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Geochemical characteristics and significance of the shale of Lower Cambrian Hetang Formation in the southern Anhui Province of Lower Yangtze area
The Lower Cambrian organic-rich black shale is well developed in southern China, which is wide in distribution, large in thickness and high in total organic carbon. It has great resource potential of shale gas and is expected to be an important succeeding field to meet the future increase in shale gas demand. This paper is devoted to the first parameter well XY1 of the Lower Cambrian Hetang Formation shale gas in the lower Yangtze area. Using cores and geochemical data, element geochemical characteristics and their paleoenvironmental significance are studied. The results show that the major elements SiO2 and K2O are relatively rich, and the others are lower to certain extent. As for trace elements, Sr and Rb are depleted, and the elements of Ni, Co and Ba are obviously enriched. The black shale of Hetang Formation is a kind of continental margin deposits. Silica mainly came from siliceous organisms under a warm and humid climate, and deposited in saline water, which is favorable to the deposition of organic matter. It is inferred that paleoproductivity of the Hetang Formation is high. The anaerobic water environment is conducive to the preservation of organic matter.
YAO Hongsheng, HE Xipeng, WANG Kaiming
doi: 10.16028/j.1009-2722.2021.123
Marine Geology Frontiers. 2022, 38(4): 32-41
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Composition of minerals in surface sediments of the Yellow Sea and their provenance
Based on the grain size, clay mineral and detrital mineral data of 66 surface sediment samples collected from the Yellow Sea, this paper is devoted to the grain size distribution and mineral composition characteristics of the samples with a detailed discussion on sediment provenance. The results suggest that the average grain size of surface sediments in the Yellow Sea is around 5.2Φ, with poor sorting. Clay minerals are characterized by the assemblage of illite-kaolinite-smectite-chlorite. Illite dominates and smectite is the lowest. The distribution of detrital minerals shows a similar pattern as the mean grain size. The light minerals mainly consist of quartz and feldspar. Heavy minerals mainly occur in the southern part of the Yellow Sea, dominated by hornblende and epidote. Study of material sources suggest that the sediments in the northeastern Yellow Sea are mainly from the Yalu River, while the provenance of the northern part is the modern Yellow River. In the western South Yellow Sea, sediments are mainly from the modern Yellow River either transported by coastal currents, or resuspended from the abandoned Yellow River delta in the northern Jiangsu Province. In the central South Yellow Sea, sediments are mainly from the Yellow River, followed by some supplement of sediments from the Yangtze River.
HAN Zongzhu, WANG Yibing, SUN Yuangao, AI Li'na, WU Xiao, YANG Yepiao
doi: 10.16028/j.1009-2722.2021.112
Marine Geology Frontiers. 2022, 38(4): 10-19
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The elements phase associations of ferromanganese nodules in the seamounts of the South China Sea
The study on the association phase of major and trace elements in ferromanganese nodules is of great significance for further understanding the formation and element enrichment process in ferromanganese nodules. In this paper we applied the in-situ X-ray fluorescence spectrum (XRF) and scanned the transects for 3 nodules collected from the Jiaolong seamount (3 300 meters in depth) in the South China Sea and divided the nodules’ transects into several layers for elements sequential-leaching experiment in order to determine the adsorption phases of main and trace elements. The carbonate phase, manganese mineral phase, iron mineral phase and residual phase components in the nodules were leached respectively, and the contents of major and trace elements before and after leaching in different layers were determined by ICP-OES(MS). The results show that the most of the host phases of elements in nodules are similar to that of hydrogenetic nodules in open oceans, with Al, K, Mg, Li, Ti more enriched in residual phase, showing the unique phase pattern of marginal sea hydrogenetic nodules. From the core to the rim of the nodules, the proportion of Mg, Cu, Ni and Zn in manganese mineral phase increases with the increase of Mn/Fe ratio, which may reflect the changes in chemical and mineral composition. In addition, compared with the previous publications, we found that the experimental reagent and reaction time had a great influence on the leaching result.
XU Yajing, ZHOU Huaiyang
doi: 10.16028/j.1009-2722.2021.146
Marine Geology Frontiers. 2022, 38(4): 20-31
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Hydrothermal sedimentary origin of the Ningguo Formation in Jiangshan, Zhejiang Province: evidence of elemental geochemistry and C-O isotopes
In recent years, many carbonate interlayers, including lenticular limestones and siderites, have been discovered in the Lower Member of Ningguo Formation of Ordovician in the Jiangnan Area of East China. Controversies occur with regards to the origin of such carbonate rocks. In this paper, the carbonate rocks are studied by means of the petrogeochemistry and C-O isotopes. The Σ(CaO+MgO+LOI) values of these carbonate rocks vary in a relatively narrow range from 95.67% to 89.89%, and the SiO2 and TFe2O3 values are negatively correlated with the Σ(CaO+MgO+LOI) values. However, the values of Al2O3, MnO, P2O5 and TiO2, are not significantly correlated with the Σ(CaO+MgO+LOI) values. The Co/Ni values of these carbonate rocks vary within the range from 0.24 to 0.28, much lower than 1.0, and the Mn/Sr ratios change from 0.14 to 0.33, much lower than 10. In the ternary plots of Al-Fe-Mn, (Cu+Co+Ni)×10-Fe-Mn and Ni-Co-Zn as well as the crossplot of LgU-LgTh, all the studied samples fall in the domain of hydrothermal carbonates. The ΣREE values of these carbonate rocks vary between 13.89×10−6 and 40.73×10−6, much less than the average ΣREE value of the upper crust (146.37×10−6) and slightly higher than the ΣREE value of chondrite (about 2.56×10−6). The δ13CV-PDB, δ18OV-PDB and δ18OSMOW of these carbonate rocks are 0.33‰~0.67‰, −9.76‰~−10.1‰ and 12.56‰~12.9‰ respectively, which are obviously different from those of Marine and lacustrine limestones. Fault systems are well developed in the area, which may provide channels for the downward infiltration of seawater, of which the mixing effects the hydrothermal solution. As a result, the convective activities between seawater and hydrothermal continuously supply heat and diagenetic ions for the ocean basin. This marine hydrothermal deposition event represents a special genetic mode. It lasted for a long time and occurred in a wide range, depending on the provenance of hydrothermal materials and their properties.
YANG Qingkun, LIU Yong, ZHANG Xiaoliang, LI Hailong
doi: 10.16028/j.1009-2722.2021.197
Marine Geology Frontiers. 2022, 38(1): 24-32
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Characteristic of detrital zircon U-Pb geochronology in the southern Okinawa Trough and its implication for sediment provenance
The southern Okinawa Trough is the area with the fastest deposition rate since the Holocene, and its sediments record the evolution of provenance, Kuroshio and the East Asian monsoon. In this paper, detrital zircon U-Pb geochronology is used to study the provenance of H4-S2 sediments in the southern Okinawa Trough. By means of Kernel Density Estimation (KDE), Cumulative Age Distribution (CAD) and correlation analysis, the visual analysis and similarity test for potential provenances of two layers of sediments are carried out for the trough, and thus the chronology and provenance of detrital zircon revealed. The provenance analysis suggests that the detrital zircon in the sediments from the southern Okinawa Trough are sourced from the East China Sea shelf, Yangtze River and Lanyang River during the last 200 years, which means that the East China Sea shelf and Yangtze River dominated the provenance of the Late Quaternary sediments in the southern Okinawa Trough.
ZHU Bowen, ZENG Zhigang
doi: 10.16028/j.1009-2722.2020.190
Marine Geology Frontiers. 2022, 38(1): 14-23
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Characteristics of submarine hydrate pingos and mud volcanoes and their effects on gas hydrate accumulation
Submarine hydrate pingos and mud volcanos are both the products of upward migration and discharge of fluids in different phases to the surface. The shallow gas hydrate reservoirs related to these two special geological bodies have unique formation process and occurrence, and at the same time, they are also an important way of carbon-rich fluid emission. However, due to the lack of systematic investigation and research about these two geological bodies, and the lack of attention to shallow gas hydrate resources and carbon leakage, there are still obstacles in fine characterization and accurate discrimination of submarine hydrate pingos and mud volcanoes. This makes it difficult to scientifically evaluate the accumulation process and environmental effects of their associated gas hydrate resources. In this study, by summarizing the existing researches on the submarine hydrate pingos and mud volcanos, the two special geological bodies are compared from the aspects of geomorphic characteristics, internal structure and formation mechanism. The evolution the process of the two geological bodies and their influence on the related gas hydrate accumulation process are systematically analyzed, and the essential differences and relations between the two geological bodies are discussed. We hope this study might provide an important reference for the research on submarine carbon leakage and its contribution to the carbon cycle, as well as the evaluation of global shallow gas hydrate resources.
