2015 Vol. 37, No. 5
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2015, 37(5): .
Abstract:
2015, 37(5): 1-14.
doi: 10.3969/j.issn.0253-4193.2015.05.001
Abstract:
The Qiongdongnan Basin experienced a series of tectonic activities from faulting,through fault-depression and post-faulting thermal subsidence to post-faulting accelerated subsidence,had a sedimentary environment from coast in Eocene to deep-sea in present,formed a set of strata combination including littoral sediments,offshore sediments,shelf-slope sediments and bathyal sediments,and possessed favorable source-reservoir-cap conditions for hydrocarbon accumulation. Thus it is considered as an important region of hydrocarbon exploration and development. In this study,the key strata interfaces (T20,T30,T40,T50,T60 and T70) in the wells-through seismic profiles were identified,then were tracked and correlated combined with the regional wells-tie seismic profiles in the basin. On this basis,the regional stratigraphic framework of the Qiongdongnan Basin was established associated with the age of fossil assemblages. The Neogene strata (T60-T20) are primary in the shallow water area,in which the faults are rarely distributed,the stratigraphic thickness has little variation,and onlaps and truncations can be rarely found. Delta sedimentary system,which is beneficial to hydrocarbon reservoir,develops highly in local area. The evidence mentioned above indicates that tectonism exerted trivial influence on the Qiongdongnan Basin during the Neogene. The characteristics of the Neogene strata (T60-T20) in the deep water area are similar to that in the shallow water except seismic reflection characteristics. The internal sequence structure of the Paleogene strata (T100-T60) is dominantly sphenoid or subparallel with obvious onlaps and truncations. The thickness of the strata is large,and obvious faults result in strata fractures. These characteristics imply that the deep water area in the Qiongdongnan Basin was controlled mainly by tectonism,accompanying with the strong extension and rapid subsidence,and being in neritic environment during the Paleogene. Three stages of sand bodies are identified in the Central Canyon from east to west: the first stage (depth of 3 528-3 336 m,thickness of about 192 m) formed during 11.6-5.5Ma B.P. (T40-T30) distributes in the Lingshui-Songnan-Baodao segment of the Central Canyon,which includes turbidite channel deposit,turbidite sheet sand,mass flow deposit,deep-sea politic deposit,natural levee and overflow deposit; the second stage (depth of 4 100-3 900 m,thickness of about 200 m) formed during 5.5~4.2Ma B.P. (T30-T29),spans Ledong-Lingshui segment of the Central Canyon,being primarily composed of gravity flow deposits; the third stage(depth of 3 630-3 400 m,thickness of about 230 m) formed during 4.2-3.6Ma B.P. (T29-T28),presents in the Ledong-Yingdong segment of the Central Canyon,consisting mainly of turbidite channel deposits. The three stages of sand bodies from oldest in the east to youngest in the west,constituted the favorable reservoirs in the Central Depression Belt of the Qiongdongnan Basin.
The Qiongdongnan Basin experienced a series of tectonic activities from faulting,through fault-depression and post-faulting thermal subsidence to post-faulting accelerated subsidence,had a sedimentary environment from coast in Eocene to deep-sea in present,formed a set of strata combination including littoral sediments,offshore sediments,shelf-slope sediments and bathyal sediments,and possessed favorable source-reservoir-cap conditions for hydrocarbon accumulation. Thus it is considered as an important region of hydrocarbon exploration and development. In this study,the key strata interfaces (T20,T30,T40,T50,T60 and T70) in the wells-through seismic profiles were identified,then were tracked and correlated combined with the regional wells-tie seismic profiles in the basin. On this basis,the regional stratigraphic framework of the Qiongdongnan Basin was established associated with the age of fossil assemblages. The Neogene strata (T60-T20) are primary in the shallow water area,in which the faults are rarely distributed,the stratigraphic thickness has little variation,and onlaps and truncations can be rarely found. Delta sedimentary system,which is beneficial to hydrocarbon reservoir,develops highly in local area. The evidence mentioned above indicates that tectonism exerted trivial influence on the Qiongdongnan Basin during the Neogene. The characteristics of the Neogene strata (T60-T20) in the deep water area are similar to that in the shallow water except seismic reflection characteristics. The internal sequence structure of the Paleogene strata (T100-T60) is dominantly sphenoid or subparallel with obvious onlaps and truncations. The thickness of the strata is large,and obvious faults result in strata fractures. These characteristics imply that the deep water area in the Qiongdongnan Basin was controlled mainly by tectonism,accompanying with the strong extension and rapid subsidence,and being in neritic environment during the Paleogene. Three stages of sand bodies are identified in the Central Canyon from east to west: the first stage (depth of 3 528-3 336 m,thickness of about 192 m) formed during 11.6-5.5Ma B.P. (T40-T30) distributes in the Lingshui-Songnan-Baodao segment of the Central Canyon,which includes turbidite channel deposit,turbidite sheet sand,mass flow deposit,deep-sea politic deposit,natural levee and overflow deposit; the second stage (depth of 4 100-3 900 m,thickness of about 200 m) formed during 5.5~4.2Ma B.P. (T30-T29),spans Ledong-Lingshui segment of the Central Canyon,being primarily composed of gravity flow deposits; the third stage(depth of 3 630-3 400 m,thickness of about 230 m) formed during 4.2-3.6Ma B.P. (T29-T28),presents in the Ledong-Yingdong segment of the Central Canyon,consisting mainly of turbidite channel deposits. The three stages of sand bodies from oldest in the east to youngest in the west,constituted the favorable reservoirs in the Central Depression Belt of the Qiongdongnan Basin.
