Velocity structure in the South Yellow Sea basin based on first-arrival tomography of wide-angle seismic data and its geological implications

The South Yellow Sea basin is filled with Mesozoic-Cenozoic continental sediments overlying pre-Palaeozoic and Mesozoic-Palaeozoic marine sediments.Conventional multi-channel seismic data cannot describe the velocity structure of the marine residual basin in detail,leading to the lack of a deeper understanding of the distribution and lithology owing to strong energy shielding on the top interface of marine sediments.In this study,we present seismic tomography data from ocean bottom seismographs that describe the NEE-trending velocity distributions of the basin.The results indicate that strong velocity variations occur at shallow crustal levels.Horizontal velocity bodies show good correlation with surface geological features,and multi-layer features exist in the vertical velocity framework(depth:0–10 km).The analyses of the velocity model,gravity data,magnetic data,multichannel seismic profiles,and drilling data showed that high-velocity anomalies(>6.5 km/s)of small(thickness:1–2 km)and large(thickness:>5 km)scales were caused by igneous complexes in the multi-layer structure,which were active during the Palaeogene.Possible locations of good Mesozoic and Palaeozoic marine strata are limited to the Central Uplift and the western part of the Northern Depression along the wide-angle ocean bottom seismograph array.Following the Indosinian movement,a strong compression existed in the Northern Depression during the extensional phase that caused the formation of folds in the middle of the survey line.This study is useful for reconstructing the regional tectonic evolution and delineating the distribution of the marine residual basin in the South Yellow Sea basin.

Role of Resuspended Sediments as Sources of Dissolved Inorganic Phosphorus Along Different Dimensions in the Subei Shoal, South Yellow Sea, China

Several studies have documented that during‘green tide’events,comprising green macroalgae blooms in aquatic ecosystems,dissolved inorganic phosphorus(DIP)levels remain relatively steady despite the absorption of a large amount of DIP.In this study,surface sediment samples and a sediment core were extracted using a modified sequential extraction scheme,and water and surface sediment samples were analyzed in April 2017 to better understand phosphorus(P)cycling and replenishment in Subei shoal.We used a simple model on equilibrium of adsorption-desorption to present the buffering capacity of phosphate.The total P(TP)in the surface sediments ranged from 12.2 to 28.4μmol g^(-1)(average 15.5μmol g^(-1))and was dominated by inorganic P.TP,exchangeable P,reactive and reductive Fe/Al bound P,and authigenic apatite P significantly decreased northward and eastward from Subei shoal,contrary to the detrital P and organic P results.Dissolved and particulate inorganic P in the water samples ranged from 0.01 to 0.54μmol L^(-1)(average 0.19μmol L^(-1))and 0.9 to 19.6μmol g^(-1)(average 4.9μmol g^(-1)),respectively.The applied model showed that suspended particulate matter is an important regulator of DIP behavior.Thus,modification of SPM can alter the DIP buffering capacity.The calculated buffering capacity in the surface layer of the sea water was>60 within Subei shoal and always>10 along the path of floating Ulva prolifera,providing a reasonable explanation for the steady concentration of DIP and its replenishment during the blooming of this green macroalgae.

Organic geochemical characteristics and significance of Permian Gufeng formation siliceous shale in well CSDP-2 of South Yellow Sea central uplift

In order to understand the hydrocarbon generation potential of the siliceous shale in the Permian Gufeng Formation of the South Yellow Sea,the organic geochemistry and organic petrology of the siliceous shale in the Gufeng Formation of the CSDP-2 well were studied and analyzed.It is found that the TOC of the samples is mainly between 9%and 12%,and Tmaxis mainly distributed between 510 and 540℃.The value of the organic microscopic type index(TI)is between 25.71 and 31.00,which is a set of II_(2)high-quality source rocks with high organic matter abundance in the over mature stage of largescale gas generation.According to the distribution characteristics of Molecular fossils in siliceous shale of Gufeng Formation of well CSDP-2,bacterial organic matter is the main hydrocarbon generating parent material,and aquatic animal organic matter is an important hydrocarbon generating parent material.The siliceous shale in Gufeng Formation of CSDP-2 well is in the stage of large-scale gas generation;Therefore,the Gufeng Formation in the central uplift of the South Yellow Sea has the material basis for the formation of large-scale shale gas reservoirs.At the same time,the siliceous metasomatism of the siliceous shale reservoir of Gufeng Formation is not conducive to the primary migration of oil,and there is much oil and gas remaining in the reservoir.