YAN Dawei, SUN Zhilei, GENG Wei, LI Ang, CAO Hong, XU Cuiling, ZHANG Xilin, ZHAI Bin, ZHANG Xianrong, LI Qing, WU Nengyou, CAI Feng, LUO Di, SUN Yunbao, ZAHNG Dong, ZHOU Yucheng, LV Taiheng
doi: 10.16028/j.1009-2722.2021.192
Marine Geology Frontiers. 2022, 38(1): 1-13
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JOINT INVERSION OF GRAVITY, MAGNETIC, SEISMIC DATA OF THE CFT LINE ACROSS THE SOUTHWEST SUB-BASIN AND ADJACENT AREAS AND ITS APPLICATION
Joint inversion of the 1093 km of integrated geophysical detecting section (CFT) is made across the southwestern sub-basin of the South China Sea and the two sides of the continental margin. The data involved in the inversion includes the ocean bottom seismograph (OBS) data, the long-arranged multi-channel seismic profiles, and the gravity and magnetic profiles. Based on the results of joint inversion and segmented interpretation, many pre-Cenozoic residual sedimentary deposits and multiple periods of magmatic activities are observed. The crustal structure of the South China Sea is quite complex, which includes continental crust, thinned continental crust, continental-oceanic transitional crust and ocean crust. The high-speed layer under the crust is widely distributed. The observations prove that the joint inversion of gravity, magnetism, and seismic data is an effective tool to study the structural characteristics of the sea and deep crustal structures.
DU Wenbo, QIU Yan, WANG Jun, NIE Xin, WANG Yanlin, HUANG Wenkai
doi: 10.16028/j.1009-2722.2021.006
Marine Geology Frontiers. 2021, 37(12): 38-48
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CENOZOIC FAULT CHARACTERISTICS AND BASIN GENESIS OF THE ENPING SAG, PEARL RIVER MOUTH BASIN
Detailed description of fault systems and basin structures is devoted by this paper to the Enping Sag of the Pearl River Mouth Basin, South China Sea. The main basin controlling fault systems formed in different periods are determined and classified by means of fault activity rate calculation and equilibrium profile analysis, upon which the evolution process of the basin is reconstructed, and the dynamic mechanism of basin development and transformation discussed. The results suggest that the evolution of the basin is controlled by both the pre-existing basement structure and the regional dynamic field. During the early rifting stage, the subduction of the Pacific plate retreated as the subduction rate decreased under the joint action of Indian plate, that led to the change in stress into an extension field in NW—SE direction and the negative inversion of the early formed NE trending low angle reverse faults. As the results, a detached half graben was formed under the control of NE trending fault. During the late rifting stage, under the joint action of the rotation and extrusion of Indosinian block and the southward subduction of the paleo-South China Sea, the regional stress field changed from clockwise transformation into nearly NS stretching, and the basin controlling faults changed from NE to nearly EW trending. And the lithospheric extension was changed from a wide rift mode to a narrow rift mode as the basin framework changed from isolated half grabens to connected extensional grabens. During the depression period, the lithospheric thinning center migrated towards the South China Sea spreading center, leading to weak tectonic activity and thermal subsidence. In the tectonic reactivation stage, the NW trending Luzon island arc collided with the Eurasian plate, which caused the NNE stretching, the revival of pre-existing near EW faults and the formation of the secondary strike slip fault zone, in addition to complex uplifting and falling of fault blocks.
SHI Xiaoguang
doi: 10.16028/j.1009-2722.2021.167
Marine Geology Frontiers. 2021, 37(12): 1-9
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APPLICATION EXPLORATION, THEORETICAL AND TECHNOLOGIACL INNOVATION OF GEOLOGICAL SURVEY RESULTS IN COASTAL BEDROCK CITY:TAKING QINGDAO AS AN EXAMPLE
Urban geological work is an important development direction of geological work in the future, and has become an important basic support for urban planning and construction, economic and social development. This paper systematically expounds the positioning, service effect, theoretical and technological innovation of urban geological work in Qingdao, as well as the strategic thinking of future urban geological work of Qingdao. Since 2018, the multi factors urban geological survey project of Qingdao organized and implemented by China Geological Survey Bureau has achieved remarkable results in serving the land and space planning of Qingdao, demonstration of major engineering construction planning, coastal ecological environment protection and restoration, and work of natural resources management center. This work has realized innovation of theory and technology for coastal bedrock urban geological survey. The future development direction of Qingdao urban geological survey is to strengthen the leading role of urban geological services for economic and social development, strengthen monitoring and early warning and realize multi network integration, and effectively solve major geological problems closely related to urban development and urban residents' life.
DOU Yanguang, YIN Ping, CHEN Bin, XUE Biying, WANG Milei, ZOU Liang, HU Rui, XU Gang, YUE Baojing, SONG Weiyu, LIN Xi, DONG Jie, FU Jiani, XU Rui, HE Song, LIN Qingang
doi: 10.16028/j.1009-2722.2021.122
Marine Geology Frontiers. 2021, 37(9): 1-9
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DIFFERENCE ANALYSIS OF HYDROCARBON GENERATION IN THE SOUTHERN PART OF THE WESTERN CONTINENTAL MARGIN OF THE SOUTH CHINA SEA
Two basins, the Wan'an and Mekong basins, occur in the southern part of the western continental margin of the South China Sea (SCS), separated by a swell called Con Son. The former contains natural gas, whereas the latter produces oil. In order to study the cause of the difference as such, heat flow background, structural pattern, sedimentary environment and hydrocarbon kerogen of the two basins are reexamined and compared in this work, based on existing geologic data and references. Research results indicate that in addition to the differences in contained hydrocarbon, there are differences in heat flow, structural pattern, sedimentary environment and hydrocarbon kerogen as well between the two basins. Affected by fault activities, the geothermal gradient and heat flow value of the Wan'an Basin are obviously higher than that of the Mekong Basin. In the Wan'an Basin, the major source rocks include the Oligocene to Early Miocene lacustrine-estuarine sediments deposited in a fault-depressed basin, and the kerogen of the Oligocene source rock mainly comes from lacustrine algae, aquatic plants and some higher plants, while the kerogen of Early Miocene mainly from terrestrial higher plants such as mangrove forest, dominated by type Ⅱ2-Ⅲ of kerogen, which largely generates natural gas. In the Mekong Basin, however, the major source rock deposited in Oligocene is dominated by lacustrine sediment of rift type, with hydrocarbon generation material coming mostly from algae and aquatic plants, and the kerogen of type Ⅰ-Ⅱ that generates mainly oil. Therefore, it is concluded that the difference in structural pattern controls the sedimentary environment, the difference in sedimentary environment controls the hydrocarbon generation material, and the difference in hydrocarbon generation material controls the type of hydrocarbon generated.
GUO Jia, YANG Shuchun, HU Wenbo, SONG Shuang, WANG Yibong, WANG Long
doi: 10.16028/j.1009-2722.2021.041
Marine Geology Frontiers. 2021, 37(10): 1-7
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CHARACTERISTICS OF REE AND HEAVY METALS IN THE SURFICIAL SEDIMENTS OF LAIZHOU BAY, BOHAI SEA AND THEIR IMPLICATIONS FOR PROVENANCE
With the surface sediment samples collected from the 32 stations of Laizhou Bay, some critical environment problems, such as the composition and distribution patterns of rare earth elements (REE) and heavy metals, heavy metal pollution degree and the sources of pollutants are studied in this paper. Upon the basis, we made discussion on such environmental factors as the distribution of heavy metals and rare earth elements by means of heavy metal provenance, chemical alteration index (CIA) and REE characteristics. The results show that the total amount of rare earth elements increases from southeast to north in the bay, and the contents of some rare earth elements, such as Eu, Gd and Tb, are obviously related to fine grained clay minerals and organic carbon, and little affected by chemical weathering. Some stations in the study area are polluted by Cd and Hg obviously enriched by human activities; Cu, Pb and Zn might be the products of natural weathering of the earth crust; and Cu and Zn are also closely related to human activities; while Cr is influenced by both natural weathering and human activities; the accumulation of most heavy metals is affected by the hydrodynamic forces of the bay. Provenance discrimination results suggest that the average value of CIA in the study area is 50.83, close to the value of the Yellow River sediments (50.9~59.7), but lower than the value of the Chinese loess; the REE distribution pattern and characteristic parameters of the study area are also very close to the Yellow River, which indicates that the Yellow River is the most important source of surface sediments of Laizhou Bay; The Guangli River and Weihe-Mihe delta only contribute some sediments in the south and southwest, while the contribution of the Chinese Loess and the local soil in Shandong Province is relatively little.
DUAN Yunying, PEI Shaofeng, LIAO Mingwen, ZHAI Shikui, YANG Shixiong, HE Lei, YE Siyuan
doi: 10.16028/j.1009-2722.2021.067
Marine Geology Frontiers. 2021, 37(10): 8-24
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GEOCHEMICAL CHARACTERISTICS OF SOURCE ROCKS IN DIFFERENT SEDIMENTARY FACIES ZONES AND THEIR CONTRIBUTIONS TO THE HYDROCARBON RESERVOIRS IN THE BAIYUN SAG
Based on the data of biomarkers, sporopollen and algae assemblages and carbon isotopes of source rocks, combined with the study of sedimentary background, the geochemical characteristics of source rocks in different sedimentary facies zones and their contributions to the formation of hydrocarbon reservoirs in the Baiyun Sag are discussed in this paper. The results show that the abundance of organic matter in the middle and deep lacustrine source rocks of the Wenchang Formation is on a medium level, dominated by the organic matter of type Ⅱ1 coming from algae and aquatic organisms, and characterized by the lightest δ13C value of kerogen less than −28‰. However, the organic matters of the shallow lacustrine source rocks of the Enping and Wenchang Formations are from terrestrial higher plants, of which the δ13C value of kerogen is about −27‰, and the abundance of organic matter is on medium to high levels, dominated by type Ⅱ2-Ⅲ of organic matter. The transgressive lacustrine source rocks of the Enping Formation are rich in marine limbic algae and Triaryl dinoflagellate sterane, and the δ13C value of kerogen is about −25‰. The δ13C value of the crude oil in the Baiyun Sag is changed within the range of −28‰~−27‰. It suggests that the crude oil of the Baiyun Sag mainly comes from the shallow lake source rocks of Wenchang and Enping Formations and the distribution of crude oil types is controlled by sedimentary facies. The deep lake source rocks of Wenchang Formation are the main hydrocarbon contributor to the wells near the sag, while the transgressive source rocks of Enping Formation make little contribution to the formation of reservoir.
