2007 Vol. 13, No. 4

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MAGNETOSTRATIGRAPHY OF A LOESS-SOIL SEQUENCE IN THE GARZE AREA, WESTERN SICHUAN
QIAO Yan-song, LIU Dong-yan, LI Chao-zhu, LI Ming-ze, WANG Yan, ZHAO Zhi-zhong
2007, 13(4): 289-296.
Abstract (136) HTML (78) PDF (330KB)(8)
Abstract:
The western Sichuan Plateau is located on the southeastern margin of the Qinghai-Tibet Plateau, and its climate is mainly controlled by the Indian monsoon and Plateau monsoon.The loesspaleosol sequence distributed widely on the western Sichuan Plateau is among the best continuous records of the Quaternary climate and environment on the margins of the plateau.It records the evolutionary process of the above-mentioned circulation system and its relation to the phased evolution of the QinghaiTibet Plateau and is crucial for understanding the regional environmental response to the uplift of the plateau.A systematic magnetostratigraphic study was conducted on the Garzê-A section in the Garzê area, western Sichuan.The results indicate that the B/M boundary appears at the top of L7 and that the Jaramillo normal polarity subzone of the Matuyama negative polarity zone appears in the lower part of the section.Extrapolation from the paleomagnetic boundary point yields a basal age of ~1.16 Ma for typical eolian deposits of the Garzê-A section.
LATE CENOZOIC NORMAL FAULTING OF THE QUNGDO'GYANG GRABEN IN THE CENTRAL SEGMENT OF THE CONA-OIGA RIFT, SOUTHEASTERN TIBET
WU Zhong-hai, ZHANG Yong-shuang, HU Dao-gong, ZHAO Xi-tao, YE Pei-sheng
2007, 13(4): 297-306.
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Abstract:
The Qungdo'gyang graben in Qusum County, Tibet, belongs to the central segment of the NNE-trending Cona-Oiga (or Cona-Sangri)rift zone, which is the only rift located at the easternmost end of the nearly N-S-trending Yadong-Gulu rift zone in southern Tibet.It is a Quaternary semi-graben downfaulted basin formed by extension of the upper crust occurring in the N108-115°E direction after the nearly E-W-trending thrust zone in the study area ceased its activity.The main boundary normal fault controlling the development of the late Quaternary basin is located at the western margin of the basin.It generally strikes NNE and dips E with a length of ~40 km.Displacement measurements and isotopic dating indicate that:this boundary normal fault began activity at ~5 Ma BP; the total cumulative vertical displacement ranged from 2.6 to 2.8 km; and the minimum long-term average throw rate was ~0.5 mm/a.The most rational estimate of the average throw rate since the last maximum glaciation (MIS2)of the fault is 1.2±0.6 mm/a.
LATE QUATERNARY CRUSTAL UPLIFT AND SOUTHWARD SHIFT OF THE LHASA RIVER IN THE LHASA AREA, TIBET
CHEN Zheng-wei, CAO Zhong-quan, XIE Ping, JIN Hua, HONG Shun-ying
2007, 13(4): 307-314.
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On the basis of the field investigation, digital elevation modeling and remote sense data analysis, the authors think that the nearly E-W-trending watersheds and valleys in the Lhasa area are distributed alternately from north to south under the nearly N-S compression, parallelly to the WNWtrending main faults.From the erosional surfaces of the summits near the watersheds to catchment basins, the hill slope changes from being gentle to being relatively steep and again to being gentle, indicating a successive change from the hilltop erosion zone through intense erosion zone to sedimentation zone and a complete process of erosion and sedimentation under the tectonic-climatic control.Under the same climatic conditions, the Lhasa block tilted to the south during the late Quaternary neotectonic movement, and as a result, the northern Lhasa block has been eroded more intensely than the southern block, and therefore the downstream reaches carry more sand and mud.As more alluvial-diluvial fan deposits from the northern block flow to the Lhasa River than those from the southern block and in addition the crust tilts from north to south, the Lhasa reach of the Lhasa River has shifted toward the south and so has the alluvial fan of the Doilung Qu river mouth.
GRAIN-SIZE DISTRIBUTION AND GENESIS OF LOESS IN THE QINGZHOU AREA, SHANDONG
PENG Shu-zhen, GAO Zhi-dong, WU Xiu-ping, ZHANG Lian-bing, LIANG Ming-ying, QIAO Yan-song
2007, 13(4): 315-321.
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Loess deposits with varying thicknesses are widely distributed on intermontane valleys and piedmont zones on the northern side of the central Shandong mountainous region.A systematic grain-size analysis was performed along the Fujiazhuang loess section of the Qingzhou area.The analytic results of the samples were correlated with those of the samples taken from Quaternary loess-paleosol of the Loess Plateau, modern dust fallouts in Beijing and fluvial deposits.The results show that the grain-size distribution of the Qingzhou loess is very similar to that of modern dust fallouts in Beijing and loess of the Loess Plateau but notably different from that of the fluvial samples.In the whole loess-paleosol sequence, the grain-size variation of the Qingzhou loess is consistent with the typical eolian loess and paleosol of the Loess Plateau.The loess is coarse in size, while the paleosol is fine in size.The above-mentioned results provide evidence for the eolian origin of the Qingzhou loess in the sedimentological context.The grain-size distribution of the Qingzhou loess combined with the previous studies indicates that the main provenances of the Qingzhou loess are the marine strata exposed in the flood plain of the Yellow River and Laizhou Bay north of the sedimentary region and less commonly distal silt and dust carried by high-layer circulation from northwest inland.
