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	JOPC 2021 Vol.23 Number 4
	2021, Vol.23 Num.4
	Online: 2021-08-01

	GEOCHEMISTRY AND SEDIMENTA RY ENVI RONMENTS LITHOFACIES PALA EOG EOGRAPHY AND SEDIMENTOLOGY BIOPALAEOGEOGRAPHY AND PALAEOECOLOGY PALAEOG EOGRAPHY AND MINERAL RESOURCES PALA EOG EOGRAPHY AND MINERAL RESOURCES QUATERNARY PALAEOGEOGRAPHY AND SEDIMENTOLOGY

GEOCHEMISTRY AND SEDIMENTA RY ENVI RONMENTS

	651	Qu Hong-Jun, Li Wen-Hou, Yao Tian-Xing, Wu Long-Fa, Wang Yan-Xin, Hu Jia-Sen, Cheng Yi-Shan

		Characteristics,origin and significance of strata-bound chalcedonization siliceous rocks of the Jixianian Luonan Group in Luonan Country,Shaanxi Province
		Quasi-lamellar siliceous chalcedonies and lenticular flints developed at the top of the Xunjiansi Formation of Mesoproterozoic Luonan Group of the Jixian System,in northern Luonan of Shaanxi Province,southern margin of the North China Plate. The siliceous chalcedonies and flints have become jade of gay colors and fine texture,with high-grade quartzite jade level,which are claimed as the national gemstone minerals,budding in the gemstone market,with great economic development potential. At present,no research has been conducted on the characteristics,origins and diversity of jade in this siliceous layer. This paper used petrological and geochemical analyses to study the siliceous layer and grained the following findings. (1)The quasi-lamellar siliceous chalcedonies and lenticular flints were found in the fuchsia and sage green lamellar arenaceous pelitic slate at the bottom of the Xunjiansi Formation,with a thickness of 0.5~4 m;the quasi-lamellar chalcedonies are mostly fuchsia,sage green,smoke gray and colorless;most of the lenticular flints are ring-shaped with agate lines in fuchsia and sage green,and part of lenticular flints are brecciated and in sage green. (2)The main components of the silica chalcedonies are quartz;they have crypto-to microcrystalline or blocky structures,fine and hard texture,glassy luster,translucent-slightly transparent. Based on the geochemical analysis of Al/(Al+Fe+Mn)(0.62 on average),Zr/Hf(34.83 on average),Sr/Ba(0.50 on average,except an abnormal sample),V/Ni(0.37 on average),ΣREE(5.11 on average),δCe(1.02 on average),δEu(0.86 on average),and La_N/Ce_N(0.85 on average),the results suggest that the depositional environment is freshwater settings,and the silicon is mainly terrigenous origin. (3)The quasi-lamellar siliceous chalcedony layer in the Luoguan Group of the Jixian System is a hardgroud surface of seabeds or a siliceous crust formed by fresh-water leaching and siliceous metasomatism caused by rapid regression. Lenticular flints with agate lines and colorful quasi-lamellar siliceous chalcedonies formed during diagenesis under changes of redox conditions during deposition and post-deposition. Transformation of purple and green coloring trace element was caused by late hydrothermal invasion and baking. Brecciated flints resulted from tectonic brecciation of structural breakup zone formed by the soft and hard difference and crack deformation between the upper and lower strata of the quasi-lamellar siliceous chalcedony layer due to the strong tectonic movements of the Qinling Mountains.
		2021 Vol. 23 (4): 651-667 [Abstract] ( 489 ) [HTML 1KB] [PDF 8760KB] ( 305 )

