南海北部白云深水区东北部小型峡谷内的块体搬运

The process of mass movements and their consequent turbidity currents in large submarine canyons has been widely reported, however, little attention was paid to that in small canyons. In this paper, we document mass movements in small submarine canyons in the northeast of Baiyun deepwater area, north of the South China Sea(SCS), and their strong effects on the evolution of the canyons based on geophysical data. Submarine canyons in the study area arrange closely below the shelf break zone which was at the depth of –500 m. Within submarine canyons, seabed surface was covered with amounts of failure scars resulted from past small-sized landslides. A complex process of mass transportation in the canyons is indicated by three directions of mass movements.Recent mass movement deposits in the canyons exhibit translucent reflections or parallel reflections which represent the brittle deformation and the plastic deformation, respectively. The area of most landslides in the canyons is less than 3 km2. The trigger mechanisms for mass movements in the study area are gravitational overloading, slope angle and weak properties of soil. Geophysical data indicate that the genesis of submarine canyons is the erosion of mass movements and consequent turbidity currents. The significant effects of mass movements on canyon are incision and sediment transportation at the erosion phases and fillings supply at the fill phases. This research will be helpful for the geological risk assessments and understanding the sediment transportation in the northern margin of the SCS.     

南海北部西沙海槽北侧陆坡块体搬运沉积体系的发育特征及演化

Triple mass-transport deposits(MTDs) with areas of 625, 494 and 902 km2, respectively, have been identified on the north slope of the Xisha Trough, northern South China Sea margin. Based on high-resolution seismic reflection data and multi-beam bathymetric data, the Quaternary MTDs are characterized by typical geometric shapes and internal structures. Results of slope analysis showed that they are developed in a steep slope ranging from 5° to 35°. The head wall scarps of the MTDs arrived to 50 km in length(from headwall to termination). Their inner structures include well developed basal shear surface, growth faults, stepping lateral scarps, erosion grooves, and frontal thrust deformation. From seismic images, the central deepwater channel system of the Xisha Trough has been filled by interbedded channel-levee deposits and thick MTDs. Therefore, we inferred that the MTDs in the deepwater channel system could be dominated by far-travelled slope failure deposits even though there are local collapses of the trough walls. And then, we drew the two-dimensional process model and threedimensional structure model diagram of the MTDs. Combined with the regional geological setting and previous studies, we discussed the trigger mechanisms of the triple MTDs.     

南海陆坡大型块体搬运体系的结构与识别特征

近年来的地质与地球物理调查发现,在大陆坡第四系中发育有大规模块体搬运体系(现今的块体搬运体系也称海底滑坡)。块体搬运体系是深水常见的一种沉积物搬运机制,主要包括滑动、滑塌和碎屑流等重力流过程及其沉积物。南海陆坡白云块体搬运体系面积逾10 000 km2,可划分为3个结构单元,即头部拉张区、体部滑移-挤压区和趾部挤压区。在地震剖面中,发育多种构造:正断层、杂乱反射、逆冲断层、挤压脊和褶皱等。块体搬运体系严重威胁深水设施安全,并可能诱发海啸,是海洋地质灾害之一。同时,块体搬运体系与海洋油气及天然气水合物关系密切,物源决定块体搬运体系的物性,泥质物源的块体搬运体系通常作为良好的油气盖层,砂质物源形成的块体搬运体系可以成为储层。     

珠江口盆地白云凹陷陆坡区10.5Ma以来的沉积体系

通过对珠江口盆地白云凹陷陆坡区10.5Ma以来的地震相分析,共识别出席状平行亚平行地震相、透镜状前积地震相、深切河谷地震相、帚状地震相和杂乱地震相,不同的地震相分别代表不同的沉积体系类型。综合所识别的地震相类型,分析了陆架边缘下切谷、浊积扇和陆架边缘三角洲3种主要的沉积体系及其配置关系。物源供给是影响陆坡区沉积体系发育的最重要因素,是沉积体系发育的物质基础,海平面变化和构造运动为沉积体系发育提供了可容纳空间,3种影响因素共同影响了陆坡区沉积体系的发育。     

