Table of Content

20 December 2005, Volume 11 Issue 4

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Article

The Contributions of Professor Guo Lingzhi, Academician of Sciences, China

MA Rui-shi, LU Hua-fu

2005, 11(4):  469-472. 

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Professor Guo was born in 1915 and is 90 years old now bearing his brilliant scientific life. He made great contributions to the earth sceinces of China including identification of the existence of the Proterozoic Jiangnan island arc and trench system, establishment of the plate tectonic framework of southeastern China expressed in the continental crust growth through continental collision and terrane accretion from Proterozoic through Early Paleozoic, Late Paleozoic to Mesozoic from northwest to southeast, proposition of eight criteria to identify the paleo-trench-arcback arc basin system on the continent, and demonstration of marginal sea and their evolution model from origin to collaps and extinction. Professor Guo approached fruitful results in scienfific research and teaching work, being a paragon of virtue and learning. He has noble character and high prestige, exhibiting the characteristic style of great scholar master.

Characteristics of Helium Isotopes in the Ordos Basin

DAI din-xing1 2, LI dian2, HOU Lu3

2005, 11(4):  473-478. 

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The Ordos Basin is a basin, which contains the largest amount of gas fields with proved geological reserves over 100 b m^3 in China. It is also the most stable craton petroliferous basin in China. According to the helium isotope analyses for 46 gas samples from the basin, the following results have been obtained： ^3He/^4He values, range from 3.1×10^8～1.2×10^-7, averaging 4.36×10^-8 ; R/Ra values, range from 0. 022 to 0. 085. These data show the character of crust-derived helium. The values of ^3He/^4He and R/Ra show no relation with the formation types, occurrence, autogenetic characteristics and catageneic changes of natural gases in the basin. The values of R/Ra quantitatively demonstrate the extremely stable structure of Ordos Basin.

Superimposed-Composite Characteristics of Micro-Craton Basins and Its Bearing Petroleum Systems, Central-Western China

JIA Cheng-zao1, WEI Guo-qi2, LI Ben-liang2

2005, 11(4):  479-492. 

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There are rich hydrocarbon resources in the basins located in western and central China. They are many micro-craton basins surrounded by large orogenic belts of Hercynian-Indosinian and Himalayan, which are characteriied by small structurally stable in the kernel craton and structurally active in margin foreland thrust belts. Compared with large petroliferous basins in North America and Europe continent etc. the petroliferous basins in China are small in scale and strncturlly more active. These basins commonly underwent four tectonic evolution stages：①Micro-craton plates floating in the ocean separately during Cambrian to Silurian; ②Terrane accreting along south flank of the Eurasian plate during Devonian to Permian; ③Tethys ocean closing and continental depression （or rift ） basins during Triassic to Paleogene; ④Rejuvenation foreland basins since Neogene. Accordingly there formed and superposed four structural sequences, the lower Paleozoic marine craton basins, the upper Paleozoic paralic craton basins, intra-continental depression （or rift ） basins and rejuvenation foreland basins. Tectonic movements of Paleozoic craton basins are relatively stable; while multiphase unconformable contacts and large palaeohighs developed during Paleozoic ; and forland basins compositing and superimposing on their margin and formed structures distributing in rows and zones during Mesozoic-Cenozoic. The superimposedcomposite petroleum system, determined by the nature of composition-superimposition of petroliferous basins in China, comprises multiple petroleum systems and several source layers, experienced multiple stages of hydrocarbon generation and multiple periods of hydrocarbon accumulation, consequently there are multi-layers bearing oil and gas. There are two major fields in petroleum exploration in central and western China basins： the Paleozoic microcraton sequence and the Mesozoic-Cenozoic foreland sequence. The factors controlling the hydrocarbon accumulation and enrichment include palaeohighs and slopes in the lower Paleozoic craton sequence, large-area lithological reservoirs in the upper Paleozoic craton sequence and large scale thrust belts in the Mesozoic-Cenozoic foreland basins.

The Late Cenozoic Basin/Mountain Coupling Mechanics of the Tarim Basin and the Tianshan Mountains

LU Hua-fu, WANG Sheng-li, JIA Dong, WANG Liang-shu, LIU Shao-wen

2005, 11(4):  493-503. 