	668	Qian Yi-Xiong, Li Yue-Jun, Chu Cheng-Lin, Yang Xin, Li Wang-Peng, Chen Yue, Ma Hong-Qiang

		Characteristics and sedimentary environment of siliceous rock in the Neoproterozoic Cryogenian Binggounan Formation at Hongliugou section Ⅰ in Ruoqiang County,Xinjiang
		The fine-grained sediments and carbonate rocks with a thickness of 300 m are discovered at the Binggounan Formation of Neoproterozoic Cryogenian system in Hongliugou section Ⅰ of Altyn in Xinjiang,and the asphalt which is the indicator of oil and gas is also found. Based on the section measurement,petrology and geochemistry of the 160 m thickness of siliceous rocks,it shows that siliceous rocks in the profile are mainly composed of quartz,clay,and tiny amounts of iron,manganese and phosphorus-bearing independent minerals. It has three types of structures,including cryptocrystalline,microcrystalline quartz and coarse-megacrystalline quartz with a “mosaic structure”. The concents of SiO₂,Fe₂O₃,Ba and δEu_n in siliceous rocks are relatively high,while the contents of Al₂O₃,MnO,MnO/TiO₂,U/Th, Sr/Ba are much lower. The values of ∑REE,Sr/Ba,MnO₂/TiO₂ and δCe_n change regularly. The average δ³⁰Si is -0.43‰(-0.8‰~0.3‰),and the average $\delta^{18}O_{Snow}$ is 20.42‰(16.0‰~26.0‰),and the estimated average temperature is 90 ℃(52~127 ℃),which indicates that there are multiple sedimentary cycles for the siliceous rocks. They deposit in the continental margin basin that is characterized as the mixing of sea water and hydrothermal fluid. Afterwards,they underwent the early diagenesis,shallow burial period,the superimposition and reworking of thermal and fresh water related with the multiple strike slipping activities.
		2021 Vol. 23 (4): 668-682 [Abstract] ( 437 ) [HTML 1KB] [PDF 4804KB] ( 247 )

	683	He Yuan, Wen Long, Luo Bing, Zhou Gang, Wang Qi-Yu, Li Kun-Yu, Jia Min, Chen You-Lian, Bai Xiao-Liang

		Source and tectonic background analysis of the Sinian Doushangtuo Formation in Well WT1 in Kaijiang area,Sichuan Basin
		The clarification of the geologic tectonic background of the Doushantuo Formation in Well WT1 in Kaijiang area,Sichuan Basin,and reconstruction of its archetypal sedimentary basin,will provide scientific basis for the palaeogeography reconstruction and the further exploration and development of oil and gas. Petrology,petrogeochemistry and U-Pb geochronology of detrital zircons were used to analyze the provenance of Doushantuo Formation. The petrogeochemical results show the source rocks of Doushantuo Formation in Well WT1 are intermediate-basic volcanic rocks and have undergone moderate chemical weathering. The detrital zircon U-Pb ages mainly record three stages of tectonic magmatic activity,including 915-850Ma,794-714.5Ma and 622-700Ma,which are mainly related to the disintegration and evolution of the Rodinia supercontinent in the northern margin of Yangtze Craton and its adjacent area. The intermediate-basic volcanic rocks in this tectonic background are the main source of the Doushantuo Formation deposition in Well WT1. The results show that the Doushantuo Formation in Kaijiang area of Sichuan Basin is developed in the extensional tectonic setting and belongs to the craton inner rifting basin deposits,which is favorable for the development of hydrocarbon source rocks. At the same time,this work provides important chronologic evidence for the break up evolution of the Rodinia supercontinent. This study is of great scientific significance in understanding of the geological structure,tectono-sedimentary evolution and the strategic development of oil and gas exploration in the Sichuan Basin.
		2021 Vol. 23 (4): 683-702 [Abstract] ( 486 ) [HTML 1KB] [PDF 24561KB] ( 238 )

