Abstract:Abstract：This paper deals with the geological, geophysical and geochemical characteristics of ore deposits in the middle and lower Yangtze River valley and proposes the main targets of ore search at depth in the future, i.e.: hidden mineralized intrusions and related various types of orebody, large porphyry ore deposits in intrusions and stratiform deposits controlled by intrusions and the Wutong sandstone. It also discusses several main problems that should be solved in applications of geophysical and geochemical methods and emphasizes that we should bring into play the roles of integrated methods including the gravity method, magnetic method, induced polarization method, electromagnetic method and petrosonde, as well as several seismic methods and geochemical methods, which are closely combined with studies of geology and metallogenic characteristics of ore deposits. Some problems that should be paid attention to in applied tests of the methods are also discussed. Finally, the paper discusses the regional tectono-magmatic activity and metallogenic prospects from the tectonic evolution in the study region. The author thinks that: this region is the continent-continent collision-compression orogenic belt between the Yangtze plate and North China plate and its foreland area and strong lithospheric compression resulted in crustal thickening and extrusion and exhumation of deep materials, thus pushing the deep high-pressure (HP) and ultrahigh-pressure (UHP) metamorphic rocks to the shallow crustal level; HP and UHP minerals such as coesite formed at depth and molten mantle magma intruded upward simultaneously; large amount of calc-alkaline magma was generated and stored in the middle crustal level, and a long period of material exchange between the calc-alkaline magma and metallic materials in the middle and lower crust formed concentrated ore fluids, which entered the superficial layer of the crust through tensile faults that occurred in the late stage；finally after physical and chemical Processes occurred between the ore fluids and country rocks, metallic minerals were deposited to form ore deposits. A new tectonic model in the continent-continent collisional orogenic belt of the Yangtze plate and North China plate has been summed up.

Abstract:Abstract：On May 12, 2:28 pm, an earthquake (Ms 8.0) struck the Longmenshan area (centred in Wenchuan County of Sichuan Province), the eastern segment of the Tibetan Plateau. According to the field survey, the earthquake occurs on the NE striking Longmenshan fault belt. The belt has been with the thrusting rate smaller than 1 mm/a and the shortening rate smaller than 3 mm/a according to GPS measurement. The causative mechanism is mainly the thrust (from NW to SE), accompanied with dextral strike-slip. The earthquake produced several co-seismic surface rupture zones that were 275 km long and 15 km wide in general. The Yingxiu-Beichuan rupture zone is 275 km long and dominative；The Hanwang rupture zone takes the second place, which is 70 km long and occurs along the south part of the Guanxian-Anxian fault, the frontal fault of the Longmenshan fault belt. There are another two minor rupture zones between two zones mentioned above, one is the Shenxigou rupture zone, is in NE direction and about 10 km long, close to the southern segment of the main rupture zone, whose deformation characteristics are similar to and can be involved into the Yingxiu-Beichuan rupture zone; the other is named as Xiaoyudong rupture zone, is in NW direction and 6 km long, produced by the thrust from SW to NE and associated lateral slip, which is the link between Yingxiu-Beichuan and Hanwang rupture zone and characterized by the lateral ramp. Besides, in the Sichuan Basin that eastern to the Guanxian-Anxian fault, a sand liquefaction belt with NE direction strike developed from Juyuan town of Dujiangyan to Jiangyou, which might be the result of the activity of a blind fault deep in the western Sichuan Basin. According to the feature of surface coseismic rupture zones, active tectonics in the Longmenshan fault belt have intense thrusting accompanied with significant dextral strike-slip. The fault is developing toward the Sichuan Basin. The recurrence intervals of great earthquake such as the Wenchuan earthquake can be 3000-6000 years.

Abstract:Abstract：The approach to investigation and assessment of organic contaminants in regional groundwater is presented based on the practical conditions in China and by referring to the experience in regional groundwater contamination investigation of foreign countries. The approach includes selection of indices of organic contaminant investigation, selection and rinsing procedures of sampling wells, sample collection, preservation and transportation for detection, analytical methods and target detection limit, quality control of field sampling and analysis, assessment of organic contaminant detection and assessment of methods for assessment of organic contaminants in excess of standards and relevant analytical methods.

