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1.
Late Cenozoic sedimentation from four varied sites on the continental slopes off southeastern Canada has been analysed using high-resolution airgun multichannel seismic profiles, supplemented with some single channel data. Biostratigraphic ties are available to exploratory wells at three of the sites. Uniform, slow accumulation of hemipelagic sediments was locally terminated by the late Miocene sea-level lowering, which is also reflected in changes in foraminiferan faunas on the continental shelf. Data are very limited for the early Pliocene but suggest a return to slow hemipelagic sedimentation. At the beginning of the late Pliocene, there was a change in sedimentation style marked by a several-fold increase in accumulation rates and cutting of slope valleys. This late Pliocene cutting of slope valleys corresponds to the onset of late Cenozoic growth of the Laurentian Fan and the initiation of turbidite sedimentation on the Sohm Abyssal Plain. Although it corresponds to a time of sea-level lowering, the contrast with the late Miocene lowstand indicates that there must also have been a change in sediment delivery to the coastline, perhaps as a result of increased rainfall or development of valley glaciers. High sedimentation rates continued into the early Pleistocene, but the extent of slope dissection by gullies increased. Gully-cutting episodes alternated with sediment-draping episodes. Throughout the southeastern Canadian continental margin, there was a change in sedimentation style in the middle Pleistocene that resulted from extensive ice sheets crossing the continental shelf and delivering coarse sediment directly to the continental slope. 相似文献
2.
High-resolution seismic profiles were acquired in the north Sicily offshore region with an innovative, multi-tip sparker array which lacks ringing and has a base frequency around 600 Hz. The new data, combined with published data, suggest that intra-slope and extensional basins formed as a consequence of the late Miocene (?)–early Pliocene shortening and thrusting, and the middle (?)–late Pliocene continental rifting affecting the internal side of the Sicilian-Maghrebian chain. Early (?) Pleistocene to Holocene high-amplitude and high-frequency sea-level changes resulted in repeated sub-aerial exposure and flooding of the shelf, and the deposition of cyclically arranged hemipelagic and shelf sediments. An uplift of the shelf could explain the non-preservation of the transgressive and of the lowstand wedge systems tracts in the oldest sequences. 相似文献
3.
《Marine Geology》2005,216(3):145-154
The Eastern Basin in the Ross Sea (Antarctica) contains a sedimentary sequence that is a direct record of advance and retreat of the West Antarctic Ice Sheet.We analyzed a sedimentary section ranging from the upper Miocene to present.The joint tomographic inversion of refracted and reflected arrivals of pre-stack multi-channel seismic data revealed in this area the presence of layers with anomalous high velocity. These anomalies are correlated with sediments that were eroded and compacted by the load of the West Antarctic Ice Sheet during its expansion on the continental shelf.The deepest and stronger velocity anomaly correspond to a basin-wide seismic unconformity (RSU2, Late Miocene–Early Pliocene in age). This anomaly is interpreted as evidence of a major advance of the West Antarctic ice sheet on the continental shelf that resulted in high velocity and low porosity in sediment immediately above the unconformity. 相似文献
4.