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Based on the data of tectonic geometry and kinematics, oil and gas exploration seismic profiles, seismic sounding reflection, seismic tomography and geothermy, the authors bring forward a conception model of coupling mechanics of the Tarim block＇s and the Junggar block＇s lithosphere mantles collision and delamination under the Tianshan Mountains. Due to India-Asian collision, the north frontier lithosphere mantle of the Tibet Plateau collided with the Tarim lithosphere mantle in V-shape, which pushes the high strength Tarim lithosphere to move northward and to subduct horizontally under the Tianshan Mountains. The subducted lithosphere mantle of the Tarim block collided with the southward subducted lithosphere mantle of the Junggar block and then delaminated in the back peel style under the Tianshan Mountains. While the Tarim block lithosphere mantle was subducting, the Kuqa rejuvenation foreland basin and rejuvenation Tianshan Mountains were formed. The thrust slip in the Kuqa rejuvenation foreland thrust belt accounts for 20% of the Tarim block subduction. This basin and mountain coupling mechanics model may reasonably interpret the features of the basin structures, basin depression, mountain uplift, lithosphere structure and geothermy in this region.

Geological Process of Early to Middle Permian Magmatism in Tarim Basin and Its Geodynamic Significance

YANG Shu-feng1, CHEN Han-lin1, JI Deng-wu1, LI Zhi-long1, DONG Chuan-wan1, JIA Cheng-zao2, WEI Guo-qi2

2005, 11(4):  504-511. 

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Through systematical research of early to middle Permian basic igneous rocks the focus on the trace element and REE geochemistry, the deposition characteristics, the source of basic igneous rocks and the deep geological process of early to middle Permian Magmatism are put forward. The basic magma originated from homogeneous enriched mantle with relatively intense differentiation. Moving up of magma resulted in fast uplift of upper lithosphere, regional uplift and recession toward west. The lithosphere of Tarim basin was broken up and large scale magmatism occurred while the uplift force exceeded the tortuosity of lithosphere. The Early to Middle Permian magmatism was related to Paleo-Tethys evolution The magmatism in Tarim basin with the Permian magmatism happened in Tarim basin, Turpan-Hami basin and adjacent area, Hongliuhe area, Beishan area and western margin of Yangzhi plate Permian, comprised an intense nmgnmtism belt in the northern margin of PaleoTethys.

Earthquake Dynamics and Plate Tectonics： Seismic Hazard Assessment

Chen Sheng-zao

2005, 11(4):  512-520. 

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The main topic in earthquake dynamics is to deal with rupture processes, faulting mechanism, source radiation, and propagation of the radiated seismic waves and ground motions, on which seismic hazard assessment is based. Critical theories of earthquake mechanics, source radiation and energy release are intensively studied in this paper for a completeness of systematic investigation on the topic. Using the state - of- the - art methods for seismic hazard analysis, with which the seismological, geological and geodetic inputs are combined into logic trees, samples of the ground - motion evaluation are applied to the typical tectonic sources of earthquakes including the crustal seismogenic zones, subduction interfaces and intraslabs. Various ground motion attenuation models with respect to faulting mechanism were examined and demonstrated through both the probabilistic and deterministic approaches. Uncertainties exist in either aleatory variability or epistemic uncertainty, but a weighted average of various alternatives in probabilistic seismic hazard analysis （PSHA） and the combination in methodology of PSHA and DSHA （deterministic seismic hazard analysis） should better prevent it from producing an extremely biased output of hazard estimates.

Discovery, Nomenclature of the Centimeter Scale Grinding Gravels and the Nanometer Scale Grinding Grains in Fault Shearing Zones and the Significance for Oil-Gas Geology

SUN Yan1, LU Xian-cai1, LIU De-liang2, SHU Liang-shu1, ZHU Wen-bin1, GUO Ji-chun1

2005, 11(4):  521-526. 

