Table of Content

20 June 2002, Volume 8 Issue 2

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Article

Tectonic Subdivision of Dabie Orogenic Belt，Central China： Evidence from Geochemical Characteristics of Mantle-Derived Rocks Since the Hercynian

KUANG Shao-ping, ZHANG Ben-ren

2002, 8(2):  129-140. 

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Qinling-Dabie orogenic belt(DOB)represents the composite convergence zone between the North China and the Yangtze blocks(NCB and YB)．It is in doubt that Qinling orogenic belt(QOB)is composed of the southern margin of NCB(SNCB)，northern QOB(NQOB)，southern QOB(SQOB)and the northern margin of YB(NYB)；Shangdan fault zone between NQOB and SQOB was a megasuture between NCB and YB during Neopmtemzoic-Paleozoic period；and the Mianlue fault zone，a subsuture between SQOB and NYB，was formed within the Yangze plate during the Late Paleozoic．Th geochemical characteristics of mantle—derived rocks provide some new evidence for DOB subdivision in the present paper．Actually，there are abundant mafit-ultra-mamic rocks distributed in different units of Dabie orogenic belt since the Late Paleozoic For example，along the Tonghai-Shangcheng fault zone occur the Chuqiurniao-Wangmuguan gabbros of the Hercynian；in both northern and southern Dabie complex outcrop many post-collisionally mafites and ultramafites of the earLy Late Yanshanian；and in centra1 and southern Dabie orogenic belt present volume mumber of the basalts of the late Late Yanshanian．Geochemical research indicates that these mantle-derived rocks are featured by enrichment of Sc and Cu，depletion of MgO，with higher Rb／Sr，Ba／St，Ba／La， Nb/Ta and Yb/Hf ratios, as well as 1ower Zr/Hf ratio. These characteristics are similar to those of the mantle in Yangtze block，and can be further compared to those of the mantle in southern Qinling orogenic belt This result has been supported by the results，obtained from the research in geology，structural geology，petrology，geophysics and isotopic geochemistry for DOB，which suggests that Tongbai-Shangcheng-Mozitan-Xiaotian fault zone in DOB be an eastern extension of the Shangdan fault zone in Qinling orogenic belt．Based on the synthetic information，it is concluded that Dabie orogenic belt developed from Yangtze mantle and belongs to the eastern part of southern Qinling orogenic belt．

Characteristics and Geochemical Significance of the Fatty Acid Biomarkers from the Pyrolysis of Pine Pollen

Jl Li-ming1 2, CHEN Jian-fa2, ZHENG Jian-ling2

2002, 8(2):  141-151. 

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A large number of fatty acids in the light hydrocarbons and aromatic fractions of the extracts from thermally simulated samples of modern pine pollens were identified by GC-MS analysis. These biomarkers are clearly even carbon predominated. The major components of light hydrocarbons are palmitic(C16)，stearic(C18)，methyl esters(Cl6，C18)and ethyl esters(C16，Cl8). Aromatic hydrocarbons are relatively complex，consisting of saturated fatty acids，unsaturated fatty acids and fatty acid internal esters．The carbon number of the light hydrocarbons is from C15 to C30，and the relative distribution of C16，C18 acids(esters)is of absolute predominance. The carbon number of aromatic hydrocarbons is from C20 to C30，and the main components are C26，C28 and C30. Lower abundance of Cl8 unsaturated fatty acid was identifed at low temperature stage(<250℃ ) The expulsion of fatty acids(esters)occurred at very low temperature stages. There are two expulsion peak stages from 200℃ to 300℃ and from 300℃ to 400℃. The controlling factor is probably due to difference in hermal stabilization of different fatty acids. The free state fatty acids(esters)in the cytoplasm of pine pollens and the unsaturated fatty acid are easily banished at low temperature stage. Saturated fatty acids and the fatty acids in the lipoid of the wall of pollens would be degraded at the higher temperature stage. Original pollens and the simulated samples at low tempe rature stage mainly contain fatty esters． Simulated samples at 250℃ and higher temperatures contain more fatty acids due to hydrolysis．Fatty acids(esters)can be easily decarboxylated to produce chain hydrocarbons as the simulation temperature continuously rises. The contents of fatty acids(esters)remarkably drop down because of strong pyrolysis at the higher temperature stage over 400℃. This is consistent with the appearance of large quantity of odd carbon n-alkanes in light hydrocarbons and saturated hydrocarbons at 350～ 450℃ stage. The studies indicate that plant pollens are one of the important origins of Cl6，C18 saturated and unsaturated fatty acids(esters)in sedimentary organic of mattters．