A 33 Ma lithostratigraphic record of tectonic and paleoceanographic evolution of the South China Sea
Qianyu Li Pinxian Wang Quanhong Zhao Lei Shao Guangfa Zhong Jun Tian Xinrong Cheng Zhimin Jian Xin Su 《Marine Geology》2006,230(3-4):217-235
The 853 m thick sediment sequence recovered at ODP Site 1148 provides an unprecedented record of tectonic and paleoceanographic evolution in the South China Sea over the past 33 Ma. Litho-, bio-, and chemo-stratigraphic studies helped identify six periods of changes marking the major steps of the South China Sea geohistory. Rapid deposition with sedimentation rates of 60 m/Ma or more characterized the early Oligocene rifting. Several unconformities from the slumped unit between 457 and 495 mcd together erased about 3 Ma late Oligocene record, providing solid evidence of tectonic transition from rifting/slow spreading to rapid spreading in the South China Sea. Slow sedimentation of 20–30 m/Ma signifies stable seafloor spreading in the early Miocene. Dissolution may have affected the completeness of Miocene–Pleistocene succession with short-term hiatuses beyond current biostratigraphical resolution. Five major dissolution events, D-1 to D-5, characterize the stepwise development of deep water masses in close association to post-Oligocene South China Sea basin transformation. The concurrence of local and global dissolution events in the Miocene and Pliocene suggests climatic forcing as the main mechanism causing deep water circulation changes concomitantly in world oceans and in marginal seas. A return of high sedimentation rate of 60 m/Ma to the late Pliocene and Pleistocene South China Sea was caused by intensified down-slope transport due to frequent sea level fluctuations and exposure of a large shelf area during sea level low-stands. The six paleoceanographic stages, respectively corresponding to rifting (33–28.5 Ma), changing spreading southward (28.5–23 Ma), stable spreading to end of spreading (23–15 Ma), post-spreading balance (15–9 Ma), further modification and monsoon influence (9–5 Ma), and glacial prevalence (5–0 Ma), had transformed the South China Sea from a series of deep grabens to a rapidly expanding open gulf and finally to a semi-enclosed marginal sea in the past 33 Ma. 相似文献
5.
Abstract Submarine faults and slides or slumps of Quaternary age are potential environmental hazards on the outer continental shelf (OCS) of the northern Gulf of Alaska. Most faults that approach or reach the seafloor cut strata that may be equivalent in age to the upper Yakataga Formation (Pliocene‐Pleistocene). Along several faults, the seafloor is vertically offset from 5 to 20 m. A few faults appear to cut Holocene sediments, but none of these shows displacement at the seafloor. Submarine slides or slumps have been found in two places in the OCS region: (1) seaward of the Malaspina Glacier and Icy Bay, an area of 1200 km2 with a slope of less than 0.5°, and (2) across the entire span of the Copper river prodelta, an area of 1730 km2, having a slope of about 0.5°. Seismic profiles across these areas show disrupted reflectors and irregular topography commonly associated with submarine slides or slumps. Potential slide or slump areas have been delineated in areas of thick sediment accumulation and relatively steep slopes. These areas include (1) Kayak Trough, (2) parts of Hinchinbrook Entrance and Sea Valley, (3) parts of the outer shelf and upper slope between Kayak Island and Yakutat Bay, and (4) Bering Trough. 相似文献
6.
《Marine Geology》2001,172(3-4):331-358
Analyses of over 6600 km of reflection seismic profiles on the northern continental margin of the South China Sea permit the recognition of four Quaternary high-frequency type 1 sequences of the 4th order, deposited during the past ca. 690 kyr. At the present-day shelf edge, only lowstand systems tracts characterised by a prograding clinoformal internal reflection pattern are preserved. The prograding complexes can be considered as regressive units accumulated during relative sea-level falls. They exhibit internal discontinuities which might point to minor sea-level fluctuations of the 5th order. A preliminary regional relative sea-level curve for the past 630 kyr is established using the present positions of the delta fronts mapped. The neotectonics curve derived by subtracting eustatic sea-level changes from the relative sea-level curve shows that the depths of the delta fronts today are controlled primarily by regional tectonic movements and the global sea-level.Our seismo-stratigraphic interpretation documents that the area off Hong Kong and around the Dongsha Islands experienced two uplift episodes during the past 5 ma, namely at the Miocene/Pliocene boundary and at the end of the lower Middle Pleistocene, respectively. These uplift events which are centred on the Dongsha Rise led to its subaerial exposure and to the erosion of the Pliocene and most of the Pleistocene strata. The change from thermal subsidence of the continental margin initiated at the end of the drift phase to the phase of magmato-tectonic uplift was caused by a reorientation of the tectonic regime.The Recent depositional environment on the northern continental margin of the South China Sea is dominated by sediment accumulation within the inner shelf and the Zhujiang (Pearl River) estuary. The outer shelf and upper slope, especially around the Dongsha Islands, are characterised by bypass of terrigenous material.The sedimentary column in the deepsea basin has a thickness of more than 2 km and comprises 14 depositional units starting with terrestrial rift deposits. It overlies oceanic as well as transitional crust. 相似文献
7.
