Geoscience

Tectonic Geomorphology Analysis of Piedmont Rivers in the Southern Section of Longmenshan Based on Hypsometric Integral

SHAO Chong-jian1，LI Yong1，ZHAO Guo-hua1，YAN Zhao-kun1，NIE Zhou2，YAN Liang1，LI Ji

2015, 29(4): 727-737.

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The southern section of Longmenshan fault belt happened Dayi Ms 6.2 earthquake in 1970 and Lushan Ms 7.0 earthquake in 2013，indicating that this area has active neotectonics movement and is the ideal place to study the relation of structure, topography and river. This paper extracted the drainage basins of six rivers in the study area and their sub-drainage basins using GIS technology based on DEM data. These rivers are Xi River (R₁)，Chujiang River (R₂)，Xiejiang River (R₃)，Wenjing River (R₄)，Sanlang River (R₅) and Tai’an River (R₆).The hypsometric integral values of these six rivers were calculated and their curves were drawn to analysis the tectonic activity and geomorphological evolution of the study area. The conclusion can be drawn as follows:(1) The hypsometric integral values descend from NW to SE,indicating that the regional activity descends from NW to SE and the contemporary strata exposed in the SE are younger than those in the NW.(2)The hypsometric integral value of SW segment on the hanging wall of Shuangshi-Dachuan fault is larger than that of SE segment, indicating that the tectonic activity of Shuangshi-Dachuan fault becomes waken from NW to SE. (3)According to Ohmori’s model，with the pre-show style over thrust advancing forward to foreland, the evolutions of mountains, hills and plains can be speculated that ① in mountains, the uplift of mountain will continue until it reaches the highest point with hypsometric integral value equaling to 0.6，and hypsometric integral curves begin to change from S shape to convex shape, and the river will develop from mature stage to juvenile stage; ② in hills, the hypsometric integral curves begin to change from concave shape to S shape，and the river will develop from old stage to mature stage，then the hill will develop to be the mountain; ③ in plains, although the thrusting uplift increases,the local-rain belt will gradually close to the plain, causing the erosion intensity larger than uplift strength，thus the development mode will gradually become to be the hill development mode.

Geological Phenomena of Indosinian Event in Southern Anhui，Eastern Jiangnan Orogenic Belt

ZHOU Shu-zhao，YU Xin-qi，CHEN Zi-wei，LIU Xiu

2015, 29(4): 738-746.

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The Indosinian structural features in the adjacent regions of Anhui (Wan)，Zhejiang (Zhe) and Jiangxi (Gan) in eastern Jiangnan Orogen were largely ignored due to the lack of directly structural age data. Based on regional geological information at scale of 1∶50,000 and field observation on southern Anhui，this study found and concluded some new evidences of Indosinian tectonic events in southern Anhui. Three-period distinct structural features have been identified in Liutang area of Xiuning in Anhui，and among which the angular unconformity between the Upper Triassic and the Lower Triassic belongs to the Indosinian event. The NE-trending fault developed in Lantian relict synclinal basin was formed during Indosinian，which experienced a process from slipping to collapse. The age of Triassic Dongkengkou quartz porphyry is about 245.2 Ma, implying that the Early Indosinian event had caused a partial extension. In addition，the age of sericites in Sanyangfault is (230.5±2.3) Ma(⁴⁰Ar-³⁹Ar)，indicating that the Jinningian fault had been affected by Indosinian movement. Upon these findings，this study discussed the evolution process of Indosinian movement，and provided important implications for understanding the Indosinian tectonic events of southern Anhui，even those of Wan-Zhe-Gan adjacent areas.

Features and Dynamic Mechanism of the Southern End of Muping-Jimo Fault

GE Jun, ZHANG Ze-kun, NI Jin-long, HAN Shuai, HOU Xiao-huan, LI Min

2015, 29(4): 747-754.

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The southern end of Muping-Jimo fault is located in the western coastal region of Qingdao. Based on detailed field geological investigation, the characteristics of the fault were discovered in the area, and the paleo-stress state and dynamic mechanism were also discussed. The results show that, firstly, the structure of the fault along the western coast of Qingdao mainly consists of large numbers of shear joints, smaller faults and dikes; secondly, the dominant directions of shear joints are mainly four groups, i.e.NW-SE, NE-SW, E-W and S-N trending,and the extending direction of faults is mainly near NE trending; thirdly, the inversion of paleo-stress state reflected that the study area had undergone two compressional activities since Late Cretaceous, S-N trending compression in the early stage and nearly E-W trending compression in the later stage; fourthly, the compression in the early stage might be associated with NW-SE trending compression occurred in the North China Craton, which derived the local stress field with the SN direction in the Late Yanshan movement, and the E-W trending compression in the later stage might be related to Qinghai-Tibet Plateau extrusion toward the east since Paleogene and the westward extrusion caused by Japan sea expansion since Miocene; and lastly, Muping-Jimo fault successively occurred at least two strike slip motions since Late Cretaceous, i.e.sinistral strike slip and dextral strike slip.