Abstract:Abstract：The seismic sections show that the development of the North China basin is represented by accordion-style evolution. Generally three-layer“faulted-downwarped” structure formed：(1) Meso- and Neoproterozoic “faulting” and Paleozoic-Triassic “downwarping”, (2) Jurassic “faulting” and Upper Cretaceous “downwarping”, and (3) Paleogene "faulting" and Neogene “downwarping”. Faulting and downwarping resulted from extensional and compressional stress fields respectively. The change in the stress field was caused by the change of the dip angles of subduction of the adjacent oceanic plate from low to high. Due to the polycyclic crustal movements, structural and sedimentary evolution took place several times, forming several source-reservoir-cap associations and several trap types of oil/gas accumulations. Geological conditions of oil/gas accumulations may have formed in various downfaulted-downwarped basins from the Meso- and Neoproterozoic → Paleozoic → Mesozoic → Cenozoic,

Abstract:Abstract：The Altyn Tagh fault as an important component part of the northern boundary of the Qinghai-Tibet Plateau has long attracted attention of the geoscience communities both at home and abroad. Based on an analysis of the regional gravitational field, the authors think that the southwestern part of the Altyn Tagh fault does not end at Gozha Co but is divided into two branches near the northeast of Gozha Co. One branch passes through Gozha Co and continues to extend in a WSW direction, and after passing Lungmu Co the branch enters Kashmir via the Kongka Pass. The other branch continues to extend toward the SW and ends in the Bangong Co-Nujiang junction near Bangong Co via west of Gyipug. The latter branch formed earlier than the former branch.

Abstract:Abstract：LA-ICP-MS zircon U-Pb dating of the Kubusunan granodiorite and its enclaves in the Kalamaili area, eastern Junggar, Xinjiang, indicates an age of 287±2 Ma (MSWD=0.15) for the granodiorite and an age of 286±3 Ma (MSWD=0.22) for its enclaves. The two ages are the same within the error limits, suggesting that granodiorite and dark enclaves formed synchronously. Enclaves resulted from magma mixing, i.e. they were the result of mixing of supercool mafic magma into intermediate-acid magma and then fast condensation. In the process of magma mixing，basic magma of enclaves and acid magma of host rocks changed their components by chemical diffusion, and thus enclaves were modified and assimilated by granodiorite magma. This might be why the Kubusunan granodiorite and its enclaves have the same LA-ICP-MS U-Pb zircon age. The ages of the Kubusunan granodiorite is in the range of 330-265 Ma for post-collisional magmatic activity in East Junggar, slightly younger than the age (300± Ma) of the Wulungu River alkali granite and Kalamaili alkali granite, all being the product of post-collisional magmatic activity at peripheries of East Junggar, and their formation and evolution indicate that underplating of post-collision mantle-derived magma in Junggar resulted in vertical growth of continental crust.

Abstract:Abstract：The contents of platinum group elements (PGE；Ir, Ru, Rh, Pt, Pd) in the Cretaceous mafic-ultramafic rocks of the Northern Dabie have been determined by nickel sulfide fire assay preconcentration, combined with ICP-MS. The PGE abundances for all the twelve samples are low. Primitive mantle-normalized PGE distribution patterns have a positive slope and are slightly depleted in PPGE and strongly depleted in IPGE relative to the primitive mantle with Pd/Ir values far higher than their corresponding mantle ratios. Strong PGE fractionation in the samples is mainly controlled by sulfide phase in the process of low degrees of partial melting of the mantle. Ir occurs in non-sulfide phase such as spinel and possibly also in Os-Ir alloys. The Distribution characteristics of PGE suggest that these mafic-ultramafic rocks are the product of magmatic crystallization differentiation.