Igneous rocks in the northern margin of the South China Sea (SCS) have been identified via high resolution multi-channel seismic data in addition to other geophysical and drilling well data. This study identified intrusive and extrusive structures including seamounts and buried volcanoes, and their seismic characteristics. Intrusive features consist of piercement and implicit-piercement type structures, indicating different energy input associated with diapir formation. Extrusive structures are divided into flat-topped and conical-topped seamounts. Three main criteria (the overlying strata, the contact relationship and sills) were used to distinguish between intrusive rocks and buried volcanos. Three criteria are also used to estimate the timing of igneous rock formation: the contact relationship, the overlying sedimentary thickness and seismic reflection characteristics. These criteria are applied to recognize and distinguish between three periods of Cenozoic magmatism in the northern margin of the SCS: before seafloor spreading (Paleocene and Eocene), during seafloor spreading (Early Oligocene–Mid Miocene) and after cessation of seafloor spreading (Mid Miocene–Recent). Among them, greater attention is given to the extensive magmatism since 5.5 Ma, which is present throughout nearly all of the study area, making it a significant event in the SCS. Almost all of the Cenozoic igneous rocks were located below the 1500 m bathymetric contour. In contrast with the wide distribution of igneous rocks in the volcanic rifted margin, igneous rocks in the syn-rift stage of the northern margin of the SCS are extremely sporadic, and they could only be found in the southern Pearl River Mouth basin and NW sub-sea basin. The ocean–continent transition of the northern SCS exhibits high-angle listric faults, concentrated on the seaward side of the magmatic zone, and a sharply decreased crust, with little influence from a mantle plume. These observations provide further evidence to suggest that the northern margin of the SCS is a magma-poor rifted margin. 相似文献
8.
9.
Pliocene to Recent shallow-water contourite deposits on the shelf and shelf edge off south-western Mallorca, Spain 总被引：2，自引：2，他引：0
Thomas Philippe Vandorpe David Van Rooij Dorrik A. V. Stow Jean-Pierre Henriet 《Geo-Marine Letters》2011,31(5-6):391-403
This paper presents evidence for the presence of shallow-water contourite drifts on the south-western shelf and shelf edge off Mallorca in water depths between 150 and 275?m. These are called the Mallorca contourite depositional system (CDS). The elongate-mounded shallow-water CDS in this area is ascribed to an offshoot of the Balearic Current, which flows north to south through the Mallorca Channel as part of the overall thermohaline circulation in the Mediterranean Sea. Drift geometry suggests that the north?Csouth current is deflected into an east?Cwest flow pattern by interaction with a marked seafloor bathymetry, associated with major fault displacement. Four seismic units separated by three prominent discontinuities can be identified. The three internal discontinuities are correlated to large-scale basin-wide events: the lower Pliocene revolution (4.2?Ma), the upper Pliocene revolution (2.4?Ma) and the mid-Pleistocene revolution (0.9?Ma). The Plio-Quaternary succession has been deposited on top of a Miocene reef, which serves as an acoustic basement and is affected by a large fault, offsetting the basement on average by 150?m. Marked erosional features throughout and further incision of the Sant Jordi Channel along the basement fault in the Pleistocene deposits indicate stronger currents in this period. The Pleistocene deposits also show a pronounced cyclicity, which is tentatively ascribed to climatic variations and the effects of eustatic sea-level fluctuation over the south-western Mallorca shelf at that time. 相似文献
10.