LITHOFACIES PALA EOG EOGRAPHY AND SEDIMENTOLOGY

	703	Wu Meng-Ting, Fang Hao, Sun Long-Fei, Shi Xiao-Ying, Tang Dong-Jie

		Variations in precipitation pathways of Mesoproterozoic shallow seawater carbonates from North China Platform:response in seawater redox fluctuations?
		It has been considered that the precipitation pathways of marine carbonates are closely related to seawater redox conditions. Due to the presence of carbonate precipitation inhibitor(e.g.,Fe²⁺ and Mn²⁺)-rich shallow seawaters during Archean and Paleoproterozoic,nucleation of calcite mud in water column was inhibited but formation of seafloor aragonite precipitates was allowed. In contrast,the oxidative removal of carbonate precipitation inhibitors in Neoproterozoic shallow seawaters promoted the direct precipitation of carbonate mud from water column. However,it needs more detailed case studies to test the connection between seawater redox and pathways of carbonate precipitation,since the secular variation in the pathways of carbonate precipitation may controlled by other factors. This study focuses on the fabric and geochemistry of carbonates deposited during the Mesoproterozoic,a transitional period of carbonate precipitation. Abundant carbonate mud occurs in the Member Ⅲ of the Gaoyuzhuang Formation(~1.56 Ga),the Member Ⅳ of the Wumishan Formation(~1.48 Ga),and the Member Ⅱ of the Tieling Formation(~1.44 Ga)in North China. These water column precipitated carbonate mud has relatively high Ⅰ/(Ca+Mg)ratios(generally>0.5 μmol/mol)and negative Ce anomalies(down to 0.8),indicating moderately oxygenated conditions. In contrast,abundant seafloor precipitated aragonite fans occur in the lower Member Ⅳ of the Gaoyuzhuang Formation(~1.55 Ga)and the Member Ⅱ of the Wumishan Formation(~1.50 Ga). These seafloor precipitates have near zero Ⅰ/(Ca+Mg)ratios,suggesting suboxic to anoxic conditions. Therefore,this study,firstly using detailed cases,proves that the texture of Precambrian carbonates was largely controlled by the redox conditions of seawaters and could be used as a redox proxy to conduct long-term and multi-section study of marine redox conditions directly and efficiently based on outcrop observations in the field.
		2021 Vol. 23 (4): 703-722 [Abstract] ( 440 ) [HTML 1KB] [PDF 9858KB] ( 216 )

	723	Cao Hong-Xia, Li Wen-Hou, Wu Hai-Yan, Wang Zhen-Guo, Wu Yu, Ren Xing-Min

		Lithofacies palaeogeography evolution of the Member 5 of Ordovician Majiagou sedimentary stage in northern Shaanxi Province
		The carbonates of the Member 5 of Majiagou Formation in the northern Shaanxi Province are important natural gas reservoir. In order to clarify the lithofacies palaeogeography evolution of each sedimentary period of Majiagou Formation in the study area,the lithofacies palaeogeography characteristics of M5₁₀-M5₁ submembers were restored based on the investigation of surrounding field outcrops,core observation of 98 wells,and well logging curve analyses. The results show that the marine carbonate platform is the major sedimentary microfacies in each layer of M5₁₀-M5₁,including three subfacies: restricted platform,open platform and evaporate platform,and further subdivided into 10 sedimentary microfacies: dolomite flat,gypsum-dolomite flat,gypsum-bearing dolomite flat,muddy dolomite flat,carbonate-dolomite flat,carbonate flat,grain beach,dolomite-carbonate flat,muddy carbonate flat and gypsum salt lake. The palaeogeography unit of M5₁₀-M5₁ is distributed in a ring belt shape from east to west with the central part located in Yanchang,Yanchuan and Qingjian. It is worth noting that the center of palaeogeography unit ring belt of M5₂ submember move northwestward to Jingbian and Zichang due to strong tectonic uplift in the south occurred in that period. Dolomite flat,gypsum-dolomite flat,gypsum-bearing dolomite flat,and grain beach microfacies are favorable for the formation of reservoir space. In vertical,M5₁₊₂,M5₄,M5₅,M5₇ and M5₉ submembers are relatively rich in these microfacies,which are the focused areas of regional hydrocarbon exploration and development.
		2021 Vol. 23 (4): 723-734 [Abstract] ( 476 ) [HTML 1KB] [PDF 26435KB] ( 260 )

