2022, Volume 29 Issue 4
    25 July 2022
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    Deep-sea sediments and global change: Research frontiers and challenges
    LIU Zhifei, CHEN Jianfang, SHI Xuefa
    2022, 29(4): 1-9. 
    DOI: 10.13745/j.esf.sf.2022.6.28

    Abstract ( 127 )   HTML ( 9 )   PDF (3375KB) ( 136 )  

    Present-day oceans are experiencing the effects of global change such as warming and acidification caused by human activities. Deep-sea sediments store a detailed archive of past global changes driven by nature during Earth’s evolution. By exploring today’s and past global change processes, we can reveal the characteristics and laws of global change and provide a basis for predicting future changes. The outstanding research progresses made in recent years were the discovery in the deep-sea of a variety of analogous scenarios that humans, when choosing future greenhouse gas emission trajectories, can reference to for evaluating future changes—their processes and consequences —in the Earth system. Among such scenarios, millennium-scale climate events, represented by the Dansgaard-Oeschger oscillation, and decadal-scale climate events, represented by the El Nino-Southern Oscillation (ENSO) and the North Atlantic Oscillation (NAO), are the closest rapid climate change analogues to today’s global warming. The Earth system is currently at the beginning of a “Hothouse Earth” emission trajectory. If the system passes the “tipping points”, it will follow an irreversible path to a “Hothouse Earth” state; whereas an alternative path may lead to a “Stabilized Earth” state. Analogous scenarios in the deep-sea sedimentary archive can provide societies with valuable information in choosing future emission trajectories. The major challenges for researchers are to fully understand the mechanisms of the key processes of global change. Taking the example of ocean warming and acidification’s influence on diatom and coccolithophore functioning as marine biological pump. The conventional knowledge has suggested that acidification is beneficial to diatom formation; but recent mesocosm experiments have found that global diatom output is significantly reduced. Likewise, the suggestion that acidification leads to calcification crisis in marine life has also been proven wrong, as recent black shale studies of Mesozoic oceanic anoxic events showed that calcium carbonate output from coccolithophores increased significantly during ocean acidification. The above examples demonstrate that conventional knowledges of the key processes of global change are under serious challenge.

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    Research progress in global sea level change: A critical review on international ocean drilling
    HU Zhaobin, WEI Jiangong, XIE Zhiyuan, ZHANG Huodai, ZHONG Guangfa
    2022, 29(4): 10-24. 
    DOI: 10.13745/j.esf.sf.2022.1.16

    Abstract ( 85 )   HTML ( 10 )   PDF (5443KB) ( 97 )  

    The international scientific ocean drilling programs (DSDP, ODP, IODP) began focusing on global sea level changes in the early 1980s. So far, 23 related expeditions have been implemented in areas including passive continental margins, isolated carbonate platforms, mixed platform margins and guyots. As a result, a large number of drilling data have been collected to provide key research data. Based on these data, many achievements have been made, including the reconstruction of the history of global sea level changes during the past 100 Ma. In addition, the sea level hypothesis presented by scientists from EXXON was tested, the stratigraphic response to sea level change was clarified, and the relationship between the evolution of the Antarctic ice sheet and sea level changes was established. Nevertheless, research deficiencies still exist, such as inadequate representation of drilling areas, entanglement of sea level information with local geological effects (e.g., tectonic subsidence), inaccurate sea level change recording, and a lack of understandings of the stratigraphic responses to and mechanisms of sea level changes (especially the influence of ice sheet dynamics and the cause of sea level changes in warm period). Under the background of today’s climate warming, resolving these issues will help making sea level change predictions more reliable.

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    Depositional patterns of the Bengal-Nicobar Fan system since the Late Miocene: Seesaw-like stepwise changes and the source-sink model
    GONG Chenglin, LIU Li, SHAO Dali, GUO Rongtao, ZHU Yijie, QI Kun
    2022, 29(4): 25-41. 
    DOI: 10.13745/j.esf.sf.2022.1.1

    Abstract ( 84 )   HTML ( 10 )   PDF (11080KB) ( 53 )  

    Tectonic and climate reconstruction based on punctuated, abrupt changes in depositional patterns represents a new research focus in source-sink analysis. Since the Cenozoic, the convergence of the India and Asian plates, and the subsequent Himalayan exhumation, erosion and sediment transport to the Bengal Bay, formed the world largest source-sink system. Our current study mainly employed 3D seismic and detrital zircon U-Pb age data to address the punctuated, abrupt changes in the depositional patterns of the Bengal-Nicobar Fan system since the Late Miocene, and explore the genetic mechanism of these changes according to the source-sink model. Our findings suggest a seesaw-like stepwise evolution and development of the Bengal-Nicobar Fan system. The Nicobar Fan experienced progradation in the Late Miocene, slow growth in the Pliocene and dormant growth in the Quaternary, which run opposite to the evolution of the Bengal Fan. The U-Pb detrital zircon chronology of the Himalayan-Bengal source-sink system by normalized kernel-density estimates suggest that since the Late Miocene, the 60-0 Ma zircon age populations (indicative of the Brahmaputra sediment routing system) progressively decreased in the Rakhine-Nicobar Fan while increased gradually in the Bengal Fan, revealing an overall stepwise evolutionary pattern of the Brahmaputra sediment routing system. In the Late Miocene, the Brahmaputra River with robust delivery capacity developed along the eastern Bengal Bay delivering large volume of clastic detritus into the Nicobar Fan; whereas the Tista and Ganges Rivers with low delivery capacity developed along the western Bengal Bay transporting small volume of detrital sediments into the Bengal Fan. Such a sediment routing system fostered progradation in the Nicobar Fan and dormant growth in the Bengal Fan. In the Pliocene, the uplift of the Shillong Plateau led to divergence of the Brahmaputra River into eastern and western tributaries. The eastern Brahmaputra tributary with deceased delivery capacity delivered less clastic detritus into the Nicobar Fan, whereas the western Brahmaputra River merged with the Tista and Ganges Rivers to deliver more detrital sediments into the Bengal Fan. Such a sediment routing system fostered slow growth in the Nicobar and Bengal Fans. In the Quaternary, convergence of the Shillong Plateau and Indo-Burman Ranges disrupted sediment transport to the Nicobar Fan via the eastern Brahmaputra tributary; whereas the merge of Brahmaputra River with Tista and Ganges Rivers ensured all sediment budget going into the Bengal Fan. Such a sediment routing system fostered progradation in the Bengal Fan and relatively slow growth in the Nicobar Fan. The most prominent changes in the depositional patterns of the Bengal-Nicobar Fans happened in the Late Pliocene reflecting the source-sink depositional response to the most intense collision between the Indian and Asian plates.

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    Mineralogical and geochemical constraints on the origin of rhythmic layering of Late Miocene reddish-brown and greenish-gray sediments in the northern South China Sea
    DONG Hongkun, WAN Shiming, LIU Chang, ZHAO Debo, ZENG Zhigang, LI Anchun
    2022, 29(4): 42-54. 
    DOI: 10.13745/j.esf.sf.2022.1.11

    Abstract ( 83 )   HTML ( 3 )   PDF (3091KB) ( 43 )  

    Sediment color is an important indicator of sediment composition and formation environment and can be used for the reconstruction of paleoceanographic environments. During the International Ocean Discovery Program (IODP) Expedition 368, hundreds of meters of rhythmic reddish-brown and greenish-gray sedimentary layer were found in the sediment core at Site U1502 in the northern South China Sea (SCS); however, the origin of the rhythmic layers remains unclear. In order to understand its causes, we carried out mineralogical and geochemical analyses of core samples on grain size, clay minerals, major and trace elements, Sr-Nd isotopic compositions, organic carbon contents and carbonate C-O isotopic compositions. The sediments are mainly sourced from the Pearl River, with a minor contribution from the Luzon Island and the material input was slightly higher in the reddish-brown layer than in the greenish-gray layer. The geochemical indicators showed that the formation of the reddish-brown and greenish-gray layers was not affected by hydrothermal and cold seep fluids, rather it was influenced by a combination of tectonic evolution of SCS in the Late Miocene and changes of deep-water ventilation and redox environment and early diagenesis during the glacial-interglacial cycle. Combined with the previous provenance studies in northern SCS and spectral analysis of sediment color in this study, we suggest that the reddish-brown and greenish-gray layers may be associated respectively with the interglacial and glacial periods. The redox indicator indicated that the reddish-brown and greenish-gray layers were formed respectively in more oxidative and more reductive bottom water environments. Since the Middle Miocene, following the collision between the Luzon arc and Eurasian plate, the SCS basin evolved from an open environment to a relatively closed marginal sea, and its deep ventilation and redox conditions began to reflect typical glacial-interglacial cycling. The reddish-brown layer corresponds to the sedimentary environment with well ventilated and more oxidized deep water during the interglacial period with high sea level; while the greenish-gray layer indicates an environment of strengthened stratification and partial reduction of deep water during the glacial period with low sea level. Distinct redox conditions control the formation and transformation of chromogenic iron-bearing authigenic minerals such as hematite in the early diagenesis, and thus give rise to the rhythmic variation of sediment color.