Abstract:Abstract：This paper introduces a newly discovered meteorite crater in Daba on the southeastern margin of the Dabie Mountains in Anhui Province. Preliminary survey has revealed that the Daba meteorite crater is elliptic in shape with its major-axis oriented in a NNE direction, ~19 km long, and its minor-axis being ~12 km and the maximum depth being 2 km. This is a compound meteorite crater with a central uplift. The Daba crater has a circular image in satellite photos and shows a depression topographically. The base of the Daba meteorite crater is well preserved and its boundary may be directly observed and traced. All types of impact metamorphic rocks formed at ~230 Ma are well developed, of which there are rocks containing typical impact metamorphic minerals such as coesite and typical ultramicro-structures such as impact cataclastic structures and especially desiccation auto-breccia found structure commonly on the inner walls of the crater's base, which serves as the most reliable indication for indentifying the meteorite crater. All the evidence has confirmed that the Daba circular image is a typical meteorite crater structure. This new discovery is of great significance both scientifically and economically. A model may be constructed for guiding further search and investigation of meteorite craters in the folded mountainous areas. Meanwhile, it also greatly enriches the geological evidence for establishing the Dabie Global Geopark. This discovery will undoubtedly promote the development of tourism of the Dabie Mountains as well as popularization of knowledge of meteorite impact.

Abstract:Abstract：The Liuchapo chert in Anhua County, Hunan Province, South China, was deposited in a terminal Ediacaran (551-542 Ma) deep-sea basin. It has the following REE geochemical characteristics： it has very low REE concentrations (range 8.6×10－6-18×10－6；average 13.6×10－6) and high Y/Ho ratios (range 33.6-43.9; average 37.4), indicating that the ratio is close to that of modern seawater. They are also characterized by positive La anomalies (LaN/CeN 1.46 on average), moderate negative Ce anomalies (average 0.65), weak positive Eu anomalies (average 1.1), positive Gd anomalies (average 1.07), positive Y anomaly (average 1.22) and depletion of LREE and MREE relative to HREE (LaN/YbN 0.17 on average；GdN/YbN 0.45 on average). These characteristics are similar to those of modern seawater but notably different from those of hydrothermal fluids or jasper related to seafloor hydrothermal sulfide deposits, suggesting the influence of terrigenous detrital input and hydrothermal fluids on is trivial and negligible. The Liuchapo chert formed by chemical deposition of huge amount of dissolved silica that was produced by chemical weathering and brought to the sea. Biological processes promoted precipitation of dissolved silica in seawater.

Abstract:Abstract：There are three types of Yanshanian mineralized granite in southern Hunan, and the chemical compositions and species of their ore-forming minerals are notably different. The characteristics of variations in chemical compositions of the minerals all indicate a mantle-crust magma mixing origin. Systematic analyses show the following：(1)Hornblendes belong to Ca-hornblende.(2)Biotites in most early-stage MC-type granite are Mg-biotite; those in late-stage CM-type granite are mainly meroxene; and biotites in C-type granite are mainly sideophyllite and meroxene, most of which zinnwaldite. The variation in biotite composition of the three types of granite shows a linear relation, implying a genetic relation.(3)Plagioclases in the three types of granite are significantly distinguished. Plagioclases are mainly andesine in MC-type granite, oligoclase in CM-type granite and albite in C-type granite. The zoning structures of plagioclases are developed to different degrees, with the zoning of plagioclases in the early-stage CM-type granite best developed.(4)Alkali plagioclases in CM-type granite and its dark micro-inclusions are mainly K-rich orthoclase, and a few grains of plagioclase in inclusions are anorthoclase, indicating higher temperatures of plagioclase crystallization. Alkali plagioclases in C-type granite are relatively K-poor microcline and Na orthoclase.(5)The characteristics of rock-forming minerals and their compositional variations indicate that the formation of mineralized granites is related to crust-mantle magma mixing. The magmatic evolution that generated MC-and CM-type early-stage granites was mainly magma mixing, while the magmatic evolution that formed CM-type late-stage granitoids and C-type granitoids might be fractional crystallization in addition magma mixing.

