Table of Content

20 February 2014, Volume 28 Issue 1

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palaeontology

Oncolites from Lower-Middle Cambrian Transition of the Western North China Platform：A Study of Their Ultra-fabrics and Biomineralizatio

ZHANG Wen-hao, SHI Xiao-ying, TANG Dong-jie, JIANG Gan-qing

2014, 28(1):  1-15. 

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The lowermost Middle Cambrian carbonate succession at western margin of the North China Platform is rich in oncolite. In order to explore biomineralization mechanisms and microbemineral interactions in ancient microbialite, microfabrics of the oncoids at micro-and nano-meter scales were investigated using microscopy and FESEM techniques. The study shows that abundant bacterial and organic relics exist in both nucleus and cortex of the oncoids. Microscopically, the nucleus is mainly of micrite, with few of fine bio-and terrigenous detritus, while the cortex consists of light/dark lamina couplets at sub-millimeter scale. The light lamina consists of mixed microspar and micrite, with filamentous cyanobacteria predominant, and the dark lamina is largely micritic, rich in heterotrophs and pyrite grains, suggesting that they may have resulted from different biomineralization mechanisms．We think that the formation of oncoid cortex in early Middle Cambrian basically coincides with those in present microbial mats, all resulting from carbonate precipitation induced by complex interactions between microbes and geochemistry, and from mineralization of grown mats as well. FESEM observation indicates that there exist abundant nanoglobules (40-200 nm in size) associated closely with extracellular polymeric substances (EPS), pointing a derivation from anaerobic degradation of EPS. Nanoglobules tend to coalesce into polyhedrons (0.2-5 μm in diameter)，which further aggregate into submicron-scaled micritic peloid encased with microsparitic rim. Bacterial filaments mainly occur in interstitials between polyhedrons or peloids, while EPS often constitute walls of alveolar structures, or exist in various forms at or near the edges of polyhedrons and peloids. The oriented assembly of microfabrics at various scales and regular association of bacteria and organic relics observed within oncoid interior are reminiscent of those recognized in present calcified microbial mats and those revealed in culture experiments, possibly implying a general situation for biomineralization of microbialites. We may, therefore, conclude that the formation of oncoid cortex in early Middle Cambrian may basically coincide with those in present microbial mats, all resulting from carbonate precipitation induced by complex interactions between various microbes and geochemistry as well as from mineralization of grown mats.

Petrology and Study of Ore Deposits

LA-ICP-MS U-Pb Geochronology, Petrogenesis and Its Geological Implications of Kungeyite Plutons in Southern Altay Orogenic Belt

ZHANG Ya-feng, LIN Xin-wang, WANG Xing,GUO Qi-ming, ZHAO Duanchang,Lu Jun-li

2014, 28(1):  16-28. 

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The Kungeyite plutons, outcropped in Qingeli River in Qinghe County of southern margin of Altay orogenic belt are mainly hornblende biotite tonalite, which were determined for LA-ICP-MS zircon U-Pb ages. The result shows that the zircon ²⁰⁶Pb/²³⁸U weighted average age is (403.4±7.4) Ma (MSWD=1.07), indicating the plutons were formed at Early Devonian. The SiO_² contents range from 52.39% to 71.89% and σ from 0.68 to 1.53, A/CNK from 0.76 to 1.06, indicating that the plutons are midK calcalkaline, metaluminousweakly peraluminous rocks. In addition, the plutons are enrichment in LILE (Cs, Rb, Th, U) and LREE, obvious negative anomaly in HFSE (Nb, Ta, Hf, Ti), HREE and Eu (δEu=0.56-0.86), thus resembling granitoid rocks formed in islandarc. Combined with the data of southern margin of Altay, the Kunge yite plutons were generated by partial melting of the lower crust underplayed by mafic magma of the mantle in a continental arc setting of active continental margin, and occurred magma mixing and differentiation.

Fluid Inclusions and S, Pb, C Isotope Geochemistry of Pb-Zn Deposits Hosted by Lower Cambrian  in Western Hunan-Eastern Guizhou Area

CAI Ying-xiong, YANG Hong-mei, DUAN Rui-chun, LU Shan-song, ZHANG Li-guo

2014, 28(1):  29-41. 

