘盆地侏罗系地层越过中央隆起,在南羌塘盆地发育滑脱构造并形成薄皮逆冲推覆构造及大型逆冲岩席;尼玛以南主要发育自南向北运动的逆冲推覆构造体系,造成侏罗—白垩系、白垩系岩石组合逆冲在红层之上。逆冲推覆构造普遍控制了红层盆地的生长,并被中新世湖相沉积角度不整合覆盖。逆冲推覆构造活动时代为早白垩世晚期至古近纪,其中中央隆起和班公—怒江构造带最早经历了早白垩世晚期—晚白垩世的抬升,随后整个研究区经历了古近纪的构造抬升,分别与新特提斯洋板片的北向俯冲以及印度—拉萨地块陆陆碰撞存在动力学相关;中新世以来的东西向伸展构造则导致局部差异抬升。逆冲推覆构造破坏了早期油气成藏,但同时伴生的断褶系统也促进地层增厚和有机质成熟,为二次生烃提供了有利的构造圈闭条件,桑列勒以及尼玛一带背斜圈闭是有利的油气靶区。     

羌塘盆地隆鄂尼—昂达尔错古油藏逆冲推覆构造隆升

沿隆鄂尼—昂达尔错古油藏发现大量逆冲推覆构造,如北雷错东西两侧、隆鄂尼西北侧、比洛错东南侧、鲁雄错东西两侧,侏罗系烃源岩及含油白云岩沿低角度缓倾斜断层自北向南逆冲推覆于上白垩统红层之上,昂达尔错西北侧中侏罗统含油碳酸盐岩和碎屑岩自北向南逆冲推覆于三叠系灰黑色碎屑岩之上,形成不同规模的逆冲岩席、逆冲岩片、飞来峰和构造窗。高分辨率二维地震反射剖面显示,隆鄂尼—昂达尔错古油藏深部发育多重逆冲推覆构造;比洛错中侏罗统含油白云岩沿顶部双重推覆构造自北向南运移7~11km和12~15km,分别形成隆鄂尼古油藏和德如日古油藏;下伏三叠系及石炭系—二叠系沿底部双重推覆构造自北向南发生大规模逆冲推覆,前锋被向北逆冲的反向断层切割错断。野外观测表明,隆鄂尼—昂达尔错古油藏与羌中隆起北侧油苗带之间发育大量侏罗系逆冲岩席和飞来峰;深地震反射剖面构造解释进一步揭示,三叠系和侏罗系海相烃源岩经历自北羌塘向南羌塘长距离逆冲推覆构造运动,自北向南逆冲推覆运动导致侏罗系烃源岩及中侏罗统含油白云岩构造隆升,形成昂达尔错、隆鄂尼、德如日等古油藏。隆鄂尼—昂达尔错古油藏逆冲推覆及构造隆升主要发生于晚白垩世—古近纪。     

青藏高原羌塘盆地南部古近纪逆冲推覆构造系统

西藏羌塘地块南部古近纪发育肖茶卡-双湖逆冲推覆构造、多玛-其香错逆冲推覆构造、赛布错-扎加藏布逆冲推覆构造,构成古近纪大型逆冲推覆构造系统。沿逆冲推覆构造的前锋断层,二叠系白云岩与大理岩化灰岩、三叠系砂岩与页岩、侏罗系碎屑岩与碳酸盐岩和三叠纪—侏罗纪蛇绿岩自北向南逆冲推覆于古近纪红色砂砾岩之上,形成规模不等的构造岩片与飞来峰。羌塘盆地南部主要的逆冲断层和下伏的褶皱红层被中新世湖相沉积地层角度不整合覆盖,表明逆冲推覆构造运动自中新世以来基本停止活动。羌塘盆地南部古近纪逆冲推覆构造运动在近南北方向产生的最小位移为90km,指示新生代早期上地壳缩短率约为47%。古近纪逆冲推覆构造对羌塘盆地油气资源具有重要影响。     