琼东南盆地第四纪块体搬运体系的地震特征

第四纪以来,琼东南盆地的陆坡区域广泛发育深水块体搬运体系。深水块体搬运体系是广泛发生在外陆架/上陆坡的一种沉积物搬运机制,包括滑动、滑塌和碎屑流等重力流作用过程。利用深水3D地震资料,提取振幅和相干数据,通过地震剖面、构造图和时间切片分析,揭示块体搬运体系具有丘状外形、波状反射结构、弱振幅和连续性差的地震特征,内部整体比较杂乱,主体发育褶皱,趾部发育逆冲断层,具有塑性流体特征。结合南海构造背景分析,认为研究区第四纪沉积速率高并位于地震多发带,构成了块体搬运体系的形成条件和触发机制。     

琼东南盆地中央峡谷上新统块体搬运沉积体系地震特征及其分布

根据琼东南盆地深水区高分辨率2D/3D地震资料精细解释,和基于三维地震资料的相干分析,在琼东南盆地中央峡谷区发现了多期次的块体搬运沉积体系(MTDs)。研究表明,该区域块体搬运沉积体系包括3个主要的结构单元,即头部拉张区、体部滑移区和趾部挤压区,不同位置地震特征不同。大规模的块体搬运沉积体系构成了琼东南盆地中央峡谷区新近系以来地层中的重要沉积单元,并对深海沉积物的空间展布有重要的控制作用。上新世发育的一期块体搬运沉积体系,分布面积达300 km2,厚度达240 m,平面展布形态似扇形。高沉积物供给速率和不断的构造活动可能是该区域MTDs发育的主要原因。此外,地震活动、海平面变化也间接影响了MTDs的发育。     

南海北部白云凹陷及其邻区的岩石圈强度分析

选取纵穿南海北部陆缘的长排列多道地震剖面,利用挠曲回剥和重力异常模拟相结合的过程导向法(process-oriented gravity modelling,POGM),计算了研究区内不同构造单元同张裂及裂后阶段的岩石圈有效弹性厚度(effective elastic thickness,Te),并对其分布特征进行了详细分析。计算结果显示:张裂过程中岩石圈强度很弱;而裂后阶段岩石圈强度在不同构造单元并不相同,其中番禺低隆起和下陆坡区强度较高,Te约为15km,而在北部坳陷带为7km左右,白云凹陷地区强度最低,仅为5km左右。获得的岩石圈强度结果,加深了对南海北部大陆边缘盆地特征和岩石圈构造演化过程的认识,具有重要的意义。     

白云凹陷陆坡峡谷沉积与迁移特征及其对天然气水合物成藏的影响

利用高分辨率地震资料,研究了南海北部白云凹陷中新世以来的陆坡峡谷沉积和迁移特征及其对动态似海底反射（BSR）的影响。白云凹陷陆坡区浊流和底流共同作用形成了大型单向迁移峡谷沉积体系。峡谷的沉积过程包括侵蚀为主阶段、侵蚀-沉积共同作用阶段及沉积为主阶段。峡谷沉积相主要包括峡谷侵蚀基底、谷底沉积、谷内滑塌块体搬运沉积及侧向倾斜沉积层等4个单元。峡谷的迁移造成含天然气水合物脊部两侧不同的侵蚀-沉积环境,因此,脊部两侧BSR反射特征也不同。随着峡谷迁移的进行,在峡谷侵蚀侧翼处,沉积物被侵蚀,天然气水合物稳定带底界将发生下移,BSR反射特征为多轴较连续反射;而峡谷沉积侧翼处,沉积物增厚,天然气水合物稳定带将发生上移,BSR反射特征为单轴连续反射。     

歧口凹陷滩海区下第三系地震反射特征及层序划分

本文主要利用地震反射同相轴的终止形式和不连续类型 ,对歧口凹陷滩海区下第三系地层进行层序的划分 ,并对不同体系域内部及层序界面的地震反射特征进行较为详尽的描述。研究结果表明 ,歧口凹陷下第三系发育有六个层序 ,每个层序的顶、底界面分别对应于区内七个地震反射界面。不同成因及不同沉积环境的层序内部具有不同的地震反射相。并讨论体系域与油气赋存的关系     