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The western Hunan-eastern Guizhou area is an important Pb-Zn polymetallic ore district, some of which hosted in the algal limestone of the Lower Cambrian Qingxudong Formation. In this study, fluid inclusions and S, Pb, C isotope compositions were studied for four typical Pb-Zn deposits (Limei, Shizishan, Xiunao and Pukouchang) hosted in the Qingxudong Formation. The results show the ore-forming fluid with low temperature and medium to high salinity. The δ³⁴S values of sulfides are high. The δ¹³C and δ¹⁸O_V-SMOW values of wall-rock and calcite show the same characteristic with the normal marine carbonate. The Pb isotope of the wall-rocks and ore have a little variation scope, showing the linear distribution in the ²⁰⁷Pb/²⁰⁴Pb -²⁰⁶Pb/²⁰⁴Pb diagram. Our results indicated that ore-forming materials of the Pb-Zn deposits in the western Hunan-eastern Guizhou area mostly derived from the carbonate wall-rocks. Meanwhile, migrating fluid added Pb, Zn materials to the deposits as well. Pb, Zn and associated minerals were precipitated due to the changes of the physical and chemical conditions, resulted from mixing of two sources, indicating that the genesis type of our studied deposits is the Mississippi Valleytype (MVT) lead-zinc deposit

Fluid Inclusion Characteristics of Alunite in Zijinshan Gold-copper Deposit Fujian Province

XIN Xiu, WANG Cui-zhi

2014, 28(1):  42-50. 

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Zijinshan Au-Cu deposit of Fujian Province which located in the middle part of Zijinshan ore field is controlled by volcanic mechanism. Its characteristics of mineralization are well-developed the crypto-explosion breccia vein, and obvious alteration zoning with controls the corresponding mineralization strictly. With the crypto-explosion breccia dike as the center, from center to outside, top to bottom, there are the silicified zone, the alunite alteration zone, the dickite alteration zone and the phyllic alteration zone. The silicified zone controls gold ore body in the upper, the alunite alteration zone controls high sulfidation type copper ore body in the lower. Four occurrence status types of the alunite are classified, which are the alterated-rock type, the intergrowthwith-Cu-sulphide type, the alunite-vein type and the powder type. The results of microthermometry of fluid inclusion in alunite show that (1) Most of inclusions have two phases (liquid and vapor), which belong to NaCl-H₂O system; (2) The ore-forming fluid is of the density ranges from 0.5 to 1.0 g/cm³, the homogenization temperature concentrated in 200-360 ℃, and the salinity less than 20%，which belongs to a fluid system with medium-low temperature and medium-low salinity; (3)The values of homogenization temperature and salinity of the fluid inclusions of alunite have a decreasing trend from the alteratedrock type, the intergrowth-with-Cu-sulphide type, the alunite-vein type to the powder type;(4) The range of ore-forming pressure is concentrated in 40×10⁵-160×10⁵Pa, corresponding to the depth range from 500 to 1,600 m; (5)The mineralizing fluid is mainly from magmatic water and later mixed with atmospheric precipitation. Boiling and immiscibility occurred during the ore-forming processes.

Geology and C, O, S and Pb Stable Isotope Geochemistry of Lamasayi Cu Deposit in Western Tianshan, Xinjiang, China

DUAN Shi-gang, XUE Chun-ji, SHI Hai-gang, LI Ye, JIA Zhi-ye

2014, 28(1):  51-60. 

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The Lamasayi copper deposit is a representative copper deposit in the Sailimu massif in Western Tianshan, Xinjiang, China. However, the genesis of this ore deposit is controversial. This study tries to discuss the problem through tracing the origin of ore forming material using stable isotopes of C, O, S and Pb and investigating the geological characteristics of the Lamasayi copper deposit. The δ¹³C values of gangue calcite vary between -1.04‰ and -0.87‰ which are  lower than those of wall-rock limestone (δ¹³C = 3.51‰-5.47‰); the δ¹⁸O values of gangue calcite are from 9.33‰ to 9.61‰ and are quite lower than those of normal marine carbonate (δ¹⁸O =20‰-26‰). The C and O isotopic compositions reflect that the ore-forming fluid may be a mixture of magmatic water and ground water. The δ³⁴S values of sulfides mainly vary from 3.75‰ to 8.64‰ which is close to the sulfur isotope composition of the Hercynian porphyries (for example, the δ³⁴S values of sulfides from the Dabate porphyry copper-molybdenum deposit are from 4.9‰ to 7.9‰) and which reflects that the sulfur may be originated mainly from porphyry. The Pb isotope compositions of chalcopyrite are from 18.264 to 19.544 for  ²⁰⁶Pb/²⁰⁴Pb,from 15.575 to 15.656 for ²⁰⁷Pb/²⁰⁴Pb,and from 38.103to 38.705 for ²⁰⁸Pb/²⁰⁴Pb, respectively, which shows characteristic of two-stage abnormal lead and being rich in radiogenic lead, similar to the Pb isotope composition of the Hercynian porphyries (for example, the Dabate rhyolitic porphyry) and which also indicates that the ore-forming metal may be derived from the porphyry. In summary, the Lamasayi copper deposit may be skarn type deposit related to porphyry.

