One specimen belonging to the family Comatellinae was collected from the Zhenbei Seamount(332.5–478.2 m)in the South China Sea in July 2022.Based on the morphological characters,the specimen was identified as Palaeoc...One specimen belonging to the family Comatellinae was collected from the Zhenbei Seamount(332.5–478.2 m)in the South China Sea in July 2022.Based on the morphological characters,the specimen was identified as Palaeocomatella hiwia McKnight,1977.It is first recorded from China Sea and redescribed in detail.This specimen differs from the original description from New Zealand for never showing syzygy at br4+5 or br5+6 on interior and br1+2 on exterior arms.However,it is much conform to the redescription to specimens from Indonesia,with only differences in position of the second syzygy and distalmost pinnule comb.Specimen is deposited in the Institute of Oceanology,Chinese Academy of Sciences.Phylogenetic analyses based on the mitochondrial c oxidase subunit I(COI)and 16S rRNA genes indicated that P.hiwia was nested within the tribe Phanogeniini and clustered with Aphanocomaster pulcher.Furthermore,P.hiwia showed same morphological features in terms of mouth placement,comb location,and number of comb teeth rows as other genera of Phanogeniini.Therefore,we suggest that the genus Palaeocomatella should be put in the tribe Phanogeniini.展开更多
Pyrite is one of the common authigenic minerals in marine sediments.Previous studies have shown that the morphological and isotopic characteristics of pyrite are closely related to the geochemical environment where it...Pyrite is one of the common authigenic minerals in marine sediments.Previous studies have shown that the morphological and isotopic characteristics of pyrite are closely related to the geochemical environment where it is formed.To better understand the for-mation mechanism of authigenic pyrite,we analyzed the isotopic composition,morphology,and distribution of pyrite in the sediment at 500m below the seafloor from Xisha Trough,South China Sea.Mineral morphologies were observed by scanning electron micros-copy and Raman spectrography.X-Ray computed tomography was applied to measure the particle size of pyrite.The size of pyrite crystals in the matrix sediment mainly ranged between 25 and 65µm(av.ca.40µm),although crystals were larger(av.ca.50μm)in the veins.The pyrites had a fine-grained truncated octahedral shape with occasionally well-developed growth steps,which implies the low growth rate and weak anaerobic oxidation of methane-sulfate reduction when pyrite was formed.Theδ^(34)S values of pyrites ranged from+20.8‰Vienna-defined Canyon Diablo Troilite(V-CDT)to+33.2‰V-CDT and from+44.8‰V-CDT to+48.9‰,which suggest two growth stages.In the first stage,with the continuous low methane flux,the pyrite possibly formed in an environment with good access to seawater.In the second stage,the pyrites mainly developed in sediment fractures and appeared in veins,probably due to the limited availability of sulfate.The less exposure of pyrite to the environment in the second stage was probably caused by sediment accumulation or perturbation.In this study,an episodic pyritization process was identified,and the paleoenvironment was reconstructed for the sediment investigated.展开更多
Many locations with concentrated hydrates at vents have confirmed the presence of abundant thermogenic gas in the middle of the Qiongdongnan Basin(QDNB).However,the impact of deep structures on gasbearing fluids migra...Many locations with concentrated hydrates at vents have confirmed the presence of abundant thermogenic gas in the middle of the Qiongdongnan Basin(QDNB).However,the impact of deep structures on gasbearing fluids migration and gas hydrates distribution in tectonically inactive regions is still unclear.In this study,the authors apply high-resolution 3D seismic and logging while drilling(LWD)data from the middle of the QDNB to investigate the influence of deep-large faults on gas chimneys and preferred gasescape pipes.The findings reveal the following:(1)Two significant deep-large faults,F1 and F2,developed on the edge of the Songnan Low Uplift,control the dominant migration of thermogenic hydrocarbons and determine the initial locations of gas chimneys.(2)The formation of gas chimneys is likely related to fault activation and reactivation.Gas chimney 1 is primarily arises from convergent fluid migration resulting from the intersection of the two faults,while the gas chimney 2 benefits from a steeper fault plane and shorter migration distance of fault F2.(3)Most gas-escape pipes are situated near the apex of the two faults.Their reactivations facilitate free gas flow into the GHSZ and contribute to the formation of fracture‐filling hydrates.展开更多
High-resolution sea-level data and high-precision dating of corals in the northern South China Sea(SCS)during the Holocene provide a reference and historical background for current and future sea-level changes and a b...High-resolution sea-level data and high-precision dating of corals in the northern South China Sea(SCS)during the Holocene provide a reference and historical background for current and future sea-level changes and a basis for scientific assessment of the evolutionary trend of coral reefs in the SCS.Although sporadic studies have been performed around Hainan Island in the northern SCS,the reconstructed sea level presents different values or is controversial because the indicative meaning of the sea-level indicators were neither quantified nor uniform criteria.Here,we determined the quantitative relationship between modern living coral and sea level by measuring the top surfaces of 27 live Porites corals from the inner reef flat along the east coast of Hainan Island and assessed the accuracy of results obtained using coral as sea-level indicators.Additionally,three in situ fossil Porites corals were analyzed based on elevation measurements,digital X-ray radiography,and U-Th dating.The survey results showed that the indicative meanings for the modern live Porites corals is(146.09±8.35)cm below the mean tide level(MTL).It suggested that their upward growth limit is constrained by the sea level,and the lowest low water is the highest level of survival for the modern live Porites corals.Based on the newly defined indicative meanings,6 new sea-level index points(SLIPs)were obtained and 19 published SLIPs were recalculated.Those SLIPs indicated a relative sea level fluctuation between(227.7±9.8)cm to(154.88±9.8)cm MTL between(5393±25)cal a BP and(3390±12)cal a BP,providing evidences of the Mid-Holocene sea-level highstand in the northern SCS.Besides that,our analysis demonstrated that different sea-level histories may be produced based on different indicative meanings or criteria.The dataset of 276 coral U-Th ages indicates that coral reef development in the northern SCS comprised the initial development,boom growth,decline,and flourishing development again.A comparison with regional records indicated that synergistic effects of climatic and environmental factors were involved in the development of coral reefs in the northern SCS.Thus,the cessation of coral reef development during the Holocene in the northern SCS was probably associated with the dry and cold climate in South China,as reflected in the synchronous weakening of the ENSO and East Asian summer monsoon induced by the reduction of the 65°N summer insolation,which forced the migration of the Intertropical Convergence Zone.展开更多
This study aims to investigate characteristics of continental shelf wave(CSW)on the northwestern continental shelf of the South China Sea(SCS)induced by winter storms in 2021.Mooring and cruise observations,tidal gaug...This study aims to investigate characteristics of continental shelf wave(CSW)on the northwestern continental shelf of the South China Sea(SCS)induced by winter storms in 2021.Mooring and cruise observations,tidal gauge data at stations Hong Kong,Zhapo and Qinglan and sea surface wind data from January 1 to February 28,2021 are used to examine the relationship between along-shelf wind and sea level fluctuation.Two events of CSWs driven by the along-shelf sea surface wind are detected from wavelet spectra of tidal gauge data.The signals are triply peaked at periods of 56 h,94 h and 180 h,propagating along the coast with phase speed ranging from 6.9 m/s to18.9 m/s.The dispersion relation shows their property of the Kelvin mode of CSW.We develop a simple method to estimate amplitude of sea surface fluctuation by along-shelf wind.The results are comparable with the observation data,suggesting it is effective.The mode 2 CSWs fits very well with the mooring current velocity data.The results from rare current help to understand wave-current interaction in the northwestern SCS.展开更多
As one of the micro-blocks dispersed in the South China Sea(SCS), the basement of the Xisha Islands has rarely been drilled because of the thick overlying Cenozoic sediments, which has led to a confused understanding ...As one of the micro-blocks dispersed in the South China Sea(SCS), the basement of the Xisha Islands has rarely been drilled because of the thick overlying Cenozoic sediments, which has led to a confused understanding of the pre-Cenozoic basement of the Xisha Islands. Well CK-1, a kilometer-scale major scientific drill in the Xisha Islands in the northwestern SCS, penetrated thick reefal limestone(0–888.4 m) and the underlying basement rocks(888.4–901.4 m). In this study, we present the zircon U-Pb ages of basement basaltic pyroclastic rocks from Well CK-1 in the Xisha Islands of the northwestern SCS to investigate the basement nature of the Xisha microblock. The basement of Well CK-1 consists of basaltic pyroclastic rocks on the seamount. The zircon grains yielded apparent ages ranging from ca. 2 138.9 Ma to ca. 36 Ma. The old group of zircon grains from Well CK-1 was considered to be inherited zircons. Two Cenozoic zircons gave a weighted mean 206Pb/238U age of(36.3 ± 1.1) Ma,Mean Squared Weighted Deviations(MSWD) = 1.2, which may represent the maximum age of the volcano eruption. The Yanshanian inherited zircons(116.9–105.7 Ma and 146.1–130.2 Ma) from Well CK-1 are consistent with the zircons from Well XK-1, indicating that the basement of Chenhang Island may be similar to that of Well XK-1. We propose that the Xisha micro-block may have developed on a uniform Late Jurassic metamorphic crystalline basement, intruded by Cretaceous granitic magma.展开更多
