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Human-driven dynamics of land cover types in the Tarim Basin are able to affect potential dust source regions and provide particles for dust storms. Analyses about dynamics of potential dust source regions are useful for understanding the effects of human activities on the fragile ecosystem in the extremely arid zone and also provide scientific evidence for the rational land development in the future. This paper therefore selected the Tarim Basin, NW China, as a representative study area to reveal spatiotemporal dynamics of land cover and their impacts on potential dust source regions. The results showed that farmland, desert and forest increased by 28.63, 0.64 and 29.27%, while grassland decreased by 10.29% during 1990-2010. The largest reclamation, grassland loss and desertification were 639.17 × 10, 2350.42 × 10 and 1605.86 × 10 ha during 1995-2000. The relationship between reclamation and grassland loss was a positive correlation, while a highly positive correlation was 0.993 between the desertification and grassland loss at different stages. The most serious dust source region was the desertification during 1990-2010 (1614.58 thousand ha), and the serious region was stable desert (40,631.21 thousand ha). The area of the medium and low dust source region was 499.08 × 10 and 2667.27 × 10 ha. Dramatic reclamation resulted in the desertification by destroying natural vegetation and breaking the balance of water allocation in various regions. [ABSTRACT FROM AUTHOR]

The tight sandstone reservoir of the Donghetang Formation underwent complex diagenetic processes for which the controlling factors remain unknown. Here, we present a case study of the lower member of this formation and show that this part of the reservoir consists mostly of lithic quartz sandstone with poor physical characteristics. Using core observation, thin section identification, electronic microprobe, scanning electronic microscopy, X-ray diffraction, and inclusion fluorescence microscopy, we identified five major diagenetic processes: compaction, cementation, dissolution, metasomatism, and hydrocarbon charging. Compaction and cementation have negative effects on petrophysical properties (referred to porosity and permeability of sandstone in this paper), and dissolution improves these properties. Diagenesis is affected by the depositional environment, and clastic constituents control compaction and dissolution; burial history and the geotemperature field control diagenesis at the macroscopic scale, while hydrocarbon charging affects the degree of cementation and dissolution. As oil saturation increases, the percentage of calcareous cements decreases and the development of secondary dissolved pores improves. [ABSTRACT FROM AUTHOR]

A new method for characterizing architectural elements of fractured-cavernous carbonate reservoirs was proposed, with application to an Ordovician reservoir in the Tahe Oilfield, Tarim basin. The new method integrates observations from outcrop analogs and concepts from modern karst theory for the mapping and modeling of fractured-cavernous reservoirs. In this paper, fractured-cavernous reservoirs were divided into 4 architectural element types—underground river caverns, sinkholes, discrete internal caverns, and faults. Architectural elements of the Ordovician reservoir in Tahe oilfield were identified and characterized by integrating well logs and seismic data. A new method constrained by faults, karst zones, and seismic acoustic impedance data, was introduced to build a 3D model of architectural elements of fractured-cavernous reservoir in the S48 unit of Tahe Oilfield. A porosity model was then derived from the architectural element model using facies-constrained method. The research provides a work-flow for the characterization of fracturedcavernous reservoirs and determining optimal methods for maximizing oil recovery in the study area or in similar areas. [ABSTRACT FROM AUTHOR]

With the breakthrough of exploration in Well TP16-1, the lower Kepingtage Formation becomes a key target for petroleum exploration of deep clastic reservoir in Tahe area. In this paper we focused on the research of the reservoir characteristics and its controlling factors in two sub-member formations (S1 k and S1 k ). Based on X-ray diffraction, conventional physical properties data (porosity and permeability) and reservoir storage space data (casting thin section and scanning electron microscope), we determined that the S1k1 Formation belongs to extra-low porosity and permeability reservoir, although the upper S1 k Formation shows relative better physical characteristic than the lower S1 k Formation. The development of storage space in the study area is controlled by sedimentary microfacies, diagenesis process. Reservoirs in S1k1 Formation are mainly located in channel (S1 k sandstones) and sand flat (S1 k sandstones). The sand flat sediments with a more coarse grain size compared with the channel. In diagenesis, compaction is the major controlling factor for reducing the porosity, followed by cementation. Dissolution of diagenesis is the major controlling factor in enhancing the reservoir porosities. Compared with channel (S1 k ) sandstones, sand flat sandstones (S1 k ) have better reservoir quality for its weaker compaction, cementation and stronger dissolution. On the basis of sedimentary characteristics (grain size and subfacies), physical property (porosity and permeability) and reservoir storage space, we divide the S1k1 reservoir into three categories (I, II and III). Type I reservoir is high quality reservoir. It is mainly distributed in the south area of S1 k and S1 k reservoir. Type II is moderate reservoir. It is located in the middle of S1 k reservoir and in the north of S1 k reservoir. Type III is the poor reservoir. It is only located in the north of S1 k reservoir. [ABSTRACT FROM AUTHOR]