Genesis of Skarn from Dunde Iron Deposit in Western Tianshan,Xinjiang: Mineralogical and REE Constraints

GE Song-sheng, DU Yang-song, WANG Shu-xing, LI Da-peng, PANG Zhen-shan

2014, 28(1):  61-72. 

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The Dunde iron deposit, discovered in recent years, is one of the large-scale iron deposits in the Awulale ore belt in Xinjiang. The ore body is hosted in the metamorphosed volcaniclastic-sedimentary sequence of Dahalajunshan Formation of Lower Carboniferous, and is obviously controlled by fracture and closely associated with skarn. Detailed study on main skarn minerals such as garnet, diopside and magnetite by means of electron microprobe analysis and microscopic observation show that the skarn from the Dunde iron deposit can be divided into two types, i.e.volcanic metamorphic skarn and hydrothermal metasomatic skarn. Volcanic metamorphic skarn is composed of garnet (mainly grossularite) and augite(mainly diopside) and was formed in a reductive environment. Hydrothermal metasomatic skarn is composed of garnet (mainly andradite) and augite (mainly diopside), and was formed in a oxidizing environment. Volcanic metamorphic stage magnetite contains high Al₂O₃, TiO₂ and low MgO, belonging to magmatic origin type. Hydrothermal metasomatic stage magnetite contains high Al₂O₃, MnO, low MgO, TiO₂, belonging to hydrothermal metasomatic type. The skarn has similar total REE content to that of the andesitic tuff in the stratum, and both show similar patterns. The above characteristics indicate that the skarn in the Dunde iron deposit might be resulted from thermal metamorphim and hydrothermal metasomatism. The iron ores and skarn spatially coexist and have experienced similar development and evolution.

Mineral Composition of Bianjiadayuan Pb-Zn-Ag Polymetallic Deposit in Inner Mongolia and Its Origin Significance

WANG Xi-long, LIU Jia-jun, ZHAI De-gao, YANG Yong-qiang, WANG Jian-ping

2014, 28(1):  73-86. 

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Located in the southern Daxinganling metallogenic belt，Bianjiadayuan Pb-Zn-Ag deposit is a new  discovery in recent years of higher ore grade lead-zinc-silver polymetallic deposit. Detailed microscopic identification and electron analysis show that metalliferous minerals of this deposit mainly consist of galena，sphalerite，pyrite，chalcopyrite，pyrrhotite，arsenopyrite and stannine. Silver minerals mainly consist of tetrahedrite，freibergite and pyrrhotite. In addition，we also found a large number of falkmanites in the mine，which are intimately accompanied by galena，chalcopyrite and tetrahedrite. Falkmanite crystals show as needle，pillar，bunchiness and anhedral grain forms，and their grain sizes commonly vary from 5 to 150 μm.Electron microprobe analysis also shows that its corresponding formula is(Pb_4.77Cu_0.05Fe_0.04Zn_0.06)_4.92Sb_3.91S_11.00，and its simplified formula isPb₅Sb₄S₁₁.Falkmanite is generally the product of the late mineralization with a low tempreture. The formation of falkmanite may be favored by a low temperature，increasing f_S2 and reduced fluid conditions in the ore-forming process.

Geological and Geochemical Characteristics of Qibaoshan Ca-skarn and  Mg-skarn Intergrowth-type Polymetallic Deposit in Hunan Province

ZHENG Luo, GU Xue-xiang, CAO Hua-wen, LI Qing

2014, 28(1):  87-97. 

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Qibaoshan polymetallic deposit is a rare skarn intergrowthtype deposit that the Ca-skarn and Mg-skarn types occur together in the same deposit but different locations. The polymetallic deposit is located in the contact zone between Indosinian-Early Yanshanian porphyritic granite and carbonate beds of the mid-upper series of Carboniferous. Mineralization of the deposit can be divided into two periods. The early period is characterized by the formation of Ca-Mg skarn and magnetite, and  the late period is characterized by multi-polymetallic sulfide mineralization. The ore composition of the deposit is complicated. Besides Cu, Pb, Zn, elements such as Ga, Ge, In, Cd, Au, Ag, Te, Fe also can be utilized. The results of isotopic geochemical analysis show that the porphyritic granite is the product of assimilation and hybridization of mantle-origin magma and upper crust material. Ore-forming fluid is mainly magmatic water while ore-forming material mainly comes from magma. Metal particles transport in the magmatic water in the form of chlorine complexes, and precipitate due to chemical reaction after the formation of skarn. Geologic and geochemical evidences suggest that porphyritic granite is the parent rock of mineralization. The chemical property of wall rock determines the type of skarnization. The Qibaoshan polymetallic deposit is not only special in genesis, but also is of  great economic industrial value, and it should be researched further.