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    Quaternary Qiongdongnan Basin in South China Sea: Shelf-edge trajectory migration and deep-water depositional models
    MA Chang, GE Jiawang, ZHAO Xiaoming, LIAO Jin, YAO Zhe, ZHU Jitian, FANG Xiaoyu, XIANG Zhu
    2022, 29(4): 55-72. 
    DOI: 10.13745/j.esf.sf.2022.1.2

    Abstract ( 44 )   HTML ( 3 )   PDF (7553KB) ( 37 )  

    The shelf-edge trajectory is comprehensively controlled by tectonics, sediment supply, sea level and climate, and its migration and evolution are closely related to the deep-water depositional systems. The shelf-edge clinoform stacking pattern, sediment-budget partition in deep-water areas and reservoir evaluations are current geoscience hot topics. Based on the newly acquired high-precision, high-density 2D seismic data of the Qiongdongnan Basin (QDNB), this paper quantitatively characterized the Quaternary shelf-edge trajectory and identified three trajectory types in QDNB: flat to slightly rising, moderately rising and steeply rising types. Since 2.4 Ma the temporal evolution of the shelf-edge trajectory in QDNB can be divided into three stages with lateral differences: 2.4-1.9 Ma, mainly the slightly rising type; 1.9-0.8 Ma, the slightly rising type in the western part and moderately rising type in the eastern part; 0.8 Ma-present, the moderately rising type in the western part and steeply rising type in the eastern part. The vertical migration of the shelf-edge trajectory is jointly controlled by the rise and fall of sea level caused by climate change and associated with sediment supply. The differences in tectonic activity and provenance supply lead to lateral variations of the shelf-edge trajectory and progradation or aggradation stacking patterns. According to the above studies, when the shelf-edge trajectory angle, α, is between 0° and 4°, the continental slope canyons are small-scaled and shallow mostly, with developments of multistage large-scale submarine fan deposits in the deep-water area but less mass-transport deposits (MTDs). When 4° <α< 35° the continental slope canyons increase in scale, with occurrences of both submarine fan deposits and MTDs. When 35°<α<90° a few but steep continental slope canyons are developed, along with developments of mainly large-scale MTDs in the deep-water plains, almost without submarine fan deposits. Since the Quaternary the temperature in QDNB continues to drop while the East Asian winter monsoon increases significantly, causing the sediment supply to increase; while decreasing sea level results in progradation at the northwestern shelf edge. In comparison, frequent fault activities and relatively low sediment supply at the northeastern shelf edge result in a much shorter slope advance distance and developments of multistage MTDs. Results of this study have theoretical significance for the predictions of continental shelf-edge system and deep-water deposition in QDNB and other basins.

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    Provenance and paleoclimatic significance of clay minerals from Izu-Ogasawara Ridge since Pliocene
    YANG Jiayi, JIANG Fuqing, YAN Yu, ZHENG Hao, CHANG Fengming
    2022, 29(4): 73-83. 
    DOI: 10.13745/j.esf.sf.2022.1.8

    Abstract ( 58 )   HTML ( 5 )   PDF (2465KB) ( 23 )  

    The composition and mineralogical characteristics of clay minerals in sediments from ODP Hole 782A, Izu-Ogasawara Ridge since the Pliocene were analyzed. According to the results, the clay minerals were mainly composed of illite (average 42%) and smectite (average 42%), with moderate chlorite (average 14%) and minor kaolinite (average 2%). The low crystallinity (average 0.25°Δ2θ) and chemical index (average 0.31) of illite indicated the mineral was mainly from a cold, dry environment. By comparing clay mineralogy and clay mineral assemblages and contents between ODP Hole 782A and potential source areas, we argue that smectite is mainly derived from island arc volcanic materials around Izu-Ogasawara Ridge, and that illite, chlorite and kaolinite are mainly from aeolian dust of the Asian continent. The (illite + chlorite)/smectite ratio increased overall since the Pliocene and varied in three stages: 5.3-3.6 Ma, 3.6-1.6 Ma and 1.6-0 Ma. The variations are roughly synchronized with the global cooling recorded by deep sea δ18O, the enhanced aridity in Asia recorded by dust flux in ODP Hole 885/886 in North Pacific, the sedimentary rate of Lingtai loess, and the illite/smectite ratio in IODP Site U1430 in Japan Sea. These evidences suggested that the (illite + chlorite)/smectite ratio in ODP Hole 782A is sensitive to global cooling and aridity in Asia. Since the Pliocene, the (illite + chlorite)/kaolinite ratio oscillates between high and low in accordance with the high/low changes of magnetic susceptibility of Lingtai loess. As the loess magnetic susceptibility records the dry/wet changes in Asia, we argue that the (illite + chlorite)/kaolinite ratio in ODP Hole 782A is sensitive to the paleoclimate changes in Asian inland, and, therefore, can be used as a reliable proxy of the dry/wet changes in Asia.

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    Carbon and oxygen isotopic characteristics of benthic foraminifera in the Okinawa Trough since MIS6 and their palaeoceanographical significance
    DOU Yanguang, LI Qing, WU Yonghua, ZHAO Jingtao, SUN Chenghui, CAI Feng, CHEN Xiaohui, ZHANG Yong, FAN Jiahui, SHI Xuefa
    2022, 29(4): 84-92. 
    DOI: 10.13745/j.esf.sf.2022.1.14

    Abstract ( 44 )   HTML ( 2 )   PDF (2229KB) ( 27 )  

    Based on the stratigraphic age framework constructed by AMS14C ages and benthic foraminiferal oxygen isotopic analysis, the δ13C characteristics of benthic foraminifera and their palaeoceanographical significance were analyzed for core CHHC-15 in central and northern Okinawa Trough since marine isotope stage 6 (MIS6) around 200 ka BP. According to the results, the δ13C negative deviation in MIS4 and MIS 6 and positive deviation in MIS1, MIS3 and MIS5 mainly reflect the changes in surface primary productivity and organic matter flux during glacial-interglacial cycles; whilst the δ13C positive deviation in MIS2 indicates NPIW incursion into the Okinawa Trough since the LGM which resulted in enhanced ventilation and weak oxidation of the bottom water. The large δ13C negative deviation in MIS4 is likely caused by methane anaerobic oxidation (AOM).

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    Exploring biomineralization in the tropical western Pacific sediments based on phospholipid fatty acid analysis
    YANG Ziyang, REN Denglong, HE Zhipeng, LI Xuegang, SONG Jinming, YUAN Huamao, DUAN Liqin, LI Ning, ZHANG Qian
    2022, 29(4): 93-102. 
    DOI: 10.13745/j.esf.sf.2022.1.3

    Abstract ( 41 )   HTML ( 0 )   PDF (2208KB) ( 19 )  

    Identification of marine sediment mineralization processes plays an important role in the study of biogeochemical cycling of biogenic elements, although such processes—including aerobic respiration, nitrate reduction, iron and manganese reduction, sulfate reduction, etc. —can be difficult to distinguish one from another. In this study, gas chromatography-mass spectrometry (GC-MS) was used to analyze the phospholipid fatty acid (PLFA) profiles and their influencing factors in different mineralization processes, and further explore the use of PLFAs as sediment mineralization indicator in the tropical western Pacific. The total PLFA content was found to be highest in aerobic respiration and lowest in nitrate reduction. The obvious decrease of the sum of 14:0, i14:0, i15:0 and i19:0—the main components of microbial PLFA in aerobic respiration—could have certain indication for the occurrence of nitrate reduction; whilst the decrease of the sum of 10:0, 17:0, 20:0 and 22:0 could indicate the occurrence of sulfate reduction. In the sediments of the tropical western Pacific, the total organic carbon (TOC), total organic nitrogen (TON) and NO3-N content in porewater were important factors influencing PLFA. as the total PLFA content decreased with decreasing TOC and TON, whilst the degradation of TOC and TON promoted the degradation of PLFA, which had a more direct impact on the PLFA composition.

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    Silicon limitation and replenishment in central Arctic Chukchi Sea Shelf region during ice melting period
    LIU Jie, LI Zhongqiao, ZHANG Anyu, REN Jian, BAI Youcheng, ZHUANG Yanpei, LI Yangjie, LI Hongliang, JIN Haiyan, CHEN Jianfang
    2022, 29(4): 103-112. 
    DOI: 10.13745/j.esf.sf.2022.1.17

    Abstract ( 45 )   HTML ( 2 )   PDF (2601KB) ( 26 )  

    The relatively nitrogen-deprived (16>N:P≈7) nutrients carried by Pacific water inflow provide important support to the upper Arctic Ocean ecosystem. In the Chukchi Sea Shelf region nutrient consumption is strong as sea ice retreats and light becomes more accessible. It is generally believed that the primary production of this region is mainly limited by nitrogen, while little is known about other nutrients including silicate. In this study, based on the results of two simultaneous voyages—the 2016 Chinese Arctic Research Expedition and the 2016 Chinese-Russian “Arctic Silk Road” Expedition—we revealed the distribution pattern of nutrients in the entire shelf region during ice melting period. The nitrite and nitrate surface layers are nearly exhausted over a wide area, while silicate is low in the shelf center and high in the surrounding areas, indicating silicon and nitrogen are both limited at the shelf center. Along the path of Pacific water inflow, silicate concentrations are higher at depths above 30 m at stations S01, R01 and LV77-01 than at the end of water inflow, indicating silicate is released to the bottom water from sediment pore water. Therefore, sediment pore water can be potential source of silicate for the upper ocean in shallow shelf areas. In this study, combined with literature data, the calculated average silicate flux at the shelf sediment-water interface was 630.78 mmol·m-2·a-1, or 3.75×1011 mol·a-1 in total silicate, which equaled to half of silicate carried by Pacific water inflow (6.59×1011 mol·a-1). Thus sediment pore water is also an important source of silicate in the Chukchi Sea Shelf region.

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    The evolution of paleoproductivity since the Middle Holocene in the Cosmonaut Sea, Antarctic
    HU Bingyao, LONG Feijiang, HAN Xibin, ZHANG Yongcong, HU Liangming, XIANG Bo, GE Qian, BIAN Yeping
    2022, 29(4): 113-122. 
    DOI: 10.13745/j.esf.sf.2022.1.12

    Abstract ( 53 )   HTML ( 1 )   PDF (2176KB) ( 33 )  

    Aiming to reconstruct the paleoproductivity evolution and its constraints in the Cosmonaut Sea since the Middle Holocene (6500 Cal a BP), a series of experiments including AMS14C dating, radionuclide 210Pb testing, XRF core scan, multi-parameter spectrophotometer probe as well as major and trace elemental analysis were conducted on sediment core ANT36-C4-05 collected from the Cosmonaut Sea, Antarctic. The results showed that paleoproductivity in the Cosmonaut Sea fluctuates strongly since the Middle Holocene, and its evolutionary trend is largely consistent with the temperature change in Antarctic constrained mainly by the change of sea ice range. During the period of 6500-5200 Cal a BP, paleoproductivity increased rapidly with increasing temperature and decreasing sea ice range, and remained high with little fluctuation between 5200-3350 Cal a BP. During 3350-2000 Cal a BP siliceous and calcareous productivity decreased with decreasing temperature and expanding sea ice range. Paleoproductivity variability became complex with smaller fluctuation during 2000-0 Cal a BP. Moreover, sedimentary records of the Cosmonaut Sea since the Middle Holocene showed that the most obvious paleoproductivity fluctuations were associated with the cold period of 5500 Cal a BP, the Dark Age Cold Period, the Medieval Warm Period, and the Little Ice Age.

