川中雷口坡组四~3亚段地震相分析——应用波形分类技术研究沉积相的实例

在工区面积大、钻井少的情况下开展地震相研究,可以有效绘出沉积相展布图。对四川盆地中部雷口坡组四3亚段利用GS1和YS104两口井进行地震地质标定,建立了膏盐湖、白云岩坪及颗粒滩等几种不同沉积微相的地震响应模式。膏盐湖相表现为强振幅、高连续的地震响应,而颗粒滩及白云岩坪主要表现为中振幅、低连续的地震响应特征。在地质标定基础上,对全区利用波形分类技术开展地震相研究,恢复了古沉积环境,获得了颗粒滩相及白云岩坪的展布图,这些分布区是有利储层的发育区。龙岗—营山—南充—蓬溪一带处于颗粒滩、白云岩坪有利相带,且处于雷四3亚段地层剥蚀线附近,受岩溶改造强烈,储层较为发育,是川中地区的重要勘探对象。     

碎屑流与浊流的流体性质及沉积特征研究进展

受浊流沉积模式(即鲍马序列和浊积扇模式)的驱动和浊积岩思维定势的影响,自1970s浊流与浊积岩的概念逐渐扩大,特别是通过"高密度浊流"术语的引入,以及将水下浊流与陆上河流的错误类比,使得一部分碎屑流与底流的沉积被认为是浊积岩。随着现代观测设备的应用以及详细的岩芯观察,碎屑流(特别是砂质碎屑流)和浊流被重新认识。浊流是一种具牛顿流变性质和紊乱状态的沉积物重力流,其沉积物支撑机制是湍流。碎屑流是一种具塑性流变性质和层流状态的沉积物重力流,其沉积物支撑机制主要是基质强度和颗粒间的摩擦强度。浊流沉积具特征的正粒序韵律结构,底部为突变接触而顶部为渐变接触;碎屑流沉积一般具上、下两层韵律结构,即下部发育具平行碎屑结构的层流段,上部发育具块状层理的"刚性"筏流段。但当碎屑流被周围流体整体稀释改造且改造不彻底时,强碎屑流可变为中—弱碎屑流,相应自下而上可形成逆—正粒序的沉积韵律结构,其中发育有呈漂浮状的石英颗粒和泥质撕裂屑等碎屑颗粒,明显区别于浊流沉积单一的正粒序韵律结构特征。碎屑流沉积顶、底部均为突变接触。浊流的沉积模式为简单的具平坦盆底的坡底模式,而碎屑流则为复杂的斜坡模式。     

中国东北地区西部~500Ma泛非期孔兹岩系地球化学特征及其地质意义

最近在兴安、额尔古纳地块均发现原岩为中基性-中酸性火山岩、陆源碎屑沉积岩及碳酸盐岩组合组成的孔兹岩系,岩石组合主要分为富铝片岩-片麻岩类和斜长角闪岩两类。岩石地球化学特征表明,富铝片岩-片麻岩类的原岩为泥岩和砂岩,主量和微量元素的分配形式接近澳大利亚后太古宙页岩(PAAS)和北美页岩(NASC),稀土元素的分布特征与NASC相似,显示轻稀土元素富集及Eu负异常,(La/Yb)N=4～17,δEu=0.32～0.79。其Cr/Ti(0.01～0.03)、Zr/Y(1.2～13.3)、Cr/Th(0.1～8.63)、Cr/Zr(0.02～0.47)、Th/U(1.5～7.7)、CIW(68～99)表明物源区以花岗岩类为主,并可能含有碎屑沉积岩。其Ceanom(-0.04～-0.01)、Ce/Ce#(0.90～1.30)表明富铝片岩-片麻岩类原岩沉积环境为亚稳定的大陆边缘沉积。斜长角闪岩原岩为玄武岩或安山质玄武岩,其富Fe2O3(1.83%～12.37%)、MgO(4.28%～7.29%)、贫SiO2(47.06%～56.13%),呈低碱性。轻稀土元素相对富集,MORB标准化的微量元素配分型式为大隆起型,Zr/Nb、Hf/Th值均类似于板内拉斑玄武岩的特征。因此,研究区孔兹岩系应形成于裂谷沉积背景。这与佳木斯地块麻山群孔兹岩系形成环境一致,表明东北地区各地块的变质基底均为孔兹岩系,其原岩均形成于裂谷沉积环境,并统一经历～500Ma泛非期变质事件,这为研究我国前寒武纪的大陆演化、再造我国东北地区的构造格局及其在Gondwana大陆重建中的位置都将具有重大的理论意义。     