Characteristics of Meso-Cenozoic Igneous Complexes in the South Yellow Sea Basin,Lower Yangtze Craton of Eastern China and the Tectonic Setting

The South Yellow Sea Basin is partially surrounded by the East Asian continental Meso- Cenozoic widespread igneous rocks belt. Magnetic anomaly and multi-channel seismic data both reveal the prevalent occurrence of igneous rocks. We preliminarily defined the coupling relation between magnetic anomalies and igneous rock bodies. Some igneous complexes were also recognized by using multi-channel seismic and drilling data. We identified various intrusive and extrusive igneous rock bodies, such as stocks, sills, dikes, laccoliths and volcanic edifice relics through seismic facies analysis. We also forecasted the distribution characteristics of igneous complexes. More than fifty hypabyssal intrusions and volcanic relics were delineated based on the interpretation of magnetic anomaly and dense intersecting multi-channel seismic data. It is an important supplement to regional geology and basin evolution research. Spatial matching relations between igneous rock belts and fractures document that extensional N-E and N-NE-trending deep fractures may be effective pathways for magma intrusion. These fractures formed under the influence of regional extension during the Meso- Cenozoic after the Indosinian movement. Isotopic ages and crosscutting relations between igneous rock bodies and the surrounding bedded sedimentary strata both indicate that igneous activities might have initiated during the Late Jurassic, peaked in the Early Cretaceous, gradually weakened in the Late Cretaceous, and continued until the Miocene. Combined with previous studies, it is considered that the Meso-Cenozoic igneous activities, especially the intensive igneous activity of the Early Cretaceous, are closely associated with the subduction of the Paleo-Pacific Plate.

Basin modeling in the initial stage of exploration： a case study from the North Subbasin of the South Yellow Sea Basin

Basin modeling has become an important tool for analyzing sedimentary basins. The North Subbasin of the South Yellow Sea Basin is filled with thick Meso-Cenozoic terrigenous deposits during the rift evolution stage. The accumulation of data and achievements of geological investigations in recent years have provided the preconditions for basin modeling. The necessary parameters and geological elements for simulations are collated and summarized. Modeling of tectono-thermal evolution is performed and the related trend in heat flow is reconstructed and calibrated. The heat flow value commences from an average level of 61 m W/m2during MiddleLate Jurassic, rises to about 80 m W/m2from circa 145 Ma to circa 74 Ma, and then undergoes a gradual decline to65 m W/m2until the end of Oligocene.Three evolutionary phases, namely, the initial rifting phase, syn-rifting phase, and post-rifting phase, have been identified. The modeling results show that the North Subbasin generally enters into a stage of strong rifting during Cretaceous and undergoes rapid subsidence until the Late Cretaceous,then follows by a stage of moderate rifting during the Paleogene. The input and general workflow involved in 3-D modeling are introduced. Reconstruction of the petroleum system in the North Subbasin reveals that the threshold depth of hydrocarbon generation is located near the top of the Paleogene Funing formation, and the underlying Jurassic and Cretaceous source rocks have reached or exceeded peak oil generation and have almost completed the generation and expulsion of hydrocarbons. The main generation and expulsion in the Jurassic source rocks take place during the syn-rifting and post-rifting phases, whereas the peak generation and expulsion in the Cretaceous and Paleogene source rocks take place during the post-rifting phase. Although the study area is still a relatively less explored sedimentary basin, the results of modeling can provide valuable information for exploration. A preliminary discussion of the main uncertainty factors is also presented.