Abstract:Abstract：The Fangzheng fault depression can be divided into five second-order structural units from south to north; they are the southern slope, southern subdepression, central rise, northern subdepression and northern slope. The Paleogene System was the main phase of formation, development and evolution of the Fangzheng fault depression. The period of deposition of the Wuyun and Xin'ancun formations was an intense fault downfauting period. The period of deposition of the Dalianhe Formation was a continued downfaulting period. The period of deposition of the First Member of the Baoquanling Formation was a period of transformation for downfaulting to downwarping, and the period of deposition of the Second Member of the Baoquanling Formation was a period of shrinking of the fault depression. In the period of deposition of the Wuyun-Xinancun Formation and the Second Member of the Baoquanling Formation, a fan delta-lakeshore and shallow lake deposition system developed by the drainage system in the basin. In the period of deposition of the Dalianhe Formation and the First Member of the Baoquanling Formation, in the basin there occurred a fan delta to semi-deep lake deposition system, in which a horizontal water system was developed. From the Wuyun-Xinancun Formation to the Second Member of the Baoquanling Formation, the depocenter migrated from north to south and then again to the north, and simultaneously the large lake area became small and again became large and the shallow lake became deep and then again became shallow.

Abstract:Abstract：Based on an analysis of the core, well logs and seismic data and by using sedimentological and sequence stratigraphical theories, the Upper Submember of the Fourth Member of the Shahejie Formation in the Lijin subbasin is divided into one sequence and three systems tracts and subdivided into seven parasequence sets. The sedimentary characteristics of beach-bar sandstone and its distribution in the parasequence sets have been studied. The beach bars of lakeshores and shallow lakes in parasequence sets 1 and 2 are best developed and storm beach bars of parasequence sets 3 and 4 are also best developed. The sandy beach bars in parasequence sets 6 and 7 are poorly developed but carbonate beach bars are well developed. The controlling factors of beach bars are analyzed. The paper presents the concept of controls on beach bars by the system of "paleoclimate-provenance-basin". This concept is an improvement and supplement of the traditional "source-controlled theory" and may more rationally explain the origin and distribution of beach bars.

Abstract:Abstract：The 21st century is a great development period of China's oil and gas exploration and development of marine carbonate rocks. For the moment, the majority of China's marine carbonate oil and gas fields are buried below 4000 m depth in the Paleozoic sequence. How to look for favorable reservoirs in deep carbonate rocks has become the focus of attention of petroleum geologists. The Puguang gas field discovered recently is a gas accumulation with the best developed secondary pores among carbonate reservoirs discovered in China at present and is strictly controlled by the distribution of sedimentary facies, dolomitization and buried dissolution. In this paper, a detailed study and anatomy of the “reservoir facies”-favorable sedimentary facies and diagenetic facies-is conducted under the guidance of the“facies control theory”, which controls the formation and evolution of the reservoir of the Lower Triassic Feixianguan Formation in the Dawan - Maoba - Tieshanpo area in the surroundings of Puguang. According to the outcrop section, drilling, logging and seismic data, combined with the “single-factor analysis and multifactor comprehensive mapping method”, four sedimentary units are proved to be developed in the Feixianguan Formation in the Dawan - Maoba - Tieshanpo area; they are platform slope, platform shoal, open platform and restricted platform. Based on the detailed description of cores and indoor observations and studies of large numbers of core and cutting thin sections and casting slices, the authors think that the key factors which control the reservoir formation are dolomitization, buried dissolution, and so on. According to casting slice identification, scanning electron microscopy, analysis of mercury and other means of analysis, it is found that the favorable reservoir is characterized by large sets of porous finely and very finely crystalline residual oolitic dolostone. Solution pores in rocks are very well developed, consisting dominantly of the large pore and coarse throat type, medium pores and medium throat type. The physical properties of the gas reservoir are better, marked mainly by high porosity and permeability and medium porosity and permeability. The correlation of porosity and permeability is obvious. The role of “facies control” is pronounced in this reservoir. Vertically, the reservoir is mainly distributed from the Second Member to the top of the First Member of the Early Triassic Feixianguanan Formation.. Laterally, the favorable area for reservoir distribution is the platform-margin shoal. The platform-margin shoal facies zone controls the lithology and distribution of the favorable reservoir, while dolomitization and buried dissolution control the final distribution limits and performance of the favorable reservoir. Through a study of the “facies control theory” in the reservoir of the platform-margin shoal in the Dawan - Maoba - Tieshanpo area.