The properties of salinity in the South China Sea(SCS),a significant marginal sea connecting the Pacific and Indian Oceans,are greatly influenced by the transport of fresh water flux between the two oceans.However,the...The properties of salinity in the South China Sea(SCS),a significant marginal sea connecting the Pacific and Indian Oceans,are greatly influenced by the transport of fresh water flux between the two oceans.However,the long-term changes in the intermediate water in the SCS have not been thoroughly studied due to limited data,particularly in relation to its thermodynamic variations.This study utilized reanalysis data products to identify a 60-year trend of freshening in the intermediate waters of the northern South China Sea(NSCS),accompanied by an expansion of low-salinity water.The study also constructed salinity budget terms,including advection and entrainment processes,and conducted an analysis of the salinity budget to understand the impacts of external and internal dynamic processes on the freshening trend of the intermediate water in the NSCS.The analysis revealed that the freshening in the northwest Pacific Ocean and the intensification of intrusion through the Luzon Strait at intermediate levels are the primary drivers of the salinity changes in the NSCS.Additionally,a weakened trend in the intensity of vertical entrainment also contributes to the freshening in the NSCS.This study offers new insights into the understanding of regional deep sea changes in response to variations in both thermodynamics and oceanic dynamic processes.展开更多
The South China Sea is a hotspot for regional climate research.Over the past 40 years,considerable improvement has been made in the development and utilization of the islands in the South China Sea,leading to a substa...The South China Sea is a hotspot for regional climate research.Over the past 40 years,considerable improvement has been made in the development and utilization of the islands in the South China Sea,leading to a substantial change in the land-use of the islands.However,research on the impact of human development on the local climate of these islands is lacking.This study analyzed the characteristics of local climate changes on the islands in the South China Sea based on data from the Yongxing Island Observation Station and ERA5 re-analysis.Furthermore,the influence of urbanization on the local climate of the South China Sea islands was explored in this study.The findings revealed that the 10-year average temperature in Yongxing Island increased by approximately 1.11℃from 1961 to 2020,and the contribution of island development and urbanization to the local warming rate over 60 years was approximately 36.2%.The linear increasing trend of the annual hot days from 1961–2020 was approximately 14.84 days per decade.The diurnal temperature range exhibited an increasing trend of 0.05℃per decade,whereas the number of cold days decreased by 1.06days per decade.The rapid increase in construction on Yongxing Island from 2005 to 2021 led to a decrease in observed surface wind speed by 0.32 m s^(-1)per decade.Consequently,the number of days with strong winds decreased,whereas the number of days with weak winds increased.Additionally,relative humidity exhibited a rapid decline from 2001 to 2016 and then rebounded.The study also found substantial differences between the ERA5 re-analysis and observation data,particularly in wind speed and relative humidity,indicating that the use of re-analysis data for climate resource assessment and climate change evaluation on island areas may not be feasible.展开更多
This study involved outcrop,drilling,seismic,gravity,and magnetic data to systematically document the geological records of the subduction process of Proto-South China Sea(PSCS)and establish its evolution model.The re...This study involved outcrop,drilling,seismic,gravity,and magnetic data to systematically document the geological records of the subduction process of Proto-South China Sea(PSCS)and establish its evolution model.The results indicate that a series of arc-shaped ophiolite belts and calcalkaline magmatic rocks are developed in northern Borneo,both of which have the characteristics of gradually changing younger from west to east,and are direct signs of subduction and collision of PSCS.At the same time,the subduction of PSCS led to the formation of three accretion zones from the south to the north in Borneo,the Kuching belt,Sibu belt,and Miri belt.The sedimentary formation of northern Borneo is characterized by a three-layer structure,with the oceanic basement at the bottom,overlying the deep-sea flysch deposits of the Rajang–Crocker group,and the molasse sedimentary sequence that is dominated by river-delta and shallow marine facies at the top,recording the whole subduction–collision–orogeny process of PSCS.Further,seismic reflection and tomography also confirmed the subduction and collision of PSCS.Based on the geological records of the subduction and collision of PSCS,combined with the comprehensive analysis of segmented expansion and key tectonic events in the South China Sea,we establish the“gradual”subduction-collision evolution model of PSCS.During the late Eocene to middle Miocene,the Zengmu,Nansha,and Liyue–Palawan blocks were separated by West Baram Line and Balabac Fault,which collided with the Borneo block and Kagayan Ridge successively from the west to the east,forming several foreland basin systems,and PSCS subducted and closed from the west to the east.The subduction and extinction of PSCS controlled the oil and gas distribution pattern of southern South China Sea(SSCS)mainly in three aspects.First,the“gradual”closure process of PSCS led to the continuous development of many large deltas in SSCS.Second,the deltas formed during the subduction–collision of PSCS controlled the development of source rocks in the basins of SSCS.Macroscopically,the distribution and scale of deltas controlled the distribution and scale of source rocks,forming two types of source rocks,namely,coal measures and terrestrial marine facies.Microscopically,the difference of terrestrial higher plants carried by the delta controlled the proportion of macerals of source rocks.Third,the difference of source rocks mainly controlled the distribution pattern of oil and gas in SSCS.Meanwhile,the difference in the scale of source rocks mainly controlled the difference in the amount of oil and gas discoveries,resulting in a huge amount of oil and gas discoveries in the basin of SSCS.Meanwhile,the difference of macerals of source rocks mainly controlled the difference of oil and gas generation,forming the oil and gas distribution pattern of“nearshore oil and far-shore gas”.展开更多
The existing genetic models of the South China Sea(SCS)include an extrusion model of the Indochina Peninsula,a back-arc extension model,and a subduction and dragging model of the Proto-South China Sea(PSCS).However,no...The existing genetic models of the South China Sea(SCS)include an extrusion model of the Indochina Peninsula,a back-arc extension model,and a subduction and dragging model of the Proto-South China Sea(PSCS).However,none of these models has been universally accepted because they do not fully match a large number of geological phenomena and facts.By examining the regional tectonics and integrating them with measured data for the SCS,in this study,a back-arc spreading-sinistral shear model is proposed.It is suggested that the SCS is a back-arc basin formed by northward subduction of the PSCS and its formation was triggered by left-lateral strike-slip motion due to the northward drift of the Philippine Sea Plate.The left-lateral strike-slip fault on the western margin caused by the Indo-Eurasian collision changed the direction of the Southwest Sub-basin's spreading axis from nearly E–W to NE–SW,and subduction retreat caused the spreading ridge to jump southward.This study summarizes the evolution of the SCS and adjacent regions since the Late Mesozoic.展开更多
