Table of Content

20 September 2015, Volume 21 Issue 3

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EffectsofPaleosalinityonClayMineralAssemblagesandChlorite CompositioninMudstoneofTabeiUplift,Xinjiang,China

ZHAOMing*,JIJunfeng,CHENXiaoming,CAIYuanfeng,WUChangzhi,CHENYongquan,WUBing

2015, 21(3):  365. 

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 Clay mineral assemblages and chlorite composition are often analyzed to study diagenesis of sediments and burial paleotemperature in basins. A number of previous studies show that clay mineral assemblages and chemical compositions of chlorites are related to the progressive burial depth/temperature in many sedimentary basins. However, some phenomena show that this opinion could not explain features in mudstones from some particular regions on the Earth. In order to investigate the main factors that influence diagenesis in basins, this paper focuses on the characteristics of clay mineral assemblages, and composition of chlorites in the mudstone in Xinjiang Tabei Uplift, China, as well as the relationship between the characteristics and the paleosalinity of the basin. The results show the following four points. (1) The assemblages of the clay minerals in the depth range of 2777.37 m to 4604.41 m, which were generated during Jurassic Period and Eogene Period (J1-N2), are I+Chl and I+Chl+Ka; while the assemblages in the depth range of 5071.52 m to 5299.37 m, which were generated during Triassic period (T1), are R0I/S+ Chl+I and R0I/S +Chl. (2) The diagenetic chlorite in this area is brunsvlgite in TypeⅡb polymorphism; its composition features show that (a) the average value of octahedral occupancy is 11.532; (b) the octahedral Al amount is obviously greater than the tetrahedral Al amount; (c) the average value of（Fe+Mg）is 4.016; (d) the ratio of Si/Al is higher than 1. (3) According to the distribution of the mineral salts and the data of ancient salinity in the area, it is proposed that paleosalinity was the main factor that affects the clay mineral assemblages and the compositional changes of chlorites in the area. In this paper, paleosalinity is utilized to explain an abnormal phenomenon in the clay mineral assemblages. There is not a disorderly mixed layer of illite / smectite (R0I/S) in the samples from the depths less than 5000 m, while there is a disorderly mixed layer of illite/smectite(R0I/S) in the samples from the depths greater than 5000 m. Also, it is revealed that the composition of chlorites is affected by the paleosalinity in a certain depth range (2777.37~4405.27 m) and certain ancient salinity conditions (Sr/Ba ratio≥0.4 with the appearance of salt minerals). While the salinity is higher, its influence is greater. With the increase of salinity, the contents of Al, ⅣAl, Na, Na2O, Al/Si in chlorites increase, while Si/Al decreases. The temperature obtained by the chlorite composition thermometer increases with higher salinity, which indicates that the temperature calculated by the chlorite composition thermometer cannot represent the actual burial paleotemperature in the area. (4) Between the composition of the chlorites and the host rocks in the area, such as SiO2chl-SiO2rock and FeOchl -FeOrock, there are negative correlations, which are not disturbed under the influence of paleosalinity.

Isolationand Sr²⁺ MineralizationMediatedbyCarbonate MineralizationBacteria

XU Fengqin, DAI Qunwei*, HOU Lihua, ZHAO Yulian, WU Qinqin, QIN Yonglian,

2015, 21(3):  376. 

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 Soil pollution has increasingly become a serious problem, especially by radionuclide pollution, and has attracted wide attention. Microbial remediation of radionuclide contaminated soil has been studied and proposed as a potential strategy. Because some microorganisms in soil can consolidate heavy metal to form mineralization, heavy metal inos can be removed from soil. A strain of carbonate mineralization bacterium was isolated from the soil and was used for the mineralization of Sr2+. The final removal rate of 1.0 g/ L and 0.5 g/L Sr2 + was as high as 98% and 99% , respectively. Scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR) analyses revealed that the mineralized product was strontium carbonate. It is suggested that indigenous bacteria can survive soil radionuclide toxicity and strontium ions could be mineralized as stable carbonate minerals, which indicates important practicability for radionuclide or heavy metal bioremediation. Also, the finding will provide new insights into carbonate biomineralization.

