Submarine landslides on the north continental slope of the South China Sea

Recent and paleo-submarine landslides are widely distributed within strata in deep-water areas along continental slopes, uplifts, and carbonate platforms on the north continental margin of the South China Sea (SCS). In this paper, high-resolution 3D seismic data and multibeam data based on seismic sedimentology and geomorphology are employed to assist in identifying submarine landslides. In addition, deposition models are proposed that are based on specific geological structures and features, and which illustrate the local stress field over entire submarine landslides in deep-water areas of the SCS. The SCS is one of the largest fluvial sediment sinks in enclosed or semi-enclosed marginal seas worldwide. It therefore provides a set of preconditions for the formation of submarine landslides, including rapid sediment accumulation, formation of gas hydrates, and fluid overpressure. A new concept involving temporal and spatial analyses is tested to construct a relationship between submarine landslides and different time scale trigger mechanisms, and three mechanisms are discussed in the context of spatial scale and temporal frequency: evolution of slope gradient and overpressure, global environmental changes, and tectonic events. Submarine landslides that are triggered by tectonic events are the largest but occur less frequently, while submarine landslides triggered by the combination of slope gradient and over-pressure evolution are the smallest but most frequently occurring events. In summary, analysis shows that the formation of submarine landslides is a complex process involving the operation of different factors on various time scales.     

海南及邻区现今地壳三维运动特征及地球动力学环境分析

利用海南及邻区1999年以来GNSS资料及1970年以来水准数据获取三维运动速度场，分析地壳运动特征，结合东南亚水平运动背景场分析周缘板块对海南地块及华南地块陆缘速度场的影响。结果表明，海南岛三维运动以白沙断裂为界，岛北部以海口-屯昌为界。华南地块各观测点E向运动速率自西向东逐渐减小，至陆缘区域速率最小，各观测站间运动速率差异性小；S向运动速率自西向东逐渐增大；位于23°～26°N区域观测点的速度场与其南北两侧存在差异。华南地块运动受印度板块与欧亚板块碰撞和挤压影响，陆缘地带还受太平洋板块、菲律宾海板块活动及南海扩张运动影响，澳大利亚板块对区域运动影响较小。     

Late Cenozoic Tectonic Deformation in the Dongsha Islands and Adjacent Sea Area

Dongsha Island and the adjacent sea area locate at the northern continental margin of the South China Sea (SCS), and is connected to the east by the Manila Trench. Analyses of seismic stratigraphy and gravity, magnetic and drilling wells data led to the discovery of three post-fault sequences (Ⅴ, Ⅵ, Ⅶ). Extensive tectonic uplift, magma activity and erosion occurred in Dongsha Island and the adjacent area, where most of the faults in the northeastern SCS were still active during Pliocene and Quaternary. Two groups of faults trending NEE and NW were developed during Late Cenozoic. We conclude that three important tectonic movements, especially Dongsha movement(4.4 - 5.2 Ma) and Liuhua movement (1.4 - 1.89 Ma), controlled the structural framework in the Dongsha rise; whose deformation in the east is stronger than that in the west and whose stress field variation suggests that the tectonic uplift in the study area contributed to magmato-tectonic events correlated to the main collision phases between the East China and Taiwan 5 - 3 and 3 - 0 Ma ago.     

Geophysical Signature of the Shallow Water Flow in the Deepwater Basin of the Northern South China Sea

Shallow water flow (SWF), a disastrous geohazard in the continental margin, has threatened deepwater drilling operations. Under overpressure conditions, continual flow delivering unconsolidated sands upward in the shallow layer below the seafloor may cause large and long-lasting uncontrolled flows; these flows may lead to control problems and cause well damage and foundation failure. Eruptions from over-pressured sands may result in seafloor craters, mounds, and cracks. Detailed studies of 2D/3D seismic data from a slope basin of the South China Sea (SCS) indicated the potential presence of SWF. It is commonly characterized by lower elastic impedance, a higher Vp/Vs ratio, and a higher Poisson’s ratio than that for the surrounding sediments. Analysis of geological data indicated the SWF zone originated from a deepwater channel system with gas bearing over-pressured fluid flow and a high sedimentation rate. We proposed a fluid flow model for SWF that clearly identifies its stress and pressure changes. The rupture of previous SWF zones caused the fluid flow that occurred in the Baiyun Sag of the northern SCS.     