Features of Distributary Channels and Their Diagnosis Methods：Exemplified by the Eastern Dongying Depression

YU Jian-guo1 3, LIN Chun-ming1, YANG Yun-ling2, ZHU Ying-ke3, WANG Jin-duo3, ZHAO Yah-yan1

2002, 8(2):  152-159. 

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With the further exploration，the research on sedimentary facies of distributary channels becomes more and more important. The reservoirs of distributary-channels are of a special hydroearbon pool type．Due to their intense concealment and unique rotating conditions，the study on such reservoirs is very difficult．In this article，we made systematic research on the distributary-channel reservoirs for the second member of Shahejie Formation，eastern Dongying Depression，from the following aspects：sedimentation characteristies ，reservoir characteristies, the 1ogging characteristics，and 3D-seismic coherence analysis．Our study suggests that the sediments of distributary-channels in the eastern Dongying Depression are mainly composed of sand and silt with small amount of mud flasers．The sand and silt are usually wel1 sorted and rounded，and often contain large-scale tabular or trough cross-beddings，parallel 1aminations and masive beddings etc．The distributary-channels are lenticular，with flat-top and convex-bottom in their cross-sections．On the plan, they are fan-shaped with dipping limbs. During low lake level stages, the deposits of distributary-channels move lakeward；and during high lake level stages，hasinward. Such fluctuation of Lake level often leads to formation of distributary-charnnels’sediments largely under subaquatic condition．These reservoirs are mainly composed of cross-stratified diaras and pointbars, with monolayers ranging from 2m to 10m．The spontaneous potential(SP)curves well indlcating the logging characteristics consist of smoothing column，dentate column，dentate funnelshaped，dentate pendulum and smoothing ovum which represent five different positions of distributary-channels from the center to the margin respectively. Their seismic profiles are lenticular or hummocky，with poor continuity，middle-amplitude and oulapping-filling features．Compared with others，these reservoirs in distributary-channels are widespread，complex and thin in vertial direction for their swift wandering. Therefore，we should analyze the data in geology，1ogging，drilling and 3D-seismic materials integratedly to prognose the configuration and distribution of the distributary-channels．The discusion about the recognition methods of distributary-channels in eastern Dongying Depression in this paper is of significance for exploration and development of the subtle reservoirs.

The Coupling of Sedimentary Characteristics and Tectonic Development of Turpan-Hami Basin and Adjacent Areas in Early Permian

ZHU Wen-bin, MA Rui-shi, GUO Ji-chun，SUN Yan, GUO Ling-zhi, XU Ming-jie, HU De-zhao

2002, 8(2):  160-168. 

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Great changes took place in geological structure and geomorphology of Xinjiang area during the Late Permian ．The Early Permian marks an important tectonic transition in the Tianshan region of northwestern China between Carboniferous continental amalgamation and recurrent Mesozoic-Cenozoic intracontinental orogenic reactivation. The Turpan-Hami Basin accormmodated up to 3000m of sediments and is ideally positioned to provide constraints on this transition．It indiates the end of evolution history of the basin basement and the beginning of evolution history of the basin cover. Multi-type Late Permian sedimentary sections are found which include marine sediments, continental sediments and alternative facies sediments of marine and continent．Based on the anlysis of different cross sections and wells we suggest that there are three sedimentary facies which are ：1 rift-type marine volcanic eruption sedimeatary facies ；2．rift type continental volcanic eruption sedimentary facies ；3 orogenic belt molasse facies. The Lower Permian occurs in the southern Turpan-Hami Basin as continental molasse consisting of conglomerates，glutenite，greywacks, silicalite and bioclastic limestones. The conglomerates are composed of pebbles of volcanics，granite，limestone，marble，silicalite and metamorphic rocks．Lower Permian rocks in the northern and southeastern Turpan-Hami Basin unconformably overlie a Late Carboniferous volcanic are sequence．These Lower Permian strata include shallow-marine carbonate rocks and maric to felsic volcanic rocks that are in turn overlain by 1ittorol to profundal lacnstrine facies．It is considered that there are two types of basins in Turpan-Hami Basin and adjacent area ：the foreland basins and the rift basins according to different sedimentary characteristics and structural analyses．The origin of these two types of basins in continent-continent collision zone is also discussed in this paper．