Tectonics

Genesis of Piedmont Terraces and Its Neotectonic Movement Significance in Langshan Mountain Area, Inner Mongolia

HE Ze-xin, ZHANG Xu-jiao, JIA Li-yun, WU Fa-dong, ZHOU Yi-qun, BAO Shu-yan

2014, 28(1):  98-108. 

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Langshan Mountain is located in the western segment of Yinshan orogenic belt and the northwestern margin of the Hetao rift zone in Inner Mongolia. Piedmont faults and tectonic uplifts in this region developed widely since the Late Cenozoic. The research on the tectonic uplift process of Langshan Mountain since the Late Pleistocene has significance in having a good knowledge of the formation and evolution mechanism of Hetao rift zone and the influence of the uplift process to the paleogeographic framework of Hetao basin. The sedimentological, geomorphological and geochronological study of the piedmont terraces in Wenggeleqige and Ulaan Ovoo, indicates that T1 terrace formed at 47.4 kaB.P. is characterized by lacustrine deposits from Hetao megalake, and T2 terrace developed at 69 kaB.P.is characterized by fluvial deposits which may be the products of the Yellow River when it flows through the pediment of Langshan Mountain. The analysis on characteristics of terraces shows that the two terraces are mainly tectonic genesis. Therefore, the two terraces recorded the rapid uplift process in Langshan Mountain after 69 kaB.P. Between 69 kaB.P. and 47.4 kaB.P. the time-averaged uplift rates in Wenggeleqige and Ulaan Ovoo were 1.34 m/ka and 1.25 m/ka, respectively, and the uplift rates were 0.81 m/ka and 1.18 m/ka during the past 47.4 kaB.P.,respectively suggesting that the uplift rate have a decreasing trend in the southwest part of Langshan Mountain (Wenggeleqige region). Since the late Late Pleistocene (Qp^3-2), the rapid uplift of the Langshan Mountain led to east moving of the Yellow River continuously by the evidence of the ancient channel on Hetao plain. The research on the lake terraces in Langshan Mountain further confirmed the existence of the Hetao megalake in Late Pleistocene.

Characteristics and Genesis of Two Types of Tectonic Deformation During Caledonian in Eastern Guizhou and Northern Guangxi

TANG Shi-kai, MA Xiao, YANG Kun-guang, DENG Xin, DAI Chuan-gu, ZHANG Qi

2014, 28(1):  109-118. 

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 Taking place in Eopaleozoic, Caledonian movement caused strong deformation in southern China and was mainly represented by episodic movements of Duyun and Guangxi. Comprehensive research on tectonic deformation and sedimentary environment holds that Duyun movement, as a local one, evidently influenced the middle and southern parts of Guizhou, the western area of Kaili-Sandu fault. Whereas, Guangxi movement originated from the squeezing of the Yangtze block and the Cathaysian block along the Jiangshan-Shaoxing fault. Under the influence of time and space, together the two movement events have formed two types of tectonic characteristics bordered by fault fracture. To the west of the fault fracture, this area is mainly influenced by Duyun movement and structures like EW folds and normal faults are developed. To the east, Guangxi movement shows its power, and structures such as NE folds and shear zones can be seen. The time of the occurrence of Guangxi movement is determined by samples collected from the study area. Among which samples from the ductile shear zone in Gaowu show that the plateau age of ⁴⁰Ar/³⁹Ar of muscovite is (416.4±1.8) Ma, and isochron dating is (417.7±1.8) Ma; those from NE cleavage belt in Liping show that the plateau age of ⁴⁰Ar/³⁹Ar of sericite is (426.5±2.3) Ma, and isochron age is (437±10) Ma.

Neotectonics Research Based on Tectonic Geomorphologic Parameters：Progress and Discussion

HE Xiang-li，ZHANG Xu-jiao，HE Ze-xin

2014, 28(1):  119-130. 