南海北部陆丰凹陷内LF14井记录了早中新世至早上新世的海相沉积地层。古水深重建结果显示研究井位在早中新世突然发生海侵, 水深迅速上升至最大值275m, 随后经数次波动, 整体处于中—外陆架环境, 共记录了5个完整的海侵—海退层序。回剥分析方法重建的LF14井沉降史揭示了研究井位在中中新世(17.5—10Ma)处于快速沉降期, 快速沉降导致的凹陷内沉积物的可容纳空间发育速率高和陆源物质供给充足是造成该阶段沉积速率高的两个重要因素; 晚中新世—早上新世(10—4.53Ma)处于弱沉降期, 推测东沙运动导致凹陷内的沉积物可容纳空间发育速率变小和陆源物质供给减少, 造成该时期内研究井位沉积速率低。最后, 依据定量重建的古水深变化在研究层段识别出一系列短暂存在的构造上升事件。 相似文献
11.
Acouso-physical properties of sea floor sediments in the southeast offshore sea area of Hainan Island on the northern continental shelf of the South China Sea are analyzed. In many cruises, conductivity-temperature-depth measurements of seawater, measurements of shallow stratum and side-scan sonar have been made. Acoustic parameters, basic sedimentary parameters, physical-mechanical parameters and 14C age, etc., have been measured. The sediment elastic parameters, including Young's modulus, bulk modulus, constrained modulus, rigidity modulus, Poisson's ratio, Lames constant, etc., have been calculated. Results show that the compression wave velocity of the seafloor sediment in the sea area ranges from 1474–1700 m/s, and there are high and low sound velocity sediment types in the different sea areas; the shear wave velocity is 150–600 m/s; at 100 kHz the sediment sound attenuation is 35–260 dB/m, the sediment density is 1.4–2.0 g/cm3; the sediment porosity is 42–88%. Sound field parameters and describing sound reciprocity between sea and seafloor are described. 相似文献
12.
Crustal features of the northeastern South China Sea: insights from seismic and magnetic interpretations 总被引：1，自引：0，他引：1
Yi-Ching Yeh Shu-Kun Hsu Wen-Bin Doo Jean-Claude Sibuet Char-Shine Liu Chao-Shing Lee 《Marine Geophysical Researches》2012,33(4):307-326
We interpret seven two-dimensional deep-penetration and long-offset multi-channel seismic profiles in the northernmost South China Sea area, which were collected by R/V Marcus G. Langseth during the TAIwan GEodynamics Research (TAIGER) project in 2009. To constrain the crustal characteristics, magnetic inversion and forward magnetic modeling were also performed. The seismic results clearly show tilted faulting blocks in the upper crust and most of the fault plane connects downward to a quasi-horizontal detachment as its bottom in the south of the Luzon-Ryukyu transform plate boundary. North of the plate boundary, a small-scale failed rifted basin (minimum 5 km in crustal thickness) with negative magnetization probably indicates an extended continental origin. Significant lower crustal material (LCM) was imaged under a crustal fracture area which indicated a continent and ocean transition origin. The thickest LCM (up to 6.5 km) is located at magnetic isochron C15 that is probably caused by the magma supply composite of a Miocene syn-rift volcanic event and Pliocene Dongsha volcanic activity for submarine volcanoes and sills in the surrounding area. The LCM also caused Miocene crustal blocks to be uplifted reversely as 17 km crustal thickness especially in the area of magnetic isochron C15 and C16. In addition, the wide fault blocks and LCM co-existed on the magnetic striped area (i.e. C15–C17) in the south of the Luzon-Ryukyu transform plate boundary. Magnetic forward modeling suggests that the whole thick crustal thickness (>12 km thick) needs to be magnetized in striped way as oceanic crust. However, the result also shows that the misfit between observed and synthetic magnetic anomaly is about 40 nT, north of isochron C16. The interval velocity derived from pre-stack time migration suggests that the crust is composed of basaltic intrusive upper crust and lower crustal material. The crustal nature should refer to a transition between continent and ocean. Thus, the magnetic reversals may be produced in two possible ways: basaltic magma injected along the crustal weak zone across magnetic reversal epoch and because some undiscovered ancient piece of oceanic crust existed. The crustal structure discrimination still needs to be confirmed by future studies. 相似文献
13.