藏北改则新生代早期逆冲推覆构造系统

藏北改则及邻区新生代早期发育大型逆冲推覆构造系统,由不同方向的逆冲断层、不同时代的构造岩片、不同规模的飞来峰和构造窗、不同类型的褶皱构造组成。羌塘中部发育羌中薄皮推覆构造,石炭系板岩和二叠系白云质灰岩自北向南逆冲推覆于上白垩统与古近系红层之上,形成大型逆冲岩席和弧形逆冲断层,原地系统古近纪红层下伏三叠系—侏罗系海相烃源岩。羌塘南部发育南羌塘薄皮推覆构造,导致班公—怒江蛇绿岩、三叠系—侏罗系海相地层及侏罗纪混杂岩自北向南逆冲推覆于古近纪红层与下白垩统海相沉积岩层之上,形成三条蛇绿岩片带、大量飞来峰和厚度较大的构造片岩。中新世早期火山岩层和湖相沉积呈角度不整合覆盖逆冲断层、褶皱构造和逆冲岩席,不整合面上覆火山岩年龄为23.7～19.1Ma,指示中新世早期改则及邻区基本结束了强烈逆冲推覆构造运动。估算羌中逆冲推覆构造的推覆距离约100～115km,南羌塘逆冲推覆构造的推覆距离约82～110km;新生代早期改则逆冲推覆构造系统近南北方向逆冲推覆总距离为182～225km,对应地壳缩短率为(50.3±2.7)%。     

西藏阿里推覆构造与蛇绿岩构造侵位

通过野外观测和ETM遥感解译,结合1∶25区域地质调查相关资料,发现西藏阿里地区晚白垩世—古近纪发育自北向南长距离逆冲推覆构造运动,形成大型逆冲推覆构造系统,导致班公—怒江缝合带发生解体和蛇绿岩构造侵位。阿里逆冲推覆构造系统由大量逆冲断层、不同时代的构造岩片、不同规模的飞来峰和构造窗、不同方向的褶皱构造组成,前锋逆冲断层呈弧形分布于拉萨地块北部狮泉河—左左—革吉—麦岗沿线。沿主要逆冲断层,中生代蛇绿混杂岩、三叠纪和侏罗纪碎屑岩-碳酸盐岩、石炭纪板岩、二叠纪白云质灰岩自北向南逆冲推覆于早白垩世碎屑岩-碳酸盐岩、晚白垩世—古近纪红层之上,形成比较典型的薄皮双重推覆构造系统,估算最小推覆距离160～180 km。根据构造关系和同位素年龄资料,推断阿里薄皮推覆构造主要形成时代为75～20 Ma,对应自北向南逆冲推覆构造运动速率约2.91～3.28 mm/a。研究阿里逆冲推覆构造对深化认识班公—怒江缝合带及蛇绿混杂岩的构造属性、合理评价羌塘盆地西段油气资源潜力具有重要意义。     

羌塘盆地逆冲推覆构造特征及油气资源效应

羌塘盆地南羌塘坳陷地表古油藏作为了解盆地石油地质条件的良好窗口,经过多年来对古油藏详细解剖,通过详细的地表构造填图、二维地震和地质浅钻综合揭示了盆地存在大量的逆冲推覆构造。古油藏为盆地自北向南逆冲推覆至地表的大型构造岩席,主要表现为中生代海相地层推覆至晚白垩—中新世湖湘红层之上,古油藏含油层位是中侏罗布曲组砂糖状含油白云岩。针对古油藏石油地质条件解剖表明逆冲推覆构造虽然破坏了上坪油气藏,但是该构造活动不但能够使地层增厚利于有效烃源岩二次生烃,并对下坪地层有效遮挡封盖,同时构造活动有利于优质白云岩储集层和构造圈闭的形成,为二次成藏创造了良好的生储盖时空匹配关系,有利于逆冲推覆型油气藏的形成。     