MA Ning, LONG Zulie, LIU Baojun, CHEN Cong, LI Qingquan
doi: 10.16028/j.1009-2722.2020.169
Marine Geology Frontiers. 2021, 37(10): 25-32
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DEPOSITIONAL CHARACTERISTICS OF THE LOW-RESISTANCE OIL RESERVOIRS OF THE GUANTAO FORMATION IN THE BOHAI SEA AND THEIR CONTROL FACTORS: A PERSPECTIVE OF QHD OILFIELD
A comprehensive study is made in this paper on the lithology and depositional characteristics of the low-resistivity oil reservoirs of the Guanxi section of Guantao Formation, based upon the seismic, logging, and coring data and laboratory testing data collected from the QHD oil field of the Bohai Sea. The reservoirs in the Guanxi section is dominated by lithic feldsparthic sandstone and feldsparthic lithic-sandstone, consisting of subangular and sub-rounded sand deposits with gravels in an ordered sequence from medium-sized cross bedding, trough-shaped cross bedding, plate-shaped cross bedding, wavy cross bedding, to horizontal bedding from bottom to top. The mudstone is mainly variegated, which also indicates a shallow water environment under weak oxidation-weak reduction and/or oxidizing environment. In general, the low-resistivity reservoir suggests a weak hydrodynamic environment, dominated by such microfacies as braided channels, mid-channel bars, flood plain and small gullies. The integrated study suggests that sedimentary environment, diagenesis and micro-clay minerals are the reasons which caused the poor physical properties of the reservoirs and the complicated pore structure, which made up the high water saturation of the Guan Xi section is also a major factor for the formation of the low-resistance oil reservoirs.
JIN Baoqiang, CHEN Jianbo, SHU Xiao, ZHOU Junliang, DENG Meng
doi: 10.16028/j.1009-2722.2020.105
Marine Geology Frontiers. 2021, 37(8): 17-22
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STRUCTURE-CORRECTION METHOD WITH SEISMIC DATA AND ITS APPLICATION TO IGNEOUS ROCK AREAS
Cenozoic igneous rocks are widely and unevenly distributed in the BZ Oilfield of the Bohai Sea. The underground structure of igneous rocks varies with depth. It is not able to correctly describe the underground structure by the conventional time-depth conversion method with seismic data, and as the result it will increase the risk and uncertainty in hydrocarbon exploration and development. In this paper, a new method for structure correction is proposed specifically for igneous rock areas. Firstly, the impact of igneous rock is studied by means of numerical simulation method so as to establish the relationship between the igneous rock thickness and the time span to be corrected. Secondly, the total thickness of igneous rocks is calculated using the interval velocity constrained inversion, then the time-correction for seismic events is obtained. Finally, time-depth relationship is adopted to eliminate the effects of igneous rock, and get more accurate structural maps by time-depth conversion. The drilling results show that this method can effectively improve the precision of structural mapping and may provide strong technical support for the first time to carry out the oilfield evaluation under the Cenozoic igneous rocks in the Bohai Sea.
HAN Zijun, PEI Xiaogang, GUO Ying, WU Qingxun, GUO Shuai
doi: 10.16028/j.1009-2722.2020.203
Marine Geology Frontiers. 2021, 37(8): 23-27
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SEDIMENTARY CHARACTERISTICS AND EVOLUTION OF POST-SALT CLASTIC DEPOSITS OF SANTOS BASIN, EASTERN MARGIN OF BRAZIL
The Santos Basin on the eastern margin of Brazil is one of the hot spots for oil and gas exploration in recent years. Hydrocarbon discoveries in the post salt clastic series are mainly distributed in the Late Cretaceous Cenomanian-Turonian period, Late Cretaceous Coniacian-Maastrichtian period and Paleocene period. Based on the analysis of regional depositional settings, provenance characteristics of the surrounding drainages with the drilling, seismic, logging data, this paper makes a systematic study on the main depositional characteristics and the evolution of the three post salt sandstone reservoirs. The results suggest that the south part of the Santos Basin is dominated by shallow-bathyal argillaceous sediments in the Cenomanian-Turonian period, while the small deltas and turbidite channels dominate the middle and northern part of the basin. In the Coniacian-Maastrichtian period, sufficient sediment supply made larger scale deltas continuously prograded seaward into the shallow water shelf area, leaving submarine fans developed on the slope, forming a pattern of "channels dominating the early stage, lobes dominating the later stage". During the period of Paleogene, due to the migration of regional drainage system, sediment supply was reduced, and argillaceous sediments increased. As the results, the scale of delta was obviously reduced, and small channels or channelized lobes dominate the deep-water areas.
LIU Ziyu, LV Dong, XIE Dongning
doi: 10.16028/j.1009-2722.2020.121
Marine Geology Frontiers. 2021, 37(8): 1-8
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ANALYSIS OF THE GAS HYDRATE MIGRATION AND ACCUMULATION MODEL IN THE DEEP WATER AREAS OF QIONGDONGNAN BASIN
Natural gas hydrate is one of the focuses nowadays in hydrocarbon resource researches. Physical and chemical properties, reservoir forming factors and gas hydrate migration and accumulation mechanisms have been carefully studied in previous references. However, there still remain different opinions and discrepancies on the migration and accumulation process of gas hydrate. Systematic induction and summarization are required. In order to better understand the migration and accumulation model of gas hydrate, which is critical to the exploration and evaluation of gas hydrate and the optimization and prediction of favorable enrichment zones, this paper, taking the reservoir forming types of gas hydrate in the Qiongdongnan Basin as the research focus, made a comprehensive analysis of 3D seismic data and geological research results based on the previous studies. According to the differences in gas source supply, migration and accumulation mode and occurrences of gas hydrate, the migration and accumulation modes of gas hydrate in the Qiongdongnan Basin are systematically classified, and also analyzed and discussed are the distribution pattern and their control factors. According to the difference in gas source and reservoir models, the hydrate accumulation in the Qiongdongnan basin can be divided into three types: the type of lower generation and upper storage, the type of self generation and self storage and the type of compound and mixed genesis. The former two types are further divided into five subtypes, of which the type of lower generation and upper storage includes four subtypes: gas chimney dominated subtype, mud diapir dominated subtype, micro-cracks dominated subtype and fault dominated subtype; and there is only one subtype under the type of self generation and self storage, i.e. the type of shallow in-situ deposits.
YAO Zhe, ZHANG Jinfeng, ZHU Jitian, FANG Xiaoyu, LUO Junsheng
doi: 10.16028/j.1009-2722.2021.124
Marine Geology Frontiers. 2021, 37(7): 22-32
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SHALLOW MIGRATION AND ACCUMULATION SYSTEMS IN THE DEEP WATER AREAS OF THE QIONGDONGNAN BASIN AND THEIR CONTROL ON NATURAL GAS HYDRATE ACCUMULATION
Continuous 3D seismic survey has been carried out in the Qiongdongnan Basin, and various types of migration channels are discovered. Based on the characteristics of shallow migration and accumulation system in the deep-water areas of the basin, this paper is devoted to the mechanisms which controls the deposition and accumulation of natural gas hydrate (NGH). Favorable target areas for NGH exploration are predicted upon the basis. It is revealed that the shallow fluid migration channels of the Qiongdongnan Basin mainly consist of faults, gas chimneys, fractures, erosion unconformities and large reservoirs along the border of the basin. Various types of migration channels are always combined in space to form shallow migration and accumulation systems. The development status of the shallow fluid migration channels system varies from place to place. The most developed areas include the Lingnan - Songnan Low Uplift and the Central Depression of the basin, while in the shallow water areas, the systems are relatively undeveloped. The shallow fluid migration and accumulation systems in the deep-water areas of the Qiongdongnan Basin not only control the distribution of NGH, but also influence the gas exploration of the middle and deep layer deposits. To sum up, the shallow fluid migration channels are relatively developed in the Qiongdongnan Basin, and the Lingnan-Songnan Low Uplift is the most favorable zone within the basin, and the continental slope areas of the Songnan-Baodao Sag also have excellent conditions for NGH accumulation.