琼东南陆坡深水水道主控因素及勘探应用 总被引：8，自引：0，他引：8
结合全球海平面变化、气候变化、物源供给特征和地形条件,深入地分析和研究了发育在琼东南盆地陆坡区上新世和更新世地层中水道的形成主控因素及其在深水油气勘探中的应用价值和前景。提出琼东南陆坡上新世水道的主要因素是物源供给,包括来自红河和海南岛的物源,构造活动是关键诱发因素,上新世早期莺歌海盆地发育的大规模滑塌体与该水道的形成关系密切;给出更新世水道形成模式,其形成与第四纪冰期海平面的大幅度下降有关,地震活动诱发了中南半岛的小型山脉河流复苏,并对南海西部陆坡直接供给形成了该期水道。深水水道对于全球海平面变化、陆坡区物源供给情况和陆坡层序界面具有指示作用,并可作为良好的深水油气勘探目标,具有重要的深水油气勘探意义。 相似文献
14.
Seismic data and sediment cores collected offshore from the Sanaga River and Nyong River mouths were used to analyse a loose mantle of yellow to reddish sandy gravel with a range of fluvial and deltaic characteristics cropping out in the middle part (25–65 m water depth) of the continental shelf of Cameroon. Contrary to most of the Atlantic shelves, where the lowstand systems tract was destroyed by erosion, we found 80–120 ms (60–90 m) of sediment mainly in the middle part of the shelf, which correspond credibly to MIS 2–4. Fluvial paleodrainage systems are preserved beneath the shelf and individual filled channels with planar infillings were mapped that cross the shelf along two surfaces of erosion. These incisions suggested westerly and northwesterly drainage shifts during presumed lowered base level. The presence of closely spaced channel fills suggests repeated avulsion of a single stream during a long-lasting sub-aerial erosion period. The seismic facies of these Pleistocene deposits distinguish themselves clearly from well-stratified older strata showing deformation (Pliocene) or intense folding (Miocene). The orientation of the paleovalleys appears strongly controlled by the N60°E trending cross faults within Mesozoic–Cenozoic strata. 相似文献
15.
During summer of 2009, multi-channel marine seismic reflection data and wide-angle refraction data were acquired as part of the joint NSF and Taiwanese-funded TAIGER program with the goal of understanding the dynamics of arc-continent collision in Taiwan. One of the principle difficulties of crustal-scale imaging with marine reflection data such as these is the prevalent multiple contamination that obscures many of the deep crustal targets. Without effective treatment of multiples, many of the objectives of the TAIGER active source program may not be achieved. We present three profiles, one from each acquisition leg, that demonstrate the effectiveness of 2D surface-related multiple elimination (SRME) and radon filtering in attenuating much of this unwanted energy in broad ranges of water depths, seafloor topographies and lithologies. Two profiles from south of Taiwan image 3–4 km of sedimentary strata overlying moderately extended continental crust along the Eurasia continental shelf and a 5–6 km thick sedimentary section overlying thin crust consisting of faulted blocks and volcanic bodies along the continental slope. Our multiple attenuation efforts also reveal a seaward-dipping normal fault that penetrates into the upper mantle and separates thick crust of the continental shelf from thin crust of the continental slope. A profile from east of Taiwan reveals thin ocean crust of the Philippine Sea plate subducting beneath the Ryukyu trench that may be traced beneath the accretionary prism and Ryukyu forearc. These profiles demonstrate the success of our imaging strategy in the range of imaging environments spanned by the TAIGER marine reflection seismic data. 相似文献
16.