Sandbox Modeling of Fold and Thrust Belt Based on Particle Image Velocimetry(PIV)

ZHOU You1, LI Yong1, LI Jing-bo1, SHAO Chong-jian1, YAN Zhao-kun1, YAN Liang1, L

2015, 29(4): 755-764.

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Based on previous studies, this study used sandbox modeling to analyze the constraint of the number, intensity and depth of slip layers to the fold-thrust belt. Using particle image velocimetry (PIV) as a real-time monitoring technology, six sandbox modeling experiments were designed to calculate the velocity and vorticity of models to quantitative analyze kinematic and deformational mechanism of the fold-thrust belt. The results show that (1) the strength and depth of slip layers constrain the tectonic evolution of fold faults; (2) the smaller the strength of slip layers is, the farther the deformation propagation of overlying strata is; (3) the slipping depth is deeper, and the control action on entire structure is larger, thus the deformation spreads farther. The slip layer which is composed of micro-glass beads mainly produces preshow type of thrust imbricate structure, with faster rate of upper horizontal displacement at the nappe front edge.The upper layer which consists of silica gel mainly generates imbricated structure,with washed form from the lower part of the formation. The upper and lower portions of the slip layer show distinct characteristics of hierarchical deformation. The PIV analysis shows that the ramp off the floor forms and develops into a combination of structural-style ramps when the disk speed arrests and the vorticity of the leading edge rapidly decreases, and the following fault forms in the same manner at the front edge, leading to the forward expansion of the fold-thrust belt.The comparative analysis of the southern section of the Longmenshan fold-thrust belt and experimental results shows good consistency.

Study of High Resolution Sequence Stratigraphy of Quan 4^th Member, Sanzhao Area in the Northern Songliao Basin

HU Ming-yi1,，SUN Chun-yan，XUE Dan，ZHANG Hong-jun

2015, 29(4): 765-776.

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Fuyu oil layer of Sanzhao Depression is one of the important oil-gas exploration areas in the north of Songliao Basin. Fuyu oil layer mainly is a set of river-shallow water delta deposition. Because single layer thickness of channel sand body is thin and its lateral change is quick, the study of sedimentary microfacies is necessary to conduct, which guide the exploration of stratigraphic-lithologic oil and gas reservoirs. Taking Zhao 35 block as an example, applying the high-resolution sequence stratigraphy principle, sequence boundary is identified and sequence stratigraphic is divided. Taking short-term base level cycles as mapping units, sedimentary facies distribution maps within the framework of the sequence stratigraphic are drawn, the vertical evolution laws are analyzed and sedimentary microfacies model is established. The results show that Quan 4^th Member is a long rising half cycle, which can be divided into 7 short-term base-level cycles (SSC1-SSC7). The study area mainly develops delta plain and delta front subfacies, which can be further classified into (underwater)distributary channel, (underwater) crevasse splay, natural levee and so on. SSC1 and SSC2 periods of 7 short-term base-level cycles are unsymmetry cycles dominated by ascending half cycles because of slowly rising base level. SSC3 and SSC4 periods are unsymmetry cycles dominated by ascending half cycles and symmetry cycles because of quickly rising base level. SSC5 to SSC7 periods are unsymmetry cycles dominated by ascending half cycles and base level rises to the highest. Sedimentary facies and its distribution are mainly controlled by the change of base level. The study area experiences the evolution of delta plain subfacies—plain, front subfacies transition—delta front subfacies—local shallow lake facies. In vertical direction, Quan 4th Member exhibits a lake transgression process, whose sedimentary water changed from shallow to deep.

Distribution and Source Analysis of Elements from Sediments in the Northern South Yellow Sea since the Late Pleistocene

LAN Xian-hong，MEI Xi，LI Ri-hui，ZHANG Zhi-xun，LI Jie，GU Zhao-feng

2015, 29(4): 777-788.