Notable differences in the structural characteristics and evolution of three adjacent sub-sags,i.e.,the Wenchang sub-sags A,B,and C,on the downthrown side of the Zhu IlI South Fault in the Wenchang Sag,are significant...Notable differences in the structural characteristics and evolution of three adjacent sub-sags,i.e.,the Wenchang sub-sags A,B,and C,on the downthrown side of the Zhu IlI South Fault in the Wenchang Sag,are significant as they affect the formation and distribution of the oil and gas in these three sub-sags.However,the differences in their tectonic evolutions and formation mechanisms have not yet been adequately explained.In this paper,stress analysis,equilibrium profiles,and paleogeomorphic restora-tion,are used to investigate the dynamic settings,formation mechanisms,and influencing factors of the structural deformation related to the formation of the Wenchang Sag based on interpretation of seismic data.The results of the stress analysis suggest clockwise deflection of the regional tensile stress direction from a WNW-ESE trend during the Early Paleocene to NW-SE and NNW-SSE trends during the Eocene,to a nearly N-S trend during the Oligocene,and finally to a NNE-SSW trend during the Miocene.This clockwise rotation of the regional tensile stress direction led to the formation of a dextral strike-slip stress component parallel to the NE-trending Zhu I South Fault.This strike-slip stress component formed a releasing bend in sub-sag A,and may be associated with the continuous subsidence of a thick sedimentary layer in sub-sag A.It also created a restraining bend in sub-sag B,which underwent multiple structural inversions during its extension and subsidence and has a relatively s mall sedimentary thick-ness.The double restraining bend in sub-sag C is considered to have been strongly uplifted and eroded in response to this strike-slip stress component.Four obvious structural inversions in sub-sag B are iden-tified in this paper.These structural inversions correspond to the last four regional tectonic movements.This interpretation suggests that the formation of the structural inversions was likely related to the strong tensile stress and the small intersection angle between the direction of the regional tensile stress and the pre-existing boundary fault.The rotation of the tensile stress direction was responsible for the strike-slip movement on the pre-existing boundary fault and the formation of the releasing bend and restraining bend,which controlled the structural evolutions of the sub-sags.This reasonably explains the differential tectonic evolution of these three sub-sags in the Wenchang Sag,and provides a crucial idea forstructuralanalysisof similarbasins.展开更多
This paper uses the Coupled Ocean-Atmosphere-Wave-Sediment Transport(COAWST)model to analyze the impact of typhoon‘Hongxia’on the velocity and position movement of the Kuroshio axis,the impact of typhoons on the Kur...This paper uses the Coupled Ocean-Atmosphere-Wave-Sediment Transport(COAWST)model to analyze the impact of typhoon‘Hongxia’on the velocity and position movement of the Kuroshio axis,the impact of typhoons on the Kuroshio intrusion into South China Sea(SCS),the corresponding water,heat,and salt fluxes,and the impact of Kuroshio water in the northeastern SCS.When typhoon‘Hongxia’passed,the Kuroshio intrusion into the SCS was the most significant at 21?N latitude.In the vertical direction,the Kuroshio intrusion was strongest in the subsurface layer,leading to the most significant changes in temperature and salinity in the northeastern part of the SCS in the subsurface layer.Under the influence of the southeastern monsoon in summer,a large amount of low-salinity water accumulates at the surface of the northeastern part of the SCS,and Kuroshio intrusive water remains in the bottom and middle portions of the subsurface layer.The westward deviation of the Kuroshio axis caused by the typhoon displays a certain lag compared with the hot and salty water intrusion into the SCS approximately 7 d later.The impact of the typhoon on the Kuroshio intrusion into the SCS lasts for 20 d.The typhoon caused increases in the water,heat,and salt fluxes associated with the Kuroshio intrusion into the SCS,and the contribution of the typhoon to these fluxes was as high as 40%.Under typhoon conditions,the maximum Kuroshio intrusion flux reached more than twice that before the typhoon.展开更多
Submarine volcanism is widely developed in the South China Sea(SCS).However,the characteristics,distribution,and genesis of submarine volcanoes in the southern margin of the SCS remain obscure.In this study,we analyze...Submarine volcanism is widely developed in the South China Sea(SCS).However,the characteristics,distribution,and genesis of submarine volcanoes in the southern margin of the SCS remain obscure.In this study,we analyzed the characteristics of submarine volcanoes and identified a total of 43 submarine volcanoes in the southern margin of the SCS,based on a newly acquired 310-km seismic reflection profile,along with previous 45 multi-channel seismic(MCS)profiles,petrological results from volcanic rocks sampled by dredging and drilling,nearby ocean bottom seismometer(OBS)wide-angle seismic profiles,and gravity and magnetic data.The study ascertains that most of these volcanoes are located in fault-block belts and graben-horst zones with strong crustal stretching and thinning.These volcanoes exhibit positive high-amplitude external seismic reflections,weak and chaotic internal seismic reflections,and are accompanied by local deformation of the surrounding sedimentary strata.Meanwhile,they have higher positive gravity anomalies and higher magnetic anomalies than the background strata.The petrological dating results show that volcanic ages are primarily in the Pliocene-Pleistocene,with geochemical characteristics indicating dominance of oceanic island basalt(OIB)-type alkali-basalts.Extensional faults have obviously spatial correspondence with post-spreading volcanism,suggesting these faults may provide conduits for submarine volcanism.The high-velocity bodies(HVBs)in the lower crust and magma underplating exist in the southern SCS,which could provide a clue of genesis for submarine volcanism.The inference is that the intensity of post-spreading volcanism in the southern margin might be affected by stretching faults,crustal thinning and magma underplating.展开更多
There are many large-scale Cenozoic sedimentary basins with plentiful river deltas,deep-water fans and carbonate platforms in the southern South China Sea.The Crocker Fan was deposited as a typical submarine fan durin...There are many large-scale Cenozoic sedimentary basins with plentiful river deltas,deep-water fans and carbonate platforms in the southern South China Sea.The Crocker Fan was deposited as a typical submarine fan during the late Eocene–early Miocene,and stretches extensively across the entire Sarawak–Sabah of the northern Borneo area.However,systematic analyses are still lacking regarding its sediment composition and potential source suppliers.No consensus has been reached yet on the provenance evolution and sedimentary infilling processes,which seriously impeded the oil-and-gas exploration undertakings.By combining with sedimentaryfacies identification,heavy mineral assemblages,elemental geochemistry and detrital zircon U-Pb dating,this paper aims to generalize an integrated analysis on the potential provenance terranes and restore source-to-sink pathways of the Crocker Fan.In general,the Crocker Fan was initially formed over the Cretaceous–lower/middle Eocene Rajang Group by an angular Rajang unconformity.The continual southward subduction of the protoSouth China Sea resulted in magmatic activities and subsequent regional deformation and thrusting along the Lupar Line in the northern Borneo.The lowermost Crocker sequence is featured by a thick conglomerate layer sourced from in-situ or adjacent paleo-uplifts.From the late Eocene to the early Miocene,the Crocker Fan was constantly delivered with voluminous detritus from the Malay Peninsula of the western Sundaland.The Zengmu Basin was widely deposited with delta plain and neritic facies sediments,while the Brunei-Sabah Basin,to the farther east,was ubiquitously characterized by turbiditic sequences.The Crocker Fan successions are overall thick layers of modest-grained sandstones,which formed high-quality reservoirs in the southern South China Sea region.展开更多
This study identifies break events of the South China Sea(SCS)summer monsoon(SCSSM)based on 42 years of data from 1979 to 2020,and investigates their statistical characteristics and associated atmospheric anomalies.A ...This study identifies break events of the South China Sea(SCS)summer monsoon(SCSSM)based on 42 years of data from 1979 to 2020,and investigates their statistical characteristics and associated atmospheric anomalies.A total of 214 break events are identified by examining the convection evolution during each monsoon season.It is found that most events occur between June and September and show a roughly even distribution.Short-lived events(3–7 days)are more frequent,accounting for about two thirds of total events,with the residual one third for long-lived events(8–24 days).The SCSSM break is featured by drastic variations in various atmospheric variables.Particularly,the convection and precipitation change from anomalous enhancement in adjoining periods to a substantial suppression during the break,with the differences being more than 60 W m−2 for outgoing longwave radiation(OLR)and 10 mm d−1 for precipitation.This convection/precipitation suppression is accompanied by an anomalous anticyclone in the lower troposphere,corresponding to a remarkable westward retreat of the monsoon trough from the Philippine Sea to the Indochina Peninsula,which reduces the transportation of water vapor into the SCS.Besides,the pseudo-equivalent potential temperature()declines sharply,mainly attributable to the local specific humidity reduction caused by downward dry advection.Furthermore,it is found that the suppressed convection and anomalous anticyclone responsible for the monsoon break form near the equatorial western Pacific and then propagate northwestward to the SCS.展开更多
Intraseasonal oscillation of the mixed layer and upper ocean temperature has been found to occur over the South China Sea(SCS)in the summer monsoon season based on the multiple reanalysis and observational data in thi...Intraseasonal oscillation of the mixed layer and upper ocean temperature has been found to occur over the South China Sea(SCS)in the summer monsoon season based on the multiple reanalysis and observational data in this study.The method of composite analysis and an upper ocean temperature equation assisted the analysis of physical mechanisms.The results show that the mixed layer depth(MLD)in the SCS has a significant oscillation with a 30-60 d period over the SCS region,which is closely related to boreal summer intraseasonal oscillation(BSISO)activities.The MLD can increase(decrease)during the positive(negative)phase of the BSISO and usually lags behind by approximately one-eighth of the lifecycle(5 days)of the BSISO-related convection.The BSISO may cause periodic anomalies at the air-sea boundary,such as wind stress and heat flux,so it can play a dominant role in modulating the variation in MLD.There also are significant intraseasonal seawater temperature anomalies in both the surface and subsurface layers of the SCS.In addition,during the initial phase of the BSISO,the temperature anomaly signals of the thermocline are obviously opposite to the sea surface temperature(SST),especially in the southern SCS.According to the results from the analysis of the temperature equation,the vertical entrainment term caused by BSISO-related wind stress is stronger than the thermal forcing during the initial stage of convection,and it is more significant in the southern SCS.展开更多