FungalInvolvementinBiogeologicalProcessesandApplication to EnvironmentalBioremediation

LI Han, CAI Lin, YAO Qizhi, ZHOU Gentao

2015, 21(3):  382. 

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 In the Earth's lithosphere, fungi are of fundamental significance as organism decomposers, animal and plant pathogens and symbionts, being ubiquitous in subaerial and subsoil environments. The ability of fungi to interact with rock or mineral substrates through their growth and metabolic activities, makes them an important participator in geochemical processes. The principal roles include the fungi-promoted mineral weathering, mycogenic mineral formation, nutrient and metal elements transformation and immobilization. In recent years, the bioleaching technologies derived from biological weathering have beneficial applications in the biomining, bio-beneficiation, as well as the bioremediation of contaminated soils and industrial solid waste. Moreover, the research on fungi as the biosorbents reveals that fungi can be applicable to remove metal or organic pollutants from the industrial wastewater and contaminated groundwater. Therefore, it is fully essential to understand the fungal activities encompassed within geomicrobiology. This mini review summarized current progresses of biological geological process for fungi, with focuses on biological weathering,biomineralization and environmental bioremediation, and future perspectives were proposed to better understand the important fungal functions in geomicrobiology and to catalyze further research in the field.

“DolomiteProblem”andExperimentalStudiesof DolomiteFormation

ZHANG Yifan, MA Yifei, YAO Qizhi, QIAN Feijing, WANG Yuhan, LI Han, ZHOU Gentao

2015, 21(3):  395. 

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Dolomite problem is undoubtedly one of the most interesting and confusing problems in geology. As a common carbonate mineral, dolomite is abundant in geological history but rarely occurs in modern ocean sediments. It is nearly impossible to precipitate dolomite below 100℃ . Dolomite, [CaMg(CO3)2], has a cation ordering structure and its space group is R-3. Additionally, it is thermodynamically stable under the condition of earth's surface. Although researchers tried to mimic physical and chemical conditions of natural environments which can form dolomite, these experiments still can not successfully precipitate ordered dolomite. Fully ordered dolomite can only form in hydrothermal experiments upper 200℃. It seems that the formation of dolomite is a dynamically controlling process. Recently, microbial dolomite model has been widely accepted. In this model, microbial activity is considered as the key of dolomite formation at low temperature. Many microbial mineralization experiments have confirmed that the existence of microorganisms canindeedpromotetheformationofhigh-magnesiumcalcite.Solving“dolomiteproblem”cannotonlyhelpunderstandingthegenesisof dolomite, but also promote the development of mineralogy theory. This review summarized current progresses of dolomite synthetic experiments,includingexperimentsathighandlowtemperaturesandmicrobiallyinducedexperiments.Wealsoclarifiedthelimitationsof currentunderstandingto“dolomiteproblem”.Futureperspectiveswereproposedtobetterunderstandandfinallysolvedolomiteproblem

ExperimentalStudyonMicrobialOxiadationofRhodochrositeby PseudomonasputidaMnB1

CHEN Xiaoye, LU Xiancai*, LI Juan, LIU Huan, XIANG Wanli, ZHANG Rui

2015, 21(3):  407. 