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The sediment samples derived from drillhole DLC70-3(71.20 meters in depth) in the northern South Yellow Sea were measured for analysis of element geochemistry and their provenances were discriminated with the purpose of studying the indicator significance of element geochemistry information for the stratigraphic division and provenance analysis of mud area in northern South Yellow Sea. According to the changing law of element contents and their ratios，the sediments from drillhole DLC70-3 can be divided into five layers, reflecting the fluctuation of sea level and the change of sediment sources in northern South Yellow Sea since the late of the last interglacial cycle (warm period). Combined with discriminate function，the scatter diagrams of MgO/Na2O vs. CIA were drawn to determine the material source of sediments from drillhole DLC70-3. The results revealed that the material sources of sediments mainly came from the Yellow River，and sediments in the upper-middle and in the lower of the drillhole were apparently influenced by materials from the Changjiang River. The sediments above the depth of 4.50 m in the upper and between 27.80 m and 38.80 m in the middle of drillhole DLC70-3 mainly belong to the Yellow River source; the sediments from 4.50 m to 27.80 m in the upper-middle，from 38.80 m to 55.00 m in the lower and from 55.00 m to 71.20 m at the bottom were mainly derived from the Changjiang River. It is concluded that the Yellow River is playing an important role in northern South Yellow Sea at the middle stage of Late Pleistocene and the Changjiang River has started to obviously influence northern South Yellow Sea since early Late Pleistocene.

Geochemical Characteristics of Sedimentary Rocks from the Triassic Kanglu Formation,North Qiangtang Basin(Tibet): Implications for Provenance and Tectonic Setting

QU Li-hua，LIU Xi-fang，LI Jin-suo2，QI Lu-jing

2015, 29(4): 789-803.

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The geochemical characteristics of clastic sedimentary rocks in sedimentary basin are mainly controlled by the origins of the rocks. In this paper, we report on the whole-rock major and trace element compositions of clastic sedimentary rocks in North Qiangtang Basin. The results show that the index of compositional variability and the chemical index of alteration for different samples are similar, revealing a relatively fresh, weakly matured origin with weak-medium chemical weathering. The rocks are characterized by high SiO₂ contents, and relatively high TFe₂O₃+MgO contents, but K₂O/Na₂O ratios vary largely for different samples. The rocks have the similar trace and REE patterns with the post-Archean Australia shales and upper continental crust, characterized by enrichment in LREE, evident Eu depletions, and weak Ce depletions.Furthermore, the ratios of Th/U, La/Sc, Th/Sc, Ba/Sr of Kanglu Formation and the binary diagrams TiO₂ vs.Ni, La/Th vs.Hf, Co/Th vs.La/Sc and Th/Sc vs.La/Sc denote that the origin of the sediments is characterized by superficial and felsic.The tectonic setting discrimination diagrams, such as of SiO₂ vs.K₂O/Na₂O, La vs.Th, La/Y vs.Sc/Cr and La vs.Th vs.Sc, Th vs.Sc vsZr/10, Th vs.Co vs.Zr/10, and the ratios of Th/U, Rb/Sr suggest that the source material of Kanglu Formation in North Qiangtang mainly belongs to continental arc setting, and partially belongs to passive continental margin and oceanic island arc setting.

Structure Palaeogeomorphology Characteristics and Sand Bodies Distribution Regularities of Paleogene Wenchang Formation in Enping Sag：Under the Conditions of Lack of Drilling Data to Predict and Evaluate the Reservoir Sand Bodies

ZENG Zhi-wei1, 2，YANG Xiang-hua1, 2，SHU Yu3， CHEN Sheng-hong3， WU Jing3，WANG Wei

2015, 29(4): 804-815.

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Taking advantage of the extensive seismic data, the structure palaeogeomorphology characteristics and sand bodies distribution regularities of Paleogene Wenchang Formation in Enping Sag are discussed by correlated theories on the characteristics of palaeogeomorphology, identification of ancient valley and joint phase tracking. The causes and plane distribution of the sand bodies of Wenchang Formation are closely associated with the deposition of ancient geographical background and the ancient valley. The northern steep slope of Enping Sag is controlled with the fault and the ancient valley. It develops a series of north offlap fan-delta glutenite bodies which interactively touches with the mid-deep lake facies mudstones, and its development period and scale is closely related to the boundary fault activity. The EP18-1 inherited palaeohigh has controlled the ancient valley development and ancient landform pattern of the southern slope, and the southern slope zone is divided into two ancient valley source supply systems. They control the distribution direction of the braided river delta in the south slope of EP17 and EP18, while the EP18-1 inherited palaeohigh develops largescale beach bar sand body.

Discovery of Ice-wedge Casts in the Northern Margin of Loess Plateau and Their Implications

WANG Jian-yong，ZHANG Xu-jiao，HE Ze-xin，ZHAO Qiu-chen，HE Xiang-li，SHENG Yu-ying

2015, 29(4): 816-824.