A Study on the Tectonic Basement of Late Mesozoic Igneous Rocks in Southeastern China

DENG Ping, SHU Liang-shu, XIAO Dan-hong

2002, 8(2):  169-179. 

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According to middle-high grade metamorphic rock assemblages，structural defomational styles and newer data of isotopic ages, this paper suggests that a Precambrian continental block existed in the southern Zhejiang-northern Fujian-central-southern Jiangxi-eastern Guangdong region,South China．This oldland, with the oldest isotopic age of 2100 Ma and named the Cathaysian Oldland，is characterized by large scale development of schist，gneiss and migmatic rocks with the interval from l8O0Ma to 1200 Ma，which comprise the continental crustal basement About 1100- 90OMa, the Cathaysiml Oldland collided with the Yangzi continental plate to form the Shaoxing-Jiangshan-Dongxiang-Pingxiang Fault Zone．Not long time later, about 800 Ma, the Cathaysian 0ldland was dispersed into three blocks with different strikes and distinct outline，that is，the NEE striking Southeastern Zhejiang—-Northwestern Fujian Block，the sub-N-S-striking Central Jiangxi-Southern Jiangxi Block and the NE striking Yunkaidashan Block，respectively. The Sinian-Early Paleozoic sedimentary materials with a large thickness filled among these three blocks Study proposes that this oldland subjected to three-phase tectonic-thermal events at least，the Luliang event(1 800-1 600Ma)，the Jinning event(1 100—900Ma)and the Caledonian event(420—40OMa)since the Neo-Proterozoic to become the tectonic basement of the Late Mesozoic (mainly Cretaceous) volcanic-lntrusive complexes. The basement feature of the Southeastern Coasta1 Region is not clear due to 1ack of Precambrian outcropped rocks and isotopic age data．But according to the geochronological age of 1806Ma by the whole rock Rb-Sr method on the core of gneissic rock from the Linfeng hole NO．1 in East China Sea(East of Wenzhou)，we guess that a Proterozoic metamorphic block should exist under the Meso-Cenozoic sedimentary rocks of the East China Sea. During the Late Mesozoic-Paleogene，a large-scale intra-continental rift basin was formed along the Shaoxing-Jiangshan Dongxiang-Pingxiang Fault Zone, in which red bed was filled．This ancient tectonic framework constrains 1arge scale Mesozoic tectonics-magmatism and difference in magmatic compositions and distributrion.

Chengdao Composite Petroleum System Analysis and Evaluation，Bohai Bay Basin，China

YANG Feng-li1, ZHOU Zu-yi1, ZHANG Shan-wen2

2002, 8(2):  180-189. 

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Chengdao area is located in the southern part of Chengbei lower convex of Bohai Bay basin，China．This area contains stratigraphic sequences of almost all ages from Archaean to Tertiary. The structure style shows the characteristics of dyadic structures，and belongs to a typical burial hill-drape anticline Petroleum exploration in the area demonstrates that Chengdao area itself is weak in hydrocarbon generation and the hydrocarbon in the pool came from surrounding depressions including Chengbei depression，Shanan depression，Bozhong depression an d Zhuangdong depression．The hydrocarbon accumulation system in the area is complex，with more than one source rocks，and multiple stages of migration and accumulation．Based on various fundamental geological factors and processes that dominate the hydrocarbon formation and accumulation，the Chengdao composite petroleum system is identified．Four hierarchy levels of the composite petroleum system is subdivided and described，which include 1 composite petroleum system,3 petroleum systems,12 sub-systems and 48(12×4)4th order systems.