SONG Peng
doi: 10.16028/j.1009-2722.2021.088
Marine Geology Frontiers. 2021, 37(7): 11-21
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HYDRODYNAMIC CHARACTERISTICS OF COLD SEEP DIFFERENTIAL DEVELOPMENT IN THE QIONGDONGNAN BASIN AND THEIR DEEP CONTROLLING MECHANISMS
The submarine cold seeps are closely related to some important scientific issues, such as the occurrence of natural gas hydrate, global climate change, and extreme environmental ecosystems. There are many factors affecting the formation and evolution of cold seep systems. Their spatial and temporal distribution, activity characteristics, and related physical, chemical, and biological effects are very different from place to place. The coupling relationship between shallow surface cold seeps activities and their deep controlling factors, the hydrodynamic process and control mechanism of differential development of cold seeps need to be further studied. This paper tries to take the Qiongdongnan Basin as the research object and select some typical cold seep active stations as cases to solve the problem of cold seep differential activity process and their control mechanisms. Based on previous researches, taken the hydrodynamic research as the key, and combined the observation data of shallow cold seeps together with the deep geological environment and formation pressure, some numerical models are set up in this paper for the cold seep fluid flow and energy conversion process. The dynamics process of fluid migration from deep to shallow are portrayed. And analyzed are also the geological conditions and control factors for different cold seep systems. Afterward, the coupling relationship between the shallow surface responses of cold seeps to the deep elements is identified. Then a dynamic model of cold seep differential development is established. In the end, the control mechanisms of cold seep differentiation are discussed. This work may provide a theoretical basis for hydrate exploration and trial mining, study of deep-sea material and energy migration and transformation, and research of the extreme environmental ecosystem of cold seep.
WAN Zhifeng, ZHANG Wei, CHEN Chongmin, SU Pibo, WANG Xianqing, ZHANG Jinfeng, LUO Junsheng
doi: 10.16028/j.1009-2722.2021.113
Marine Geology Frontiers. 2021, 37(7): 1-10
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SPATIAL DISTRIBUTION OF ANKERITE AND DOLOMITE IN THE XISHA ISLANDS: EVIDENCE FROM GEOCHEMISTRY
Dolomite and ankerite are widely distributed in the Xisha Islands. So far, seven layers of dolomite have been found in the well Xike 1. The seven layers of dolomite may be grouped into three zones, the shallow, the middle and the deep. The shallow zone is less than 600 meters in depth including the layer 1, layer 2 and layer 3 with a total thickness of 203 m; the middle zone includes the layer 4, layer 5 and layer 6 with a total thickness of 79 meters and occurs in a range of 600~1 000 m in depth; the deep zone includes the layer 7, 155 m in thickness buried underground more than 1000 meters in depth. The geochemical characteristics of major and trace elements of the seven layers of dolomite are studied in this paper, while diagenetic environment and genetic model discussed based on the newly acquired geochemical data combined with previous research results. Dolomite in the well Xike 1 was far beyond the affection of terrigenous materials, high content of SiO2 may come from the volcanic activities surrounding the islands. It is evidenced that the dolomitization in the Xisha area happened in an oxidation diagenetic environment, but the intensity of oxidation is different in the shallow, middle and deep zones. The paleosalinity of sea water was high when the dolomites formed, and there are slight differences between the three zones. The content of strontium in the dolomite of the well Xike 1 is generally low, as it was strongly leached by fresh water in an environment of reef platform with relatively shallow water. Comparatively, the influence of atmospheric fresh water was strongest in the shallow zone, followed by those in the middle and deep zones. The diagenesis of dolomite in the Xisha Islands is influenced by many factors, such as high palaeosalinity seawater, atmospheric fresh water and water reflux infiltration.
SHENG Jiangyuan, FU Heping, MA Xiao, XU Hong, ZHAO Qiang, CHEN Xiangyu, LI Xushen, ZHANG Daojun, LIU Xinyu, YAN Zhuoyu
doi: 10.16028/j.1009-2722.2020.198
Marine Geology Frontiers. 2021, 37(6): 18-30
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ELEMENT GEOCHEMISTRY OF WELL XIKE 1 ON THE XISHA ISLANDS AND ITS BEARING ON SEA LEVEL FLUCTUATION
This study focused on major and trace element geochemistry of the carbonate platforms of the Xisha Islands, northern South China Sea (SCS), based on the sedimentary characteristics of the succession since early-Miocene. A total of 1268 carbonate samples are collected and analyzed by ICP-MS. Both the major elements of Na2O/K2O, Na2O/SiO2, P2O5, and the trace elements of B/Ga, Zr/Al, Li, V show perfect consistence with petrographic, stratigraphic and paleontological variations caused by the changes in paleo-salinity, Eh, pH and sea level fluctuation, which can be well applied for the study of depositional sequences of the isolated carbonate platforms. However, Mg/Ca are hard to be used as a proxy to reveal sea level changes, owing to the strong dolomitization. Na2O/K2O, Na2O/SiO2, P2O5 B/Ga, Zr/Al, Li, V suggest that the bioherms started blooming with the sea water invasion since early-Miocene. During early middle-Miocene, bioherms with lagoonal and beach facies were well formed when the sea level reached its first peak. Then the sea level dropped in late middle-Miocene and early late-Miocene. In the late middle-Miocene, bioherms were strongly leached and eroded, as dominated by reef-beach facies. The sea level started to rise again during late late-Miocene and got to its second peak in Pliocene and then dropped for the second time during Pleistocene period.
LIU Xinyu, SHAO Lei, SHI Defeng, SHI Wenfang, OUYANG Jie
doi: 10.16028/j.1009-2722.2020.199
Marine Geology Frontiers. 2021, 37(6): 8-17
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SEASONAL MONITORING OF PHOTOSYNTHESIS CHARACTERISTICS OF SCLERACTINIAN CORALS IN THE NORTHERN SOUTH CHINA SEA
Systematic investigations of scleractinian corals in the natural environment are relatively lacking since the global decline of coral reefs. In this study, we selected three corals with typical morphology from Sanya, including Pocillopora damicornis, Porites lutea and Pavona decussata. We investigated the symbiodinium density, chlorophyll-a content and effective quantum yield (Φ PSII) for one year. The results show that: ① There are significant interspecific differences among the three corals. The scleractinian density and chlorophyll-a content of P. lutea are the highest, while the Φ PSII is the lowest. ② About symbiodinium density, the lowest value of P. damicornis appeared in winter, while the lowest value of P. damicornis and P. decussata appeared in spring. The chlorophyll-a content and Φ PSII of the three corals show similar pattern of seasonal changes, higher in autumn and winter, lower in spring and summer. ③ The photosynthetic characteristics of corals are related closely to the ecological health of coral reefs, and have clear interspecific differences and seasonal differences. Therefore, the interspecific differences and environmental dynamic changes of scleractinian corals, as an important indicator, need serious consideration in the coral reef monitoring and health assessment.
ZHANG Haiyang, ZHAO Meixia, ZHONG Yu, LU Li, LIU Guohui, YANG Hongqiang, YAN Hongqiang
doi: 10.16028/j.1009-2722.2020.186
Marine Geology Frontiers. 2021, 37(6): 84-91
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ANTI-ERODIBILITY OF CORAL REEF LIMESTONES ON THE XISHA-NANSHA ISLANDS
In the South China Sea, carbonate debris and fragments are commonly transported by air and waterflow in forms of typhoon, wind wave, swell, storm surges and astronomic tide etc. accompanied by strongly erosion of the reef limestones. The research work presented in this paper confirmed the reliability of the abrasion theoretical model we developed via abrasion and compression experiments firstly. And then, the anti-erodibility factor with the dimension of pressure is defined using compressive strength and elastic modulus to quantificationally describe the anti-erodibility of rocks against wind and water. Finally, the preliminary investigation reveals that the aeolianites on the southwest of Shidao island have relative low anti-erodibility. The study of the anti-erodibility of reef limestones will provide certain scientific support for protection of the islands and reefs in the South China Sea.
WANG Zhenting, LIU Xuyang, LI Xiaoze, QU Jianjun
doi: 10.16028/j.1009-2722.2020.200
Marine Geology Frontiers. 2021, 37(6): 71-76
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doi: 10.16028/j.1009-2722.2021.079
Marine Geology Frontiers. 2021, 37(5): 77-80
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RESEARCH EXPERIENCES AND APPLICATION OF SEISMIC EXPLORATION TECHNOLOGY TO THE MESOZOIC– PALEOZOIC MARINE STRATA IN THE SOUTH YELLOW SEA BASIN
The South Yellow Sea Basin is the only large sedimentary basin without oil and gas fields discovered so far in the offshore area of China. There occur two sets of strata, the continental Mesozoic-Cenozoic and the marine Mesozoic-Paleozoic, for hydrocarbon exploration. The marine Mesozoic-Paleozoic strata are thick and widely distributed. However, the quality of seismic data is always a problem which restricts effective oil and gas exploration. The marine Meso-Paleozoic basin is characterized by deep burial, complex basin-forming background, and strong tectonic deformation in the later stage. The research of seismic exploration technology for the Meso-Paleozoic has experienced three stages of progress: seismic geological research, tackling key technical problems, and technical breakthrough and application. In the first stage, seismic geological conditions and rock physical properties were analyzed. Then, with the help of continuous updating of geophysical prospecting vessels, in addition to seismic instruments and equipment, the seismic acquisition parameters are continuously improved through large number of theoretical simulations, targeted physical simulations and continuous offshore trials. As the results, the seismic exploration technology called “HRS” took place, which broke the “bottleneck” of the seismic data interpretation for the marine Mesozoic-Paleozoic strata in the South Yellow Sea Basin. This technology is characterized by high coverage, low-frequency and strong source energy. By using this technology, three sets of seismic reflection markers which can be continuously traced and seven reflection surfaces were identified on the Laoshan Uplift where the original reflection of the marine Mesozoic-Paleozoic strata are blank. Upon the basis, stratigraphic sequences were established, residual basin tectonic units revealed, and the oil and gas prospect areas predicted. The Gaoshi stability zone of the Laoshan Uplift was selected as a favorable exploration target. Key structures were delineated, and drilling targets locked. The works mentioned above made clear the direction and conditions for further exploration and the breakthrough of oil and gas exploration in the new strata of the South Yellow Sea Basin. The “HRS” seismic exploration technology has great significance for expanding the spatial areas of hydrocarbon exploration in offshore China, and push forward the exploration and development of oil and gas resources in deep offshore areas. The technology may be used for oil and gas exploration in the sea areas with similar seismic and geological conditions in the other part of the world.