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Tectonic geomorphology is the result of interaction between neotectonics and exogenic geological process at the basis of rock, which is also the most intuitional information carriers reflecting neotectonics. Tectonic geomorphologic parameters are the quantitative expression of the morphological features of landform generated by internal forces, showing great potential in quantitative uncovering neotectonics. Based on tectonic landform evolution^,s sensitive impact on tectonic uplift, geomorphic characteristics of river and hillslope gradually become ideal information carriers of neotectonics. This paper analyzed the application principles of river geomorphologic parameters based on stream-power incision model, and introduced the latest research about the hillslope geomorphologic parameters corresponding to tectonic uplift delayed response reported by Martin D. Hurst et al in 2013, and tried to discuss the parameters^, indicative significance to tectonic uplift. It comes to the conclusion that tectonic geomorphologic parameters can preferably reflect neotectonics information implicated in tectonic geomorphology. Acquiring these parameters in different time can realize the dynamic study on modern tectonic geomorphic process to get the latest information of crustal activity. However, tectonic geomorphic research cannot settle geochronological sequence of tectonic activity, and is hard to eliminate the impact of nontectonic factors. Nowadays, the application of tectonic geomorphologic parameters in neotectonics is still a “bottleneck” in qualitative study. Integrating tectonic geomorphologic parameters with geologic and geomorphic records and experimental simulations to build a comprehensive model of geomorphologic parameters is the most efficient path to realize the quantification of neotectonics research.

Coupling Between Inchoate-nowadays Geological Structures and Hydrocarbon Reservoirs in Mabei Area, Northern Margin of Qaidam Basin

2014, 28(1):  131-138. 

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 Based on the new interpretation on seismic data, integrated with drilling and regional geology, the paper dissected the fault assemblage, fault forming phases, fault evolution and the rule of structural high development by means of fault growth index, balanced section, and trend thickness method. According to fault assemblage, Anderson fault mode and Harding^,s statements on stress and strain of strike-slip fault, stress condition since Cenozoic in Mabei area was discussed. Meanwhile, by adopting the dynamic approach, the coupling between inchoate-nowadays geological structures and hydrocarbon reservoirs is studied. Multi-stage faults in Mabei area is the strike-slip fault system dominated by Maxian fault. The fault evolution in the study area is closely linked with Maxian fault. There was significant coupling relationship between the fracture and inchoate-nowadays geological structures, and it is the fault and the inchoate-nowadays geological structures that jointly controlled the formation, reconstruction and distribution of Cenozoic hydrocarbon reservoirs.

Deformation Superimposition Characteristics Resulting from Stretching Direction Changes in Nanpu Sag: Insight from Physical Modeling

LIANG Jie, YU Fu-sheng, LIU Guo-xi, WANG Tong-kui, LI Ding-hua, MA Kui

2014, 28(1):  139-148. 

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According to the comparison of the previous modeling results and the actual geological conditions in Nanpu sag, different series of physical models which are in different stretching directions and different pre-existing basin structures have been conducted. Furthermore, the Cenozoic fault systems in Nanpu sag are discussed. The results can be concluded as follows: (1)The Cenozoic fault systems in Nanpu sag are the result of two-phase extensions with different stretching directions.(2)The NE-SW fault systems had undergone NW-SE extension during the Shahejie depositional period; while the EW fault systems had undergone SN extension since Dongying depositional period. The early Dongying period witnessed the changes of regional stress direction of Nanpu sag.(3)The structural characteristics in different depositional periods were controlled by particular boundary geometry, basal heterogeneity, and distribution of pre-existing faults.

Petroleum Geology

Characteristics and Main Controlling Factors of Karst Caves in the Southern Margin of Kepingtage Tectonic Belt, Tarim Basin

LI Bao-gang，GAO Ri-sheng

2014, 28(1):  149-155. 

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In the Middle Caledonian period, extensive lateral compression and vertical uplift occurred in Keping area, Tarim basin. Ordovician Yijianfang Formation and the top of Yingshan Formation were exposed for three times, resulting in wide karst and different types of paleocaves, which were uplifted to the surface in Himalayan movement and became outcrops now, with a variety of shapes and sizes. Based on the outcrops observation, types of the paleocaves were categorized by their shapes and textures, and the features and main controlling factors of each type were studied as well. Research shows that paleocaves could be classified into four types. The tubular and branching types of caves are slender pipes, with circular or ellipse shape in cross section and many branches possibly, which  were caused by underground rivers; Controlled by faults, fractures, and corrosion along layers, single isolated type could be funnel-shaped, inverted funnel-shaped, plate profile or combined shape; Karst caverns type caves scattered around the ancient water table and were connected by fault, fractures or small resolved channels, layering vertically. Karst caves with broad halls and many small scale branches are formed by corrosion along layers.