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In the early 1970s, the cm-scale grinding gravels were discovered in reverse faults in Jiangning, Jiangsu Province. In general, there grinding gravels can be found in ductile-brittle fault shearing zones. In the end of the 1980s, based on the observation of the deep bore cores from of California, USA using scanning electron microscope the spherical particulate texture with the ultra-size of nm scale was discovered from the slipping lamellae in the granitic mylonite in Late Mesozoic period. The spherical particulates （usually 2-5 nm in diameter） show a close concentration and distinct orientation. It may be the product of the dynamic processes involving tumbling, grinding and shearing functions. Consequently the spherical particulates with ultra-size are called ＇grinding grain： Afterwards, a very similar phenomenon （ mostly in um size） was found again from the slipping lamellae in the Carboniferous-Permian mudstone in the deep bore cores from North Shanxi and Yellow Sea. In recent year, the nm scale grinding grain structures were also discovered in Tanlu fault and Middle Tectonic Line gigantic fault zones of Japan as well as various shearing slipping structures in different strata from Cambrian to Triassic system. In the mudstone slipping beds containing grinding grains may possess a sealing effect through systematic analyses of the samples, and it is fully proved in the North Shanxi oil-gas field. The grinding grain textures may contain more detailed geological information in particular the micro-dynamic aspect （including the dynamo-thermal metamorphism, fluid transferring, particulate autorotation and geological catalysis） owing to increasing research.

The Characters of Magmatism in the Western Section of the Jiangnan Orogenic Belt

ZHOU Jin-Cheng, WANG Xiao-Lei, QIU Jian-Sheng

2005, 11(4):  527-533. 

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The highly depleted basalts-diabases with N-MORB features have been found in the Mesoproterozoic Lenjiaxi strata from Nanqiao, Liuyang, Hunan province. K20 in the basahs are very low. The basahs and diabases show highly depleted geochemical features. Abundances of their incompatible HFSE, such as Nb, Zr, Hf, Ti , and REE are lower than （ some are close to） those of N-MORB. Their εNd（ 1271 Ma） varies from 6.86 to 8.98. These basalts distributed along an ancient subducting zone provide a new evidence for ancient Jiuling island arc. The Neoproterozoic basalts and diabases from Qianyang and Guzhang, western Hunan, are classified as alkaline basahs. Their geochemical features of trace elements are similar to those of OIB. Their scale of distribution in the field should be further examined. The mafic-ultramafic rocks in Danzhou group from northern Guangxi have lower TiO2, Ta and Nb, and lower Hf/Th, Ti / Y and Ti / Zr ratios and higher La/Ta and Th / Yb ratios, Showing arc affinities. They did not show any CFB and OIB signatures. In tectonic discrimination diagrams, they are plotted in the field of “volcanic arc basahs”. Some samples are within “back-arc basalts” field. Both high-Mg lavas with high temperature features and giant radiating dyke swarms have never been found so far in the area. The exposed area of these mafic rocks in the field is very small （ about 100 km^2 ） without the characters of the plume-derived mafic magmas. The features of Neoproterozoic peraluminous S-type granites from northeastern Hunan and northern Guangxi provinces are similar to those of the Jiuling granites in Jinagxi province, and the Xiuning, Xucun and Shexian granites in Anhui province. They are distributed along the Jiangnan orogenic belt with zonal features. The generation of the S-type granites are related with the continent-continent collisional event between the Yangtze and Cathaysia blocks. Most S-type granites occur in the orogenic belts with various ages in the world. In the mafic large igneous province formed by plume magmatism, the granites associated with continental flood basalts are non-orogenic, intraplate and A-type granites rather than S-type. S-type granites should not be considered as the evidence of plume magmatism. It is suggested that the confirmation of “Jiangnan orogenic belt” has been supported by full petrological evidences.

Analysis of Northern Jiangsu Prototype Basin from Late Cretaceous to Neogene

SHU Liang-shu, WANG Bo, WANG Liang-shu, HE Guang-yu

2005, 11(4):  534-543. 