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The ice-wedge casts were considered to be an important indicator on paleoenvironment. The climatostratigraphic information in them could implicate the geomorphic evolution. In this paper, the ice-wedge casts were described in detail, which were found in the lower terrace of Huanjiang river in the northern margin of Loess Plateau. Through the field investigation and optically stimulated luminescence (OSL)dating, the age of sandy gravel deposited in the wedges was about (30.01±3.31) ka B.P., the fluvial silty sand layer on the upper of the ice wedges was deposited about (28.64±3.13) ka B.P.. This finding shows that a cold event occurred in the phase of Marine Oxygen Isotope Stage 3 (MIS 3)in the Last Glaciation. Also, the average ground temperature then was estimated to be 17.7 ℃ lower than the temperature nowadays. Besides, the discovery of the ice-wedge casts provided evidence for the phasic variation of the permafrost boundary during the Last Glaciation. In addition, the climatostratigraphic position of ice-wedge casts in the river terrace indicated that the fluvial aggradation occurred slowly and even ended during the freezing period. When the climate was getting warmer in (28.64±3.13)ka B.P., the river started to undercut and the terrace was forming. This provided a basis for the formation mechanism of river terrace and showed the development of terrace was controlled by the changing climate.

Characteristics and Geological Significance of Microbially Induced Sedimentary Structures (MISS) in Changzhougou Formation of Mesoproterozoic in Licheng County, Shanxi Province

ZHENG Wei1, 2，XING Zhi-feng1, 2

2015, 29(4): 825-832.

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Many microbially induced sedimentary structures (MISS) in Mesoproterozoic Changzhougou Formation were found in Huangyadong Geopark and beside road of Pengzhuang to Dajingpan in Licheng County, Shanxi Province. It mainly developed on the surface of sandstones and were often mistakenly regarded as a special kind of trace fossils or irregular mudcracks because of its distinctive structural forms. On the basis of previous classification schemes, according to their MISS in Licheng County were divided into three genetic categories morphological features and origins (mat growth feature, mat destruction feature and mat destruction feature) and nine types small growth postulas, big dome growth postulas, irregular lateral growth ridges,big growth ridges, spindle-shaped cracks, polygonal desiccation cracks, curved cracks, microbial sand chips and sand volcano.These nine types of MISS were described and discussed in detail.Compared with MISS and strata characteristics of Lushan area of western Henan, Suyukou area of Helan Mountain, Nankou area of Beijing and Xinglong area of Hebei Province, we conclude that the MISS of the Mesoproterozoic in North China Platform is significant to the study of stratigraphic correlation and paleoenvironment.

Biological Burrow Explanation of Leopard Limestone and Its Diagenetic Evolution in the Third Member of Majiagou Formation in Ordovician, Northwest of Henan Province

DONG Xiao-bo, NIU Yong-bin

2015, 29(4): 833-843.

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The development characteristics and origin of leopard limestone in the third member of Majiagou Formation in Ordovician of north-western Henan Province were studied by using methods of outcrop observation and thin section analysis. The results show that the ‘leopard’ can be divided into five types of biological burrows according to their morphological characteristics and ichnology, i.e.Psilonichnus, Chnodrites, Thalassinoides, Helminthopsis and Planolites. The emergence of different types of biological burrow was mainly restricted by sedimentary environment. The burrow fillings can be divided into two types according to their different dolomitization degrees: (1)micritic dolomite fillings, mainly exist in Psilonichnus and Chnodrites; (2)powder-fine crystal dolomite fillings, mainly exist in Thalassinoides, Helminthopsis and Planolites. The process of dolomitization can be divided three stages,i.e. the preparation stage before dolomitization, the formation stage of dolomites and the adjustment stage of dolomites,and the different dolomitization statuses of burrow fillings are formed in this process.

Geochemistry and Significance of the Neoarchean Meta-mafic Rock of Jianping Metamorphic Complex in Western Liaoning Province

CAI Chun-hong，ZHAO Guo-chun，REN Liu-dong，LI Chong，GUAN Jia-min

2015, 29(4): 844-854.

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Based on the field work, LA-ICP-MS ziron U-Pb geochronology and geochemistry of the amphibolite and granulite from Jianping metamorphic complex in Western Liaoning Province, this study suggests that the metamorphic event of late Neoarchean and early Paleoproterozoic are mainly focused in 2 465-2 453 Ma and the age of crystallization is ~2 593 Ma. The two types of samples have relatively high Al₂O₃ (average is 14.49%) and high TiO₂ (average is 1.15%), which are similar to the rocks originated from ocean basalt. Mg# values of samples have a larger variation(35-63)which indicate that magma maybe contaminated by mantle substances during their ascent. Ce/Yb-Ce diagram reflect that samples stem from garnet lherzolite mantle. Amphibolite and most granulites are characterized by enriched LREE ((La/Yb)N=5.67-10.87), and obvious depletion of Nb, Ta, Ti, which is similar to that of island arc basalt, while flat curve has a character of N-type MORB. Comprehensive analysis shows that the mafic magmatism is formed in an active continental margin tectonic setting in the late Neoarchean, and then metamorphosed during the process of collision. So it is suggested that the study area exists a tectonic regime similar to modern plate in late Neoarchean.

