2022, Volume 29 Issue 5
    25 September 2022
    Previous Issue    Next Issue

    For Selected: Toggle Thumbnails
    Marine science in China: Current status and future outlooks
    WU Lixin, JING Zhao, CHEN Xianyao, LI Caiwen, ZHANG Guoliang, WANG Shi, DONG Bo, ZHUANG Guangchao
    2022, 29(5): 1-12. 
    DOI: 10.13745/j.esf.sf.2022.4.60

    Abstract ( 1935 )   HTML ( 117 )   PDF (4828KB) ( 662 )  

    Oceans as the cradle of life, the treasure trove of resources, and the protective barrier for national security play an important strategic role in the future sustainable development of mankind. Until now only 5% of oceans have been explored. For the national development it is vital to accelerate the marine science and technology innovation, improve the marine resources exploration capability, and protect the marine ecological environment. However, due to its inherent complexity, the “ocean problem” cannot be solved within a single discipline. Presently marine study in China is gradually catching up with the world, yet research originality is still lacking. This paper reviews the domestic marine research progresses and trends, points out the gaps between China and advanced countries, and proposes future directions. Focusing on the major scientific frontiers e.g., multiscale inter-ocean interaction, climate change, healthy ocean, marine life cycle, cross-sphere fluid-solid interaction, rapid changing polar system, and sustainable development of coastal zone-this paper proposes that China should strengthen its top-level design and strategic planning, carries out cross-scale, cross-sphere interdisciplinary research, and pursues leadership roles in major international scientific programs. These efforts are essential to enhancing China's influence in international marine research, effectively improving its national security capability, supporting its socioeconomic development, and providing scientific and technological support in achieving maritime power and building a global community with a shared future.

    Figures and Tables | References | Related Articles | Metrics
    Observational studies in the Kuroshio Extension region, Northwest Pacific—a review and outlook
    CHEN Zhaohui, LIN Xiaopei, MA Xin, GUAN Yanfeng, ZHOU Chun, ZHANG Yueqi, MA Ke
    2022, 29(5): 13-22. 
    DOI: 10.13745/j.esf.sf.2021.3.16

    Abstract ( 524 )   HTML ( 31 )   PDF (6979KB) ( 307 )  

    The Kuroshio Extension (KE) in the Northwest Pacific is one of the regions that are dynamically most complex, most sensitive to climate change and have the most productive fishing ground in the global ocean. However, it is also a region with the least long-term continuous observation, which can hinder our understanding of the physical, ecological and biogeochemical processes in the region. This paper reviews the recent progress and accomplishments in the international KE observations as well as the ongoing efforts by Chinese scientists-including in 2020 the successful construction of the Kuroshio Extension Mooring System (KEMS), the first real-time data-transmission mooring array in the Northwest Pacific. During the construction of the KEMS, it was found that subduction by eddy lateral advection accounted for more than 50% of the total subduction rate for mode waters. The mesoscale eddies could trap and transport such mode waters southwestward to the western boundary of the subtropical gyre within one and a half year. By simultaneous temperature/salinity measurements and velocity measurement from the mooring arrays, the dynamic features of subthermocline eddies (STEs) in the KE region were examined in detail. For the first time in situ evidence of three types of STEs were obtained in this region, which provided a solid observational basis for further investigation of the detailed generation and erosion mechanisms of the KTEs as well as the global subsurface mass/heat transport processes. The paper proposes that future observational systems should include integrated open-ocean observational platforms for multisphere, multidisciplinary studies, which can provide important observational support for the understanding of multiscale physical biological coupling, deep-ocean energy cascade and its climate effects, and deep-ocean carbon cycle.

    Figures and Tables | References | Related Articles | Metrics
    Environmental magnetic characteristics of sediments of the western tropical Pacific: Response to the East Asian Winter Monsoon
    HOU Xiaolin, XU Jishang, JIANG Zhaoxia, CAO Lihua, ZHANG Qiang, LI Guangxue, WANG Shuang, ZHAI Ke
    2022, 29(5): 23-34. 
    DOI: 10.13745/j.esf.sf.2020.5.55

    Abstract ( 207 )   HTML ( 18 )   PDF (4233KB) ( 88 )  

    The Western Pacific Warm Pool (WPWP) refers to a vast sea area located in the middle and west of the tropical Pacific Ocean (including the southern South China Sea and the Sulu Sea) with an average annual water temperature of over 28 ℃. Covered by the ultra thick layer of warm surface water, with increasing prominence as a global heat source and site of water-vapor exchange, the WPWP plays an important role in driving the thermohaline circulation and regulating global climate change. The East Asian Winter Monsoon (EAWM), on the other hand, is one of the most active components of the global climate system. It can cause deep convection in tropical regions through cold waves, thereby strengthening convective activities and abnormal precipitation in the warm pool area. However, the historical interaction between WPWP and EAWM is still unclear. As aeolian dust carried by the EAWM usually contains large high-coercivity magnetic mineral particles, and these particles can cause fluctuations in environmental magnetic parameters, such as changing the mineralogy, concentration, grain size and morphology of magnetic minerals in sediments, one can assess the historical aeolian mineral inputs and EAWM intensity variations by analyzing the changes of environmental magnetic parameters of pelagic sediments in the WPWP. In this paper, we carried out environmental magnetic measurements on the B10 borehole sediments to reveal the response of the environmental magnetic characteristics of the WPWP sediments to the EAWM. We found the dominant magnetic minerals in the sediments were pseudo-single-domain (PSD) low-coercivity ferrimagnetic magnetite; and some high-coercivity magnetic minerals were also present. We also found the variabilities of high-coercive magnetic mineral content and relative content of fine-grained magnetite were highly correlated during the glacial and interglacial periods and sensitive to the EAWM intensity change: Both high-coercive magnetic mineral content and magnetic grain size increased during the glacial period and decreased during the interglacial period, in accordance with the strengthening and wakening of EAWM intensities during the respective periods.

    Figures and Tables | References | Related Articles | Metrics
    Vertical distributions of CH4 and N2O in sediments of the Bohai and Yellow Seas in spring
    LI Siqi, CHEN Ye, YIN Xia, ZANG Kunpeng, ZHEN Yu
    2022, 29(5): 35-46. 
    DOI: 10.13745/j.esf.sf.2021.9.12

    Abstract ( 357 )   HTML ( 10 )   PDF (4731KB) ( 100 )  

    In this study, the head-space equilibrium and quantitative PCR methods were used respectively to obtain the concentrations of methane (CH4) and nitrous oxide (N2O) and the vertical abundances of methanogens and SRB in five representative sediment cores in the Bohai and Yellow Seas during two cruises in spring 2018. The relationships between these measurements and the related environmental parameters in pore water were also analyzed. The CH4 and N2O concentrations showed obvious spatial and vertical variations, due to the differences in the hydrological conditions above the sediment and the complexity of carbon/nitrogen biogeochemical processes in sediment cores. The average CH4 and N2O concentrations in sediments ranged between 0.23-0.92 nmol·kg-1 and between 18.90-104.96 nmol·kg-1, respectively, and they were higher overall in the Yellow Sea than in the Bohai Sea. The CH4 concentrations in sediments increased with increasing depth, whereas the $\text{SO}_{4}^{2-}$ concentrations decreased steadily with depth as in a mirror-image relationship with CH4 concentrations, while the abundances of methanogens and sulfate-reducing bacteria followed the same trend, indicating the CH4 production rate in sediments was controlled by the $\text{SO}_{4}^{2-}$ concentration in pore water. The average copy number of the mcrA gene was lower in the Bohai Sea than in the Yellow Sea and increased with depth at all stations except station 3500-7; whilst no significant correlation was detected at all stations between the mcrA gene abundance and CH4 concentration, and the same held true for $\text{SO}_{4}^{2-}$. The copy number of the dsrB gene was at least 2 orders of magnitude higher than that of the mcrA gene and, at all stations, increased at depths above 10 cm then gradually decreased till the bottom of sediments; and there was a weak mirror-image relationship between the dsrB gene copy number and CH4 profiles at all stations, although no significant negative correlation was found between the two. The above results indicate there are other processes that consume CH4 and $\text{SO}_{4}^{2-}$ in sediments. The N2O concentrations roughly decreased with increasing depth but gradually increased at depths below 30 cm; whilst the $\text{NO}_{3}^{-}$ and $\text{NO}_{2}^{-}$ concentrations gradually decreased with depth at all stations while the $\text{NH}_{4}^{+}$ profiles followed the opposite trend. The significant positive correlation between the N2O and $\text{NO}_{2}^{-}$ concentrations and slightly weaker positive correlation between N2O and $\text{NO}_{3}^{-}$ in sediments indicate that denitrification is the main process for the N2O production in marine sediments. These results provide a reference for further understanding the source and distribution of CH4 and N2O, as well as the carbon and nitrogen cycles in the sediments of the continental shelf.

    Figures and Tables | References | Related Articles | Metrics
    The global marine silicon cycle and its major challenges
    ZHU Dongdong, Jill N.SUTTON, Aude LEYNAERT, Paul J.TREGUER, LIU Sumei
    2022, 29(5): 47-58. 
    DOI: 10.13745/j.esf.sf.2021.8.6

    Abstract ( 919 )   HTML ( 38 )   PDF (2370KB) ( 308 )  

    The marine silicon cycle is one of the key biogeochemical cycles in the marine realm. It can regulate the global atmospheric carbon dioxide concentration and seawater pH, and also plays a significant role in the geochemical cycles of many other elements, including nitrogen (N), phosphorus (P), iron (Fe) and aluminum (Al). The closely intertwined coupling relationships between the marine silicon cycle and “biological pump” as well as the carbon cycle have caused for substantial concerns under the looming threat of global climate change and increased anthropogenic influences. Silicon (Si) is transported into the ocean through rivers, submarine groundwater, atmospheric deposition, basalt weathering and hydrothermal vents, however, subpolar glaciers are becoming an important Si source to the high latitude ocean regions due to global warming. And Si is removed from the ocean through biogenic silica (bSi) deposition, silicious sponges and bSi reverse weathering. The marine silica cycle involves complex biological (organism-mediated absorption/degradation), physical (adsorption, dissolution) and chemical (mineralization, reverse weathering) processes, while studying these processes could strengthen our understanding of its “source-sink” and the silica budget. This study reviews the major processes and challenges in the marine silica cycle, re-evaluates the marine silica budget based on recent advances, and indicates the major scientific questions for future works. Current works indicated that the input and output fluxes of marine Si have increased 2.4 and 2.2 times, respectively, than the previous estimates. On a short geological time scale (< 8 ka), the total Si net inputs are approximately balanced by the total Si net output flux; therefore, the modern ocean Si cycle is generally at steady state. Nonetheless, the input fluxes of Si to marginal seas through rivers can be influenced by the climate change and human activities, which can then affect the structures of phytoplankton community, including diatoms. This issue is one of the major issues in the marine silicon cycle and requires further research in the future. The coastal and continental margin zones (CCMZ) are oceanic regions with characteristics of high sedimentation rate and rapid reverse weathering, where the bSi burial fluxes is still difficult to estimate accurately. Present studies have assessed the bSi production rates for planktonic diatoms, silicious sponges and rhizaria, but the role of benthic diatom in bSi production was ignored. This omission should be addresses in the future study of benthic diatom primary production and its role in the marine silicon cycle.

