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    25 September 1990, Volume 11 Issue 3
    ANXIAN TECTONIC MOVEMENT
    Wang Jinqi
    1990, 11(3):  223-234.  doi:10.11743/ogg19900301
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    The Late Triassic Xujiahe Group in West Sichuan Basin consists of two kinds of ab-solutely different depressed sediments.The lower basin is the depression of continental margin while the upper basin is fore deep depression resulted by intensive orogenic move-ment.The important tectonic movement leading to the above mentioned transform inquality now have been proved and is named Anxian orogenic movement(Anxian Move-ment for short),which corresponds to the second episode of the Indo-China movement—Pre-Rhaetic orogenic episode.The 4th and 5th members of the Xujiahe Group are absencein the Longmen Mountains and its foreland area,and the Jurassic Systen overlapped onunconformity,thus leading to the misunderstanding for the movement time,that is,themovement was considered to occur in between the end of the Triassic and the fore of Jurassic for a long time.The Anxian movement is not a locally geological phenomena,buta signficant geological event of Chinese Plate colliding with exotic plate.The foreland of the Longmen Mountains is the front edge of intensive zone of the orogenic movement,and the boundary between back-arc overthrust and regressive arc basin that is the boundary between active and stable belts.This movement plays an important role in hydrocarbon dis-tribution to the west part of Sichuan Basin as well as the whole region.

    CAMBRIAN CARBONATE GRAVITY FLOW DEPOSITS IN GUIZHOU AND HUNAN
    Liu Baojun, Ye Hongzhuan, Pu Xinchun
    1990, 11(3):  235-246.  doi:10.11743/ogg19900302
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    Cambrian carbonate gravity flows in Guizhou and Hunan are various in kind.Debris flow calcirudite is the main redeposited carbonate developed on the south and north slope of the Yangtze carbonate platform.Pulsation,undulation and flow-trasformation are very common in its flow process.According to the distribution range,horizon variation andcyclic property of the calcirudite,the south margin of the Yangtze carbonate platform generally progradated southeastward from the Cambrian to Early Ordovician,and the Yangtze landmass had reached the evolution stage of matured passive continental margin.

    CARBON ISOTOPE COMPOSITION OF PYROLYZED GASEOUS HYDROCARBON FROM SOURCE ROCKS AND ITS APPLICATION IN CORRELATION OF NATURAL GAS AND SOURCE ROCKS
    Li Zhi, Zhu Meiqian, Mao Hongyi
    1990, 11(3):  247-259.  doi:10.11743/ogg19900303
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    Experiments described in this paper show that carbon isotope composition of gaseous hydrocarbon from artificial maturation is similar to those from natural maturation.The same as that of natural gas,carbon isotope composition of pyrolyzed hydrocarbon can be used to indicate the type and maturity of organic matter in source rocks.Based on the re-sults of the experiments of thermal simulation of 8 source rock samples,the relationship between the yield of gaseous hydrocarbon,their carbon isotopic composition and the type,the maturity of organic matter in source rock is established,and then δ13C-value of both the pyrolyzed gaseous hydrocarbon in source rock and natural gas samples are used to study the natural gas and source rocks in Tarim and South Songliao Basins respectively.

    LACUSTRINE SEDIMENTATION AND HYDROCARBON ACCUMULATION IN THE WESTERN PACIFIC OIL-BEARING BELT
    Qian Kai, Deng Hongwen
    1990, 11(3):  260-274.  doi:10.11743/ogg19900305
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    The Western Pacific oil-bearing belt where source rocks and reservoir rocks are do-minated by lacustrine deposits extends longitudinally across the whole globe.The forma-tion of the belt is related to the subduction and collision between the oceanic plate and the continent plate,the disintegration of the ancient continent,the influence of the ancient Pa-cific Ocean(and the Indian Ocean in the southern hemisphere) on the paleoclimate of thesedimentary basins and the promotion of high geothermal value for the formation of hy-drocarbon.The lakes located in the north and the south of the belt are older (mostlyformed in the Mesozoic) than those in the central part (mostly formed in the Cenozoic),and are older in the west than in the east.Lacustrine facies have changed into marine fa-cies from west to east.The evolutionary history of the lake basins consists of three stages:faulted-subsidence stage,faulted-depressive stage and depressed subsidence stage.The ini-tial phase was dominated by filled-deposition,evaporation associated with source beds.Inthe middle phase,very thick source bed,sandstones and conglomerates derived from riverdelta,diluvial and turbidite phases as well as lacustrine carbonate were formed.The latephase was characterized by extensive and very thick sandstones and conglomerates which were deposited in fluvial environment.The duration scale and feature of each stage is alldifferent in distinct types of the basins.The Western Pacific oil-bearing belt mostly com-prises five types of hydrocarbon bearing basins which can be divided generally into threesubbelts.The first is non-marine subbelt(including near-inland depression basin,near-ocean depression basin and near-ocean faulted-subsidence basin),where both source bedsand reservoir beds (except for basement rock reservoirs) are lacustrine deposits.Big-andmedium-sized oil and gas pools are mostly bed rock pools,anticline (including drape-anticline)pools,plus small amount of faulted block pools,stratigraphic pools and lithologicpools.The second is transitional facies subbelt (including the faulted subsidence and de-pression composite basins on active and passive continent margin).This subbelt is charac-terized by the source beds of lacustrine facies which were formed in the early stage ofbasin evolution,and the reservoir beds of marine facies which were formed in the latestage.The big-and medium-sized oil and gas pools are composed of anticline (includingdrape-anticline) pools,reef pools and stratigraphic pools.The third is the Western Pacificisland arc subbelt basically consisting of marine deposits.The oil and gas pools in eachsubbelt are distributed around the hydrocarbon generation depressions.