According to the characteristics of groundwater in arid area, this paper proposes DRAV model for groundwater vulnerability assessment, where D is groundwater depth, R is the net recharge of aquifer, A is the aquifer characteristics, and V is the lithology of vadose zone. As a case study, the paper assesses the vulnerability of pore phreatic water in Tarim Basin of Xinjiang, China by using the DRAV model. The results indicate that the areas of phreatic water with vulnerability index ranges of 2–4, 4–6, 6–8 and >8 accounting for 10.1, 80.4, 9.2 and 0.2% of the total plain area of the Tarim Basin respectively, and the areas with the latter two vulnerability ranges (6–8 and >8) are mainly located in the irrigation districts with thin soil layer (20–30 cm thick surface soil of vadose zone, mainly with underlying sandy gravel) and with silty and fine sand layer. Such vadose zone generally lacks sandy loam and clayey soil and has larger recharge by infiltration of irrigation water. [ABSTRACT FROM AUTHOR]

Since the discovery of the Tahe oilfield, it has been controversial on whether the main source rock is in the Cambrian or Middle-Upper Ordovician strata. In this paper, it is assumed that the crude oil from the Wells YM 2 and TD 2 was derived from the Middle-Upper Ordovician and Cambrian source rocks, respectively. We analyzed the biomarkers of the crude oil, asphalt-adsorbed hydrocarbon and saturated hydrocarbon in bitumen inclusions from the Lunnan and Hade areas in the North Uplift of the Tarim Basin. Results show that the ratios of tricyclic terpane C/C in the crude oil, asphalt-adsorbed hydrocarbon and saturated hydrocarbon in bitumen inclusions are less than 1.0, indicating that they might be from Upper Ordovician source rocks; the ratios of C/(C+C+C) steranes in the saturated hydrocarbon from reservoir bitumen and bitumen inclusions are higher than 25, suggesting that they might come from the Cambrian source rocks, however, the ratios of C/(C+C+C) steranes in oil from the North Uplift are less than 25, suggesting that they might be sourced from the Upper Ordovician source rocks. These findings demonstrate that the sources of crude oil in the Tarim Basin are complicated. The chemical composition and carbon isotopes of Ordovician reservoired oil in the Tarim Basin indicated that the crude oil in the North Uplift (including the Tahe oilfield) and Tazhong Depression was within mixture areas of crude oil from the Wells YM 2 and TD 2 as the end members of the Cambrian and Middle-Upper Ordovician sourced oils, respectively. This observation suggests that the crude oil in the Ordovician strata is a mixture of oils from the Cambrian and Ordovician source rocks, with increasing contribution from the Cambrian source rocks from the southern slope of the North Uplift to northern slope of the Central Uplift of the Tarim Basin. Considering the lithology and sedimentary facies data, the spatial distribution of the Cambrian, Middle-Lower Ordovician and Upper Ordovician source rocks was reconstructed on the basis of seismic reflection characteristics, and high-quality source rocks were revealed to be mainly located in the slope belt of the basin and were longitudinally developed over the maximum flooding surface during the progressive-regressive cycle. Affected by the transformation of the tectonic framework in the basin, the overlays of source rocks in different regions are different and the distribution of oil and gas was determined by the initial basin sedimentary structure and later reformation process. The northern slope of the Central Uplift-Shuntuo-Gucheng areas would be a recent important target for oil and gas exploration, since they have been near the slope area for a long time. [ABSTRACT FROM AUTHOR]