    Figures and Tables | References | Related Articles | Metrics
    Benthic foraminifera in marine hypoxic environment: A review of recent research advances
    XU Zhaomeng, LIU Sumei
    2022, 29(5): 59-72. 
    DOI: 10.13745/j.esf.sf.2021.9.23

    Abstract ( 307 )   HTML ( 14 )   PDF (3244KB) ( 159 )  

    Global warming and human activities increase the frequency and scope of marine low-oxygen environments, and hypoxia has a significant impact on marine benthic communities. Benthic foraminifera, among a few eukaryotes, can widely adapt to and survive in various marine low-oxygen environments, and the response of benthic foraminifera to hypoxia and the adaptation mechanisms are hot topics in marine research with many unsolved mysteries. This article summarizes the distribution characteristics of living foraminifera in various marine hypoxic environments and their response to artificially induced hypoxic environment, chemical composition characteristics of benthic foraminiferal shells in hypoxic environment, and survival mechanisms of foraminifera in hypoxic environments, seeking to provide a reference for future research on benthic foraminifera under marine hypoxic environment. Benthic foraminifera, as an important tool for the reconstruction of the ancient marine environment, are of great significance to our understanding of the evolutionary history of ocean hypoxia. Looking forward, future researches should focus on cellular, molecular and physiological investigation of the mechanisms of foraminiferal adaptation to hypoxic environment as well as gaining phylogenic insights into the historical evolutionary processes of eukaryotic adaptation to hypoxic environment, so as to provide a theoretical basis for using foraminifera as a tool to better reconstruct and predict changes under hypoxic conditions.

    Figures and Tables | References | Related Articles | Metrics
    Compositions, sources and formation processes of abyssal and hadal sediments in the northern Yap Trench
    ZHENG Cheng, SUN Chengjun, JIN Hong, HUANG Yuhuan, YUE Xin'an, YANG Guipeng, DING Haibing
    2022, 29(5): 73-87. 
    DOI: 10.13745/j.esf.sf.2021.9.20

    Abstract ( 236 )   HTML ( 7 )   PDF (10497KB) ( 310 )  

    To investigate the sediment compositions, sources, and formation processes in the abyss and hadal zone of the northern Yap Trench, scan electron microscope (SEM) and X-ray energy spectroscopy (EDS) were used to analyze in 1 cm interval of the 0-8 cm sediment layer of five core samples collected at different depths. The compositional analysis included water content, manganese nodule content, concentrations of six major metal elements (Al, Ca, Fe, Mn, Ti, Mg) and nine trace metal elements (Ba, Co, Cr, Ni, Pb, Sr, V, Cu, Zn), and total organic carbon (TOC). According to the analysis results, sediments in the study area are mainly deep-sea ooze, a complex mixture of sediments from different eras. They contain microfossils produced by coccolithophores, such as Discoaster, sponge spicules, radiolarians, and diatoms, and various minerals, including pyroxene, barite, ilmenite, and feldspar. The sediment sources are complex, including mainly biological, volcanic and terrestrial (found in the abyss on the west side of the trench) sources as well as submarine hydrothermal fluids. Manganese nodules develop more easily in sediments off the cliffs on the west side of the trench than on the east side. The abyssal and hadal sediments in the northern Yap Trench have relatively high water content and large particle size, and the water content tends to decrease with depth. The sediment TOC content and microfossil abundance are higher in hadal than in abyssal sediments, indicating obvious funnel effect. As a whole, the water and TOC content of the sediments are lower on the west side of the trench than on the east side. The carbonate compensation depth in the northern Yap Trench ranges between 4435-4568 m, changing from below 4568 m since the Pleistocene. The sedimentary environment in the study area is oxic, where mixing and redeposition of ancient and modern sediments occur in the 0-8 cm sediment layer, causing the formation age to vary greatly. Factors influencing sediment formation include trench slope, hydrodynamic environment, gravitational collapse, turbidity current deposition, volcanic activity, and funnel effect.

    Figures and Tables | References | Related Articles | Metrics
    Heavy mineral assemblages and migration paths in the surface sediments of the northern East China Sea shelf: Tracer responses to bottom water masses
    LIU Yong, LI Guangxue
    2022, 29(5): 88-101. 
    DOI: 10.13745/j.esf.sf.2021.9.17

    Abstract ( 201 )   HTML ( 7 )   PDF (7368KB) ( 75 )  

    Based on the laboratory measurements of mud temperature, particle size and heavy mineral composition in surface sediments of the northern East China Sea, this paper examines the spatial distribution characteristics and information records of sedimentary heavy minerals carried by the bottom water masses since the sea level rise. The results show that migration paths for dominant mineral species are closely related to the regional circulation system and can be used to trace the material transport directions. Based on the characterization of migration paths for dominant heavy mineral species, such as transparent minerals (ordinary amphibole, epidote, stable minerals), metal minerals (opaque minerals), flake minerals and authigenic minerals, the study area is preliminarily divided into five types of mineral provinces: cold vortex (I), Yellow Sea coastal current and cross-shelf transport current in the East China Sea (ECSC) (II), Yangtze diluted water (III), warm current (IV) and composite (V) mineral provinces. Province I is significantly affected by the cold eddy southwest of Cheju Island, and its high authigenic pyrite content indicates a strong reducing sedimentary environment. Province Ⅱ is the main channel for the southward material transport from the old Yellow River Delta by the Yellow Sea coastal current and ECSC, and epidote minerals, metal minerals and platy minerals are the characteristic minerals indicating the path. Province III is an important channel for the eastward diffusion of the Yangtze diluted water, and common amphibole, platy mineral and garnet are the characteristic tracer minerals. Province IV is impacted by the “water barrier” from the mixing of the Taiwan and Tsushima Warm Currents with the continental shelf water masses, where its western part receives the provenance supply and forms the dominant low-value minerals and relatively high-value biogenic detrital, while its eastern part, without provenance supply, produces dominant high-value minerals from the exposed transgressive deposition. And province V is jointly affected by the seasonal variation and differential intensity of regional circulation, showing no significant mineralogical differences compared to neighboring regions in terms of heavy mineral assemblages and dominant mineral contents. Studying the material transport and accumulation processes in the northern East China Sea from the perspective of mineral migration path can help to further understand the significance of dominant mineral tracing and its response mechanism to the dynamic environment of the regional circulation system.

    Figures and Tables | References | Related Articles | Metrics
    Source-sink processes, paleoenvironment and paleomonsoon evolution in the Northeast Indian Ocean
    GUAN Yulong, CHEN Liang, JIANG Zhaoxia, LI Sanzhong, XIAO Chunfeng, CHEN Long
    2022, 29(5): 102-118. 
    DOI: 10.13745/j.esf.sf.2021.9.18

    Abstract ( 333 )   HTML ( 18 )   PDF (5438KB) ( 170 )  

    The Northeast Indian Ocean (NIO) sits at a unique geographical location, where marine sediments record the source-sink processes in the Tibetan Plateau-Bengal fan, the sea-air interaction during the Indian and Asian monsoon season, and the phase relationship between the evolution of heat transfer in the Indian Pacific Warm Pool and the high-latitude climate. It records as well the climate-tectonics-sedimentation (CTS) coupling evolution in the Himalayas, and is an ideal window to study multi-sphere interactions and explore paleoclimate and paleoenvironmental changes. This paper summarizes a series of research advances in recent years on the characteristics of monsoon and surface circulation, sediment composition and provenance, climate and environmental changes, and magnetic records of the NIO. The analysis shows that the NIO is a typical monsoon wind field where the surface circulation is strongly influenced by monsoons and obviously different between summer and winter. The sediment includes terrigenous detritus zircon ransported by rivers, calcareous and siliceous biodeposits and volcanic materials. However, there are still disagreements over the regional sediment composition, source-sink processes, migration history, monsoon evolution as well as the relationship between the Tibetan Plateau uplift and high-latitude climate change in the NIO. In addition, limited by sampling issues and weak magnetic signal, environmental magnetism, a widely accepted method for sediment source tracing and paleoclimate and paleoenvironmental restoration, has not been fully developed and applied in the NIO. Therefore, it is necessary to extend research focus further south and deeper into the NIO region and conduct a comprehensive analysis of its source-sink processes in the future. In order to solve the regional climate and environmental problems such as monsoon evolution and paleomarine environmental change, and advance local environmental and climate research, method developments are needed, which include improving high precision techniques to extract magnetic signals, and finding effective proxy indicators to increase application of environmental magnetism. Also, it is very important to establish high-resolution paleosecular variation (PSV) records for revising the global geomagnetic field model and exploring the deep dynamic process of the Earth in the NIO.