Polygonal faults(PFs)generally have a classic polygonal geometry in map view.However,under the influence of tectonic faults,diapirs,channels,and slopes,the classic polygonal geometry of PFs is not preserved,demonstrat...Polygonal faults(PFs)generally have a classic polygonal geometry in map view.However,under the influence of tectonic faults,diapirs,channels,and slopes,the classic polygonal geometry of PFs is not preserved,demonstrating differences(different characters)in map-view 3D seismic data covering an area of 334km^(2) of the Changchang(CC)sag,are used to document the mapview and cross-sectional characteristics of PFs.These data also help investigate the irregularly polygonal geometries of PFs due to the presence of influence factors,such as transtensional faults,submarine fans,channels,diapirs/gas chimneys,and the basal slope within the lower-middle Miocene strata.Results show that various irregularly polygonal geometries of PFs can be classified into enechelon and arcuate PFs,channel-segmenting and-bounding PFs,radial PFs,and rectangular PFs in map-view.En-echelon and arcuate PFs are induced by transtensional faults and exhibit a unique‘flower’structure in NE-and SE-trending cross-sections in the NW area of the study area.This finding is documented for the first time.Channel-segmenting PFs occur in the(northwest)low-amplitude muddy channel and are inhibited in the(southeast)high-amplitude sandy channel in the SW area.Radial PFs are radially aligned around a gas chimney/diapir containing some high-amplitude anomalies(HAAs)in the middle area.The presence of intrusive sandstones with HAAs along the periphery of the diapirs restricts the occurrence of PFs.Two high-amplitude submarine fans act as a mechanical barrier to the propagation of PFs.Meanwhile,the(moderate)slope in the NE area induces rectangular PFs.Additionally,the geneses of the PFs in the current study are comprehensively discussed.This study adds to our understanding of the differences between PFs with irregularly polygonal geometries.展开更多
The northern South China Sea(NSCS)is significantly influenced by the Kuroshio intrusion and the coastal currents.Our knowledge on the roles of both currents on phytoplankton spatial variations is still inadequate.Here...The northern South China Sea(NSCS)is significantly influenced by the Kuroshio intrusion and the coastal currents.Our knowledge on the roles of both currents on phytoplankton spatial variations is still inadequate.Here,we investigated the concentrations of phytoplankton biomarkers and their proportions in surface suspended particles from 47 sites of the NSCS during summer of 2017 and 2019.Brassicasterol/epi-brassicasterol,dinosterol,and C37 alkenones were used as proxies of biomass for diatoms,dinoflagellates,and haptophytes,respectively,and their sum indicating total phytoplankton biomass.A three end-member mixing model was applied to quantitatively assess the influence extent of the Kuroshio intrusion and the coastal currents.Our results showed that the Kuroshio intrusion and the coastal currents contributed equally to the overall surface water masses in the study area;however,the two currents had distinct effects on the spatial distribution of phytoplankton.For phytoplankton biomass,the eutrophic coastal currents were likely to be the main controlling factors,while the impact of the Kuroshio intrusion was weak and stimulated significant increases in phytoplankton biomass only at certain boundary sites.For phytoplankton community structures,the Kuroshio and its intrusion were the main factors,resulting in an increase in the proportions of dinoflagellates and haptophytes.The proportion of diatoms slightly increased due to the influence of the coastal currents.Our study quantifies the effects of the Kuroshio and the coastal currents on phytoplankton in the NSCS in terms of hydrological parameters,providing an important basis for the understanding of ecological functions and biogeochemical cycles in marginal sea-open ocean boundary regions.展开更多
Nan'an Basin is a giant hydrocarbon basin,but its tectonic division scheme and associated fault systems has not been well understood.Based on newly acquired seismic data from the southwestern margin of the South C...Nan'an Basin is a giant hydrocarbon basin,but its tectonic division scheme and associated fault systems has not been well understood.Based on newly acquired seismic data from the southwestern margin of the South China Sea,this study analyzed the structural units,tectonic feature and geodynamics of the sedimentary basin.The new data suggests that the Nan0 an Basin is a rift basin oriented in the NE-SW direction,rather than a pull-apart basin induced by strike-slip faults along the western margin.The basin is a continuation of the rifts in the southwest South China Sea since the late Cretaceous.It continued rifting until the middle Miocene,even though oceanic crust occurred in the Southwest Subbasin.However,it had no transfer surface at the end of spreading,where it was characterized by a late middle Miocene unconformity(reflector T3).The Nan'an Basin can be divided into eight structural units by a series of NE-striking faults.This study provides evidences to confirm the relative importance and interplay between regional strike-slips and orthogonal displacement during basin development and deformation.The NE-SW-striking dominant rift basin indicates that the geodynamic drivers of tectonic evolution in the western margin of the South China Sea did not have a large strike-slip mechanism.Therefore,we conclude that a large strike-slip fault system did not exist in the western margin of the South China Sea.展开更多
Hydrocarbon resources in the Qiongdongnan Basin have become an important exploration target in China.However,the development of high-quality source rocks in this basin,especially in its deep-water areas,are still not ...Hydrocarbon resources in the Qiongdongnan Basin have become an important exploration target in China.However,the development of high-quality source rocks in this basin,especially in its deep-water areas,are still not fully understood.In this study,evolutions of sedimentary facies and palaeoenvironment and their influences on the development of source rocks in diverse tectonic regions of the Qiongdongnan Basin were investigated.The results show that during the Oligocene and to Miocene periods,the sedimentary environment of this basin progressively varied from a semi-closed gulf to an open marine environment,which resulted in significant differences in palaeoenvironmental conditions of the water column for various tectonic regions of the basin.In shallow-water areas,the palaeoproductivity and reducibility successively decrease,and the hydrodynamic intensity gradually increases for the water columns of the Yacheng,Lingshui,and Sanya-Meishan strata.In deep-water areas,the water column of the Yacheng and Lingshui strata has a higher palaeoproductivity and a weaker hydrodynamic intensity than that of the Sanya-Meishan strata,while the reducibility gradually increases for the water columns of the Yacheng,Lingshui,and Sanya-Meishan strata.In general,the palaeoenvironmental conditions of the water column are the most favorable to the development of the Yacheng organic-rich source rocks.Meanwhile,the Miocene marine source rocks in the deep-water areas of the Qiongdongnan Basin may also have a certain hydrocarbon potential.The differences in the development models of source rocks in various tectonic regions of continental margin basins should be fully evaluated in the exploration and development of hydrocarbons.展开更多
基金the Strategic Priority Research Program of the Chinese Academy of Sciences(No.XDB42000000)the Key Program of National Natural Science Foundation of China(No.41930533)+1 种基金the Chinese Academy of Sciences Pioneer Hundred Talents Program(to Nansheng CHEN)the Taishan Scholar Project Special Fund(to Nansheng CHEN)。
文摘One specimen belonging to the family Comatellinae was collected from the Zhenbei Seamount(332.5–478.2 m)in the South China Sea in July 2022.Based on the morphological characters,the specimen was identified as Palaeocomatella hiwia McKnight,1977.It is first recorded from China Sea and redescribed in detail.This specimen differs from the original description from New Zealand for never showing syzygy at br4+5 or br5+6 on interior and br1+2 on exterior arms.However,it is much conform to the redescription to specimens from Indonesia,with only differences in position of the second syzygy and distalmost pinnule comb.Specimen is deposited in the Institute of Oceanology,Chinese Academy of Sciences.Phylogenetic analyses based on the mitochondrial c oxidase subunit I(COI)and 16S rRNA genes indicated that P.hiwia was nested within the tribe Phanogeniini and clustered with Aphanocomaster pulcher.Furthermore,P.hiwia showed same morphological features in terms of mouth placement,comb location,and number of comb teeth rows as other genera of Phanogeniini.Therefore,we suggest that the genus Palaeocomatella should be put in the tribe Phanogeniini.