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    Stable carbon and nitrogen isotope variations in sedimentary organic matter in the Sea of Japan since 37 ka: Paleoceanographic implications
    ZOU Jianjun, ZONG Xian, ZHU Aimei, DOU Ruxi, LIN Jinhui, FENG Xuguang, DONG Zhi, Sergey A. GORBARENKO, ZHENG Liwei, SHI Xuefa
    2022, 29(4): 123-135. 
    DOI: 10.13745/j.esf.sf.2022.1.6

    Abstract ( 50 )   HTML ( 2 )   PDF (3369KB) ( 33 )  

    Stable carbon and nitrogen isotopes in sedimentary organic matter (δ13C and δ15N) have been widely used in the organic matter source tracing and reconstruction of paleoproductivity and paleoenvironment. A pronounced feature of sedimentary δ13C and δ15N in the Sea of Japan is their synchronous negative excursions during the Last Glacial Maximum (LGM), yet the causes and mechanisms of this phenomenon are poorly understood. In this study, we investigated the evolutionary history of sedimentary δ13C and δ15N since 37 ka in core LV53-23-1 retrieved from the Oki Ridge of the central Sea of Japan. According to the results, sedimentary δ13C and δ15N ranged from 26.3‰ to 22.5‰ and 1.6‰ to 6.1‰, respectively, with the lower values coinciding with the deposition of dark laminated mud during the LGM (26.5-17 ka), indicating an increased contribution of terrestrial organic matter. Both δ13C and δ15N showed positive excursions during Heinrich Statidal 1 (17-14.5 ka), indicating distinct oceanic environmental changes in the Sea of Japan, which corresponds to the Tsushima Strait flooding and the Tsushima Warm Current invasion into the Sea of Japan at that time. After 14.5 ka sedimentary δ15N reached ~5‰, comparable to the average δ15N of nitrate in seawater. We estimated the relative contributions of organic sources using a binary mixing model. The contribution of terrigenous organic matter ranged between 65% to 80% in the LGM, while marine source contributed between 60% to 80% since 14.5 ka. Besides, sedimentary δ15N depletion during the LGM can be caused by (1) improved nitrogen fixation in the surface water of the Sea of Japan due to higher dust-borne Fe supply, and (2) decreased effects of early diagenesis on sedimentary δ15N due to prevailing suboxic or anoxic environment. Taken together, the variations of sedimentary δ13C and δ15N in the Sea of Japan since 37 ka are controlled by eustatic sea level and global climate changes, which modulate the organic source, nutrient supply, primary productivity, and redox conditions in water column and sediment.

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    Productivity evolution in the southeastern Bay of Bengal since the last glaciation: Insight from biogenic silica records
    ZHANG Lanlan, QIU Zhuoya, XIANG Rong, YANG Yiping, CHENG Muhong
    2022, 29(4): 136-143. 
    DOI: 10.13745/j.esf.sf.2022.1.15

    Abstract ( 37 )   HTML ( 3 )   PDF (1886KB) ( 16 )  

    Based on the biogenic silica (BSi) records, combined with the calcium carbonate (CaCO3) and siliceous radiolarian data, the evolution of productivity and climatic response in the southeastern Bay of Bengal (SEBoB) since the last glaciation is revealed. The productivity evolution in the study area is roughly divided into three stages: relatively low productivity during the last glaciation (~56-18 ka), rapid productivity increase during the last deglaciation (~18-10 ka), and ultra high productivity during the Holocene. Radiolarian species in the sediments of the last glaciation were dominated (~60%) by highly silicified Zygocircus/Amphispyris with the sagittal ring structure, whereas slender shaped ones with low degree of silicification were few. We speculated that the shell structure of siliceous organisms in the glacial sediments were affected by dissolution. Nevertheless, the calcium carbonate content (~20%), BSi content (3.5%-4.4%), and radiolarian abundance (1000-6000 inds·g-1) in the last glaciation indicated that productivity in the SEBoB had been relatively high, since the last glaciation with abundant nutrients and biomass. This conclusion was supported by the relatively high abundance of nassellarians (>50%)—an indicator of rich nutrients. In addition, the periodic fluctuation of Bsi contents in the last deglaciation might be controlled by millennium scale climate events. During the Heinrich Stadial 1 intervals (HS1) and Younger Dryas (YD), the climate cooled, enhanced northeast monsoon carried more terrigenous organic matter into the upper water, and the invasion of antarctic intermediate water enhanced intermediate water ventilation while biomass and productivity peaked.

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    Arsenic migration and transformation mechanism and microbial regulation at the sediment-water interface of the Changjiang estuary
    ZHANG Yuting, DUAN Liqin, SONG Jinming, ZHANG Naixing, YIN Meiling, LI Xuegang, YUAN Huamao
    2022, 29(4): 144-155. 
    DOI: 10.13745/j.esf.sf.2022.1.9

    Abstract ( 61 )   HTML ( 3 )   PDF (3323KB) ( 30 )  

    In order to understand the arsenic (As) migration and transformation processes at the sediment-water interface (SWI) of the Changjiang estuary, the vertical profiles of the total As concentrations and speciation and redox-sensitive element (Fe, Mn and S) concentrations in the overlaying water and porewater at four sampling sites in the Changjiang estuary in summer 2019 were analyzed. The Fe-Mn-S controlling mechanism was investigated. Combined with As-related functional genes, the microbial regulation process of As cycling at the SWI was discussed. The diffusion fluxes of total As at the SWI were also estimated. It was found that As3+ was the main species of dissolved arsenic at three sites except site A7-4. At all sites, the overlying water had the lowest As concentrations (0.748-1.57 μg·L-1); whilst As concentrations in porewater increased gradually with depth and peaked (7.14-26.9 μg·L-1) at 6-9 cm depths. The vertical profiles of total As and As3+ concentrations in porewater were similar to that of dissolved Fe2+ and Mn2+, with high concentrations in the middle layers due likely to the release of solid-phase As by Fe(Ⅲ) and Mn(Ⅳ) reduction in the Fe/Mn reduction zone. The coupling relationships between porewater As concentration and abundances of arrA and arsC genes at the transition zone between oxic layer and Fe/Mn reduction layer (except for site A1-3) suggested that the reduction of dissolved As5+ or solid As5+ to dissolved As3+, by arsenic dissimilatory reducing bacteria was another important process of As migration and transformation. The combination of decreasing total As and As3+ concentrations and low S2- concentrations in porewater in the sulfate reduction zone indicated that the removal of porewater As was probably due to As complexation with iron sulfide minerals rather than formation of As sulfides. The ambient redox potential in the bottom layer of the estuary was an important factor affecting As migration and transformation at the SWI, as, with decreasing DO concentrations, the processes were more incline to microbial reduction control. The diffusion fluxes of total As at the SWI of the Changjiang estuary were (1.18-2.07)×10-7 μmol·cm-2·s-1, all attributable apparently to As release from porewater into the overlying water, suggesting sediment might be one of the sources of total As in the Changjiang estuary study area.

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    Terrigenous detrital inputs and hydroclimate changes in the Holocene eastern Mediterranean Sea: A basin-wide geochemical view
    WU Jiawang, YAO Shengnan, Amalia FILIPPIDI, LIU Zhifei, Gert J. DE LANGE
    2022, 29(4): 156-167. 
    DOI: 10.13745/j.esf.sf.2022.1.10

    Abstract ( 64 )   HTML ( 6 )   PDF (3008KB) ( 46 )  

    The Mediterranean Sea lies at the interface between the African monsoon and the European temperate climate zones while receives from the surrounding continents significant amounts of lithogenic detritus with very different rock compositions and weathering regimes, making it an ideal area to study the Earth’s hydrological cycle. Previous works mostly focused on the Saharan dust and Nile discharge, but might have underestimated the supplies from other sources, especially overlooked the potential impact of paleo-rivers in the wider North-African margin. Focusing on the sapropel S1 layer deposited in the African Humid Period, combined with the present-day/Late-Holocene sediments collected from core tops, 30 samples from 18 core sites across the eastern Mediterranean Sea (EMS) were selected for elemental geochemical analysis. Comparing between two time slices (~9.5-8.9 ka vs. ~1.7-0 ka) having different hydroclimate backgrounds, this study permits a basin-wide detailed investigation of the terrigenous detrital inputs to EMS in the Holocene. Particularly, we aim to distinguish and characterize geochemically the various dust and riverine contributions. The Ti/Al, Zr/Al, Ca/Al, Y/Al ratios all showed longitude and latitude gradient variations, making them reliable indicators for Saharan dust; the differences between detrital elements likely reflect changes in the dust source and delivery routes originated from North Africa. Consistent north-south pattern in the dust proxies suggests a persistent interacting boundary of 36°N between the subtropical high-pressure belt and the temperate westerlies in the Holocene. Contrary to dust proxies, the riverine indicators were not only significantly higher in value for the Early Holocene than the present-day, but also exhibited different geographical patterns. The P/Al ratio showed west-east and north-south decreasing trends indicative of riverine inputs from the numerous small rivers along the coast of the northern Mediterranean Sea. Potential supply of North African paleo-rivers that were reactivated by intensified monsoon precipitation could be discerned based on the differences between the Ti/Al or K/Al and (Cr+Ni)/Al ratios. Taken together, the riverine inputs should have largely increased during the Early Holocene, while the delivery extents differed between the river systems, affected by specific hydroclimate mechanisms and the delivery of the surface currents.