Mineral distributions in surface sediments of the western South Yellow Sea:implications for sediment provenance and transportation

The South Yellow Sea(SYS) is strongly influenced by the substantial sediment loads of the Huanghe(Yellow)(including the modern Huanghe and abandoned old Huanghe subaqueous delta) and Changjiang(Yangtze) Rivers. However,the dispersal patterns of these sediments,especially in the western SYS,have not been clearly illustrated. In this study,we have analyzed clay minerals,detrital minerals,and grain sizes for 245 surface sediment samples(0–5 cm) collected from the western SYS. The clay minerals,on average,consist of 67% illite,14% smectite,11% chlorite,and 8% kaolinite. Clay minerals,detrital minerals,and grain size analyses of surface sediments,combined with water mass hydrology analysis,reveal that sediments in the western SYS are mainly derived from the modern Huanghe River,the abandoned subaqueous delta of the old Huanghe River,some material from the Changjiang,and coastal erosion. The clay minerals(especially illite and smectite) and quartz/feldspar ratio distribution patterns,reveal that the influence of modern Huanghe sediments can reach 35°N in the northwestern part of the study area,an influence that can be enhanced especially in winter owing to northerly winds. Conversely,sediments along the Jiangsu coast are mixed,in summer,with material from the Changjiang arriving via northward flow of Changjiang Diluted Water. The Subei Coastal Current carries the refreshed sediments northward into the western SYS. Sediment distribution and transport in the western SYS are mainly controlled by the oceanic circulation system that is primarily related to the monsoon.

Tectonic Evolution and Geological Characteristics of Hydrocarbon Reservoirs in Marine Mesozoic-Paleozoic Strata in the South Yellow Sea Basin

The South Yellow Sea Basin is the main body of the lower Yangtze area in which marine Mesozoic–Paleozoic strata are widely distributed.The latest geophysical data were used to overcome the limitation of previous poor-quality deep data.Meanwhile,the geological characteristics of hydrocarbon reservoirs in the marine Mesozoic–Paleozoic strata in the South Yellow Sea Basin were analyzed by comparing the source rocks and the reservoir and utilizing drilling and outcrop data.It is believed that the South Yellow Sea Basin roughly underwent six evolutionary stages:plate spreading,plate convergence,stable platform development,foreland basin development,faulted basin development,and depression basin development.The South Yellow Sea Basin has characteristics of a composite platform-fault depression geological structure,with a half-graben geological structure and with a ‘sandwich structure' in the vertical direction.Four sets of hydrocarbon source rocks developed – the upper Permian Longtan–Dalong formation,the lower Permian Qixia formation,the lower Silurian Gaojiabian formation,and the lower Cambrian Hetang formation/Mufushan formation,giving the South Yellow Sea Basin relatively good hydrocarbon potential.The carbonate is the main reservoir rock type in the South Yellow Sea area,and there are four carbonate reservoir types:porous dolomitic,reef-bank,weathered crust,and fractured.There are reservoir-forming horizons similar to the typical hydrocarbon reservoirs in the Yangtze land area developed in the South Yellow Sea,and there are three sets of complete source-reservoir-cap rock assemblages developed in the marine strata,with very good hydrocarbon potential.

