Based on numerous high-resolution seismic profiles,sediment waves and their distribution,morphological characteristics,internal structure,and potential origins were revealed in the eastern waters of Taiwan.The sedimen...Based on numerous high-resolution seismic profiles,sediment waves and their distribution,morphological characteristics,internal structure,and potential origins were revealed in the eastern waters of Taiwan.The sediment waves are located at the junction between the Taitung Canyon and other canyons in the slope.The wave length and the wave height of a single waveform ranged from 0.8 to 7.2 km and from 18 to 75 m,respectively(NE-SW direction).Sediment waves,located inside the bend of the Taitung Canyon,were characterized by an upward migration and showed mass transport deposits(MTDs)at the bottom,while the inner curve of the bend was subdivided into lower and upper wavy transition units.The sediment waves on the outer curve of the bend were characterized by vertical accumulation,and there was no mass flow deposit at the bottom.According to the geometry of the sediment waves,the calculated flow thicknesses across the entire wave field ranged from 196 to 356 m,and the current velocity ranged from 15 to 21 cm/s.The morphological characteristics,the internal structure,and the distribution of sediment waves,as well as the numerical calculations,evidenced that these sediment waves had formed by turbidity currents.The development of the sediment wave field in eastern Taiwan was found to be similar to that in southwestern Taiwan.It was the sedimentary response of the tectonic movement between 3 and^1 Ma which created the sedimentary systems where gravity flow processes predominated.Turbidity current sediments settled in the place of less topographical constraints or overflowed in the bend section of the Taitung Canyon,which resulted in the formation of sediment wave fields.展开更多
The large deep-sea area from the southwestern Qiongdongnan Basin to the eastern Dongsha Islands,within the continental margin of northern South China Sea,is a frontier of natural gas hydrate exploration in China.Multi...The large deep-sea area from the southwestern Qiongdongnan Basin to the eastern Dongsha Islands,within the continental margin of northern South China Sea,is a frontier of natural gas hydrate exploration in China.Multiform of deep-sea sedimentations have been occurred since late Miocene,and sediment waves as a potential quality reservoir of natural gas hydrate is an most important style of them.Based on abundant available data of seismic,gravity sampling and drilling core,we analyzed the characteristics of seismic reflection and sedimentation of sediment waves and the occurrence of natural gas hydrate hosted in it,and discussed the control factors on natural gas hydrate accumulation.The former findings revealed the deep sea of the northern South China Sea have superior geological conditions on natural gas hydrate accumulation.Therefore,it will be of great significance in deep-sea natural gas hydrate exploration with the study on the relationship between deep-sea sedimentation and natural gas hydrate accumulation.展开更多
Supercritical flows are ubiquitous in natural environments;however,there is rare 3D anatomy of their deposits.This study uses high-quality 3D seismic datasets from the world’s largest submarine fan,Bengal Fan,to inte...Supercritical flows are ubiquitous in natural environments;however,there is rare 3D anatomy of their deposits.This study uses high-quality 3D seismic datasets from the world’s largest submarine fan,Bengal Fan,to interpret 3D architectures and flow processes of Pliocene undulating bedforms that were related to supercritical flows.Bengal undulating bedforms as documented in this study were developed in unconfined settings,and are seismically imaged as strike-elongated,crescentic bedforms in plan view and as rhythmically undulating,upstream migrating,erosive,discontinuous reflections in section view.Their lee sides are overall 3 to 4 times steeper(0.280 to 1.19°in slope)and 3 to 4 times shorter(117 to 419 m in length)than their stoss flanks and were ascribed to faster(high flow velocities of 2.70 to 3.98 m/s)supercritical flows(Froude numbers of 1.53 to 2.27).Their stoss sides,in contrast,are overall 3 to 4 times gentler(0.120 to 0.270 in slope)and 3 to 4 times longer(410 to 1139 m in length)than their lee flanks and were related to slower(low velocities of 2.35 to 3.05 m/s)subcritical flows(Froude numbers of 0.58 to 0.97).Bengal wave-like features were,thus,created by supercriticalto-subcritical flow transformations through internal hydraulic jumps(i.e.,cyclic steps).They have crests that are positive relative to the surrounding region of the seafloor,suggesting the predominant deposition of draping sediments associated with net-depositional cyclic steps.Turbidity currents forming Bengal wave-like features were,thus,dominated by deposition,resulting in net-depositional cyclic steps.Sandy deposits associated with Bengal net-depositional cyclic steps are imaged themselves as closely spaced,strike-elongated high RMS-attribute patches,thereby showing closely spaced,long and linear,strike-elongated distribution patterns.展开更多