CHEN Jianwen, ZHANG Yibiao, CHEN Hua, LIU Jun, HE Yuhua, SHI Jian, LI Bin, YUAN Yong, LIANG Jie, ZHANG Yinguo, LEI Baohua, WANG Jianqiang, WU Shuyu, WU Zhiqiang, YAN Guijing, CHEN Chunfeng, XIAO Guolin
doi: 10.16028/j.1009-2722.2021.053
Marine Geology Frontiers. 2021, 37(4): 1-17
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THERMO-COMPRESSION CHARACTERISTICS OF HYDROCARBON GENERATION FOR THE SOURCE ROCKS IN THE FUNINGFORMATION OF SOUTH YELLOW SEA BASIN
The kinetics data of hydrocarbon generation is very important to hydrocarbon resource evaluation. The source rock samples taken from the 4th Member of the Funing Formation in the Naner Sag of the South Yellow Sea Basin are used in this paper for thermo-compression simulation and fitting experiment of kinetic parameters for hydrocarbon generation. The results suggest that the generation of hydrocarbon in the 4th Member of the Funing Formation can be subdivided into three stages. In the first stage, hydrocarbon production dominated by oil increased rapidly with the rise of temperature. In the second stage, with the increase in temperature, hydrocarbon production including both oil and gas increased slowly. In the third stage, hydrocarbon production, dominated by gas, increased rapidly with the rise of temperature. The experimental results show that the activation energy for oil generation and gas generation is 228 kJ/mol and 280 kJ/mol, Respectively. Compared with the results from conventional experiment under open system and the gold tube autoclave test for the source rock samples of the Funing Formation, a lag phenomenon is noticed. The source rock samples still have high liquid hydrocarbon production in the highly matured stage. The activation energy value of the 4th Member of Funing Formation derived from this experiment is higher than that in the other two cases of experiment. It is believed that the evolution of organic matter is protected by the high pressure porewater and influenced by the hydrocarbon generation space, which caused the delay of the thermal evolution process of the source rock. Based on the comprehensive analysis of this experiment and previous experimental results, the experiment environment of the thermo-compression simulation for hydrocarbon generation in finite space is concluded, which is closer to the geological conditions for hydrocarbon generation, and results of this experiment are useful to oil and gas resource evaluation and exploration in the South Yellow Sea Basin
CHEN Chunfeng, WAN Yanzhou, ZHANG Bocheng, FU Xiaowei, OU Ge, WANG Jun, CHEN Hao
doi: 10.16028/j.1009-2722.2021.025
Marine Geology Frontiers. 2021, 37(4): 18-24
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CHARACTERISTICS AND DEPOSITIONAL MODEL OF THE FAULT-CONTROLLED BOTTOM-CURRENT DRIFT DEPOSITS IN THEBEIKANG BASIN, SOUTHERN SOUTH CHINA SEA
Bottom current is a significant depositional process in deep sea, by which sediments can be directly transported to form contourite drifts on seafloor. Among the different types of contourite drifts, fault-controlled drifts are not well constrained and few studies have been devoted to their morphological features and depositional patterns. This study is to summarize the features for seismic identification of fault-controlled drifts based on high-resolution multibeam bathymetric and seismic data from the Beikang Basin, southern South China Sea. Two sub-types of fault-controlled drifts, i.e. the syn-depositional and post-depositional fault-controlled drifts are recognized. Their formation mechanism and relationships with faulting are discussed in this paper. According to the interaction between faulting and bottom-current processes the bottom currents can be divided into two types: 1) bottom currents simultaneous to the fault movement, generating the synchronous fault-controlled drifts; 2) bottom currents after the fault movement generating the post-depositional drifts. However, the researches conducted so far are limited to the drift deposits related to normal faults. More researches are required for the drifts formed in other active tectonic settings, such as those related to strike-slip faults and reverse faults.
LEI Zhenyu, ZHANG Li, LIU Shan, SU Ming, LUO Shuaibing, SHUAI Qingwei
doi: 10.16028/j.1009-2722.2021.028
Marine Geology Frontiers. 2021, 37(4): 46-52
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AN ATYPICAL LACUSTRINE SOURCE ROCK AND ITS PETROLEUM CHARACTERISTICS IN THE LISHUI SAG OF THE EAST CHINA SEA
The lacustrine mudstone of the Yueguifeng Formation of Paleocene is the predominant source rock in the Lishui Sag of the East China Sea. Both natural gas and condensate have been found there. However, it is rather different in hydrocarbon sources with the typical lacustrine rift basins in Eastern China where oil dominates. Comprehensive source rock evaluation on the Yueguifeng shale suggests that there occurs dead carbon to certain proportion, which cannot generate petroleum. In addition, the thermal evolution maturities are not in coupling with the requirement of the conversion index from organic matters to hydrocarbons. The organic matters in Yueguifeng Formation shale are mostly terrestrial in origin, and the percentages of lacustrine aquatic organisms varies. There occur some differences in geochemical characteristics between the Yueguifeng source rocks and the typical lacustrine source rocks. The type of lake-basin have certain control over source rock evolution. Based on the comparison of geochemical characteristics of Yueguifeng source rocks and the petroleum generated in the sag with those of the typical lacustrine source rock and petroleum generated in different lake-type basins, it is found that over compensate and balanced compensate lake basin dominated the Yueguifeng period. And the shales in Yueguifeng Formation are atypical lacustrine source rocks.
CHEN Xiaodong, JIANG Yiming, QI Binwen, YU Zhongkun
doi: 10.16028/j.1009-2722.2021.039
Marine Geology Frontiers. 2021, 37(4): 25-38
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ORIGIN AND EVOLUTION OF THE SHUANGFENG BASIN OF THE SOUTH CHINA SEA AND THEIR CONSTRAINTS ON STRUCTURAL STYLES
The deep-water area of the northern South China Sea, i.e the Shuangfeng Basin in other words, has gradually become a hot spot for oil and gas exploration. Over the others, it is of great significance to carry out the study of structural style so as to know better about the origin and evolution of the basin. Using the 2D seismic data from Guangzhou Marine Geology Survey, the main structural styles of Shuangfeng Basin are determined based on the detailed interpretation of seismic sequences and structures. The structural evolutionary history of the Shuangfeng Basin is then reconstructed with the technique of balanced section. The nature and genesis of Shuangfeng Basin are also analyzed together with regional tectonic background in the north of South China Sea. It is revealed that the Shuangfeng Basin is a depression related to thermal subsidence of oceanic crust. Since the Shenhu movement, the basin has experienced a complete tectonic cycle from continental fracturing, through continental disintegration to seafloor spreading. The Shuangfeng Basin is formed under the action of continuous extensional tectonic stress. There are four types of extensional structural styles: extensional, transition-extensional, gravity sliding structure, and igneous structures.
ZHANG Li, LEI Zhenyu, WANG Zhigang, LUO Shuaibing, SHUAI Qingwei, LIU Jianping
doi: 10.16028/j.1009-2722.2021.029
Marine Geology Frontiers. 2021, 37(4): 39-45
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DIAGENESIS OF CORAL REEFS: AN IN-SITU GEOCHEMICAL STUDY OF CORAL REEFS AT THE YONGXING ISLAND, SOUTH CHINA SEA
The geochemistry of coral reefs provides evidence for surrounding seawater conditions and may reflect the paleoceanographic, paleoclimatic and paleoenvironmental variations at the time of deposition. However, coral reefs are apt to be altered by diagenesis during and after their formation, which can lead to substantial changes in mineralogy, geochemistry and biological characteristics. In such a circumstance, the geochemistry of coral reefs is not able to reflect the characteristics of the surrounding water. Therefore, the influences of diagenesis must be excluded before the geochemical indicators are applied to coral reef research if the surrounding water conditions are studied. Our study this time focuses on the cores from the well SSZK1 drilled at the Yongxing Island, Xisha Islands. Microfacies with different fossils and carbonate cements are studied in-situ based on mineralogy, petrography and geochemistry of the reef so as to explore the history of diagenesis. Observation of hand specimens and thin sections suggests that, the carbonate rock types from the well SSZK1 core are mainly composed of branching coral skeleton, bioclast and others fossils, such as calcareous algae, gastropod and foraminifera, dominated by aragonite, high-magnesium calcite and low-magnesium calcite. Early atmospheric diagenesis, which includes cementation, neomorphism and dissolution, play critical roles in determination of the composition of reef rocks. The in-situ analysis with electronic probe and LA-ICP-MS suggests that the diagenetic minerals in different diagenetic stages are extensively dominated by low-magnesium calcite. Diagenetic aragonite is only observed in some local fossils. The primary fossils are characterized by high Sr/Ca and Sr, with low Mg/Ca, while the diagenetic cements characterized by low Sr/Ca and Sr, with high Mg/Ca). It indicates that the coral reefs have been reformed by the diagenetic fluids of different origin, which controlled the mineralogy and geochemical characteristics of the coral reef in different stages.