Magnetic storms on Mars

Based on data from the Mars Global Surveyor magnetometer we examine periods of significantly enhanced magnetic disturbances in the martian space environment. Using almost seven years of observations during the maximum and early declining phase of the previous solar cycle the occurrence pattern and typical time profile of such periods is investigated and compared to solar wind measurements at Earth. Typical durations of the events are 20-40 h, and there is a tendency for large events to last longer, but a large spread in duration and intensity are found. The large and medium intensity events at Mars are found to occur predominantly in association with interplanetary sector boundaries, with solar wind dynamic pressure enhancements being the most likely interplanetary driver. In addition it is found that, on time scales of months to several years, the dominant cause of global variability of the magnetic field disturbance at Mars is solar wind dynamic pressure variations associated with the eccentricity of the martian orbit around the Sun.     

侏罗系烃源岩发育有利环境及条件探讨——古地理古环境编图研究

烃源岩是油气勘探的物质基础,研究其形成环境对油气勘探与开发具有极其重要的意义。为了研究侏罗系烃源岩在全球范围内的分布特征及其发育的有利条件,首先依据古地磁方法以160Ma为时间节点,对全球古板块进行再造。在此基础上,辅以地理信息系统(ARCGIS)技术,并结合前人的区域地质的研究成果,在全球板块图上叠加了侏罗系岩相古地理和烃源岩分布等元素,编制了侏罗纪全球尺度的古地理、古岩相及烃源岩分布图件。同时,统计了全球含油气盆地的侏罗系烃源岩数据531个,其中具有明确干酪根类型的数据252个,且类型主要为Ⅱ型海相浮游生物,Ⅰ和Ⅲ型干酪根发育相对较少。从中得出:沉积环境、干酪根类型、气候、海平面、上升流及构造运动等因素综合控制了烃源岩的形成和保存,其中上升流对烃源岩的形成起着尤为重要的作用。侏罗纪时期泛大陆大规模裂解,新特提斯洋和中大西洋洋脊逐渐扩张,火山活动强烈。在此构造背景下,全球大范围为温带和热带,气候温暖湿润,且暖流区海水温度适宜,上升流将底层营养物质带到浅层,有利于海洋生物生存繁殖,为烃源岩形成提供了丰富的生烃母质;海平面上升以及大规模海泛事件则为烃源岩的保存提供了有利条件。因此,新特提斯域周缘和中大西洋两岸暖流区海水温度较适宜,是烃源岩的主要发育区;浅海台地相碳酸盐岩、被动大陆边缘和裂谷相泥页岩以及陆内深湖相泥页岩是其发育的优势沉积岩相,且绝大部分烃源岩分布于波斯湾、墨西哥湾、北海、中亚以及西西伯利亚等地区。     

Recognizing cryptic environmental changes by using paleoecology and taphonomy of Pleistocene bivalve assemblages in the Oga Peninsula,northern Japan

Multivariate analyses applied to Pleistocene bivalve assemblages from the Oga Peninsula (northern Japan) discriminate three distinct assemblages. The assemblages and their taphonomy were used to recognize environmental settings and changes. The Astarte–Cyclocardia–Glycymeris assemblage indicates shelf environment (below the storm wave base) where gravels and shells are transported from shallower settings. Supply of the exotic coarse sediment probably enabled epifaunal bivalves to inhabit the sea floor. The Glycymeris assemblage is characterized by dominance of G. yessoensis and represents current-swept shoreface environment (above the storm wave base). The Moerella assemblage is characterized by bivalves inhabiting bay to open-marine conditions and diverse deposit-feeders, indicating a moderately land-locked environment, such as an open bay or a bay mouth. Fine-grained substrata rich in organic matters in the bay were probably suitable for the deposit-feeders. Ordination also shows the assemblages along two environmental gradients, a bathymetrical one and the other related to open-marine and bay conditions. The environmental changes are explained mainly by glacio-eustatic sea-level changes and alternation of coastal geomorphology caused by local crustal movements. This study also suggests that fossil assemblages can be a powerful tool to reconstruct environments and depositional dynamics even in intensely bioturbated sedimentary facies.     