The study of internal-wave and internal-tide deposits is a new research field on sedimentology during the last ten years. Deep-water traction currents induced by internal waves and internal tides are developed on the ...The study of internal-wave and internal-tide deposits is a new research field on sedimentology during the last ten years. Deep-water traction currents induced by internal waves and internal tides are developed on the modern sea floor, which can form not only all kinds of small scale and dispersal deepwater traction currents deposits, but also large-scale sediment wave in km-size scale. In this paper, the concepts and features of internal waves and internal tides in oceanography are introduced, and the characteristics, sedimentary sequences, sedimentary microfacies and sedimentation models of internalwave and internal-tide deposits found and the origin of large scale sediment waves in deep sea bottom are summarized. The relationship between internal-wave and internal-tide deposits and petroleum is discussed, and finally internal-wave and internal-tide deposits are shown to be a new potential field for petroleum exploration.展开更多
The continental slope of the Taiwan Shoal, which has cultivated numerous submarine canyons, is located in a passive conti- nental margin environment. However, the trend of the Taiwan Canyon, with its 45° intersec...The continental slope of the Taiwan Shoal, which has cultivated numerous submarine canyons, is located in a passive conti- nental margin environment. However, the trend of the Taiwan Canyon, with its 45° intersection angle, is obviously different from that of the erosion valley downward along the continental slope. A distinct break is present in the lower segment of the Taiwan Canyon, which then extends from west to east parallel to the continental slope until finally joining the Manila Trench. By utilizing multiple-beam water depth data, high-resolution seismic data, and sediment cores, this study describes the topo- graphic characteristics of the Taiwan Canyon and provides a preliminary discussion on the origin of the Taiwan Canyon and its effect on deepwater sediment. The terrain, landform, and sediment of the Taiwan Canyon exhibit segmentation characteristics. The upper segment is characterized primarily by erosion, downward cutting with a V shape, and wide development of sliding, slumping, and other gravity flow types. The middle segment is characterized mostly by U-shaped erosion-sedimentation transi- tion and development of an inner levee. The lower segment is characterized primarily by sedimentation and development of a sediment wave. The bottom current has a significant reworking effect on the interior sediments of the canyon and forms re- worked sands. The formation and evolution of the Taiwan Canyon is closely related to sediment supply, gravity sliding （slumping）, faulting activities, and submarine impaling. Given the sufficient terrigenous clastic supply, the sediments along the continental shelf edge continuously proceed seaward; gliding and slumping in the front edge provide driving forces for the formation of the canyon. Faulting activities result in stratum crushing, and the gravity flow takes priority in eroding the relatively fragile stratum. Thus, the direction of the extension of the canyon crosses the surrounding erosion valley obliquely. Seamounts are formed through submarine impaling. Owing to seamount blocking, the lower segment of the canyon is turned toward the east-west direction. Large amounts of sediments overflow at the turning, formin~ sediment waves.展开更多
The integral expression for acoustic field due to a point source in shallow waterwhile sediment is either a liquid or a solid is derived. The synthetic full waveforms are simulatedusing real axis integration and FFF m...The integral expression for acoustic field due to a point source in shallow waterwhile sediment is either a liquid or a solid is derived. The synthetic full waveforms are simulatedusing real axis integration and FFF method. The effects of the seabed sediment parametersand center frequency of the source on the low frequency acoustic wave propagation in shallowwater are investigated. The conclusion is that the wave groups received in far field are thoseof the mode waves of the source center frequency. The possibility for inversely deducing thecompressional and shear sound speeds of sediment using the least square optimum through themeasured group velocities of a selected mode at different frequencies is discussed.展开更多
基金supported by the National Natural Science Foundation of China(No.41576048)the Open Fund of Key Laboratory of Marine Mineral Resourcesthe Ministry of Land and Resources(KLMMR-2015-A-11)