    Figures and Tables | References | Related Articles | Metrics
    Effects of biocomponent on the geotechnical properties of seafloor surface sediments in the Western Pacific Warm Pool
    ZHOU Shang, XU Jishang, LIU Yong, LI Guangxue, LI Anlong, CAO Lihua, ZHAI Ke, XU Jizheng, QUAN Yongzheng
    2022, 29(5): 119-132. 
    DOI: 10.13745/j.esf.sf.2021.5.2

    Abstract ( 213 )   HTML ( 6 )   PDF (15711KB) ( 54 )  

    The Western Pacific Warm Pool (WPWP) is located in the tropical western Pacific and the eastern Indian Ocean with an average annual surface water temperature of over 28 ℃. Due to the varying depositional environments under different tectonic settings, the biocomponent contents in pelagic sediments of the WPWP differ greatly. Biocomponents have a significant impact on the geotechnical properties of deep-see sediments, however, the correlation between the two has not been studied previously. To fill this gap, we investigated the geotechnical properties of surface sediments in the core of the WPWP and identified the sediment components under microscope. As results show, the natural moisture content ranges from 61.1% to 435.1%, natural density from 1.04 to 1.76 g/cm3, penetration resistance from 0 to 100 kPa, and vane shear strength from 0 to 8.6 kPa. The high natural moisture content, low natural density, and low shear strength are consistent with the characteristics of typical geotechnical properties of deep-sea sediment. Calcareous sediments of the Western Carolingian ridge, seamounts and other areas with water depths less than the CCD (Carbonate Compensation Depth) generally contain more than 50% calcareous biocomponents, and the same proportion of siliceous biocomponents is likely found in siliceous sediments of the southwestern Western Carolingian trough and surrounding deep trench areas; whereas clay sediments mainly distribute in the Western Carolingian basin. With decreasing calcareous and increasing siliceous biocomponents, the surface sediment varies from calcareous to clay to siliceous and its natural moisture content increases while its natural density, penetration resistance and vane shear strength decrease. It suggests that the geotechnical properties of deep-sea surface sediment are correlated with the contents of biocomponents—specifically, its penetration resistance, vane shear strength and natural density are positively influenced by calcareous biocomponents and negatively influenced by siliceous biocomponents, while the opposite holds true for natural moisture content. This paper establishes the relationship between biocomponent and geotechnical properties of abyssal sediments, and proposes a fitting formula between the biocomponent content and geotechnical properties, which is useful for evaluating the geotechnical properties of deep-sea sediments.

    Figures and Tables | References | Related Articles | Metrics
    Mesozoic tectonic evolution of the southwestern Bohai Sea and its dynamic mechanism: Implications for the destruction of the North China Craton
    YE Tao, NIU Chengmin, WANG Deying, WANG Qingbin, DAI Liming, CHEN Anqing
    2022, 29(5): 133-146. 
    DOI: 10.13745/j.esf.sf.2021.9.22

    Abstract ( 226 )   HTML ( 13 )   PDF (10842KB) ( 440 )  

    Mesozoic of the southwestern Bohai Sea experienced multi-stage tectonic activities and records in detail the destruction process of the North China Craton. Here, to clarify the relationship between Mesozoic tectonic evolution in the southwestern Bohai Sea and regional tectonic setting, the structural characteristics of the Mesozoic are determined, its formation and evolutionary processes are restored, and its dynamic mechanism and response to the destruction of the North China Craton are discussed based on the 3D seismic and deep drilling data, combined with regional tectonic background. As results show, (1) differing from the NEE-trending structure of the onshore oil area of the Bohai Bay Basin, the southwestern Bohai Sea develops multi-strike, multi-type structures. The 3D seismic data reveal negative-inversion, strike-slip thrusting, and folding structures that are different from the Cenozoic extensional structures; among them, the NWW-trending negative-inversion structure dominates. (2) Mesozoic of the Bohai Sea undergoes multi-stage deformation, which includes formation of the Indonesian thrust fold, sino-lateral thrust transformation in the Early Yanshan period, negative inversion in the Middle Yanshan period, and fold in the late Yanshan period; among them, thrust fold during the Indosinian movement was the key stage for the buried-hill formation, and the middle Yanshan negative-inversion stage was the key stage for the tectonic transformation. (3) Formation of the NWW-trending structure is related to the South-North China collision during the Indonesian period. The sinistral strike-slip in the early Yanshan period is the result of the NWW-ward subduction of the Pacific plate, which signifies the replacement of the Paleo-Tethys domain by the Pacific domain for controlling the deformation of the North China plate. The negative inversion in the middle Yanshan period corresponds to the large-scale regional magmatic activity, which is the shallow response to the large-scale destruction of the North China Craton. The proposed model of a NWW-trending negative-inversion towards the preexisting structure of the Indosinian in the middle Yanshanian enriches the simple traditional structural model for the destruction of the North China Craton to form the NEE-trending basins.

    Figures and Tables | References | Related Articles | Metrics
    Mesozoic-Cenozoic tectonic evolution and buried hill formation in central Bohai Bay
    ZHOU Qijie, LIU Yongjiang, WANG Deying, GUAN Qingbin, WANG Guangzeng, WANG Yu, LI Zunting, LI Sanzhong
    2022, 29(5): 147-160. 
    DOI: 10.13745/j.esf.sf.2022.3.36

    Abstract ( 410 )   HTML ( 26 )   PDF (17469KB) ( 468 )  

    The Bohai Bay Basin is a Late Mesozoic-Cenozoic faulted basin in the eastern North China Craton. Located in the continental active margin of the western Pacific Ocean, the Bohai Bay Basin experienced multi-stage tectonic movements of various types. Currently there is still much controversy over the divisions of tectonic stages and stress fields for each tectonic movement in the Bohai Bay Basin during the Meso-Cenozoic. Buried hill is a palaeogeomorphologic feature formed before the basin filled and then buried by new sedimentary cover. The pre-existing faults inside the buried hill and the contact relationship between the buried hill and the overlying new strata provide an evidence basis for studying the tectonic movement in the basin. Choosing the Bozhong 19-6 buried hill as an example, this paper proposes a new structural model for the buried hill, based on the 3D seismic interpretation and systematic structural analysis of coherent seismic profile and drilling data, and discusses the regional tectonic evolution of the eastern North China Craton. The current structural characteristics of the Bozhong 19-6 buried hill are: (1) The buried hill is bounded by a series of S-N-trending normal faults, which separates it to the east and the Shanan Depression to the west. The buried hill first appeared in the Late Triassic and formed in the Early Cretaceous. (2) The S-N-trending boundary faults and the E-W-trending faults within the buried hill are formed by the transpressive strain due to the regional strike-slip faults along either sides of the buried hill, which are the important controlling factors for the structural reservoir in the buried hill. (3) The buried hill, impacted by the scission-type collision between the North China and Yangtze Plates and the NNW-ward subduction of the Paleo-Pacific Plate, underwent six-stage tectonic evolution since the Mesozoic era: the Early Indosinian compression, the Late Indosinian extension, the Early Yanshanian sinistral transpression, the Middle Yanshanian sinistral transtension, the Late Yanshanian sinistral transpression, and the final Himalayan transtension.

    Figures and Tables | References | Related Articles | Metrics
    Fault response to the Huizhou Movement in the Pearl River Mouth Basin: Insights from a case study of the Eastern Yangjiang Sag
    ZHANG Xiangtao, PENG Guangrong, WANG Guangzeng, LIU Xinying, ZHAO Li, YANG Yue, ZHAN Huawang, YU Haiyang, MA Xiaoqian, LI Sanzhong
    2022, 29(5): 161-175. 
    DOI: 10.13745/j.esf.sf.2021.9.24

    Abstract ( 263 )   HTML ( 7 )   PDF (14362KB) ( 102 )  

    The Huizhou Movement is a newly-defined tectonic movement occurring to the Pearl River Mouth Basin during the transition period between the early and late Wenchang rifting stages. This movement is well-responded in the Zhu Ⅰ Depression of the basin, however, its impact and response characteristics in other depressions of the basin are not known. Taking the fault system of the Eastern Yangjiang Sag, Zhu Ⅲ Depression as an example, this paper first studies the geometry and kinematic characteristics of the fault system, then summarizes its response characteristics to the Huizhou Movement in terms of its preferential orientation, assemblage style, and activity and activity migration patterns. It was found that mainly NE-NEE- and EW-NWW-trending faults of different scales develop in the Paleogene strata of the Eastern Yangjiang Sag, and their formation and evolution are mainly dominated by the pre-existing fabrics/weaknesses and regional tectonic movements. The pre-existing fabrics/weaknesses determine the preferential position, array style and general orientation of the main fault belts, imparting a favorable structural condition for the formation of various later structures along the fault belts. In the Eastern Yangjiang Sag, it is the reactivation of the pre-Cenozoic left-stepping echelon array branches of the NW-trending Yangjiang-Yitong'ansha Fault Zone that leads to the formation of a series of small strike-slip pull-apart basins along the Yangjiang-Yitong'ansha Fault Zone during its sinistral motion after the Huizhou Movement. Regional tectonic movements result in structural transformation of basin's dominant fault system including both main and secondary faults. For instance, although the Paleogene fault system of the Eastern Yangjiang Sag retains the general characteristics of the pre-existing pre-Cenozoic fabrics, such as fault position, array style and orientation, its dominant fault system, like in the Zhu Ⅰ Depression, transforms from the NE-NEE-trending extensional faults in the early Wencheng deposition stage to the sub-parallel E-W-NWW-trending transtentional faults in the late Wenchang deposition stage in response to the Huizhou Movement, and fault activities also migrate from south to north and from east to west, accordingly. The consistent response of the fault system to the Huizhou Movement in the Pearl River Mouth Basin indicates the Huizhou Movement is a wide-spread tectonic movement occurring to the north margin of the South China Sea. Therefore parallel studies of fault response characteristics in different depressions of the Pearl River Mouth Basin can provide a tectonic basis for inter-depression/inter-sag comparison of the Wenchang Formation developed in isolation across the whole basin, and facilitate oil and gas exploration in the Eastern Yangjiang Sag.