Discussion on Play Types and Their Distribution Regularities in Steep Slope Zone of Fault-Depressed Lacustrine Basin

HU Shou-quan, GUO Wen-ping

2002, 8(2):  190-198. 

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A complete terrigenous sequence in fault－depressed lacustrine basin can be divided into four systems tracts：lowstand systems tract(LST)，trangressive systems tract(TST)，highstand systems tract(HST)and regressive systems tract(RST) In the steep slope zone of fault-depressed lacustrine basin，the development of source beds，reservoirs，cover rocks of hydrocarbon has specific and genetic relationship with systems tracts in terrigenous sequence，and different styles of terrigenous sequence can form different assemblages of source beds，reservoirs and cover rocks．In Biyang fault-depression the most favorable source rocks are the mudstone of semi-deep or deep lake facies in HST(belonging to regional hydrocarbon-producing formation)，and in next order the mudstone of lake facies in TSTand RSF (belonging to local hydrocarbon-producing formation)；The favorable reservoirs are distributed in sandstone body of fluvial fan-fan delta，and in slumping gravity flow fan body of delta slope gone．The regional cover rocks are mudstone of deep lake facies in HST, but the mudstone of lake facies in TST and RST can also form local cover．Synthetically considering plenty of geological factors such as：(1)stragigraphic stacking styles and strafigrapbic fray-out styles；(2)regional hydrocarbon-producing formations and cover rocks，and local hydrocarbon-producing formation and cover rocks；(3)several important and special sealed surfaces(e．g the top and bottom of sequence，downlap surface，basin-margin boundary fault，etc.)，and according to the types and characteristics of reservoirs in terrigenous sequence，the play types in terrigenous sequence of the steep slope zone of fault-depressed lacustrine basin can be generalized into three types ，eight subtypes and ten kinds．They include lithological up fray-out play type，lithological down fray-out play type，lithological facies change play type lithological lens play type，stratigraphic unconformity play type，stratigraphic trocation play type，stratigraphic overlap play type，stratigraphic downlap play type，stractural-lithological composite play type．Structural-stratigrapltic composite play type. The distribution of play type in every systems tract of terrigenous sequence is not balanced，and the most popular in TST，popular in RST and HST，the least popular in LST．From the spatial distribution regularities of play types in every systems tract of terrigenous sequeqce．the play types in TST age distributed in the transitional belt from basin borders to basin centers.Their buried depth is moderate．They are relatively close to source area．Thus，TST is a significant target to hydrocarbon exploration in the step slope zone of fault-depressed lacustrine basin．

Determination of Remaining Oil Distribution in Thin and Poor Reservoir by Useing ANN Method

LIU Bo1 2, DU Qing-1ong2, WANG Liang-shu1, LIU Shao-wen1

2002, 8(2):  199-206. 

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Artificial neural network pattern recognition technique(ANN),as a simulation and abstraction of human being’s brain thoughts，can be used to recognize and classify objectives by imitating the transmission manner of nerve cel1．The most popular ANN model at present is the error back propagation, which trains the nerve network by back propagation algorithm．A typical back propagation nerve network has three-layer feed forward structure，consisting of input layer， cryptic layer and output layer. In this study, the ANN method is applied to recognize the remaining oil of thin and poor reservoir of Daqing oilfield，associated with the data of sealing coring inspection well and development geological method. The process is first to input the known parmeters related to the formation and distribution of remaining oi1；then select the suitable mathematic algorithm for calculation，and finally to obtain the parameters，including the accurate oil saturation，water-bearing and water flooding degree．However，the key of this technique is to determine the input parameters which are related to formation mechanism and distribution of remaining oil．The authors analysed the development conditions and producing status of the thin and poor reservoir of Xing 2-1-Jian 29 well，which is located at Xingshugang，a typical district of oil field of Daqing．The results show that geological factor and the development factor are both important affecting the distribution of remaining oil．The remaining oil is usually distributed in the districts of sand bodies with discontinuous growth or incomplete injection-production. The main parameter of ANN for recognizing the remaining oil of single well and single stratum is sand body type. The recognition model of water flooding degree and oil saturation is established by the nerve network training．Th model was tested by the data of other sealing coring inspecting wells, and the average error was 8．4 ％ , which indicates that the recognition mode1 is good in use．The authors applied this model to densified wel1 pattern testing district in Sa’ertu oil field of Daqing to analyse and interpret the water-out degree of perforated reservoir，which could predict the water-out distribution of thin and poor reservoirs effectively

Optimum Estimation of the Thickness of Erosion by Porosity Data：Program and A Case

HE Jiang-qi1 2 , WANG Yi-fang2

2002, 8(2):  207-214. 