    GRAVITY STRUCTURES IN WEST PART OF SOUTH MARGIN OF JUNGGAR BASIN
    Kuang Jun
    1990, 11(3):  275-282.  doi:10.11743/ogg19900307
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    Three gravity structures,Huomatu sliding block,Tuositai sliding folds and Gaoquan gypsum-salt diapir,are recognized in the west part of the south margin of the Junggar Basin.Huomatu sliding block is located at the north Tianshan Mountains foreland to the south of Hutubi—Dushanzhi region.It is 140 km long from east to west,28 km wide inN-S direction,3.5 km thick on average.It covers an area of 2740 km2 and the volumeis 9450 km3.The sliding mass consists of Tertiary sediments.The sliding sheet is formedby less-compacted argillaceous rock of the Eogene Anjihaihe Formation.The high-pressureanomaly was resulted from the unbalance between compaction and liquor draining as wellas its hydrocarbon generation.With the methods of balanced section,bow and arrow andwidth compensation of unload area,maximum slide distance was determined to be 15 km,and primitive slide angle 5-6°.The Tuositai sliding fold is located at the north Tianshan Mountains to the south ofWusu.It is a big gravity-slide structure mainly formed by Mesozoic sediments.The slidingmass stretches 30 km long in E-W direction,10 km wide in S-N direction,2 km thick.It covers an area of 260 km2 and the volume is 540 km3.The bottom sliding sheet consistsof the Upper Triassic Xiaoquangou Formation and the less-compacted argillaceous rock ofthe Lower Jurassic Sangonghe Formation.The high-pressure anomaly is resulted by largeamount of unloading due to denudation of the upper strata in the late stage and the impe-diment of the release of argillaceous pore-pressure.Its primitive slide angle is measured tobe 8°by quantitative calculation.The Gaoquan embryonic diapir was developed in the Upper Tertiary Taxihe Forma-tion in the Sikeshu sag.It stretches nearly E-W direction,covers an area of 140 km2 andis buried at 2000 km deep.The diapir was resulted from gypsum and rock-salt that archedthe overlying strata.The formation cause of this structure are:1.the reverse of densitiesfrom gypsum and salt to overlying strata;2.the induction of fault movement;3.the dif-ferentia compaction of the overlying strata.

    FORMATION OF REEF-BOUND RESERVOIRS OF UPPER PERMIAN CHANGXING FORMATION IN EAST SICHUAN
    Wu Xiehun, Liu Xiaozeng, Yang Zhonglun, Chen Xinsheng
    1990, 11(3):  283-297.  doi:10.11743/ogg19900309
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    There are five types of organic reefs of Changxing stage in East Sichuan:patch reefs on carbonate platform rises and flat,shelf margin reefs and patch reefs in back reef la-goons,and patch reefs near restricted sea.The formation of typical patch reefs was related to the fluctuation of earth crust at the end of the Permian,forming reef core facies,constructed by saccoliths of bound-stones,interchangeably with intermittent shoal facies.Facies-selective dolomitization and dissolution in different stages resulted in the reservoirs of intermittent shoals,reef flanks,etc..The paper deals emphatically with the sedimentology and diagenesis of the reef com-plex.

    GEOCHEMICAL CHARACTERISTICS AND ORIGIN OF GASEOUS HYDROCARBON IN SANSHUI BASIN
    Du Jianguo, Xu Yongchang
    1990, 11(3):  298-303.  doi:10.11743/ogg19900311
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    The origin of gaseous hydrocarbon is discussed on the basis of geochemical featuresof natural gas in Sanshui Basin,Guangdong Province.The Cretaceous-Eogene Systems inthe basin have a thickness greater than 7600m.The Buxin Formation(E1-2b)contains morethan 500m thick source rocks in which kerogen is mainly types Ⅱ and Ⅲ.Vitrinite reflec-tivity(Ro)is between 1.2% and 1.9%.Eleven samples of natural gas have been analyzedfor gas components and isotopic composition of carbon and hydrogen.The results showthat geochemical characteristics of ignitable gases are:1.hydrocarbon-rich natural gascontains N2,He,CO2,but not H2s;2.the value of dry-wet indices (C1/ (C2+C3))has the range of 2.1-196 which can be easily separated into two groups:>18 and <8;3. iC4/nC4 ratios Change between 0.42 and 0.87;4.the value of δ13C1 and δ13C2(PDB) ranges from -61‰ to -44‰ and -33‰ to -30‰ respectively;5.δDC1 value(SMOW) has the range of -237‰ to -174‰ which reflects the genetic process ofmethane and salinity of sedimentary water.Dry gas found in the highest part of structureis distributed in the area in which oil field water is of NaHCO3 type with a lower intensityof mineralization (25-50 g/l).The carbon and hydrogen isotope composition(δ13C=-60‰ and δD=-236‰--174‰) of methane in dry gas are identical with those of bio-genetical methan.Wet gas (C1/ (C2+C3)<8)in company with crude oil is rich in13C(δ13C1=-48‰--44‰,δ13C2=-33‰--30‰).The difference between δ13C2 and δ13C1changes from 14.7‰ to 15.2‰.The isotopic compositions of wet gas conform tothose of oil-type gas from Zhongyuan and Sichuan Oilfields.Wet gas is found in the areathat has Na2SO4 type of oilfield water with a higher intensity of mineralization (50—100g/1).All of the geochemical evidences confirm that dry gas in Sanshui Basin is generatedby microbe altering organic matter (including oil and gas) after the period of oil genera-tion,wet gas originated from E1-2b source rocks.

