Table of Content

25 December 1986, Volume 7 Issue 4

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GRAVITY AND MAGNETIC ANOMALY AND THE GEOLOGICAL TECTONICS OF THE EAST CHINA SEA

Wang Heming, Yin Wenrong

1986, 7(4):  295-307.  doi:10.11743/ogg19860401

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Gravity and magnetic survey on the scale of 1:100000 is made in the East China Sea and a lot of geological informations were obtained by the first Brigade of Marine Geological survey.Based on the analysis of gravity and magnetic anomaly and the comprehensive interpretation of geological,seismic and drilling data of both continent and Islands,the authors consider that the average Bouguer anomaly in a broad range revealsthe slow uplifting of the Moho and the thinning of the crust from west to east in the East China Sea.The average Moho depth of continental shelf is 30km.The changes of gravity and magnetic anomaly and their strike show that the formationstages of the basement in the studied area progres sively turn younger from northto south and from west to east,i.e.,from the Precambrian to the Pre-Mesozoicand then to the Pre-Miocene.The shapes and distribution regularities of localgravity and magnetic anomaly indicate that the fault stages and volcanic activitiesfrom northwest to southeast have a new tendency of changing from old toyoung,and the regional tectonic framwork contains 3 uplifts and 2 basins,fromwest to east including Zhejiang-Fujian uplift zone the East China Sea shelfbasin,Diaoyu Island upwarping folded zone,Okinawa Trough basin and RyuKyu Archipelago upwarping folded zone.

SUBMARINE FAN OF TERRIGENOUS DEBRIS AND ALLOCHTHONOUS CARBONATE SEDIMENTS ON THE BASE OF SLOPE IN THE DEVONIAN TROUGH IN WEST YUNNAN

Gao Zhengzhong, Duan Taizhong

1986, 7(4):  308-323.  doi:10.11743/ogg19860402

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A deep trough which was more than 700 km long stretched from north tosouth in west Yunnan in the Devonian.Submarine fan of terrigenous debrisand the related deep water sediments were well developed there,thus formed theas semblage of both submarine fan model and carbonat slope wedge model.The fan is between high energy system and low energy system,but moreclose to high energy system.It can be divided into five subfacies such asinnerfan facies,central-fan facies,outer-fan facies,fan marginal facies and basin-plain facies.The carbonate sediments on base of the slope along the dis-tribution of carbonate slope,as a self-formed system,are not controlled by thefan body.It consist of all ochthonous sediments in carbonate gravity flow and autochthonous sediments in deep water.The provenance of the former is relat-ed to the submarine canyon which deeply cuts the slope,and that of the fateris the adjacent carbonate platform.Gravity sediment,especially the submarine fan show up distinct phases.Itcan be divided into embryonic stage(Shanjiang-Alengchu period,i.e.,the earlystage of the Early Devonian),prime stage(Banmandaodi period,i.e.,the latestage of the Early Devonian)and depauperation stage(the Middle Devonian).They constitute the evolution history of deep water sediments.

LIQUID CHROMATOGRAPH CHARACTERISTICS OF PORPHYRINS IN SEDIMENTARY ROCKS AND CRUDE OILS OF PETROLIFEROUS BASINS OF CHINA

Yang Zhiqiong, Li Xiaohui, Zhang Ling

1986, 7(4):  324-332.  doi:10.11743/ogg19860403

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Porphyrins in crude oils,source rocks and oil shales in China are mainly DPEP and ETIO.With the increase of burial depth,the ratio DPEP/ETIO of source rocks decreases gradually and high-carbon-number porphyrins(D₃₂,E₃₂)change into low-carbon-number ones.But the ratio DPEP/ETIO of oilshales does not change with burial depth.According to the contents and types of porphyrins,the chinese crude oils can be divided into 4 kinds:biodegradedoil,immatured oil,matured oil and higher matured oil.