珠江口盆地白云凹陷裂后异常沉降研究及成因分析

南海北部大陆边缘的许多盆地都发现了裂后沉降异常,位于深水陆坡区的白云凹陷是其中的典型代表。本文采用盆模软件Temis Suite 2007对穿过白云凹陷的3条地震剖面进行回剥分析,观测其不同时间基底的垂向运动特征,并将其与MCKENZIE经典拉张模型计算的理论裂后沉降值进行对比,发现白云主凹中心的裂后异常沉降量最大超过2.6 km,白云南凹最大异常沉降量接近2 km,高于白云凹陷北部边缘的异常沉降。凹陷东部的裂后沉降作用强于凹陷西部。对沉降曲线的研究发现,白云凹陷在中中新世(16.5～10.5 Ma)期间有一段沉降明显加速的过程,白云南凹尤为明显,可能与南海扩张停止事件有关。白云凹陷发育了巨厚的沉积,并且呈韧性伸展状态,本文认为下地壳流可能是导致白云凹陷裂后异常沉降最主要的因素。     

珠江口盆地白云凹陷始新世—中新世沉积物物源研究

运用地质与地球物理综合研究方法,对南海北部珠江口盆地白云深水区始新世—中新世的沉积充填特征开展研究,结果表明,在早中始新世,白云凹陷沉积环境经历了由陆相冲积扇到中深湖相的转变,晚始新世部分地区遭受海侵,沉积物源主要来自北部番禺低隆起和东沙及神狐构造高部位,以近源沉积为主。到早渐新世,凹陷沉积环境转变为海陆过渡相及海相环境,凹陷北部受番禺低隆起等局部物源控制,凹陷主体接受大量源自南海西部昆莺琼古河的物源供给。到晚渐新世,古珠江沉积范围增大,突破番禺低隆起进入白云凹陷,凹陷北部主体受古珠江搬运沉积物影响,凹陷其余地区则接受来自北部古珠江及西部昆莺琼古河双物源供给。进入中新世,由于盆地热沉降作用的加强,南海北部陆架坡折带由白云凹陷南部跃迁至北部,凹陷水深不断加深,凹陷主体受古珠江沉积物的控制,其中南部地区为深水环境,受到由浊流搬运来的北部古珠江物质、西部昆莺琼古河物质以及正常远洋沉积物的共同影响。     

Seismic evidence and formation mechanism of gas hydrates in the Zhongjiannan Basin,Western margin of the South China Sea

An analysis of 3D seismic data from the Zhongjiannan Basin in the western margin of the South China Sea (SCS) reveals seismic evidence of gas hydrates and associated gases, including pockmarks, a bottom simulating reflector (BSR), enhanced reflection (ER), reverse polarity reflection (RPR), and a dim amplitude zone (DAZ). The BSR mainly surrounds Zhongjian Island, covering an area of 350 km² in this 3D survey area. The BSR area and pockmark area do not match each other; where there is a pockmark developed, there is no BSR. The gas hydrate layer builds upward from the base of the stability zone with a thickness of less than 100 m. A mature pockmark usually consists of an outside trough, a middle ridge, and one or more central pits, with a diameter of several kilometers and a depth of several hundreds of meters. The process of pockmark creation entails methane consumption. Dense faults in the study area efficiently transport fluid from large depths to the shallow layer, supporting the formation of gas hydrate and ultimately the pockmark.     