ORIGIN OF QUATERNARY MUDDY GRAVEL DEPOSITS IN THE LUSHAN AREA
LIU Zong-xiu, ZHAO Zhi-zhong, TIAN Jiao-rong, WANG Min, LI Ming-ze
2007, 13(4): 322-332, 314.
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The gravel fabric characteristics of Quaternary muddy gravel deposits in the Lushan area indicate the following:the lithology of gravels is almost consistent with that of bedrocks in the mountains; the isometric sphere diameter of gravels is small, the weighted average diameter of gravels is lower than the median diameter of gravel; the gravels are poorly sorted with a sorting coefficient of >1;the values are relatively lower, averaging -0.66;the F values are higher, being 22.75%-37.75%;the ratios of F/φ range from 2.75 to 4.75;the φ values are lower and concentrated, ranging from 22.75 to 37.75%, and the gravels are mainly angular and subangular.Both the a-axis and ab-plane dip towards the downstream, the dip angles of the a-axis are low and concentrated, being 7-8°, the ab-plane dips at 7~21°, and the a-axis has more preferred dip of fabrics than the ab-plane; the peak of the grain-size frequency distribution curve of deposits in the Lushan area is in the range of 4 and 5φ; The quartz sand grains are subangular and have well-developed conchoidal fractures, parallel striations, upturned cleavage flakes, "V"-shaped holes and siliceous deposits.The above-mentioned sedimentary characteristics indicate that the Quaternary muddy gravel deposits in the Lushan area should be till and glaciofluvial deposits rather than fluvial deposits or mudflows.
CHARACTERISTICS OF POLLEN ASSEMBLAGES IN SURFACE SOILS IN THE MAQU-HONGYUAN AREA, ZOIGÊ PLATEAU, NORTHERN SICHUAN
CAI Yao, WANG Yan, Jiang Fu-chu, LI Chao-zhu
2007, 13(4): 333-339.
Abstract (184) HTML (102) PDF (277KB)(38)
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In order to investigate the relationship between the surface pollen and modern vegetation, 20 surface soil samples collected from the Maqu-Hongyuan area on the Zoigê Plateau, Sichuan, were analyzed and the relationship between the surface pollen assemblages and modern vegetation in the study area were studied.The results show that the surface pollen assemblages in the area approximately reflect the whole features of the modern vegetation and are basically similar to the features of the modern vegetation in respect to vegetation types, spatial arrangement of vegetation zones and main assemblageestablished and dominant genera and species.Three vegetation zones may be distinguished by pollen percentages; they are the subalpine shrub, subalpine shrub and subalpine meadow, and alpine meadow and steppe vegetation zones.The representation of surface pollen varies with genera and species.Pinus and Compositae pollen are overrepresented and Picea pollen is moderately represented, while Gramineae and Cyperaceae pollen are underrepresented.Betula pollen is not overrepresented, which is possibly due to difficulty in transport.The genera and percentages of the surface pollen in the three vegetation zones show certain difference from those of the modern vegetation, which may be related to vegetation degeneration.
STRUCTURAL DEFORMATION CHARACTERISTICS OF THE KALPIN THRUST BELT ON THE NORTHWESTERN MARGIN OF THE TARIM BASIN
MA De-ming, CHEN Jiang-li, ZENG Chang-min, SHANG Xin-lu, SHI Jun, ZHANG Xian-jun, JING Bing
2007, 13(4): 340-347.
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The Kalpin thrust belt, located at the NW margin of the Tarim basin, is a part of the southern South Tianshan marginal thrust system.On the basis of field investigation and seismic section interpretation, the Kalpin thrust belt has the following structural deformation characteristics:the thrust belt occurs in Paleozoic strata; the major detachment fault occurs in a Middle Cambrian gypsum-salt lay er; the thrust sheets are imbricate; various thrust fronts are subaerially exposed; fault propagation folding and piggyback thrusting are found; and the thrust belt formed during the Pliocene-Holocene. According to the reconstructed balanced section, the minimal shortening rate of the thrust belt is 29.1%-40.7%.
SEISMIC REFLECTION CHARACTERISTICS OF HALITE AND RELATED HYDROCARBON ACCUMULATION TYPES OF THE WENLIU OILFIELD IN THE DONGPU SUBBASIN
SUN Si-min, LIANG De-fu, HUANG Shu-wang
2007, 13(4): 348-354.