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A new approach is briefly introduced for the optimum estimation of the thickness of erosion using primary porosity data．There are two keys that should be considered in this method ：(1)the porosity data must be primary；(2)the porosity on the ground surface is not a fixed constant，but a variable changing with the sedimentation condition and other factors. In this paper we deal with these two aspects separately．For the former，we revise the porosity based on study of diagenesis．For the latter，optimum statistic principle is used. The method is applied to both the mudstone and sandstone from Mingshui Formatlon of Changling Depression in southern Songliao Basin. Both two estimations yield a similar result of about 500 m of erosion by using computer program．Considerations that should be taken into account in geological application are also discussed in this paper．

An Attempt on Quantitative Calculation of Lake Palaeoproductivity

LI shou-jun, ZHENG De-shun, GENG Fu-lan

2002, 8(2):  215-219. 

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palaeoproductivitity is defined as the rate of energy absorbed by organism during the course of circulation of energy，that is，the quantity of organic matter per unit time and per unit area．The method of calculating palasoproductlvity in the ocean was studied by Müiller and Suess(1979)and the formula：R=C x×ρs×(1-φ)／(0．0030×s0.30)was obtained．This formulais deduced on the basis of surface sediments from Pacific Ocean，Atlantic Ocean, and Baltic Sea regions， and the majority of its sedimentary organic matter is of marine origin. Therefore，this for mula can only be used for sea regions where the nonmarine organic matters are basically absent．In our country most Mesozoic and Cenozoic basins containing oi1 and gas are nonmarine lakas．The organism transported to the lakes from the land occupies a large proportion．It has obvious difference from the organism deposited in ocean. Consequently，the relation(formula)between palaeoproductivity and organic carbon in the nonmarine 1akes should be rededuced．Based on the method of calculating palaeoproductivity in the ocean and using related sedimentologica l and biological data of modern nonmarine downfaulted basins in Yunnan Province，we obtained a formula for calculating palaeoproductivity using the method of organic carbon in the lake：R =C × ρs×(1-φ )／(0.00421 × S0.0826) Furthermore，we compared the palaeoproductivity values calculated by this formula with those calculated by the ocean formula for the Third Member of the Shahejie Formation of the Jiyang Depression．Shadong Province The results show that the productivity of the lakes is much higher than that of the ocean．This new formula is of significance in quantitative calculation of pa1aeoproductivity for the Cenozoic lakes，such as the Bohai Bay Basin which is a dovnafaulted basin．

On A New Marine Reptile Yangliujing Formation from Middle Triassic of Guizhou，China

LIU Guan-bang1, YIN Gong-zheng2, WANG Xue-hua2, WANG Shang-yan2, HUANG Li-zhong3

2002, 8(2):  220-226. 