    Figures and Tables | References | Related Articles | Metrics
    Crude oil in the uplifts of the Huizhou depression, Pearl River Mouth Basin, South China Sea: Source and formation mechanisms
    DUAN Wei, TIAN Jinqiang, LI Sanzhong, YU Qiang, CHEN Ruixue, LONG Zulie
    2022, 29(5): 176-187. 
    DOI: 10.13745/j.esf.sf.2021.9.19

    Abstract ( 290 )   HTML ( 10 )   PDF (5831KB) ( 131 )  

    The Huizhou depression is the most important hydrocarbon-rich depression in the eastern Pearl River Mouth Basin, South China Sea. The uplifts, located in the southeastern margin of the Huizhou depression, are far from source rocks with no in-situ deposition of source rock strata. They are typical remotely sourced petroleum reservoirs, whose source and formation mechanisms are not yet known. This study systematically compared the biomarker compositions and isotopic characteristics between crude oil and source rock samples from the Huizhou depression. Combined with analysis of the fault-sand-unconformity migration pathways and blocking conditions, the Pathway software was used to simulate and analyze the three-dimensional hydrocarbon migration pathways, and the hydrocarbon accumulation process was analyzed in dynamic mode to overcome the limitations of static analysis. We suggest the source rock of the Wenchang formation is responsible for the crude oil in the uplifts. The crude oil samples were characterized by low C19/C23 tricyclic terpane ratio (<0.7), low C20/C23 tricyclic terpane ratio (<0.8), high C27 rearranged sterane/C27 regular sterane ratio (>0.25), low ETR value (<0.4), high 4-methylsterane/C29 sterane ratio (BBB>4), and low bicadinane T/C30 hopane ratio (<1). The simulated three-dimensional hydrocarbon migration pathways indicated that under the control of the Hui-Liu mid-ocean ridge, hydrocarbon generated in sag H26 of the Huizhou depression migrated to the Dongsha uplift along the dominant migration pathway and accumulated in the L11-1 oilfield in the uplifts far from the source rocks at the top of the mid-ocean ridge. The biomarker and carbon isotopic characteristics of crude oil samples from the uplifts were similar to those from other oilfields along the same predominant migration pathway. Therefore, we infer that the crude oil in the uplifts is predominantly sourced from the middle-deep lacustrine source rock of the Wenchang formation of sag H26.

    Figures and Tables | References | Related Articles | Metrics
    Source rock evaluation based on paleotopographic and source-to-sink analysis: An example of the Yangjiang Sag, Pearl River Mouth Basin
    PENG Guangrong, DU Xiaodong, JIANG Suhua, LI Sanzhong, GUAN Xueting, WEI Dong, JIANG Yan, LU Leilei
    2022, 29(5): 188-202. 
    DOI: 10.13745/j.esf.sf.2021.9.14

    Abstract ( 265 )   HTML ( 15 )   PDF (9294KB) ( 154 )  

    Source rock evaluation in offshore basins is crucial to the success of marine oil and gas exploration and also a key scientific problem to be solved urgently. Recently, a great breakthrough has been made in the Yangjiang Sag, Pearl River Mouth Basin revealing its excellent exploration potential in marine oil and gas. However, it is difficult to objectively evaluate the hydrocarbon generation potential of source rocks by seismic data alone when there are few exploratory wells in the study area. In order to determine the hydrocarbon generation potential of the Wenchang Formation-the primary hydrocarbon generating layer of the Yangjiang Sag, 4-dimensional sequence-stratigraphic simulation (Bandlands) is conducted to reconstruct the paleo-topography of the Yangjiang Sag during the Paleogene. The predicted paleoenvironmental characteristics better reveal the corresponding relationship between the paleo-topography and the sedimentary systems of the Wenchang Formation, and demonstrate the paleotopographic background of the Wenchang Formation has important impacts on the sedimentary development of source rocks. According to the analysis of sedimentary systems, the source-to-sink characteristics of the Wenchang Formation are summarized, which show that the sedimentary period of the Lower Wenchang Formation is the most favorable period for the source rock development. Combined with the paleo-topographic features, degree of source rock development (mainly the thickness and area of semi-deep lacustrine facies), connection status between source rocks and oil-source faults, and match between source rocks and shallow traps, the source rocks in each subsag are divided into three categories: high-quality source rocks (Enping sag 20, 21), relatively good source rocks (Enping subsag 27), and general source rocks (Enping subsag 19, Yangjiang subsag 24). On the basis of source rock distribution prediction and core analysis, combined with geological data and paleotopographic simulation results, the sedimentary burial history, thermal history and hydrocarbon generation history of source rocks in the Lower and Upper Wenchang Formations are analyzed, and the hydrocarbon generation potential of source rocks in the Wenchang Formation are simulated using PetroMod. The simulation results show that the source socks of the Lower Wenchang Formation has greater hydrocarbon generation strength than the Upper Wenchang Formation in the Enping subsag 20, 21, 27, indicating the Lower Wenchang Formation layer has the best hydrocarbon generation potential of source rocks, and the eastern and southern Yangjiang Sag (Enping subsag 20, 21, 27) have the best exploration potential. Source rock evaluation based on peleo-topographic analysis and source-to-sink characteristics is very important for guiding marine oil and gas exploration.

    Figures and Tables | References | Related Articles | Metrics
    Focal mechanism solutions for global tsunami earthquakes and future tsunami threat to China
    JIA Zhongjia, ZHU Junjiang, OU Xiaolin, ZHANG Shengsheng, HUANG Chang, CHEN Ruixue, ZHANG Shaoyu, LI Sanzhong, JIA Yonggang, LIU Yongjiang
    2022, 29(5): 203-215. 
    DOI: 10.13745/j.esf.sf.2021.9.13

    Abstract ( 361 )   HTML ( 20 )   PDF (8977KB) ( 142 )  

    Tsunamis are one of the five major marine natural disasters that can seriously threaten human life and property. In recent years international researchers have conducted a large number of studies on earthquake-induced tsunamis. These studies mainly focused on numerical simulation of tsunami generation, propagation, climb and inundation, as well as on paleo-tsunami sediments, but lacked attention to the focal mechanism of tsunami earthquakes, especially of those below magnitude 6.5. As revealed by the most recent studies in China on earthquake-induced tsunamis, tsunami hazards caused by earthquakes of magnitude less than 6.5 cannot be ignored. In this paper, 766 global earthquake-generated tsunamis are summarized; focal mechanism solutions for tsunami earthquakes are classified using triangulation techniques; and focal mechanism solutions for 341 tsunami earthquakes (since 1976) are analyzed in detail, with 633 wave heights analyzed by statistical methods. As results show, all types of earthquakes—strike-slip, normal and thrust earthquakes as well as unusual earthquakes—can cause tsunamis; whilst most tsunamis are caused by thrust fault earthquakes, and tsunami earthquakes below magnitude 6.5 can produce tsunami wave height up to 10 m to cause major damages. Mechanistically, thrust and normal earthquakes as well as unusual earthquakes can directly cause vertical changes in submarine topography to generate tsunamis; whereas strike-slip earthquakes can cause tsunamis for one of two reasons: they are not pure strike-slip type but have normal/thrust component, or they trigger submarine landslide to cause changes in seabed topography in generating tsunamis. According to focal depth analysis, more than 97% of tsunami earthquakes are shallow earthquakes less than 30 km deep, but intermediate and deep earthquakes can also cause tsunamis. Based on seismic source characteristics, geographical location of China mainland, as well as historical occurrences of tsunamis, we propose that earthquake-induced tsunamis that may threaten China's coastal areas in the future are concentrated in the Manila trench and Taiwan strait. These areas should be monitored closely and early warning systems should be established to reduce disaster damage.

    Figures and Tables | References | Related Articles | Metrics
    Development and application of long-term in situ monitoring system for complex deep-sea engineering geology
    SUN Zhiwen, JIA Yonggang, QUAN Yongzheng, GUO Xiujun, LIU Tao, MENG Qingsheng, SUN Zhongqiang, LI Kai, FAN Zhihan, CHEN Tian, TANG Haoru
    2022, 29(5): 216-228. 
    DOI: 10.13745/j.esf.sf.2021.9.15

    Abstract ( 422 )   HTML ( 8 )   PDF (8281KB) ( 143 )  

    Geohazards such as submarine landslides and turbidity currents are an urgent safety issue to be solved in marine engineering during national deep sea development. To avoid such risks and achieve geohazard monitory and early warning, we develop an in-situ monitory system for complex deepwater engineering geology (SEEGeo), using resistivity, acoustic and pore pressure monitoring to monitor the physical and mechanical changes in deep seabed sediments. This monitoring system mainly includes the seabed carrying platform, monitoring system, communication control system, and power supply system. The monitoring system performs long-term in-situ monitoring of resistivity, acoustic and pore pressure changes in seabed sediments; the communication control system is responsible for communication and data transmission from seabed to sea surface then to land; and the power supply system provides power for one year of long-term operation on the seabed via an unique seawater battery process. So far, SEEGeo has completed the offshore test and carried out multiple sea trials in the South China Sea on board scientific research ships (e.g., “Marine Geology No. 6”, “Dongfanghong No. 3”, “Zhang Jian”), and collected large amounts of survey data. For example, using Wenner method, resistivity monitoring obtained an average resistivity of 0.207 Ω·m at the water-soil interface location. Super excess pore pressure monitoring, using open-structured optical fiber-based differential pressure sensing, observed four landmark stages: 1) pressure accumulation during penetration (up to 34.942 kPa over 0.182 h); 2) pressure decay after penetration (down to 9.973 kPa over 0.810 h); 3) real-time response to environmental stress (pressure change between 8.327-14.384 kPa); and 4) residual pressure (average 11.150 kPa). And acoustic monitoring, adopting two sets of one transmit-three receive setup, obtained a seawater average sound velocity of 1 533 m/s, as well as average sound velocities of 1 586, 1 587, 1 784, 1 735 and 1 831 m/s in seafloor sediments from the top to the bottom layers. The successful development of SEEGeo will significantly improve the current technical capabilities for long-term in-situ marine engineering geology monitoring, complex engineering geology evaluation and geohazard monitoring and early warning.