The Discovery of Late Triassic-Early Jurassic Volcanic Rocks and Their Geological Implications in Northern Songnen Block, Heilongjiang Province

Lv Chang-lu1,2，XIAO Qing-hui3，FENG Jun-ling4， LI Xin-peng2， DENG Chang-zhou2， R

2015, 29(4): 855-865.

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Basaltic andesites are widely distributed in the northern Songnen Block, Heilongjiang Province and their ages are critical to understand the regional tectonic evolution in this area. This study presents LA-ICP-MS zircon U-Pb age data and geochemical data for the basaltic andesite from the Banzifang Formation previously considered to be Early Cretaceous. Two samples yield U-Pb ages of (200.0±1.4)Ma and (200.0±1.3) Ma respectively，demonstrating that they were formed in Late TriassicEarly Jurassic rather than Early Cretaceous. The basaltic andesites are metaluminous, mainly high-K calc-alkaline. They are characterized by enrichment of large ion lithophile elements (LILE) such as Ba, Rb, K, Pb and LREE, depletion of high field strength elements (HFSE) such as Nb, Ce, Nd, Ti and HREE, indicating that the basaltic andesites belong to continental arc volcanic rocks. The results demonstrate that there has been Late Triassic-Early Jurassic volcanic belts in Xiaoxinganling-Zhangguangcailing, these occurrence, together with synchronous granites, comprise a Mesozoic N-S-striking magmatic belt.

Geochemical and Sr-Nd Isotopic Characteristics of the Volcanics from the Qi’eshan Group in Eastern Tianshan and Its Implications

YANG Zhen，MUHETAER Za-ri，WU Zhao-ning，SHE Jian-zhong，YU Niu-ben

2015, 29(4): 866-872.

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Based on the geochemical data including major elements, trace elements and Sr-Nd isotopes of the volcanics from Qi’eshan Group occurring in the Jueluotage tectonic belt in eastern Tianshan, the volcanic rocks can be divided into theoleiitic series and calc-alkaline series. All of these volcanics show relative enrichment in aluminium, LREE, LILE and depletion in titanium. The calc-alkaline basalt has a characteristic of Eu anomalies, and the contents of incompatible trace elements are higher than those of the tholeiite basalt. The calc-alkaline basalt is the product of crystallization differentiation, and the tholeiite basalt is the product of partial melting from the La/Sm-La diagram. Initial Sr and Nd isotopic compositions show that the basalts from the Qi’eshan Group are derived from depleted mantle. In the discrimination diagram, samples from the Qi’eshan Group are plotted in the field of island arc basalt. The characteristics of the rock combination, geophysics, geochemistry，and the results of previous studies suggest that Qi’eshan Group formed in Dananhu island arc setting owing to the northward subduction of the Kanggur ocean.

Geochronology of Volcanic Rocks in Cretaceous Red-bed Basin in Lishui, Zhejiang Province and Its Geological Significance

WANG Jia-en，LIU Yuan-dong，WANG Zhen

2015, 29(4): 873-883.

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The geochemistry characteristics of volcanic rocks in three basins indicate that the basins of Bihu, Lishui, Zhangcun have the same composition of the petrochemistry, and that the three basins mentioned above were formed in volcanic island arc. From LA-ICP-MS zircon U-Pb data of volcanic rocks in three basins，we found that the volcanic age of Chaochuan Formation in Bihu basin was (123±2) Ma, Guantou Formation in Zhangcun basin was (111±3) Ma, Tangshang Formation in Lishui basin was (95±1) Ma. The age data for those volcanic rocks in three basins show that the time of volcanic activity continued 28 Ma or so, and those data also reflect the activity continuation of Lishui-Yuyao fault.

Geochronological and Geochemical Study for the Paleoproterozoic A-type Granite in the Nucleus of the Yangtze Craton and Its Tectonic Implication

QIU Xiao-fei，YANG Hong-mei，LU Shan-song，TAN Juan-juan，CAI Ying-xiong

2015, 29(4): 884-895.