The high-supply,current-dominated continental margin of southeastern South America during the late Quaternary

The continental margin off the La Plata Estuary (SE South America) is characterized by high fluvial sediment supply and strong ocean currents. High-resolution sediment-acoustic data combined with sedimentary facies analysis, AMS-¹⁴C ages, and neodymium isotopic data allowed us to reconstruct late Quaternary sedimentary dynamics in relation to the two major sediment sources, the La Plata Estuary and the Argentine margin. Sediments from these two provinces show completely different dispersal patterns. We show that the northward-trending La Plata paleo-valley was the sole transit path for the huge volumes of fluvial material during lower sea levels. In contrast, material from the Argentine margin sector was transported northwards by the strong current system. Despite the large sediment volumes supplied by both sources, wide parts of the shelf were characterized by either persistent non-deposition or local short-term depocenter formation. The location and formation history of these depocenters were primarily controlled by the interplay of sea level with current strength and local morphology. The high sediment supply was of secondary importance to the stratigraphic construction, though locally resulting in high sedimentation rates. Thus, the shelf system off the La Plata Estuary can be considered as a hydrodynamic-controlled end-member.     

克拉通演化的超大陆背景与克拉通盆地的成因机制

研究表明克拉通的形成与超大陆的汇聚和裂解有着重要关系。本文对近年来超大陆重建的研究进行了分析对比,对克拉通发展与超大陆事件的关系做出了总结。前人对超大陆的研究表明,其形成与地幔动力有直接联系,地幔柱重组的旋回导致了超大陆的旋回。Phillips and Bunge（2007）在前人三维球体地幔对流模型的基础上加入大陆进行了模拟实验,结果显示周期性的超大陆旋回只发生在理想模型中,而Senshu et al.（2009）对代表陆壳的英云闪长岩-奥长花岗岩-花岗岩（TTG）地壳进行了研究,提出随着俯冲的TTG地壳产热速率的下降,超大陆旋回的周期随之变长;更有许多学者指出,历史上哥伦比亚超大陆存在时间明显较长,因此超大陆的旋回并不具有周期性。对近年来不同学者提出的哥伦比亚、 罗迪尼亚、 冈瓦纳、 潘基亚4个超大陆新的重建证据进行分析,大致确定出上述4个超大陆的形成时间、 格局及演化过程。此外,对华北、 东欧、 西伯利亚、 亚马孙、 刚果、 西非6个克拉通各自的演化进行分析,也显示出克拉通演化与超大陆汇聚及裂解在时间与空间上有对应关系。通过分析得出克拉通演化与超大陆旋回有关,且确定出克拉通演化的4个超大陆旋回。本文最后讨论了克拉通盆地的成因机制以及3种端元类型,并将盆地的发育与超大陆演化的巨旋回相联系。     

大别山东端早-中侏罗世地层对构造事件的指示

本文通过对安徽桐城挂车河、宿松河塌下-中侏罗统剖面岩石特征、沉积构造、粒度和碎屑组分的分析,揭示了燕山早期大别山隆升和侵蚀的演化历史,并结合构造变形分析,探讨了研究区区域动力学背景。结果显示,两地在早-中侏罗世时期分别为扇三角洲-半深湖和河道-河泛平原沉积,物源都来自北部的大别山。又因为挂车河剖面富含大别山变质碎屑颗粒,而河塌剖面相对缺少,由此提出大别山带南部在早-中侏罗世时期,东南部比西南部隆升较高,而相比大别山北麓的砾石和碎屑组成,则认为大别山北部隆升剥蚀更快,且剧烈。两剖面碰撞造山-火山岛弧和再旋回造山带大洋物质的物源,指示由北向南海沟-岛弧和盆地的构造格局。依据两地断层面和擦痕产状进行古应力分析,显示研究区晚侏罗世受到了燕山主幕近南北向的挤压应力。桐城挂车河的另一近东西向挤压应力可能表明该时期大别山东南部地区已受古太平洋构造的改造。     

贵州松桃—印江地区“含锰岩系”沉积微相特征与远景预测

本文通过对松桃—印江地区大塘坡组一段"含锰岩系"的岩石组合特征分析,阐述了含锰岩系"三个微相"的划分方案,认为杨立掌、大塘坡、大屋、黑水溪等锰矿聚集区属盆地中心微相,其周围附近属盆地外围微相,距盆地较远地带属水下隆起带微相。依据盆地中心与水下隆起带的位置关系、盆地中心之间的间距、控矿构造等分析,认为乌罗司—望秀—石门坎一带极有可能存在一个较大的聚锰盆地。