    Figures and Tables | References | Related Articles | Metrics
    Long-term in situ observation of pore pressure in marine sediments: A review of technology development and future outlooks
    CHEN Tian, JIA Yonggang, LIU Tao, LIU Xiaolei, SHAN Hongxian, SUN Zhongqiang
    2022, 29(5): 229-245. 
    DOI: 10.13745/j.esf.sf.2021.9.30

    Abstract ( 521 )   HTML ( 18 )   PDF (8204KB) ( 177 )  

    Pore pressure in marine sediments is an important seabed stability indicator due to its sensitivity to marine geological hazards. Seabed stability can be assessed by measuring pore pressure accumulation in marine sediments, which is important for the forecast and early warning of marine geological hazards. However, there are several technical challenges in deep-ocean pore pressure observation, such as (1) high-resolution measurement under ultra-high background hydrostatic pressure; (2) sensor over-range damage during penetration process; (3) long-term power supply and sensor drift; and (4) equipment deployment and recovery off deep ocean floor. The international deep-ocean pore pressure observation technology has been developed since the 1960s to yield a series of core technologies and commercial products. The NGI-Illinois Differential Piezometer Probe System, jointly developed by Norwegian Geotechnical Institute and University of Illinois, is known as the earliest observational equipment. Since then, USGS, Sandia National Laboratory, Oxford University, etc. have developed various observational equipments covering shallow to the deep sea. Thereinto, PUPPI, a pop-up pore pressure instrument developed by UK's Institute of Oceanographic Sciences, marked an important historical achievement. At the time it was the most successful observational equipment that could continuously operate 6000 m underwater for one year, and its advanced design concept was widely borrowed by subsequent equipment developers. Since the 21st century, benefited from the overall progress in marine science and technology, the technology development for pore pressure observation has shown an accelerated trend. At the moment, the Piezometer series equipment, developed by the French Research Institute for Exploitation of the Sea (IFREMER), represents today's advanced level and is probably the most frequently used equipment worldwide. China started late in its deep-ocean exploration and observation technology development, including deep-ocean pore pressure observation. Currently, exploratory observational technology developments are carried out by Ocean University of China, Ministry of Natural Resources First Institute of Oceanography, etc. In recent years, a large number of national marine construction projects are in full swing, marked by the construction of the Hong Kong-Zhuhai-Macao Bridge and the test mining of natural gas hydrate in the South China Sea, and new marine industries start quickly in the areas of deep-sea oil and gas resources development and deep-sea natural gas hydrate exploitation. Therefore, it is urgent to develop domestic long-term in situ marine observation technology with independent intellectual property rights. In providing a reference for such endeavor, this paper reviews the international and domestic research progress in observation technology for pore pressure in seabed sediments, sought to summarize its core technologies and key application problems.

    Figures and Tables | References | Related Articles | Metrics
    Deep sea-lithosphere fluid exchange in subduction zones and its effects: A critical review
    XING Huilin, WANG Jianchao, PANG Shuo, WANG Ruize, LIU Dongyu, MA Zihan, ZHANG Yuling, TAN Yuyang
    2022, 29(5): 246-254. 
    DOI: 10.13745/j.esf.sf.2021.9.16

    Abstract ( 257 )   HTML ( 8 )   PDF (3487KB) ( 164 )  

    The subduction zone has the most complex and intense tectonic activities on Earth and is also an important part of the Earth's material circulation system. In-depth study of subduction zones will help deepen our understanding of the earth system. According to published results, it is believed that the oceanic lithosphere brings large amounts of water into the mantle through subduction at the boundary of the convergent plate, and this phenomenon is responsible for the control of subduction earthquakes, mantle melting, magma production, continental crust formation, and even mineral enrichment. The lithospheric mantle of the fore-arc uplift area is intensively hydrated by deep seawater infiltration along faults, and mantle hydration is one of the main ways of water accumulation in the lithosphere. With the increase of subduction depth, the hydrous serpentinized mantle dehydrates under certain temperature and pressure conditions, leading to intermediate earthquakes in the subduction zone. Moreover, due to differences in water migration, the separated water not only can cause hydrofracturing in the plate, but also can affect subduction interface coupling to form slow slip zones. Hence, fluid exchange between the deep sea and lithosphere in the subduction zone and its effect in the deep earth are complex dynamic processes with multiphysics couplings between chemical reaction, temperature, fluid migration and stress deformation. However, current researches mainly focus on exploratory observation and analysis of specific factors, phenomena or processes under certain conditions. Future research, therefore, needs to focus on the comprehensive, multidisciplinary study of multiphysics coupling dynamics from the perspective of earth system science, integrating fluid migration and chemical reaction into conventional solid earth research to quantitatively characterize/analyze the deep sea-lithosphere fluid exchange and its effects on the subduction dynamics at multiple spatiotemporal scales.

    Figures and Tables | References | Related Articles | Metrics
    Seafloor visualization and graphic user interface design
    ZHU Junjiang, OU Xiaolin, YANG Yue, CHEN Ruixue, ZHANG Shaoyu, JIA Zhongjia, ZHANG Shengsheng, WANG Pengcheng, LI Sanzhong, LIU Yongjiang, JIA Yonggang
    2022, 29(5): 255-264. 
    DOI: 10.13745/j.esf.sf.2021.9.21

    Abstract ( 223 )   HTML ( 8 )   PDF (10241KB) ( 128 )  

    Marine survey data increase steadily with the continuous progress in global marine surveying and the development of marine exploration techniques. So far various specialized softwares have been used to display/plot all types of marine survey data for visualization. However, it is necessary to create a data visualization tool for quick data display and analysis for today's global ocean observation and seafloor exploration. Here, for visualization and simultaneous display of multi-type data, we design and develop (using Matlab) a simple, easy-to-use data visualization and graphic user interface called OceanVis1.0. Using OceanVis1.0, all types of marine survey data—global bathymetric data, marine gravity anomaly data, marine magnetic anomaly data, earthquake waveform data, etc.—can be easily visualized for mapping analysis, and comprehensive visual analysis of key oceanic areas can be achieved. In OceanVis1.0, multi-type survey data can be displayed using 2D lines and 3D space variations, and visual manipulation such as zoom and rotation is also easy to do. For multi-beam, marine gravity and magnetic anomaly data, free cutting 2D lines and graphic output without saving intermediate graphics provide real-time visualization and a quick display. Meanwhile, OceanVis1.0 allows quick display and analysis of marine exploration data obtained from survey voyages, thus can be used in designing ship surveying lines for a specific research area.

    Figures and Tables | References | Related Articles | Metrics
    R&D and application of the Abyssal Bottom Boundary Layer Observation System (ABBLOS)
    JI Chunsheng, JIA Yonggang, ZHU Junjiang, HU Naili, FAN Zhihan, HU Cong, FENG Xuezhi, YU Heyu, LIU Bo
    2022, 29(5): 265-274. 
    DOI: 10.13745/j.esf.sf.2021.9.28

    Abstract ( 436 )   HTML ( 9 )   PDF (8188KB) ( 144 )  

    In order to further study the influence of marine dynamics on the bottom boundary layer (BLL) of the northern slope, South China Sea, the Abyssal Bottom Boundary Layer Observation System (ABBLOS) was developed for in situ observations. The ABBLOS—a carrier platform with a maximum operating water depth of 6700 m (actual depth limits depend on the carried equipment)—is an important technological innovation for studying the deep-sea BBL. The platform is compose of upper and lower frames. The upper frame is used to carry and recover observation equipment, and the lower supporting frame is a counterweight and used to provide an observational space 1 meter from the seabed. A simple and effective “slot positioning with bolt fastening” connection was designed to connect the two frames to ensure a successful upper frame recovery. The ABBLOS integrates 75k-ADCP, high-frequency ADCP, ADV, high-precision pressure gauge, as well as sensors for methane, temperature, salinity, turbidity, dissolved oxygen, and ORP. For the first time, the ABBLOS achieves simultaneous observation of marine dynamic processes (such as internal waves and midscale vortices) and dynamic changes of physical and chemical parameters in the deep-sea BBL. In particular, the water flow velocity profile at 1 meter height above the seafloor can be observed with a 7 mm vertical layer resolution. The platform was successfully deployed and recovered in 2020 in the Shenhu sea area, northern slope of the South China Sea, at water depths of 655 and 1405 m. The total observation time was 34 days, and the seawater velocity profile structure was obtained. Also captured were a once-a-day (on average) internal wave action process and a set of physicochemical parameters for the BBL. After a preliminary analysis of the observation data at 655 m water depth, it was found that the temperature, pressure, dissolved oxygen, density and salinity in the BBL were controlled by the tidal process; especially, the change of temperature and pressure was in synch with tide. During a tidal cycle, the oxidative environment of the BBL was relatively stable, whilst the concentration of dissolved methane decreased with time but kept within the global background value range. Compared to the tidal process, internal waves had little impact on the abyssal BBL, but could obviously cause sediment resuspension. The turbidity of the BBL caused by internal waves increased from 0.01 to 48 NTU and meanwhile the submarine cameras also recorded turbid seawater in the BBL during the internal wave propagation, indicating the internal waves in the South China Sea can affect the transport of submarine sediment.

    Figures and Tables | References | Related Articles | Metrics
    Subsurface structure of seabeach revealed by seismic tomographic velocity model: An example of the Qingdao Shilaoren beach
    GAO Fujian, ZOU Zhihui, WANG Yonghong
    2022, 29(5): 275-284. 
    DOI: 10.13745/j.esf.sf.2021.3.15

    Abstract ( 311 )   HTML ( 15 )   PDF (7843KB) ( 95 )  

    Understanding the subsurface structure of seabeach is an important part of coastal zone research and fundamental to seabeach protection and coastal development. Current seabeach researches are mainly focused on beach surface dynamics, but the internal structure and basement morphology of seabeach is little studied. Although drilling and other conventional exploration methods can be used for structural analysis of shallow sand, they are inadequate for building a complete seabeach model from surface to the bottom of basement. Without such a model it is difficult to calculate the sandbody volume or study seabeach evolution; therefore, a wide-range, effective detection method is needed for the structural analysis of sand body. Here, as an example, we apply multiscale seismic tomography to the Qingdao Shilaoren beach, a typical seabeach on the granite rocky coast of southeastern Shandong Peninsula, to investigate its detailed subsurface structure from surface to the crystalline basement. By using the newly developed heavy hammer source, we obtained the seismic data with high signal-to-noise ratio at offset as far as 150 m under noisy beach environment. The multiscale seismic tomography method performed well in modeling the subsurface structure of the seabeach, which allowed us to establish a velocity model to a depth of ~50 m below the Qingdao Shilaoren beach for interpreting the internal structure of sand body. The resulting velocity structure model fits well with the previously reported sand depth and particle size variation results obtained from drilling experiments. The inverted velocity structure shows that the sand body beneath the north end of the survey line (coastal side) is thicker than that beneath the south end near the shoreline, with ~15 m thickness beneath the backshore and only 5 m beneath the foreshore. We infer that there may be underground vertical rocks and partially weathered rocks in the sand body. The uneven weathering resulted in a concave-shaped basement that might have stabilized the sand body. Our method can be used to quickly and effectively build velocity models of subsurface sand body and other subsurface structures of seabeach, which is significant to the study of seabeach structure and evolution and beach protection.