Abstract:Abstract：This paper relatively intensively discusses the characteristics, distribution and controlling factors of reefs of the Changxing Formation and beaches of the Feixianguan Formation in the northern Sichuan basin. It is thought that: the reefs are transgressive reefs formed during the regional sea-level rise and vertically mainly distributed in the middle and upper parts of the Changxing Formation, and the oolitic beaches mare mainly regression beaches developed in the process of regional sea-level fall and vertically distributed in Members 1 to 3 of the Feixianguan Formation. In a plan view, reefs and beaches mainly occur in zones on both sides of the Guangyuan-Liangping sea trough. In the period of Changxing, with the rise of sea level reefs moved in the direction of transgression and their horizon was gradually uplifted; in the Feixianguan period, with the fall of sea level the beaches migrated toward the trough and their horizon had a trend of gradual rise. The main factors that controlled the formation and development reefs and beaches of the strata are sea-level fluctuation, tectonics, contemporaneous faults and paleoclimate.

Abstract:Abstract：Detailed core description, log study and intensive interpretation of nearly 3,000 km long seismic profiles show that the southern margin of the Manjia'er subbasin was a gentle slope continental margin in the Early Silurian. An onlap line that is nearly parallel to the pinching-out line of the Silurian is recognized at the bottom of the Upper Member of the Silurian Kalpintag Formation between well Mancan 2 and Tazhong 32. The onlap line is considered the coastline of the initial transgression in sequence 1 in the Upper Member of the Silurian Kalpintag Formation in the Mannan area. Based on the aforesaid understanding, combined with the effective recognition of the sequence boundary of wells, the Upper Member of the Silurian Kalpintag Formation in the Tazhong 32, Tazhong 34, Mancan 2 and Mancan 1 well areas is divided into two third-order sequences. Braided-delta deposits occur in both sequences but the oil storage capacities of “the sandstones of the same facies in different systems tracts” have different features. The main influence factors are the grain size and sorting of detrital grains, types and contents of cements and different burial characters of the reservoirs. The early-stage braided-delta front deposits are developed in the lowstand systems tract (LST) of sequence 1 in the Mancan 2 well area in the lower part of the slope. The main reservoir sandstone is subaqueous distributary channel sandstone of the braided-delta front, where the grains are relatively fine and the compositional maturity is relatively low. As the reservoir is buried at ~5,000 m depth and the calcite cement content is high, the storage capacity is relatively poor. By contrast, the main reservoir in the Tazhong 32 and 34 wells area in the uplift is subaqueous distributary channel sandstone of the regressive braided-delta front in the transgressive systems tract of sequence 1. As such sandstone is characterized by relatively coarse grains, relatively high compositional maturity, relatively shallow burial depth and relatively low cement contents, its porosity and permeability are notably better than those of the early-stage subaqueous distributary channel sandstone of the braided-delta front in LST.

Abstract:Abstract：Analyses of six balanced seismic sections or forward tectonic models across the Jiyang and Linqing depressions and Luxi area show that the extension rate in the region in the Paleocene, especially in the early Paleocene, was greatly higher than that in the Mesozoic, the extension rate for the Jiyang depression being higher than that for the Linqing depression and the extension rate for the Luxi area lowest. The development of the proto basin of the Dongying and Huimin subbasins in the Jiyang depression broadly went through five phases. In the Mesozoic the amount of extension in the east was markedly large than that in the west, and strong erosion occurred in the east during the Late Cretaceous. From the above, it is inferred that： this was related to the rifting along the Tanlu fault in the Mesozoic, and rifting was intense in the east and tectonic inversion was also strong at the end of the Cretaceous. The amounts of extension of the Dongying and Huimin subbasins were close during the deposition of the Four Member of the Shahejie Formation and Kongdian Formation. They belong to strike-slip pull-apart sedimentary subbasins. After the deposition of the Third Member of the Shahejie Formation, differential development again occurred in the east and west parts: the amount of extension in the east was noticeably larger than that in the west. The whole of Meso-Cenozoic witnessed strong vertical rifting and inversion, and in a plan view movement similar to a seesawing movement was manifest. Located in the transitional place of strong rifting, the Linqing subbasin had well-developed transitional structure and thus a downfaulted lake basin was unable to develop steadily; so the hydrocarbon-forming conditions were poor.