In order to find the impact of regional tectonic evolution of Tarim basin on the inside distribution of sedimentary facies and reservoir development, this paper, based on the research of plate-tectonic evolution of Tarim basin, conducts an in-depth analysis on the basin's inside sedimentary response to the Eopaleozoic regional geodynamic reversion from extension to convergence around Tarim plate, and concludes that the regional geodynamic environment of surrounding areas closely contributes to the formation and evolution of paleo-uplifts, differentiation of sedimentary facies in platform, distribution of high-energy reef and bank facies belts, conversion of sedimentary base level from fall to rise, obvious change of lithology from dolomite to limestone, and formation of several unconformity surfaces in Ordovician system in the basin. A series of sedimentary responses in the basin are controlled by regional dynamic setting, which not only controls the distribution of reservoirs in reef and bank facies but also restricts the development and distribution of karst reservoirs controlled by the unconformity surfaces. This offers the macro geological evidences for us to further analyze and evaluate the distribution of favorable reservoirs. [ABSTRACT FROM AUTHOR]

The crude oils typically from the Cambrian-Lower Ordovician source rocks of Tarim Basin, NW China, such as TD2Є and TZ62S, are C-enriched with the stable carbon isotopic ratios (VPDB) approaching −28 ‰. In this paper, the main research viewpoints on this issue are summarized, and combined with results from organic and inorganic carbon isotope stratum curves of the outcrop at the Ya'erdang Mountain in Tarim Basin. In addition, more alternative interpretations are discussed. On one hand, the inverse fractionation features of stable carbon and hydrogen isotopes of these crude oils may imply their protogenous nature. On the other hand, the anisotropy of source rocks and contribution from older stratum source rocks need verifying as well. For the sake of the final resolution of this issue, some further study topics are recommended. [ABSTRACT FROM AUTHOR]

Meso-Cenozoic extensional structures are important for understanding the tectonics of the Chinese Central Asia. This paper presents a systematic investigation on the Meso-Cenozoic extensional structures in the Northern Tarim Basin. Close interpretations of seismic data reveal that the Meso-Cenozoic extensional structures were widely developed in the Northern Tarim Basin. These extensional structures are regionally composed of many small normal faults, which usually group into left- or right-step en echelon and form several transtensional fault zones. Combinations of normal faults in profile become small graben-horst or staircase-like cross-sections. Based on the areal distribution, structural style, combination relationship, formation and evolution time, and formation mechanism of the extensional structures, we found that the Meso-Cenozoic extensional structures in Northern Tarim Basin can be classified into two conjugate normal fault systems, which were formed separately in Jurassic-Early Cretaceous and Late Cretaceous-Neogene. The former is likely associated with the stress relaxation after a collisional orogeny accompanied with a certain degree of anticlockwise rotation of the Tarim block relative to the South Tianshan; the latter is possibly induced by the east by south tectonic escape of the Tarim block with a certain degree of clockwise rotation relative to the South Tianshan triggered by the far-field effect of the Himalayan orogeny. [ABSTRACT FROM AUTHOR]

The polymetallic (Pb, Zn, Cu, etc) ore belt on the southwestern margin of Tarim is one of the major regions with the greatest prospecting potential in Xinjiang. Reported in this paper are the lead isotope data for 66 sulfide samples (including 50 galena samples, 15 chalcopyrite samples and 1 pyrite sample) collected from such representative deposits as Tamu, Tiekelike, Kalangu, Abalieke, etc. in this ore belt. The Pb isotopic ratios of Pb/Pb, Pb/Pb and Pb/Pb in the galena samples range from 17.931 to 18.176, 15.609 to 15.818 and 38.197 to 38.944, with the average values of 18.017, 15.684 and 38.462, respectively. Those in the chalcopyrite samples range from 17.926 to 18.144, 15.598 to 15.628 and 38.171 to 38.583, with the average values of 18.020, 15.606 and 38.262, respectively. The pyrite sample has the Pb isotopic ratios of Pb/Pb, Pb/Pb and Pb/Pb to be 17.980, 15.604 and 38.145, respectively. In combination with the previous Pb isotope data for sulfides, it is found that there is only a slight variation in the Pb isotopic composition of galena, chalcopyrite, sphalerite and pyrite in the ore belt. However, there is some difference in Pb isotopic characteristics between galena and chalcopyrite, especially the Pb isotopic composition of galena shows an obvious linear correlation with some other relevant parameters (e.g. Δβ and Δγ). The comprehensive analysis suggested that lead in galena (maybe including sphalerite and pyrite) was derived principally from wall rocks and underlying basement, and that in chalcopyrite only originated from the basement. The single-stage model ages of these sulfides couldn't indicate the time limit of metallogenesis (Pb, Zn, Cu, etc.), and the positive linear correlations for the Pb isotopic composition of galena are of no single-stage and two-stage Pb-Pb isochron significance. Furthermore, there are significant differences in Pb isotopic composition characteristics between the genetic type of deposits in this polymetallic ore belt and the Mississippi Valley type (MVT). In addition, the authors also pointed out that there is a phenomenon of differentiation (not paragenesis) for lead and copper elements during the process of metallogenesis in this ore belt. [ABSTRACT FROM AUTHOR]