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    ENSO-like patterns and its driving mechanism in Western Pacific Warm Pool during the glacial cycles
    ZHANG Yang, XU Jishang, LI Guangxue, LIU Yong
    2022, 29(4): 168-178. 
    DOI: 10.13745/j.esf.sf.2022.1.5

    Abstract ( 63 )   HTML ( 9 )   PDF (3258KB) ( 32 )  

    The Western Pacific Warm Pool (WPWP) region affects the global climate change through El Niño-Southern Oscillation (ENSO) and monsoons, as it receives the most solar radiation and has the warmest surface temperature in the world. Abundant sedimentary records indicate WPWP also experienced ENSO-like events throughout geological history. However, the relationships between ENSO and glacial-interglacial cycles or East Asian Monsoon (EAM), as well as the driving mechanism behind ENSO-like patterns, still remain unclear. In this study, we reconstructed the paleoclimate records since Marine Isotope Stage (MIS) 8 by using oxygen isotope, Mg/Ca ratio from planktonic foraminifera, and clay mineral proxy data obtained from sediment core B10 at WPWP. Combined with previously published paleoenvironment records of tropical region, δ18O data of Chinese cave stalagmite, and sea surface temperature records of the Southern Ocean, we studied the evolution of ENSO-like patterns during glacial-interglacial cycles and their relationship with EAM, and discussed the driving mechanism behind ENSO-like patterns. We found that during the glacial period the thermocline in WPWP became shallower, with the temperature gradient decreasing between the Eastern Equatorial Pacific and WPWP. Meanwhile, weakened East Asian Summer Monsoon (EASM) was accompanied by reduced rainfall, similar to modern El Niño. During the interglacial period, the thermocline in WPWP deepened, the temperature gradient along the equatorial Pacific increased, and EASM strengthened with increased precipitation, which was very similar to modern La Niña. Spectral analysis revealed the sea surface temperature in WPWP followed a significant eccentricity cycle (96 ka). During the interglacial period, increasing solar radiation in tropical region increased the latitudinal sea surface temperature gradient, and led to heat accumulation in subsurface water. The accumulated heat in turn regulated heat transfer to WPWP via subsurface circulation and ultimately controlled the long-term changes in the Walker circulation intensity and ENSO-like patterns in equatorial Pacific. During the glacial period, the southeast trade wind and ocean circulation anomalies caused by the cooling of the Southern Ocean might also regulate the ENSO-like patterns.

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    Provenance of sediments in the Amundsen Sea, West Antarctic since the mid-Holocene and paleoclimate reconstruction
    LEI Ziyan, GE Qian, CHEN Dong, ZHANG Yongcong, HAN Xibin, YE Liming, BIAN Yeping, XU Dong
    2022, 29(4): 179-190. 
    DOI: 10.13745/j.esf.sf.2022.1.7

    Abstract ( 51 )   HTML ( 2 )   PDF (2719KB) ( 23 )  

    Grain size and geochemical analyses were carried out on sediment core samples from core A11-02 in the Amundsen Sea, West Antarctic to trace the sediment sources and reconstruct the history of paleoclimatic evolution since the mid-Holocene. By analyzing and comparing the North American Shale Composite normalized rare earth element (REE) patterns and indicators such as (La/Yb)N, (Gd/Lu)N and (La/Sm)N, we concluded that the core sediments mainly originate from the Marie Byrd Land, with contributions, to some extent, from the Bellingshausen Sea. By multi-index analysis comparing the Chemical Index of Alteration, Na/K ratio and grain contents for grain sizes less than 22.1 μm or greater than 63 μm with other paleoclimate records, we identified four distinct cooling phases in the Amundsen Sea since the mid-Holocene. We found the millennial-scale climate changes are temporally and spatially consistent across the Antarctic and mainly controlled by changes in insolation and atmospheric circulation.

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    Hydrate dissociation on the northern slope of the South China Sea: Potential effects from climate warming in the current warm period
    JIA Yonggang, RUAN Wenfeng, HU Naili, QIAO Yue, LI Zhenghui, HU Cong
    2022, 29(4): 191-201. 
    DOI: 10.13745/j.esf.sf.2022.1.4

    Abstract ( 65 )   HTML ( 0 )   PDF (1985KB) ( 39 )  

    The global temperature has been rising during the current warm period (CWP, 1850-present). The rise of the bottom water temperature and sea level is affecting the stability of hydrates on the northern slope of the South China Sea. To explore the effects of the CWP climate warming on hydrate dissociation, we simulated the change of hydrate saturation during the past millennium at the shallowest depth in the hydrate reservoirs in the Dongsha, Shenhu, Xisha and Qiongdongnan sea areas, and revealed the depth range of the hydrate stability zone affected by the CWP climate warming, and discussed the extent of hydrate dissociation and its environmental impact. We showed that (1) hydrate dissociation occurred in the Dongsha, Xisha and Qiongdongnan sea areas due to the CWP climate warming, but only at water depths above 665 m, 770 m and 725 m, respectively; no hydrate dissociation observed in the Shenhu sea area. (2) Since the start of CWP, dissociated hydrates on the northern slope of the South China Sea amounted to (1.54-6.28)×1010m3, with (9.36-38.3)×107 m3 methane released. (3) The annual hydrate dissociation affected by the CWP climate warming reached (5.5-22.5)×105m3and produced (9.02-36.9)×107m3 methane. The amount of methane that reached the atmosphere was (3.61-14.8)×105m3, which accounted for 0.01%-0.06% of the annual methane contribution from human activities in China. Meanwhile, (1.77-7.23)×107 m3 methane might be oxidized to form weak acids in seawater, which worsened acidification of the northern slope of the South China Sea.

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    Deep-water coral of multiple benthal strategies discovered from mounds in Dongsha Waters, the South China Sea
    YAN Pin, WANG Yanlin, JIN Yongbin, ZHAO Meixia, ZHONG Guangjian
    2022, 29(4): 202-210. 
    DOI: 10.13745/j.esf.sf.2022.1.13

    Abstract ( 52 )   HTML ( 1 )   PDF (3526KB) ( 24 )  

    The Dongsha Waters surrounding the Dongsha Island, northern South China Sea hosts populous deep-water mounds (200-2000 m), likely of mud volcanic origin. In recent years from a dozen dredging expeditions to many such mounds, skeletal as well as living deep-water corals have been collected in large quantity (~1000), yet the cause of such coral flourishment is not known. In terms of their life strategies judging by morphology, the corals included the common immobile ones which attached with their base steadfastly to hard carbonate-nodules (Madrepora oculate, Lochmaeotrochus, Enallopsammia, Solenosmilia variabilis, Dendrophyllia, Bamboo Coral and Golden Gorgonians), the ones that weakly attached with duck-webbed uneven base (Desmophyllum dianthus) to or rooted with conic base (Flabellum, Crispatotrochus and Balanophyllia) onto sandy-muddy biogenic clastics on the seafloor, as well as the newly discovered, mobile epifauna (Fungiacyathus and Deltocyathus vaughani). The co-occurrence of various corals of diverse life strategies reflected widely variable benthic environments—from hard to soft substrates, and from strong to weak bottom currents. As these mobile, weakly attached corals thrive on mounds with weak bottom current, they may take sufficient nutrients from local geofluids rather than relying on nutrients transported by current. This implies that hydrocarbon leaked from local mud volcanoes may be the main feeder for the deep-water corals. Thus mud volcanoes and deep-water corals may be mutually dicative.

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    Grain size characteristics of terrigenous clastics in surface sediments of the Gulf of Thailand and their significance for sedimentary dynamic environment
    FENG Shuo, LIU Zhifei, Penjai SOMPONGCHAIYAKUL, LIN Baozhi, Martin G. WIESNER
    2022, 29(4): 211-220. 
    DOI: 10.13745/j.esf.sf.2022.1.18

    Abstract ( 59 )   HTML ( 6 )   PDF (3369KB) ( 44 )  

    The grain size characteristics of marine clastic sediments can directly reflect the marine sedimentary dynamic environment, thus can be used to study the variation of marine dynamic environment. In particular, the grain size distribution of surface sediments on the continental shelf plays an important role in studying the modern marine dynamic environment of coastal and water column bottom boundary layer. This research investigated the grain size distribution characteristics of terrigenous clastics in surface sediments collected from the Gulf of Thailand and the Mekong River estuary, to obtain the marine dynamic environmental processes affecting the particle sedimentation in specific sea areas. The results of grain size analysis show that the terrigenous clastics in surface sediments in the Gulf of Thailand are composed mainly of poorly sorted fine sand to fine silt, characterized mostly by positive skewness in frequency distribution patterns. The fine to very fine sand components are mainly distributed at the bay of Bangkok and shelves off Cambodia. The sediments off the Mekong River are fine sand and the sorting is better than that in the Gulf of Thailand. These grain size characteristics of surface sediments can serve as good proxies to explicitly indicate the environmental variations in this area. The well sorted medium sand with nearly normal distribution patterns in sediments off the Mekong River indicate the depositional environment under the influence of the waves. The poorly sorted medium sand to fine sand sediments in the bay of Bangkok and off Cambodia reflect the combined effect of tides and waves. The very fine sand to medium silt sediments with medium sorting and positive skewness in the east and west coast of the Gulf of Thailand reflect the controlling effect of tides. And the sediments in the central Gulf of Thailand with poorly sorting indicate the influence of surface currents. This study shows that the grain size distribution characteristics of terrigenous clastics in surface sediments of the Gulf of Thailand and off the Mekong River can be used to distinguish the control effects of different marine dynamic factors, and to reveal that the sedimentary dynamic environment in the Gulf of Thailand is mainly affected by tides, waves and currents and the sedimentary dynamic environment off the Mekong River is affected by waves.