Seismic Acquisition Parameters Analysis for Deep Weak Reflectors in the South Yellow Sea

The Mesozoic-Paleozoic marine residual basin in the South Yellow Sea(SYS) is a significant deep potential hydrocarbon reservoir. However, the imaging of the deep prospecting target is quite challenging due to the specific seismic-geological conditions. In the Central and Wunansha Uplifts, the penetration of the seismic wavefield is limited by the shallow high-velocity layers(HVLs) and the weak reflections in the deep carbonate rocks. With the conventional marine seismic acquisition technique, the deep weak reflection is difficult to image and identify. In this paper, we could confirm through numerical simulation that the combination of multi-level air-gun array and extended cable used in the seismic acquisition is crucial for improving the imaging quality. Based on the velocity model derived from the geological interpretation, we performed two-dimensional finite difference forward modeling. The numerical simulation results show that the use of the multi-level air-gun array can enhance low-frequency energy and that the wide-angle reflection received at far offsets of the extended cable has a higher signal-to-noise ratio(SNR) and higher energy. Therefore, we have demonstrated that the unconventional wide-angle seismic acquisition technique mentioned above could overcome the difficulty in imaging the deep weak reflectors of the SYS, and it may be useful for the design of practical seismic acquisition schemes in this region.

Hydrocarbon Geological Conditions and Exploration Potential of Mesozoic–Paleozoic Marine Strata in the South Yellow Sea Basin

No substantial breakthroughs have been made in hydrocarbon exploration of the South Yellow Sea Basin.It is believed that the Mesozoic-Paleozoic marine sedimentary formation in the South Yellow Sea Basin is similar to that in the Sichuan Basin.Therefore,outcrop,drilling,and seismic data were determined and compared with the research results on petroleum geological conditions in the Yangtze land area,and the hydrocarbon geological conditions were analyzed comprehensively from multiple aspects,such as basin evolution and main source rocks,reservoir characteristics,preservation conditions,and structural traps.The results show that two main stages in the South Yellow Sea Basin(the stable evolution stage of the Mesozoic-Paleozoic marine basin and the Mesozoic-Cenozoic tectonic reformation and basin formation stage)were important for the development and evolution of four sets of main source rocks.Reservoirs dominated by carbonate rocks,three sets of capping beds with good sealing capability,relatively weak magmatic activity,and multiple types of structural traps jointly constituted relatively good hydrocarbon-reservoir-forming conditions.There were four sets of main source-reservoir-cap assemblages and three possible hydrocarbon reservoir types(primary residual-type hydrocarbon reservoir,shallow reformed-type hydrocarbon reservoir,and composite-type hydrocarbon reservoir)developed in the marine strata.It is concluded that the marine strata in the South Yellow Sea Basin have relatively good hydrocarbon potential.The Laoshan Uplift is characterized by stable structure,complete preserved source reservoir cap assemblage,and large structural traps,and thus it is the preferred prospect zone for marine Paleozoic hydrocarbon exploration in this area.

Numerical study on effect of tidal phase on storm surge in the South Yellow Sea

Because of the special topography and large tidal range in the South Yellow Sea,the dynamic process of tide and storm surge is very complicated.The shallow water circulation model Advanced Circulation(ADCIRC)was used to simulate the storm surge process during typhoon Winnie,Prapiroon,and Damrey,which represents three types of tracks attacking the South Yellow Sea,which are,moving northward after landing,no landing but active in offshore areas,and landing straightly to the coastline.Numerical experiments were carried out to investigate the effects of tidal phase on the tide-surge interaction as well as storm surge.The results show that the peak surge caused by Winnie and Prapiroon occurs 2-5 h before the high tide and its occurring time relative to high tide has little change with tidal phase variations.On the contrary,under the action of Damrey,the occurring time of the peak surge relative to high tide varies with tidal phase.The variation of tide-surge interaction is about 0.06-0.37 m,and the amplitude variations of interaction are smooth when tidal phase changes for Typhoon Winnie and Prapiroon.While the interaction is about 0.07-0.69 m,and great differences exists among the stations for Typhoon Damrey.It can be concluded that the tide-surge interaction of the former is dominated by the tidal phase modulation,and the time of surge peak is insensitive to the tidal phase variation.While the interaction of the latter is dominated by storm surge modulation due to the water depth varying with tide,the time of surge peak is significantly affected by tidal phase.Therefore,influence of tidal phase on storm surge is related to typhoon tracks which may provide very useful information at the design stage of coastal protection systems.