2015, 37(5): 15-23.
doi: 10.3969/j.issn.0253-4193.2015.05.002
Abstract:
The provenance analysis is the premise and basis of lithofacies-paleogeography studies because sediment supply controls the distribution and physical properties of sandstone. In this paper,the provenance characteristics of Huangliu formation in the central Canyon are studied using the new drilling data,combining seismic profiles,through methods like heavy minerals assemblage and zircon U-Pb age. From seismic profiles,it is presumed that sediments coming from the Hainan Uplift and Kuntum Uplift were deposited on the deltas,which were re-transported into the shelf-slope and submarine fans supplying abundant debris sediments to fill the Central Canyon. Samples of Huangliu Formation from new wells show high content in leucoxene,garnet and magnetite,which is similar to the strata under the influence of Blue River in Yinggehai Basin and Lishui-Qiubin River in Qiongdongnan Basin. Zircon U-Pb dating analysis shows that,characteristics of zircon U-Pb age distribution of the samples in Huangliu Formation of the central canyon with age Atlas 30-2 000 Ma range,is similar as the drilling samples effected by Kontum uplift provenance in Yinggehai Basin and the samples gathered from modern river of Vietnam with very consistent ages and abundance.In summary,the Central Canyon System is under the influence of various provenance including the ancient Hainan Uplift and the Kunchong Uplift. The western provenance system,which is mainly composed of Kunchong Uplift in Vietnam,was the main sediment supply for the submarine fan developed during late Miocene in Ledong Sag and the turbidity sandstone deposited later in the Central Canyon System.
The provenance analysis is the premise and basis of lithofacies-paleogeography studies because sediment supply controls the distribution and physical properties of sandstone. In this paper,the provenance characteristics of Huangliu formation in the central Canyon are studied using the new drilling data,combining seismic profiles,through methods like heavy minerals assemblage and zircon U-Pb age. From seismic profiles,it is presumed that sediments coming from the Hainan Uplift and Kuntum Uplift were deposited on the deltas,which were re-transported into the shelf-slope and submarine fans supplying abundant debris sediments to fill the Central Canyon. Samples of Huangliu Formation from new wells show high content in leucoxene,garnet and magnetite,which is similar to the strata under the influence of Blue River in Yinggehai Basin and Lishui-Qiubin River in Qiongdongnan Basin. Zircon U-Pb dating analysis shows that,characteristics of zircon U-Pb age distribution of the samples in Huangliu Formation of the central canyon with age Atlas 30-2 000 Ma range,is similar as the drilling samples effected by Kontum uplift provenance in Yinggehai Basin and the samples gathered from modern river of Vietnam with very consistent ages and abundance.In summary,the Central Canyon System is under the influence of various provenance including the ancient Hainan Uplift and the Kunchong Uplift. The western provenance system,which is mainly composed of Kunchong Uplift in Vietnam,was the main sediment supply for the submarine fan developed during late Miocene in Ledong Sag and the turbidity sandstone deposited later in the Central Canyon System.