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The specimen described in this paper was collected by Li Gui-yuan from the grey-black middle-thin layered limestone beds of the Middle Triassic Yangliujing Formation at a quarry of Luyin Cement Plant some 150m west of Luyin village in Dingxiao Ecomomie Development Zone，Guizhou. It is a new genus and species of the marine reptile represented by the hind limbs，partial vertebrae and scattered ribs which are briefly described as follows．Order Ichthyosauria(?) Family Dingxisosauridac ram.nov．Genus Dingxiaosaurus gen.nov．Type species Dingxiaosaurus luyinesis sp.nov．Diagnosis Marine reptiles of moderate size Hind limbs longer，larger and paddle-shaped. Femur not expanded distally. Tibia and fibula elongated．Tarsals large，polygonally blocky，and arranged closdy in two rows，three ones in the proximal，and four in the distal row of the tarsus．Digits five．Metatarsals elongated．Phalanges of I —V digits long and number obviously increased．Vertebrae longer and amphicoelous. Etymology Dingxiao and Luyin from the Chinese Phonetic Alphabet of the fossil-producing district and village．Dingxiaosaurus luyinensis sp.nov.(P1．I，fig．1)Holotype Hind limbs，partial vertebrae and scattered ribs of a marine reptile Diagnosis as for the genus(only species)．Locality and horizon Luyin village in Dingxiao Eeomomic Development Zone，Guizhou；Middle Triassic Yangliujing Formation(Ladinian)Description (omitted here)．Remarks The new genus DingMaosaurus，although based on the hind limbs．partial vertebrae and scattered ribs, is highly distinctive．The morphology and the structure of the limb bones show a blend of the characters of the primitive ichthyosaurs and the earliest plesiosaurs．The elongated tibia and fibula are very similar to those of the primitive iehthyosaurs，and the phalanges somewhat similar in shape and number to those of the earliest plesiosaurs．However．the new genus is different form all the known ichthyosaurid and piesiosaurid genera and species，and represents an isolated form of the early marine reptiles．It cannot be placed in any the known family of the ichthyosaurids and the pleslosaurids．Therefore we propose for it a new family Dingxiacsauridae．From the characters of the femur，tibia，fibula，and tarsals，it seems that Dingxiaosaurus shows closer affinity with the primitive ichthysaurs and remoter affinity with the earliest plesiosaurs.

Comprehensive Assessment of Environmental Hydrogeology in Xiluodu Hydropower Station

ZHOU Zhi-fang, WANG Jin-guo

2002, 8(2):  227-235. 

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The planned Xiluodu Hydropower Plant is the second largest hydropower plant in China，next to the Three Gorges Power Station. It is situated on the upper reaches of the Jinshajiang River．There exist many problems related to groundwater around the dam district：(1)Groundwater level is buried deeply and its hydraulic gradient is gentle．(2)Temperature of groundwater is locally abnormal and the groundwater head is locally confined (3)Modern karst is developed in the limestone of both banks and in valley (4)Recharge Source comprises precipitation，surface water，groundwater of other aquifers and water bodies of different altitudes and times ．The fluctuation of groundwater levels of various holes on banks and in valley keeps synchonously with that of the Jinshajiang River．Furthermore．the synchronism of 1evel rising is better than that of falling. In this paper，the groundwater flow system around the dam district is analyzed according to geologic structure and lithologic features. The environmental hydrogeological characteristics are studied in many aspects，such as temperature field，hydroehemical field，isotopes and dynamic conditions,etc. The major conclusions are as follows：The hydrogeological conditions are fine．The penetrability of rock mass is relatively weak. There is no potential leakage．The deep karst is developed weakly．There exist relatively water-proofing strata at some depth of dam foundation and valley sides. Despite the groundwater level buried deeply and its gradient is gentle，it is estimated that the backwater level corresponding to reservoir level will be formed after reservoir ponding due to the special basin structure of the dam district． Finally，it is pointed out that the hydrogeological engineering problems may exist which include seepage deformation within inter-layer and inner-layer faulted planes and the effect of these planes under the action of uplift pressure to the safety and stability of hydraulic constructions after reservoir ponding. Especially，in the rock mass of dam abutments，the hydraulic gradient is large because the seepage tracking is short. The effect of seepage force will be strong after reservoir filling. So the effect scope of uplift pressure on the surrounding rocks will be large so that the overall load should not be underestimated. In order to assure the safety and stability of hydraulic constructions，seepage control and decompression of rock mass are of special importance.

Improvement Effects of DJM Piles on Marine Soft Soil Ground

SHAO Li, LIU Song-yu, FANG Lei

2002, 8(2):  236-240. 

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In Lianyungang area, there is much marine soft soil which is of low bearing,high compression and high natural water content．Several methods are used to test the improvement effect of DlM (Dry Jet Mixing)for marine soft soil ground．These methods include the standard penetration test(SPT)，the unconfined compression test of boring samples，and the static loading test of composite ground．The relationship between SPT blow counts and the strength of unconfined compression is established ．The results show that SPT is good method for testing quality of DJM piles．