Abstract:According to the stratigraphic framework across late Ediacaran-Early Cambrian boundary in Yichang, western Hubei, there existed uplifts alternating with sags during the Precambrian-Cambrian transition. The sags were favorable for the deposition of the rich organic shale of the Lower member of Cambrian Shuijingtuo Formation. V/Cr, Ni/Co, V/(V+Ni) and chemical indexes of alteration (CIA) indicate that these shales were formed in an anoxic or euxinic environment. However, a relatively oxic water and a synchronous decrease in total organic carbon (TOC) and biogenic Mo (Moxs) were found in the Lower Member Shuijingtuo Formation, which demonstrates that TOC was affected by both redox environment and marine organic carbon flux. The correlation between TOC and Moxs is much better than that of the TOC and biogenic Ni(Nixs). This phenomenon, together with the composition of the δ¹³Ccarb and δ¹³Corg in the same interval strata, indicates that there might exist dissociation of gas hydrate or release of methane. The high correlation between TOC and shale gas content and brittle minerals, (e.g. quartz, pyrite and some other minerals) indicates that TOC is one of the most important factors for evaluating the quality of shale gas reservoirs. Thus the lowermiddle part of the Lower member of Shuijingtuo Formation characterized by high TOC should be the best reservoir of the shale gas in the Shuijingtuo Formation. The study of burial and evolution history of the marine sedimentary in Yichang area indicates that the source rock of the Lower Cambrian had not gone through secondary hydrocarbon generation after reaching its gas generation peak in middle Late Triassic because of the restriction from the Huangling uplift, and thus avoided the excessive thermal evolution of the organic matter and the destruction of the shale gas reservoirs. Enrichment of the shale gas in the Cambrian Shuijingtuo Formation in Yichang was controlled by TOC, Huangling uplift and its evolution.

Abstract:Based on geological investigation of several outcrops, the analyses of 75 samples and the previous achievements, the authors studied the paleoproductivity conditions of lower member of Cambrian Xiaoerbulak Formation in Kalpin thrust belt. In order to get the reliable content of biogenic elements, the authors used the Ti element to deduce the terrigenous elemental content of Ba,Cu and Zn and obtain the corrected values of the biogenic elements Ba_xs, Cu_xs and Zn_xs. According to the results, it can be concluded that the lower member of Cambrian Xiaoerbulake Formation has a high level of paleoproductivity. The values of the biogenic elements Ba_xs, Cu_xs and Zn_xs of individual layers are higher, and this indicates that individual layers have higher paleoproductivity. The acritarchs microfossils such as Leiomarginata sp., Granomarginata squamacea Volkova, Dictyotidium priscum Kirjanov and Volkova and Lophosphaeridium sp. were found in the Cambrian Xiaoerbulak Formation, and all these factors provided a good material basis for the deposition of organic matter. The identifying indices such as Pr/Ph,V/(V+Ni), U/Th and δCe indicate that the lower member of Cambrian Xiaoerbulak Formation source rocks were developed under a favorable condition with an anaerobic sedimentary environment. The type of organic matter is Type I-Ⅱ, and the organic matter has the characteristics of high maturity stage and potential of hydrocarbon generation. In summary, the lower member of Cambrian Xiaoerbulak Formation can be regarded as the potential source rock.

Abstract:The Qiangtang Basin is located between the Hoh Xil-Jinsha River suture zone and the Bangong-Nujiang suture zone. Its sedimentary evolution is of great significance for understanding the tectonic evolution of the Paleo-Tethys and Meso-Tethys Oceans. In this study, the authors established the sedimentary evolution mode of the Mesozoic basin (T₃-K₁) based on the sedimentary sequences, lithofacies paleogeography, analysis of sedimentary basin, and the latest research results of chronostratigraphy, and then discussed the relationship between the evolution of the Qiangtang Basin and the closure of the PaleoTethys Ocean as well as the opening of the Meso-Tethys Ocean. The Mesozoic (T₃-K₁) Qiangtang Basin was affected by the diluvial-alluvial facies sedimentary overlap. The sedimentary sequence has undergone an evolution from diluvial-alluvial facies, lacustrine to coastal and shallow-seas facies, which shows a deepening upward transgressive sequence. It can be divided into three typical sedimentary overlap types and five major stages of sedimentary evolution sequence. The Mesozoic Qiangtang Basin is a superimposed basin that evolved from foreland basin into rift basin, then into passive continental marginal basin, and finally into an active continental marginal basin through shrinking and vanishing. The closure of the Early-Middle Triassic foreland basin for the Qiangtang Basin was related to the closure of the Paleo-Tethys Ocean basin. The evolution of Mesozoic (T₃-K₁) Qiangtang Basin was restricted by the rapid opening and closing of the Meso-Tethys Tethys Ocean basin.