2015, 37(5): 24-33.
doi: 10.3969/j.issn.0253-4193.2015.05.003
Abstract:
Turbulent microstructure data in sections of 16°N and 14.5°N in May 2010 has been analyzed. The spatial variation of upper turbulent mixing in central South China Sea is investigated. The results show that,in the upper 10 to 400 m layer of 16°N section,the averaged vertical dissipation rate of turbulent kinetic energy <ερ> in the eastern sites is slightly stronger than that in the western sites. On the contrary,in 14.5°N section,it is found that <ερ> in western sites is 4 times of eastern sites; <ερ> declines from a averaged value of 2.6×10-6 W/m3 in the western sites (110.5°E to 111°E) to 5.89×10-7 W/m3 in the eastern sites (118.5°E). It is found that strong fine structure current shear and <ερ> are well correlated,which suggests that the strong current shear may be the main driving force for the strong turbulent mixing. Further study has revealed that the internal wave breaking of higher mode may be the main mechanism of turbulent mixing. In addition,three kinds of parameterization models are examined. MacKinnon-Gregg (MG) model for coastal sea is preferable because that the model could estimate turbulence dissipation rate of the upper layer of the central South China Sea with buoyancy frequency and shear.
Turbulent microstructure data in sections of 16°N and 14.5°N in May 2010 has been analyzed. The spatial variation of upper turbulent mixing in central South China Sea is investigated. The results show that,in the upper 10 to 400 m layer of 16°N section,the averaged vertical dissipation rate of turbulent kinetic energy <ερ> in the eastern sites is slightly stronger than that in the western sites. On the contrary,in 14.5°N section,it is found that <ερ> in western sites is 4 times of eastern sites; <ερ> declines from a averaged value of 2.6×10-6 W/m3 in the western sites (110.5°E to 111°E) to 5.89×10-7 W/m3 in the eastern sites (118.5°E). It is found that strong fine structure current shear and <ερ> are well correlated,which suggests that the strong current shear may be the main driving force for the strong turbulent mixing. Further study has revealed that the internal wave breaking of higher mode may be the main mechanism of turbulent mixing. In addition,three kinds of parameterization models are examined. MacKinnon-Gregg (MG) model for coastal sea is preferable because that the model could estimate turbulence dissipation rate of the upper layer of the central South China Sea with buoyancy frequency and shear.
2015, 37(5): 34-43.
doi: 10.3969/j.issn.0253-4193.2015.05.004
Abstract:
Modulated by the Madden-Julian Oscillation (MJO),the diurnal range of sea surface temperature (SST) peaks on the convection suppressed phase and drops to its lowest on the convection active phase. What's more,this kind of diurnal range on the developing phase of MJO is much larger than that on the decaying phase. Using a one-dimensional ocean mixed layer model,forced by the newly developed hourly reanalysis of sea surface fluxes,the cause of the difference of diurnal range of SST during the evolution of MJO is diagnosed quantitatively. It is demonstrated that the intro-seasonal variation of sea surface shortwave radiation is the main reason for the striking difference of diurnal range of SST between suppressed phase and active phase of MJO (40%). The intra-seasonal variation of wind stress (38%) and latent heat flux (14%) are also important. Due to the scale interaction between MJO perturbation and background circulation,the asymmetry of zonal wind stress determines the asymmetry of diurnal range of SST between developing and decaying phase of MJO.
Modulated by the Madden-Julian Oscillation (MJO),the diurnal range of sea surface temperature (SST) peaks on the convection suppressed phase and drops to its lowest on the convection active phase. What's more,this kind of diurnal range on the developing phase of MJO is much larger than that on the decaying phase. Using a one-dimensional ocean mixed layer model,forced by the newly developed hourly reanalysis of sea surface fluxes,the cause of the difference of diurnal range of SST during the evolution of MJO is diagnosed quantitatively. It is demonstrated that the intro-seasonal variation of sea surface shortwave radiation is the main reason for the striking difference of diurnal range of SST between suppressed phase and active phase of MJO (40%). The intra-seasonal variation of wind stress (38%) and latent heat flux (14%) are also important. Due to the scale interaction between MJO perturbation and background circulation,the asymmetry of zonal wind stress determines the asymmetry of diurnal range of SST between developing and decaying phase of MJO.
2015, 37(5): 44-53.
doi: 10.3969/j.issn.0253-4193.2015.05.005
Abstract:
Three sea surface wind products(CCMP,NCEP,and ERA) have been cross compared and evaluated using moored-buoy observations in Taiwan Strait in 2011. The main conclusions are as follows: (1) The horizontal pattern of the surface wind from the three products are similar and the time variation are consistent with each other; the wind speed forecast of NCEP in the middle and southern Taiwan Strait in winter is bigger than that of CCMP and ERA. (2)The wind speed bias,wind speed RMSE and wind direction RMSE of CCMP are -0.62 m/s,1.67 m/s and 31° respectively,compared with those of NCEP being 0.15 m/s,1.64 m/s and 31°,and those of ERA being -1.36 m/s,2.4 m/s and 33°; CCMP and NCEP are found to be more close to observations than ERA. (3) During the south-west monsoon and at low wind speed range(≤10 m/s),CCMP shows higher credibility while NCEP's wind speed is over-estimated; during the east-north monsoon and at high wind speed range(>10 m/s),NCEP shows higher credibility while CCMP's wind speed is under-estimated. (4) The wind direction RMSE of the three products are close to each other and show the same characteristic that the RMSE is bigger at low wind speed range (<5 m/s). Those findings will provide references for choosing appropriate sea surface wind product in Taiwan Strait.