Geochemistry Characteristics of Sediment and Provenance Relations of Sediments in Core NT1 of the South Yellow Sea

The contribution of substance from Yellow River, Yangtze River, and Korean rivers to the sedimentation of Yellow Sea is studied through geochemical analysis and through characterization of the source of the substance about sediment from Core NT1 among the lutaceous area in Central South Yellow Sea. The research finds out that the sediment in Core NT1 mainly comes from Yangtze River and Yellow River, the sediment between 0-7.70 m in upper Core NT1 mainly belongs to Yangtze River source; the sediments between 7.70-16.60 m and 42.0-54.80 m in middle Core NT1 are mainly from Yellow River, the 26 m thick sediment interlayer in it mainly comes from Yangtze River; and the sediment between 54.80-69.76 m in the bottom of Core NT1 is mainly from Yangtze River. The results demonstrate that Yangtze River has been playing a main role in the lutaceous area in the Central South Yellow Sea since early Late Pleistocene, and Yellow River started to influence the continental sedimentation of Yellow Sea from early Warm Glaciation of late Late Pleistocene.

An N-shape thermal front in the western South Yellow Sea in winter

An N-shape thermal front in the western South Yellow Sea (YS) in winter was detected using Advanced Very High Resolution Radiation (AVHRR) Sea Surface Temperature data and in-situ observations with a merged front-detecting method.The front,which exists from late October through early March,consists of western and eastern wings extending roughly along the northeast-southwest isobaths with a southeastward middle segment across the 20-50 m isobaths.There are north and south inflexions connecting the middle segment with the western and eastern wings,respectively.The middle segment gradually moves southwestward from November through February with its length increasing from 62 km to 107 km and the southern inflexion moving from 36.2°N to 35.3°N.A cold tongue is found to coexist with the N-shape front,and is carried by the coastal jet penetrating southward from the tip of the Shandong Peninsula into the western South YS as revealed by a numerical simulation.After departing from the coast,the jet flows as an anti-cyclonic recirculation below 10 m depth,trapping warmer water originally carried by the compensating Yellow Sea Warm Current (YSWC).A northwestward flowing branch of the YSWC is also found on the lowest level south of the front.The N-shape front initially forms between the cold tongue and warm water involved in the subsurface anti-cyclonical recirculation and extends upwards to the surface through vertical advection and mixing.Correlation analyses reveal that northerly and easterly winds tend to be favorable to the formation and extension of the N-shape front probably through strengthening of the coastal jet and shifting the YSWC pathway eastward,respectively.

New insights into marine hydrocarbon geological conditions in the South Yellow Sea Basin:evidence from borehole CSDP-2

The South Yellow Sea Basin(SYSB) has multiple sets of proven source rocks and good hydrocarbon prospects,but no industrial oil and gas has been explored at present.To solve this puzzle for petroleum geologists,we systematically investigated the marine hydrocarbon geological conditions based on cores and testing data from borehole CSDP-2,the first exploration well with continuous coring in SYSB.The qualities of source rocks are evaluated in detail according to organic matter abundance,type,and maturity.The reservoir characterization mainly includes porosity,permeability,and reservoir space.Displacement pressure test and stratum thickness are the main foundations for defining the caprocks.Then,the oil-source rock correlation in the Permian and stratum model are analyzed to determine the favorable source-reservoir-caprock assemblages.The results show that three sets of effective source rocks(the Lower Triassic,Upper Permian,and Lower Permian),two sets of tight sandstone re servoirs(the Upper Permian and Lower Silurian-Upper Devonian),and two sets of caprocks(the Lower Triassic and Carboniferous) combine to constitute the hydrocarbon reservoir-forming as se mblages of "lower-ge neration and upper-accumlation" and "self-generation and self-accumlation",thus laying a solid foundation for promising petroleum prospects.The three sets of marine source rocks are characterized by successive generation and expulsion stages,which guarantees multistage hydrocarbon accumulation.Another three sets of continental source rocks distributed across the Middle Jurassic,Upper Cretaceous,and Paleogene depression areas,especially in the Northern Depression,may supplement some hydrocarbons for the Central Uplift through faults and the Indosinian unconformity.The favorable Permian exploration strata have been identified in the Central Uplift of SYSB.First,the Lower Permian and Upper Permian source rocks with high organic matter abundance and high thermal maturity supply sufficient hydrocarbons.Secondly,the interbedding relationship between the source rocks and sandstones in the Upper Permian strata ensures that hydrocarbons have been migrated into the nearby Upper Permian sandstones,reflecting near-source hydrocarbon accumulation.Finally,the good sealing property of the Lower Triassic Qinglong Formation caprocks plays an indispensable role in hydrocarbon preservation of the Permian reservoirs.This conclusion is supported by direct oil shows,gas logging anomalous layers,and hydrocarbon-bearing fluid inclusions.

