The stability of estuarine channel-shoal systems is important for port utilization,navigation maintenance,habitat protection and ecosystem service functions.This paper uses the South Channel of the Changjiang(Yangtze ...The stability of estuarine channel-shoal systems is important for port utilization,navigation maintenance,habitat protection and ecosystem service functions.This paper uses the South Channel of the Changjiang(Yangtze River)Estuary as a typical example to investigate the channel-shoal adjustment mechanism and its future trend.The combined approaches of bathymetric data analysis and process-based modeling(Delft3D)are applied.Quantitative analysis of morphological changes indicates that the South Channel experienced remarkable channel-shoal adjustment during 1958–2018.Periodic evolution was identified,including shoal migration,incision and emergence under natural conditions before the mid-1980s.Since then,fluvial sediment decline and local human intervention have interrupted the periodic processes.After 1986,as river sediment discharge started to decline,the South Channel converted to net erosion,and both the mid-channel shoal at the bifurcation node and the tail of the Ruifeng Shoal showed significant scour.Process-based hydrodynamic simulations revealed that the northern rotation of the mainstream downstream of Wusong triggered the erosion of the Ruifeng Shoal,while unordered sand mining at the shoal tail in approximately 2002 enhanced shoal shrinkage.In addition,the self-adjustment of the transverse section shape resulted in abnormal accretion in 2002–2007.Afterward,the South Channel underwent overall erosion as sediment discharge decreased to a low level(<150 Mt/a).Five stages of channel-shoal pattern adjustment and accretion/erosion status during the past 60years were defined,i.e.,the accretion stage(1958–1965),remarkable channel-shoal adjustment stage(1978–1986),slow erosion stage(1986–1997),shoal scour and shrinkage stage(1997–2007)and overall channel-shoal erosion stage(2007–2018).Model prediction of the evolutionary trend indicates that overall erosion within the South Channel is most likely to continue in 2015–2050.Further adjustment of the South Channel under extremely low sediment discharge may threaten the riverbed stability and the sustainable development of this large-scale estuary.Future work on adaptive strategies for varying conditions is recommended.展开更多
Based on more than 4000 km 2D seismic data and seismic stratigraphic analysis, we discussed the extent and formation mechanism of the Qiongdongnan deep sea channel. The Qiongdongnan deep sea channel is a large incised...Based on more than 4000 km 2D seismic data and seismic stratigraphic analysis, we discussed the extent and formation mechanism of the Qiongdongnan deep sea channel. The Qiongdongnan deep sea channel is a large incised channel which extends from the east boundary of the Yinggehai Basin, through the whole Qiongdongnan and the Xisha trough, and terminates in the western part of the northwest subbasin of South China Sea. It is more than 570 km long and 4–8 km wide. The chaotic (or continuous) middle (or high) amplitude, middle (or high) continuity seismic facies of the channel reflect the different lithological distribution of the channel. The channel formed as a complex result of global sea level drop during early Pliocene, large scale of sediment supply to the Yinggehai Basin, inversion event of the Red River strike-slip fault, and tilted direction of the Qiongdongnan Basin. The large scale of sediment supply from Red River caused the shelf break of the Yinggehai Basin to move torwards the S and SE direction and developed large scale of prograding wedge from the Miocene, and the inversion of the Red River strike-slip fault induced the sediment slump which formed the Qiongdongnan deep sea channel.展开更多
Quaternary buried ancient river channels are widespread in the shallow-level sediments of the northern shelf of the South China Sea. The sedimentary sequence mainly of fluvial deposits comprise an important component ...Quaternary buried ancient river channels are widespread in the shallow-level sediments of the northern shelf of the South China Sea. The sedimentary sequence mainly of fluvial deposits comprise an important component part of the low-stand system tract and transgressive system tract in the study region. The plannar variation and spatial association of the sedimentary features such as incised valley fillings, deltaic foreset wedges and block slides of shelf-marginal fans reflect the palaeogeographic environment during the fall of the regional sea level in the northern part of the South China Sea. Based on the high-resolution seismic reflection data and gelogical data from boreholes, the present paper makes an integrated interpretation of the Quaternary ancient river channels in the shallow sediments of the study area, studies the sedimentary features of the ancient channels such as their spatial distribution, seismic facies reflection indicators, sedimentary facies and sand -body types, and discusses their formational setting and evolutionary model, with the main purpose to render a service to the hydrocarbon resources exploration and development and marine engineering in the northern shelf of the South China Sea.展开更多