Abstract:Abstract：Most of turbidite sandstones are fluxoturbidite in the delta front in the deep zone of the eastern part of the Dongying subbasin. The turbidite sandbody reservoir of the deep zone consists predominantly of feldspathic fine sandstone, lithic fine sandstone and siltstone with low compositional maturity and textural maturity. The micro-properties of the reservoir show that the reservoir space types include primary pores, micro-pores in clay mineral matrix, intergranular dissolution pores, intragranular dissolution pores and micro-fissures, and the pore textures are mainly of low-permeability, fine-throat type, and that the reservoir has medium- and low porosity and low permeability and so poor physical properties. Study of the influence factors of the reservoir physical properties indicates that the rock fabric, sedimentary micro-facies, diagenesis and the generation and distribution of abnormally high pressures are the main factors for influencing the physical properties of the turbidite sandbody reservoir in the study area, of which diagenesis has obviously modified the physical properties of the turbidite sandbody and compaction and cementation are the main factors which caused the porosity and permeability of turbidite sandstones become poor. On the other hand, dissolution and diagenetic shrinking improved the porosity and permeability of the reservoir. The existence of the abnormal high pressures, high geothermal field and early hydrocarbon injection play a good role in conserving and improving the physical properties of the reservoir.

Abstract:Abstract：The authors made measurements of sections of the Middle-Upper Triassic Badong and Shazhenxi Formations on the south margin of the Zigui basin and 1:100,000 geological mapping of the Zigui Sheet and found that the Middle Triassic Badong Formation is missing to different degrees on the southeastern margin of the basin and that only the first and second members of the formation were deposited in the vicinity of Guojiaba, Zigui. The whole Badong Formation is absent in Nanjiawan; as a result, the Upper Triassic Shazhenxi Formation directly rests on the Lower Jialingjiang Formation. However, the Badong Formation is complete in Shazhenxi and Jiziyan on the western margin of the basin. The aforesaid phenomena indicate that there occurred appreciable difference in the Badong Formation because of the influence of the Indosinian movement at the end of the Early Triassic. The Shazhenxi Formation, varying greatly in thickness, inherited the characteristics of rugged ancient landforms of the Badong Formation when it was deposited. The authors suggest that the Middle Triassic Badong Formation and Late Triassic Shazhenxi Formations in different areas of the basin are not in fault contact but in conformable or disconformable contact.

Abstract:Abstract：Manganese deposits, ferromanganese deposits and manganiferous siderite deposits occurring in the Second Member of the Middle Permian Maokou Formation in Guizhou are all distributed in platform gullies in central Guizhou. There are carbonate manganese deposits in the Zunyi area in the east and mainly manganese gossan-type secondary manganese oxidized deposits in the Xuanwei-Shuicheng area in the west. The purpose of this paper is to discuss the mineralization conditions of manganese deposits in order to extend ore prospects. Study shows that various manganese ore types and rocks of ore embryo layers formed by hydrothermal processes. The evidence is as follows：(1) there are many diagnostic minerals of hydrothermal deposition；(2) major and trace element and REE data all show characteristics of hydrothermal deposition；and (3) he homogenization temperatures of fluid inclusions range from 90 to 275℃. The formation of the manganese deposits is probably closely related to the middle and late stages of the evolution of the Emeishan mantel plume. The outpouring of Maokouan basalt was favorable to the formation of the silica-lime-mud-manganese association in the platform gullies of central Guizhou. Manganese deposits in the Zunyi area in the east are strictly confined in the area of siliceous breccia formed by hydrothermal eruption. Based on these, combined with other characteristics, it is thought that the formation of manganese deposits in the study area is related to strong hydrothermal eruption.