文摘Based on numerous high-resolution seismic profiles,sediment waves and their distribution,morphological characteristics,internal structure,and potential origins were revealed in the eastern waters of Taiwan.The sediment waves are located at the junction between the Taitung Canyon and other canyons in the slope.The wave length and the wave height of a single waveform ranged from 0.8 to 7.2 km and from 18 to 75 m,respectively(NE-SW direction).Sediment waves,located inside the bend of the Taitung Canyon,were characterized by an upward migration and showed mass transport deposits(MTDs)at the bottom,while the inner curve of the bend was subdivided into lower and upper wavy transition units.The sediment waves on the outer curve of the bend were characterized by vertical accumulation,and there was no mass flow deposit at the bottom.According to the geometry of the sediment waves,the calculated flow thicknesses across the entire wave field ranged from 196 to 356 m,and the current velocity ranged from 15 to 21 cm/s.The morphological characteristics,the internal structure,and the distribution of sediment waves,as well as the numerical calculations,evidenced that these sediment waves had formed by turbidity currents.The development of the sediment wave field in eastern Taiwan was found to be similar to that in southwestern Taiwan.It was the sedimentary response of the tectonic movement between 3 and^1 Ma which created the sedimentary systems where gravity flow processes predominated.Turbidity current sediments settled in the place of less topographical constraints or overflowed in the bend section of the Taitung Canyon,which resulted in the formation of sediment wave fields.
基金Supported by the National Basic Research Program of China(973 Program)(Nos.2009CB219508,2009CB219502)the National High Technology Research and Development Program of China(863 Program) (No.2006AA09A202)
文摘The large deep-sea area from the southwestern Qiongdongnan Basin to the eastern Dongsha Islands,within the continental margin of northern South China Sea,is a frontier of natural gas hydrate exploration in China.Multiform of deep-sea sedimentations have been occurred since late Miocene,and sediment waves as a potential quality reservoir of natural gas hydrate is an most important style of them.Based on abundant available data of seismic,gravity sampling and drilling core,we analyzed the characteristics of seismic reflection and sedimentation of sediment waves and the occurrence of natural gas hydrate hosted in it,and discussed the control factors on natural gas hydrate accumulation.The former findings revealed the deep sea of the northern South China Sea have superior geological conditions on natural gas hydrate accumulation.Therefore,it will be of great significance in deep-sea natural gas hydrate exploration with the study on the relationship between deep-sea sedimentation and natural gas hydrate accumulation.
基金jointly funded by PetroChina Hangzhou Research Institute of Geology(No.2019D-4309)。
文摘Supercritical flows are ubiquitous in natural environments;however,there is rare 3D anatomy of their deposits.This study uses high-quality 3D seismic datasets from the world’s largest submarine fan,Bengal Fan,to interpret 3D architectures and flow processes of Pliocene undulating bedforms that were related to supercritical flows.Bengal undulating bedforms as documented in this study were developed in unconfined settings,and are seismically imaged as strike-elongated,crescentic bedforms in plan view and as rhythmically undulating,upstream migrating,erosive,discontinuous reflections in section view.Their lee sides are overall 3 to 4 times steeper(0.280 to 1.19°in slope)and 3 to 4 times shorter(117 to 419 m in length)than their stoss flanks and were ascribed to faster(high flow velocities of 2.70 to 3.98 m/s)supercritical flows(Froude numbers of 1.53 to 2.27).Their stoss sides,in contrast,are overall 3 to 4 times gentler(0.120 to 0.270 in slope)and 3 to 4 times longer(410 to 1139 m in length)than their lee flanks and were related to slower(low velocities of 2.35 to 3.05 m/s)subcritical flows(Froude numbers of 0.58 to 0.97).Bengal wave-like features were,thus,created by supercriticalto-subcritical flow transformations through internal hydraulic jumps(i.e.,cyclic steps).They have crests that are positive relative to the surrounding region of the seafloor,suggesting the predominant deposition of draping sediments associated with net-depositional cyclic steps.Turbidity currents forming Bengal wave-like features were,thus,dominated by deposition,resulting in net-depositional cyclic steps.Sandy deposits associated with Bengal net-depositional cyclic steps are imaged themselves as closely spaced,strike-elongated high RMS-attribute patches,thereby showing closely spaced,long and linear,strike-elongated distribution patterns.