The apatite (U-Th)/He thermochronometry has been used to study the tectono-thermal evolution of mountains and sedimentary basins for over ten years. The closure temperature of helium is important for the apatite (U-Th)/He thermochronometry and has been widely studied by thermal simulation experiments. In this paper, the apatite He closure temperature was studied by establishing the evolutionary pattern between apatite He ages and apatite burial depth based on examined apatite He ages of natural samples obtained from drillholes in the Tarim basin, China. The study showed that the apatite He closure temperature of natural samples in the Tarim basin is approximately 88±5°C, higher than the result (∼75°C) obtained from the thermal simulation experiments. The high He closure temperature resulted from high effective uranium concentration, long-term radiation damage accumulation, and sufficient particle radii. This study is a reevaluation of the conventional apatite He closure temperature and has a great significance in studying the uplifting events in the late period of the basin-mountain tectonic evolution, of which the uplifting time and rates can be determined accurately. [ABSTRACT FROM AUTHOR]

Polychaete serpulids are globally distributed tubeworms mostly in marine environments from Late Triassic to modern time. These calcareous tubeworms could be rock-forming, reef-building, or a principal fouling organism in harbor and bays. Carbonates of the Paleogene Kalatar Formation in southwest Tarim Basin yield abundant serpulid fossils, which, together with oyster fossils, constitute the characteristic fossil assemblage of the Kalatar Formation. Other common fossils include bivalves, gastropods, ostracods, echinoderms, and bryozoans. Lithologies that yielded serpulid fossils are characterized by micritic bioclastic limestone, sandy limestone, and shelly limestone, indicating a semi-restricted to open shallow marine environment with medium to low water energy. The research data about serpulids and their fossil materials from China are relatively rare. Based on the studies of fossils taxonomy, community palaeoecology, and fossil taphonomy, this paper analyzed and studied the types, occurrence, distribution, and morphological characteristics of serpulids and their palaeoecological features in the Kalatar Formation. Two serpulid community compositions were recognized in the Kalatar Formation, including a rock-forming Ditrupa community and a cluster-growth Propomatoceros community. The Ditrupa community was distributed in coastal environment of the west Kunlun piedmont, lived on sandy hard substrates with little mud, and rarely occurred in lagoon and tidal settings. The Propomatoceros community occurred in offshore middle carbonate ramp in the piedmont of the south Tianshan Mountains and in offshore shelf in the piedmont of the west Kunlun Mountains. According to the analysis on the host-rock lithologies, preservation and symbionts, it is inferred that serpulids in the Kalatar Formation grew on the oyster shell or other hard substrate, and they did not form reefs or bioherms. [ABSTRACT FROM AUTHOR]

The salt beds of the Middle-Lower Cambrian are widespread in the middle-west parts of the Central Uplift and adjacent areas, the Tarim Basin. This paper presents the results of seismic interpretation and drilling data analysis, which discovered that the salt beds were formed in an old geologic age, deeply buried, with relatively small scaled flowing and gathering and uneven distribution. As the regional detachment layers, the salt sequences considerably control the structural deformation of the up-salt Paleozoic, forming a series of hydrocarbon traps. In due course, the salt beds of the Middle-Lower Cambrian provide excellent cap rocks and trap conditions; thus the value of exploring hydrocabon reservoir in the target strata of the sub-salt Sinian-Cambrian is greatly increased. Research has shown that the salt-related structures of the Middle-Lower Cambrian in the area mainly exist in the form of salt pillow, salt roller, up-salt anticline, salt diapir, assemblage of the salt arch and up-salt fault-block, assemblage of basement fault and salt anticline, assemblage of the basement fault-block and salt dome, assemblage of salt detachment and fault-related fold, and assemblage of basement fault-block, salt arch and up-salt imbricated thrusts. The evolution and deformation mechanisms of the salt-related structures are controlled largely by basement faulting, compressional shortening, plastic flowing and gathering, superstratum gravitation, and up-salt faulting and detaching. They are distributed in rows or belts along basement faults or fault block belts. [ABSTRACT FROM AUTHOR]