Three sea surface wind products(CCMP,NCEP,and ERA) have been cross compared and evaluated using moored-buoy observations in Taiwan Strait in 2011. The main conclusions are as follows: (1) The horizontal pattern of the surface wind from the three products are similar and the time variation are consistent with each other; the wind speed forecast of NCEP in the middle and southern Taiwan Strait in winter is bigger than that of CCMP and ERA. (2)The wind speed bias,wind speed RMSE and wind direction RMSE of CCMP are -0.62 m/s,1.67 m/s and 31° respectively,compared with those of NCEP being 0.15 m/s,1.64 m/s and 31°,and those of ERA being -1.36 m/s,2.4 m/s and 33°; CCMP and NCEP are found to be more close to observations than ERA. (3) During the south-west monsoon and at low wind speed range(≤10 m/s),CCMP shows higher credibility while NCEP's wind speed is over-estimated; during the east-north monsoon and at high wind speed range(>10 m/s),NCEP shows higher credibility while CCMP's wind speed is under-estimated. (4) The wind direction RMSE of the three products are close to each other and show the same characteristic that the RMSE is bigger at low wind speed range (<5 m/s). Those findings will provide references for choosing appropriate sea surface wind product in Taiwan Strait.
2015, 37(5): 54-67.
doi: 10.3969/j.issn.0253-4193.2015.05.006
Abstract:
Breakup,rafting and ridging of ice cover exists widely in the polar and sub-polar regions. These processes affact the growth,vanishing and drifting of sea ice significantly. Considering the discrete distribution of sea ice on various scales,a discrete element model (DEM) should be developed to improve the sea ice numerical model and its computational precission. Thus,a modified discrete element model (MDEM) is established in this study to simulate the sea ice dynamics. Different with the traditional DEM,the ice cover is subdivided into a series of disks with their own characteristics including thickness,velocity,size and concentration,adopting the concept of smoothed particle hydrodynamics (SPH) of sea ice dynamics. Each sea ice element which is an assembly of ice floes changes in its size,concentration and thickness,according with the mass conservation law during drifting and inter-element collisions. According to the non-continuous distribution and rheology characteristics of ice cover,the viscous-elastic constitutive model is adopted. And the Mohr-Coulomb friction law is considered to determine the plastic deformation and tangential friction. To assess the reliability of this MDEM for sea ice dynamics,the drifting and ridging of ice cover in a various-width channel is simulated,and the simulated distribution of ice thickness is validated by the analytical solution. The drifting of sea ice in a rotational wind field is also simulated efficiently with high precision. Moreover,the sea ice dynamics in the Bohai Sea is simulated for 48 h. The simulated results match well with the satellite remote images and field observed data. In the future study,the MDEM will be improved by coupling dynamics and thermodynamics of sea ice. The growth,vanishing and drifting of sea ice will be simulated more accurately by consideringthe refrozen effect and breakage feature of ice cover.
Breakup,rafting and ridging of ice cover exists widely in the polar and sub-polar regions. These processes affact the growth,vanishing and drifting of sea ice significantly. Considering the discrete distribution of sea ice on various scales,a discrete element model (DEM) should be developed to improve the sea ice numerical model and its computational precission. Thus,a modified discrete element model (MDEM) is established in this study to simulate the sea ice dynamics. Different with the traditional DEM,the ice cover is subdivided into a series of disks with their own characteristics including thickness,velocity,size and concentration,adopting the concept of smoothed particle hydrodynamics (SPH) of sea ice dynamics. Each sea ice element which is an assembly of ice floes changes in its size,concentration and thickness,according with the mass conservation law during drifting and inter-element collisions. According to the non-continuous distribution and rheology characteristics of ice cover,the viscous-elastic constitutive model is adopted. And the Mohr-Coulomb friction law is considered to determine the plastic deformation and tangential friction. To assess the reliability of this MDEM for sea ice dynamics,the drifting and ridging of ice cover in a various-width channel is simulated,and the simulated distribution of ice thickness is validated by the analytical solution. The drifting of sea ice in a rotational wind field is also simulated efficiently with high precision. Moreover,the sea ice dynamics in the Bohai Sea is simulated for 48 h. The simulated results match well with the satellite remote images and field observed data. In the future study,the MDEM will be improved by coupling dynamics and thermodynamics of sea ice. The growth,vanishing and drifting of sea ice will be simulated more accurately by consideringthe refrozen effect and breakage feature of ice cover.