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The physical properties, seismic reflection features, geometry and halite-related hydrocarbon accumulation types in the Wenliu oilfield of the Dongpu subbasin were studied by using seismic reflection data, combined with geological and drilling data.The studies show that halite is characterized by a constant low density low and a high stable velocity, which in the main do not change with depth.The boundary between halite and areno-argillaceous rocks show distinct reflection features because there is a strong impedance difference between them.However, due to the flow feature, halite has several modes of occurrence and their seismic reflection features are different, which makes it difficult to recognize halite. A discrimination model for halite beds (bodies)has been summarized by using seismic data.There are three main modes of occurrence for halite in the study area:primary platy halite, post-deformational halite and secondary salt wall.The flow deformation and facies change of halite formed three types of hydrocarbon accumulations, namely, graben-type anticlinal accumulations above salt, lateral salt-sealed accumulations and anticlinal accumulations below salt.
DOMINANT CONTROLLING FACTORS AND REGULARITIES OF FORMATION OF PETROLEUM ACCUMULATIONS IN THE TAZHONG AREA
LIU Chun-xiao, QIAN Li, DENG Guo-zhen
2007, 13(4): 355-367.
Abstract (197) HTML (81) PDF (757KB)(5)
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Because of many influence factors, the formation of petroleum accumulations is complex in the Tazhong area.Analysis of drilled petroleum accumulations shows that the main controlling factors affecting the formation of petroleum accumulations in the area include:① source rock; ② migration channels (faults controlled the vertical and lateral distribution of petroleum, carrier layers affected the lateral movement of petroleum and unconformity controlled the lateral movement of petroleum); ③ types of structure (types of trap, structure styles and paleo-uplift during petroleum generation); ④ tectonic evolution; ⑤ physical properties and distribution of accumulations; ⑥ reservoir and seal association; and ⑦ influence of igneous rocks on petroleum accumulations.The regularities of formation of accumulations are as follows:① traps and source-related faults are necessary conditions for the formation of accumulations in the Donghe sandstone; ② controls of structure and reservoir on petroleum, multistage formation of accumulations and later-stage injection are basic features of Silurian formation of accumulations; ③ the degree of development of accumulations is the key to the formation of Ordovician accumulations; and ④multi-stage injection of petroleum produced the features of occurrence of petroleum in several layers and north-south differentiation.The study area is characterized by good conditions for formation of petroleum accumulations and a higher level of exploration, and it is particularly the case with the Ordovician carbonate petroleum accumulations which are marked by more types and longer petroleumbearing well intervals.Their shapes were controlled by irregular pores, cracks, and cavities because of their very strong heterogeneity.The reservoir quality is the dominant controlling factor for the concentration of Ordovician petroleum.
UPSCALE METHOD FOR THE FINE 3D GEOLOGICAL MODEL OF HYDROCARBON RESERVOIRS AND ITS APPLICATION EFFECTIVENESS
SUN Zhi-xue, LU Hong-jiang, SUN Zhi-lei
2007, 13(4): 368-375.
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In general, the fine grid model constructed from the reservoir description stage contains more than one millions grids.However, it is not possible to import the fine grid to a traditional simulator directly.On the basis of previous research, a relative rapid and efficient method of upscaling is proposed in this paper.The proposed method, in which the anisotropy of permeability can be considered, is based on the heterogeneity DP (Dykstra-Parsons)coefficient and upper and lower permeability limits (Cmin, Cmax).The computational performance of the method is much faster than the traditional upscaling technique.The fine 3D geological model of Chang 6 layer of the Yanchang Formation in the central Ordos basin was calculated by the proposed method.The reservoir simulation was performed on the coarse grids. Furthermore, according to the geological setting of the study area and the low compressibility of the fluids and rocks, a numerical simulation study of the reservoir was conducted on the fine geological model by using the streamline simulator, and then the effectiveness of the upscaling method for a period of time was evaluated systematically with the results of the study as the standard.The contrast of results indicates that not only the computational performance of the proposed method is much faster, but also the results of the method are reliable.The proposed method provides an efficient technique for resolving the highly accurate simulation of strongly heterogeneous, complex reservoirs of continental origin.
ANALYSIS OF SURFACE SPECTRAL FEATURES IN THE SHUICHANG IRON MINING AREA
CONG Nan, XU Gang, ZHENG Da-xing, QIAO Zi-jiang, DONG Fa-xian
2007, 13(4): 376-384.
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The eco-environment in the Shuichang iron mining area has continuously deteriorated after many years of extensive and substantial mining operations.Surface spectral testing indicates that the spectral curves of vegetation commonly display the phenomenon of "blue shifts of red edges and down shifts of green peaks", which is a typical aberrance character of poisoning of iron compounds.From the operation site to peripheries, the values of red edge "blue shifts" have a trend of decreasing markedly, which indicates that the poisoning symptom of iron compounds is reduced gradually.Testing and analysis of the typical surface spectral features of the mine furnish important evidence for the determination of characteristic spectral bands or diagnostic spectral bands of various surface features and also provide a theoretical basis for the hyperspectral remote sensing survey of the eco-environment of the mine.