基金supported by the Guangdong Major Project of Basic and Applied Basic Research(No.2020B0301030003).
文摘Pyrite is one of the common authigenic minerals in marine sediments.Previous studies have shown that the morphological and isotopic characteristics of pyrite are closely related to the geochemical environment where it is formed.To better understand the for-mation mechanism of authigenic pyrite,we analyzed the isotopic composition,morphology,and distribution of pyrite in the sediment at 500m below the seafloor from Xisha Trough,South China Sea.Mineral morphologies were observed by scanning electron micros-copy and Raman spectrography.X-Ray computed tomography was applied to measure the particle size of pyrite.The size of pyrite crystals in the matrix sediment mainly ranged between 25 and 65µm(av.ca.40µm),although crystals were larger(av.ca.50μm)in the veins.The pyrites had a fine-grained truncated octahedral shape with occasionally well-developed growth steps,which implies the low growth rate and weak anaerobic oxidation of methane-sulfate reduction when pyrite was formed.Theδ^(34)S values of pyrites ranged from+20.8‰Vienna-defined Canyon Diablo Troilite(V-CDT)to+33.2‰V-CDT and from+44.8‰V-CDT to+48.9‰,which suggest two growth stages.In the first stage,with the continuous low methane flux,the pyrite possibly formed in an environment with good access to seawater.In the second stage,the pyrites mainly developed in sediment fractures and appeared in veins,probably due to the limited availability of sulfate.The less exposure of pyrite to the environment in the second stage was probably caused by sediment accumulation or perturbation.In this study,an episodic pyritization process was identified,and the paleoenvironment was reconstructed for the sediment investigated.
基金supported by the National Natural Science Foundation of China(42376221,42276083)Director Research Fund Project of Guangzhou Marine Geological Survey(2023GMGSJZJJ00030)+2 种基金National Key Research and Development Program of China(2021YFC2800901)Guangdong Major Project of Basic and Applied Basic Research(2020B030103003)the project of the China Geological Survey(DD20230064).
文摘Many locations with concentrated hydrates at vents have confirmed the presence of abundant thermogenic gas in the middle of the Qiongdongnan Basin(QDNB).However,the impact of deep structures on gasbearing fluids migration and gas hydrates distribution in tectonically inactive regions is still unclear.In this study,the authors apply high-resolution 3D seismic and logging while drilling(LWD)data from the middle of the QDNB to investigate the influence of deep-large faults on gas chimneys and preferred gasescape pipes.The findings reveal the following:(1)Two significant deep-large faults,F1 and F2,developed on the edge of the Songnan Low Uplift,control the dominant migration of thermogenic hydrocarbons and determine the initial locations of gas chimneys.(2)The formation of gas chimneys is likely related to fault activation and reactivation.Gas chimney 1 is primarily arises from convergent fluid migration resulting from the intersection of the two faults,while the gas chimney 2 benefits from a steeper fault plane and shorter migration distance of fault F2.(3)Most gas-escape pipes are situated near the apex of the two faults.Their reactivations facilitate free gas flow into the GHSZ and contribute to the formation of fracture‐filling hydrates.
基金The National Natural Science Foundation of China under contract Nos 42366002 and 41702182the National Key R&D Program of China under contract No.2017YFA0603300the Guangxi Scientific Projects under contract No.2018GXNSFAA281293。
文摘High-resolution sea-level data and high-precision dating of corals in the northern South China Sea(SCS)during the Holocene provide a reference and historical background for current and future sea-level changes and a basis for scientific assessment of the evolutionary trend of coral reefs in the SCS.Although sporadic studies have been performed around Hainan Island in the northern SCS,the reconstructed sea level presents different values or is controversial because the indicative meaning of the sea-level indicators were neither quantified nor uniform criteria.Here,we determined the quantitative relationship between modern living coral and sea level by measuring the top surfaces of 27 live Porites corals from the inner reef flat along the east coast of Hainan Island and assessed the accuracy of results obtained using coral as sea-level indicators.Additionally,three in situ fossil Porites corals were analyzed based on elevation measurements,digital X-ray radiography,and U-Th dating.The survey results showed that the indicative meanings for the modern live Porites corals is(146.09±8.35)cm below the mean tide level(MTL).It suggested that their upward growth limit is constrained by the sea level,and the lowest low water is the highest level of survival for the modern live Porites corals.Based on the newly defined indicative meanings,6 new sea-level index points(SLIPs)were obtained and 19 published SLIPs were recalculated.Those SLIPs indicated a relative sea level fluctuation between(227.7±9.8)cm to(154.88±9.8)cm MTL between(5393±25)cal a BP and(3390±12)cal a BP,providing evidences of the Mid-Holocene sea-level highstand in the northern SCS.Besides that,our analysis demonstrated that different sea-level histories may be produced based on different indicative meanings or criteria.The dataset of 276 coral U-Th ages indicates that coral reef development in the northern SCS comprised the initial development,boom growth,decline,and flourishing development again.A comparison with regional records indicated that synergistic effects of climatic and environmental factors were involved in the development of coral reefs in the northern SCS.Thus,the cessation of coral reef development during the Holocene in the northern SCS was probably associated with the dry and cold climate in South China,as reflected in the synchronous weakening of the ENSO and East Asian summer monsoon induced by the reduction of the 65°N summer insolation,which forced the migration of the Intertropical Convergence Zone.
基金The National Key R&D Program of China under contract No.2022YFC3104805the National Natural Science Foundation of China under contract Nos 42276019,41706025 and 41976200+4 种基金the Innovation Team Plan for Universities in Guangdong Province under contract No.2019KCXTF021the First-class Discipline Plan of Guangdong Province under contract Nos 080503032101and 231420003the Program for Scientific Research Start-up Funds of Guangdong Ocean University under contract No.060302032106the Open Fund Project of Key Laboratory of Marine Environmental Information Technology(2019)Ministry of Natural Resources。
文摘This study aims to investigate characteristics of continental shelf wave(CSW)on the northwestern continental shelf of the South China Sea(SCS)induced by winter storms in 2021.Mooring and cruise observations,tidal gauge data at stations Hong Kong,Zhapo and Qinglan and sea surface wind data from January 1 to February 28,2021 are used to examine the relationship between along-shelf wind and sea level fluctuation.Two events of CSWs driven by the along-shelf sea surface wind are detected from wavelet spectra of tidal gauge data.The signals are triply peaked at periods of 56 h,94 h and 180 h,propagating along the coast with phase speed ranging from 6.9 m/s to18.9 m/s.The dispersion relation shows their property of the Kelvin mode of CSW.We develop a simple method to estimate amplitude of sea surface fluctuation by along-shelf wind.The results are comparable with the observation data,suggesting it is effective.The mode 2 CSWs fits very well with the mooring current velocity data.The results from rare current help to understand wave-current interaction in the northwestern SCS.