Characterization of microbial communities in sediments of the South Yellow Sea

Illumina sequencing and quantitative PCR(qPCR)based on the 16 S ribosomal RNA(rRNA)gene were conducted to characterize the vertical distribution of bacterial and archaeal communities in the sediments of two sites from the South Yellow Sea.Both bacterial and archaeal communities showed a clear stratified distribution with sediment depth.The microbial communities in the upper layers were distinct from those in the deeper layers;the relative abundances of sequences of Thaumarchaeota,Gammaproteobacteria,and Actinobacteria were higher in the upper than in the deeper sediments,whereas the sequences of Bathyarchaeia,Lokiarchaeota,Euryarchaeota,Chloroflexi,and Deltaproteobacteria were relatively more abundant in the deeper sediments.Sediment depth and total organic carbon(TOC)can significantly influence both the bacterial and archaeal communities.Furthermore,bacterial and archaeal groups potentially involved in nitrogen,sulfur,and methane metabolism were detected in both sites.In our study,both ammonia-oxidizing bacteria(Nitrospira)and ammonia-oxidizing archaea(Candidatus Nitrosopumilus)were responsible for ammonia oxidization.Additionally,sulfur-reducing bacteria SEEP-SRB1 forming consortia with anaerobic methane-oxidizing archaea ANME-2 a-2 b were capable of anaerobic methane oxidation(AOM)in the 3400-02 sediment samples.

Spatiotemporal variability of physical-biogeochemical processes and intrinsic correlations in the semi-enclosed South Yellow Sea

Investigating the spatiotemporal variability of biogeochemical processes and ecological responses under multiple physical controls in shelf seas is of great importance for obtaining an in-depth understanding of marine ecosystem.Based on a compiled data set of historical observations and remote sensing data,the spatiotemporal variability and heterogeneity of physical-biogeochemical processes in the semi-enclosed South Yellow Sea(SYS)are investigated,and the intrinsic connectivity among different subregions and the associated mechanisms are examined.The results show that the seasonal alternation between southward transport in cold seasons and upwelling-induced vertical delivery in warm seasons is the primary physical control of the biogeochemical processes and primary production off Shidao and in the area adjacent to the Haizhou Bay.The northeastward expansion of coastal waters in the Subei Shoal constitutes an important physical driver for the offshore transport of Ulva prolifera in summer.Stratification significantly affects the biogeochemical processes in the Yellow Sea Cold Water Mass(YSCWM)-dominated area during warm seasons,and nutrients can accumulate in bottom waters from spring to autumn,making the Yellow Sea Cold Water Mass(YSCWM)be an important nutrient pool.Upwelling around the YSCWM boundary in the stratified season leads to consistency among the high chlorophyll a(Chl a)area,high primary productivity region and low-temperature upwelling zone.During cold seasons,the interactions of the southward cold waters in the western nearshore area and the northward warm waters in the central region lead to an“S”-shaped front in the SYS.In summer,upwelling can extract nutrients from the YSCWM;thus,the biogeochemical-ecological processes inside the cold-water mass and in the frontal zone are well connected via upwelling,and three typical physical-biogeochemical coupling regions are generated,namely,the Shidao coast,the area beyond the Haizhou Bay and the area off the Subei Shoal.This work refines and integrates studies on regional oceanography in the SYS and provides a comprehensive and systematic framework of physical-biogeochemical-ecological processes.