TD-2 structure is located in the eastern part of the Central Uplift zone of the Tarim Basin, China. It is a basement-uplift anticline-type structure confirmed by seismic and gravity prospecting, and it is expected to have good potential for oil and gas according to the analysis of regional geological evolution history. But further exploration such as drilling is suspended because of lacking direct geochemical information. Therefore, multi-parametric geochemical surveys, such as free hydrocarbons (C-C), acid hydrocarbons (C-C) and ΔC, Hg of soil, were conducted. It is concluded in this paper that free hydrocarbons are obviously better than other geochemical parameters and could be used for evaluation of oil and gas potential of TD-2 structure in the desert area. Shapes of near-surface geochemical anomalies and geochemical characteristic parameters suggested that TD-2 structure was a dry gas-bearing structure at the early-middle dissipation stage. So TD-2 structure should have some promising potential for oil-gas. Multi-parametric geochemical survey provided important information for further drilling exploration. [ABSTRACT FROM AUTHOR]

This paper examines the teleconnection between the Arctic Oscillation Index (AO) and dust activities in the Tarim Basin [in terms of the Total Ozone Mapping Spectrometer (TOMS) Aerosol Index (AI) level]. In this study, High Dust Active years (H) and Low Dust Active years (L) in terms of dust loading are identified. Composites of geopotential height at both 850 and 500 hPa level show that, the geopotential height level of H years is generally lower than the average, especially over the south end of the Central Siberian Plateau. The geopotential height level of L years is generally higher than the average, especially over the same region of Siberia. By correlating the AO and TOMS AI with geopotential height at different pressure levels, a South Siberia Geopotential Height Index (SSGI) is constructed. A strong positive correlation is found between AO and SSGI. Strong negative correlations are found between TOMS AI and AO, and between TOMS AI and SSGI. Through investigating the relation among these three measures (TOMS AI, AO and SSGI), we found that in the positive phase of AO, geopotential gradient between the inside and outside of the basin is small. The northerly wind from Siberia is weak and decreases when it encounters the north barrier of the basin. As a result, dust activities in the Tarim Basin is weak and Eddy Kinetic Energy (EKE) level measured in the basin is lower. In the negative phase of AO, geopotential gradient between the inside and outside of the basin is big. The northerly wind from Siberia is strong, and passes the north barrier of the basin. When it encounters the Tibetan Plateau, a component of the wind goes into the basin. During this process, the wind accelerates given the higher pressure gradient. As a result, dust activities in the Tarim Basin are frequent and intensive, and the EKE level in the basin is higher. [ABSTRACT FROM AUTHOR]

Some large-scale oil-gas fields have recently been discovered in marine carbonate in China, especially the significant discoveries in deep reservoir that reveals a favorable exploration prospect. Tazhong area is the first-order tectonic unit in Tarim Basin, where there are nearly trillion cubic meters of natural gas resources in the Ordovician limestone reef flat complex in Lianglitage Formation. The reservoir is shelf edge reef flat complex, characterized by ultra-low porosity, low permeability and strong heterogeneous, with a current burial depth of 4500-6500 m. Studies find that the formation and distribution of deep reservoir of the Lianglitage Formation were controlled not only by the early high-energy sedimentary facies and corrosion, but the fracture network formed by the strong gas-charging process since the Himalayan epoch, which played an important role in optimizing and improving reservoir properties. This paper discusses the relationship between the strong later gas-charging and the improvement of the reservoir capacity in deep Ordovician carbonate reservoir, and also builts the corresponding mechanisms and modes, which is favorable for the prediction and evaluation of the advantageous exploration targets. [ABSTRACT FROM AUTHOR]