西藏羌塘盆地上侏罗统索瓦组油藏发现及地球化学特征

在青藏高原羌塘盆地发现规模较大的上侏罗统索瓦组油藏带,主要分布在双湖南、鸭湖、才多茶卡及阿木错一带。利用抽提、分离、GC—MS等地球化学分析手段详细分析了油苗的族组分、有机质来源,沉积环境以及成熟度。生物标志化合物参数分析表明油藏中有机质沉积环境为具有一定盐度的还原性较强的环境,其中,才多茶卡油藏有机质的来源主要为低等水生生物;而双湖南、鸭湖油藏有机质来源则具有低等水生生物和高等植物共同输入;阿木错油藏中有机质以陆源有机质的贡献为主。成熟度参数分析显示油藏样品有机质热演化已达到低成熟—成熟阶段,说明烃源岩的成熟度均已达到生油门限,暗示这些烃源岩曾经有过一定规模的生烃。双湖地区古油藏普遍受自北向南的逆冲推覆构造影响,而位于逆冲推覆构造根带的北羌塘地块索瓦组地层出露较好且具有良好圈闭条件。因此,双湖地区索瓦组古油藏的发现及地球化学特征对于北羌塘盆地上侏罗统油气资源的勘探具有重要指示意义。     

塔里木盆地西南部齐姆根逆冲推覆构造的特征及其与油气的关系

齐姆根逆冲推覆构造带位于喀什凹陷与叶城凹陷之间的齐姆根凸起上,由3个与盆地边缘大体平行的次级逆冲构造带组成,即阿尔塔什推覆构造带、科克然达坂-希根纳孜吉勒嘎推覆构造带、库斯拉甫推覆构造带。3个次级逆冲构造带分别将石炭系—二叠系推覆在侏罗系、白垩系及古近系—新近系之上,将泥盆系推覆在石炭系—二叠系之上,将元古宙变质岩及古生代花岗岩逆冲在泥盆系及泥盆系之上不整合覆盖的侏罗系之上。根据推覆体地层的叠置关系及逆冲断层的发育特征,齐姆根逆冲推覆构造带是由北向南演化的、后展式发展的逆冲推覆构造系统,其间发育横向调节的走滑断层。逆冲推覆体系的主体断裂沟通了源岩与储层,推覆体下盘发育的大型背斜圈闭为油气聚集提供了有利的场所,运聚条件的合理配置为该区油气勘探提供了良好的前景。     

The terrestrial fauna of the Late Triassic Pant-y-ffynnon Quarry fissures,South Wales,UK and a new species of Clevosaurus (Lepidosauria: Rhynchocephalia)

Pant-y-ffynnon Quarry in South Wales yielded a rich cache of fossils in the early 1950s, including articulated specimens of new species (the small sauropodomorph dinosaur Pantydraco caducus and the crocodylomorph Terrestrisuchus gracilis), but no substantial study of the wider fauna of the Pant-y-ffynnon fissure systems has been published. Here, our overview of existing specimens, a few described but mostly undescribed, as well as freshly processed material, provides a comprehensive picture of the Pant-y-ffynnon palaeo-island of the Late Triassic. This was an island with a relatively impoverished fauna dominated by small clevosaurs (rhynchocephalians), including a new species, Clevosaurus cambrica, described here from a partially articulated specimen and isolated bones. The new species has a dental morphology that is intermediate between the Late Triassic Clevosaurus hudsoni, from Cromhall Quarry to the east, and the younger C. convallis from Pant Quarry to the west, suggesting adaptive radiation of clevosaurs in the palaeo-archipelago. The larger reptiles on the palaeo-island do not exceed 1.5?m in length, including a small carnivorous crocodylomorph, Terrestrisuchus, and a possible example of insular dwarfism in the basal dinosaur Pantydraco.     

Définition d'une limite multicritère ; stratigraphie du passage Campanien–Maastrichtien du site géologique de Tercis (Landes,SW France)Definition of a multi-criteria boundary; stratigraphy of the Campanian–Maastrichtian interval of the geological site at Tercis (Landes,SW France)

Lithostratigraphy, physicochemical stratigraphy, biostratigraphy, and geochronology of the 77–70 Ma old series bracketing the Campanian–Maastrichtian boundary have been investigated by 70 experts. For the first time, direct relationships between macro- and microfossils have been established, as well as direct and indirect relationships between chemo-physical and biostratigraphical tools. A combination of criteria for selecting the boundary level, duration estimates, uncertainties on durations and on the location of biohorizons have been considered; new chronostratigraphic units are proposed. The geological site at Tercis is accepted by the Commission on Stratigraphy as the international reference for the stratigraphy of the studied interval. To cite this article: G.S. Odin, C. R. Geoscience 334 (2002) 409–414.     