2015, 37(5): 68-75.
doi: 10.3969/j.issn.0253-4193.2015.05.007
Abstract:
This study analyzed 42 surface sediment samples and hydrological data observed in Aprial,2007 in the Cu Lao Cau Bay. The obtained data,combined with the Gao-Collins Grain Size Trend Analysis Model (GSTA model),were used to infer the characteristics and transportation trend of sarface sediment in the Cu Lao Cau Bay,Vietnam. The results suggested that the surface sediments were mainly composed of coarse particles. Under the influences of the tidal currents and waves,the particles were coarse in the central and western part of the Bay,and fine in the eastern part. In the western part of the Bay,the sediments were transported from southwest into the Bay along the coast. In the central part of the Bay,the sediments were transported from nearshore to offshore. In the eastern part of the Bay,the sediments were transported from northeast to the southwest. A convergent area of sediments was formed by the sediment from the western and eastern part of the Bay,and then they moved westward under the influence of residual currents. The surface sediment movement was mainly induced by the superimposed effect of wave and tidal current,of which the sediment was left by wave and transported by the tidal current. The coastline of the Cu Lao Cau Bay is being eroded under the influence of wave (a main factor),and it generally takes on a tendency of moving backward.
This study analyzed 42 surface sediment samples and hydrological data observed in Aprial,2007 in the Cu Lao Cau Bay. The obtained data,combined with the Gao-Collins Grain Size Trend Analysis Model (GSTA model),were used to infer the characteristics and transportation trend of sarface sediment in the Cu Lao Cau Bay,Vietnam. The results suggested that the surface sediments were mainly composed of coarse particles. Under the influences of the tidal currents and waves,the particles were coarse in the central and western part of the Bay,and fine in the eastern part. In the western part of the Bay,the sediments were transported from southwest into the Bay along the coast. In the central part of the Bay,the sediments were transported from nearshore to offshore. In the eastern part of the Bay,the sediments were transported from northeast to the southwest. A convergent area of sediments was formed by the sediment from the western and eastern part of the Bay,and then they moved westward under the influence of residual currents. The surface sediment movement was mainly induced by the superimposed effect of wave and tidal current,of which the sediment was left by wave and transported by the tidal current. The coastline of the Cu Lao Cau Bay is being eroded under the influence of wave (a main factor),and it generally takes on a tendency of moving backward.
2015, 37(5): 76-86.
doi: 10.3969/j.issn.0253-4193.2015.05.008
Abstract:
Based on the foreshore topography,water dynamics and wind data on Houjiangwan beach in East Guangdong,this paper used the method of canonical correlation analysis to identify different morphodynamic foreshore processes under the influence of the typhoon "Sepat" (No. 0709),and revealed some primary dynamic factors controlling these foreshore processes and attempted to present the physical interpretations. The analytical results included that (1) the primary foreshore process consisted of the eroded subaerial zone with the destroyed berm,the slightly depositional submarine slope zone and the bar zone with sediment movement offshore,and the process was controlled by several factors such as the eastern component of the wind speed,the maximum wave heights and the surf scaling parameter; (2) the secondary terrain process was the formation of submarine bar due to the sediment being transported from the foreshore to offshore,and the process was dominated by two dynamic factors such as the maximum wave periods and the beach underground water levels; and (3) the foreshore morphology was also characterized by the accumulation of the upper zone and the erosion of the lower zone of the foreshore,and the process was controlled by the following factors,i.e.,the longshore currents,the beach underground water levels and the maximum wave heights. Finally,this study proposed that the morphodynamic processes of the foreshore are coupled by many different morphological and dynamic processes.
Based on the foreshore topography,water dynamics and wind data on Houjiangwan beach in East Guangdong,this paper used the method of canonical correlation analysis to identify different morphodynamic foreshore processes under the influence of the typhoon "Sepat" (No. 0709),and revealed some primary dynamic factors controlling these foreshore processes and attempted to present the physical interpretations. The analytical results included that (1) the primary foreshore process consisted of the eroded subaerial zone with the destroyed berm,the slightly depositional submarine slope zone and the bar zone with sediment movement offshore,and the process was controlled by several factors such as the eastern component of the wind speed,the maximum wave heights and the surf scaling parameter; (2) the secondary terrain process was the formation of submarine bar due to the sediment being transported from the foreshore to offshore,and the process was dominated by two dynamic factors such as the maximum wave periods and the beach underground water levels; and (3) the foreshore morphology was also characterized by the accumulation of the upper zone and the erosion of the lower zone of the foreshore,and the process was controlled by the following factors,i.e.,the longshore currents,the beach underground water levels and the maximum wave heights. Finally,this study proposed that the morphodynamic processes of the foreshore are coupled by many different morphological and dynamic processes.