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This study carries out systematical geochemical and geochronological investigations on the Quanyi-shang granitic pluton intruding into the Kongling Complex, and discusses the petrogenesis and Paleoproterozoic evolution of the nucleus of the Yangtze craton. The zircon LA-ICP-MS U-Pb dating shows that crystallization age of the granite is (1 822±44) Ma, hence a typical product of Paleoproterozoic magmatism of the Yangtze continental interior. The geochemical research illustrates a depletion of Al, Mg and enrichment of Rb, Th, as well as negative anomalies of high field strength elements (HFSE) and Eu, Ba and Sr. High Ga/Al ratio and Zr+Nb+Ce+Y content and relatively high calculated zircon saturation temperature (＞862 ℃), combined with other geochemical features, indicate that the Quanyishang granitic pluton is aluminous A-type granite. The εNd(t) value varies between -12.4 to -10.3 and the correspondent two-stage Nd isotopic modal ages range from 3.3 to 3.2 Ga. These characteristics imply that the granite may have formed by partial melting of ancient felsic crustal material in the nucleus of the Yangtze craton under a low-pressure, high-temperature condition at a post-collisional extensional tectonic setting. Combined with the documented work, it may have relationship with the regional tectonic transition from collisional extrusion to extention in a post-collisional setting during the period from 2.0 to 1.9 Ga. The Paleoproterozoic tectonic magmatic events of the Yangtze craton is consistent with the global 2.1-1.8 Ga collisional orogeny to breakup events related to the evolution of Columbia supercontinent, indicating that the nucleus of the Yangtze craton may have been an important part of Columbia supercontinent.

Geochemistry and Mineral Characteristics of Zijinshan Alkaline Complex from Linxian, Shanxi Province and Its Petrogenesis

WANG Ya-ying，CAI Jian-hui，YAN Guo-han，YAN Zhi-jiao，SONG Jian-qiang

2015, 29(4): 896-911.

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With pyroxene, feldspar and nepheline as the study objects and by using electron microprobe technology, the authors discussed the petrogenesis for Zijinshan complex on the basis of petrography and petrogeochemistry study. The petrochemistry data shows that Zijinshan complex is a potash-rich alkaline-parlkaline rock. According to the mineral assemblages in rocks for different periods, the rocks in seven periods can be divided in two magma series: classical alkaline magma series and non-classical magma alkaline series. Rocks belong to classical alkaline magma series contain feldspathoid (nepheline or leucite), orthoclase, and aegirine-augite (sodic pyroxene) except rocks at the third stage, and there is no plagioclase. However, rocks belonging to non-classical alkaline magma series contain diopside (calcium pyroxene), and parts of them contain plagioclase without feldspathoid. Combined with the data of Sr-Nd isotope for whole rock in two magma series and the regional geological materials, it can be speculated that the petrogenesis of Zijinshan complex is as following: continuous asthenospheric upwelling made asthenosphere mantle，lithosphere mantle and lower crust melt and mixed by different proportions for several times，and then each episodic of mixed magmas welled up to the shallow area of the crust. The proportions of crust-derived material in rocks from different stages are different, and they can be divided into two rock series by their mineral assemblages.

Geological Characteristics of Ronghua Manganese Deposit in Guangxi and Its Significance

LI She-hong1，YUAN Hong-qing1，PEI Qiu-ming3，YAN Song1，LIU Xiang2，ZHANG Ling-xiang

2015, 29(4): 912-921.

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Ronghua manganese deposit located in the the Baifeng Formation in Triassic Baifeng stratum is initial reported as industrial deposit. Based on large-scale geological survey, exploration project, analytical testing and other means, we study the geological background, sedimentary environment, ore body and ore characteristics, sedimentary evolution, and so on. Ronghua manganese deposit, in which the ore bodies are controlled by the stratigraphy and structure, are distributed along the layers of mudstone,muddy siltstone and marl in Baifeng Formation, belonging to deposited-leaching cap-type manganese deposits. The lowgrade ore associated Co and other metal elements consists of pyrolusite and other manganese oxide minerals. The carbonate under Baifeng Formation and turbidite conglomerate upper part of the first segment in Baifeng Formation are typical prospecting signs in northwest Guangxi where there is a large number of Baifeng Formation outcrop. There were terraces surrounded by basins in Triassic northwest Guangxi region. Such Mn-rich terraces formed in the late Paleozoic suffer from weathering denudation and the ore-forming elements were brought into the basins. When the Tethys Ocean closed, the manganese initial enrichment in the first segment in Baifeng Formation under the condition of basin area reduced, the water level deepened and fluctuations in the redox interface as the basins suffered compression. The oxide manganese deposits were ultimately formed through weathering and leaching, then Youjiang Basin uplift out of the water and began to accept the denudation.

Controlling of Hydrocarbons Expulsion of Source Rock on Buried Hill Hydrocarbon Reservoir in Nanpu Depression by Acoustic Logging Methodology

DONG Yue-xia，LI Su-mei，CHEN An-ding，WANG Zheng-jun，ZHANG Peng，CHEN Jun

2015, 29(4): 922-929.