Paleokarst Characteristics and Their Significances on Reservoir Potential for the Yingshan Formation, Xiker Outcrop Area, Tarim Basin

GAO Da, LIN Chang-song, HUANG Li-li, ZUO Fan-fan, LI Hao, GENG Xiao-jie

2014, 28(1):  156-162. 

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The Yingshan Formation is one of the most important oil and gas reservoirs for Tarim Basin due to the karstification developed in upper part of the formation. However, the detailed characteristics of reservoir can not be precisely unraveled on the basis of limited well data. The Xiker outcrop area, located in the west of Tarim Basin, has undergone multiple tectonic movements since Ordovician. Karstification developed at these tectonic unconformities. Therefore, the exposed Yingshan Formation shows varied paleokarst characteristics. By field and thin-section observation and description, diverse karst-characteristics have been identified, including large caves, cave breccias, vugs, fractures and dissolution channels. Caves and breccias, produced by intense dissolution and collapse, can directly form reservoir. Dissolution vugs are widely developed and usually generated with dissolution channels and fractures. Multiple tectonic fractures can significantly increase the permeability of the karst reservoir. Combining with the lithofacies of the Yingshan Formation, the grain-dominated limestones have greater density of dissolution vugs than lime mud dominated limestones have. In addition, dissolution channels and tectonic fractures are more likely to be generated in limestones with higher grains ratio. As a result, the high-quality fracture reservoir and compound reservoir with vug, cave and fracture are produced.

Distribution Characteristics and Controlling Factors of the Lower Cretaceous  Lacustrine Dolomitic Rock in Erlian Basin

WANG Hui-lai, GAO Xian-zhi, YANG De-xiang, LI Hao, ZHANG Zhi-yao, WANG xu

2014, 28(1):  163-172. 

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A set of the mixed clastic-carbonate deposits were developed in the Lower Cretaceous of Erlian Basin. In recent years, abundance of hydrocarbon shows have been found in the dolomitic rocks, but there is little research on this kind of mixed deposits. Therefore, combined with core observation, microscopic identification and bore log analysis, we made a comprehensive study of petrologic features and distribution of mixed clastic-carbonate deposits in the main sags. According to this study, some knowledge on the dolomitic rocks were recognized: (1) Dolomitic rocks mainly affected by the source area lithology is typical parent material mixing. (2)Different types of lacustrine basin evolution lead to sedimentary facies differences, which determine the vertical distribution of dolomitic rocks. (3)Devitrification of volcanic glass provides a large number of Mg²⁺ and Fe²⁺ ions for buried dolomitization, resulting in the high iron content of dolomite. (4)Distribution of dolomitic rocks is less affected by paleoclimate.

Reservoir Evaluation on Mixing Deposit of Shizigou Formation in Xiaoliangshan, Northwest of Qaidam Basin

SIMA Li-qiang，YANG Yi，WU Feng， YAO Jun-peng, ZHAO Wei-yong

2014, 28(1):  173-180. 

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The mixing deposit of N³₂ in Xiaoliangshan region is simply classed as argillaceous mixing deposit, arenaceous mixing deposit and carbonate mixing deposit for reservoir evaluation. On this basis，combining the data of core analysis，the casting thin sections, porosity and permeability analysis, mercury injection test and log, this paper investigates the mixing deposit reservoir of Shizigou Formation in Xiaoliangshan, northwest of Qaidam Basin: The mixing deposit has complex rock structure and various rock type. The pore space of reservoir mainly includes the primary intergranular pores and micropores. The reservoir properties are mainly mediumhigh porosity and low permeability, high displacement and saturation median point pressure, small pore throat radius. The pore structure are generally poor. The sedimentation and diagenesis have played important roles in evolution of resevoir. The sand flat microfacies is the main favorable reservoir facies. Compaction is the major factor that has influence on the reservoir physical property.N³₂are divided into three types according to parameters like physical property, capillary pressure and so on, reservoirs of the typeⅠand type Ⅱ can be taken as the major target zones for increasing reserves.

Sedimentary Characteristics of Fan Delta of the Badaowan Formation, Sikeshu Section, Southern Junggar Basin

TAN Chen-peng, YU Xing-he, LI Sheng-li, XU Lei, CHEN Bin-tao, LI Shun-li

2014, 28(1):  181-189. 