2015, 37(5): 87-100.
doi: 10.3969/j.issn.0253-4193.2015.05.009
Abstract:
The modern depocenter in the East China Sea is the mud area on the inner shelf,and the clay fraction of the sediments in the area is the main component. In the study of sedimentology,the clay minerals assemblage was widely used as an indicator of provenance and transportation of particulates. In this study,we used the method of XRD to study the variation of clay mineral contents in two gravity cores collected from the mud area. The clay minerals,together with the analysis of grain size and radioactive dating on the samples,have been used to discuss their environmental implications. The result shows that sediments in the mud area of East China Sea are mainly derived from the supply of Changjiang River,and contain a little from the Huanghe River and Oujiang River. And,clay mineral records have exhibited significant changes in the last one hundred years,which may be influenced by the fluctuations of East Asian Monsoon and the decreasing of sediment discharge of the Changjiang River.
The modern depocenter in the East China Sea is the mud area on the inner shelf,and the clay fraction of the sediments in the area is the main component. In the study of sedimentology,the clay minerals assemblage was widely used as an indicator of provenance and transportation of particulates. In this study,we used the method of XRD to study the variation of clay mineral contents in two gravity cores collected from the mud area. The clay minerals,together with the analysis of grain size and radioactive dating on the samples,have been used to discuss their environmental implications. The result shows that sediments in the mud area of East China Sea are mainly derived from the supply of Changjiang River,and contain a little from the Huanghe River and Oujiang River. And,clay mineral records have exhibited significant changes in the last one hundred years,which may be influenced by the fluctuations of East Asian Monsoon and the decreasing of sediment discharge of the Changjiang River.
2015, 37(5): 101-111.
doi: 10.3969/j.issn.0253-4193.2015.05.010
Abstract:
This study attempted to reveal the distribution patterns of magnetic minerals in the various sedimentary environments of Changjiang River mouth and adjacent continental shelf,and assessed proxies of magnetic parameters for identifying sedimentary environments,and the obtained results would be used to better perform the paleo-environmental reconstruction. We collected surficial sediments from the following six sedimentary environments at the Changjiang River mouth and adjacent continental shelf: distributary channel,river mouth shoal,delta front slope,prodelta,transitional regions and relict sand,and measured their grain size and magnetic properties. The results showed that,significantly high χ and SIRM values were obtained for sediments from the distributary channel and river mouth shoal,and high values of HIRM,χfd%,χARM,χARM/χ and χARM/SIRM were measured for sediments from prodelta and delta front slope,indicating that the distribution of magnetic minerals was controlled by the dispersal of terrigenous sediments and hydrodynamic sorting. We proposed that for the Holocene stratigraphy,magnetic parameter assemblage of HIRM,χARM,χARM/χ and χARM/SIRM could be the effective indicator for identifying prodelta and delta front slope,and χ、SIRM and S-20mT can be used to recognize the distributary channel and river mouth shoal.
This study attempted to reveal the distribution patterns of magnetic minerals in the various sedimentary environments of Changjiang River mouth and adjacent continental shelf,and assessed proxies of magnetic parameters for identifying sedimentary environments,and the obtained results would be used to better perform the paleo-environmental reconstruction. We collected surficial sediments from the following six sedimentary environments at the Changjiang River mouth and adjacent continental shelf: distributary channel,river mouth shoal,delta front slope,prodelta,transitional regions and relict sand,and measured their grain size and magnetic properties. The results showed that,significantly high χ and SIRM values were obtained for sediments from the distributary channel and river mouth shoal,and high values of HIRM,χfd%,χARM,χARM/χ and χARM/SIRM were measured for sediments from prodelta and delta front slope,indicating that the distribution of magnetic minerals was controlled by the dispersal of terrigenous sediments and hydrodynamic sorting. We proposed that for the Holocene stratigraphy,magnetic parameter assemblage of HIRM,χARM,χARM/χ and χARM/SIRM could be the effective indicator for identifying prodelta and delta front slope,and χ、SIRM and S-20mT can be used to recognize the distributary channel and river mouth shoal.