The results of continuous seismic profiling thermodynamics performed in the northern part of the Japan Basin in the region of the Tarasov Rise and the data of a micropaleontological examination of the diatom remains encountered in the sediment samples from the rise and continental slope are presented. In the area studied, the topography of the acoustic basement features a vast rise (plateau) buried under the sedimentary cover outlined by the depth contour 5.8 s. The plateau has a relatively smooth top surface crossed by a series of rises of the acoustic basement. The two largest rises are represented by the ridges of the Tarasov Rise. The plateau is separated from the continental slope by a depression in the acoustic basement with a depth up to 6.8 s. From the end of the Middle Miocene up to the beginning of the Paleocene, the region of the plateau represented an area of active volcanism; it coincided in time with the stage of subsidence of the floor of the acoustic basement depression. At the end of the Late Miocene, the ridges of the Tarasov Rise started to sink. In the Pliocene, this process accelerated, and, at the beginning of the Pleistocene, it stopped. In the Middle Miocene-Early Pleistocene time, the portion of the continental slope adjacent to the plateau remained stable and suffered no significant vertical movements. 相似文献
17.
Martyn S. Stoker Daniel Praeg Berit Oline Hjelstuen Jan Sverre Laberg Tove Nielsen Pat M. Shannon 《Marine and Petroleum Geology》2005,22(9-10):977
A regional correlation of Neogene stratigraphy has been attempted along and across the NW European Atlantic continental margin, between Mid-Norway and SW Ireland. Two unconformity-bounded successions are recognised. These are referred to as the lower and upper Neogene successions, and have been dated as Miocene–early Pliocene and early Pliocene–Holocene, respectively, in age. Their development is interpreted to reflect plate-wide, tectonically driven changes in the sedimentary, oceanographic and latterly climatic evolution of the NE Atlantic region. The lower Neogene succession mainly preserves a record of deep-water sedimentation that indicates an expansion of contourite sediment drifts above submarine unconformities, within this succession, on both sides of the eastern Greenland–Scotland Ridge from the mid-Miocene. This is interpreted to record enhanced deep-water exchange through the Faroe Conduit (deepest part of the Southern Gateway), and can be linked to compressive inversion of the Wyville–Thomson Ridge Complex. Thus, a pervasive, interconnected Arctic–North Atlantic deep-water circulation system is a Neogene phenomenon. The upper Neogene succession records a regional change, at about 4 Ma, in the patterns of contourite sedimentation (submarine erosion, new depocentres) coeval with the onset of rapid seaward-progradation of the continental margin by up to 100 km. This build-out of the shelf and slope is inferred to record a marked increase in sediment supply in response to uplift and tilting of the continental margin. Associated changes in deep-water circulation may be part of an Atlantic-wide reorganisation of ocean bottom currents. Glacial sediments form a major component of the prograding shelf margin (shelf-slope) sediment wedges, but stratigraphic data indicate that the onset of progradation pre-dates significant high-latitude glaciation by at least 1 Ma, and expansive Northern Hemisphere glaciation by at least 3 Ma. 相似文献
18.