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The Northern Jiangsu basin is an oil-gas bearing half graben-like basin of Middle Caenozoic era in Eastern China, and is mainly made up of three structural units： the Dongtai sag, the Yancheng - Funing sag and the Jianhu upheaval. The heaves in sags and depressions in upheavals are the minor units of the basin. Based on the prototype analysis method, this paper deals with erosion source area, subsidence history, evolution of sedimentation center, borderline structure and sedimentation intervals of the northern Jiangsu basin, and also estimates its subsidence quantity and denudation quantity. The paper suggests that basin＇s formation and evolution process can be divided into four stages： compressed foreland basin, back arc tensile rift basin, massive tensile fault basin and heatsinking sag basin. Its rich sediments came from following five erosion source areas： the Binhai upheaval on the northeast of the basin, the Shandong- Jiangsu upheaval on the northwest of the basin, the Dabie mountain on the west of the basin, the Zhangbaling mountains on the southwest of the basin, and the Paleozoic sedimentary area of Yangzhou - Nanjing and Zhenjiang on the south of the basin ; There were four uplifting and denudation events （ the Yizheng event, the Wubao event, the Zhenwu event and the Sanduo event） during the basin evolution, which played a very important role for the formation of the asymmetric dustpan-shaped basin. The resumed subsidence history of the basin commendably reflects the evolution history of the basin from Late Cretaceous to Neogene.

From Seismic Anisotropy to Anisotropic Seismology： A Review

WANG Liang-Shu, CHEN Yun-Ping, MI Ning, LIU Shao-Wen, LI Cheng, XU Ming-Jie, LI Hua

2005, 11(4):  544-551. 

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History and recent important advances about seismic anisotropy are briefly reviewed. The seismic anisotropy in different layers especially the crust and upper mantle of the Earth and its＇ application in geodynamics and earthquake monitoring are emphasized. Seismic anisotropy provides a new means in the study of dynamic Earth process and comes into being an important branch of seismology： anisotropic seismology.

Particularity and Diversity of the Foreland Basins in the Central and Western China and the Natural Gas Exploration in the Foreland Basins

WEI Guo-qi1, JIA Cheng-zao2, LI Ben-liang1

2005, 11(4):  552-557. 

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This paper systematically summarizes the evolution features and distinctiveness of the foreland basins in the central and western China through the all-around analysis of the structural characters, tectonic settings, and geophysical data of the typical foreland basins. It is pointed out that the aggregation and collision of the numerous diverse micro-cratons is the dynamic genesis of the foreland basin group in the central and western China, which also caused the diversity and particularity of these foreland basins. These foreland basins comprise the HercynianIndosinian foreland basins and the Himalayan rejuvenated foreland basins, which can also be subdivided into three types： the Hercynian-Indosinian peripheral foreland basins, the Hercynian-Indosinian back-arc foreland basins and the Himalayan rejuvenated foreland basins. According to the basin construction and evolution, these foreland basins can be grouped into four assemblages： the superimposed, the reconstructed, the presenile and the regenerated. In the end, this paper presents five dominant effects to the migration and congregation of oil and gas in the foreland basins of different types.

Mesozoic-Cenozoic Relationships between Tianshan Mountain and Peripheral Basins： Evidences from Sedimentology and Exhumation of Jurassic in Houxia Area, Urumchi

GUO Zhao-jie, WU Chao-dong, ZHANG Zhi-chen, WANG Mei-na, FANG Shi-hu

2005, 11(4):  558-567. 

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The Houxia depression is now an intermountain basin near Urumchi, Xinjiang. In the southern Houxia section were developed the alluvial fans in Badaowan Formation （J1b） of the earlest Jurassic, while braided river was developed in the northern section. Therefore, the Houxia area was close to the south edge of the basin in the beginning of Jurassic. The ancient current directions of early to middle Jurassic in the south and north sides of Houxia depression were all northward. We propose that Houxia and southern Junggar were joined together and constituted a unifeied basin in Jurassic, while the border between basin and mountain was close to Houxia area and differed largely from present time. There exist a few intermountain depressions within Tianshan Mountain and they all have Jurassic sediments with coal-containing strata of lower to middle Jurassic. These indicate that their sedimentary environment was very similar and swamps were developed. Based on these facts, we may conclude that there were no high mountains in Tianshan area in Jurassic and it just was hilly. To constrain the sedimentation and exhumation history of Jurassic in Houxia area, we conducted integrated research on apatite fission track dating and vitrinite reflectance （Ro） of coals. The results show that the middle Jurassic coals in Houxia area were buried at least 3 km in depth, and the apatite fission track dating records a rapid cooling event beginning at about 10 Ma, which is interpreted as exhumation of rocks because of the uplift of the mountains and foreland thrusting northward in Cenozoic caused by the India-Asia collision.