Architecture of lacustrine mass-transport complexes in the Mesozoic Songliao Basin,China

3-D seismic data and wireline log profiles of the Central Depression in the Songliao Basin exhibit four lacustrine mass-transport complexes (MTCs) in the second and the third members of the Upper Cretaceous Nenjiang Formation. The mass-transport complex named MTC-A lies in the north of the Daqing Anticline with an area of approximately 95 km² and a maximum thickness of 62 m. It consists of five laterally and vertically stacked blocks striking E-W and has a convex-downslope front. The mass-transport complex named MTC-C is located in the south of the Daqing Anticline consisting of seven blocks. This MTC strikes NNE-SSW and has an area of approximately 61.5 km² and a maximum thickness of 55 m. MTC-B, the mass-transport complex lying in the middle of the Daqing Anticline, consists of three vertically stacked blocks and has a semi-circular outline striking E-W. MTC-B has an area of approximately 24 km² and a maximum thickness of 92 m. Along the Daqing Anticline from north to south, the three MTCs distribute in lacustrine facies in the NNE direction. The mass-transport complex named MTC-D located in the southeast of the Daqing Anticline has an area of approximately 150 km² with a maximum thickness of 135 m striking E-W, which is rich in mudstones. MTC-D is characterized by the three-layer architecture vertically consisting of a dragged layer at the bottom, a slumped layer in the middle, and a stable layer at the top. Besides, in the plane view, MTC-D can be divided into three parts according to the sliding distance and stacking pattern of the slip blocks: the detaching area, the stacking area and the drifting area. The MTCs are characterized by thickening upslope and thin-out downslope. Siltstones and very fine sandstones occur in 2–4 beds that are cumulatively 0.8–7 m thick in the upslope and central parts of the MTCs. The edges of the blocks are composed of mudstone. Seismic amplitude slices reveal arcuate or straight ridges on the block surfaces with a spacing density of 4–10 per kilometer and a height ranging from 25 to 40 m. The arcuate ridge paleo-morphology on the MTC surfaces suggests that blocks are slump bodies. The estimated minimum water depth at the time of the MTC emplacement is 30–70 m, and the sliding distance is 2–10 km. From 3-D seismic amplitude slices, no feeding channel connected to the mass-transport complexes is found. Besides, coupled with the continuous ridges on blocks and the clear and flat lateral edges suggest that mass-transport complexes belong to the prodelta slump bodies. Thus, the triggering mechanism of the MTCs may be closely related to earthquakes caused by volcanic activities with the evidence of three cinerite layers shown in the well cores.     

南海中尺度涡温盐结构的季节特征及形成机制

本文利用最新的涡旋数据集和ARMOR3D数据,研究了南海中尺度涡温盐结构的季节特征及形成机制。合成分析的结果表明,在冬季,涡旋引起温度异常的水平分布在50米以浅表现为类似偶极型分布,而在50m以深则趋向于中心对称分布;在夏季,温度异常的水平分布均表现为中心对称的特征。涡旋引起盐度异常的水平分布也具有类似的季节特征,但是偶极型中的不对称性相对较弱。在垂向上,涡旋所致的温度异常表现为单层结构,而盐度异常则为三层结构。进一步的分析表明,涡旋所致温盐异常的垂向分布特征与背景温盐的垂向分层有关;而在50m以浅,温盐异常的水平分布的不对称特征主要由背景温盐场的水平平流所致。     

南海东北部陆缘浊流活动的地貌记录及其形成机制分析

超临界浊流影响下的周期阶坎广泛分布在南海东北部台西南盆地的西澎湖峡谷中。由于频繁的构造活动, 常年的台风影响, 以及来自中国台湾河流的大量沉积物供给, 导致这个区域的浊流活动经常发生。本文利用高分辨率的地貌资料, 对西澎湖峡谷发育的23个净侵蚀周期阶坎和10个净沉积周期阶坎进行了形态的定量分析, 并且统计了流经这些周期阶坎的浊流流速。结果显示, 浊流在流经净侵蚀周期阶坎过程中的速度有明显突变, 而在净侵蚀到净沉积周期阶坎的过程中速度也发生了明显的降低, 前者由峡谷中的坡折带导致, 后者则是由限制性环境到非限制性环境的转变造成的。此外, 净沉积周期阶坎主要分布于靠近峡谷口外的西南侧, 这是由于科氏力对浊流影响的结果。研究此区域周期阶坎的形态特征和形成机制能够帮助我们更好地理解海底地形地貌与浊流的相互关系, 对于理解峡谷中的地貌演化具有重要意义。     