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Rhodochrosite (MnCO3) is a solid Mn(Ⅱ) origin mineral and its oxidation into Mn oxides is a very common phenomenon. Although microbially mediated oxidation of Mn(II) to Mn oxides have been demonstrated in previous studies, the mechanisms of bacteria how to dissolve and oxidize using a solid Mn(II) origin are poorly understood. In this study, we examined the role of Pseudomonas putida MnB1 cell in enhancing dissolution and oxidation of rhodochrosite from Wuzhou, Guangxi province. By using Field Emission Scanning Electron Microscopy (FESEM), Scanning Transmission X-ray Microscopy imaging analysis (STXM) as well as other techniques, the changes of the mineral surfaces and the distribution of manganese in cells were identified. The result show that bacteria significantly promote the dissolution of the rhodochrosite. Moreover, the contribution of bacteria to the oxidation of rhodochrosite was discussed. The results will enrich the research of secondary manganese deposits

OntheTectonicPropertyoftheProvenanceAreaoftheUpper TriassicYanchangFormationinLongdongArea,OrdosBasin

ZHU Xiaomin，LIU Fen，ZHU Shifa，XU Liming，NIU Xiaobing，LIANG Xiaowei

2015, 21(3):  416. 

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 Tectonic setting and orientation of the provenance area of the Yanchang Fm remain unclear. To understand the tectonic property of the provenance area of this formation, this paper describes the sandstone petrologic characteristics, geochemical characteristics and distribution patterns of rare earth elements of Chang8 to Chang6 Member in Longdong area, Ordos Basin to determine the tectonic settings and diversity of provenance rocks in different areas. The results show that source rocks during Chang8 to Chang6 sedimentary period mainly came from volcanic arc source and transitional continental source associated with fold-thrusting, but source rocks of Chang7 and Chang6 in Huanxian and Yanwu, western basin were different from Chang8, part of which came from stable craton continental source. The REE abundance indicates that REE model was characterized by enrichment in light REE, depletion in heavy REE, and negative Eu anomaly. The provenance was involved with granitic crust materials which were characterized by containing more felsic rocks. Comparing samples from the northeast, northwest, southwest, and south Longdong area with various lithologies from ancient land surrounding the basin, this study shows that REE distribution patterns generally had the right-leaning

ProvenanceAnalysesoftheLowerThirdMemberofthePaleogene ShahejieFormationinSanhecunSub-sag,ZhanhuaSag

WANG Yunhe, LIU Qianghu, ZHU Xiaomin*, ZHU Shifa, JIANG Long, GENG Mingyang

2015, 21(3):  426. 

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Sanhecun Sub-sag in Zhanhua sag is an important target zone for future exploration due to its large sediment thickness, and low level of exploration in the lower third member of Shahejie Formation (Es3L). Detailed depiction of the provenance system using Es3L is of practical significance for reconstructing depositional system and forecasting favorable areas. This paper analyzes in detail the provenance system of Es3L in Sanhecun Sub-sag from various aspects and at different levels: the source area and the depositional area are macroscopically distinguished, while sediment transport pathways (valley I to VI) of the southwestern and southern are quantitatively described according to palaeogeomorphology; the types of sedimentary facies and prime material components in deposition area are identified based on cores and debris compositions; the sediment-dispersal patterns of “source-to-sink” systems and the spatial and temporal evolution of fans in the basin are finely pictured according to seismic profile analyses and stratal slices. The results show that of the southwestern gentle slope zone (about 3°) was originated from the western section of Chenjiazhuang Uplift (transport by valley I and II), which developed a gravel-rich fan delta and is mainly composed of carbonates debris; while of the southern slope break zone (about 8°) was originated from the eastern section of Chenjiazhuang Uplift (transport by valley III, IV, V and VI), which developed a sand-rich fan delta and contain quartz or crystal quartz grains. The scales of fan delta system in the deposition area have a positive correlation with the width-to-thickness ratios and the length of sediment transport pathway. The vertical changes show that the fan scale of lowstand system tracts (LST) of Es3L was larger than its highstand system tracts (HST), and the provenance system of convergence zone has transferred from the southern to the southwestern.

FineStratigraphicCorrelationofBraidedDeltaFormationinSparse WellArea：ACaseStudyoftheWenchangFormation inHZ-AOilField,HuizhouDepression

GE Jiawang, ZHU Xiaomin, HUANGHandong, SONG Shuang, ZHOU Qinbo, DONG Xiaoyun

2015, 21(3):  440. 