    Figures and Tables | References | Related Articles | Metrics
    Variation of atmospheric dust loading and its climate impacts in different geological periods
    LIU Yonggang, ZHANG Ming, LIN Qifan, LIU Peng, HU Yongyun
    2022, 29(5): 285-299. 
    DOI: 10.13745/j.esf.sf.2021.9.51

    Abstract ( 290 )   HTML ( 16 )   PDF (16177KB) ( 215 )  

    Dust in the atmosphere can affect the Earth's surface temperature by absorbing and scattering sunlight, and thus further affects the atmospheric circulation and precipitation. However, the mechanism of atmospheric dust loading variability and its effects on the climate during different geological periods, especially the deep time, remain unclear. This paper investigates the change of atmospheric dust loading and its climate effects during four different geological periods via numerical modeling. The four periods are the Precambrian when there was no terrestrial vegetation; the Pangea supercontinent period with terrestrial vegetation and a global temperature significantly higher than the present day; the Last Glacial Maximum with continental configuration close to the modern one but a much colder climate than the present day; and the mid-Holocene with a slightly warmer climate than the present day. Compared to the present day, the Precambrian atmospheric dust loading was nearly 10 times as much due to larger dust source area, which led to a decrease in global surface temperature by about 10 ℃. In the Pangea supercontinent period, the dust loading was slightly higher because of slightly larger land area in the subtropical zone, and its impact on the global mean temperature was small. During the Last Glacial Maximum, dust loading was about twice as much due to a colder and drier climate, yet dust had a strong warming effect—without it, the global temperature would have decreased by about 2.5 ℃. In the mid-Holocene, global dust loading was much less as shown by observational evidence, while simulation results suggest that the effect of removing global dust on the global mean temperature can be ignored for this period even as the Atlantic Meridional Overturning Circulation changed significantly.

    Figures and Tables | References | Related Articles | Metrics
    Numerical simulation of the climate effects of the Tibetan Plateau uplift: A review of research advances
    SUN Hui, LIU Xiaodong
    2022, 29(5): 300-309. 
    DOI: 10.13745/j.esf.sf.2021.9.54

    Abstract ( 349 )   HTML ( 11 )   PDF (3390KB) ( 143 )  

    The uplift of the Tibetan Plateau is a major Cenozoic geological event that profoundly impacted the Asian as well as global climate and environmental changes. For nearly half a century, researchers have investigated the effects of the uplift through numerical simulation using various models, and the results have substantially improved the mechanistic understanding of the uplift induced climate change and its role in driving the evolution of paleoclimate. This paper briefly reviews the advances in the numerical simulation of the climate effects of the uplift, then summarizes and introduces the main achievements by three stages of simulation studies. The most recent studies show that during its uplift, growth and northward movement since the Cenozoic, the dynamic and thermal effects of the Tibetan Plateau have a profound impact on the formation of the East Asian monsoon, evolution of the South Asian monsoon, development of aridity in inner Asia, and change in the Asian monsoon-arid environmental pattern. The climate effects of the uplift are different in different parts of the plateau and surrounding regions, and closely related to the changes in land-sea distribution and paleogeographic patterns under the background of continental drift. The establishment of the south subtropical monsoon is determined by the location of continental drift and the seasonal movement of the tropical convergence zone; whilst the establishment of the East Asian monsoon is primarily determined by the uplift and the northward movement of the plateau. The existence of Asian subtropical arid areas depends on the position of the continent and the control of planetary-scale subtropical highs. The formation of Asian inland arid areas at mid-latitude is the result of the plateau uplift. Finally, we discuss the existing problems and possible improvements to the numerical simulation.

    Figures and Tables | References | Related Articles | Metrics
    Modeling study of the impact of tropical seaway changes on East Asian climate
    TAN Ning, ZHANG Zhongshi, GUO Zhengtang, WANG Huijun
    2022, 29(5): 310-321. 
    DOI: 10.13745/j.esf.sf.2021.9.58

    Abstract ( 236 )   HTML ( 14 )   PDF (11545KB) ( 118 )  

    The closure or constriction of tropical seaways during the early to mid-Pliocene (4.2-3 Ma) are highly relevant to paleoclimate due to their roles in modulating the global heat and moisture transport; however, their potential impacts on the East Asian (EA) climate and the underlying mechanism are unclear. Here, based on a set of sensitivity experiments using the NorESM-L AOGCM model, we systematically analyzed the influence of the Indonesian throughflow constriction and shallow central American seaway (CAS) closure on the EA climate. Our results reveal that the closure of tropical seaways leads to ocean surface warming in tropical regions and cooling in the mid-to-high-latitude North Pacific. The resulting sea surface temperature changes produce contrasting thermal effects in the northern (cooling) and southern China (warming), which leads to more precipitation along the mid-to-east elongated region of East Asia in summer, but causes warmer, drier condition in China in winter. This climate effect mainly results from the constriction of the Indonesian throughflow, with minimal impact from the shallow CAS closure. Combined with qualitative model-data comparison, our results further reveal that the closure/constriction of shallow tropical seaways can act to some extent on the EA climate transition during the Early to Mid-Pliocene but is not the major driver for this transition.

    Figures and Tables | References | Related Articles | Metrics
    Two types of millennial-scale climate oscillations during the last Quaternary and their triggering mechanism
    ZHANG Xiao, ZHANG Xu
    2022, 29(5): 322-333. 
    DOI: 10.13745/j.esf.sf.2021.9.56

    Abstract ( 499 )   HTML ( 35 )   PDF (3037KB) ( 196 )  

    Dansgaard-Oeschger events (DO) and Heinrich Stadial (HS) are the most pronounced millennial-scale climate oscillations during the Quaternary. HS, also called HS-DO event, is considered a special DO type in some occasions. Massive ice sheet melting associated with HS occurs during the cold phase of DO cycles, in contradiction to the expectation that ice sheets expand in colder climates and shrink in warmer climates. These events have global climate impacts and thus have been the focus of paleoclimate community for the past several decades, but their triggering mechanism are still under debate. This work summarizes all current available proxy records that contain fingerprints of these abrupt climate oscillations, and discusses limitations in the mechanistic explanations for DO and HS-DO based on current available modeling results, as well as future prospects especially the prospects of modeling these events.

    Figures and Tables | References | Related Articles | Metrics
    The Glacial North Atlantic “Capacitor” effect controlled by seasonal sea ice change
    ZHANG Xu, ZHANG Weichen, WANG Zhenqian, ZHENG Kai, DENG Fengfei
    2022, 29(5): 334-341. 
    DOI: 10.13745/j.esf.sf.2021.9.57

    Abstract ( 226 )   HTML ( 8 )   PDF (7711KB) ( 83 )  

    Millennium-scale climate fluctuations, known as Dansgaard-Oeschger (D-O) events during the last glacial cycle, have been a hot topic in paleoclimatology research. Previous modeling studies show that during the cold DO-stadials the amplitude of interannual-interdecadal climate variability in the subpolar North Atlantic is greater than during the warm DO-interstadials. This phenomenon provides valuable implications for interpreting temperature proxies during D-O events, yet its dynamic mechanism remains unclear. Here, via simulation of a typical D-O event during marine isotope stage 3 (MIS 3) using a fully coupled atmosphere-ocean general circulation model, we explore the mechanism behind the amplitude change in interannual-interdecadal climate variability. We find that subpolar seasonal sea-ice in the northern North Atlantic plays an important role by regulating atmosphere-ocean heat exchange. During stadials, sea subsurface gradually warms up due to the northward transport of tropical warm water masses, weakening the density stratification between sea surface and subsurface, which eventually leads to upwelling of the subsurface warm water masses, promoting sea ice melting and sea surface warming. In turn, the sea level pressure lowers and the associated cyclonic wind stress anomaly accelerates the vertical mixing by Ekman suction, which further promote local upwelling. This positive feedback mechanism results in the rapid release of sea subsurface heat and rapid sea surface warming. As the heat release gradually ceases, surface warming is deaccelerated and even paused, allowing sea ice to regrow. This weakens the low-pressure system and stimulates anti-cyclonic wind anomaly, which in turn reduces the vertical mixing. Consequently, sea temperature drops quickly, meanwhile heat starts accumulating in sea subsurface until the vertical stratification is broken again. During interstadials, with the disappearing of seasonal sea ice in the key convection sites of the North Atlantic, the atmosphere-ocean heat exchange is no longer affected by sea ice. This enables a quasi-static heat exchange between the sea subsurface layer and atmosphere. Our results suggest that the existence of seasonal sea ice effectively regulates sea subsurface heat accumulation and release (as termed sea-ice driven “capacitor” effect) in the subpolar North Atlantic, shining a light on our understanding of the glacial amplification of interannual-interdecadal climate variability.

    Figures and Tables | References | Related Articles | Metrics
    Centennial to millennial variability of the Asian monsoon during the Holocene: Progress in simulation studies
    SUN Weiyi, LIU Jian, YAN Mi, NING Liang
    2022, 29(5): 342-354. 
    DOI: 10.13745/j.esf.sf.2021.9.53

    Abstract ( 338 )   HTML ( 19 )   PDF (4017KB) ( 184 )  

    The development of climate reconstruction greatly promotes the study of Asian monsoon variability in the Holocene. However, the current reconstruction result on the characteristics and mechanisms of the Asian monsoon evolution remains controversial. Meanwhile, paleoclimate simulation can contribute significantly to the understanding of the temporal-spatial characteristics and genetic mechanisms of the Asian monsoon evolution in the Holocene. This paper reviews simulation studies on the centennial to millennial-scale Asian monsoon variations during the Holocene from the perspective of climate modeling, and discusses the mechanisms from the perspectives of external forcing and internal variability. Among the main progresses, the Holocene transient simulation results show a downward trend in the Asian monsoon precipitation since the early Holocene, which is thought to be affected mainly by the earth orbital parameters, as well as changes in land-sea thermal contrast and inter-hemispheric temperature gradient. For centennial-scale weak monsoons, simulation of a 8.2 ka BP weak monsoon event reveals glacial melting water as the main trigger for the weakening of Atlantic meridional overturning circulation and atmospheric teleconnection; whilst simulation of a 4.2 ka BP weak monsoon event indicates such event may be controlled by internal variability rather than external forcing. Simulation studies on the centennial-scale changes mainly focus on the past 2 000 years. The results show an obvious increase of Asian monsoon precipitation during the Medieval Climate Anomaly but a gradual decrease during the Little Ice Age. Solar radiation and volcanic activity play a crucial role in centennial-scale Asian monsoon variations through influencing land-sea thermal contrast and Indo-Pacific sea surface temperature change.