	735	Huang Dao-Jun, Zhong Shou-Kang, Zhang Dao-Feng, Wang Bao-Bao, Liao Jian-Chu, Xie Kang, Lu Zi-Xing, Tan Xiu-Cheng

		Datailed characterization and interpretation of sedimentary sequences under evaporitic environments: a case from the Ma5₆ submember of Middle Ordovician in central Ordos Basin
		Assemblages of co-occurred dolomite and gypsum are controlled by chemical sedimentary differentiation,and precise characterization of sedimentary sequences is conducive to revealing sedimentary information in evaporatic environments. Based on drilling and coring data of the Ma5₆ submember of the Ordovician Majiagou Formation in the central Ordos Basin,we studied characterization of typical sedimentary sequences based on macro-and microscopic observation of rocks. The study shows that: (1)paragenetic assemblage of carbonate and evaporite rocks is widely developed in the Ma5₆ submember of the Ordovician Majiagou Formation in the central Ordos Basin,including 10 subtypes of facies;(2)five kinds of sedimentary sequences were summarized,characterized by the lithological assemblage of the lower dolomite and upper gypsum facies and exposed surfaces at the top of each sequence,which shows shallowing and salinizing upward due to gradual replenishment of superposed seawater from evaporative platforms;(3)in the restricted evaporation platform environment,there are mainly four sedimentary subfacies and 11 sedimentary microfacies: lagoon/inter-shoal marine,shoal,lime mud mound and platform flat. Furthermore,the sedimentary sequences in the study area and those in typical evaporative tidal flat are distinguished from each other in terms of lithologic association and sedimentary structures;(4)there were two cycles of sea-level rises and falls recorded in the Ma5₆ submember,and the sedimentary environments could be corresponding to dolomite lagoon,lime mud mound and carbonate shoal,gypsum lagoon,evaporite lagoon,and tidal flat. The above results can provide systematic petrological evidence for the study of sedimentary environments and sea-level change of the Ma5₆ submember in Ordos Basin.
		2021 Vol. 23 (4): 735-755 [Abstract] ( 485 ) [HTML 1KB] [PDF 25966KB] ( 430 )

	756	Zou Zhi-Wen, Guo Hua-Jun, Niu Zhi-Jie, Xu Yang, Shan Xiang, Li Ya-Zhe, Shen Jin-Long

		Sedimentary characteristics and controlling factors of river-dominated fan delta: a case study from the Upper Urho Formation in Mahu sag of Junggar Basin
		In recent years,the study of fan-delta is helpful for the exploration of oil and gas,which attracts more attention on the detailed classification of fan-delta. The sedimentary characteristics and controlling factors of the river dominated fan-delta in the upper Urho Formation in Mahu sag of the Junggar basin is analyzed based on the core data from 23 wells,logging data,geomorphology and seismic data. There are 3 classes,8 subclasses and 22 types of lithofacies in the upper Urho Formation. Among them,the lithofacies linked to traction current takes a large proportion and the space between gravels and pebbles are filled or partly-filled by sandy grains. Ten types of microfacies such as braided channel,debris flow unit,subaqueous distributary channel and mouth bar are distinguished and the braided channel and subaqueous distributary channel are the dominated microfacies. The plane morphology of the river dominated fan-delta is usually fan shape with a high length-width ratio. There are four major fan-delta system named Zhongguai,Karamay,Baijiantan and Dabasong in Mahu sag. The sedimentation in the river dominated fan-delta is controlled by humid climate and paleo-geomorphology. According to paleoclimate and paleogeomorphology analysis of the Upper Urho Formation,the depositional sequence model of fan-delta in Mahu sag is established,which can provide the geological basis for the identification of microfacies in the fan delta and the petroleum exploration of similar sedimentary basins.
		2021 Vol. 23 (4): 756-770 [Abstract] ( 464 ) [HTML 1KB] [PDF 5814KB] ( 242 )