    JURASSIC HYDROCARBON EXPLORATION IN EAST SICHUAN
    Chen Zongqing
    1990, 11(3):  304-312.  doi:10.11743/ogg19900312
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    The oil and gas pools of the Lower Jurassic Daanzhai and Lianggaoshan Formations in central Sichuan are distributed in semi-deep lake and shallow lake facies.The east partis similar to Central Sichuan in this respect.They are two symmetric parts of the same fa-cies zone deposited in the same lake basin.The difference is that exploration level is verylow in East Sichuan.The reservoir beds in the above regions are compact lenticular shell-limestone and sandstone formed by shelly beaches,sand barries and sandbars.Fracturesare well developed in the reservoir beds,formed fracture-lithologic reservoirs.Though thisregion is intensively folded and seriously denuded,the Jurassic reservoir beds inwide-gentle synclines separated from high-steep anticline zones are well preserved.Amongthem,lower and gentle structures,buried structures,the axes of synclines,the affectedzones in the upper end of buried overthrusts and flexural zones are all favourable places toseek for fracture-lithologic trapped hydrocarbon pools.

    GRAVITY FLOW DEPOSITS OF PRODELTA SLOPE FROM 3RD MEMBER OF SHAHEJIE FORMATION,NIUZHUANG REGION,SHANDONG
    Feng Youliang, He Likun, Zheng Herong, Wang Ning, Jiang Xiufang
    1990, 11(3):  313-319.  doi:10.11743/ogg19900313
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    The prodelta slope of the third member of the Oligocene Shahejie Formation in Niuzhuang region,Shandong,is composed of slump slope,proximal gentle slope and distal slope.The slump and the debris flow sediments are well developed on slump slope;theliquefied-flow and the turbidity current sediments developed on gentle slope and the un-complite turbidity assemblage developed on distal slope.The controlling factors for the de-velopment of gravity-flow deposits on prodelta slope are deltaic progradation and the dou-ble-layer structure of the slope.Favourable regions for hydrocarbon enrichment are gentle slope.

    COMPOSITE TERRANE AND ITS HYDROCARBON POTENTIAL IN LOWER YANGTZE REGION
    Gong Yujin
    1990, 11(3):  320-333.  doi:10.11743/ogg19900315
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    The basement nature,the cover facies,the structural feature and magmatic activity in the lower Yangtze Region have presented obvious differentiae in the north and south parts of the region.The reason caused these differences is the existence of south (the Qiantang) and north (the Yangtze) terranes.These two terranes,under went long tectonicevolution,were connected as a unified composite terrane in the end of the Triassic.The Qiantang Terrane is the primary place for hydrocarbon generation and accumulation from Lower Paleozoic;the Yangtze Terrane is the most favourable place for thatfrom Upper Paleozoic (including the Middle and Lower Triassic).The former will be themain target for oil and gas exploration.

    PRIMARY MIGRATION OF LACUSTRINE HYDROCARBON FROM MUDSTONE TO TURBIDITE IN LIANGJIALOU REGION
    Zhang Dunxiang, Zhang Fanghou, Luo Guanghua
    1990, 11(3):  334-344.  doi:10.11743/ogg19900316
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    In Liangjialou region of the Shengli Oilfield,Shandong Province,the mudstone of deep lake facies which is the source rock is closely connected with reservoir rock—deeplake turbidite.This paper describes the thickness of oil drainage belt and oil drainage ratio.The influence of stratic chromatography on soluble organic matter is also discussed in the paper.

    BRIEF INTRODUCTION OF SHALLOW GAS POOLS IN BAISE BASIN,GUANGXI
    Dai Jiaqing
    1990, 11(3):  345-348.  doi:10.11743/ogg19900318
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    This paper briefly describes 4 shallow gas pools in the Baise Basin,Guangxi.Based on isotopic data,the author considers that the natural gas of these pools as well as that of the underlying pools are biogenetic gas.