2015, 37(5): 112-120.
doi: 10.3969/j.issn.0253-4193.2015.05.011
Abstract:
A sea clutter statistical method based on similarity fitting is proposed in this paper. We first estimate five classical probability density functions of the sea clutter distribution in synthetic aperture radar (SAR) imagery,which include Rayleigh distribution,lognormal distribution,Weibull distribution,K distribution and G0 distribution. Thereafter,we fit all these five models to a new sea clutter distribution by an optimization method based on a similarity criterion. In the experiment,we evaluate the fitting precision based on the Kullback-Leibler distance using four SAR images. The results show the K-L distance between the fitting model and observations is only 0.015 84 when using the proposed algorithm. The fitting model is concluded to be superior to five classical distribution models. When we conduct ship detection using the fitting model and CFAR algorithm,the mean detection accuracy can reach up to 95.75%.
A sea clutter statistical method based on similarity fitting is proposed in this paper. We first estimate five classical probability density functions of the sea clutter distribution in synthetic aperture radar (SAR) imagery,which include Rayleigh distribution,lognormal distribution,Weibull distribution,K distribution and G0 distribution. Thereafter,we fit all these five models to a new sea clutter distribution by an optimization method based on a similarity criterion. In the experiment,we evaluate the fitting precision based on the Kullback-Leibler distance using four SAR images. The results show the K-L distance between the fitting model and observations is only 0.015 84 when using the proposed algorithm. The fitting model is concluded to be superior to five classical distribution models. When we conduct ship detection using the fitting model and CFAR algorithm,the mean detection accuracy can reach up to 95.75%.
2015, 37(5): 121-135.
doi: 10.3969/j.issn.0253-4193.2015.05.012
Abstract:
Multi-proxy investigations were performed on core 08P31 collected from the Chukchi Plateau,Western Arctic Ocean,during the Third Chinese National Arctic Expedition. The core was dated back to Marine Isotope Stage (MIS) 3 by a combination of AMS 14C dating and regional core correlation. Results obtained for total organic carbon contents (TOC) and Biogenic opal content (Opal) in the core show that since MIS 3,the total productivity showed a trend of rising,but the siliceous biological productivity was generally low. CaCO3 contents in the core suggested input of not only marine organic carbon,but also of detrital carbonate. By comparing C/N ratio with TOCmar/TOC,TOCmar and TOCter which are calculated from the value of δ13Corg by "both two end-element method",we suggested that it was very reliable to use the value of δ13Corg, as the specification of organic sources. The δ results showed that the source of organic matter of core 08P31 was indicated to be marine organic matter. And,terrigenous organic matter could also contribute to the increased TOC% in the brown layer B2 and white layer W3. The co-variations light δ18O and-13C values of Neogloboquadrina pachyderma (Sin.) (Nps) in core 08P31 indicated that the light values in the brown layer B2 and gray layer G1 in MIS 3 and MIS 1 were resulted from meltwater events; and those in the top of yellow brown layer Yb1 to white layer W3 were caused by the enhanced sea ice formation and light brine injection. The occurrence of heavy δ18O and-13C values in the middle of yellow brown layer Yb1 and white layer W3 concurrent with low foraminiferal abundances could indicate cold water temperature and nutrition environment. The Nps-δ18O values varied inversely with Nps-δ13C values in yellow brown layer Yb2 could indicate that the study area was covered by thick sea ice or ice sheet with cold temperatures and little meltwater,which prevented the bio-productivity and sea-atmosphere exchange,as well as water mass ventilation.
Multi-proxy investigations were performed on core 08P31 collected from the Chukchi Plateau,Western Arctic Ocean,during the Third Chinese National Arctic Expedition. The core was dated back to Marine Isotope Stage (MIS) 3 by a combination of AMS 14C dating and regional core correlation. Results obtained for total organic carbon contents (TOC) and Biogenic opal content (Opal) in the core show that since MIS 3,the total productivity showed a trend of rising,but the siliceous biological productivity was generally low. CaCO3 contents in the core suggested input of not only marine organic carbon,but also of detrital carbonate. By comparing C/N ratio with TOCmar/TOC,TOCmar and TOCter which are calculated from the value of δ13Corg by "both two end-element method",we suggested that it was very reliable to use the value of δ13Corg, as the specification of organic sources. The δ results showed that the source of organic matter of core 08P31 was indicated to be marine organic matter. And,terrigenous organic matter could also contribute to the increased TOC% in the brown layer B2 and white layer W3. The co-variations light δ18O and-13C values of Neogloboquadrina pachyderma (Sin.) (Nps) in core 08P31 indicated that the light values in the brown layer B2 and gray layer G1 in MIS 3 and MIS 1 were resulted from meltwater events; and those in the top of yellow brown layer Yb1 to white layer W3 were caused by the enhanced sea ice formation and light brine injection. The occurrence of heavy δ18O and-13C values in the middle of yellow brown layer Yb1 and white layer W3 concurrent with low foraminiferal abundances could indicate cold water temperature and nutrition environment. The Nps-δ18O values varied inversely with Nps-δ13C values in yellow brown layer Yb2 could indicate that the study area was covered by thick sea ice or ice sheet with cold temperatures and little meltwater,which prevented the bio-productivity and sea-atmosphere exchange,as well as water mass ventilation.