BIOPALAEOGEOGRAPHY AND PALAEOECOLOGY

	771	Xu Hong, Shi Guo-Ning, Liao Bao-Lin, Chen Gang, Dong Shu-Yi, Qiu Long-Wei, Li Qi, Luo Jin-Xiong, Shen Jian, Zeng Xiao-Qi, Wang Ya-Min, Su Da-Peng, He Jing, Dong Gang, Yan Gui-Jing, Wang Yu-Zhe, Zhou Xing-Lei, Hu Xi-Peng, Luo Qiao-Qiao, Chen Zhu, Tao Meng, Na Qin, Wang Qing, Wang Ying, Shen Jiang-Yuan, Ma Xiao, Fu He-Ping, Wu Han-Ru, Ma Ya-Zeng, Chen Shu

		Coral-coral reefs in China seas: the biodiversity characteristics of coral-coral reefs in the central South China Sea
		Coral is the oldest aboriginal residents on the earth, with a nearly 600 million years evolution history. As the master of the sea, it is characterized by poor social status, favoring the warm environment and in situ growth. The biodiversity of the coral ecosystem exceeds that of the tropical rain forest ecosystem. In this paper, the basic characteristics of coral-coral reef are briefly introduced, and the precious photos and relevant understandings of coral coral reefs in the research area investigated over the past decade are summarized. It is pointed out that China is a major coral coral reef country and plays an important role in the world. Coral-coral reef as a representative of the earth’s biological diversity, has created islands, solidified reef, protected fishes and protected island from erosion, which result in the formation of four large islands and more than 280 small islands in the South China Sea. The reefs, beaches and sands of coral coral reefs related islands have built an incomparable marine ecological resources and increased the China territory in the South China Sea. The authors put forward two distribution areas of coral coral reef in the South China Sea, the central area and the peripheral area. The basic characteristics of coral-coral reef in the central area are described. The paper systematically reports the findings of snorkeling in shallow reefs, shallow dives to 20 m depth in water, deep dive reef investigation, and the geological surveys of islands, reefs, shoals and sand, including the scientific naming of 46 species of hexagonal corals and 6 species of octagonal soft corals. At the same time, coral photos of Xisha, Zhongsha, Dongsha and Nansha Islands were collected to reveal the characteristics and distribution of single atoll and compound atoll. A preliminary comparison between these atolls is also carried and suggested that the Yongle Atoll is the only truly Darwinian atoll in the South China Sea, and it is the product of the highest stage of atoll development, which makes it a best natural laboratory for the research on the formation and evolution of modern marine coral coral reef.
		2021 Vol. 23 (4): 771-788 [Abstract] ( 504 ) [HTML 1KB] [PDF 10139KB] ( 249 )

PALAEOG EOGRAPHY AND MINERAL RESOURCES

	789	Jiao Xin, Liu Yi-Qun, Zhou Ding-Wu, Li Hong, Meng Zi-Yuan, Zhao Min-Ru, Yang Yi-Yao

		Progress on coupling relationship between volcanic and hydrothermal-originated sediments and hydrocarbon generation in lacustrine source rocks
		Intracontinental lacustrine source rocks are hydrocarbon-rich fine-grained sedimentary rocks with complex mineral compositions, which are widely distributed in Chinese petroliferous basins. The rocks are important unconventional oil and gas reservoirs amid increasingly demand for unconventional hydrocarbon resources. However,they have been mis-understood as simple terrestrial sedimentary rocks for a long time because the great difficulties in petrological and mineralogical research caused by their fine-grained size. Recent studies found abundant sediments generated by volcanic eruption and hydrothermal exhalation in this type of source rocks; the sediments show a significant control on hydrocarbon generation and accumulation. Hence,the mechanisms and controlling factors of volcanic-hydrothermal sediments in hydrocarbon generation of this type of source rocks require in-depth studies. This paper summarizes and discusses recent research status on some new discoveries and viewpoints on the relationship between volcanic and hydrothermal-originated sediments and hydrocarbon formation. The connotation of the coupling relationship was preliminarily studied using detailed petrological and mineralogical as well as inorganic and organic geochemical data,on the basis of our new viewpoints on source rocks in the Permian Lucaogou Formation in Santanghu Basin. The volcanic and hydrothermal-originated sediments not only have played a significant role in deposition and diagenesis of the source rocks,but also show a co-influence on hydrocarbon generation and accumulation with conventional lacustrine sediments. We suggest that the mineral and lithological features of lacustrine source rocks should be re-studied. The result will expand the theory of hydrocarbon generation in terrestrial sediments and,practically,serve as a guide for unconventional hydrocarbon exploration of similar source rocks.
		2021 Vol. 23 (4): 789-809 [Abstract] ( 473 ) [HTML 1KB] [PDF 15853KB] ( 466 )