南海及周围地区的现今构造运动

利用南海及其周围地区的GPS数据,分析南海及周围地区速度场和应变场的空间变化,以及相邻块体之间的相对运动.研究发现,南海现今仍在继续扩张,西部是从其北边缘向南沿NW-SE方向逐渐扩张的,东部是从中心向北与向南逐渐扩张的.由主张应变率计算的中央海盆近SN方向的平均扩张速率为3.1 mm/a.在南海东部(117.0°E),南北之间(11°～22°N)SN方向的扩张速率为9.3 mm/a,小于65Ma以来NNW-SSE方向13.0 mm/a的平均扩张速率.南海的扩张运动是印度板块、太平洋和菲律宾海板块与欧亚板块之间的相互作用,以及南海地区地幔物质上涌共同作用的结果.     

Tectonic Evolution of the Northern Continental Margin of North China Platform in Middle Proterozoic

An orogenic belt developed in late middle Proterozoic in the northern margin of North China Plate extends from Inner Mongolia to Western Liaoning Province and Eastern Jilin Province. It is over 2000km long. The orogenic belt was formed by collision between North China Platform and Siberia Platform during the Rodinian Super- Continent period. From sedimentary formation, magmatic activity and crustal tectonic deformation, it is suggested that along the tectonic belt the paleocontinental margin experienced four stages of tectonic evolution in middle Proterozoic, they are: continental margin rift,passive continental margin, active continental margin and collisional orogenic stages.     

辽河断陷中元古代构造演化

辽河断陷的中元古代构造演化与华北北缘和郯庐断裂带的构造演化密切相关。大红峪期,华北北缘在大陆裂谷的基础上进一步发展成被动大陆边缘,郯庐断裂带随之响应发生张裂接受沉积。之后海平面升降,辽宁境内表现为杨庄上升和凌源上升,其不整合面均为沉积属性,在这期间,郯庐断裂带与华北北缘一致保持着裂解趋势。由兴城上升至芹峪上升,辽河断陷沉积了大红峪组、高于庄组、杨庄组和雾迷山组,洪水庄组和铁岭组尚待确定。芹峪上升表示华北北缘开始由被动大陆边缘转换成主动大陆边缘,洋壳低角度俯冲使华北北缘挤压抬升并迫使华北克拉通向南挤压,NE向郯庐断裂由张裂转换成挤压滑动,辽河断陷抬升遭受剥蚀。辽河断陷内的杨庄组和雾迷山组可能就在这一时期剥蚀殆尽。随后洋壳高角度俯冲,华北北缘形成弧后盆地,辽河断陷与燕山地区一样沉积下马岭组。蔚县上升为华北北缘陆陆碰撞造成,陆陆碰撞使华北北缘再次抬升,郯庐断裂挤压走滑增强,辽河断陷褶皱抬升,下马岭组遭受剥蚀。直到罗迪尼亚大陆开始裂解,郯庐断裂带再次张裂,辽河断陷沉积长龙山组和景儿峪组。     

Contribution of Mountain River Materials to the Continental Shelf off Southeastern Hainan Island Since the Mid-Holocene

The concentrations of rare earth elements(REEs) in the bulk sediment of Core X2, which was collected from southeastern Hainan Island, were analyzed to investigate the relative contributions of various provenance regions since mid-Holocene. The results show that sediments in Core X2 were primarily derived from Hainan Island with lesser amounts from Taiwan and limited input from the Pearl River. Based on the application of quantitative inversion to model the REE data, the average contributions of river materials from southeastern Hainan Island and southwestern Taiwan to the study area were 68% and 32%, respectively. Furthermore, starting at 4.0 kyr BP, the transport of fluvial sediments from Taiwan to the study region increased due to enhanced hydrodynamics in South China Sea(SCS). These results indicate that the contributions of mountain river materials from Hainan Island and Taiwan to the continental shelf of northern SCS are non-negligible. Furthermore, these results demonstrate that mountain rivers can play an important role in the material cycle of continental margins and may feature a greater impact than large river systems in specific continental shelf areas.     