THE DETERMINATION OF THE CANGXIAN-TIANJIN PALAEO-SYNCLINORIUM AND ITS GEOLOGICAL EVIDENCE

Liu Chiyang

1986, 7(4):  333-343.  doi:10.11743/ogg19860404

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According to data about the texture of the geological section,stratigraphy,hydrogeology,structural movement and sedimentation,and through restorationof palaeo-tectonics and synthetic analysis,the author suggests that in Pre-Jurassic,there was a great NE trend synclinorium,called the Cangxian-Tianjin syncli-norium,in the central-western part of the present Bohai Bay Basin.It spread along the Tianjin-Cangxian-Guantao zone,including the whole Cangxian Uplift,most ofthe Huanghua Depression and a part of the Jizhong Depression,Linqing Depression and Xingtai-Hengshui Uplift.During the Jura-Cretaceous,the synclinorium was remade and further developed as a result of shearing and compressing.However,from the Eocene,itbegan to break up under the tensil-shear stress and developed into uplifts alter-nated with depressions in the central-western part of the basin.The determination of the synclinorium is significant for the study of geological tectonics and further exploration of oil and gas in the region.

PALEOGEOGRAPHY OF BEFORE AND AFTER DEPOSITION OF GREEN-BEAN ROCK (ALTERED TUFF) BETWEEN THE EARLY AND MIDDLE TRIASSIC IN THE UPPER YANGTZE PLATFORM AND ITS ADJACENT AREAS

Zhu Zhongfa, Wang Guangxin

1986, 7(4):  344-355.  doi:10.11743/ogg19860405

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The sedimental facies of 3 m thick around the roof and bottem of the green-bean rock（altered tuff）between the Early and Middle Triassic can bedivided into 9 kinds of rock association,belonging to 5 sedimental facies zones respectively in the Upper Yangtze Plat form and its adjacent areas.The westpart of the studied region is a extensive sabkha platform,the facies zones aredistributed in circles.The outer part is constituted by purphish red clastic rock and massive dolomite of the sabkha;the middle circle consists of striped dolomite and anhydrite rock,striped magnesite,anhydrite intercalated with nodular polyhalite of salt playa;the inner one is made up of striped argillaceous anhy-drite rock.The sedimental facies of the east part are distributed as parallelribbon,which consists of striped argillaceous anhydrite rock,lamellar mudstoneand marl of desiccation bay in the west side,and massive gypsum microdolomite,micrite intercalated with oolitic limestone,dolomite of sabkha salt marsh andshallow sea in the east side.δ¹³C-value indicates that negative abnormal region of low value corresponds to paleodepression within the platform,and is considered to be salt lake or saltswamp;the one of the high value is corresponding to sabkha salt marsh or saltflat of the paleo-uplift within the platform;the normal region is considered tobe the open sea of south Guizhou and west Yunnan Provinces.

EVOLUTION STACKING AND HYDROCARBON POTENTIAL OF THE ORDOS BASIN——PROTOTYPEL ANALYSIS OF A HUGE BASIN IN CHINESE CONTINENTAL PLATE

Sun Guofan, Xie Qiuyuan, Liu Jingping, Xie Shiying, Liu Keqi, Yuan Weiguo

1986, 7(4):  356-367.  doi:10.11743/ogg19860406

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Based on Prof.Zhu Xia's theory of double classification of oil-and gas-bearing basin,the authors studied the evolution stacking and hydrocarbon potential of the Ordos Basin.The basin has experienced several development stages in tectonic evolution,there were a number of basin prototypes.During the Middle Proterozoic,thereexisted a series of aulacogens within the craton,then they changed into anunified syneclise.In the Early Paleozoic,regenerated aulacogens could onlybe found in the western margin of the basin while the main part of it was occupied by craton depression.Although the whole of the North China was uplifted and denuded by the Caledonian Movement,the inside of Ordos continuedto develop craton depression,only a collision valley of the Middle and Late Carboniferous was formed in the north part of the western margin of it.The Permian and Early-Middle Triassic were a transitional period in its evolutionhistory.In this period,structural differentiations were closed and a unified sedimentary environment was formed.From the Late Triassic on,a differential subsided basin was formed by push-compression stress of the peripheral struc-tures in the Ordos and the broad North China region,only the western marginof it developed into a front depressed basin on the move from west to east.Fromthe Cenozoic,the whole of the Ordos uplifted,only some fault-depressedbasins were formed by regional strike-slip faults outside the Ordos.Oil potential of the Ordos Basin is characterized by multi-sequence gene-ration,multicycle accumulation,multi-type traps and broad distribution.Thepivotal zone and overthrust nappe belts on the west margin may possibly be hy-drocarbon enriching zones.