珠江口东南近海海区污损生物研究

为研究珠江口东南近海海区污损生物状况,于1986年5月至1987年6月,在香港东南约114和160km,水深为95和113m处布设了两个生物浮标站,并对距香港约172km,水深为115m处的Marex水文气象浮标上的污损生物群落进行调查.此次调查共采集和鉴定出污损生物78种,其中在浸海只有3个月的试板上,主要有柄蔓足类、水螅和藻类,优势种是细板条茗荷、茗荷和直杯螅.至于浸海时间达6～12个月的浮标(包括沉标)及锚链系统,其上还有相当数量的多种双壳类软体动物、无柄蔓足类和苔藓动物等硬性污损生物附着.在种类垂直分布方面,污损生物群落组成随深度发生明显变化.     

南海北部陆丰凹陷中新世底栖有孔虫组合与古环境演化研究

The Miocene epoch marks the most crucial period during the Cenozoic cooling trend, characterized by the Middle Miocene Climatic Optimum(MMCO) and a series of short–lived cooling events(Miocene isotope events).To understand the paleoenvironmental evolution along the shallow water shelf in the South China Sea during the Miocene, the benthic foraminiferal assemblage and total organic carbon content(TOC) were analyzed at Hole LF14 located in the Lufeng Sag, northern South China Sea. Three benthic foraminiferal assemblages(e.g., the Uvigerina spp. assemblage, the Cibicides spp. assemblage, and the Cibicidoides spp. assemblage), corresponding to different watermass conditions, were recognized based on Q–mode factor analysis. Early studies suggested that Hole LF14 was deposited under semienclosed bay, middle to outer shelf or even upper bathyal environment during ～18.7–4.53 Ma. The dominant Uvigerina spp. assemblage was characterized by low diversity and shallow infaunal to infaunal species, indicating a warm, low–oxygenation and eutrophic conditions since the Early Miocene to MMCO(～18.7–14.24 Ma). An abrupt sea level drop and significant faunal changes were recorded during 14.24–13.41 Ma, suggesting development of the East Antarctic Ice Sheets, which resulted in a drop of sea level and change in benthic foraminiferal assemblages along the shallow water shelf. Beyond the Uvigerina spp.assemblage, the Cibicides spp. assemblage became important during the middle–late Middle Miocene(14.24–11.54 Ma). This assemblage was dominated by epifaunal species with relative high diversity, suggesting high–energy, high–oxygenation and oligotrophic conditions with episodic supply of organic food. The dominant Cibicidoides spp. assemblage with high diversity, indicates a mesotrophic conditions with relative high–oxygen content during the Late Miocene to Pliocene(11.54–4.53 Ma). The appearance and continuous occurrence of Ammonia spp. and Pseudorotalia spp. since 10.02 Ma, may reflect the influence of the Kuroshio Current.     

南海热带气旋纬向分布特征

根据中国气象局整编的1949~2003年台风年鉴资料,对南海热带气旋的源地、消亡地、强度、移向移速、活跃地等纬向分布的特征进行分析,旨在为南海热带气旋各纬度带的活动特征,为南海热带气旋的预报业务工作提供参考依据,并为研究工作奠定基础.     

Several significant hydrographic characteristics and their formation mechanism in the South China Sea during the spring and summer of 1998

INTRODUCTIONTheSCSisthelargestmarginseainthewestoftheNorthPacificOcean .Theprevailingwindinwinterisnortheast,whileinsummeritissouthwest .Itisstilluncertainthathowthecirculationandtemperature -salinityfieldassociatewiththemonsoonforcingandaccompanywithseveralkindsofvariationsbeforeorafterthesummermonsoonburst .DuringSECMEXin 1 998,twointensiveobservationperiods (IOP)havebeencarriedoutntheSCS (Fig 1 ) :IOP1 ,from 1 0Aprilto 5May ;IOP2 ,from 1 2JunetoJuly 6 ,inordertounderstandthe…