WU Jiaqing, LIU Gang, HAN Xiaohui, ZHAO Yanyan, WEI Haotian, YANG Jun
doi: 10.16028/j.1009-2722.2020.006
Marine Geology Frontiers. 2021, 37(1): 31-44
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SEISMIC REFLECTION CHARACTERISTICS OF NEOGENE CARBONATE PLATFORMS IN THE XISHA SEA AREA AND THEIR CONTROLLING FACTORS
Based on the latest acquired high resolution 2D seismic data, drilling data, and combined with previous research results in the Xisha area of northern South China Sea, the sequence stratigraphic framework is established by this paper, and four different types of reef, i.e. the point reef, tower reef, platform edge reef and atolls reef, are identified. Upon the basis, seismic reflection characteristics of different kinds of reefs are summarized. It is revealed that carbonate platforms began to develop from Early Miocene, when the platforms were few and limited in scale. During Middle Miocene, the sea level continuously kept rising. When the sea level rise rate was closed to the growth rate of carbonate platforms, carbonate platforms reached their maximum in both number and scale. The sea level continued to rise after Late Miocene, and the sea level rise rate was much greater than the growth rate of carbonate platform. With the rapid increase in water depth, the platform was then submerged. It was no longer suitable for the development of carbonate platform excluding some local highlands, and atolls surrounding them. Facts demonstrate that tectonic movement and relative sea-level changes are the main factors predominating the development of carbonate platforms in the Xisha area.
DU Wenbo, CAI Guanqiang, HUANG Wenkai, CHEN Jiale, NIE Xin, WAN Xiaoming
doi: 10.16028/j.1009-2722.2020.173
Marine Geology Frontiers. 2021, 37(1): 20-30
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GEOCHEMICAL CHARACTERISTICS OF THE MORBS OF THE SWIR AND THEIR IMPLICATIONS FOR MAGMATIC PROCESS
Five fresh MORBs samples collected from the 50°E of the SWIR have been studied for petrology and geochemistry. The major elements, TAS and AFM diagrams suggest that the samples from the SWIR are dominated by low potassic tholeiite. The primitive mantle-normalized sprider diagram shows negative anomalies of Ba, Nb and Sr, while K is positive in all of the samples. The MORBs of the SWIR show a depleted pattern of light REE in chondrite-normalized REE diagram, with slightly positive Eu and Ce anomalies; The MORBs from the SWIR are all derived from the upper mantle and obviously migrate to the end member of EMII. Most of the SWIR basalts enriched in the region are sourced from mantle. It is composed of both DM and EMII, includes small amount of continental crustal components. The basaltic magmas of SWIR are originated from the spinel peridotite zone. The samples of the SWIR are formed under a moderate reducing environment, experienced obvious fractional crystallization from olivine, clinopyroxene to plagioclase.
HAN Zongzhu, SUN Yuangao, WANG Chuan, SUN Xiaoxia, LIU Ming, LAI Zhiqing
doi: 10.16028/j.1009-2722.2020.045
Marine Geology Frontiers. 2021, 37(1): 11-19
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PETROLEUM GEOLOGICAL CHARACTERISTICS AND EXPLORATION DIRECTIONS OF DEEP WATER BASINS IN SOUTH CHINA SEA
Based on the in-depth investigation of petroleum geological conditions, we discussed in this paper the distribution pattern of oil and gas in the South China Sea deep-water basins and their controlling factors on reservoir formation, petroleum resources potentials and favorable exploration directions, so as to provide a scientific basis for decision-making in deep-water oil and gas exploration of the region. The results show that the deep-water basins in the South China Sea are formed on the typical continental margin of a marginal sea, with specialpetroleum geological conditions and significant north-south differences. The deep-water Pearl River Mouth Basin and Qiongdongnan Basin in the northern South China Sea are dominated by structural traps, the southern Zengmu Basin and Brunei Shaba Basin in the south dominated by structural traps; the northern Zengmu Basin dominated by lithologic reservoirs (reef bank type reservoirs); while the Wan’an Basin by structural trap and buried hill types of reservoirs. The petroleum geological characteristics of the deep-water basins in the northern South China Sea and the South Central South China Sea suggest that the deep-water basins in the South China Sea have greatpotential of oil and gas accumulation. The favorable exploration directions include: ① the Central Canyon and Lingnan Slope of Ledong-Lingshui Depression of the Qiongdongnan Basin, the reversed structural zone of Songnan-Baodao Depression, the submarine fan on the north slope of Baodao Depression, the trap belt around A sub-depression (submarine fan) of Changchang Depression, the deep water fan and the two wings of main depressions, and southwest fault step belt of the Baiyun Depression in Pearl River Mouth Basin, and the deep water fan in Liwan Depression. ② Brunei-Sabah, Zengmu and Wan’an basins are favorable exploration directions in the Southern Central of South China Sea.
WANG Xuefeng, LI Lin, WANG Guoyu, WANG Bin, LIU Yanhong, YAN Chun, MAO Chaolin, SUN Guozhong
doi: 10.16028/j.1009-2722.2020.041
Marine Geology Frontiers. 2021, 37(1): 1-10
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NUMERICAL SIMULATION OF THE INFLUENCE OF ARTIFICAL REEFS ON MARINE HYDRODYNAMICS TO THE WEST OF QIANLIYAN ISLAND
Based on the Mike21FM model, the hydrodynamic conditions of the artificial reef construction area and the surrounding sea area in Qianliyan West are simulated. The Euler residual current is calculated for 720 hours, and the residual flow velocity before and after engineering is calculated. The influence of engineering construction on hydrodynamic condition of surrounding sea area is studied. Furthermore, it provides reference for the study of the rationality of reef site selection, nutrient loss or enrichment area and water quality. The research shows that the resistance effect of engineering construction can reach 0.4 m·s−1. The area where the current velocity increases during the period of surge is located in the north and south sides of the project area, with an area greater than 0.05 m·s−1 of about 4.52 km2; The area where the current velocity decreases over 0.05 m·s−1 is about 4.28 km2. The mean decrease of euler residual current velocity in the project area was around 0.01 m/s, and the overall increase of euler residual current velocity in the surrounding sea area outside the project area, and the area with the maximum increase of more than 0.1 m·s−1 appeared in the east of the project with an area of 0.41 km2.
CUI Enping, ZHANG Yongqiang, ZHU Lin, MA Xiaoge
doi: 10.16028/j.1009-2722.2020.040
Marine Geology Frontiers. 2021, 37(2): 10-20
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COASTLINE CRITERIA FOR LAND AREA OF THE HUANGHE RIVER DELTA AND THEIR SIGNIFICANCE
The land area of the Huanghe River Delta is significant to the integrated estuary administration and management, national land planning, conservation and development of natural reserves and oil-gas exploitation and development. The adopted criteria for the time being include high tide line, low tide line, 0 m line upon the Huanghai datum and −2 m line upon the Huanghai datum from measured data, and high tide line, low tide line, water body line from Remote sensing satellite images. There are large differences in the figures of land increment per 1×108 t sediment or so-called “land increment efficiency” among the data from the Lijin Station, the modern delta, the Qingshuigou course, and the Qing 8 course. The coastline from satellite images have big differences in some periods, due to the broad tidal flat with gentle slope. It is suggested that the −2 m line on the Huanghai datum is proper for studies of coastal progradation and retrogradation, water course avulsion and migration, and influences on lower reaches of the River. The main problem of the existing studies on the sediment for coastline dynamic balance is that data are not sufficient from recession periods. In order to maintain long term stabilization of current course, more work is required to study the sediment budget and coastal dynamic balance along the Qingshuigou course.