Modern movement and deformation in the South China Sea shown by GPS measurements and numerical simulation

To better understand the crustal deformation of the South China Sea Basin, we produce a mechanically consistent 2-dimensional model for observing regional velocity field in the South China Sea (SCS). We studied the dominating regional tectonic stress field by geodetic measurements and finite element analysis, the spatial variations of velocity field and strain field, and relative movements among different blocks, using a 2-dimensional model describing crustal deformation of the South China Sea Basin. Strain results show that the SCS is extending at present. The western part of SCS is opening gradually in NWSE direction from its northern margin to the south, but the eastern part of SCS is opening gradually from its central part to the north and south. In addition, we analyzed the plate kinematics to the deformation of the SCS, using a two-dimensional finite element model. Our simulations results are well explained by available geodetic data. The movement of SCS is resulted from interactions among Indian Plate, Pacific Plate, Philippine Sea Plate, and Eurasian Plate.     

东非大陆边缘构造演化与油气成藏模式探析

近年来,东非海上不断有大型天然气田发现,已成为国际能源勘探的新兴热点。东非地区蕴藏着巨大的油气资源潜力,但其勘探和研究程度很低。在调研大量区域地质和油气地质资料的基础上,通过对东非大陆边缘构造演化特征的分析,从油气成藏要素(烃源岩、储盖组合以及圈闭类型)入手,探讨了油气成藏模式,并对其勘探前景和方向进行了分析。研究结果表明,东非大陆边缘经历了4期构造演化,形成了裂谷叠加被动大陆边缘的双层系盆地结构;主力烃源岩形成于卡鲁裂谷期,主力储层形成于被动陆缘期,在大型三角洲发育区,油气保存条件最好,以构造和构造-地层圈闭为主;油气成藏模式受到构造演化的阶段性、构造变形的横向分带性以及成藏要素的配置关系所控制。      

Seasonal variation and modal content of internal tides in the northern South China Sea

A nine-month mooring record was used to investigate seasonal variation and modal content of internal tides(ITs) on the continental slope in the northern South China Sea(SCS). Diurnal tides at this site show clear seasonal change with higher energy in winter than in spring and autumn, whereas semidiurnal tides show the opposite seasonal pattern. The consistency of ITs with barotropic tides within the Luzon Strait, which is the generation region of the ITs, implies that the seasonal variation of ITs depends on their astronomical forcing, even after extended propagation across the SCS basin. Diurnal tides also differ from semidiurnal tides in relation to modal content; they display signals of high modes while semidiurnal tides are dominated by low modes. Reflection of the diurnal tides on the continental slope serves as a reasonable explanation for their high modes. Both diurnal and semidiurnal tides are composed of a larger proportion of coherent components that have a regular 14-day spring-neap cycle. The coherent components are dominated by low modes and they show obvious seasonal variation, while the incoherent components are composed mainly of higher modes and they display intermittent characteristics.     

Reversal process of the South China Sea western boundary current in autumn 2011

Using merged sea level anomaly and absolute geostrophic velocity products from satellite altimetry and Argos drifter data,we analyzed the reversal process of the South China Sea(SCS) western boundary current(SCSwbc) from a summer to winter pattern in 2011 and important oceanic phenomena during this process.Results show that the outbreak time of the northeast monsoon over the southern SCS lagged that over the northern SCS by about 1 month.During the SCS monsoon reversal period,the SCSwbc reversed rapidly into the winter pattern at the Guangdong continental slope in late September.Subsequently,the southward Vietnam coastal boundary current strengthened.However,the northward Natuna Current maintained a summer state until mid-October.Thus,the balance between the southward and northward currents was lost when they met,their junction moved gradually southward.However,a loop current formed southeast of Vietnam because the main stream of the Vietnam Offshore Current(VOC) remained near its original latitude.Meanwhile,the VOC and associated dipole circulation system strengthened.After midOctober,the northward Natuna Current began to weaken,the loop current finally shed,becoming a cool ring.The VOC and its associated dipole sub-basin circulation system also weakened gradually until it disappeared.     