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On the basis of observation and measurement in field, and with the application of sedimentology and high resolution sequence stratigraphy theories, a detailed study on the sedimentary characteristics of the Badaowan Formation in Sikeshu section, southern Junggar Basin has been conducted. The fan delta system developed fan delta plain and fan delta front subfacies, and the sedimentary characteristics of the two kinds of subfacies are concluded. In the outcrop, two longterm stratigraphic cycles are identified and Badaowan Formation can be subdivided into three medium-term cycles, as well as the composition of a number of short-term cycles. This paper summarized the relationship between the A/S ratio with stratigraphic stacking patterns in outcrop area. A thick stacked sand body with good connectivity was formed in the low A/S ratio condition, and the types of sedimentary microfacies are single; In the medium A/S ratio condition, thin and blanket-like monolayer superimposed in vertical, and formed compacted multilayer sand body. Mudstone and isolated sand bodies are developed in the high A/S ratio condition rifely, and their internal structures are compacted with limited lateral extension. Eventually, through detailed anatomy of the sedimentary characteristics of Badaowan Formation in the outcrop section, a fan delta sedimentary model of Badaowan Formation has been established, and provides reference for fan deltas reservoir research in southern margin of Junggar Basin.

Characterization Technique of Pore Structure by 3D Digital Core Based on CT Scanning and Its Application：An Example from Sangonghe
Formation of 116 Well Field in Mobei Oilfield

QU Le ,SUN Wei,DU Huan-hong,ZHANG Chuang,JIANG Li-ming,WEI Hu

2014, 28(1):  190-196. 

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 In order to characterize the pore structure of reservoir rock really, accurately and intuitively, different rock cores are scanned by CT imaging technology and the 3D digital cores are reconstructed. Then the model of pore network is extracted by maximal ball algorithm form the 3D digital core. And finally the reservoir properties and pore structure parameters are characterized quantitatively. This method of pore structure characterization has a good result after it is applied in Sangonghe Formation of 116 well field in Mobei oilfield. Our research indicates that the pore type here is mainly intergranular pore, emposieu pore and a little intercrystal pore. The average pore radius is 33.11 μm and the throat radius is 1.47 μm. The small throat is the main reason of low permeability in this area. Compared with the result of NMR Coates model, digital core can give a more accurate permeability result. The pore structure of digital core has a good concordance with mercury penetration result. However, the digital core method can identify the pore and throat respectively and it is more vivid, more direct, more accurate with little sample broken. So it is more applicative for pore structure characterization.

Diagenetic Fluid Evolution of Reservoirs in Es^s₄ in the North Zone of the Bonan Sag

CAO Ying-chang，JIA Yan-cong, WANG Yan-zhong, MA Ben-ben

2014, 28(1):  197-207. 

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With multi-period of acid-alkaline fluid evolution as well as multi-period of hydrocarbon charging during the burial, the reservoir physical property went through a complex evolution in the upper part of the fourth member of the Shahejie Formation (Es^s₄) in the north zone of the Bonan sag. With the comprehensive analysis of burial history, the thermal evolution of organic matter and dehydration of gypsum-salt bed, combined with characteristics of different hydrocarbon inclusions and salt-water inclusions, the diagenetic sequence of Es^s₄ in the north zone of the Bonan sag is studied. During the deposition of Es^s₄ , the original formation-water is of weak alkalescence because of the dry climate; from the beginning of the deposition ofEs^s₄ to 42.5 Ma，the formation fluid keeps weak alkaline with immaturate organics, and the main type of diagenesis is compaction, and early spherulitic pyrites are formed. From 42.5 Ma to 30 Ma，the formation fluid becomes acid for the existence of organic acid, and feldspar dissolution and quartz overgrowth take place. From 30 Ma to 24.6 Ma, the dehydration with alkaline water of gypsum-salt bed in the top of Es^s₄  occurs as well as decarboxylation of organic acid, thus the formation water becomes alkaline, and carbonate cementation and quartz dissolution simultaneously take place. During this period the first phase of hydrocarbon filling takes place from 28.8 Ma to 24.6 Ma, and from 24.6 Ma to 6 Ma, the organic acid is generated for the second time resulting from the uplifting stratum, and the formation water becomes acid, so the second phase of acid dissolution and quartz overgrowth begins, and the second phase of hydrocarbon filling take place in the period of 10 Ma to 6 Ma. From 6 Ma till now, the dehydration occurs again in gypsumsalt beds of Es^s₄  and the formation fluid becomes alkaline once more, so a few of later pyrite cementation can be found.

Characteristics of Overpressure Fluid Compartments in Mingbulak Oil Field,Fergana Basin

XU Hong, YANG Yu-feng

2014, 28(1):  208-215. 