In this paper, a 2D velocity structure of the crust and the upper mantle of the northern margin of the Tarim Basin (TB) has been obtained by ray tracing and theoretical seismogram calculation under the condition of 2D lateral inhomogeneous medium using the data of seismic wide angle reflection/refraction profile from Baicheng to Da Qaidam crossing the Kuqa Depression (KD) and Tabei Uplift (TU). And along the Baicheng to Da Qaidam profile, 4 of the 10 shot points are located in the northern margin of the TB. The results show that the character of the crust is uniform on the whole between the KD and TU, but the depth of the layers, thickness of the crust and the velocity obviously vary along the profile. Thereinto, the variation of the crust thickness mainly occurs in the middle and lower crust. The Moho has an uplifting trend near the Baicheng shot point in KD and Luntai shot point in TU, and the thickness of the crust reduces to 42 km and 47 km in these two areas, respectively. The transition zone between the KD and TU has a thickest crust, up to 52 km. In this transition zone, there are high velocity anomalies in the upper crust, and low velocity anomalies in the lower crust, these velocity anomalies zone is near vertical, and the sediment above them is thicker than the other areas. According to the velocity distributions, the profile can be divided into three sections: KD, TU and transition zone between them. Each section has a special velocity structural feature, the form of the crystalline basement and the relationship between the deep structure and the shallow one. The differences of velocity and tectonic between eastern and western profile in the northern margin of the Tarim Basin (NMTB) may suggest different speed and intensity of the subduction from the Tarim basin to the Tianshan orogenic belt (TOB). [ABSTRACT FROM AUTHOR]

The Ordovician system is an important target for exploration in the Tarim Basin. Restoration of the Ordovician tectono-depositional environment is a key basis for the study of the structural development history in Tarim block and the prediction of the favorable Ordovician reservoir belts (zones). Based on the surrounding tectonic settings, the litho-facies and sedimentary fill, the palaeo-geography, palaeoclimate and palaeo-ecology, and the structural deformation and magmatic eruptions, in this paper we combine the sedimentary fill in the basin with the development of the surrounding orogenic belts and re-build the proto-type basins of the different Ordovician periods. During the Ordovician period, the Tarim region was characterized by the composite of the interior cratonic depression with the peripheral cratonic depression. The interior cratonic depression in the central and western parts is mainly the depositional area of the platform facies while the peripheral cratonic depression in the eastern part is mainly the zone of deepwater basin facies, with the slope acting as the transition belt between them. During the Late Ordovician period, the closure of the Northern Kunlun Ocean and destruction of the trench- arc-basin system in the Altyn Tagh region put the southern part of the Tarim block under compression and uplifting and turned the central and western parts of the carbonate platform into the mixed depositional continental shelf. The eastern region of the basin had the over-compensated flysch sedimentation with huge thickness, marking the drastic turn of the basin nature. The basin tectonic framework turned to the south-north differentiation of the Silurian period from the east-west differentiation of the Ordovician period. [ABSTRACT FROM AUTHOR]

The identification of marine source rocks in the Tarim Basin is debated vigorously. The intention of this paper is to investigate the asphaltenes in heavy oils from the Lunnan and Tahe oilfields and Well TD2 with ruthenium-ions-catalyzed oxidation technique (RICO), in order to explore its role in oil-oil and oil-source correlations. The RICO products included n-alkanoic acids, α, ω-di-n-alkanoic acids, branched alkanoic acids, tricyclic terpanoic acids, hopanoic acids, gammacerane carboxylic acid , regular sterane carboxylic acids and 4-methylsterane carboxylic acids. The n-alkyl chains and biomarkers bounded on the asphaltenes were of unsusceptibility to biodegradation. The distribution and absolute concentrations of n-alkanoic acids in the RICO products of heavy oils from the Lunnan and Tahe oilfields are different from those of Well TD2. The biomarkers bounded on the asphaltenes, especially steranes, have a distribution trend similar to that of the counterparts in saturates. The sterane carboxylic acids and 4-methylsterane carboxylic acids in the RICO products of heavy oils from the Lunnan and Tahe oilfields, dominated by C30 sterane and C31 4-methylsterane carboxylic acids, respectively, are significantly different from those of the heavy oils of Well TD2, whose dominating sterane and 4-methylsterane carboxylic acids are C28 sterane and C29 4-methylsterane acids, respectively. The RICO products of the asphaltenes further indicate that the Middle-Upper Ordovician may be the main source rocks for heavy oils from the Lunnan and Tahe oilfields. [ABSTRACT FROM AUTHOR]