2015, 37(5): 136-147.
doi: 10.3969/j.issn.0253-4193.2015.05.013
Abstract:
Rare earth elements (REEs) are important tracers for geochemical cycles,and are also world strategic resources. In this study,we investigated the mineral and REEs characteristics of Co-rich crusts from Johnston island to show that REEs distributions are constrained by their mineral compositions. On the basis of their mineral characteristics,the Co-rich crusts can be classified into type A,type B,and type C. The vernadite contents decrease from type A via type B to type C; and type B shows the highest apatite contents. Birnessite and todorokite are enriched in type C crust. Type A crusts are enriched in REE3+ and Ce,whereas type B crusts are characterized by high contents of Ce and Y. In type A crust,REE3 and Y that originated from seawater are specified adsorbed on the Fe-phase. Cerium is enriched in Mn-mineral via the oxidation from Ce3 to Ce4 and separation from other REEs. In type B crust,REEs mainly form independent minerals,part of Ce and LREE3 are absorbed in the Fe-phase,and part of Y enter in apatite. In type C crust,REEs show the enrichment phenomena in Mn-minerals,and also part of Y are absorbed in apatite.
Rare earth elements (REEs) are important tracers for geochemical cycles,and are also world strategic resources. In this study,we investigated the mineral and REEs characteristics of Co-rich crusts from Johnston island to show that REEs distributions are constrained by their mineral compositions. On the basis of their mineral characteristics,the Co-rich crusts can be classified into type A,type B,and type C. The vernadite contents decrease from type A via type B to type C; and type B shows the highest apatite contents. Birnessite and todorokite are enriched in type C crust. Type A crusts are enriched in REE3+ and Ce,whereas type B crusts are characterized by high contents of Ce and Y. In type A crust,REE3 and Y that originated from seawater are specified adsorbed on the Fe-phase. Cerium is enriched in Mn-mineral via the oxidation from Ce3 to Ce4 and separation from other REEs. In type B crust,REEs mainly form independent minerals,part of Ce and LREE3 are absorbed in the Fe-phase,and part of Y enter in apatite. In type C crust,REEs show the enrichment phenomena in Mn-minerals,and also part of Y are absorbed in apatite.
2015, 37(5): 148-158.
doi: 10.3969/j.issn.0253-4193.2015.05.014
Abstract:
The underwater topography at the South Channel,North Passage,Channel of Hengsha and North Channel of the Yangtze Estuary were surveyed by using multibeam echo-sounding system,wave height,wavelength,inflow angle,the dorsal stream angle and sediment characteristics of sand waves in these areas were calculated statistically,and the net displacement of sand waves in one tidal period was estimated on the basis of data for flow rate,grain sizes of sediments and water depths. The results showed that the sand waves in the Yangtze Estuary were basically large,and there took on a proportional relationship between wavelengths with sediment particle sizes. The symmetry of sand waves is different among all surveyed area in the Yangtze Estuary. The more obvious the ebb flow is,the worse the symmetry of sand wave and the more net displacement is. The symmetry of sand waves can reflect the power of water and net displacement of sand waves.
The underwater topography at the South Channel,North Passage,Channel of Hengsha and North Channel of the Yangtze Estuary were surveyed by using multibeam echo-sounding system,wave height,wavelength,inflow angle,the dorsal stream angle and sediment characteristics of sand waves in these areas were calculated statistically,and the net displacement of sand waves in one tidal period was estimated on the basis of data for flow rate,grain sizes of sediments and water depths. The results showed that the sand waves in the Yangtze Estuary were basically large,and there took on a proportional relationship between wavelengths with sediment particle sizes. The symmetry of sand waves is different among all surveyed area in the Yangtze Estuary. The more obvious the ebb flow is,the worse the symmetry of sand wave and the more net displacement is. The symmetry of sand waves can reflect the power of water and net displacement of sand waves.
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