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Mingbulak oil field in Fergana Basin is an over deep oil and gas reservoir, which is characteristic with the prevalence of abnormal overpressure, pressure coefficient up to 2.0, and with the development of rock salt, gypsum salt bed, low porosity reservoir with abundant fracture. These characteristics have close relationship with the formation and existence of overpressure fluid compartments. By researching these properties, it is found that sediment undercompaction due to rapid subsidence and tectonic compression are main formation mechanisms of overpressure in Upper Tertiary formation，and the development of rock salt layers and its accumulated thickness over 200 m are important conditions for oil formations. Two overpressure fluid compartments can be identified in Tertiary formations; the pressure coefficient of the upper compartment is bigger than the lower one. The fluid properties of both compartments are clearly different, and they are two relatively independent accumulation systems; The upper compartment can further be divided into three sub-compartments separated by two sealed salt beds, and compose a ladder style complex compartment. Three sub-compartments are named as upper Ⅰ, upper Ⅱ and upper Ⅲ respectively from up to low. Overpressure, micro fracture and rock salt in compartments are the main reasons to cause drilling trouble such as well kick, circulation loss and drill pipe sticking, and so on. In addition to oil and gas pools found in the lower compartment and upper Ⅲ sub-compartment, the bottom of upper Ⅱ sub-compartment also has a certain exploration potential; Ultra deep formations accumulated high density oil is related to overpressure fluid compartment. Compartment^,s reservoirs developed abundant fractures due to high pressure, which is not only conductive to high oil production, but also easy to early water breakthrough.

Geochemical Characteristics of Biomarkers of the Upper Triassic Source Rocks from Tumengela Formation in Qiangtang Basin of Tibet

CHEN Wen-bin, FU Xiu-gen,TAN Fu-wen, FENG Xing-lei

2014, 28(1):  216-223. 

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This paper firstly reported the study on biomarkers^, characteristics of the Upper Triassic Tumengela Formation in Qiangtang Basin. Some typical biomarkers can be used to determine the biologic source nature and maturity of the organic material, and the depositional environment. The result reveals that the main sources of the organic matters are mixed sources, which originated from high-grade plants and algaes and bacteria. Some of the biomarkers indicate that the sedimentary environment of source rocks is a reducing environment with certain salinity. The maturity parameters of source rock indicate that the degree of maturity of organic matter is high. The above characteristics of biomarkers of source rocks in the Tumengela Formation further confirmed that the formation has good hydrocarbon potential.

Stratigraphy

Application of Crust Correction to the Teleseismic Tomography in the Middle and Lower Reaches of Yangtze River Region

XU Yao, ZHANG Gui-bin, JIANG Guo-ming, YAO Yong-bo

2014, 28(1):  224-233. 

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This paper applied a crust correction method to study the middle and lower reaches of Yangtze River region, and the data used in the study were derived from 473 teleseismic events collected by 47 permanent stations. The results show that (1)the low crust velocity anomaly is beneath inland area and the high crust velocity anomaly is beneath coastal area; (2)there are slight velocity-anomaly differences between before and after crust correction, indicating that the crust structure of the middle and lower reaches of Yangtze River region is stable; (3)with the depth increasing, the difference of velocity anomaly is becoming smaller, which means the impact of crust correction method in shallow depth is big while in deep depth is small. Therefore, in the teleseismic tomography study, if shallow information is shortage, the crust correction can be used to eliminate or reduce the influence of crust velocity structure to the final inverse results, and improve the quality of results in deep depth.

Study on the Position of North West Section of Nankou-Sunhe  Fault in Beijing and Its Activity

ZHANG Lei, BAI Ling-yan, CAI Xiang-min, WANG Ji-ming, WANG Zhi-hui

2014, 28(1):  234-242. 

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The composite profile of some geophysical exploration methods, including controlled source audio-frequency magnetotellurice method, shallow seismic and radon methods, was used to pinpoint the position of Baifu-Baishan section of Nankou-Sunhe fault. By studying the borehole sedimentary facies and the magnetostragigraphy characteristics, this paper discussed the activity of Nankou-Sunhe fault in Quaternary. The results show that the position displacement of the main fault is from 500 to 800 meters along NE direction compared with previous reports. The result of two boreholes in Baishan shows that the fault^,s vertical rate is 0.12 mm/a, 0.58 mm/a and 0.31 mm/a in Middle Pleistocene, Late Pleistocene and Holocene, respectively. The activity of the fault is weak to strong, and then weak. Therefore, combined with borehole profiles, the comprehensive geophysical profile can pinpoint the location of buried active faults in cities, and can be used to analysis the faults^,characteristics, providing valuable information for taking effective preventive measures to reduce the disaster in urban areas and to protect the lives and properties of people.