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 The oil producing interval of braided river delta reservoir of the HZ-A oil field is buried at the depth of more than 3500 m. It is characterized by low frequency seismic data, sparse wells distribution, and big sand-body thickness variation in target zones, which lead to great difficulties in stratigraphic correlation. In this paper, an integrated and practical method of isochronous correlation is put forward. Specific steps are as follows. First, the braided river delta sedimentary characteristics are achieved from the detailed analysis of its provenance and catchment system; Second, based on precise well-to-seismic calibration and fine seismic facies analysis, three-order stratigraphic framework and sub-layer correlation trend are obtained; Based on geophysical inversion, an inversion method for small-scale correlation is proposed to the sub-layer division and contrast; Finally, high resolution sequence stratigraphy theory combined with the correlation of fluid properties, sedimentary micro-facies sequence is applied to logging cycle division from big to small, and the stratigraphic subdivision and sand body correlation of target interval is accomplished. This method can effectively reduce the uncertainty of sub-layer division and contrast. Advantages have been achieved in the application of this method for fine-scale stratigraphic classification and correlation of braided river delta in the HZ-A oilfield.

Micro-faciesModelingofAlluvialFanReservoirBasedonGeological VectorInformation:ACaseStudyontheTriassicLowerKaramay Formation,YizhongArea,KaramayOilfield,NWChina

FENG Wenjie, WU Shenghe*, XIA Qinyu, LI Junfei, WU Shunwei

2015, 21(3):  449. 

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 As alluvial fan reservoir is typical in non-stationary distribution, the traditional modeling algorithm based on the steady-state assumption cannot simulate it accurately. On the basis of full analysis of the reservoir distribution, a case study of alluvial fan reservoir on the Triassic Lower Karamay Formation, Yizhong Area, Karamay Oilfield was carried out to integrate modern sediments, underground dense well group, outcrops and other information, using the latest Vector Information based Multiple-Point Simulation to reproduce a fine and reasonable three-dimensional geological model of reservoir architecture, which can be used as a reference for similar reservoir stochastic simulations. First, based on modern sediment and underground alluvial fan reservoir architecture analysis, an alluvial fan training image in line with the study area was constructed under the instruction of pattern guiding and scale constraints. Second, the vector coordinate system of an alluvial fan was constructed. Then the vector information of both training image and the target modeling area was characterized in this system. Finally, the reservoir architecture was reproduced by using the Vector information based on the Multiple-Point Simulation method. The reliability analysis of the realizations was performed. The result shows that the realizations are faithful to well data. Alluvial fan facies distribution in the model is suitable to geological model. Architecture element characteristics including shape configuration, distribution, combination style and scales matches training image and understanding reservoir architecture acknowledgment perfectly.

TheDevelopmentCharacteristicsofTightClasticReservoirs intheLowerPermianFengchengFormationin Wu-XiaAreaoftheJuggarBasin

ZHU Shifa, LIU Xin, MA Xun, MA Aiyu, ZHU Xiaomin*, JIA Ye

2015, 21(3):  461. 

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 Typical tight clastic reservoirs were developed in the Lower Permian Fengcheng Formation in Wu-Xia area in the northwestern margin of the Junggar Basin. Based on the geological and geophysical data, the reservoirs′ characteristics have been studied. The results show that the fans are relatively large during the early and late periods of the Fengcheng Formation, with small-scale slump turbidite fans and shoal-bar sand bodies sporadically distributed. The water bodies expanded and the fan bodies were not developed in the middle stage of the Fengcheng Formation. The physical properties of shoal-bar sandstones are better than those of the sandstones of fan delta front and turbidite fans. Glutenites with high maturity are high-quality reservoir rocks. The volcanic materials in the rocks had an impact on the reservoir diagenetic evolution, thereby affecting the reservoir quality. The plastic tuff debris reduced the compressive strength; the tuff debris were exposed to the hydrolysis and alteration during the burial process, precipitating different minerals, which destroyed the porosity; the dissolution of the feldspar, rock debris, matrix and various authigenic minerals increased the porosity to some extent. The clastic reservoirs in the Fengcheng Formation are overall tight sandstones with low porosity and permeability, and the development of “sweet spots” are under the compound control of many factors, including the sedimentary facies, rock components, particle sizes, maturity, and the development of dissolution.