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Industrial petroleum was discovered from Palaeozoic deep horizons in the Nanpu Depression, Bohai Bay Basin, which suggests significant deep petroleum potential in the area. One of the issues in exploration is forecasting favorable place for prospecting in the area. Hydrocarbons expulsion downward from the source rocks immediately overlapped buried hill should be useful in this aspect. Acoustic logging combined with geochemical approaches was utilized in this study to identify hydrocarbons expulsion and evaluate hydrocarbon potential. After a detailed correlative acoustic logging and geochemical study, a combined hydrocarbons expulsion model of the source rocks in the Nanpu Depression was established, which was used to investigate hydrocarbons expulsion of the source rocks from 33 wells in the Nanpu Depression. The results suggest that the average depths of the source rocks with the hydrocarbons expelled downward into the burial hill in the No.2 and 3Tectonic Belts are about 248 m and 358 m, respectively, and only 35 m for the No.1 Tectonic Belt. No obvious hydrocarbons expulsion into burial hill was observed in the No.4 and 5 Tectonic Belts in the depression. This result coincides with the hydrocarbons discovered up to now in the burial hills. We suggest that these factors including contact style between the source rock and the burial hill, the position of the hydrocarbon kitchen, the thermal maturity of the source rocks, the volcanic rock acting as barrier bed and faults developed, have a controlling of the amounts and characteristics of the hydrocarbons expelled by the source rocks and charged into the burial hill in the Nanpu Depression. A comprehensive study of hydrocarbons expulsion, migration and accumulation indicate that the No.2 and 3 Tectonic Belts and next the No.1 Tectonic Belt are prospective areas with burial hill hydrocarbons reservoir developed. This study also indicated that acoustic logging could be an important tool identifying hydrocarbons expulsion and would be useful in petroleum exploration.

Control of Faults on the Hydrocarbon：A Case Study in Nanpu Sag

PEI Li-xin，GANG Wen-zhe，GAO Gang，MENG Ling-jian，LI Jie，HUANG Zhi-long

2015, 29(4): 930-936.

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Different vertical accumulation of hydrocarbon in the faults means different enrichment degree and different maturity of hydrocarbon. According to different vertical accumulation of hydrocarbon in the faults, vertical distribution of hydrocarbon can be predicted from the analysis on the found hydrocarbon show and variation of reservoirs. Combination pattern of faults has a control on the oil-gas migration and accumulation; parallel combination results in hydrocarbon enrichment near the hydrocarbon source kitchen and scarcity far from that in the plane, whereas vertical combination may result in hydrocarbon enrichment both near and far from that; Comb pattern transports more hydrocarbon to the shallow reservoirs and umbrella pattern transports less hydrocarbon relatively in the profile.

Analysis of Geological Controls on the Lower Cretaceous Continental Shale Gas Accumulation in Suibin Depression，Sanjiang Basin

HE Jian-hua1,2,3，DING Wen-long1,2,3，BAO Shu-jing4, LI Ang1,2,3，PANG Fei4，TONG Ch

2015, 29(4): 937-949.

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Suibin depression is one of secondary tectonic units in the western Sanjiang Basin. As an unique sedimentary basin in Mesozoic, which developed marine and marine-continental transitional formations in the northeast China, conventional oil-gas breakthrough has not been made. So the study of unconventional oil-gas geology is of great importance. The Chengzihe-Muleng coal-bearing formation organic-rich shale in the Lower Cretaceous, the Mesozoic, are the main source rock in these areas. By analysis of the distribution, geochemical indicators, reservoir characteristics and gas-bearing of the Lower Cretaceous shale in Suibin depression, the results indicate that the Lower Cretaceous dark shale is broadly distributed (＞2,000 km²) and extents widely in large thickness (＞1,000 m) with a high TOC content (＞1.3%), a high thermal maturation (1.19%) influenced by the local volcanic activity, and typeⅡ₂-Ⅲ kerogens. The shale reservoir has high brittle mineral content with a large proportion of the quartz and feldspar content, which indicates that the shale can be well fractured. Additionally, the abnormal responses of gasbearing shale on well logging also indicate that it is qualified for the geological conditions to accumulate shale gas. Compared with the main parameters of North American marine and China marine or lacustrine shale, the favorable area of shale gas exploration in Suibin depression is located in the northern of PuyangNandalinzi sag and the southern of Jixian-Dongrong. And Chengzihe Formation shale may be the most favorable layers for shale gas exploration, followed by Muleng Formation shale, with a huge resource potential of shale gas.

Application and Utilization of CO₂ Flooding in Low-permeability Reservoir

CHEN Zu-hua

2015, 29(4): 950-957.

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As a kind of tertiary oil recovery technology, CO₂ flooding can substantially improve the oil recovery ratio which in China started late on its researching and applying, and now is more likely to be sporadic pilot tests. After more than ten years of exploration in Qintong sag, Subei basin, CO₂ flooding pilot tests has been conducted and applied in 5 low permeability oil fields. This paper studied the 5 low permeability oil fields with one-dimensional tubule simulation and reservoir numerical simulation, and on this basis, carried out researches of gas injection timing, the slug size, and the gas injection parts. This text stated that improving the miscible pressure in the early injection can more effectively shorten the two phase transition zone, increase the CO₂dissolution rate, reduce the viscosity of oil phase and interfacial tension of oil and gas, thus,can increase the degree of miscible. In terms of the low permeability reservoir in Subei basin, early injection as well as large size slug can be considered as a mature and effective method to improve oil recovery.