STUDY OF SEISMIC STRATIGRAPHY OF THE TERTIARY HYDROCARBON RESERVOIR BODIES IN JIZHONG DEPRESSION

Liu Qianzhi, Wan Liping

1986, 7(4):  369-378.  doi:10.11743/ogg19860407

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3 types(including 10 kinds)of reservoir bodies are discovered by means of seismic stratigraphy in the Tertiary strata in the Jizhong Depression.The first type are high energy reservoir bodies which deposited rapidly in the environment of higher hydrodynamic energy or gravity energy.This type of reservoir bodies generally have particular forms and reflective textures of the seismic facies.For instance,the seismic response of deep-water fans are high amplitude-mound facies,the shellow-water fans are draping facies with imbricated texture ininternal reflection,the alluvial fans are low amplitude-mound facies,the deltas are oblique foreset facies and the colluvlal cones are chaotic moundfacies.The second type are geomorphic reservoir bodies which were controlledby paleogeomorphology.The seismic reflectance of slope washes are generally discontinuous high amplitude facies in the form of pancake or wedge and the filled sand and conglomerate bodies are filling facies with concave-down baseplates and the arcual top surfaces.The third type are reservoir bodies with special lithology.The seismic reflectance of volcanic rock reservoirs are cha-racterized by high amplitude,low frequent,fine continuity and high layervelosity and the carbonate rocks are mainly determined by their thickness and stability,when the rocks are thin,dispersed and less stable,seismic reflec-tance will occur contortion and branch;when the rocks are thick and continu-ous,the properties of reflectance will show a high wave and a low wave withlight-undulatory contortion.The above reservoir bodies were controlled by paleo-current direction,strengh and paleogeomorphology as well as tectonic move-ment.

DISCUSSION ON PETROLEUM SEISMOGEOLOGY

Yuan Bingheng, Sun Tingju

1986, 7(4):  379-385.  doi:10.11743/ogg19860408

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Petroleum seismogeology contains 10 basic aspects:the structure maps,geo-tectonics,basin affection,structural properties inside basins,local structures,regional seismic stratigraphy,subtle traps,oil generation,reservoirs and the comprehensive evaluation of oil-bearing areas.The formation process of this subject can be divided into 3 phases.

GEOMECHANICAL ANALYSIS AND HYDROCARBON ACCUMULATION OF THE KARAMAY OVERTHRUST BELT

You Qimei

1986, 7(4):  386-394.  doi:10.11743/ogg19860409

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Karamay overthrust belt is located at the front of the compresso-shear beltin west Junggar.It is on the active boundary of the convergent transforma-tion type and has special mechanical model:1.With a nappe as the main part,the three subbelts of the overthrus tbelt developed into two divergent brush structures in reverse directions onboth sides of each nappe.The whole form of the overthrust belt looks likethree S-shaped or reversed S-shaped structures.2.The stronger the compressed stress that each subbelt underwent,thesmaller the curvature of arc faults in divergence parts was.The stronger the shear,the larger the curvature.3.On the starting end of the shear stress of each subbelt,the structure developed stronger,and it is known as“strong head”;the other end maybe called“weak tail”.The fracture of the“strong head”divergens towards mountain,and that of the“weak tail”divergens towards the basin.4.The fault blocks on the overthrust belt can be divided into four kindsaccording to their mechanical properties:echelon fault block;flank faultblock;λ-type fault block and branch reclosing fault block.5.The fault belt consists of many faults stacked by different mechanical properties during different geological times.The more the number of paleofaultsstacked,the better the fractures developed.The relationship between mechanical model and hydrocarbon accumulationon the fault belt are shown in follwing:1.In planar and vertical hydrocarbon distribution,the“strong head”hasan advantage over“weak tail”,2.The high production rate of echelon fault block is greater than that offlank fault block,that of the flank fault block is greater than that of λ-typefault block,the one of λ-type fault block is greater than that of fault block.3.All the fault blocks mentioned above which formed under rotation stress and the places where most paleofaults stacked are favourable for the explo-ration of high production hydrocarbon.

