A numerical study of linear wave scattering over a floating platform has been simulated by an efficient numericalmodel in this letter.The non-hydrostatic model is used to simulate the free surface and the uneven botto...A numerical study of linear wave scattering over a floating platform has been simulated by an efficient numericalmodel in this letter.The non-hydrostatic model is used to simulate the free surface and the uneven bottom.For thesolid body modelling,the immersed boundary method(IBM)is implemented by introducing a virtual boundaryforce into the momentum equations to emulate the boundary conditions.This implementation enhances theability of the model to simulate interactions between waves and floating structures.A numerical case involvingwave interactions with a floating platform is studied to validate the numerical model.By simulating the wavepropagation,the numerical model captures the variation of the wave scattering very well,which verifies theperformance of the numerical model and the robust strategy of the IBM.展开更多
During Permian and Triassic the western margin of Upper Yangtze platform had experienced an evolution from early rift stage to thermal subsidence and then to foreland basin. The tectonic transformations have resulted...During Permian and Triassic the western margin of Upper Yangtze platform had experienced an evolution from early rift stage to thermal subsidence and then to foreland basin. The tectonic transformations have resulted in five supersequences and nineteen third-order se- quences.During the rift stage,transgeressive carbonate platform was built up,while in the thermal subsidence stage,regressive carbonate platform with foreslope was formed.The closure of the Garze-Litang narrow oceanic basin resulted in the migration of foreland flexure toward the ctaton.The carbonate ramp in foreland basin setting was formed during the relative sea level rise which was caused by the change in basin volume.展开更多
The Cambrian of the North China platform consists chiefly of shallow water deposits and shows the sedimentary characters of an epicontinental sea basin. Controlled mainly by global sea level changes and sedimentary in...The Cambrian of the North China platform consists chiefly of shallow water deposits and shows the sedimentary characters of an epicontinental sea basin. Controlled mainly by global sea level changes and sedimentary influx, the depositional sequences all exhibit as composite sequences. From bottom upward, 14 sequences (3rd order) are recognized, which may be grouped into 5 sequence sets and further into 2 mesosequences (2nd order). It is suggested herein that the Cambrian/Ordovician boundary may better be set at the MFS (maximum flooding surface) of the sequence OSq1, above which the conodont Cordylodus lindstroemi occurs. This position is about 40 m above the traditional Cambrian/Ordovician boundary and is within the Yeli Formation.展开更多
Ocean platforms are subjected to a variety of environment loads, such as those from winds, waves, currents, etc. In this study, the torsion problems of a gravity platform column with cracks under wind load were invest...Ocean platforms are subjected to a variety of environment loads, such as those from winds, waves, currents, etc. In this study, the torsion problems of a gravity platform column with cracks under wind load were investigated. The colmnn was assumed to be a composite cylinder. Therefore the torsion fracture problem of a composite cylinder was considered, and new boundary integral equations for the Saint-Venant torsion problem of a composite cylinder with curvilinear cracks were derived. The problem was re- duced to solving the boundary integral equations on every boundary. By using the new boundary element method, the torsion prob- lem of the gravity platform colunm with a straight crack under various wind loads was calculated. The obtained results were com- pared with those obtained for a torsion problem of the same column without cracks to prove the applicability of the present method. The comparison showed that the detrimental effect of cracks in a column should be considered in marine engineering.展开更多
Interesting classifications of basinogenesis and basins were proposed by many seientists. They classified basinogenesis and basins mainly from a single angle, either from a historical angle or from a dynamie angle. In...Interesting classifications of basinogenesis and basins were proposed by many seientists. They classified basinogenesis and basins mainly from a single angle, either from a historical angle or from a dynamie angle. In order to more comprehensively understand them for moore effectively guidlilg prospeeting and exploration, the author integrates the two methods of analysis wilh cach other and proposes an integrative classification. According to the historieal-dynamic integrative classification, basinogenesis and basins can be divided into three types: occanic erust type. embryo-continental (transitional ) erust iype and continental crust type. Oceanie erust type call be subdivided into mobile region type (mainly tensional) and stable region type. Embryo-continental type includes pre-geosynclinal type (divisible into several mobile region types and stable region types with tensional type predoiminating among mobile region trpes) and early-geosynelinal type (mainly tensional). Continental erust type ineludes late-gcosynelinal (fold belt) type (compressional or tensional), platform type (mainly sinking and rarely tensional subsidence-aulacogen) and gcodepression (diwa) type (compressional, tensional or compressional-tensional ).展开更多