文摘The study of internal-wave and internal-tide deposits is a new research field on sedimentology during the last ten years. Deep-water traction currents induced by internal waves and internal tides are developed on the modern sea floor, which can form not only all kinds of small scale and dispersal deepwater traction currents deposits, but also large-scale sediment wave in km-size scale. In this paper, the concepts and features of internal waves and internal tides in oceanography are introduced, and the characteristics, sedimentary sequences, sedimentary microfacies and sedimentation models of internalwave and internal-tide deposits found and the origin of large scale sediment waves in deep sea bottom are summarized. The relationship between internal-wave and internal-tide deposits and petroleum is discussed, and finally internal-wave and internal-tide deposits are shown to be a new potential field for petroleum exploration.
基金supported by National Natural Science Foundation of China(Grant Nos.41372115,40972077)
文摘The continental slope of the Taiwan Shoal, which has cultivated numerous submarine canyons, is located in a passive conti- nental margin environment. However, the trend of the Taiwan Canyon, with its 45° intersection angle, is obviously different from that of the erosion valley downward along the continental slope. A distinct break is present in the lower segment of the Taiwan Canyon, which then extends from west to east parallel to the continental slope until finally joining the Manila Trench. By utilizing multiple-beam water depth data, high-resolution seismic data, and sediment cores, this study describes the topo- graphic characteristics of the Taiwan Canyon and provides a preliminary discussion on the origin of the Taiwan Canyon and its effect on deepwater sediment. The terrain, landform, and sediment of the Taiwan Canyon exhibit segmentation characteristics. The upper segment is characterized primarily by erosion, downward cutting with a V shape, and wide development of sliding, slumping, and other gravity flow types. The middle segment is characterized mostly by U-shaped erosion-sedimentation transi- tion and development of an inner levee. The lower segment is characterized primarily by sedimentation and development of a sediment wave. The bottom current has a significant reworking effect on the interior sediments of the canyon and forms re- worked sands. The formation and evolution of the Taiwan Canyon is closely related to sediment supply, gravity sliding （slumping）, faulting activities, and submarine impaling. Given the sufficient terrigenous clastic supply, the sediments along the continental shelf edge continuously proceed seaward; gliding and slumping in the front edge provide driving forces for the formation of the canyon. Faulting activities result in stratum crushing, and the gravity flow takes priority in eroding the relatively fragile stratum. Thus, the direction of the extension of the canyon crosses the surrounding erosion valley obliquely. Seamounts are formed through submarine impaling. Owing to seamount blocking, the lower segment of the canyon is turned toward the east-west direction. Large amounts of sediments overflow at the turning, formin~ sediment waves.
文摘The integral expression for acoustic field due to a point source in shallow waterwhile sediment is either a liquid or a solid is derived. The synthetic full waveforms are simulatedusing real axis integration and FFF method. The effects of the seabed sediment parametersand center frequency of the source on the low frequency acoustic wave propagation in shallowwater are investigated. The conclusion is that the wave groups received in far field are thoseof the mode waves of the source center frequency. The possibility for inversely deducing thecompressional and shear sound speeds of sediment using the least square optimum through themeasured group velocities of a selected mode at different frequencies is discussed.