Abstract:Abstract：The phenomena of petroleum geology are rich and colorful in marginal basins of the northern South China Sea. The genetic types and distribution of natural gas are complex. Based on the previous research and exploration, the discovered natural gas can be divided into three types: biogenic and sub-biogenic gas, normal and high-mature petroliferous gas and coal-related gas, high and over-mature natural gas. There are also three types of non-hydrocarbon gas (CO2), which are crust-derived type, mantle-derived type and crust-mantle mixed type. The biogenic and sub-biogenic gas, which was derived from Pliocene and Quaternary marine deposits, is distributed widely in shallow layers of the Ying-Qiong basin and Zhujiangkou (Pearl River Mouth) basin. The normal mature petroliferous gas, which was derived from Eocene middle- and deep-lake facies, is mainly found in the Beibuwan basin, northeastern Qiongdongnan basin and Zhujiangkou basin. The normal and high-mature coal-related gas, which was derived from Oligocene coal measures and Miocene marine source rocks, and high and over-mature natural gas, which was derived from different types of high and over-mature source rocks, are mainly found in the Ying-Qiong basin and some areas of the Zhujiangkou basin. CO2 is mainly concentrated in the diapiric zone of the Yinggehai sea basin, eastern Qiongdongnan basin and some areas of the Zhujiangkou basin. It was derived from Miocene marine calcareous arenaceous-argillaceous rocks affected strongly by mud diapiric hydrothermal activity and deep volcanic mantle-derived materials.

Abstract:Abstract：Paleozoic reefs are mainly distributed in Early Cambrian, Early Silurian and Late Permian strata in the Sichuan basin. Geographically, they occur in the Daba and Micang mountains on the northern and northeastern margins of the Sichuan basin (Early Cambrian reefs), on the northern and southern margins of the Sichuan basin (Early Silurian reefs) and western Hubei, eastern Chongqing and northeastern Sichuan (Late Permian reefs). The Early Cambrian reef-bank association includes patch reefs, lime-mud mounds and oolitic shoals. Reef-building organisms are archaeocyatha and cyanobacteria and organisms attached to reefs are trilobites, brachipods, crinoids and sponges. Controlled by sea-level fluctuation, reefs have cycliciy and from west to east the horizons are raised gradually.Early Silurian reefs include patch reefs, lime-mud mounds and biostromes. Reef-building organisms are mostly corals, stromatoporoids, polyzoa and cyanobateria. Their distribution are controlled by terrigenous clastic-carbonate gentle slope affected by oldland and also related to sea-level fluctuations. Late Permian reefs are inner platform patch reefs and platform marginal reefs. Reef-building organisms are primarily sponges. Reef growth and distribution have a close relation with the paleogeomorphological framework and sea level fluctuations.

Abstract:Abstract：The safety factor of slope is calculated by using the limit equilibrium method based on the finite element analysis (LEMFEA). The results are compared with the results of the strength reduction of the Mohr-Coulomb criterion and circumscribed circle D-P criterion and results of the Spencer method. The comparison shows that the safety factor calculated by LEMFEA is in good agreement with those calculated by the strength reduction of the Mohr-Coulomb criterion Spencer method but is significantly deviated from the result obtained by the strength reduction of the D-P criterion. The calculation method of LEMFEA is described for the existence of the known sliding surface and non-existence of the sliding surface. Large-scale general finite element softwares, such as ANSYS, are used；therefore the calculation of the slope safety factor with this method may be performed easily and has a enough accuracy.

Abstract:Abstract：By using high-resolution laser grain-size instrument Mastersizer 2000, the authors performed a systematic study of the grain-size distribution characteristics of loess samples from Weinan in Shanxi province, Linshan in Beijing and Mangshan in Henan province, summed up the differences in multimodal grain-size distribution among three types of loess and discussed the influence of the dust source distance on the multimodal grain-size distribution characteristics of loess. The main conclusions are as follows： (1) Suspended particles with a diameter of <70 μm are dominant. There are three fractions for grain size distribution of loess： fine, mediun and coarse (the median sizes are <1 μm, 1-10 μm and 10-70 μm, respectively). The coarse fraction, which has the highest percentage, has the most distinct peak. The grain sizes and percentages of the coarse and medium fractions are controlled by the source distance. (2) The grain sizes of loess dust in different areas are notably different. The median grain size of the coarse fraction decreases with increasing source distance, showing a negative correlation; whereas the percentage of the medium fraction increases with increasing source distance, showing a positive correlation. (3) The separation of grain size fractions can reflect the minute difference in grain size in the same source region and has advantages. (4) The relation between the median size of the coarse fraction of loess and the dust source distance may be deduced theoretically and its correctness may be checked and validated by the actual fitting function.