Water masses in the South China Sea (SCS) were identified and analyzed with the data collected in the summer and winter of 1998. The distributions of temperature and salinity near the Bashi Channel (the Luzon Strait) ...Water masses in the South China Sea (SCS) were identified and analyzed with the data collected in the summer and winter of 1998. The distributions of temperature and salinity near the Bashi Channel (the Luzon Strait) were analyzed by using the data obtained in July and December of 1997. Based on the results from the data collected in the winter of 1998, waters in the open sea areas of the SCS were divided into six water masses: the Surface Water Mass of the SCS (S), the Subsurface Water Mass of the SCS (U), the Subsurface-Intermediate Water Mass of the SCS (UI),the Intermediate Water Mass of the SCS (I), the Deep Water Mass of the SCS (D) and the Bottom Water Mass of the SCS(B). For the summer of 1998, the Kuroshio Surface Water Mass (KS) and the Kuroshio Subsurface Water Mass (KU) were also identified in the SCS. But no Kuroshio water was found to pass the 119.5°E meridian and enter the SCS in the time of winter observations. The Sulu Sea Water (SSW) intruded into the SCS through the Mindoro Channel between 50-75 m in the summer of 1998. However, the data obtained in the summer and winter of 1997 indicated that water from the Pacific had entered the SCS through the nor-thern part of the Luzon Strait in these seasons, but water from the SCS had entered the Pacific through the southern part of the Strait. These phenomena might correlate with the 1998 El-Nio event.展开更多
Triple mass-transport deposits （MTDs） with areas of 625, 494 and 902 km^2, respectively, have been identified on the north slope of the Xisha Trough, northern South China Sea margin. Based on high-resolution seismic...Triple mass-transport deposits （MTDs） with areas of 625, 494 and 902 km^2, 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 three- dimensional structure model diagram af the MTDs. Combined with the regional geological setting and previous studies, we discussed the trigger mechanisms of the triple MTDs.展开更多
基金Natural Science Foundation of China-Ministry of Water Resources-China Three Gorges Corporation Joint Fund for Changjiang Water Science Research,No.U2040202National Natural Science Foundation of China,No.42006156,No.52009008+1 种基金Fundamental Research Funds for Central Public Welfare Research Institutes,No.CKSF2021530/HLResearch Project on Major Scientific and Technological Issues in Watershed Water Management,No.CKSC2020791/HL。
文摘The stability of estuarine channel-shoal systems is important for port utilization,navigation maintenance,habitat protection and ecosystem service functions.This paper uses the South Channel of the Changjiang(Yangtze River)Estuary as a typical example to investigate the channel-shoal adjustment mechanism and its future trend.The combined approaches of bathymetric data analysis and process-based modeling(Delft3D)are applied.Quantitative analysis of morphological changes indicates that the South Channel experienced remarkable channel-shoal adjustment during 1958–2018.Periodic evolution was identified,including shoal migration,incision and emergence under natural conditions before the mid-1980s.Since then,fluvial sediment decline and local human intervention have interrupted the periodic processes.After 1986,as river sediment discharge started to decline,the South Channel converted to net erosion,and both the mid-channel shoal at the bifurcation node and the tail of the Ruifeng Shoal showed significant scour.Process-based hydrodynamic simulations revealed that the northern rotation of the mainstream downstream of Wusong triggered the erosion of the Ruifeng Shoal,while unordered sand mining at the shoal tail in approximately 2002 enhanced shoal shrinkage.In addition,the self-adjustment of the transverse section shape resulted in abnormal accretion in 2002–2007.Afterward,the South Channel underwent overall erosion as sediment discharge decreased to a low level(<150 Mt/a).Five stages of channel-shoal pattern adjustment and accretion/erosion status during the past 60years were defined,i.e.,the accretion stage(1958–1965),remarkable channel-shoal adjustment stage(1978–1986),slow erosion stage(1986–1997),shoal scour and shrinkage stage(1997–2007)and overall channel-shoal erosion stage(2007–2018).Model prediction of the evolutionary trend indicates that overall erosion within the South Channel is most likely to continue in 2015–2050.Further adjustment of the South Channel under extremely low sediment discharge may threaten the riverbed stability and the sustainable development of this large-scale estuary.Future work on adaptive strategies for varying conditions is recommended.