Abstract:There are more than 50 basins in northeastern China with different sizes. The relatively large basins include Songliao Basin, Erlian Basin, Hailar Basin and 5 cross-border basins. The potential of oil and gas resources in Northeast China is huge, the oil and gas reserves increase significantly, but there still exists the difficulty in continuous increasing of oil and gas production and stability of production. Based on the analysis of the evolution of the tectonic and sedimentary paleogeography in Northeast China, this paper summarizes the differential development characteristics of the reservoirs under the synergetic action of tectonics and sedimentation in Northeast China. Combined with the practice of exploration, aimed at solving the existing problems in oil and gas exploration and focusing on the thought of new area and new strata, the authors put forward the directions of oil and gas exploration in northeastern China, which include the fine exploration of middle and shallow oil and gas in the central depression of Songliao Basin, the exploration of deep volcanic hydrocarbon exploration in the south of Songliao Basin, western slope and north end of Songliao Basin oil and gas, the exploration of Paleozoic oil and gas in Northeast China, the exploration of oil and gas in the Dasanjiang Basin, and the exploration of shale oil and oil shale resources in northeastern China. These suggests provide a scientific basis for the future exploration and deployment of oil and gas resources in Northeast China.

Abstract:Pore types and structures are of great significance for shale gas resources evaluation. In order to study the pore structure features and evolution regularity of shale, the authors used field emission-scanning electron microscopy (FE-SEM) and nitrogen adsorption method to study the pore characteristics and structures of black shale samples from the Late Ordovician-Lower Silurian Wufeng-Longmaxi Formation of the marine shale gas reservoir in northwest Guizhou. The results show that the shale has various kinds of reservoir space, mainly comprising intragranular pores, intergranular pores, organic pores and microfractures. Low temperature nitrogen adsorption experiment results show that the pores in the shale are mainly mesopores in size, and mainly include ink bottle-like and parallel plate-like pores in structure. The authors investigated the main factors influencing the shale pore development, organic carbon content, degree of thermal evolution and content of mineral composition and found that their actions were not conducted singly but restricted each other in influencing the development of shale pores. Quartz content is correlated positively with micro-and mesopores, but has no evident relationship with macropores. Clay content has no obvious relationship with micro-and mesopores, but has negative relationship with macropores. The organic matter pore is at its peak of development, has an important contribution to shale pores, and increases with the increase of maturity.

Abstract:Sequence stratigraphy is a key technology for exploration of stratigraphic-lithological reservoirs. For the purpose of pushing forward the stratigraphic-lithological reservoirs exploration of Baiyinchagan Sag in Erlian Basin, on the basis of previous researches, and through delicate stratigraphical correlation of over 200 wells, detailed core description of 759.42 meters from 33 wells, and analysis of regional tectonic-sedimentary evolution, the authors recognized the sequence stratigraphic characteristics of the main target for petroleum exploration in Baiyinchagan Sag (i.e., the Lower Cretaceous Aershan-Duhongmu Formation) and redefined the sequence boundary properties according to various kinds of data such as tectonic geology, paleontology, petrology, logging and seismic reflection. The results show that the Lower Cretaceous Aershan-Duhongmu Formation of Baiyinchagan Sag can be divided into two super long-term sequences and five long-term sequences. The two super long-term sequences correspond to the Aershan-Tenggeer Formation and the Duhongmu Formation. The five long-term sequences correspond to the 1^st member of Aershan Formation, the 2^nd member of Aershan Formation, Tenggeer Formation, the 1^st member of Duhongmu Formation and the 2^nd to the 3^rd member of Duhongmu Formation. Meanwhile, this paper indicates that the long-term sequence bottom boundary of Tenggeer Formation in Baiyinchagan Sag is a conformity surface, which can not form the favorable pathways for oil-gas migration. In another word, even if there are good trap conditions in bottom boundary of Tenggeer Formation of Baiyinchagan Sag, for example Xi40-Xi43 wellblock, there is no hydrocarbon accumulation due to lacking the favorable pathways of oil-gas migration and the associated insufficient hydrocarbon supply.