Geometry and Kinematics of Complex Folds, Illustrated with Examples from Quilitake Anticline of Kuqa and Bapanshuimo Anticline of Keping, Southern Tianshan

WANG Xin

2005, 11(4):  568-576. 

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The foreland fold-and-thrust belts develop much more complex imbricate structures that continue to offer substantial and rich challenges. Quilitake anticline in Kuqa thrust belt and Bapanshuime anticline in Keping thrust belt along the piedmonts of the southern Tianshan are such complex imbricate folds. In order to determine the geometry and kinematics of these two folds, we present the models of the folds that are constructed using dipping and strike data of surface strata, 2-D seismic reflection profiles, and well drilling ＆ logging data. The concepts and methods of fault-related folding are used in our research which are helpful to understand the imbricate thrusts and folds in quantitative details.

Discussion on Northward Extension of the Tanlu Fault Zone and Its Tectonic Regime Transformation

ZHANG Qing-long, WANG Lian-shu, XIE Guo-ai, DU Ju-ming, XU Shi-ying, HU Xu-zhi

2005, 11(4):  577-584. 

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The northern part of Tanlu fault zone in NE China can be mainly subdivided into three faults of NE-NNE strike. They are Shenyang - Changchun - Harbin fault, Yilan - Yitong fault and Dunhua - Mishan fault from west to east. The faults have different tectonic background and dynamics in different periods. We find that these faults have five periods in tectonic regime transformation. 1 ） Extension mainly during Early-Middle Jurassic period, resuiting in a series of down-faulted basins or sunken basins, accompanied with intermediate-acidic magmatic intrusions and eruptions, forming special volcano-lake sedimentation basins; 2） Compression in NW-SE direction in Early Cretaceous period, resulting in NE trending thrusting nappe of Middle-Late Jurassic strata in basins ; 3 ） Leftlateral shear in Late Cretaceous period, leading to folding of Jurassic and Early Cretaceous sediments, which are unconformable with upper layers; 4 ） Extension in NW-SE direction in Eogene Period. Japan Sea pulled open in Eogene and completed as the patterns as nowadays in Neocene period; 5） Compression in NW-SE direction in Neocene Period, making Neocene sediments folding slightly.

Features of Gravitational and Magnetic Fields in the Tarim Basin and Basement Structure Analysis

XU Ming-jie, WANG Liang-shu, ZHONG Kai, HU De-zhao, LI Hua, HU Xu-zhi

2005, 11(4):  585-592. 

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In terms of gravitational and magnetic anomaly data, various information after the processing （ upward continuation and horizontal direction derivative, etc. ）, the features of gravitational and magnetic field in the Tarim Basin are analyzed. The basement depth and the Moho depth are also computed. The gravitational and magnetic anomalies vary changefully on the basin edge and gently inside the basin. The Moho upheaves at the basin center and dips toward the basin edge. The basement depressions appear at the foreland basin. The faults of edge are parallel to basin boundary and extend to large scale. It may be explained that the rigid lithosphere is flexed and the large faults are developed at the basin edge due to the remote effects from the India and Qinghai-Tibet collision. The energy is mainly released during the activity of faults, and the activity on basin edge is stronger than in the basin interior.

Fission-Track Dating Technique and Its Applications to the Problems of Tectonic Evolution

ZHU Wen-Bin1, WAN Jing-Lin2, SHU Liang-Shu1, SUN Yan1, ZHAO Zhong-Yan1

2005, 11(4):  593-600. 

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Fission-track analysis as a geological dating ades there has been a major expansion in application to tool was first proposed in the early 1960s. In the past decmore general geological problems. It reflects progress in understanding the temperature dependence of fission-track annealing and in interpreting the information contained in fission-track length distributions. The length distribution of projected tracks can be successfully applied to thermal analysis despite the fact that it is heavily biased against the real length distribution. A partial track annealing concept based on the projected length distribution is proposed, which provides detailed information on the low-temperature thermal histories of rocks, below - 120℃ for tracks in apatite and below - 350℃ for zircon. Fission-track dating technique has been applied to a variety of tectonic problems, including ： （ 1 ） to determine the uplifting time and rate of orogenic belt ; （2） to study the thermal history of orogenic belt ; （3） to date the rapid unroofing or cooling event,（4） to date the time of the basin inversion; （5） to unravel a long-term multi-event thermal record in basement rocks of the basin; and （6） to research the coupling process between basin and mountain.