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    Crustal structure of the Cona rift, eastern Himalaya
    WU Jiajie, XU Xiao, GUO Xiaoyu, LU Zhanwu, WU You, XIANG Bo, YU Yang, LI Chunsen, YU Jiahao, TONG Xiaofei, LUO Xucong
    2022, 29(4): 221-230. 
    DOI: 10.13745/j.esf.sf.2022.4.66

    Abstract ( 75 )   HTML ( 6 )   PDF (6467KB) ( 89 )  

    The Himalayan mountain range is the result of continental-continental collision between the Indian and Eurasian plates. It has been under great debate as to why the rifts of southern Tibet are formed at the front of the collision zone. To answer this question, it is necessary to understand the crustal structure of the rifts. The age of each rift zone tends to be younger from west to east. In this study, we revealed the crustal structure of the Cona rift, a relatively young continental rift, using the P-wave receiver function calculated from teleseismic data received by a dense array across the rift, and analyzed the rift formation process based on the crustal structure. We showed that the Cona rift is a crustal-scale rift, where Moho offsets beneath the rift and significant lateral variations develops. We suggest that the formation of the rifts may be associated with regional tectonic activities, and further studies are needed to ascertain whether a single gravity collapse can form crustal-scale rifts. Based on the previous studies of magmatic rocks and geophysical observations, we infer that the asthenospheric upwelling caused by tearing of the subducting Indian plate weakened the lower crust of the Cona rift region where the middle and upper crust is also weakened as shown by the study of Himalayan leucogranites. Considering all the study results, we hypothesize that the formation of crustal-scale rift requires crustal weakening at different depths.

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    Fold-thrust belt of South Qiangtang, Tibet and the double-layer structure of the South Qiangtang accretionary complex
    LI Dian, WANG Genhou, LIU Zhengyong, LI Pengsheng, FENG Yipeng, TANG Yu, LI Chao, LI Yang
    2022, 29(4): 231-248. 
    DOI: 10.13745/j.esf.sf.2022.3.30

    Abstract ( 69 )   HTML ( 4 )   PDF (6045KB) ( 64 )  

    The accretionary orogens formed in the active continental margin are represented by extensive and stable accretionary complexes. During the slow and complex oceanic subduction and collision, oceanic plate, intra-oceanic arc, seamount, and continental fragments are accreted onto the retreating oceanic trench through off-scrapping, underplating, and tectonic erosion at the leading edge of the overriding plate. Continental crust thus grows laterally as significant accretion of oceanic crusts at the inner wall of the trench. Via a similar tectonic process during the continental collision passive margin are incorporated into the subduction channel, where a crustal accretionary wedge similar to but much larger than oceanic accretionary prisms are expected to form. Therefore the composition, structure, and evolution of accretionary complex in orogenic belt play a key role in understanding the complex geodynamic process during the ocean to continent transformation. The accretionary complex of South Qiangtang, Tibet was recently recognized through corridor geological mapping and multidisciplinary research. However, the composition and structure of the complex are not well studied, which greatly hinders the understanding of its formation mechanism and evolution. Therefore in this paper, focusing on its spatiotemporal evolution, we researched in detail the composition and structure of the South Qiangtang accretionary complex to understand its formation and evolutionary processes. We show that (1) the South Qiangtang accretionary complex has a double-layer structure, with the subduction complex at the bottom, the fold-thrust belt at the top, and a regional detachment fault system separating the upper and lower layers. (2) The subduction complex contains not only the ocean plate stratigraphy but also a large part of the South Qiangtang passive margin. (3) Although the fold-thrust belt is mainly deformed passive continental margin, it also contains ocean plate stratigraphic units like seamounts and intra-oceanic arcs. Based on the spatiotemporal distribution of fore-arc basin and wedge-top basin during subduction and Late Triassic syn-collisional magmatism, the double-layer structure of the South Qiangtang accretionary complex should mainly be induced by subduction of passive continental margin during continental collision, and probably also by subduction reversal during oceanic subduction. The double-layer structure of the South Qiangtang accretionary complex and its continental subduction origin proposed in this paper are of great significance for understanding the crustal structure of the South Qiangtang terrane and the evolution of Mesozoic basement.

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    Early Cenozoic rotation feature in the northern Qaidam marginal thrust belt and its tectonic implications
    LI Bingshuai, YAN Maodu, ZHANG Weilin
    2022, 29(4): 249-264. 
    DOI: 10.13745/j.esf.sf.2022.3.31

    Abstract ( 54 )   HTML ( 13 )   PDF (3594KB) ( 71 )  

    The northeastern Tibetan Plateau (NETP) is the frontal region of the northeastward propagation of the Tibetan Plateau with intensive deformation during the Cenozoic. It is one of the key regions to study the uplift and deformation processes and decipher the growth pattern of the Tibetan Plateau. However, controversies still exist regarding the time of NETP involvement with the India-Eurasia convergent deformational system, the kinematic and geodynamic processes as well as the growth mechanism of the Tibetan Plateau. Continental collision and continuous indentation are generally accompanied by vertical-axis rotation (VAR) of blocks and their internal structures. Paleomagnetic declination has its unique advantage to quantitative determination of block rotation about a vertical axis. However, the lack of Early Cenozoic paleomagnetic rotation records in NETP, especially in the Qaidam Basin, limited our understanding of the rotation patterns in NETP as well as the far-field effect of India-Eurasia collision since the Early Cenozoic. The northern Qaidam Basin contains well exposed near successive Lulehe and Xiaganchaigou Formations and is an ideal place to study Early Cenozoic VARs of NETP. Here, we conducted detailed paleomagnetic rotation study on the Lulehe and Xiaganchaigou Formations at the Tuonan and Gaoquan localities in the northern-middle part of the northern Qaidam Basin. In total, 260 drill cores from 24 sites within 4 time-intervals from Tuonan, and 150 drill cores from 14 sites within 2 time-intervals from Gaoquan were collected. Detailed rock magnetic and thermal demagnetization experiments indicated that hematite is the dominant while magnetite the subordinate magnetic carriers. The obtained total of 31 site-mean characteristic remanent magnetization directions were validated by both fold and reversal tests, indicating they were likely primary magnetization directions. The obtained paleomagnetic results, together with results from the Hongliugou locality in the mid-northern Qaidam Basin, revealed a remarkable (~20°) counterclockwise rotation of the northern Qaidam Basin during ~45-35 Ma, which appeared to be a conjugate rotation to the significant clockwise rotation of the contemporary Longzhong Basin. Taking into account the Early Cenozoic (~52-46 Ma) rotations and Oligocene-initiated strike-slip faulting around eastern Tibetan Plateau, we believe that 1) conjugate rotations occur no later than the mid-Eocene (~45 Ma) in NETP and are the far-field effects of the India-Eurasia collision. 2) The Early Cenozoic conjugate rotation deformation from the eastern Himalayan syntaxis (EHS) to NETP are mostly related to a dextral, sinistral shear generated by NNE indentation of EHS into Eurasia. The compressional shear and related crustal shortening and VAR exhibit a stepwise NNE propagation from EHS to NETP during the Eocene. 3) Tectonic deformation in the Tibetan Plateau is likely mainly accommodated via NS compression and crustal-thickening in the Paleocene-Eocene, while lateral-extrusion along major faults is likely since the Oligocene.

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    Crustal anisotropy study in the central Qilian Mountains: Evidence from teleseismic P wave receiver functions
    ZHOU Pengzhe, GAO Rui, YE Zhuo
    2022, 29(4): 265-277. 
    DOI: 10.13745/j.esf.sf.2022.4.23

    Abstract ( 64 )   HTML ( 2 )   PDF (4045KB) ( 38 )  

    The Tibetan Plateau uplift is driven by the collision between the Indian and Eurasian plates. Its growth and evolution, especially the mechanism of its outward expansion, is still controversial. At the forefront of its northeastward expansion lies the Qilian Mountains, whose crustal structure and anisotropy are of great significance for understanding the northward growth of the Tibetan Plateau. The central Qilian Mountains on the northeastern margin of the Tibetan Plateau experienced strong crustal compressional deformation. Existing studies have described phenomenons of non-coupling non-uniform deformations of crust and upper mantle, while understanding the deformation mechanism has become a frontier scientific issue. Previous anisotropy researches in this region mostly relied on seismic network data using large station spacing, however, which could not reflect the fine changes in the crustal anisotropy across the mountain range. To solve this problem, this study used the stacking method based on a dense linear seismic array to obtain the lateral variation of the crustal thickness, Poisson’s ratio and crustal anisotropy. The crust was found to be at its thickest in the Central Qilian and northern South Qilian, while the average Poisson’s ratio was the lowest in these areas, indicating loss of mafic lower crust and shortening of felsic upper-middle crust during crustal thickening. In addition, the Poisson’s ratio of felsic component did not support the existence of crustal flow in this region. In the interior of the mountain range, the fast polarization directions (FPDs) of the crust followed the direction of crustal outward expansion and were nearly perpendicular to the FPDs of the upper mantle, suggesting the crust-mantle deformation might be decoupled. In southern South Qilian and southern North Qilian where the crust is thinner, FPDs were parallel to the strike of the ancient suture, indicating the Early Paleozoic tectonic frame still had an impact on the shortening and uplifting of the Qilian Mountains.