TestingaNewMethodforQuantitativeAnalysisof AmorphousSiO2 inTerrestrialShale

LIU Guoheng, GAO Xiaoyu, CHEN Changchao

2015, 21(3):  471. 

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The Yanchang Formation shale of Ordos Basin contains a certain amount of amorphous SiO2, which is proved by SEM observations and X-ray diffraction analyses of bulk rocks. Three methods proposed to calculate the quantity of amorphous SiO2 have their own flaws. The disadvantages of chemical denudation are experimental period and dissolution of other minerals. XRD quantitative analysis possesses high personal errors in the integrated intensity of dome-shaped scattering curves in XRD spectrum of amorphous SiO2. The doping method has high deviation and needs to compound standard sample. On the basis of summarizing previous researches, a new method that combines QEMSCAN and XRD is proposed for calculating the amorphous SiO2 in a multiphase system. The new method avoids the flaws in the three approaches, and calculates the amount of amorphous SiO2 indirectly according to the quantities of quartz and SiO2 measured, respectively. However, super high experimental cost is the main factor to limit the method for wide use.

ImplicationsofMineralTexturesforMagmaMixing:ACaseStudy ofPyroxenesfromHoloceneRuapehuAndesite,NewZealand

HONG Wentao, WANG Tiangang, XING Guangfu, YAO Zhongyou, LIN Peijun

2015, 21(3):  478. 

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Mineral textures and zoning provide a way to investigate the evolution process of an open magmatic system. In this study, petrographic and EMPA mineral analysis have been taken in the pyroxene phenocrysts from Holocene Ruapehu andesite. These pyroxenes are augite and enstatite, and can be divided into three types based on their texture and compositional features, including homogeneous pyroxenes (HP), green-core pyroxenes (GCP) and skeletal pyroxenes (SP). HP pyroxenes are crystallizing in a steady, showing homogeneous composition from core to rim, and lacking any dissolution texture. GCP exhibit the core-mantle-rim texture. Comparing with the core and the rim, the mantle zones show higher En, Mg#, CaO, MgO and Cr2O3 contents, while lower FeOT, TiO2 contents, displaying clearly reverse zoning. Broken cellular core of SP show similar compositions to the crustal meta-igneous xenolith,indicating a xenocrystic origin for the SP and crustal contamination during magma ascent. The reverse zoning of pyroxenes and other petrographic features suggest that the mixing mainly take place in the rigid and mush zone of shallow magma chamber, and just prior to the eruption.

InvestigationofReverseZoninginPyroxenePhenocrystsfrom WudalianchiPotassicLavasanditsConstraintsonMagmaticEvolution

MAO Fugen, CHEN Lihui*, YANG Huairen, ZENG Gang, LIU Jianqiang

2015, 21(3):  492. 