基金The National Natural Science Foundation of China under contract Nos 42030502, 42090041 and 42166003the Guangxi Scientific Projects under contract Nos AD17129063 and AA17204074+1 种基金the Guangxi Youth Science Fund Project under contract 2019GXNSFBA185016the Ph.D. Research Start-up Foundation of Guangxi University under contract No. XBZ170339。
文摘As one of the micro-blocks dispersed in the South China Sea(SCS), the basement of the Xisha Islands has rarely been drilled because of the thick overlying Cenozoic sediments, which has led to a confused understanding of the pre-Cenozoic basement of the Xisha Islands. Well CK-1, a kilometer-scale major scientific drill in the Xisha Islands in the northwestern SCS, penetrated thick reefal limestone(0–888.4 m) and the underlying basement rocks(888.4–901.4 m). In this study, we present the zircon U-Pb ages of basement basaltic pyroclastic rocks from Well CK-1 in the Xisha Islands of the northwestern SCS to investigate the basement nature of the Xisha microblock. The basement of Well CK-1 consists of basaltic pyroclastic rocks on the seamount. The zircon grains yielded apparent ages ranging from ca. 2 138.9 Ma to ca. 36 Ma. The old group of zircon grains from Well CK-1 was considered to be inherited zircons. Two Cenozoic zircons gave a weighted mean 206Pb/238U age of(36.3 ± 1.1) Ma,Mean Squared Weighted Deviations(MSWD) = 1.2, which may represent the maximum age of the volcano eruption. The Yanshanian inherited zircons(116.9–105.7 Ma and 146.1–130.2 Ma) from Well CK-1 are consistent with the zircons from Well XK-1, indicating that the basement of Chenhang Island may be similar to that of Well XK-1. We propose that the Xisha micro-block may have developed on a uniform Late Jurassic metamorphic crystalline basement, intruded by Cretaceous granitic magma.
基金National Natural Science Foundation of China(92158204,42076019)Innovation Group Project of the Southern Marine Science and Engineering Guangdong Laboratory(Zhuhai)(31020004)Open Project of the State Key Laboratory of Tropical Oceanography(LTOZZ2001)。
文摘The properties of salinity in the South China Sea(SCS),a significant marginal sea connecting the Pacific and Indian Oceans,are greatly influenced by the transport of fresh water flux between the two oceans.However,the long-term changes in the intermediate water in the SCS have not been thoroughly studied due to limited data,particularly in relation to its thermodynamic variations.This study utilized reanalysis data products to identify a 60-year trend of freshening in the intermediate waters of the northern South China Sea(NSCS),accompanied by an expansion of low-salinity water.The study also constructed salinity budget terms,including advection and entrainment processes,and conducted an analysis of the salinity budget to understand the impacts of external and internal dynamic processes on the freshening trend of the intermediate water in the NSCS.The analysis revealed that the freshening in the northwest Pacific Ocean and the intensification of intrusion through the Luzon Strait at intermediate levels are the primary drivers of the salinity changes in the NSCS.Additionally,a weakened trend in the intensity of vertical entrainment also contributes to the freshening in the NSCS.This study offers new insights into the understanding of regional deep sea changes in response to variations in both thermodynamics and oceanic dynamic processes.
基金National Natural Science Foundation of China(U21A6001,42075059)Specific Research Fund of The Innovation Platform for Academicians of Hainan Province(YSPTZX202143)+1 种基金Guangdong Major Project of Basic and Applied Basic Research(2020B0301030004)Science and Technology Project of Guangdong Meteorological Service(GRMC2020M29)。
文摘The South China Sea is a hotspot for regional climate research.Over the past 40 years,considerable improvement has been made in the development and utilization of the islands in the South China Sea,leading to a substantial change in the land-use of the islands.However,research on the impact of human development on the local climate of these islands is lacking.This study analyzed the characteristics of local climate changes on the islands in the South China Sea based on data from the Yongxing Island Observation Station and ERA5 re-analysis.Furthermore,the influence of urbanization on the local climate of the South China Sea islands was explored in this study.The findings revealed that the 10-year average temperature in Yongxing Island increased by approximately 1.11℃from 1961 to 2020,and the contribution of island development and urbanization to the local warming rate over 60 years was approximately 36.2%.The linear increasing trend of the annual hot days from 1961–2020 was approximately 14.84 days per decade.The diurnal temperature range exhibited an increasing trend of 0.05℃per decade,whereas the number of cold days decreased by 1.06days per decade.The rapid increase in construction on Yongxing Island from 2005 to 2021 led to a decrease in observed surface wind speed by 0.32 m s^(-1)per decade.Consequently,the number of days with strong winds decreased,whereas the number of days with weak winds increased.Additionally,relative humidity exhibited a rapid decline from 2001 to 2016 and then rebounded.The study also found substantial differences between the ERA5 re-analysis and observation data,particularly in wind speed and relative humidity,indicating that the use of re-analysis data for climate resource assessment and climate change evaluation on island areas may not be feasible.
基金The National Natural Science Foundation of China under contract No.91528303the National Science and Technology Major Project under contract No.2016ZX05026-004the CNOOC Basic Geology and Exploration Strategy of Natural Gas in the South China Sea under contract No.2021-KT-YXKY-05。
文摘This study involved outcrop,drilling,seismic,gravity,and magnetic data to systematically document the geological records of the subduction process of Proto-South China Sea(PSCS)and establish its evolution model.The results indicate that a series of arc-shaped ophiolite belts and calcalkaline magmatic rocks are developed in northern Borneo,both of which have the characteristics of gradually changing younger from west to east,and are direct signs of subduction and collision of PSCS.At the same time,the subduction of PSCS led to the formation of three accretion zones from the south to the north in Borneo,the Kuching belt,Sibu belt,and Miri belt.The sedimentary formation of northern Borneo is characterized by a three-layer structure,with the oceanic basement at the bottom,overlying the deep-sea flysch deposits of the Rajang–Crocker group,and the molasse sedimentary sequence that is dominated by river-delta and shallow marine facies at the top,recording the whole subduction–collision–orogeny process of PSCS.Further,seismic reflection and tomography also confirmed the subduction and collision of PSCS.Based on the geological records of the subduction and collision of PSCS,combined with the comprehensive analysis of segmented expansion and key tectonic events in the South China Sea,we establish the“gradual”subduction-collision evolution model of PSCS.During the late Eocene to middle Miocene,the Zengmu,Nansha,and Liyue–Palawan blocks were separated by West Baram Line and Balabac Fault,which collided with the Borneo block and Kagayan Ridge successively from the west to the east,forming several foreland basin systems,and PSCS subducted and closed from the west to the east.The subduction and extinction of PSCS controlled the oil and gas distribution pattern of southern South China Sea(SSCS)mainly in three aspects.First,the“gradual”closure process of PSCS led to the continuous development of many large deltas in SSCS.Second,the deltas formed during the subduction–collision of PSCS controlled the development of source rocks in the basins of SSCS.Macroscopically,the distribution and scale of deltas controlled the distribution and scale of source rocks,forming two types of source rocks,namely,coal measures and terrestrial marine facies.Microscopically,the difference of terrestrial higher plants carried by the delta controlled the proportion of macerals of source rocks.Third,the difference of source rocks mainly controlled the distribution pattern of oil and gas in SSCS.Meanwhile,the difference in the scale of source rocks mainly controlled the difference in the amount of oil and gas discoveries,resulting in a huge amount of oil and gas discoveries in the basin of SSCS.Meanwhile,the difference of macerals of source rocks mainly controlled the difference of oil and gas generation,forming the oil and gas distribution pattern of“nearshore oil and far-shore gas”.
基金funded by the projects of the China Geological Survey(DD20160138,GZH201300502,DD20190378)the Major Special Project for talent team introduction of the Southern Marine Science and Engineering Guang Dong Laboratory(Guang Zhou)(GML2019ZD0207)。
文摘The existing genetic models of the South China Sea(SCS)include an extrusion model of the Indochina Peninsula,a back-arc extension model,and a subduction and dragging model of the Proto-South China Sea(PSCS).However,none of these models has been universally accepted because they do not fully match a large number of geological phenomena and facts.By examining the regional tectonics and integrating them with measured data for the SCS,in this study,a back-arc spreading-sinistral shear model is proposed.It is suggested that the SCS is a back-arc basin formed by northward subduction of the PSCS and its formation was triggered by left-lateral strike-slip motion due to the northward drift of the Philippine Sea Plate.The left-lateral strike-slip fault on the western margin caused by the Indo-Eurasian collision changed the direction of the Southwest Sub-basin's spreading axis from nearly E–W to NE–SW,and subduction retreat caused the spreading ridge to jump southward.This study summarizes the evolution of the SCS and adjacent regions since the Late Mesozoic.
基金supported by the National Natural Science Foundation of China(Grant No.9132820142006068)Shandong Special Fund of Qingdao National Laboratory of Marine Science and Technology(No.2021QNLM020001-1).