Spatiotemporal distribution and influencing factors of Ulva prolifera and Sargassum and their coexistence in the South Yellow Sea,China

Marine ecological disasters occurred frequently in recent years and raised widespread concerns about the ecological health of the ocean.We analyzed the spatiotemporal distributions of Ulva prolifera and Sargassum from April to July each year between 2016 and 2020 in the South Yellow Sea using multisource(GF-1 and HJ-1A/1B)remote sensing images,combined with the MODIS sea surface temperature(SST)data,photosynthetically active radiation(PAR)data,and Quick SCAT sea surface wind(SSW)data,to explore the potential influencing factors.The results show that(1)U.prolifera and Sargassum appeared mainly from May to July and April to June,respectively;(2)U.prolifera showed an impact in larger spatial scope than that of Sargassum.U.prolifera originated in the shoal area of northern Jiangsu and finally disappeared in the sea near Haiyang-Rongcheng area.The spatial scope of the impact of Sargassum tended to expand.Sargassum was first detected in the ocean northeast of the Changjiang(Yangtze)River estuary and disappeared near 35°N;and(3)correlation analysis showed that the SST influenced the growth rate of U.prolifera and Sargassum.PAR had varied eff ects on U.prolifera and Sargassum at different times.A moderate light conditions could accelerate the growth and reproduction of U.prolifera and Sargassum.High irradiance levels of ultraviolet radiation may cause photoinhibition and damage on U.prolifera and Sargassum.The southeast monsoon and surface currents promoted the drift of U.prolifera and Sargassum from the southeast to the northwest and north.Therefore,the spatial and temporal similarities and differences between U.prolifera and Sargassum were influenced by a combination of factors during their growth processes.

Rates and fluxes of centennial-scale carbon storage in the fine-grained sediments from the central South Yellow Sea and Min-Zhe belt, East China Sea

The global carbon cycle has played a key role in mitigating global warming and climate change.Long-term natural and anthropogenic processes influence the composition,sources,burial rates,and fluxes of carbon in sediments on the continental shelf of China.In this study,the rates,fluxes,and amounts of carbon storage at the centennial scale were estimated and demonstrated using the case study of three fine-grained sediment cores from the central South Yellow Sea area(SYSA) and Min-Zhe belt(MZB),East China Sea.Based on the high-resolution temporal sequences of total carbon(TC)and total organic carbon(TOC)contents,we reconstructed the annual variations of historical marine carbon storage,and explored the influence of terrestrial and marine sources on carbon burial at the centennial scale.The estimated TC storage over 100 years was 1.18×10~8 t in the SYSA and 1.45×10~9 t in the MZB.The corrected TOC storage fluxes at the centennial scale ranged from 17 to 28 t/(km^2·a)in the SYSA and from 56 to 148 t/(km^2·a)in the MZB.The decrease of terrestrial materials and the increase of marine primary production suggest that the TOC buried in the sediments in the SYSA and MZB was mainly derived from the marine autogenetic source.In the MZB,two depletion events occurred in TC and TOC storage from 1985 to 1987 and 2003 to 2006,which were coeval with the water impoundment in the Gezhouba and Three Gorges dams,respectively.The high-resolution records of the carbon storage rates and fluxes in the SYSA and MZB reflect the synchronous responses to human activities and provide an important reference for assessing the carbon sequestration capacity of the marginal seas of China.