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    Characteristics and provenance significance of iron-rich heavy minerals in Quaternary fluvial sediments in Yibin area, eastern margin of Tibetan Plateau
    YOU Wenzhi, XIANG Fang, HUANG Hengxu, YANG Kunmei, YU Xiantao, DING Li, YANG Qi
    2022, 29(4): 278-292. 
    DOI: 10.13745/j.esf.sf.2022.1.24

    Abstract ( 42 )   HTML ( 2 )   PDF (4485KB) ( 34 )  

    The development and evolutionary history of large river systems have attracted much attention from geoscientists. Exploring the characteristics of iron-rich heavy minerals in the Quaternary sediments in Yibin area where the Jinsha and Minjiang Rivers meet may reveal important evidence for the evolution of the Yangtze River; it can also be of great significance for understanding the uplift and sedimentary response of the eastern margin of the Tibetan Plateau. The chemical and morphological characteristics of iron-rich heavy minerals were analyzed by electron probe and backscatter imaging to explore the provenance evolution of the Yangtze River and its tributaries. Sediments of terraces Ⅴ and Ⅳ of the lower reaches of the Minjiang River contained a lot of magnetite from mainly the Longmenshan tectonic belt. Although sediments of terrace Ⅲ contain plentiful ilmenite, their provenance is still mainly in the Longmenshan tectonic belt. More iron-rich heavy minerals with inclusions such as kyanite and apatite can be found in the modern sediments, which proves that both the Longmenshan tectonic belt and the Songpan-Ganzi fold belt provided materials to the sediments. So we can conclude that when terraces V to III of Minjiang River formed, the source of Minjiang River was located in the Longmenshan tectonic belt. After the formation of terrace Ⅲ, the Minjiang River continued to erode upward to the source area and entered the Songpan-Ganzi fold belt to gradually form the modern Minjiang River. In terrace Ⅴ of the Jinsha and Yangtze Rivers the Panzhihua vanadium titanomagnetite was not found, which means the Panzhihua-Yibin section of the Jinsha River was not cut-through, and the provenance of the Yangtze River in the study area at this time was mainly the Minjiang River sourced from the Longmenshan tectonic belt. However, the Panzhihua vanadium titanomagnetite is abundant in terrace Ⅳ of the Jinsha River, indicating that the Panzhihua-Yibin section of the Jinsha River was cut-through at the time (~0.5-0.3 Ma B.P.) of sediment deposition in terrace Ⅳ.

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    Continental drift process revealed by high precision seismic survey in the central basin of the South China Sea
    LIANG Guanghe
    2022, 29(4): 293-306. 
    DOI: 10.13745/j.esf.sf.2022.6.10

    Abstract ( 45 )   HTML ( 3 )   PDF (5335KB) ( 45 )  

    The formation and evolution of the South China Sea have been widely studied. More than five genetic models have been proposed. The current popular model is seafloor spreading, but the model could not reasonably explain the mid-ocean ridge jumping in the South China Sea and the continental fragments found in the central basin of the South China Sea. In this study, based on two high precision seismic exploration sections in the central basin of the South China Sea, a new tectonic geological interpretation of the two seismic exploration sections was given on the basis of an in-depth analysis of the layered structure of the oceanic crust. Then, through examination of the formation process of extensional tectonics, a model of continental drift driven by mantle upwelling and continental crust gravity slip was developed. Finally, the formation mechanism and evolutionary process of the South China Sea was studied in detail. The formation of the South China Sea can be described by a “tectonic extrusion+active drift” model, where “tectonic extrusion” refers to large-scale passive extrusion of the microcontinents in the southeastern margin of the Eurasia plate caused by the India-Eurasia collision, while “active drift” refers to active drift of the microcontinents after extrusion. The residual seismic reflection in the central basin of the South China Sea is a phenomenon of seafloor spreading caused by active drift of microcontinents. Furthermore, the geotectonic evolution of the microcontinents surrounding the South China Sea was restored. The proposed new model can reasonably explain the phenomenon of mid-ocean ridge jumping in the South China Sea and the genetic mechanism of continental debris. The proposed new continent drift model provides a new dynamic model for plate movement.

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    Multiphase rift and migration mechanism in the Pearl River Mouth Basin
    ZHAN Cheng, LU Shaoping, FANG Penggao
    2022, 29(4): 307-318. 
    DOI: 10.13745/j.esf.sf.2022.3.29

    Abstract ( 57 )   HTML ( 5 )   PDF (4477KB) ( 43 )  

    The formation and evolution of the South China Sea is controlled by the mutual movements of the Indo-Australian, Eurasian and Pacific plates, which provides an important window for the study of plate collisions and their long-range effects in the context of plate convergence. To reveal the multi-episodic rifting process under this context, we select the entire Pearl River Mouth Basin rich in geologic information as the typical area of South China, and used three high-precision seismic sections to calculate the fault activity and tectonic subsidence rates and perform comprehensive analysis for each geological unit in the basin. According to our calculation, the average fault activity rates for the main sag-controlling faults of the eastern, central and western parts of the basin during the rifting period were 85, 203 and 93 m/Ma, respectively, and the average subsidence rates were 8.5, 34 and 12.7 m/Ma, respectively. Basinwide, rifting was strongest in the center and gradually weakened to the west and east, which, we believe, is related to the pre-existing faults and initial crustal thickness. The pre-existing NE-trending faults are known to be more active in the east than in the center. Therefore, under Cenozoic tensile stress, the east is more likely to experience the strongest rifting, followed by the center then the west. Whilst under the influence of pre-Cenozoic subduction, magmatic underplating caused the crust to thicken thus rifting intensity to drop sharply in the east, resulting in the difference in rifting intensity between west and east. In addition, the fault activity and subsidence rates in southern basin had surged during the rifting period, causing rifting to migrate to the south. We speculated that under the influence of depth-dependent extension, the southern sag witnessed increased crustal temperature and weakened crustal strength. As a result, rapid tensile thinning occurred under extensional stress, resulting in a southward migration of the rift center accompanied by mantle upwelling. At the same time, intrusive magmatic material caused the high-angle normal fault to convert into a low-angle normal fault, further promoting the southward migration of the rift center.

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    Innovative petrogenetic classification of granitoids: Perspective from metamorphic anatexis and big data
    ZHANG Qi, ZHAI Mingguo, WEI Chunjing, ZHOU Ligang, CHEN Wanfeng, JIAO Shoutao, WANG Yue, YUAN Fanglin
    2022, 29(4): 319-329. 
    DOI: 10.13745/j.esf.sf.2022.6.11

    Abstract ( 88 )   HTML ( 8 )   PDF (4021KB) ( 107 )  

    The current ISMA classification of granitoids is not systematic and lacks petrogenetic specification. Most granitoids may have originated from anatexis of metamorphic rocks under lower crustal conditions, triggered by conductive and/or advective heating from asthenosphere mantle uprising and basaltic magma underplating. Thus, granitoid petrogenesis is causally related to metamorphism, and, to some extent, there is a parent-child relation between metamorphic rocks and granitoids. If adakites are formed by partial melting of eclogites under high-pressure (HP) conditions without plagioclase, what about granitoid types formed by partial melting under medium-pressure (MP) conditions with the presence of both plagioclase and garnet, or under low-pressure (LP) conditions without garnet? On the basis of these considerations, combined with big data technology, we proposed an alternative granitoid classification scheme. Granitoids are classified into three types: (1) high Sr-low Y type formed under HP conditions without plagioclase in subducted slabs or thickened crustal regions; (2) low Sr-low Y type formed under MP conditions with both plagioclase and garnet in normal or slightly thickened crustal regions; and (3) low Sr-high Y type formed under LP conditions without garnet in extended crustal regions. Big data statistics suggested that the above three granitoid types can be roughly demarcated by the geochemical criteria-Sr content of 400×10-6 and Y content of (20-35)×10-6.

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    Carbonatite magma and crustal metasomatism: A review
    FAN Chaoxi, XU Cheng, CUI Ying, WEI Chunwan, KUANG Guangxi, SHI Aiguo, LI Zhuoqi
    2022, 29(4): 330-344. 
    DOI: 10.13745/j.esf.sf.2022.4.22

    Abstract ( 129 )   HTML ( 7 )   PDF (3375KB) ( 130 )  

    Carbonatite is a mantle-derived rock with minimal surface exposure. Carbonatite mantle metasomatism has received much attention, but the reaction between carbonate magma and the crust is little studied. Such reaction has been reported in China’s Caotan-Fengzhen regions, Germany’s Kaiserstuhl region, Russia’s Petyayan-Vara region, and Australia’s Nolans Bore deposit. The reaction is characterized by the formations of large quantities of iron-rich mica, pyroxene, sphene, hyalophane, and other silicate minerals, and disruptions to the C-O and Sr-Nd isotope systems. In the mantle, carbonatite magma reacts with peridotite to produce meta-exfoliated peridotite; in the middle and lower crust, such reaction produces antiskarn. The reaction between carbonatite magma and wall-rock can result in local Si enrichment, which encourages REE entry into apatite in the early magmatic stage and prevents REE mineralization. Carbonatite-silicate reactions in the deep crust are typically not exposed to the surface as shallow hydrothermal systems do under the same structural context, and reaction products are easily misidentified as skarn mineral assemblages. Therefore, it is critical to uncover the anti-skarn processes in the deep crust—particularly its associated mineralization, through high-temperature, high-pressure experimental research, along with re-evaluation of high-temperature skarn mineral assemblages whose sources of silicate fluids are unknown.

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    Discovery of Late Ordovician sanukitoid-like diorite in southern Altyn orogeny and its geological significance
    ZENG Zhongcheng, HONG Zenglin, BIAN Xiaowei, CHEN Ning, ZHANG Ruoyu, LI Qi
    2022, 29(4): 345-357. 
    DOI: 10.13745/j.esf.sf.2021.10.29

    Abstract ( 54 )   HTML ( 4 )   PDF (9126KB) ( 48 )  

    In this study, we report the occurrence of Late Ordovician sanukitoid-like diorites of the southern Altyn orogeny, and discuss, on the basis of detailed field work, their petrography, geochronology, whole-rock geochemistry, petrogenesis, mantle source as well as constraint on the tectonic evolution framework of the orogeny. LA-ICP-MS zircon U-Pb dating yielded weighted 206Pb/237U age of 445±3 Ma, which is interpreted as the formation age of diorite. Geochemically, the diorites had low Al2O3 (15.11%-16.19%) and high MgO (3.93%-5.29%) and K2O (1.68%-2.67%) contents belonging to high Mg, calc-alkaline and metaluminous series. In addition, the diorites possess high Cr (29.3×10-6 -140×10-6), Ni (27.1×10-6-43.5×10-6), Ba (606×10-6-936×10-6), Sr (513×10-6-734×10-6) and Y (26.4×10-6-31.1×10-6) contents, consistent with global high-Mg sanukitoid. They were enriched in REE and LILE (Rb, K), but depleted in HFSE (Nb, Ti, Zr), consistent with arc magma of the subduction zone. Moreover, the diorites could be generated from enriched lithospheric mantle metasomatized by subduction components, on account of high Ti/Zr ratio (48-60) and Mg# value (46.74-53.06), as well as high Cr (29.3×10-6-140×10-6) and Ni (7.1×10-6-43.5×10-6) contents. Thus we propose that the Late Ordovician high-Mg sanukitoid-like diorites are the product of decompression melting of mantle wedge during the slab break-off process in a post-collision tectonic setting, and represent the most intensive Paleozoic mantle-derived mafic intrusion in the southern Altyn orogeny.