Abstract:The sedimentary reservoir of Lower Cretaceous Bashijiqike Formation in Kuqa depression was studied by making full use of core observation as well as conventional and image logs. The results show that the Bashijiqike Formation was formed in the sedimentary facies zone of braided delta front subfacies, of which the underwater distributary channel and mouth bar depositional microfacies constitute the main framework of sandbodies. A suite of recognition models for typical lithologies and sedimentary structures were built by core-log calibration methods. Then the well logging recognition and division standards were built, and the control of depositional microfacies on reservoir quality was discussed. The depositional microfacies were further divided into lithologies and lithofacies such as medium-grained sandstones of underwater distributary channel and fine-grained sandstones of underwater distributary channel based on the medium grain size and compositional maturity index. In addition, the logging evaluation methods of medium grain size and compositional maturity index were built. At last, the vertical distribution law of lithologies and lithofacies in single wells were figured out by making full use of image logs, shapes of conventional logs and core observations as well as the logging calculation of medium grain size and compositional maturity index. The research results lay a solid foundation for detailed description of sedimentary reservoir as well as the natural gas exploration and development in the future.

Abstract:Kanas Group is composed of a set of thick low pressure type shallow metamorphic rocks, mainly comprising schist, gneiss, and metamorphic sandstone; nevertheless, its formation time is in debate, resulting in the controversy concerning the tectonic evolution of Altay tectonic belt. The restoration of Kanas metamorphic protolith reveals that the metamorphic rocks are parametamorphic rocks. In consideration of the influence of inheriting parent rock features of rock materials and degree of metamorphism of metamorphic rocks, the authors investigated the element geochemical characteristics of clastic rocks by using research methods for clastic rocks, and the results show that the protolith of Kanas Group metamorphic rocks was formed in an environment of continental arc and also had characteristics of active continental margin. CIA, ICV indexes show that the original rocks experienced relatively warm and humid weathering process, with low maturity. The zircon U-Pb data show that the youngest zircon age is(500 ±3.0)Ma, which represents the upper limit age of Kanas Group, and that the strata were formed before late Cambrian, being a flysch formation produced in an environment of continental island arc or active continental margin. The breakup of Neoproterozoic Qingbaikouan early basement suggests that the Altay tectonic belt had Precambrian continental crust basement.

Abstract:The granitic rocks that were formed from ophiolite or intruded into the ophiolites are important for the precise dating of ophiolites, and some of them can be the powerful evidence for constraining the timing of subduction. Based on detailed studies of field geological background and petrographical features, the authors conducted analysis of whole-rock major, trace and rare earth elements and zircon U-Pb ages as well as Lu-Hf isotopes for the plagiogranite and granodiorite. The weighted mean ages of plagiogranite and granodiorite from Hongliugou-Lapeiquan ophiolite in North Altun Mountains determined by LA-ICP-MS UPb method are 501±3 Ma and 496±2 Ma, respectively, suggesting that the subduction timing of the northern Altun Ocean might have started in the mid-Cambrian or earlier. The zircons from plagiogranite and granodiorite exhibit positive ε_Hf (t) values of 1.6-5.6 and 2.7-6.9, separately, implying that the plagiogranites and granodiorites were all derived from the depleted mantle. Geochemical analysis indicates that the plagiogranites are characterized by high SiO₂, high Sr, low Y and corresponding high Sr/Y, which are similar to features of adakitic rocks, suggesting that they resulted from the small proportion of partial melting of metabasites during the hot oceanic subduction to the depth of 40-50 km, belonging to the amphibolite facies. The granodiorite belongs to the series of high-Na calc-alkaline rocks, and may represent the product of mafic rocks remelting from the lower crustal in an island arc setting. The geochronological analysis indicates that the north Altun Ocean might have experienced both northward and southward subductions, and the northward subduction of the northern Altun Ocean may be slightly earlier than the southward subduction. The comparative study of the subduction time between the northern Altun and northern Qilian shows that the northern Altun Early Paleozoic suture zone is the extension of the North Qilian Early Paleozoic suture zone.

Abstract:The mafic rock is exposed in North Anhui province of the East China. It consists of diabase, gabro-diabase and dabaseporphyrite. This paper presents a synthetic U-Pb isotopic study of zircons and a whole-rock geochemical study on diabase that were emplaced into the Proterozoic formations in the Langan area of the North Anhui province. The SHRIMP U-Pb zircon dating results indicate that the diabase were emplaced at ca.870-890 Ma. Geochemically, the diabase swarms are characterized by enriched in SiO₂、CaO and (K₂O2O).It is therefore deduced that the diabases might belong to intraplate tholeiite occurring within the North China Plate. There are also show relative enrichment in LREE and LILE(Rb, Ba and La),a comparative enrichment in Cr and Ni, but a slight depletement in HFSE(Th, Nb, Ta, Zr and Hf).They are plotted in the within-plate tholeiite series on the tectonic discrimination diagrams. Taken together, these geochemical and isotopic data suggest that the primary magmas to form the diabase dykes in the Langan area could have been derived from a transitional mantle in the Mesoproterozoic, and were most probably emplaced under a continental margin extensional setting at ca.870-890 Ma. The results of this study demonstrate that the Neoproterozoic magmatism occurred at the Langan area of the North Anhui province, and created conditions for diamond mineralization. Taken along with the Neoproterozoic breakup of the Rodinia Supercontinent and the close relationship between the coeval magmatism and the hypothesis of a superplmue, it is reasonable to contribute the emplacement of the Neoproterozoic diabases in the Langan area to the geochemical fingerprints the contemporaneous mantle plume activity preserved in the continental margin of the North China Block.