Experimental Study on Wave Velocity of Rocks from Tarim Basin at High PT Conditions and Its Geological Implications

LI Hua, WANG Liang-shu, LI Cheng, LlU Shao-wen

2005, 11(4):  601-607. 

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The results of experimental measurements on elastic wave velocity （Vp） for rocks of different types from Tarim Basin at high temperatures and high pressures are presented here. The Vp of samples at ordinary temperature ranges from 6.007 km·s^-1 to 6.803km·s^-1, given the maximum pressure at 2.0 GPa, and the andesitic volcanoclastic rock has the largest Vp. At the temperature of 600℃, the Vp varies between 5. 871 km·s^-1 and 6.658 km·s^-1, and the largest Vp value is obtained also for andesite. Combined with the velocity structure derived from seismic converted wave in study area, here we propose that the crustal structure in the most areas of Tarim Basin is of three layers ： the upper crust consists mainly of granitic metamorphic rocks, the middle crust is mainly made of granitic diorite, and the lower crust is mainly composed of andesitic basalts.

Geometric Forward Modeling of Generalized “Fault-Bend Folding”

ZHANG Yi-kun, SUPPE John, JIA Dong, LU Hua-fu

2005, 11(4):  608-616. 

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We proposed in this paper a geometric method for the forward modeling of generalized fault-bend folding based on the kink folding theory and implemented the method with C ＋ ＋ , a widely used object-oriented computer language. The code has shown the ability to model very complicated fault-related folding structures, including multi-bend shear fault-bend folds, composite wedge structures and multi-detachment fold and thrust systems. By decomposing a sedimentary layer into kink-band and kink-wedge, we solved the difficulty in modeling multi-bend shear fault-bend folds of the curved shapes, while previous geometric methods only make the first order linear approximation of real folds with highly angular fold shapes. By decomposing fold and thrust systems into superposed detachment systems, it is possible to simulate extremely complex wedge structures and to do animation of the evolution of the structures. We applied this method to the Wheeler Ridge, California, an active wedge structure whose interpretation was constrained by well data according to Medwedeff （1992）. Our modeling successfully reproduced the main features of this wedge structure.

Study on Classification of Low-Permealility Sandstone Reservoirs Based on the Starting Pressure Gradient

WANG Yu-ming, PANG Yan-min, YANG Shu-feng, CHEN Han-lin

2005, 11(4):  617-621. 

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This paper studies the lithology, physical properties, oil-beating and seeping characteristics of lowpermeability reservoirs by using the core data from Daqing Xingshugang oilfield. Based on the starting pressure gradients measured from the cores with different permeabilities, there exists a good correlation between starting pressure gradients and permeabilities. The order of magnitude of the changing rate of different reservoir starting pressure gradients is different. Thus, a new classification method of low-permeability reservoirs is set up. Using this new classification method, the upper limit of low-permeability reservoirs is redefined and the low-permeability reservoirs are classified into three types.

The Structural Styles and Their Relation with Petroleum-Gas Resources of the Jiyang Depression, Shandong Province, China

CHEN Hai-yun1 2, YU Jian-guo2, SHU Liang-shu1, HOU Fang-ying2, WU Long-li2

2005, 11(4):  622-632. 

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According to synthetical analysis on geometry and drilling holes and seismic data in the Jiyang Depression, the authors obtained some new recognition on the structural styles of basin. Three basic styles of extensional-type, strike-slip-type and inversion-type were proposed in the paper. Of them, the extensional-type structural style is the most important one in the studied area and was describled in detail. From geometry and forming mechanism, five secondary styles of the extensional-type structural style, including tilted faulted-block, slide faulted-ramp, buried hill draping, gravitative antiform and diapir, were reported. There exists a close connection between the type of secondary structural style and the location of geological body in the depression： the tilted faulted-block style is developed mainly in the gentle slope zone of depression, the slide faulted-ramp style is mainly distributed in the steep zone, the diapir-type structure occurs in the depression zone, the buried hill draping style is developed in the uplifting areas around basin and the buried hill zone of depression, and the gravitical antiform was formed in the down-sliding side of main fault. Results suggest that with the thicken deposit of basin, gravitical working becomes more and more important in generation of structural styles. Under the strike-slip shearing of the Tan-Lu fault zone, a lot of en echelon and brush structures were formed in the eastern part of the Jiyang Depression. Owing to transformation of regional tectonic settings, a transformation of stress field from compression to extension took place in the studied area during the early Late Cretaceous, producing a series of negative inversion structures in the basins and the stress field became weaker and weaker from the east to the west. Thus, the strikeslip structural style is resulted from strong shearing of the Tan-Lu fault zone, and the inversion structural style is caused by transformation of regional tectonic settings.