    Figures and Tables | References | Related Articles | Metrics
    Mid-Holocene climate in China and the East Asian monsoon: Insights from PMIP4 simulations
    TIAN Zhiping, ZHANG Ran, JIANG Dabang
    2022, 29(5): 355-371. 
    DOI: 10.13745/j.esf.sf.2021.9.52

    Abstract ( 565 )   HTML ( 30 )   PDF (20509KB) ( 324 )  

    We revisited the climate in China and the East Asian monsoon during the mid-Holocene (6,000 years ago) via PMIP4 (Paleoclimate Modeling Intercomparison Project phase 4) simulation using 14 climate models. Similar to the previous simulation results using PMIP3 models, the mid-Holocene surface air temperatures were cooler for the annual (-0.61 ℃), winter (-1.65 ℃) and spring (-1.69 ℃) means and warmer for the summer (+0.80 ℃) and autumn (+0.08 ℃) means compared to the preindustrial period. The annual and winter cooling results run contrary to the warming results as inferred from most geological records. There was an extra cooling of 0.01-0.45 ℃ over the PMIP3 results, partly due to a reduction in the atmospheric carbon dioxide concentration. By PMIP4 simulation using 11 climate models, the mid-Holocene annual precipitation increased by 2%, evaporation decreased by 1%, and net precipitation (i.e., precipitation minus evaporation) increased by 7% relative to their preindustrial levels in terms of arithmetic means; seasonally, all three variables decreased for winter and spring and increased for summer and autumn. Comparatively, between PMIP4 and PMIP3 models for the above three variables, the differences in their national means and regional changes were relatively larger for summer and autumn than for the year and the other two seasons. And compared to the PMIP3 model results, the annual net precipitation change by PMIP4 simulation is closer to geological records. All 14 PMIP4 models reproduced a consistent strengthening of the East Asian winter and summer monsoon intensities during the mid-Holocene by 11% and 32% on average, respectively, compared to the preindustrial period. Regionally, the increases in monsoon circulation by PMIP4 simulation were larger in the north and smaller in the south of East Asia relative to the increases by PMIP3 simulation.

    Figures and Tables | References | Related Articles | Metrics
    Climate change and the associated glacier response in High-Mountain Asia during the mid-Holocene: A modeling study
    YAN Qing
    2022, 29(5): 372-381. 
    DOI: 10.13745/j.esf.sf.2021.9.55

    Abstract ( 159 )   HTML ( 13 )   PDF (5840KB) ( 94 )  

    Using a 1-km resolution ice sheet model and the results from 11 global climate models in PMIP4, we investigate the spatial features of climatic changes in High-Mountain Asia (HMA) and their effects on glaciation during the mid-Holocene. The multi-model ensemble mean demonstrates that the annual mean temperature averaged across HMA reduces by ~0.7 ℃ during the mid-Holocene relative to pre-industrial, with a warming (0.7 ℃) and cooling (0.7 ℃) in summer and winter, respectively. The annual mean precipitation during the mid-Holocene shows a slight increase (0.5%) in HMA, whereas summer (winter) precipitation changes by +16% (-16%). HMA glaciers exhibit an obvious recession during the mid-Holocene relative to pre-industrial, with a reduction in ice extent (volume) by 13% (8%). Regarding the regional pattern, glaciers of the northern and western HMA retreat by ~58% (47%) and ~26% (25%), respectively, in terms of ice extent (volume). In contrast, glacier advance is observed over the southern HMA, with an increase in ice extent (volume) by ~20% (39%). Additionally, sensitivity experiments suggest that summer warming during the mid-Holocene dominate glacier recession in the northern and western HMA, whereas enhanced precipitation contributes largely to glacier advance in the southern HMA. These results may help to deepen our understanding of the variation of HMA glaciation during the mid-Holocene.

    Figures and Tables | References | Related Articles | Metrics
    Land surface processes and weather research—a review
    CHEN Haishan, DU Xinguan, SUN Yue
    2022, 29(5): 382-400. 
    DOI: 10.13745/j.esf.sf.2021.9.59

    Abstract ( 481 )   HTML ( 25 )   PDF (4089KB) ( 184 )  

    As the lower boundary of the atmosphere, the land surface interacts with the atmosphere through momentum, heat and mass exchanges. Land surface processes have long been recognized as one of the key processes affecting weather and climate, however, although their impacts on climate have been widely studied, their impacts on weather have not received enough attention until recently. This paper reviews the recent research progress on the impacts of land surface elements (soil moisture, etc.), land cover types (topography, land use, etc.) and local circulation (valley-plain circulation, etc.) on weather events, such as strong convection, heavy rainfall, typhoon, high temperature and heat wave, to provide a reference for future study in this field. Even with some progresses made, however, it is noted that further investigation is needed to better understand the physical mechanisms for weather formation, occurrence and development under the influence of land surface processes, especially how they affect the extreme (high impact) weather events, so as to provide scientific support for the numerical modeling study and operational weather forecasting.

    Figures and Tables | References | Related Articles | Metrics
    Possible influence and predictive value of preceding winter sea ice anomalies in the Davis Strait-Baffin Bay for spring extreme precipitation frequency in eastern China
    ZHANG Mengqi, SUN Jianqi, GAO Yongqi
    2022, 29(5): 401-409. 
    DOI: 10.13745/j.esf.sf.2021.9.60

    Abstract ( 230 )   HTML ( 5 )   PDF (7228KB) ( 71 )  

    This study investigates the relationship between winter Arctic sea ice cover (SIC) and the frequency of spring extreme precipitation in eastern China and the underlying mechanisms. Furthermore, the predictive value of anomalous Arctic SIC signal for spring extreme precipitation in eastern China is explored. A close correlation is revealed between the first empirical orthogonal function mode (EOF1) of the spring extreme precipitation frequency and SIC anomalies in the Davis Strait-Baffin Bay (DSBB) in the preceding winter. In the North Atlantic, increasing in winter SIC anomaly is accompanied by anomalous winter atmospheric circulation that shows a positive North Atlantic Oscillation-like (NAO-like) distribution pattern, along with meridional tripolar sea surface temperature (SST) anomalies. North Atlantic SST anomalies can persist from the preceding winter to spring, further exciting a wave train from the North Atlantic to mid-latitude Eurasia and inducing cyclonic anomalies in East Asia. Such cyclonic anomalies can significantly increase humidity and upward air motion in eastern China, providing favorable conditions for extreme precipitation in the region. In contrast, decreasing in winter SIC anomaly causes delayed anomalous spring atmospheric circulation unfavorable for extreme precipitation in eastern China. Results of leave-one-out cross-validation further indicate that this anomalous SIC signal has positive predictive value for spring extreme precipitation in eastern China.

    Figures and Tables | References | Related Articles | Metrics
    Regional rainstorm changes in China: Ensemble projection via RegCM4 dynamical downscaling
    ZHOU Botao, CAI Yiheng, HAN Zhenyu
    2022, 29(5): 410-419. 
    DOI: 10.13745/j.esf.sf.2021.9.61

    Abstract ( 201 )   HTML ( 8 )   PDF (6127KB) ( 80 )  

    Regional rainstorms usually occur over large areas and persist for a long time, which can lead to severe flooding disasters and pose serious risks to the sustainable socioeconomic development of the affected areas. Thus, projection of regional rainstorm changes is crucial for climate change adaptation and disaster risk management in China. Based on regional dynamical downscaling with RegCM4 from four global climate models, this study firstly identifies regional rainstorm events by a “tracing” method, and then projects changes in 5 rainstorm parameters—frequency, duration, average amount, average affected area, and comprehensive intensity—during the 21st century under the RCP4.5 scenario. The resulting ensemble projection indicates national-scale rising trends in all 5 rainstorm parameters toward the end of the 21st century. Relative to 1986-2005, the proportion of regional rainstorms with high rainstorm parameter values is projected to increase during mid- and end-21st century, while small rainstorm parameter values occur less frequently. Spatially, the frequency, duration, and amount of regional rainstorms are projected to increase across eastern China, with similar spatial distribution patterns for the amplitude increase. The largest increase is in the middle and lower reaches of the Yangtze River valley and southern China, with larger increases towards the end of the 21st century.

    Figures and Tables | References | Related Articles | Metrics
    Research methods for the deep extension pattern of rock/ore-controlling structures of magmatic-hydrothermal ore deposits—a preliminary study
    HAN Runsheng, ZHAO Dong
    2022, 29(5): 420-437. 
    DOI: 10.13745/j.esf.sf.2021.11.1

    Abstract ( 250 )   HTML ( 11 )   PDF (14978KB) ( 475 )  

    The lack of understandings about the deep distribution pattern of rock/ore-controlling structures of magmatic-hydrothermal ore deposits and the spatial positioning pattern of deep deposits (or orebodies) is the main problem holding back deep mineral exploration deployment and hindering ore prospecting breakthroughs. This paper discusses first the main research methods for the deep extension patter of the controlling structures of magmatic-hydrothermal orefields (or deposits). Based on the discussed methods and following the idea that hydrothermal polymetallic ore deposits controlled by regional metallotectonics are associated with geophysical and geochemical anomalies, this paper, taking the Huangshaping-Baoshan copper-tin polymetallic orefield in southern Hunan as an example, constructs a theoretical framework for analyzing the rock/ore-controlling structures and their extension patterns as well as a comprehensive evaluation index system for assessing the depth extension of the controlling structures. Using these methods, through comprehensive analyses of the rock/ore-controlling structures as well as mineralization alteration zoning pattern for magmatic-hydrothermal porphyry in the orefield, this paper predicts the depth extension patterns of the rock/ore-controlling structures and favorable prospecting target sites (within the controlling structures) for the Huangshaping and Baoshan deposits. This paper provides a new method for deep exploration deployment and ore prospecting in the Huangshaping-Baoshan copper-tin polymetallic orefield, and, without doubt, this method can be referenced for advancing the theories of rock/ore-controlling structures and deep prospecting and exploration for other hydrothermal ore deposits.