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    Late Triassic Mg andesite of Juluotage, eastern Tianshan: Identification and tectonic implications
    KANG Huan, CHEN Yuelong, LI Dapeng, ZHANG Huiping, YANG Yi, XUE Guoliang, LIU Wei
    2022, 29(4): 358-370. 
    DOI: 10.13745/j.esf.sf.2021.10.1

    Abstract ( 64 )   HTML ( 7 )   PDF (6179KB) ( 41 )  

    The petrogenesis and sources of Indosinian magmatic rocks and the associated geodynamic settings in eastern Tianshan, Xinjiang have long been debated. In this study, the Aqishan andesites were investigated through integrated petrographic, geochemical and zircon U-Pb-Hf isotopic analyses. The andesites had a typical porphyritic texture and vesicular structure. The porphyritic texture was made of clinopyroxene and plagioclase phenocrysts in a matrix of acicular plagioclase. Zircon U-Pb dating results showed the Mg andesites erupted in ca. 235 Ma (Late Triassic) and contained Carboniferous inherited zircon grains. In-situ Hf isotopic analysis showed the magmatic zircon grains had negative εHf(t) values (-31.7--7.6) and Hf model ages of 2.2-0.7 Ga. The samples were geochemically marked by high MgO contents (3.7%-4.7%) and K2O/Na2O ratios (0.6-1.1) and low TFeO/MgO ratios (1.6-1.8) resembling high-K calc-alkaline Mg andesites. Geochemical characteristics combined with regional tectono-magmatic activities revealed the Aqishan Mg andesites were derived from partial melting of a phlogopite-bearing lithospheric mantle in an intraplate extensional setting. Therefore, during the Late Triassic, the lithosphere in eastern Tianshan was in an extension-thinning stage.

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    Rehabilitation status of denuded land in the eastern Qaidam Basin: Geophysical and thermochronological evidences
    WANG Jiaqi, LI Zongxing, LIU Kui
    2022, 29(4): 371-384. 
    DOI: 10.13745/j.esf.sf.2021.12.6

    Abstract ( 48 )   HTML ( 6 )   PDF (8860KB) ( 37 )  

    On the basis of geological field survey of the eastern Qaidam Basin, the contact relationships and development characteristics of unconformities in the basin were analyzed. Combined with geophysical and apatite fission track data and through seismic stratigraphic analysis, the rehabilitation status of denuded land in the eastern Qaidam Basin were evaluated. The results showed that during the period of Late Yanshanian movement, erosion thickness in the eastern Qaidam Basin ranged between 500-2300 m. In the basin’s southern and northern margins erosion thickness ranged between 1100-2000 and 1200-2300 m, respectively, and reduced gradually to 500-1000 m at the basin center. The overall denudation decreased gradually from the edge to the center of the basin, with its western section significantly more denuded than the eastern counterpart. The Yanshanian movement in the eastern Qaidam basin occurred between 87-62 Ma. During this period, the basin as a whole experienced weakly SE-NW compression. which caused the differential uplifting in the eastern part of the Qaidam basin to form the Olongbulukon belt prototype, further controlling oil and gas accumulation in the region. On the one hand, differential uplifting caused severe formation denudation in some areas, leading to loss of oil and gas; on the other hand, structural compression caused further burial of main source rocks in the affected area, where Jurassic source rocks further matured to generate hydrocarbons. The underlying Carboniferous source rock underwent secondary hydrocarbon generation; at the same time, a series of near-EW-trending traps were formed under compression, which favored oil and gas accumulation.

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    Genesis of Carboniferous volcanic rocks in northeastern Junggar Basin: New insights into the Junggar Ocean closure
    JIAO Xiaoqin, ZHANG Guanlong, NIU Huapeng, WANG Shengzhu, YU Hongzhou, XIONG Zhengrong, ZHOU Jian, GU Wenlong
    2022, 29(4): 385-402. 
    DOI: 10.13745/j.esf.sf.2021.12.2

    Abstract ( 52 )   HTML ( 4 )   PDF (6583KB) ( 42 )  

    The Junggar Ocean is an important branch of the northern Paleo-Asian Ocean and part of its stage evolution. However, the subduction and closure time of the Junggar Ocean and the basement property of the Junggar Basin are still unclear. In this study, Carboniferous volcanic rocks including basalts, basaltic andesites, and andesites in the northeastern margin of the Junggar Basin (Wulungu area) were investigated to reveal their magmatic provenance and formation mechanism. Combined with major and trace element and Sr-Nd isotope analysis, the closure time of the Junggar Ocean during the Late Paleozoic was further clarified. Three types of basement volcanic rocks with low TiO2 (0.60%-0.84%) and relatively high alkaline (1.18%-8.59%) contents were identified. The basalts belong to tholeiitic series while andesites to high calc-alkaline series, indicating a volcanic arc association. The low-medium 87Sr/86Sr(i) ratios (0.703250- 0.704559) and relatively depleted εNd(t) (+4.8-+6.8) and tDM2 (483-625 Ma) values suggested all three types formed from fractional crystallization of depleted mantle magmas, with andesites formed later than the others. Trace element and isotope tracing suggested the volcanic rocks originated from mantle wedge metasomatized by slab-derived fluid, with andesites more impacted by crustal contamination. The volcanic rocks were enriched in LILEs (Ba, Sr), Pb, Zr and Hf, and showed strong negative Nb and Ta anomalies. These characteristics are consistent with the tectonic setting of a subduction zone. The rock series showed enrichments of incompatible elements (Th, U, K) and LREE, high Ba/La ratio (30.14-208.86), low TiO2 content (0.60%-0.84%), and low Ce/NB (8.71-12.05) and Th/Nb (0.93-1.74) ratios. These characteristics support the continuing Carboniferous Junggar Ocean subduction along the continental block, which led to island arc accretion, followed by Junggar Ocean closure in the Late Carboniferous (ca. 305.5±4.4 Ma) and subduction-related magma superposition onto the continental crust through island arc. The above results provided new basis for the understanding of basement formation in the Junggar Basin.

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    Deeply mining the intrinsic value of geodata to improve the accuracy of predicting by quantitatively optimizing method for prospecting target areas
    FENG Jun, ZHANG Qi, LUO Jianmin
    2022, 29(4): 403-411. 
    DOI: 10.13745/j.esf.sf.2022.2.66

    Abstract ( 59 )   HTML ( 5 )   PDF (1906KB) ( 69 )  

    Ore prospecting relies on accurate target prediction. The traditional information-based qualitative metallogenic prognostic method, however, has not been able to perform geodata deep mining. In this paper, Big Data deep mining methodology and leveling technique were applied to 1∶200000 scale stream sediment geochemical survey data collected from the Qilian and Longshou Mountains region, Gansu Province to eliminate systematic errors in the raw data. Through regression analysis an information repair model was established to improve the correlation between survey results and copper ore deposits. Using discriminant analysis algorithm, a series of quantitatively optimized prediction models for copper ore prospecting were developed. These prediction models quantitatively predicted copper prospecting target areas. According to the statistical analysis, the proportion of known copper ore deposits exceeded 22% of the class 1 or class 2 predicted target areas, while the target areas only covered 1.72% of the total studied area. Thus, quantitative prediction of prospecting target area using Big Data has greatly increased prediction accuracy while markedly reduced prediction acreage. By characteristic analysis of model elements, the predictive power of the prediction model series was quantitatively evaluated, which provided a basis for the quantitative evaluation of ore genesis and regional ore control conditions.

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    Deep thermal fluid activity and its influence on the diagenesis and pore evolution of reservoirs: A case study from the Miocene Huangliu Formation reservoir in the LDX area, Yinggehai Basin, northern South China Sea
    CAO Jiangjun, LUO Jinglan, FAN Caiwei, LI Shanshan, WU Shijiu, FU Yong, SHI Xiaofan, DAI Long, HOU Jingxian
    2022, 29(4): 412-429. 
    DOI: 10.13745/j.esf.sf.2022.2.57

    Abstract ( 55 )   HTML ( 3 )   PDF (6531KB) ( 45 )  

    In order to understand the main types of deep-seated thermal fluid in the Yinggehai Basin, We studied the thermal fluid characteristics, determined the range of thermal fluid activity, and analyzed the thermal fluid influence on reservoir diagenesis and pore evolution. Combined with previous research results, we investigated the Miocene Huangliu Formation reservoir in the LDX area by blue epoxy resin-impregnated thin section, scanning electron microscope, clay mineral quantification by XRD, physical property, electron probe, fluid inclusion homogenization temperature, and stable isotope analyses. Results showed that the deep-seated thermal fluid activity—which is affected by tectonic thermal events, controlled by an abyssal fault, driven by overpressure, and dominated by CO2 thermal fluid and to a lesser extent by H2S thermal fluid—mainly influenced the middle and lower parts of the Huangliu Formation below 3900 m. The reservoir is characterized by the accelerated transformation of authigenic clay minerals, vitrinite reflectance mutation, reduced formation water salinity, inclusion homogenization temperature above the normal formation maximum temperature, and hydrothermal mineral development under the influence of deep therrmal fluids. The Huangliu Formation involves two types of reservoirs: overpressure reservoir (middle-upper parts of the Huangliu Formation) and thermal overpressure reservoir (lower-middle parts of the Huangliu Formation). The diagenetic stage of the overpressure reservoir reached substage A2 of mesodiagenesis, with relatively weak compaction, weak dissolution and strong cementation, and experienced pore evolution in three stages: porosity decrease by compaction, porosity decrease by compaction and cementation, and porosity decrease by cementation combined with porosity increase by organic acid dissolution. Overall, porosity decreased from 38.8% to 7.6%. The diagenetic stage in the thermal overpressure reservoir reached stage B of mesodiagenesis, with relatively strong compaction, strong dissolution and weak cementation, and experienced pore evolution in four stages: stages 1-3 are the same as in substage A2, and stage 4 is similar to stage 3 except the porosity increase is caused by both organic acid and inorganic acid dissolutions. Overall, porosity decreased from 38.1% to 9.2%. Favorable reservoirs mainly develope in the thermal overpressure reservoirs of the second member of the lower-middle parts of the Huangliu Formation.