The effect of water on accessory phase solubility in subaluminous and peralkaline granitic melts

The solubilities of columbite, tantalite, wolframite, rutile, zircon and hafnon were determined as a function of the water contents in peralkaline and subaluminous granite melts. All experiments were conducted at 1035 °C and 2 kbar and the water contents of the melts ranged from nominally dry to approximately 6 wt.% H₂O. Accessory phase solubilities are not affected by the water content of the peralkaline melt. By contrast, solubilities are affected by the water content of the subaluminous melt, where the solubilities of all the accessory phases examined increase with the water content of the melt, up to 2 wt.% H₂O. At higher water contents, solubilities are nearly constant. It can be concluded that water is not an important control of accessory phase solubility, although the water content will affect diffusivities of components in the melt, thus whether or not accessory phases will be present as restite material. The solubility behaviour in the subaluminous and peralkaline melts supports previous spectroscopic studies, which have observed differences in the coordination of high field strength elements in dry vs. wet subaluminous granitic glasses, but not for peralkaline granitic glasses. Lastly, the fact that wolframite solubility increases with increasing water content in the subaluminous melt suggests that tungsten dissolved as a hexavalent species.     

Quaternary stresses revealed by calcite twinning inversion: insights from observations in the Savonnières underground quarry (eastern France)

Calcite samples were extracted both from the rock matrix and the superficial coating of a karstified fault plane of an underground quarry, located in the eastern border of the Paris basin. The karstification is dated as Quaternary. Analysis of mechanical calcite twinning reveals that only the calcite matrix has also undergone a compression trending WNW that can be attributed to the Mio-Pliocene alpine collision. Both coating and matrix have undergone a strike-slip regime with σ₁ roughly trending north–south, that could correspond to the regional present-day state of stress, a strike-slip compression rather trending NNW, modified by local phenomena. To cite this article: M. Rocher et al., C. R. Geoscience 335 (2003).     

HYDROGEOLOGY

正20141756 Chen Ruige(Mathematical College,China University of Geosciences,Beijing100083,China);Zhou Xun Numerical Simulation of Groundwater Level Fluctuation in a Coastal Confined Aquifer with Sloping Initial Groundwater Level Induced by the Tide(Geological Bulletin of China,ISSN1671-2552,CN11-4648/P,32(7),2013,p.1099-1104,6 illus.,16 refs.) Key words:confined water,groundwater level     

METAMORPHIC PETROLOGY

正20141408 Cai Jia(Institute of Geology,Chinese Academy of Geological Sciences,Beijing100037,China);Liu Fulai Petrogenesis and Metamorphic P-T Conditions of Garnet-Spinel-Biotitebearing Paragneiss in Danangou Area,Daqingshan-Wulashan Metamorphic Complex Belt(Acta Petrologica Sinica,ISSN1000-0569,CN11-1922/P,29(7),     

SERIALS

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GEOPHYSICAL EXPLORATION

正20142386An Guoying(China Aero Geophysical Survey and Remote Sensing Center for Land and Resources,Beijing 100083,China)Application of Satellite Remote Sensing in Regional Hydrogeological Investigation:Taking Cenozoic Strata in Wenquan Sheet(1∶250 000)of Karakoram Range as an Example(Geosci-     

QUATERNARY GEOLOGY & GEOMORPHOLOGY

正20141016An Chengbang(Key Laboratory of Western China’s Environmental Systems,Ministry of Education,Lanzhou University,Lanzhou 730000,China);Zhao Yongtao Lake Records during the Last Glacial Maximum from Xinjiang,NW China and Their Climatic Impli-     

PETROLEUM GEOLOGY

正20141538 Cao Qing(School of Earth Sciences and Engineering,Xi’an Petroleum University,Xi’an 710065,China);Zhao Jingzhou Characteristics and Significance of Fluid Inclusions from Majiagou Formation,Yichuan Huangling Area,Ordos Basin(Advances in Earth Science,ISSN1001-8166,CN62-1091/P,28(7),2013,p.819-828,7 illus.,3 tables,43 refs.)