PALA EOG EOGRAPHY AND MINERAL RESOURCES

	810	Hu Guang-Yi, Wang Hai-Feng, Fan Ting-En, Gao Yu-Fei, Chen Fei, Xiao Da-Kun, Zhang Xian-Wen

		Analysis of fluvial compound sand-body architecturehierarchy in offshore oil field
		Based on the existing hierarchical scheme of architectural units in clastic deposits,taking account of the evolution law of natural river sedimentation,the data base and economic development scale of offshore oil fields,and following the principle and basis of the geological bodies classification,an architecture hierarchy of fluvial compound sand-body in offshore oil field is established. In this paper,the basic characteristics of 13^g rade architecture units of fluvial compound sand-body are systematically described from the aspects of geological genesis,main control factors,space-time scale,etc.,and the correlation between them and related sedimentary geological body grades is analyzed. The difference between the fluvial compound sand-body architecture hierarchy and the existing classification of reservoir architecture mainly lies in the adding of “composite point bar”,which is a composite sedimentary unit composed of multi-stage residual point bar. Composite point bar is the connecting point of reservoir architecture theory,offshore oil field data resolution and offshore oil field economic development scale. It is a good practice of “seismic guidance,well-seismic combination” research ideas in offshore oil field. It has been proved that the architecture hierarchy of fluvial compound sand-body has certain advantages for guiding offshore oil and gas development.
		2021 Vol. 23 (4): 810-823 [Abstract] ( 436 ) [HTML 1KB] [PDF 1732KB] ( 183 )

	824	Jiang Ying-Bing, Li Xing-Juan

		Development model of paleokarst caves in the Middle-Lower Ordovician of TH12402 well area in Tahe oilfield,Tarim Basin
		The TH12402 well area of the Tahe oilfield that is located in silurian overlying area is characterized by typical paleokarst fractured-cave reservoirs. It is one of the main production and construction sites of the Ordovician in the northwest of Tahe oilfield. Based on 3D seismic data,well logging data and drilling data and pickup technique of seismic attribute,the karst development conditions and reservoir development characteristics of the Lower Ordovician in this area were studied,and the dominant factors and development patterns of karst caves were illustrated. The result shows that the TH12402 well area is located in the south wing of a secondary nose-like structure oriented in the NW direction. This area records the karstification during the third phase of the Middle Caledonian,where the karst landform is mainly composed of low-relief dissolved hills and depressions,the surface water system extends from north to south without abundant branch water system. The karst reservoir space is composed of large maze karst caves and separated single caves that are unfilled,which are mainly located at 40~100m under the unconformity. Strike faults approximately oriented in WE direction,secondary nose-like structure and pinch-out lines of the Upper Ordovician together catrolled the development of paleokarst caves. A karst cave pattern is established considering the influence of strike faults on water concentration in areas within relatively flat karst landforms. These results provide a theoretical basis for paleokarst reservoir prediction and well location deployment in other well regions with similar conditions.
		2021 Vol. 23 (4): 824-836 [Abstract] ( 414 ) [HTML 1KB] [PDF 4138KB] ( 178 )