There were different opinions about the origin of petroleum property variations in the Lunnan Low Uplift of the Tarim Basin. In this paper, a software PVTsim was applied to investigate the compositions of the petroleum fluid inclusions in different sets of reservoir rocks from this area. The results show that there are three phases of petroleum inclusions in the Ordovician carbonate reservoirs and two types of petroleum inclusions in the Carboniferous and Triassic sandstone reservoirs. The three phases of the petroleum inclusions from the Ordovician reservoir rocks have similar compositions with the type 1 petroleum inclusion from the carboniferous and Triassic reservoir rocks, but the type 2 petroleum inclusion from the carboniferous and Triassic reservoirs is characterized by higher content of C1 and higher GOR values. With the combination of the geological background, it was inferred that the current petroleum pools in the Lunnan Low Uplift were formed mainly by two phases of petroleum charges, one is normal oils and another light oils, and both occurred during the late Tertiary. The light oils came from eastern-south direction, and migrated and charged into the reservoirs upward and toward northern west directions. On the basis of this, it was believed that the multiphases of the petroleum charges and some composition dissipation caused by the preserved condition changes would be the main reason of the petroleum property variations in the petroleum pools in this area. [ABSTRACT FROM AUTHOR]

The issue of source of oil/gas in the platform basin area in Tarim Basin has been debated for a long time, and the debate is focused on whether the marine oil/gas resources that have been discovered in the basin were originated from hydrocarbon source rocks in the Cambrian-Lower Ordovician or in the Mid-Upper Ordovician. In this paper a summary was made in regard to the major points and supporting data by the predecessors, and a discussion was conducted toward the core issues related to the study on the oil source in the Tarim Basin area, such as choice of correlation parameters, influence of maturation and physical differentiation on oil source correlation parameters, and geological and geochemical significance of these relevant correlation indices. It is quite probable that different interpretation results could arise from the oil source correlation due to choice of parameters severely affected by the thermal maturation and physical differentiation effect, and insisted that only those parameters that come with clearly defined geochemical significance and are less affected by thermal maturation and variations occurring during secondary evolution process are valid ones. The marine crude in Tarim Basin covers contributions that were originated from two sets of hydrocarbon source rocks as mentioned above but dominated by the one from the Mid-Upper Ordovician hydrocarbon source rocks. Here oil of mixed sources occurs extensively, and crude from Cambrian sources was also discovered. It is suggested that for further study on the origin of marine crudes in Tarim Basin, the parameters used for correlation of oil sources shall be optimized, and a comprehensive set of geological and geochemical methods shall be adopted for this purpose. [ABSTRACT FROM AUTHOR]

More and more evidence indicates that organic matter (OM) in immature organic-rich sediments and sedimentary rocks is chemically adsorbed onto the outer surfaces of minerals and into interlayer (inner) surfaces of smectitic clay minerals in the form of amorphous molecular-scale carbon. But there have been few reports about the occurrence of highly mature OM in marine black shales (petroleum source rocks). The occurrence of highly mature OM in the black shales of basal Cambrian from northern Tarim Basin is studied in this paper. Based on the comprehensive analyses of total organic carbon contents (TOC) , maximum thermoplastics temperatures (Tmax) of OM, mineral surface areas ( MSA ) , and scanning electronic microscopic (SEM) and transmission electronic microscopic (TEM) observations of the black shales, it is concluded that the highly mature OM in the marine black shales of the basal Cambrian from northern Tarim Basin occurs in particulates ranging In size from 1 to 5µm in diameter. Through the contrast of the occurrence of the highly mature OM in the black shales with that of the immature ones in modem marine continental margin sediments, some scientific problems are proposed, which are worth to study further in detail. [ABSTRACT FROM AUTHOR]