This study provides the results of the first integrated study of Oligocene–Pliocene basins around Norway.Within the study area, three main depocentres have been identified where sandy sediments accumulated throughout the Oligocene to Early Pliocene period. The depocentre in the Norwegian–Danish Basin received sediments from the southern Scandes Mountains, with a general progradation from north to south during the studied period. The depocentre in the basinal areas of the UK and Norwegian sectors of the North Sea north of 58°N received sediments from the Scotland–Shetland area. Because of the sedimentary infilling there was a gradual shallowing of the northern North Sea basin in the Oligocene and Miocene. A smaller depocentre is identified offshore northern Nordland between Ranafjorden (approximately 66°N) and Vesterålen (approximately 68°N) where the northern Scandes Mountains were the source of the Oligocene to Early Pliocene sediments. In other local depocentres along the west coast of Norway, sandy sedimentation occurred in only parts of the period. Shifts in local depocentres are indicative of changes in the paleogeography in the source areas.In the Barents Sea and south to approximately 68°N, the Oligocene to Early Pliocene section is eroded except for distal fine-grained and biogenic deposits along the western margin and on the oceanic crust. This margin was undergoing deformation in a strike-slip regime until the Eocene–Oligocene transition. The Early Oligocene sediments dated in the Vestbakken Volcanic Province and the Forlandssundet Basin represent the termination of this strike-slip regime.The change in the plate tectonic regime at the Eocene–Oligocene transition affected mainly the northern part of the study area, and was followed by a quiet tectonic period until the Middle Miocene, when large compressional dome and basin structures were formed in the Norwegian Sea. The Middle Miocene event is correlated with a relative fall in sea level in the main depocentres in the North Sea, formation of a large delta in the Viking Graben (Frigg area) and uplift of the North and South Scandes domes. In the Norwegian–Danish Basin, the Sorgenfrei-Tornquist Zone was reactivated in the Early Miocene, possibly causing a shift in the deltaic progradation towards the east. A Late Pliocene relative rise in sea level resulted in low sedimentation rates in the main depositional areas until the onset of glaciations at about 2.7 Ma when the Scandes Mountains were strongly eroded and became a major source of sediments for the Norwegian shelf, whilst the Frigg delta prograded farther to the northeast. 相似文献
19.
Based on the measured data in recent 20 years, the variation trends of the median grain size of the surface sediment, the sand-silt boundary and the mud area on the adjacent continental shelf of the Yangtze Estuary were analyzed in depth, and the effects of natural mechanism and human activities were discussed. The results show that:(1) In recent years(2006-2013), the median grain size of sediment and the distribution pattern of grouped sediments in the adjacent continental shelf area to the Yangtze Estuary have presented no obvious change compared with those before 2006;(2) The median diameter of the surface sediment in the continental shelf area displayed a coarsening trend with the decrease of sediment discharge from the basin and the drop in suspended sediment concentration in the shore area;(3) In 2004-2007, the sand-silt boundary in the north part(31°30′N) of the continental shelf area presented no significant changes, while that in the south part(31°30′S) moved inwards; In 2008-2013, both the sand-silt boundaries in the north and south parts of the continental shelf area moved inwards, mainly due to the fact that in the dry season, a relatively enhanced hydrodynamic force of the tides was generated in the Yangtze River, as well as a decreased suspended sediment concentration and a flow along the banks in North Jiangsu;(4) The mud area where the maximum deposition rate is found in the Yangtze Estuary, tends to shrink due to the drop in sediment discharge from the basin, and the decrease in suspended sediment concentration in the shore area and erosion in the delta. Moreover, it tended to shift to the south at the same time because the implement of the training works on the deep-water channel of the North Passage changed the split ratio between the North and South Passages with an increase in the power of the discharged runoff in the South Passage. 相似文献
20.
Sediment thickness was evaluated on the western flank of the East Pacific Rise (EPR) at 45°S, based on high-resolution seismic data gathered during cruise 213/2 of R/V Sonne in 2011. Two zones with distinctly different sediment thickness were identified, separated by a transitional zone bordering a pseudo-fault. Sediment in the more distal zone 2 is almost twice as thick (~120 m) as in zone 1 close to the EPR. This is in contrast to the expected progressive sedimentary column thickening with seafloor age and distance from the spreading axis. The younger of two seismic units detected within the sedimentary column (EPR-2) occurs mainly in the distal zone on crust older than 9 Ma, whereas on younger crust it is present only in small isolated bodies. Both sedimentary units drape the basement. The drape is interpreted to represent particle settling from suspension and a generally low regional primary productivity. The spatial variation in sediment thickness cannot be explained by existing models, and other processes considered in the present case are (1) higher productivity in the western sector of the survey area, where thicker sediments were observed (zone 2), (2) the formation of sediment drifts near basement highs (‘seamount effect’), due to flow of Lower Circumpolar Deep Water affecting sediment deposition, and (3) erosion and/or non-deposition of the younger EPR-2 unit, due to elevated bed shear stresses associated with eddies transferring kinetic energy to the seafloor 相似文献