Ocean anoxia has been widely implicated in the Permian-Triassic extinction. However, the duration and distribution of the ocean anoxia remains controversial. In this study, the detailed redox changes across the Permia...Ocean anoxia has been widely implicated in the Permian-Triassic extinction. However, the duration and distribution of the ocean anoxia remains controversial. In this study, the detailed redox changes across the Permian-Triassic boundary （PTB） in the shallow platform interior at Great Bank of Guizhou （GBG） has been reconstructed based on the high-resolution microfossil composition and multiple paleo-redox proxies. The shallow platform is characterized by low sulfur （total sulfur （TS） and pyrite sulfur （Spy）） concentrations, low Spy/TOC ratios, and low DOP values before the mass extinction, representing oxic conditions well. Following the mass extinction, the shift of multiple geochemical proxies, including high Spy/TOC ratios and DOP values, indicates dysoxic-anoxic conditions in shallow ocean. Furthermore, we reconstruct the transition of the redox conditions of Nanpanjiang Basin： the intense volcanic eruptions, which release huge COz and SO2 before the mass extinction, provoke the temperature rising and the collapse of terrestrial ecosystem. As a result, the increased weathering influx causes the carbon iso- topic negative excursion and the expansion of the ocean oxygen minimum zone （OMZ）. When the OMZ expanded into the photic zone, the episodic H2S release events enhance the pyrite burial at Dajiang section. Thus, intense volcanic eruptions, temperature increase, and oceanic hypoxia together lead to the PTB extinction. Recent studies show high temperature might be the key mechanism of the PTB extinction. In addition, this study confirms that the microbialites were formed in the dysoxic- anoxic shallow water.展开更多
More than 20 K-bentonite beds were discovered from the Wufeng Formation and the lowest Longmaxi Formation in two sections, both adjacent to the Ordovician-Silurian (O-S) bound-ary and located in Tongzi, Guizhou Provin...More than 20 K-bentonite beds were discovered from the Wufeng Formation and the lowest Longmaxi Formation in two sections, both adjacent to the Ordovician-Silurian (O-S) bound-ary and located in Tongzi, Guizhou Province and Yichang, Hubei Province, some 500 km apart from each other in South China. This indicates that many volcanic eruptions occurred near the southeast margin of the Yangtze Platform between the latest Ordovician and the earliest Silurian. Mainly through biostratigraphic and sequence stratigraphic studies, it was found that almost all these far-apart K-bentonite beds may be correlated with each other. This is the first time that a succession of volcanic ash deposits with high potential of correlation was discovered within a strata interval on the main platforms of China. Therefore, these K-bentonite beds may afford ex-cellent event-marker beds helpful to high-resolution research in integrated stratigraphy as well as other lines of research on the O-S boundary in South China.展开更多
基金supported by Shanghai 2021“Science and Technology Innovation Action Plan”:Scientific and Technological Projects for Social Development(Grant No.21DZ1202701).
文摘A numerical study of linear wave scattering over a floating platform has been simulated by an efficient numericalmodel in this letter.The non-hydrostatic model is used to simulate the free surface and the uneven bottom.For thesolid body modelling,the immersed boundary method(IBM)is implemented by introducing a virtual boundaryforce into the momentum equations to emulate the boundary conditions.This implementation enhances theability of the model to simulate interactions between waves and floating structures.A numerical case involvingwave interactions with a floating platform is studied to validate the numerical model.By simulating the wavepropagation,the numerical model captures the variation of the wave scattering very well,which verifies theperformance of the numerical model and the robust strategy of the IBM.
文摘During Permian and Triassic the western margin of Upper Yangtze platform had experienced an evolution from early rift stage to thermal subsidence and then to foreland basin. The tectonic transformations have resulted in five supersequences and nineteen third-order se- quences.During the rift stage,transgeressive carbonate platform was built up,while in the thermal subsidence stage,regressive carbonate platform with foreslope was formed.The closure of the Garze-Litang narrow oceanic basin resulted in the migration of foreland flexure toward the ctaton.The carbonate ramp in foreland basin setting was formed during the relative sea level rise which was caused by the change in basin volume.
文摘The Cambrian of the North China platform consists chiefly of shallow water deposits and shows the sedimentary characters of an epicontinental sea basin. Controlled mainly by global sea level changes and sedimentary influx, the depositional sequences all exhibit as composite sequences. From bottom upward, 14 sequences (3rd order) are recognized, which may be grouped into 5 sequence sets and further into 2 mesosequences (2nd order). It is suggested herein that the Cambrian/Ordovician boundary may better be set at the MFS (maximum flooding surface) of the sequence OSq1, above which the conodont Cordylodus lindstroemi occurs. This position is about 40 m above the traditional Cambrian/Ordovician boundary and is within the Yeli Formation.