Abstract:In this paper, the authors studied the chronology and geochemistry of volcanic rocks in Manketou'ebo Formation of Tulihe area within Da Hinggan Mountains to restrict the petrogenesis and the tectonic setting. Zircon U-Pb dating reveals that the volcanic rocks formed in (157±1) Ma, suggesting late Jurassic. The geochemical characteristics reveal that these rocks fall into the high-K calc-alkaline, metaluminous to slightly peraluminous rhyolite series, characterized by high SiO₂ content (69.09%-75.92%), high alkali content (8.04%-9.23%) but low MgO, CaO and Fe₂O₃ content. The REE patterns reveal that the rocks are enriched in light rare earth elements with significant fractionation of HREE and LREE ((La/Yb)_N=5.85-13.53), with no or lightly negative Eu anomaly. Rocks are enriched in LILE such as Rb, Th, U and K, relatively depleted in HFSE such as Nb, Ta and Ti. Mg^# ratios vary from 12.14 to 31.01, 22 on average; Nb/Ta ratios vary from 6.67 to 27.17, 12.23 on average; Rb/Sr ratios vary from 0.35 to 3.36, 1.58 on average, implying that the magmatic source was the lower crust. According to the geochemical features, discrimination diagrams of tectonic setting and regional tectonic evolution, the authors hold that the volcanic rocks formed in the post-orogenic extension setting after the closure of Mongol-Okhotsk Ocean.

Abstract:Abundant marine trace fossils are preserved in the Early-Middle Devonian strata of the Guixi-Shawozi section in Longmenshan area, Sichuan Province. According to the shapes, three types of trace fossils were identified that include Domichnia as Skolithos, Fodinichnia as Chondrites, Phycodes, Planolites, Rhizocorallium, Thalassinoides and Zoophycos; Food-seeking traces including Cylindrichnus and Palaeophycus; Repichnia as Cruziana and Monomorphichnus; Cubichnia as Asterichnus, Lockeia and Rusophycus. 14 kinds in total trace fossils can be identified clearly. The ichnocoenoses represent types of Domichnia, Fodinichnia, Food-seeking traces, Repichnia and Cubichnia. Four ichnocoenoses representing different sedimentary environments were recognized as follows:(1) Skolithos-Thalassinoides ichnocoenosis can be explained as Domichnia from higher-energy foreshore; (2) Rusophycus-Phycodes ichnocoenosis mainly consists of Cubichnia and Fodichnia generated in higher-energy nearshore; (3) Chondrites-Palaeophycus ichnocoenosis is from shallow shelf, which suggests sub-oxic and lower energy; (4) ZoophycosPalaeophycus ichnocoenosis is considered as Fodichnia from higher-energy shallow shelf between normal wave base to storm wave base. In terms of the ichnocoenoses, living environment and distribution pattern of trace fossils of hybrid facies were set up from Early-Middle Devonian strata in Longmen-shan area. Three kinds of Zoophycos fossils were observed, which were coexistent with concentrations of brachiopoda and shell, ripple marks, hummocky and swaley cross bedding, which reflects shallow environment sedimentary characteristics from Early to Middle Devonian in Longmenshan area and indicates that Zoophycos fossils were formed in a shallow environment.

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Abstract:Liulaowan area is located on the northern piedmont of the Dabie orogenic belt in Henan Province, neighboring MeishanGuishan regional fault in the south and the Yanshanian Shangcheng granite body in the west. Geochemical anomalies dominated by Au, Ag, Cu, Pb, Zn were delineated on the basis of 1:50000 stream sediment survey. The Au geochemical anomalies are large in size, and have obvious concentration centers and good element combinations. High-value magnetic anomalies are consistent with the geochemical anomalies. The authors carried out anomaly verification work through measuring the geological, geophysical and geochemical prospecting sections. The authors delineated multiple high-value Au soil anomalies, accompanied by highly intensified and low resistance anomalies. In this paper, based on the detailed and contrastive analysis of the geological, geophysical and geochemical anomalies as well as metallogenic conditions in the area,consider that the favorable parts of prospecting are contact zone of intermediate-acid pluton and Huyoufang Formation, NWW faults structural; there are better prospecting potential in the zones of Au high-anomaly, the part of the mutation of positive and negative magnetic anomaly, the high polarizability and the low resistivity.

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