    Figures and Tables | References | Related Articles | Metrics
    Petrogenesis of Early Cretaceous Qibaoshan alkaline intrusive rocks in the Wulian area and its geological significance
    LI Xiaowei, SHAN Wei, YU Xuefeng, LI Dapeng, XIE Yuanhui, ZHANG Guokun, CHI Naijie, WANG Wenlu, ZHANG Yan, LI Zengsheng, MA Xiangxian
    2022, 29(5): 438-463. 
    DOI: 10.13745/j.esf.sf.2022.1.19

    Abstract ( 244 )   HTML ( 11 )   PDF (7058KB) ( 186 )  

    Located in the central part of the volcanic edifice, the Qibaoshan alkaline intermediate-mafic intrusive pluton is characterized by high Ba-Sr contents, high Nb/Ta and Zr/Hf ratios, and low Ti/Eu ratio. Previous studies indicate this pluton originates from an enriched metasomatized mantle source; however, its dynamic processes—reflected by the changes in its lithology and geochemical composition—are not yet clear. Here, through detailed mineralogical and whole-rock geochemical analyses, we identified the Qibaoshan alkaline intrusive rocks are of both sodic and potassic series. These alkaline intrusive rocks display enrichments in total alkalis, light rare earth element (LREE), and large-ion lithophile elements (LILE) (e.g., Ba and Sr), as well as high (La/Yb)N and (Gd/Yb)N values. Two types of clinopyroxenes/plagioclases are identified; and they, as antecrysts, record multiple batches of magmas/melts during the formation of these alkaline intrusive rocks. Combined with previously published data, we propose that the source region of the Qibaoshan alkaline intrusive rocks is of enriched mantle metasomatized by sediments, and contains phlogopite and amphibole veins. Concurrent partial melting of these veins and ambient mantle peridotites produced primitive alkaline melts. The high Nb/Ta and Zr/Hf ratios, low Ti/Eu ratio, as well as negative Ti* and Hf* anomalies in the primitive mantle-normalized trace element patterns collectively indicate significant contribution by carbonatite melt to forming the Qibaoshan alkaline rocks. The presence of both sodic and potassic series points to the pivotal roles different dominating buffering minerals (amphibole vs. phlogopite) play in the mantle source. In addition, the potassic series exhibit abnormally high Rb-Zr-Hf-U contents, probably reflecting an upward transport of zircon melts—formed from dissolution of hydrothermal zircons—to the magma reservoir during the partial melting in the source region. This study highlights the significant contribution by carbonate melts in the formation of high Nb/Ta alkaline intermediate-mafic rocks, and also emphasizes the addition of dissolved hydrothermal zircons to form high Zr-Hf-U alkaline magmas.

    Figures and Tables | References | Related Articles | Metrics
    Machine learning-based approach for zircon classification and genesis determination
    ZHU Ziyi, ZHOU Fei, WANG Yu, ZHOU Tong, HOU Zhaoliang, QIU Kunfeng
    2022, 29(5): 464-475. 
    DOI: 10.13745/j.esf.sf.2022.2.75

    Abstract ( 471 )   HTML ( 29 )   PDF (4999KB) ( 333 )  

    Zircon, a stable paragenetic mineral in various geological environments, has been recognized as a great tool in the chronological study of primary rocks. Trace elements in zircons may reveal geological evolutionary processes, and have long been used in zircon classification and zircon formation studies by binary diagram method, such as Th-U and LaN-(Sm/La)N diagrams. However, with the massive increase of zircon research, the traditional binary diagrams are no longer adequate for a precise determination of zircon types because binary plots cannot display higher dimensional information and therefore can lead to erroneous interpretation of zircon data. To address this issue, we take a machine learning approach to analyzing 3 498 zircon trace element data for different zircon genetic types to obtain high-dimensional zircon classification diagrams. We tested four machine learning algorithms (random forest, support vector machine, artificial neural network, and k-nearest neighbor) and consider support vector machine, with an 86.8% accuracy in predicting zircon type and origin, can best contribute to zircon classification. In addition to the development of a high-dimensional zircon classification diagram, this work also greatly improves the accuracy of zircon genesis determination using trace elements, and demonstrates the applicability of modern data science technique in geochemical research.

    Figures and Tables | References | Related Articles | Metrics
    Noble gas geochemical characteristics of shallow hydrate in the deep water of the Qiongdongnan Basin and their significance
    SUN Tao, WU Tao, GE Yang, FAN Qi, LI Lixia, LÜ Xin
    2022, 29(5): 476-482. 
    DOI: 10.13745/j.esf.sf.2022.2.59

    Abstract ( 200 )   HTML ( 6 )   PDF (2507KB) ( 101 )  

    The deep water area of the Qiongdongnan Basin possesses favorable geological condition for gas hydrate accumulation and is one of the leading demonstration areas for marine gas hydrate exploration and development. Based on geochemical analyses of natural gas and noble gases, this paper selects the shallow surface hydrate of the deep water area to carry out a comparative study relating to deep conventional natural gas reservoirs. The results show that shallow surface gas in the study area shares similar carbon isotope characteristics with deep conventional natural gas. The gas source is mainly deep thermogenic gas, with no obvious contribution from biogas, and genetically relates to coal-type gas. It is speculated that the gas source is the coal measure strata of the Yacheng Formation. The Ar isotopic compositions of light noble gases show that the gas source rock is related to the Tertiary formation, whilst the high 3He/4He ratios in samples indicate certain contributions from mantle derived gas. Therefore, under the background of gas-rich depression, it is of great significance to discuss the deep thermogenic gas for hydrate accumulation. The deep thermogenic gas reservoir and shallow hydrate reservoir can form a vertical three-dimensional gas reservoir, which lends theoretical support in future “multi-gas exploitation” for improving economic benefits of gas hydrate reservoir development in deep water areas.

    Figures and Tables | References | Related Articles | Metrics
    High permeability zone of Cretaceous porous carbonate reservoir of A Field, Iraq: Genesis and distribution characteristics
    WANG Genjiu, SONG Xinmin, LIU Bo, SHI Kaibo, LIU Hangyu
    2022, 29(5): 483-496. 
    DOI: 10.13745/j.esf.sf.2022.2.60

    Abstract ( 188 )   HTML ( 6 )   PDF (19841KB) ( 243 )  

    The high permeability zone of Cretaceous porous carbonate reservoir with complex reservoir type and origin developed extensively cross the A Field, Iraq. The rock types in the high permeability zone are mainly argillaceous clastic limestone, clastic limestone and micrite bioclastic limestone, whilst bioturbation increases reservoir heterogeneity causing it to expand. Here, we carried out core and thin section analyses along with porosity, permeability, capillary pressure and probe permeability measurements to investigate the characteristics and genesis of the high permeability zone. Combined with regional geology, we conclude that the formation of high permeability zone is controlled by stratigraphic evolution, sea level change, sedimentary environment, bioturbation, etc. The high permeability zone is thought to originate in the lower Khasib Formation, where in the Kh2-1-2 layer during deposition sedimentary discontinuity is formed as sea level declines, meanwhile bioturbation leads to formation of burrow network tens of centimeters thick. As deposition ends, sea level rises and bioclastic grainstones fill the pores, without cementation, to form finely connected pores. As sea level declines again, the reservoir is exposed, and dissolved pores are generated. Thus a high permeability zone made of intergranular pores, dissolved pores and dissolved seams is formed. In the high permeability zone of the A Field, locations with physical properties consistent with strong bioturbation—such as relatively thick pore throat, high pore-throat coordination number, and good connectivity—have obvious high permeability characteristics. The high permeability zone, developing stably across the oil field with its thickness gradually increasing from west to east, greatly influences the development and production of the oil field.

    Figures and Tables | References | Related Articles | Metrics
    Effects of lomefloxacin and norfloxacin on the biological water denitrification process—an experimental study
    ZHANG Yuye, HE Jiangtao, DENG Lu, ZOU Hua, ZHANG Jingang, YANG Meiping
    2022, 29(5): 497-507. 
    DOI: 10.13745/j.esf.sf.2022.1.22

    Abstract ( 492 )   HTML ( 9 )   PDF (4377KB) ( 65 )  

    Nitrate and antibiotic pollutions in water have attracted much attention in recent years, but the effects of combination antibiotic pollution on the biological water denitrification process is not clear. To address this issue, we tested norfloxacin and lomefloxacin under simulated experimental conditions. The $\text{NO}_{3}^{-}$-N and $\text{NO}_{2}^{-}$-N degradation results showed that lomefloxacin and norfloxacin had different inhibitory effects on water denitrification: Lomefloxacin promoted denitrification slightly in the early stage but inhibited it later on, whereas norfloxacin only inhibited it. Lomefloxacin combined with norfloxacin were less inhibitory than norfloxacin alone, and the combination showed antagonistic activity. The inhibitory activities of antibiotics ranked as norfloxacin > norfloxacin + lomefloxacin > lomefloxacin. Although the simulated experimental conditions did not fully match the actual water condition, the above results implied that combination antibiotics have antagonistic effects on the denitrification process. Such effects were related largely to the microbial numbers and activities, activities of denitrification enzymes, as well as abundance variations of dominant denitrifying bacteria Achromobacter xylosoxidans, Acinetobacter baumannii, and Pseudomonas sp. KY and the nosZ and aac genes. As reaction time increased, the denitrifying bacteria gradually adapted to the environment of low-level antibiotics and the number of quinolone resistance genes increased; also on the rise were the amount and activities of denitrifying bacteria, activities of denitrification enzymes, and microbial communities.

    Figures and Tables | References | Related Articles | Metrics