PRELIMINARY APPROACH OF THE CLASSIFICATION OF LAKE BASIN DELTAS

He Zhiliang

1986, 7(4):  395-403.  doi:10.11743/ogg19860410

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The classic“Gilbert”delta is not a sole type of lake basin deltas,because the lake basin deltas though differ from those of marine basin in properties, they still have many common properties.Especially in particular situation,the deposition of deltas in marine basin is also an innegligible factor for lake basin deltas.The density of the water body of lake basins is close to that of rivers,but it may differs greatly from the river's or even exceeds that of marine basin.The effects of river of course played a decisive role in the formation of the lake basin deltas,but the effects of wave are very important.The transgression and regression of lake water even surpassed those of marine basin.Those deltasin special,such as steep slope deltas,transgres sive deltas of normal cycle andwave controlled deltas which are discovered in paleo-sediments and present sediments in succesion have provided material base for the classification in thispaper.In accordance with the combinations of the steepness or gentleness of slopes,transgression or regression of lakes and the controlling of waves or rivers,lake basin deltas can be divided into 8 end types so as to reveal their origin.

DISTRIBUTION AND OCCURRENCE OF NON-HYDROCARBON GASES IN GUANGDONG PROVINCE

Zeng Guanyun

1986, 7(4):  404-411.  doi:10.11743/ogg19860411

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More than 60 anomalous places of non-hydrocarbon gas,including CO₂, N₂, H₂S,Ar,Rn etc,are discovered in Guangdong Province.The distributionof anomaly zones of non-hydrocarbon gas closely related to fracture zones.9 anomaly zones can be divided into 3 groups:NE-NNE anomaly zones;NW anomaly zones;EW anomaly zones.The gas anomalies can be divided intosurface gas seepages,underground gas beds,water-soluble gas shows and water-soluble gas beds.The formation of the anomalies may be related to degassing ofthe globe during the Meso-Cenozoic,especially in the Middle and Late Ju-rassic and the Eocene.

A GLIMPSE OF CORAL REEFS OF THE YONGLE ISLANDS,XISHA ARCHIPELAGO

Sha Qingan

1986, 7(4):  412-418.  doi:10.11743/ogg19860412

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Yongle Islands(atoll)is situated in the west of Xisha Archipelago of the South China Sea.It consist of seven bigger separated reefs.The central lagoon of theatoll is about 40min depth.These reef-flats appear a similar in geomorphic features,and can be divided into several zones,including outer-slope,outer-crest,outer-flat,island(sand,gravel or rock island),inner-flat,inner-slope.Each zone has its own organisms and sediment features.Two lines of beachrocks occur outside the Quanfu Island.This indicatesthat the sand island has moved three times at least.Shiyu Island,consisting of cemented rock,appears to be an anticline structure.Obviously,it is a deposi-ting anticline.

APPLICATION OF GRAVITY EXPLORATION RESULTS TO DISCUSS THE BASAL STRUCTURE OF THE CHUXIONG BASIN,YUNNAN PROVINCE

Wang Chaodong

1986, 7(4):  419-426.  doi:10.11743/ogg19860413

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The Chuxiong Basin in central Yunnan is a unsymmetrical half-basin of the Mesozoic,The basin is deeper in the west and shallower in the east and ran-ges about 35000km².According to maps of the basal texture and the crust thick-ness,the basin can be divided into two units of the eastern uprising and wes-tern depression.From north to south,the former consist of the Yongren Uplift,Chuxiong Depression and Dahongshan Uplift,the later contains of Huaping Up-lift,Yanfeng Depression and Yunnanyi Uplift,All these uplifts and depres-sions are separated by fractures.Some of the secondary gravity anomalies arefound to be in coincidence with anticline structures.It is proved by study that free-air anomaly is corresponding to the thick-ness of deposition.According to the positive anomaly,the author suggest that the Yanfeng,Mouding,Shuangbai and Yao'an-west Nanhua stuctures within the basin are the deposit centers.Calculation results show that the eastern part of the basin is the uplift of the mantle,and the western part is its slope.

PYRODYNAMICS OF SOURCE ROCKS IN DONGPU DEPRESSION

Wu Zhaoliang, Wang Jianqiu, Huang Xinghan

1986, 7(4):  427-432.  doi:10.11743/ogg19860414

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The apparent activation energies and pre-exponential factors of the first order reaction are calculated in accordance with the Rock Eval data of 5 rock samples of the Tertiary Shahejie Formation buried in depth of 1801-3407min the Dongpu Depression.When the ratio x（the ratio of generated hydrocarbons amount to potential amount of hydrocarbon generation）is 0.05,then the activation energy E is 131 k Jmol^-1,and the factor A is 1.155×10⁸s^-1.While x reaches 0.95,E then increases to 249.7kJ mol^-1,and A increases to 8.215×10¹⁶s^-1.