YU Shoubing, FAN Yaoshen
doi: 10.16028/j.1009-2722.2020.026
Marine Geology Frontiers. 2021, 37(2): 1-9
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WEATHERING CHARACTERISTICS AND PROVENANCE OF THE SURFACE SEDIMENTS IN THE OFFSHORE OF NORTHERN FUJIAN
The analysis of grain size and major elements was carried out for 229 surface sediment samples collected from the coastal area of northern Fujian and 54 surface samples from the surrounding rivers. The factors controlling the distribution patterns of the major elements and grain size are studied. Two weathering indicators, the component variation index (ICV) and the chemical alteration index (CIA), are used together with the (A-CN-K)-(A-CNK-FM) triangle chart to reveal the weathering characteristics and provenance indicators. Results show that the surface sediments along the coast are distributed in a quite regular pattern. From the coast to the sea, the deposits are getting thicker, and spatially in a banded manner. Sands occur near the land followed by mud-silt-sand silt-sand towards the sea. It is believed that the banded distribution pattern depends on sediment source and water dynamics. The near shore sediments are mainly coming from the Yangtze River and surrounding rivers, and deposited in the area less than 50 m in water depth. The coarse sands found in the area under 70 m of water depth are mainly residual sediments. In the area between 50~70 m in water depth, there occur the mixed sediments of the above two. Research of weathering degree suggests that chemical weathering becomes stronger off shore. The sediments below 70 m are mainly the residual sands dominated by high quartz and low clay mineral content, indicating a weak chemical weathering. The weathering degree of fluvial sediments in the Yangtze River, Oujiang River and Minjiang River shows an increase trend with the decrease in geographical latitude, and the effect of climate is obvious. The weathering status of the study area is rather similar to the Yangtze River sediments, and thus the environments are also similar and both affected by sediment sources.
NING Ze, ZHANG Yong, LIN Xuehui, BI Shipu, HU Gang, KONG Xianghuai
doi: 10.16028/j.1009-2722.2020.055
Marine Geology Frontiers. 2020, 36(10): 12-21
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CHARACTERISTICS OF N-ALKANES IN THE SURFACE SEDIMENTS OF THE EAST CHINA SEA AND THEIR IMPLICATIONS FOR THE DISTRIBUTION OF TERRIGENOUS ORGANIC MATTER
The East China Sea (ECS) is an important sink of organic carbon with complicated and diverse sources, in which there is a huge amount of terrigenous organic carbon coming from the Yangtze River, the Yellow River and the rivers from Taiwan. Therefore, it is indispensable to identify the composition of terrigenous sedimentary organic carbon and trace its fluvial source for carbon flux research. Up to date, the study on the distribution of terrigenous organic carbon in sediments of the ECS is mainly concentrated in some areas such as the estuary areas and the middle and outer shelf regions in a water depth < 120 m, but rare is devoted to the slope of Okinawa Trough (OT) and the outer shelf of the ESC. Little is known about the source-sink process, distribution patterns, sedimentary dynamic mechanisms, and other problems concerning the origin of terrigenous organic carbon. In this paper, we discussed the distribution and transportation of terrigenous organic carbon in the sediment, through the distribution and composition of n-alkanes for 80 surface sediment samples from the ECS outer shelf, slop and trough, together with other indexes such as grain-size, total organic carbon (TOC) and stable carbon isotope δ13C. The results show that the terrigenous organic carbon content indicated by δ13C and(ΣC27+C29+C31,n-alkane)/TOC vary in a large range in the study area, and from the outer shelf to the trough, they decrease first and increase later. There is a great amount of terrigenous organic carbon deposited on slope and in some special areas of the OT. Dominated by the process of “transportation-deposition-resuspension-transportation” in the slope area, the terrigenous organic matter (TOM) is continuously transported from the interior shelf of ECS to the OT across the outer shelf. The results of CPI suggest that the TOM from ECS inner shelf was mainly sourced from the area of 28.5°—30°N in the Okinawa Trough. To the south of 28.5°N, the TOM in sediments was mainly affected by the materials from Taiwan, while to the north of 30°N, the TOM was mainly derived from the Yellow River and Japan Islands.
XIONG WEI, MEI Xi, HAN Zongzhu, WANG Zhongbo, ZHANG Yong
doi: 10.16028/j.1009-2722.2020.109
Marine Geology Frontiers. 2020, 36(10): 22-31
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AGE DATING OF MAIN GEOLOGICAL INTERFACES AND ITS SIGNIFICANCE IN OIL AND GAS GEOLOGY IN BEIKANG BASIN
Using the high-resolution 2D seismic data currently acquired and upon the basis of the regional tectonic background, the comprehensive seismic data interpretation for the Beikang Basin is carried out. Main unconformity interfaces are identified, stratigraphic age redetermined, and their geological significance to oil and gas geology discussed. The results suggest that there are six unconformities in the region respectively corresponding to the Liyue movement, Xiwei movement, South China Sea movement, Nansha movement, Wan'an movement and Guangya movement. Among them, the T3 unconformity is the boundary of the post-spreading period of the South China Sea caused by the Nansha movement, marking the cessation of the South China Sea spreading. Well-seismic correlation of Well Mulu-1 shows that the unconformity surface (T3) corresponds to the Middle Miocene unconformity surface (MMU) of 16 Ma characterized by high amplitude, strong erosion and large undulation. Abrupt changes in stratigraphic structure, occurrence, and seismic reflection characteristics occur above and below the interface. It is the boundary face between the deformed and undeformed strata, and bears great significance to local structures and hydrocarbon accumulation.
SHUAI Qingwei, ZHANG Li, LEI Zhenyu, LUO Shuaibing, QIAN Xing, LIU Jianping, ZHOU Jiawei
doi: 10.16028/j.1009-2722.2020.078
Marine Geology Frontiers. 2020, 36(10): 32-41
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BEACH STATIC EQUILIBRIUM MODEL AND ITS APPLICATION
The headland-bay coast, where prevail active human activities, is an important part of the global coastal system and the study of such a coast is of great significance to coastal construction and development. Coastal scientists and engineers have tried hard to describe and quantify this kind of coast using various mathematical formulas, especially since the 1980s, and a variety of empirical models have been obtained. With the rapid development of computer technology in the new century, these theoretical results have been integrated into software, which makes the application of the theory more convenient and user-friendly, and the application of the theory is getting more common day by day. This paper made a detailed introduction to the static equilibrium bay theory and its application, taking some examples as cases, such as the construction of artificial islands and its impacts in Sanya Bay, the unstable beach in Imbituba, Brazil, the beach maintenance improvement program in Weifang coastal resort and the beach design in Gijon, Spain. Detailed discussion is devoted to the further application of the static equilibrium theory to beach stability assessment and interpretation, the selection of schemes to protect the coast from erosion, the use of the theory to beach evaluation and beach design and the assessment, improvement and construction of subsequent coastal programs.
XU Xinhui, ZHUANG Zhenye, CAO Lihua, QIU Ruofeng, ZHANG Yonghua
doi: 10.16028/j.1009-2722.2019.173
Marine Geology Frontiers. 2020, 36(10): 1-11
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ORIGIN OF PORE WATER METHANE RECOVERED FROM MUD VOLCANOS IN THE OKINAWA TROUGH
Three important geological elements, i.e. high sedimentation rate, strong tectonic activity and high heat flow, promote the wide distribution of hydrocarbon fluid seeps and leakage structures such as mud volcanos and gas chimneys on the western slope of Okinawa Trough. Several previous studies have been conducted to reveal the mud volcano geomorphology and forming conditions, in particular the bottom simulation reflectors of gas hydrate accumulated in the mud volcano. However, rare researches focused on the geochemistry of the pore fluids and the origin of methane saturated in the pore water of sediments recovered from the mud volcano. In this work, seafloor drilling rig was deployed for two shallow holes to recover sediment and pore water samples from the mud volcanos. Geochemical analysis of pore water molecular ratios and isotopic compositions show that C1/C2 vary from 960.53 to 1 120.75 in the core 18-01 and from 1 064.66 to 1 546.74 in the core 18-05, while the carbon isotopic values of pore water methane exhibit a variation from −36.07‰ to −56.60‰ V-PDB in the core 18-01 and from −36.10‰ to −62.92‰ V-PDB in the core 18-05 respectively. Combined with molecular ratios, stable carbon and hydrogen isotopic compositions, we conclude that the pore water methane is derived from thermal degradation of organic matter. As the result of conversion from smectite to illite induced overpressure in deep sediments, thermogenic methane was driven along gas chimney and tectonic conduits and migrated to the shallow sediments, then formed mud volcanos and associated methane plumes in the overlying water.
LI Qing, CAI Feng, YAN Guijing, SUN Yunbao, LI Ang, LUO Di, WANG Xingxing, XU Cuiling, DONG Gang, YIN Xijie, YANG Xian
doi: 10.16028/j.1009-2722.2020.062
Marine Geology Frontiers. 2020, 36(9): 79-86
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CHARACTERISTICS OF SHALLOW GAS HYDRATES ACCUMULATION IN THE SEA
Based on the migration ways of the gas responsible for the gas-hydrate formation, the leaking-type accumulation system is the major model for the formation of the shallow gas-hydrate reservoirs, and it would be influenced by multiple critical controlling factors including temperature-pressure field, gas source, et al. The temperature-pressure field mainly influences the gas-hydrate distribution in plane view and vertical section. The area with low heat flow is favorable for the formation of gas hydrates, while the deep-sea area with very high heat flow and high-flux methane can also deposit dense, thick-bedded (up to several meters) shallow gas-hydrate if there are abundant gas supply, and this type of gas-hydrate reservoirs are generally accompanied with special geological bodies, such as mud volcanoes and gas chimneys. The gas responsible for the shallow gas-hydrate formation is dominated by organic pyrolysis gas, since shallow gas-hydrate reservoirs are generally presented above mature oil- and gas-bearing basins, in which source rocks are widespread and characterized by the kerogen having defined hydrocarbon generation processes, and the generated pyrolysis methane would migrate upwards along the broken zones like faults, gas chimneys, and then form gas-hydrate at the shallow layers where temperature-pressure fields are appropriate for the gas-hydrate deposition, thus the deep-sea basin with very high flow can also be favorable for the formation of the shallow gas hydrates.