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 Clinopyroxene phenocrysts with reverse zoning have been observed in Wudalianchi potassic lavas. The cores are salites characterized by lower Mg# (68~77), TiO2 (0.23~0.50 wt.%), Cr2O3 (<0.06 wt.%) and higher Al2O3 (3.4~5.0 wt.%), Na2O (0.43~0.78 wt.%), FeO (8.8~11.0 wt.%) and MnO contents than those of the exteriors. Normalized REE patterns of the cores are relatively flat, and they also exhibit prominently negative anomaly of Eu and Sr (Eu/Eu* =0.35~0.63, Sr/Sr* =0.03~0.17), suggesting an origin from metamorphic rocks in equilibrium with plagioclase. In the plot of Mg#-TiO2, the overall composition of the cores falls within the compositional range of clinopyroxenes in lower crustal low-Mg granulites from North China Craton. As a result, the cores are inferred to be xenocrysts from granulites in the lower continental crust. The exteriors and normal pyroxene phenocrysts are similar in their compositions, which are higher in Mg# (81~85), TiO2 (0.40~1.65 wt.%), Cr2O3 (0.03~0.25 wt.%), and lower in Al2O3 (2.1~3.4 wt.%), Na2O (0.34~0.63 wt.%), FeO (4.6~6.6 wt.%), MnO. Their LREE and HREE are highly fractionated (La/Yb)N=3.23~7.89, which are consistent with the basaltic whole rocks. The exteriors were in equilibrium with the host magmas, as is confirmed by both major and trace element modeling based on their partition coefficients. Thus the exteriors are suggested to be magmatic pyroxenes formed by overgrowth on the eroded cores. The Mg# of Wudalianchi normal pyroxene phenocrysts are negatively correlated with TiO2 contents, pointing to a certain extent of magmatic evolution in crustal depth, consistent with the gradual increasement of Al2O3 and Na2O contents from the inside out of the exteriors. The granulite facies nature of the cores further constrains the evolution to have occurred in the lower continental crust. Thermobarometer estimations also suggest that the crystallization of normal pyroxenes and exteriors of reversely zoned pyroxenes were in serial magma chambers in the lower crust. Pyroxene phenocrysts crystallized in a later stage are more enriched in incompatible elements than those of earlier pyroxenes, indicating that fractional crystallization have enhanced the enrichment of incompatible elements of Wudalianchi basalts. Calculated melts in equilibrium with pyroxene phenocrysts are extremely similar with the ultimately erupted lavas in their trace element patterns. Considering the remarkably uniform whole-rock trace element patterns, we suggest that the evolution of Wudalianchi basalts in the crust were mainly controlled by the fractional crystallization in magma chambers, and crustal contamination (also mixing with crust-derived magmas) has had negligible effects on whole rock compositions.

ZirconU-PbAgesandGeochemicalCompositionofthePolunshan PlutonintheTenchongBlock,WesternYunnan

WU Jiade, WANG Yan, XIE Qinglu, QI Yue, LI Junhui, HE Jianfeng, CHEN Fukun

2015, 21(3):  508. 

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 Mesozoic to Cenozoic magmatic activities, widely distributed in the Tethyan belt of western Yunnan, are induced by the long-time complicated orogenic processes. Zircon U-Pb age data and geochemical characteristics of the Polunshan granite, exposed in the Tenchong block, are reported in this study. The Polunshan granite pluton is composed mainly of porphyritic coarse-grained granodiorites. Geochemically, this granite is characterized by high alkali contents and belongs to the high-potassic calc-alkaline rock type. It enriches in large-ion lithosphile elements and depletes in high field-strength elements (Nb, Ta, Ti and P). Results of the zircon U-Pb dating suggest emplacement ages of 66~63 Ma for the magma(s) of the Polunshan granite, pointing to a magmatic product related to the closure of the Neo-Tethys Ocean. Many analysed zircon grains or crystal domains have high contents of U and Th. They yield U-Pb ages of about 35~30 Ma, significantly younger than emplacement time of the granite, but similar to the age of deformation or metamorphism of the Gaoligongshan metamorphic belt. This phanomenon implies that the U-Pb isotopic system of those zircons of high Th-U-contents was reset during the late thermal event. The Polunshan granite exhibits entrenchment feature in Sr-Nd isotopic composition, with initial 87Sr/86Srratios of 0.7158 to 0.7164 and initial εNd values of -14.5 to -15.3, corresponding to Nd modal ages of 2.04~2.10 Ga, suggesting that Paleoproterozoic crustal material as a major source of the magma(s).

DiscoveryoftheEarlyCarboniferousGraniteinGuyang,Inner Mongolia：EvidencefromZirconSHRIMPU-PbDating

LIU Chao, SUN Beilei, WU Jing,ZENG Fangui*

2015, 21(3):  519. 