文摘Notable differences in the structural characteristics and evolution of three adjacent sub-sags,i.e.,the Wenchang sub-sags A,B,and C,on the downthrown side of the Zhu IlI South Fault in the Wenchang Sag,are significant as they affect the formation and distribution of the oil and gas in these three sub-sags.However,the differences in their tectonic evolutions and formation mechanisms have not yet been adequately explained.In this paper,stress analysis,equilibrium profiles,and paleogeomorphic restora-tion,are used to investigate the dynamic settings,formation mechanisms,and influencing factors of the structural deformation related to the formation of the Wenchang Sag based on interpretation of seismic data.The results of the stress analysis suggest clockwise deflection of the regional tensile stress direction from a WNW-ESE trend during the Early Paleocene to NW-SE and NNW-SSE trends during the Eocene,to a nearly N-S trend during the Oligocene,and finally to a NNE-SSW trend during the Miocene.This clockwise rotation of the regional tensile stress direction led to the formation of a dextral strike-slip stress component parallel to the NE-trending Zhu I South Fault.This strike-slip stress component formed a releasing bend in sub-sag A,and may be associated with the continuous subsidence of a thick sedimentary layer in sub-sag A.It also created a restraining bend in sub-sag B,which underwent multiple structural inversions during its extension and subsidence and has a relatively s mall sedimentary thick-ness.The double restraining bend in sub-sag C is considered to have been strongly uplifted and eroded in response to this strike-slip stress component.Four obvious structural inversions in sub-sag B are iden-tified in this paper.These structural inversions correspond to the last four regional tectonic movements.This interpretation suggests that the formation of the structural inversions was likely related to the strong tensile stress and the small intersection angle between the direction of the regional tensile stress and the pre-existing boundary fault.The rotation of the tensile stress direction was responsible for the strike-slip movement on the pre-existing boundary fault and the formation of the releasing bend and restraining bend,which controlled the structural evolutions of the sub-sags.This reasonably explains the differential tectonic evolution of these three sub-sags in the Wenchang Sag,and provides a crucial idea forstructuralanalysisof similarbasins.
基金Tianjin Key Laboratory for Oceanic Meteorology for its support via the 2020 Open Fund Project(No.2020TKLOMZD01).
文摘This paper uses the Coupled Ocean-Atmosphere-Wave-Sediment Transport(COAWST)model to analyze the impact of typhoon‘Hongxia’on the velocity and position movement of the Kuroshio axis,the impact of typhoons on the Kuroshio intrusion into South China Sea(SCS),the corresponding water,heat,and salt fluxes,and the impact of Kuroshio water in the northeastern SCS.When typhoon‘Hongxia’passed,the Kuroshio intrusion into the SCS was the most significant at 21?N latitude.In the vertical direction,the Kuroshio intrusion was strongest in the subsurface layer,leading to the most significant changes in temperature and salinity in the northeastern part of the SCS in the subsurface layer.Under the influence of the southeastern monsoon in summer,a large amount of low-salinity water accumulates at the surface of the northeastern part of the SCS,and Kuroshio intrusive water remains in the bottom and middle portions of the subsurface layer.The westward deviation of the Kuroshio axis caused by the typhoon displays a certain lag compared with the hot and salty water intrusion into the SCS approximately 7 d later.The impact of the typhoon on the Kuroshio intrusion into the SCS lasts for 20 d.The typhoon caused increases in the water,heat,and salt fluxes associated with the Kuroshio intrusion into the SCS,and the contribution of the typhoon to these fluxes was as high as 40%.Under typhoon conditions,the maximum Kuroshio intrusion flux reached more than twice that before the typhoon.
基金Supported by the National Key Research and Development Program of China(No.2022YFC3102200)the Guangdong Research Foundation(No.2019BT02H594)+3 种基金the National Natural Science Foundation of China(No.42076071)the Key Special Project for Introduced Talents Team of the Southern Marine Science and Engineering Guangdong Laboratory(Guangzhou)(No.GML2019ZD0204)the Strategic Priority Research Program of the Chinese Academy of Sciences(No.XDA22020303)the Key Research Program of the Chinese Academy of Sciences(No.ZDRW-XH-2021-2-02)。
文摘Submarine volcanism is widely developed in the South China Sea(SCS).However,the characteristics,distribution,and genesis of submarine volcanoes in the southern margin of the SCS remain obscure.In this study,we analyzed the characteristics of submarine volcanoes and identified a total of 43 submarine volcanoes in the southern margin of the SCS,based on a newly acquired 310-km seismic reflection profile,along with previous 45 multi-channel seismic(MCS)profiles,petrological results from volcanic rocks sampled by dredging and drilling,nearby ocean bottom seismometer(OBS)wide-angle seismic profiles,and gravity and magnetic data.The study ascertains that most of these volcanoes are located in fault-block belts and graben-horst zones with strong crustal stretching and thinning.These volcanoes exhibit positive high-amplitude external seismic reflections,weak and chaotic internal seismic reflections,and are accompanied by local deformation of the surrounding sedimentary strata.Meanwhile,they have higher positive gravity anomalies and higher magnetic anomalies than the background strata.The petrological dating results show that volcanic ages are primarily in the Pliocene-Pleistocene,with geochemical characteristics indicating dominance of oceanic island basalt(OIB)-type alkali-basalts.Extensional faults have obviously spatial correspondence with post-spreading volcanism,suggesting these faults may provide conduits for submarine volcanism.The high-velocity bodies(HVBs)in the lower crust and magma underplating exist in the southern SCS,which could provide a clue of genesis for submarine volcanism.The inference is that the intensity of post-spreading volcanism in the southern margin might be affected by stretching faults,crustal thinning and magma underplating.
基金The National Natural Science Foundation of China under contract Nos 42076066,92055203 and U20A20100。
文摘There are many large-scale Cenozoic sedimentary basins with plentiful river deltas,deep-water fans and carbonate platforms in the southern South China Sea.The Crocker Fan was deposited as a typical submarine fan during the late Eocene–early Miocene,and stretches extensively across the entire Sarawak–Sabah of the northern Borneo area.However,systematic analyses are still lacking regarding its sediment composition and potential source suppliers.No consensus has been reached yet on the provenance evolution and sedimentary infilling processes,which seriously impeded the oil-and-gas exploration undertakings.By combining with sedimentaryfacies identification,heavy mineral assemblages,elemental geochemistry and detrital zircon U-Pb dating,this paper aims to generalize an integrated analysis on the potential provenance terranes and restore source-to-sink pathways of the Crocker Fan.In general,the Crocker Fan was initially formed over the Cretaceous–lower/middle Eocene Rajang Group by an angular Rajang unconformity.The continual southward subduction of the protoSouth China Sea resulted in magmatic activities and subsequent regional deformation and thrusting along the Lupar Line in the northern Borneo.The lowermost Crocker sequence is featured by a thick conglomerate layer sourced from in-situ or adjacent paleo-uplifts.From the late Eocene to the early Miocene,the Crocker Fan was constantly delivered with voluminous detritus from the Malay Peninsula of the western Sundaland.The Zengmu Basin was widely deposited with delta plain and neritic facies sediments,while the Brunei-Sabah Basin,to the farther east,was ubiquitously characterized by turbiditic sequences.The Crocker Fan successions are overall thick layers of modest-grained sandstones,which formed high-quality reservoirs in the southern South China Sea region.
基金supported by the National Natural Science Foundation of China(Grant No.42275025).
文摘This study identifies break events of the South China Sea(SCS)summer monsoon(SCSSM)based on 42 years of data from 1979 to 2020,and investigates their statistical characteristics and associated atmospheric anomalies.A total of 214 break events are identified by examining the convection evolution during each monsoon season.It is found that most events occur between June and September and show a roughly even distribution.Short-lived events(3–7 days)are more frequent,accounting for about two thirds of total events,with the residual one third for long-lived events(8–24 days).The SCSSM break is featured by drastic variations in various atmospheric variables.Particularly,the convection and precipitation change from anomalous enhancement in adjoining periods to a substantial suppression during the break,with the differences being more than 60 W m−2 for outgoing longwave radiation(OLR)and 10 mm d−1 for precipitation.This convection/precipitation suppression is accompanied by an anomalous anticyclone in the lower troposphere,corresponding to a remarkable westward retreat of the monsoon trough from the Philippine Sea to the Indochina Peninsula,which reduces the transportation of water vapor into the SCS.Besides,the pseudo-equivalent potential temperature()declines sharply,mainly attributable to the local specific humidity reduction caused by downward dry advection.Furthermore,it is found that the suppressed convection and anomalous anticyclone responsible for the monsoon break form near the equatorial western Pacific and then propagate northwestward to the SCS.