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    Scaling process simulation and anti-scaling measures in karst geothermal field in Baoding, Hebei
    HE Yujiang, LIU Xiao, XING Linxiao, TAN Xianfeng, BU Xianbiao
    2022, 29(4): 430-437. 
    DOI: 10.13745/j.esf.sf.2021.11.4

    Abstract ( 61 )   HTML ( 8 )   PDF (1863KB) ( 40 )  

    Scaling is a serious problem in geothermal power plants and certain geothermal projects in China hindering large-scale development and utilization of geothermal energy. At present, anti-scaling theory and technology is urgently needed in the geothermal market where calcium carbonate scaling is the most common problem. To solve this problem, the karst geothermal field in Baoding, northern China was selected to investigate the scale composition and the scaling mechanism, position and process as well as anti-scaling measures in a geothermal well. According to the study results, (1) the main cause of calcium carbonate scaling is flashing due to system pressure drop, caused primarily by carbon dioxide release from the liquid phase to the gas phase. (2) By combining the wellhead parameters with the laws of conservation of mass, momentum and energy and the theory of two-phase flow pressure drop, the scaling process can be simulated, and the scaling position as well as the pressure, temperature, steam quality and partial pressure of carbon dioxide at different depths can be calculated and determined. (3) Two anti-scaling measures could be implemented after identifying the flashing pressure and depth. One measure was to increase system pressure in order to prevent flashing thus inhibit carbon dioxide release. A minimum pressure was recommended via simulation. The other measure was to use chemical scaling inhibitor. An injection device was developed, anti-scaling experiment was carried out, and the chemical scaling inhibition effect was evaluated to show that chemical inhibitor could inhibit more than 90% of scaling, and thus the carbonate scaling problem could be effectively solved. From the above study, a set of valuable experiences—from scaling cause analysis, scaling position calculation, scaling process simulation, anti-scaling technology and equipment developments to field experiments and anti-scaling evaluation—were obtained. These experiences can be referenced in general for scaling control in geothermal wells.

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    Parent rock type control on cadmium background in soil and sediment: An example from Guizhou Province
    XIA Xueqi, JI Junfeng, YANG Zhongfang, LU Xinzhe, HUANG Chunlei, WEI Yingchun, XU Changyan, LIANG Zhuoying
    2022, 29(4): 438-447. 
    DOI: 10.13745/j.esf.sf.2021.11.2

    Abstract ( 63 )   HTML ( 6 )   PDF (3594KB) ( 76 )  

    Cadmium (Cd) is one of the most concerned heavy metal pollutants in soil and sediment, and the accurate determination of its natural background values is of great significance in environmental management. However, due to the inherent concentration variability associated with bedrock types and elemental enrichment/depletion caused by weathering, Cd concentrations in surface soil and sediment vary greatly spatially. In some areas, Cd concentration may exceed the safety standard for agricultural land use (GB 15618-2018) under natural conditions. In this study, Guizhou Province, which has relatively complex bedrock types and high soil Cd variation, was selected as the study area. From the perspective of elemental migration from bedrock to soil, and based on geochemical survey data of the entire province, this study sought to investigate the link between bedrock and Cd concentrations in soil and sediment and develop classification schemes for endmember rock types and regions selected for Cd background measurements. The results showed that lithology was the key factor contributing to soil Cd variation, while limestone (relative to dolomite), basalt, diabase and carbonaceous shale contributed to high Cd background value in soil. Compared with the parent rock type, rock formation age had less influence on Cd background values. Through rigorous statistical analysis, the Cd background value and variance in soil were obtained for soils developed from relatively pure rock material. For soils developed from impure rock materials or from mixed geological units, the Cd background value may be affected by more than one endmember rock types.

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    Distribution and evaluation of nitrogen, phosphorus and organic matter in sediments of the middle reaches of the Chaobai River
    CHI Minghui, QIN Yanwen, YANG Chenchen, WEN Quan, SUN Ning, ZHU Huailin, ZHANG Lei
    2022, 29(4): 448-454. 
    DOI: 10.13745/j.esf.sf.2021.11.29

    Abstract ( 47 )   HTML ( 3 )   PDF (1477KB) ( 34 )  

    The Chaobai River is a significant river that flows through Beijing, Hebei, and Tianjin areas. Taking the middle reaches of the Chaobai River as the study area, this paper sought to assess the level of nutrient pollution (organic matter, nitrogen and phosphorus) in the river sediments. One hundred thirty samples were collected from the study area and the organic matter (OM) content, total nitrogen (TN) and total phosphorus (TP) in the surface sediments were determined. Subsequently, the sources and distribution patterns of the three pollutants were analyzed, and the regional ecological risks were evaluated using a combination of organic pollution index and organic nitrogen pollution index. It was found in that (1) the OM content in the surface sediments varied from 0.17% to 13.15%, averaging 5.32%; TN ranged from 0.005-1.028 g/kg, averaging 0.192 g/kg; and TP ranged from 0.367-4.825 g/kg, averaging 1.662 g/kg. (2) Correlation analysis indicated that OM content was weakly correlated with TP or TN, while TN and TP were strongly correlated. TN and TP came from similar sources—mainly external sources, which is different from OM content. According to TOC/TN analysis, OM content was mainly affected by algae, phytoplankton and plants lack of fiber bundles. (3) According to organic pollution index evaluation results, 60% of surface sediment samples were clean (i.e., pollution free), 33.85% were relatively clean, 4.62% were almost clean, and 1.54% containd organic polutants. Organic pollution mainly occurred at the entrances of the Yunchaojian River and Tianjiazhuang drainage trunk canal into the Chaobai estuary. The organic nitrogen assessment results showed that the study area was generally free from organic nitrogen pollution and had a good overall pollution ranking.

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    Sources and influencing factors of arsenic in nearshore zone during river water infiltration
    LU Shuai, SU Xiaosi, FENG Xiaoyu, SUN Chao
    2022, 29(4): 455-467. 
    DOI: 10.13745/j.esf.sf.2021.10.3

    Abstract ( 135 )   HTML ( 10 )   PDF (3715KB) ( 44 )  

    The Shenyang Huangjia water source area is a typical riverside groundwater source area in northern China. In its nearshore zone the iron (Fe), manganese (Mn) and arsenic (As) contents were well above the safety standard. In order to find out the sources and influencing factors of groundwater As in the affected area, samples of river water, groundwater and soils of the study area were collected and tested. Water quality indexes and carbon and sulfur stable isotopes of water samples, and the contents and occurrences of typical minerals and As in soil samples were analyzed. The results showed that As contents were very low in river water samples but generally exceeded the standard in groundwater samples. In the early stage of river water infiltration, some As-bearing minerals were oxidized by oxidizing river water and As was released. Later on, the groundwater environment became reductive with the infiltration of river water, and reductive dissolution of As-bearing Fe/Mn minerals resulted in the gradual increase of groundwater As. Typical minerals in the study area were pyrite, siderite, pyrolusite, hematite, goethite, rhodochrosite, etc. Through desorption of exchangeable arsenic, oxidation of organic matter-bound arsenic, and reductive dissolution of iron-manganese oxide-bound arsenic, As was release into the groundwater. To a certain extent, As content in the groundwater was negatively correlated with groundwater pH and redox potential (Eh) and positively correlated with the dissolved organic carbon (DOC), HCO 3 -, Fe and Mn contents.

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    Submarine groundwater discharge in Longkou coastal zones under the influence of human activities
    GUO Qiaona, ZHAO Yue, ZHOU Zhifang, LIN Jin, DAI Yunfeng, LI Mengjun
    2022, 29(4): 468-479. 
    DOI: 10.13745/j.esf.sf.2022.2.71

    Abstract ( 57 )   HTML ( 7 )   PDF (2200KB) ( 32 )  

    The radium mass balance model based on 223Ra and 224Ra tracers has been widely used in the study of submarine groundwater discharge (SGD) in coastal zones. However, few researches are currently done to study the influence of human activities on SGD. In this paper, the water residence time, SGD flux and nutrient flux carried by SGD were compared between the Longkou coastal zones A and B, under the influence of two different human activities, namely an impervious dam in Zone A and land reclamation in Zone B. Results showed that the average water residence time in Zone A was 14.26 days and in Zone B 10.64 days. In addition, radium activities in groundwater and seawater in Zone B were generally higher than that in Zone A; whereas salinities were lower in Zone B than in Zone A. The discharge rates for SGD in Zone A ranged from 1.26 to 1.60 cm/d and in Zone B from 1.43 to 1.82 cm/d. Therefore the discharge rates for SGD in these two zones were comparable within the margin of error. However, the discharge rates for SGD were relatively low in these two zones compared to other natural coastal areas in the country. Moreover, the nitrogen and phosphorus nutrient concentrations in Zone B were generally higher than that in Zone A. The nitrogen and phosphorus nutrient fluxes carried by SGD were different in the two zones. Such unbalanced nutrient inputs from SGD could easily change the nutrient structure of the Longkou coastal zones, which has an adverse impact on the marine ecological environment, further confirming that SGD is important for coastal ecological environment and water pollution control.

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