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：Guyang area is located in the northern margin of the North China Craton, and Neopaleozoic granites are widespread there. In these granitic intrusions, granodiorite occurs as late intrusive veins, and diorite enclaves can be found in the granodioritic veins. For these three kinds of rocks, major and trace elements are measured to constrain their geochemical characteristics, while zircons are measured by SHRIMP to provide U-Pb ages. All these samples are calc-alkaline series, and enriched in LILE and LREEs, and show a mild fractionated REE. On a primitive-mantle normalized spidergram, these rocks show distinctly negative Nb, Ta, Ti anomalies and positive Rb, Th, K anomalies. U-Pb dating of zircon yielded crystallization ages of 330.8Ma, 324.7Ma, and 329.2Ma for the granite, the granodiorite and the diorite, respectively, which belong to the early carboniferous.The early Carboniferous magmatic rocks in northern margin of North China Craton should be associated to the subducting of Paleo-Asian Ocean to the North China plate, since this occurred before the convergence of the Siberia Craton and the North China Craton. Granites should be generated from remelting of continental crust, and granodiorite probably produced by mixing granitic magma and dioritic magma.

RockMagnetismoftheCenomanian/TuronianandSantonian/ CampanianBoundaryStratainGongzha,SouthernTibet

MA Lifeng, LI Yongxiang*

2015, 21(3):  529. 

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：In order to study the paleoceangraphic conditions following the mid-Cretaceous oceanic anoxic events （OAEs），we have carried out a rock magnetic study of the Cretaceous shallow marine strata at the Cenomanian/Turonian and Santonian/Campanian boundaries at Gongzha，Southern Tibet, China. The results show that mineral magnetic properties at the two intervals are largely similar including mineral content and particle size, except that the Cenomanian/Turonian boundary statra contain high coercivity magnetic minerals such as hematite and goethite; whereas. Santonian/Campanian boundary strata are dominated by low coercivity minearls such as magnetite. Becaue sea levels at these two intervals are similar， the effects of sea level change on the magnetic characteristics are minimal. The difference in the types of magnetic minerals is probably mainly due to changes in the marine environment. The presence of high coercivity magnetic minerals in the Cenomanian/Turonian boundary strata, but absence in the Santonian/Campanian boundary strata suggest that the shallow marine condition at Gongzha during the Cenomanian/Turonian was more oxic than that during the Santonian/Campanian interval. This observation is different from what is seen in deep ocean where anoxic conditions characterized the Cenomania/Turonian interval and oxygen-rich conditions occurred during the Santonian/Campanian interval. It can be concluded that the deep-bathyal environment represented by Gyantse area and the shallow marine environment represented by Gamba-Tingri area responded differently to climate change in the mid-Cretacrous. And the evolution of the shallow water and deep water were probably different during these time periods and the ocean circulation in these periods may be more complicated than previously thought.

TheStructuralCharacteristicsinHuangqiaoAreaintheLower YangtzeRegionandItsRelationshiptoOilandGasAccumulation

SHEN Shuxin, LI Yiquan, CUI Jian,YUAN Jingwen, JIA Dong*

2015, 21(3):  538. 

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 Huangqiao area is situated at the ramp zone in the Lower Yangtze region, which was subjected to multi-staged tectonic deformation events, and preserves complete Mesozoic-Paleozoic marine sediments, which contain multiple sets of source rocks, with fine prospects of petroleum exploration. Based on the detailed structural interpretations of the 3-D seismic profiles in Huangqiao work area and forward kinematic modeling, this paper analyzes its structural deformation characteristics and the deformation processes. The middle-upper Paleozoic and lower Mesozoic strata developed several fault-related folds by forward propagation, then formed the fault-related folding in the opposite direction in the structural front under the effect of the SE-NW regional stress in the Huangqiao area, which shaped the face to face verging structures at the middle and northwest of Huangqiao area and resulted in the strong uplift and denudation. The total structural shortening rate exceeds 47.55% on the regional cross section in this study. Then the regional stress transferred to NW-SE-trending extension, as a result of which there developed some negative inversion faults in the southeast of the work area and the inversion amount increased from the southwest to the northeast of the work area. This extensional event led to the fault back-slip, forming the half grabens which were filled with the upper Cretaceous strata, and causing some damages to the face-to-face structures. Combining previous research achievements of hydrocarbon accumulation, this paper discusses the Huangqiao structural deformation and its relationship to the oil and gas accumulation, and proposes the anticline at face to face verging structure, its footwall and the anticlinal Guangling structure in the southeast of Huangqiao area as the favorable oil and gas blocks. Therefore, the study of the structure in Huangqiao region, can not only help better understand the deformation characteristics and evolution history of Huangqiao structure, but also provide clues for the oil-gas exploration and development.