Diatom assemblages in surface sediments from the South China Sea as environmental indicators

We studied diatom distribution from 62 samples from the uppermost 1 cm of sediment in the South China Sea (SCS), using grabs or box corers in three cruises between 2001–2007. Fifty six genera, 256 species and their varieties were identified. Dominating species included Coscinodiscus africanus, Coscinodiscus nodulifer, Cyclotella stylorum, Hemidiscus cuneiformis, Melosira sulcata, Nitzschia marina, Roperia tesselata, Thalassionema nitzschioides, Thalassiosira excentrica, and Thalassiothrix longissima. Most surface sediments in the SCS were rich in diatoms, except for a few coarse samples. Average diatom abundance in the study area was 104 607 valve/g. In terms of the abundance, ecology, and spatial distribution, seven diatom zones (Zones 1–7) were recognized. Zone 1 (northern continental shelf) is affected by warm currents, SCS northern branch of the Kuroshio, and northern coastal currents; Zone 2 (northwestern continental shelf) is affected by intense coastal currents; Zone 3 (Xisha Islands sea area) is a bathyal environment with transitional water masses; Zone 4 (sea basin) is a bathyal-to-deep sea with stable and uniform central water masses in a semi-enclosed marginal sea; Zone 5 (Nansha Islands marine area) is a pelagic environment with relatively high surface temperature; Zone 6 (northern Sunda Shelf) is a tropical shelf environment; and Zone 7 (northern Kalimantan Island shelf area) is affected by warm waters from the Indian Ocean and coastal waters. The data indicate that these diatom zones are closely related to topography, hydrodynamics, temperature, nutrients and especially the salinity. Better understanding of the relationship between diatom distribution and the oceanographic factors would help in the reconstruction of the SCS in the past.     

Comparison of remote sensing data with in-situ wind observation during the development of the South China Sea monsoon

Wind measurements derived from QuikSCAT data were compared with those measured by anemometer on Yongxing Island in the South China Sea (SCS) for the period from April 2008 to November 2009. The comparison confirms that QuikSCAT estimates of wind speed and direction are generally accurate, except for the extremes of high wind speeds (>13.8m/s) and very low wind speeds (<1.5m/s) where direction is poorly predicted. In-situ observations show that the summer monsoon in the northern SCS starts between May 6 and June 1. From March 13, 2010 to August 31, 2010, comparisons of sea surface temperature (SST) and rainfall from AMSR-E with data from a buoy located at Xisha Islands, as well as wind measurements derived from ASCAT and observations from an automatic weather station show that QuikSCAT, ASCAT and AMSR-E data are good enough for research. It is feasible to optimize the usage of remote-sensing data if validated with in-situ measurements. Remarkable changes were observed in wind, barometric pressure, humidity, outgoing longwave radiation (OLR), air temperature, rainfall and SST during the monsoon onset. The eastward shift of western Pacific subtropical high and the southward movement of continental cold front preceded the monsoon onset in SCS. The starting dates of SCS summer monsoon indicated that the southwest monsoon starts in the Indochinese Peninsula and forms an eastward zonal belt, and then the belt bifurcates in the SCS, with one part moving northeastward into the tropical western North Pacific, and another southward into western Kalimantan. This largely determined the pattern of the SCS summer monsoon. Wavelet analysis of zonal wind and OLR at Xisha showed that intra-seasonal variability played an important role in the summer. This work improves the accuracy of the amplitude of intra-seasonal and synoptic variation obtained from remote-sensed data.     

柴达木北缘奥陶纪火山作用与构造机制

柴达木北缘奥陶系海相火山岩（洋脊及洋岛火山岩组合）是柴北缘奥陶纪古洋盆存在的重要证据。奥陶纪末期，柴北缘洋盆逐渐闭合，洋壳自南向北下插到祁连陆块之下。大洋消失后，俯冲作用携带柴达木陆块继续下插，祁连陆块则自北向南道冲到柴达木陆块之上，柴北缘成为陆－陆碰撞型造山带。从而在柴达木北缘地区，自北而南形成了祁连超叠壳楔、柴北缘碰撞混杂岩带以及柴达木俯冲壳楔的三单元结构模式。     

Comparison of nonlinear and linear PCA on surface wind, surface height, and SST in the South China Sea