基金supported by the National Natural Science Foundation of China(No.41830964)。
文摘Intraseasonal oscillation of the mixed layer and upper ocean temperature has been found to occur over the South China Sea(SCS)in the summer monsoon season based on the multiple reanalysis and observational data in this study.The method of composite analysis and an upper ocean temperature equation assisted the analysis of physical mechanisms.The results show that the mixed layer depth(MLD)in the SCS has a significant oscillation with a 30-60 d period over the SCS region,which is closely related to boreal summer intraseasonal oscillation(BSISO)activities.The MLD can increase(decrease)during the positive(negative)phase of the BSISO and usually lags behind by approximately one-eighth of the lifecycle(5 days)of the BSISO-related convection.The BSISO may cause periodic anomalies at the air-sea boundary,such as wind stress and heat flux,so it can play a dominant role in modulating the variation in MLD.There also are significant intraseasonal seawater temperature anomalies in both the surface and subsurface layers of the SCS.In addition,during the initial phase of the BSISO,the temperature anomaly signals of the thermocline are obviously opposite to the sea surface temperature(SST),especially in the southern SCS.According to the results from the analysis of the temperature equation,the vertical entrainment term caused by BSISO-related wind stress is stronger than the thermal forcing during the initial stage of convection,and it is more significant in the southern SCS.
基金supported by the Key Laboratory of Marine Mineral Resources,Ministry of Land and Resources of China(No.KLMMR-2018-B-07)the National Basic Research Program of China(No.2011ZX05025-006-02)the National Natural Science Foundation of China(No.41672206)。
文摘Polygonal faults(PFs)generally have a classic polygonal geometry in map view.However,under the influence of tectonic faults,diapirs,channels,and slopes,the classic polygonal geometry of PFs is not preserved,demonstrating differences(different characters)in map-view 3D seismic data covering an area of 334km^(2) of the Changchang(CC)sag,are used to document the mapview and cross-sectional characteristics of PFs.These data also help investigate the irregularly polygonal geometries of PFs due to the presence of influence factors,such as transtensional faults,submarine fans,channels,diapirs/gas chimneys,and the basal slope within the lower-middle Miocene strata.Results show that various irregularly polygonal geometries of PFs can be classified into enechelon and arcuate PFs,channel-segmenting and-bounding PFs,radial PFs,and rectangular PFs in map-view.En-echelon and arcuate PFs are induced by transtensional faults and exhibit a unique‘flower’structure in NE-and SE-trending cross-sections in the NW area of the study area.This finding is documented for the first time.Channel-segmenting PFs occur in the(northwest)low-amplitude muddy channel and are inhibited in the(southeast)high-amplitude sandy channel in the SW area.Radial PFs are radially aligned around a gas chimney/diapir containing some high-amplitude anomalies(HAAs)in the middle area.The presence of intrusive sandstones with HAAs along the periphery of the diapirs restricts the occurrence of PFs.Two high-amplitude submarine fans act as a mechanical barrier to the propagation of PFs.Meanwhile,the(moderate)slope in the NE area induces rectangular PFs.Additionally,the geneses of the PFs in the current study are comprehensively discussed.This study adds to our understanding of the differences between PFs with irregularly polygonal geometries.
基金The study was supported by the National Natural Science Foundation of China(No.41876118)the Global Climate Changes and Air-Sea Interaction Program(No.GASI-02-PAC-ST-Wwin)This is MCTL(Key Laboratory of Marine Chemistry Theory and Technology)contribution#281.
文摘The northern South China Sea(NSCS)is significantly influenced by the Kuroshio intrusion and the coastal currents.Our knowledge on the roles of both currents on phytoplankton spatial variations is still inadequate.Here,we investigated the concentrations of phytoplankton biomarkers and their proportions in surface suspended particles from 47 sites of the NSCS during summer of 2017 and 2019.Brassicasterol/epi-brassicasterol,dinosterol,and C37 alkenones were used as proxies of biomass for diatoms,dinoflagellates,and haptophytes,respectively,and their sum indicating total phytoplankton biomass.A three end-member mixing model was applied to quantitatively assess the influence extent of the Kuroshio intrusion and the coastal currents.Our results showed that the Kuroshio intrusion and the coastal currents contributed equally to the overall surface water masses in the study area;however,the two currents had distinct effects on the spatial distribution of phytoplankton.For phytoplankton biomass,the eutrophic coastal currents were likely to be the main controlling factors,while the impact of the Kuroshio intrusion was weak and stimulated significant increases in phytoplankton biomass only at certain boundary sites.For phytoplankton community structures,the Kuroshio and its intrusion were the main factors,resulting in an increase in the proportions of dinoflagellates and haptophytes.The proportion of diatoms slightly increased due to the influence of the coastal currents.Our study quantifies the effects of the Kuroshio and the coastal currents on phytoplankton in the NSCS in terms of hydrological parameters,providing an important basis for the understanding of ecological functions and biogeochemical cycles in marginal sea-open ocean boundary regions.
基金This research was financially supported by Natural Science Foundation of China(U1701245,No.91228208)CGS project(DD20190213)CNPC project(kt 2021-02-02).
文摘Nan'an Basin is a giant hydrocarbon basin,but its tectonic division scheme and associated fault systems has not been well understood.Based on newly acquired seismic data from the southwestern margin of the South China Sea,this study analyzed the structural units,tectonic feature and geodynamics of the sedimentary basin.The new data suggests that the Nan0 an Basin is a rift basin oriented in the NE-SW direction,rather than a pull-apart basin induced by strike-slip faults along the western margin.The basin is a continuation of the rifts in the southwest South China Sea since the late Cretaceous.It continued rifting until the middle Miocene,even though oceanic crust occurred in the Southwest Subbasin.However,it had no transfer surface at the end of spreading,where it was characterized by a late middle Miocene unconformity(reflector T3).The Nan'an Basin can be divided into eight structural units by a series of NE-striking faults.This study provides evidences to confirm the relative importance and interplay between regional strike-slips and orthogonal displacement during basin development and deformation.The NE-SW-striking dominant rift basin indicates that the geodynamic drivers of tectonic evolution in the western margin of the South China Sea did not have a large strike-slip mechanism.Therefore,we conclude that a large strike-slip fault system did not exist in the western margin of the South China Sea.
基金supported by the National Natural Science Foundation of China(42272162)the Natural Science Foundation of Guangdong Province(2021A1515011381 and 2021A1515011635)the Science Project of the CNOOC(KJZH-2021-0003-00).
文摘Hydrocarbon resources in the Qiongdongnan Basin have become an important exploration target in China.However,the development of high-quality source rocks in this basin,especially in its deep-water areas,are still not fully understood.In this study,evolutions of sedimentary facies and palaeoenvironment and their influences on the development of source rocks in diverse tectonic regions of the Qiongdongnan Basin were investigated.The results show that during the Oligocene and to Miocene periods,the sedimentary environment of this basin progressively varied from a semi-closed gulf to an open marine environment,which resulted in significant differences in palaeoenvironmental conditions of the water column for various tectonic regions of the basin.In shallow-water areas,the palaeoproductivity and reducibility successively decrease,and the hydrodynamic intensity gradually increases for the water columns of the Yacheng,Lingshui,and Sanya-Meishan strata.In deep-water areas,the water column of the Yacheng and Lingshui strata has a higher palaeoproductivity and a weaker hydrodynamic intensity than that of the Sanya-Meishan strata,while the reducibility gradually increases for the water columns of the Yacheng,Lingshui,and Sanya-Meishan strata.In general,the palaeoenvironmental conditions of the water column are the most favorable to the development of the Yacheng organic-rich source rocks.Meanwhile,the Miocene marine source rocks in the deep-water areas of the Qiongdongnan Basin may also have a certain hydrocarbon potential.The differences in the development models of source rocks in various tectonic regions of continental margin basins should be fully evaluated in the exploration and development of hydrocarbons.