Tectonic Evolution of the North Depression of the South Yellow Sea Basin Since Late Cretaceous

On the basis of subsidence history analysis and balanced cross-section analysis, the vertical uplift/subsidence history and horizontal extension/compression history of the north depression of the south Yellow Sea basin are quantitatively studied. The results show that the tectonic evolution of the north depression of the south Yellow Sea basin since late Cretaceous can be divided into a rifting phase(late Cretaceous to Paleogene) and a post-rifting phase(Neogene to Quaternary). The rifting phase can be further subdivided into an initial rifting stage(late Cretaceous), an intensive rifting stage(Paleocene), a rifting termination stage(Eocene), and an inversion-uplifting stage(Oligocene). Together, this division shows the characteristics of an episodic-evolved intracontinental rift-depression basin. The deformation of the north depression of the south Yellow Sea basin since late Cretaceous was mainly fault-related. The horizontal extension and tectonic subsidence were controlled by the activity of faults. The differential evolution of faults also caused variations in local uplift/subsidence movements and the regional heterogeneity in extension. The late Cretaceous initial rifting of the north depression of the south Yellow Sea basin is related to the Pacific-Eurasia convergence. From the Paleocene intensive rifting stage to present, the Pacific-Eurasia convergence and India-Eurasia convergence have played important roles in the evolution of this region.

Community structure changes of macrobenthos in the South Yellow Sea

The ecological environment in the Yellow Sea has changed greatly from the 1950s to 1990s and this has had significant impact on marine organisms. In this study, data on soft-sediment macrobenthos occurring in depths from 25 m to 81 m in the South Yellow Sea were used to compare changes in community structure. The agglomerative classification (CLUSTER) and multidimensional scaling (MDS) methods were applied. Five communities were recognized by cluster analysis: 1. The Yellow Sea Cold Water Mass community dominated by cold water species, which changed slightly in species composition since the 1950s; 2. The mixed community with the coexistence of cold water species and warm water species, as had been reported previously; 3. The polychaete-dominated eurythermal community in which the composition changed considerably as some dominant species disappeared or decreased; 4. The Changjiang (Yangtze) River Estuarine community, with some typical estuarine species; 5. The community affected by the Yellow Sea Warm Current. The greatest change occurred in the coastal area, which indicated that the change may be caused by human activities. Macrobenthos in the central region remained almost unchanged, particularly the cold water species shielded by the Yellow Sea Cold Water Mass. The depth, temperature and median grain size of sediments were important factors affecting the distributions of macrobenthos in the South Yellow Sea.

Provenance and Tectonic Implications of Paleozoic Strata in the South Yellow Sea Basin, China-Revealed from the Borehole CSDP-2

Well CSDP-2 is a fully coring deep drilling hole, penetrating the thick Paleozoic marine strata in the South Yellow Sea Basin(SYSB) in the lower Yangtze Block(LYB). Based on the petrological and geochemical analysis of 40 sandstone samples from the core CSDP-2, the provenance and tectonic features of Paleozoic detrital rocks from SYSB are analyzed and systematically delineated in this article. The results show that the Silurian – Carboniferous sandstones are mature sublitharenite, while the Permian sandstones are unstable feldspathic litharenite. The average CIA(chemical index of alteration) is 74.61, which reflects these sediments were derived from source rocks with moderate chemical weathering. The REE(rare earth element) patterns are characterized by LREE enrichment, flat HREE and obviously negative Eu anomaly, which are similar to that of the upper continental crust. Dickinson QFL discrimination results indicate the recycled orogeny provenance. Various diagrams for the discrimination of sedimentary provenance based on major and trace element data show all the sediments were derived predominantly from quartz sedimentary rocks, of which the Permian strata contain more felsic sedimentary rocks. Geochemical data for these detrital rocks suggest they occur at the passive continental margin and island arc settings, and the Permian sandstone presents active continental margin setting.