We compared nonlinear principal component analysis (NLPCA) with linear principal component analysis (LPCA) with the data of sea surface wind anomalies (SWA), surface height anomalies (SSHA), and sea surface temperature anomalies (SSTA), taken in the South China Sea (SCS) between 1993 and 2003. The SCS monthly data for SWA, SSHA and SSTA (i.e., the anomalies with climatological seasonal cycle removed) were pre-filtered by LPCA, with only three leading modes retained. The first three modes of SWA, SSHA, and SSTA of LPCA explained 86%, 71%, and 94% of the total variance in the original data, respectively. Thus, the three associated time coefficient functions (TCFs) were used as the input data for NLPCA network. The NLPCA was made based on feed-forward neural network models. Compared with classical linear PCA, the first NLPCA mode could explain more variance than linear PCA for the above data. The nonlinearity of SWA and SSHA were stronger in most areas of the SCS. The first mode of the NLPCA on the SWA and SSHA accounted for 67.26% of the variance versus 54.7%, and 60.24% versus 50.43%, respectively for the first LPCA mode. Conversely, the nonlinear SSTA, localized in the northern SCS and southern continental shelf region, resulted in little improvement in the explanation of the variance for the first NLPCA.     

抚顺东部地区太古宙花岗质侵人体的地质特征及成因

抚顺东部地区太古宙花岗质侵入体为一套组成较复杂的大陆弧花岗岩,包括紫苏花岗岩和TTG岩系,具有奥长花岗岩及钙碱性双重演化趋势,形成于晚太古代大陆边缘或大陆弧环境中,其成因直接导源于古老的板块俯冲运动及区域变质变形作用,侵位机制属于主动型岩浆底辟作用。     

Stratigraphic framework of late Paleozoic in northeastern China

Late Paleozoic strata in northeastern China are distributed in a zonal pattern around the old-land on the Jiamusi-Mongolia Block.They are composed of active deposits in the regular distributed tectonic lithofacies zones.This indicates that the late Paleozoic strata belong to continental margin deposits.According to the strong conformability of the sedimentary strata in the same continental margin and distinct differences among the three continental margins,three stratigraphical regions of the Jiamusi-Mongolia Stratigraphical Province are recognized along the northern,southern and eastern margins of the Jiamusi-Mongolia Block,named respectively as Xing’an Stratigraphical Region,Inner Mongolia grass--Songhua River Stratigraphical Region and Baoqing--Hunchun Stratigraphical Region.Due to the characteristics of continental margin deposits and active sediments,the strata can be correlated on the level of formation by the methods of analysing the rock association in the same stratigraphic region.Therefore,some revisions of the lithological formations of the late Paleozoic strata in northeastern China have been made,and a new chart of lithostratigraphic correlation has been proposed.Furthermore,the present stratigraphic framework is setting on the International Stratigraphic Chart on the level of stage,after comprehensive researches to lithostratigraphy,biostratigraphy and chronostratigraphy,especially the conodont biostratigraphy and isotopic ages of volcanic rocks obtained in recent years.     

鄂尔多斯南部地区早古生代主动大陆边缘演化特征

中—晚奥陶世期间 ,鄂尔多斯南部地区为古秦岭洋北侧具沟、弧、盆体系的主动大陆边缘。在此背景下 ,有序地发育了可分别用镶边碳酸盐陆棚模式及重力流模式概括的弧后盆地与残留海盆地沉积类型 ;构造轮廓为向洋呈阶状断落和块状错移结构特征的基本格局。晚奥陶世末 ,华北板块与扬子板块的陆 -陆碰撞作用结束了主动大陆边缘构造阶段     

A PRELIMINARY STUDY ON THE TECTONICS AND EVOLUTION OF THE FUJIAN COAST CHANGLE-NANAO METAMORPHISM ZONE

The Fujian coast Changle-Nanao metamorphism zone rocks are composed of gneiss, schist andhornblendite which had gone through metamorphism of amphilbolite facies, and followed the large-scaleintrusive mass of gneissic granite. The zone was orginally composed of Early Palaeozoiccontinental margin and island arc volcanic and sedimentary rocks. In 180-150 Ma, the zone undermentductile shear deformation and amphibolite facies metamorphism; and in 130-80 Ma, rose rap1dly andco1lided with the Southeastem China continen1al rnargln volonic rocks a10ng the NE trending ductileshear belt. The above geologic setting laid the present Fujian coast tectonic foundation whose formationand evolution are known to be interrlatal with the sueduction and collision of the Taiwan CentralRange.