CAI Feng, WU Nengyou, YAN Guijing, LI Qing, LIANG Jie, SUN Yunbao, DONG Gang, LUO Di, LI Ang, WANG Xingxing
doi: 10.16028/j.1009-2722.2020.117
Marine Geology Frontiers. 2020, 36(9): 73-78
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RESEARCH PROGRESS IN BASIC CHARACTERISTICS OF GAS HYDRATE
The basic characteristics of gas hydrate, such as its structure type, thermodynamics, dynamics, interface process and surface morphology, are the major topics in gas hydrate research, which founded the cornerstone for the development of the science of natural gas hydrate. In addition, the micro-distribution of gas hydrate in sediments, as the research focus of hydrate reservoir, and its influence on gas seepage are also the basic characteristics of gas hydrate. Based on the published literatures in the past three years, the latest progress in the structural type, thermodynamics and dynamics, interface process, micro-distribution of gas hydrate and its influence on seepage characters are summarized in this paper, aiming to track the frontier of the discipline and comprehensively expounds the latest progress in the related research fields of gas hydrate both at home and abroad. Meanwhile, future direction and trend of the study on basic characteristics of gas hydrate are discussed in this paper, so as to provide a reference for multi-scale and multi-dimensional research on the basic theory of gas hydrate.
LIU Changling, HAO Xiluo, MENG Qingguo, LI Chengfeng, SUN Jianye
doi: 10.16028/j.1009-2722.2020.080
Marine Geology Frontiers. 2020, 36(9): 1-10
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APPLICATION OF FRACTAL THEORY TO NATURAL GAS HYDRATE RESEARCHES
Natural gas hydrate is widely regarded as a potential new energy source and a possible trigger of environmental issues. However, the research community of gas hydrate are still faced with difficulties in quantifying pore-scale structures of the hydrate-bearing sediments. Based on our observation, the difficulties can be well solved by using fractal theory. In this paper, we firstly made an introduction to the basis of the fractal theory, followed by a review of fractal theory applications in the gas hydrate community. Then, a fractal theory for quantifications of the effective pore space in hydrate-bearing sediments is presented, and a summary and some suggestions for gas hydrate related fractal researches in the future are finally provided.
LIU Lele, LIU Changling, MENG Qingguo, ZHANG Yongchao
doi: 10.16028/j.1009-2722.2020.064
Marine Geology Frontiers. 2020, 36(9): 11-22
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CHARACTERISTICS OF FLUID INCLUSIONS AND HYDROCARBON ACCUMULATION PHASES OF THE MESOZOIC IN THE JIYUAN SAG
The Jiyuan Sag is a Mesozoic-Cenozoic superimposed basin, formed on the basis of the Paleozoic platform of North China by complex tectonic movement. The sag is characterized by complicated hydrocarbon accumulation systems, after multi-stages of charging, destruction and transformation of hydrocarbons. So far the Mesozoic hydrocarbon accumulation phases in the sag have still remained unclear. Fluid reservoir inclusions, as an effective tool, may provide various information related to hydrocarbon accumulation, such as temperature, pressure, fluid composition and paleoenvironmental characteristics, etc., and are commonly used for definition of thermal evolution stages of source rocks and division of hydrocarbon generation and charging stages, the restoration of fluid paleopressure, as well as the analysis of hydrocarbon accumulation process. In this paper, fluid inclusions are used to study the hydrocarbon accumulation phases for the thermal evolution of the two set of major source rocks, the Lower Jurassic Anyao Formation and the Upper Triassic Tanzhuang Formation, in the sag.Systematic analysis method and the indirect projection dating method for homogenization temperature-burial history were used to analyze the characteristics of fluid inclusions for dividing the hydrocarbon accumulation phases.The results suggest that there are 7 kinds of hydrocarbon inclusions in the Mesozoic reservoirs of the Jiyuan Sag, including oil inclusions with three kinds of fluorescence colors in blue-green, yellow-green and blue respectively, and pure gas-phase inclusions; According to the fluorescence color and homogenization temperature of inclusions, host mineral occurrence and its diagenetic sequence in addition to other characteristics, it is considered that at least 3 phases of oil charging (163 Ma, 101~95 Ma and 27~23.8 Ma) and 1-period of gas charging (119~115 Ma) have occurred in the sag.
LIU Shihao, LIN Xiaoyun, LIU Jian
doi: 10.16028/j.1009-2722.2019.151
Marine Geology Frontiers. 2020, 36(4): 55-60
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IMPACTS OF MANGROVE ON THE DYNAMIC PROCESS OF BOTTOM BOUNDARY LAYER
As an important coastal wetland plant, mangrove and its biogeomorphologic process are crucial for coast protection. In order to study the sediment transport mechanism near the bottom of a mangrove, hydrodynamic observations were carried out in the Zhangjiang Estuary, Fujian Province; and the hydrodynamics and sediment transport between the bare flat and mangrove were studied.The results indicate that tidal current speed was obviously decreased and deflected by mangrove, and prominent sediment deposition and resuspension observed at the bare flat, and sediment deposition predominates the mangrove. It means that the mangrove has the capability to trap sediment from movement.Further more, the calculation of the transport equation also shows that the sediments on the bare flat were transported towards the mangrove through tidal creeks, and then intercepted by mangrove, implying that the mangrove exerts significant effect on siltation through reducing water movement and plant adsorption.
JIANG Ruijie, CHENG Peng, GAO Jianhua, WANG Aijun
doi: 10.16028/j.1009-2722.2019.108
Marine Geology Frontiers. 2020, 36(4): 37-44
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GEOMORPHOLOGICAL CHARACTERISTICS AND CONTROLLING FACTORS OF THE YITONG CANYON GROUP ON THE NORTHERN SLOPE OF THE SOUTH CHINA SEA
Based on the latest high-resolution multi-beam bathymetric data, as well as the single-channel and multi-channel seismic profiles, this paper analyzed the topographic and depositional features of the group of nine canyons on the northern slope of the South China Sea. The canyon group converges from the continental slope to the deep-sea basin, in "V" shaped cross-sections, with rather symmetrical valley walls and steep slopes. The submarine strata in the study area are disturbed by faults, and developed in a stepped manner. Unstable geological hazards, such as submarine faults, gravity sliding surfaces and small landslides are highly developed, which suggests that the submarine environment of the canyon group is very unstable. Cenozoic tectonic movements, such as the regional subsidence of Xisha Trough, doubtlessly contributed to the formation of the geomorphic pattern of the canyon groups. Agreat amount of sediment debris from the northern shelf was mainly contributed by high-density turbidity currents derived from submarine landslides, collapses and other submarine disasters, which accelerated the further development of the canyon group. Relative sea level changes directly change the sedimentary environment of the study area and provide a more direct channel for the transport of enormous terrigenous clastic materials. This is also one of the important factors that induced the instability of the seabed on the slope and shaped the geomorphological characteristics of the canyon group.
YI Shantang, HU Xiaosan, LUO Zongjie, LUO Weidong
doi: 10.16028/j.1009-2722.2019.185
Marine Geology Frontiers. 2020, 36(4): 18-26
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GLOBAL PROGRESS IN EXPLORATION AND DEVELOPMENT OF UNCONVETIONAL HYDROCARBONS AND ASSESSMENT OF RESOURCES POTENTIAL
Unconventional hydrocarbons occupy an enormous proportion in the world energy budget nowadays. Both the progress in exploration and development of them as well as resources assessment results are the major factors to determine the future pattern of the world energy market. Although there are problems and difficulties, opportunities always coexist together with challenges. So far, the evaluation method of shale oil and gas has become matured, while the development of coalbed methane is rapidly driven by both demand and technology. The contribution of tight oil and gas reservoirs is increasingly prominent. For the timebeing, unconventional hydrocarbons in North America is dominated by shale gas and tight reservoirs, and the exploration and development of them are growing rapidly. In the Asia-Pacific region, shale gas projects in China and coalbed methane projects in Australia are developed in full swing and can be considered successful examples. The Europe has also started its ice-breaking travel, eventhough the European environmental and social impacts will greatly restrict local development of shale oil and gas in Europe. Meanwhile, other regions and countries such as Brazil and Argentina in South America are also having hot spots. Although the technology in exploration and development has been gradually optimized and put into practice worldwide, technological levels and geological conditions still vary considerabley in different countries. In particular, many problems such as economic evaluation, ecological environment evaluation, social impact evaluation and standardized operations, urgently need more concerns from various countries all over the world. Among issues that should be paid attention to presently are atmospheric pollution, water scarcity and pollution, wastewater treatment and utilization, possible land subsidence, environmental ecology, and social impacts of local communities.
WU Xishun, SUN Zhangtao, YANG Tiantian, WANG Shuling, ZHANG Wei
doi: 10.16028/j.1009-2722.2019.065
Marine Geology Frontiers. 2020, 36(4): 1-17
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