	837	Feng Qiang-Han, Xu Shu-Mei, Chi Xin-Qi, Shu Peng-Cheng, Kong Jia-Hao, Cui Hui-Qi, Ma Hui-Lei

		Development regularity and genetic mechanism of weathering crust reservoirs in the western Ordos Basin: take the sub-members 1-4 of Member 5 of Majiagou Formation in Tao 2 block as an example
		The top of the Majiagou Formation of the Lower Paleozoic in the Ordos Basin suffered from long-term weathering and denudation and formed a weathered crust karst reservoir dominated by gypsodolomite. The sub-members 1-4 of Member 5 of Majiagou Formation of the Tao 2 block in the western part of Ordos Basin are mainly made up of gypsodolomite interbedded with dolomite and calcite dolomite. Based on core observation,polarized microscopic analysis,and scanning electron microscopy analysis,the multi-layered gypsodolomite are identified. Through comparing the physical and chemical properties among anhydrite,dolomite and calcite,it is concluded that the main pore space of the sub-members 1-4 of Member 5 is dissolution pores of anhydrite nodules and crystals and the accompanying swelling microfracture. The pore size is self-limited,which is restricted by the size of anhydrite nodule and crystal. Gypsodolomite and anhydrite bearing tidal flat of the supratidal zone is the prerequisite material basis and environmental condition for the formation of reservoirs,and thus lead to the strata-controlled distribution of gypsodolomite gas reservoirs. Four stages of pores dissolution are identified,with fabric selective dissolution and phased filling dissolution pores of anhydrite nodule and crystal are the key processes of reservoir formation. The reservoir is a lithologic gas reservoir controlled by the karstification of anhydrite bearing dolomite. Karstification palaeogeomorphology no longer has a critical control on the reservoir distribution. The diffusive percolation corrosion of the dispersive fresh water on the gypsodolomite strata is the main reason for the lack of the large cavities. The viewpoint of “stratified and karstified sedimentary facies controlled lithologic gas re servoirs” will promote the deep transformation of reservoir forming mechanism in the Lower Paleozoic of the study area from “karstification palaeogeomorphic-controlled gas reservoirs” to “sedimentary facies controlled lithologic gas reservoirs”.
		2021 Vol. 23 (4): 837-854 [Abstract] ( 427 ) [HTML 1KB] [PDF 4408KB] ( 202 )

QUATERNARY PALAEOGEOGRAPHY AND SEDIMENTOLOGY

	855	You Wen-Zhi, Xiang Fang, Yang Kun-Mei, Jiang Yue-Hua, Yu Xian-Tao, Li Lei

		Implication of iron rich heavy minerals in Quaternary sediments in Yichang area of Hubei Province for cutting through time of Three Gorges
		The evolution of the Three Gorges has been the focus of debate in the field of geosciences. In recent years,many scholars have successfully analyzed the provenance of the Yangtze River through the isotope composition and trace elements in heavy minerals such as zircon,garnet and amphibole. However,the single-grain iron-rich heavy minerals are seldom used as provenance indicators and applied in the determination of the cutting-through time of the Three Gorges. Therefore,in this paper,the chemical properties and morphologic analysis of iron-rich heavy minerals in Quaternary sediments of Yichang area were analyzed by electron probe,scanning electron microscope and energy disperse spectroscopy,which were compared with the analytical results of possible provenance samples. The evolution process of provenance and the cutting-through time of the Three Gorges were analyzed based on the occurrence of materials in Yichang area that may belong to the west of the Three Gorges. The results show that the source rocks of the iron-rich heavy minerals in the Quaternary sediments in Yichang are mainly from the Panzhihua vanadium titanomagnetite,Emeishan basalt that are located to the west of the Three Gorges and Huangling granite located to the east of the Three Gorges. After the deposition of the Shanxiyao Formation,the provenance of the Quaternary sediments in Yichang area changed obviously,and the material that belong to the west of the Three Gorges appeared in this area,which indicates that the Three Gorges was cutted-through. Combined with ESR dating data and previous studies,it can be assumed that the cutting-through time of the Three Gorges occurred in 0.75-0.73Ma B.P..
		2021 Vol. 23 (4): 855-870 [Abstract] ( 405 ) [HTML 1KB] [PDF 2368KB] ( 193 )

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		2021 Vol. 23 (4): 871-872 [Abstract] ( 345 ) [HTML 1KB] [PDF 418KB] ( 173 )

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