基金Supported by the National High Technology Research and Development Program of China (863 Program, 2006AA09Z349)the National Basic Research Program of China (2007CB411703)
文摘Based on more than 4000 km 2D seismic data and seismic stratigraphic analysis, we discussed the extent and formation mechanism of the Qiongdongnan deep sea channel. The Qiongdongnan deep sea channel is a large incised channel which extends from the east boundary of the Yinggehai Basin, through the whole Qiongdongnan and the Xisha trough, and terminates in the western part of the northwest subbasin of South China Sea. It is more than 570 km long and 4–8 km wide. The chaotic (or continuous) middle (or high) amplitude, middle (or high) continuity seismic facies of the channel reflect the different lithological distribution of the channel. The channel formed as a complex result of global sea level drop during early Pliocene, large scale of sediment supply to the Yinggehai Basin, inversion event of the Red River strike-slip fault, and tilted direction of the Qiongdongnan Basin. The large scale of sediment supply from Red River caused the shelf break of the Yinggehai Basin to move torwards the S and SE direction and developed large scale of prograding wedge from the Miocene, and the inversion of the Red River strike-slip fault induced the sediment slump which formed the Qiongdongnan deep sea channel.
基金The present paper represents the result of a scientific research subject of the UNDP-assisted Project "Marine Engineering Geological Investigation of the Pearl River Mouth Basin in the Northern Party of the South China Sea" (Project No. UNDP.CPR/85/044)
文摘Quaternary buried ancient river channels are widespread in the shallow-level sediments of the northern shelf of the South China Sea. The sedimentary sequence mainly of fluvial deposits comprise an important component part of the low-stand system tract and transgressive system tract in the study region. The plannar variation and spatial association of the sedimentary features such as incised valley fillings, deltaic foreset wedges and block slides of shelf-marginal fans reflect the palaeogeographic environment during the fall of the regional sea level in the northern part of the South China Sea. Based on the high-resolution seismic reflection data and gelogical data from boreholes, the present paper makes an integrated interpretation of the Quaternary ancient river channels in the shallow sediments of the study area, studies the sedimentary features of the ancient channels such as their spatial distribution, seismic facies reflection indicators, sedimentary facies and sand -body types, and discusses their formational setting and evolutionary model, with the main purpose to render a service to the hydrocarbon resources exploration and development and marine engineering in the northern shelf of the South China Sea.
基金supported by the Research Fund for the Doctoral Program of Higher Education,China(No.2000042301)Ministry of Science and Technology of China supported this study through South China Sea Monsoon Experiment(SCSMEX)National Key Program for Developing Basic Science under contract(No.G1999043800).
文摘Water masses in the South China Sea (SCS) were identified and analyzed with the data collected in the summer and winter of 1998. The distributions of temperature and salinity near the Bashi Channel (the Luzon Strait) were analyzed by using the data obtained in July and December of 1997. Based on the results from the data collected in the winter of 1998, waters in the open sea areas of the SCS were divided into six water masses: the Surface Water Mass of the SCS (S), the Subsurface Water Mass of the SCS (U), the Subsurface-Intermediate Water Mass of the SCS (UI),the Intermediate Water Mass of the SCS (I), the Deep Water Mass of the SCS (D) and the Bottom Water Mass of the SCS(B). For the summer of 1998, the Kuroshio Surface Water Mass (KS) and the Kuroshio Subsurface Water Mass (KU) were also identified in the SCS. But no Kuroshio water was found to pass the 119.5°E meridian and enter the SCS in the time of winter observations. The Sulu Sea Water (SSW) intruded into the SCS through the Mindoro Channel between 50-75 m in the summer of 1998. However, the data obtained in the summer and winter of 1997 indicated that water from the Pacific had entered the SCS through the nor-thern part of the Luzon Strait in these seasons, but water from the SCS had entered the Pacific through the southern part of the Strait. These phenomena might correlate with the 1998 El-Nio event.
基金The National Natural Science Foundation of China under contract Nos 41306057 and 40906028the Open Fund of the Key Laboratory of Submarine Geosciences,State Oceanic Administration under contract No.KLSG1406
文摘Triple mass-transport deposits （MTDs） with areas of 625, 494 and 902 km^2, 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 three- dimensional structure model diagram af the MTDs. Combined with the regional geological setting and previous studies, we discussed the trigger mechanisms of the triple MTDs.