基金supported by the National High-Technology Research and Development Program of China (No.2007AA09Z317)
文摘Ocean platforms are subjected to a variety of environment loads, such as those from winds, waves, currents, etc. In this study, the torsion problems of a gravity platform column with cracks under wind load were investigated. The colmnn was assumed to be a composite cylinder. Therefore the torsion fracture problem of a composite cylinder was considered, and new boundary integral equations for the Saint-Venant torsion problem of a composite cylinder with curvilinear cracks were derived. The problem was re- duced to solving the boundary integral equations on every boundary. By using the new boundary element method, the torsion prob- lem of the gravity platform colunm with a straight crack under various wind loads was calculated. The obtained results were com- pared with those obtained for a torsion problem of the same column without cracks to prove the applicability of the present method. The comparison showed that the detrimental effect of cracks in a column should be considered in marine engineering.
文摘Interesting classifications of basinogenesis and basins were proposed by many seientists. They classified basinogenesis and basins mainly from a single angle, either from a historical angle or from a dynamie angle. In order to more comprehensively understand them for moore effectively guidlilg prospeeting and exploration, the author integrates the two methods of analysis wilh cach other and proposes an integrative classification. According to the historieal-dynamic integrative classification, basinogenesis and basins can be divided into three types: occanic erust type. embryo-continental (transitional ) erust iype and continental crust type. Oceanie erust type call be subdivided into mobile region type (mainly tensional) and stable region type. Embryo-continental type includes pre-geosynclinal type (divisible into several mobile region types and stable region types with tensional type predoiminating among mobile region trpes) and early-geosynelinal type (mainly tensional). Continental erust type ineludes late-gcosynelinal (fold belt) type (compressional or tensional), platform type (mainly sinking and rarely tensional subsidence-aulacogen) and gcodepression (diwa) type (compressional, tensional or compressional-tensional ).
基金supported by National Basic Research Program of China (Grant No. 2011CB808800)National Natural Science Foundation of China (Grant Nos. 41172312, 41272372, 41172036, 41240016, 41302271)+1 种基金Fundamental Research Funds for the Central Universities, China University of Geosciences (Wuhan)Fund of State Key Laboratory of Biogeology and Environmental Geology (Grant No. BGEG1016)
文摘Ocean anoxia has been widely implicated in the Permian-Triassic extinction. However, the duration and distribution of the ocean anoxia remains controversial. In this study, the detailed redox changes across the Permian-Triassic boundary （PTB） in the shallow platform interior at Great Bank of Guizhou （GBG） has been reconstructed based on the high-resolution microfossil composition and multiple paleo-redox proxies. The shallow platform is characterized by low sulfur （total sulfur （TS） and pyrite sulfur （Spy）） concentrations, low Spy/TOC ratios, and low DOP values before the mass extinction, representing oxic conditions well. Following the mass extinction, the shift of multiple geochemical proxies, including high Spy/TOC ratios and DOP values, indicates dysoxic-anoxic conditions in shallow ocean. Furthermore, we reconstruct the transition of the redox conditions of Nanpanjiang Basin： the intense volcanic eruptions, which release huge COz and SO2 before the mass extinction, provoke the temperature rising and the collapse of terrestrial ecosystem. As a result, the increased weathering influx causes the carbon iso- topic negative excursion and the expansion of the ocean oxygen minimum zone （OMZ）. When the OMZ expanded into the photic zone, the episodic H2S release events enhance the pyrite burial at Dajiang section. Thus, intense volcanic eruptions, temperature increase, and oceanic hypoxia together lead to the PTB extinction. Recent studies show high temperature might be the key mechanism of the PTB extinction. In addition, this study confirms that the microbialites were formed in the dysoxic- anoxic shallow water.
基金the National Natural Science Foundation of China(Grant No.49802002)the State Key Project of Sequence Stratigraphy and Earth Rhythms the Lab of Earth Surface Systems of Hubei Province.
文摘More than 20 K-bentonite beds were discovered from the Wufeng Formation and the lowest Longmaxi Formation in two sections, both adjacent to the Ordovician-Silurian (O-S) bound-ary and located in Tongzi, Guizhou Province and Yichang, Hubei Province, some 500 km apart from each other in South China. This indicates that many volcanic eruptions occurred near the southeast margin of the Yangtze Platform between the latest Ordovician and the earliest Silurian. Mainly through biostratigraphic and sequence stratigraphic studies, it was found that almost all these far-apart K-bentonite beds may be correlated with each other. This is the first time that a succession of volcanic ash deposits with high potential of correlation was discovered within a strata interval on the main platforms of China. Therefore, these K-bentonite beds may afford ex-cellent event-marker beds helpful to high-resolution research in integrated stratigraphy as well as other lines of research on the O-S boundary in South China.