Fault Analysis Based on ASTER Imaging Information： Introduced by an Application Test in Baiyin Area, Gansu Province

HUANG Sheng-hai, SHI Huo-sheng

2005, 11(4):  633-641. 

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ASTER sensor provides 14 bands of spectral information including visible and near infrared （VNIR）, short wave infrared （SWIR） and thermal infrared （TIR） . The highest spatial resolution is 15 meters which lies in VNIR bands. Besides, the stereo imaging of the same area can be obtained simultaneously by the nadir- and aft-looking of 03 N and 03 B bands respectively. Topographic information can then be derived from them by certain algorithm. All these characteristics make it very convenient in geological application. The fault system may cause differences in geology and morphology inside and outside the system. Accordingly, these differences may produce different spectral and textural characteristics in the image. In the reverse, the characteristics can be emphasized by enhancing the difference of intensity and texture by using certain image processing technology. Analysis then can be done on their difference, some tally with certain laws can be regarded as fault system, and its attribute may be concluded. An application of ASTER data in Baiyin area of Gansu province was introduced in this paper. The results show a high consistency with the field survey as shown in the local geology map.

Relationship between Meso-Cenozoic Tectonic Subsidence of the Jiyang Depression and Plate Convergence Rate

ZHANG Qie, JIA Dong, CHEN Zhu-xin, WANG Liang-shu, LU Jian-jun, CHEN Xiao-ming

2005, 11(4):  642-648. 

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We modelled the subsidence history of three sags （the Dongying, Zhanhua, and Huimin sags） in the Jiyang depression of Bohai Basin by using well data and seismic profiles. The subsidence curves of six wells demonstrate that the Meso-Cenozoic geological history of the Jiyang depression can be divided into six phases ： （ 1 ） Mesozoic characterized by low subsidence rate; （2） Kongdian Formation when the rift originated; （3） the fourth and third members of Shahejie Formation with the rapidest subsidence; （4） the second and first members of Shahejie Formation when the fault-depression continued; （5） Dongying Formation, the terminal fault-depressed phase; （6） Neogene which is occupied by post-rift thermal subsidence. The comparison between the tectonic subsidence rate and the convergence rate of Pacific plate relative to Eurasia indicates that the Meso-Cenozoic tectonic evolution of the Jiyang depression is mainly controlled by the plate convergence.

Characteristics of Magnetic Fabrics of Feixianguan Fault-Propagation Fold in the Front of Longmenshan Fold-Thrust Belt and Its Structural Significance

HU Qian-wei, JIA Dong, CHEN Zhu-xin, LUO Liang, JIA Qiu-peng

2005, 11(4):  649-655. 

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Along Feixiangnan fault-propagation fold cross-section in the southern Longmenshan front, 270 oriented specimens were drilled to conduct the analysis of magnetic minerals and anisotropy of magnetic susceptibility （AMS）. We find that hematite is the main magnetic carrier mineral according to isothermal remanent magnetization acquisition and demagnetization of three orthogonal isothermal remanent magnetization. The AMS results show two types of magnetic fabrics： intermediate magnetic fabric and tectonic magnetic fabric. Based on the kinematic model of fauh-propagation fold and distribution features of magnetic fabrics, we deduce the evolution of magnetic fabrics through the development of fault-propagation fold： primary sedimentary fabrics were transformed into intermediate fabrics by the pre-folding layer parallel shortening; during the propagation of fault, simple shear caused by limbs＇ rotation and lift affects the AMS at limbs, which make Pj rise locally within limbs, and structural fabric appears in strong deformation area.