Geochemical Characteristics of Groundwater in Chengjiang Area of the Hongshui River in Guangxi

FAN Lian-jie，PEI Jian-guo，DU Yu-chao，LU Li，LIN Yong-sheng

2015, 29(4): 958-966.

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Based on the groundwater data obtained from the karst groundwater pollution investigation and evaluation in Southwest China, geochemical characteristics of 30 elements or indicators on 26 karst groundwater samples which have been analyzed and tested are studied in this paper. The type of hydrochemical component, characteristics of ion contents relativity, distribution characteristics and influence factor are described. Results indicate that the hydrochemical type of karst groundwater is Ca-HCO₃ or Ca·Mg-HCO₃；the background values of the items are lower than the values of grade Ⅲ of the National Water Standard. The results show that only several indicators (such as Zn, Se and Hg) in karst groundwater of the study area have changed significantly and are unevenly distributed．Other indicators have changed insignificantly and are evenly distributed in groundwater. All the elements have no correlation with pH, while there is clear positive correlation among HCO^-3, Ca²⁺, Mg²⁺, K⁺, Na⁺, SO^2-₄, NO^-3, I^-,total hardness. HCO^-3, Ca²⁺ and Mg²⁺ play a decisive part on the elemental relationship. The spatial distribution of elements assumes sheet distribution characteristics, which is controlled by the geologic background, geographic condition and human activities.

Subarea of Hydrogeological Parameters and Numerical Simulation of Groundwater Flow Field in the Unconsolidate Confined Aquifer

CHEN Lu-wang，HE Jian-dong，SHI Xiao-ping，XIE Wen-ping，FENG Xiao-qing

2015, 29(4): 967-974.

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In order to study hydrogeological parameters of unconsolidated confined aquifer of North China type coal field and its significance to groundwater numerical simulation, the fourth aquifer of the Quarternary (4th aquifer) in Qidong coal mine, Sunan mining area, Huaibei coal field, Anhui Province, is studied as an example. Based on the hierarchical analysis-fuzzy comprehensive analysis method, the study area is divided into ten divisions under hydrogeological parameters of 4th aquifer. The hydrogeological parameters of each division are properly determined, which are used for dynamic numerical simulation of groundwater flow under mining circumstances. The results of numerical simulation show that the variation of groundwater flow field is unconspicuous in the process of mining of shallow coal seam from 2008 to 2012 in Qidong coal mine, but the differences of groundwater level between the north and the south increases year by year; therefore, groundwater always flows from the south to the north, which hydraulic gradient decreases in the north and increases in the south gradually. The results also show that the decrease zone and the increase zone of hydraulic gradients are separated by the Weimao fault with a dip of 60-70 degree and a slip of 10-320 meters. It is concluded that a fault with great dip and slip in the bedrock are keys to hydraulic gradient anomaly in the overlying unconsolidated confined aquifer.

Susceptibility Assessment of Debris Flows in the Semiarid Region Based on AHP Method: An Example from the Benzilan-Changbo Segment of the Upper Jinsha River

LI Yan，CHEN Jian，XU Chong，LI Ling-jing，YAO Xin

2015, 29(4): 975-982.

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The semiarid region is characterized by sparse vegetation and rich source of loose sediments, which is favorable for the development of debris flows. A typical example was selected from the Benzilan-Changbo segment of the upper Jinsha River. Based on field investigation and interpretation of remote sensing images, the distribution of debris flows in this area was studied and six factors were selected as the assessment index, including rock type, structural fault, slope gradient, relative relief, annual average rainfall and normalized vegetation index. GIS technology and AHP (analytical hierarchy process) method are combined to build assessment model of debris flow susceptibility for semiarid region, then the grid map of debris flow susceptibility assessment in the study area was obtained. Dividing the study area into small basins, performing the statistical analysis and classification based on small basin units, the debris flow susceptibility assessment map of the study area was finally obtained. The susceptibility assessment map show that the high susceptibility area mainly distributed in the northeast, central and southwest along the banks of the Jinsha River; the area with high and little high susceptibility accounts for about 1,040.9 km²，occupying 35.7 percent of the study area. In addition, after using test curve to inspect the results of debris flow susceptibility assessment, the area of debris flow in high and slightly high susceptibility accounts for about 651.4 km²，occupying 51.1 percent of the total debris flow area. It indicates that the result is reasonable.

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