MajorElementsGeochemicalCharacteristicsoftheGranite-type LateriteProfileinGanXian,Jiangxi Province

XIONG Pingsheng

2015, 21(3):  553. 

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 The chemical weathering intensity and element migration features of the Granite-type Laterite Profile in Tiancun, Gan xian are studied in this paper. The results indicate that: (1) The laterite is mainly composed of SiO2, Al2O3, Fe2O3, which account for over 90% of the total and the SiO2is the highest. The content of soluble constituents such as K2O, CaO, Na2O, MgO, are relatively lower. (2) Major element geochemistry behavior present the migration leaching during the process of weathering in the Granite-type Laterite Profile and the degree of migration is strengthened gradually from the bottom to the top. CaO, Na2O migration amount are 97.34%, 94.94% on average, respectively, and belong to the strong migration elements; MgO, K2O, SiO2 average migration quantity are 52.50%, 39.89% and 22.72%, respectively, belong to the easy transition element, the element characterized by high concentration was Fe. (3) We found the Granite-type Laterite Profile suffered strong chemical weathering in hot and humid environment in Gan xian and the weathering intensity became gradually weak form the top to the bottom, on the basis of the comprehensive analysis of the coefficient of aluminum and iron, chemical alteration and weathered eluvial.

EffectofHeterogeneityonTemporospatialVariationsof WaterFlowinanUnsaturated-saturatedSystem

YANG Chen, ZHANG You-Kuan, LIANG Xiu

2015, 21(3):  559. 

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 Under white noise infiltration, the temporospatial variations of pressure head in an unsaturated-saturated system were studied. Both the homogeneous and heterogeneous systems were considered. Damping effect of the system and effect of the heterogeneity on the fluctuations of the water flow were analyzed. Results show that both the homogeneous and heterogeneous systems damp the fluctuations of the pressure head as the variance, auto-covariance and power spectrum decrease with depth. The fluctuations of pressure head are non-stationary at early time due to the initial conditions and become stationary at late time. Heterogeneity strengthens the fluctuations of the pressure head and weakens the short-term correlation. The fluctuations of pressure head are mainly caused by the heterogeneity of the system.

StudyontheFailureCharacteristicsoftheOverburdenStrata InducedbyMiningofUnderlyingOrdovicianLimestoneNappeAquifer

CHU Chengcheng

2015, 21(3):  569. 

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 Similarity model test and numerical simulation were combined to analyze failure characteristics of the overburden and the laws of ground subsidence, which was induced by mining of the underlying Ordovician limestone nappe aquifer. The comparative analysis of empirical formula, numerical simulation, and similarity model test shows that under this special geological condition, without the consideration of the influence of seepage, the height of water flowing in a fractured zone and caving zone is 14.0~19.1 times and 2.2~ 4.5 times of mining thickness, respectively; when the influence of seepage is taken into account, the height of water flowing in a fractured zone and caving zone increases to 20.6 times and 4.8 times of mining thickness, respectively. Therefore, from the safety perspective, the influence of seepage should be considered in the process of actual mining, and the height of water flowing in a fractured zone with seepage-stress field coupling is more reasonable for designing safety coal (rock) pillars.