Ten series of aromatic hydrocarbon compounds (biphenyl, naphthalene, phenanthrene, anthracene, retene, chrysene, benzoanthracene, dibenzofuran, fluorene, dibenzothiophene) isolated from seven Triassic and Jurassic lacustrine mudstone samples and three swamp coal samples, as well as five crude oil samples collected in the Kuche depression of the Tarim Basin, NW China, have been analysed by GC-MS techniques. It is found that the relative abundances of dibenzofuran series are higher in the three swamp coal samples than those in the lacustrine mudstone samples. Based on the similar relative abundances of dibenzofuran series, especially dibenzofuran compound, in the TICs of aromatic hydrocarbons, crude oils from wells SA3 ( K ) , YTK5 ( E , K) and QLl (E) are thought to have been derived predominantly from the coals of the Lower Jurassic Yangxia Formation or Middle Jurassic Kezilenuer Formation, whereas those from wells YM7 ( 0 ) and YH1 (E) were derived mainly from Triassic and Jurassic lacustrine mudstones in the Kuche depression. This is the first report about how lo distinguish coal-generated oils from lacustrine mudstone-generated oils in the Kuche depression in terms of the dibenzofuran series. The present paper has enlightening and directive significance for further oil-source rock correlations and oil and/or gas exploration in the Kuche depression of the Tarim Basin. [ABSTRACT FROM AUTHOR]

Reports that the Kuqa depression bears not only plenty of natural gas, but also a large amount of condensate and small quantity of crude oil. Confirmation in this paper that, based on the geochemical correlation between the Jurassic and Triassic terrestrial hydrocarbon source rock, the natural gas in Kuqa depression belongs to coal-type gas and the main gas source rock is attributed to the middle to lower Jurassic coal series formation, while the main oil source rock is the upper Triassic lacustrine mudstone; Indication by the authors that Kuqa depression was slowly subsided in Mesozoic, but rapidly went down in Late Tertiary, which made the Jurassic and Triassic source rock suddenly deep-buried and rapidly evolved to high and over-mature phase since 5 Ma; Statement that the Triassic source rock is postponed to the Early Miocene during 23-12 Ma when entering the oil-generating peak, while the Jurassic is suspended to the latest 5 Ma, especially since 2.5 Ma to the dry gas-generating period, which is one of the characteristics of the source rock thermal evolution in Kuqa depression; Presentation in this paper of a two-stage trapping and late gas trapping model in Kuqa depression whose characteristics are: The main oil and gas reservoirs have different sources; Formation of the oil reservoir is early while the gas reservoir is formed lately; Reference to the fact that, during the early stage, it, mainly as oil, takes long distance lateral migration, while in the later stage, it, mainly as gas, takes the vertical migration and also has lateral migration; Formation of the trap formed in different time on the south and north sides of the depression and evolution into a distributional pattern with oil in the south part and gas in the north, also oil on the outer ring and gas on the inner ring; Reference in this paper to the fact that late trapping of the natural gas in Kuqa depression is favorable for the preservation of large gas fields.

Reports that the Lunnan area in the Tarim Basin has become an important onshore oil production base in China. Statement that the formation of the oil and gas pools in the low uplift of Lunnan has experienced a comparatively complex process of dynamics; Reference to the fact that, based on the hydrocarbon generation period of source rocks, the formation period of cap rocks and traps, the analysis of organic inclusion and the analysis of bitumen in the reservoir, this paper draws the conclusion that the low uplift area of Lunnan has experienced three pool formation periods: the Permian period, the Cretaceous-Early Tertiary period and the Late Tertiary-Quaternary period and two oil and gas reservoir adjustment periods: the Late Permian period and the Late Tertiary-Quaternary period; Indication of the comprehensive study that the large-scale Ordovician buried hill, formed in Early Hercynian, became the reservoir during the Permian period, because the Cambrian-Lower Ordovician oil was discharged laterally into the reservoir along the top of the Ordovician weathering crust from south to north; Claim that the reservoir experienced a complicated process—reconstruction in the end of Permian, adjustment in Cretaceous-Early Tertiary and re-discharging process in Late Tertiary-Quaternary, leading to the early original heavy oil reservoir of marine facies and the late original light oil reservoir and gas pool; Statement that carboniferous, Triassic and Jurassic oil and gas reservoirs result from upward adjustment and re-distribution of Ordovician oil and gas reservoirs; Reference to the fact that, of those results, the formation of Triassic-Jurassic oil and gas pools came under the influence of the northward-tilting structure; Vertical migration of the oil and gas sourcing from the different hydrocarbon source rock intervals into the base unconformity of Triassic system; Migration of the the oil and gas laterally from north to south and accumulated into th

Reports that, based on the theory of plate tectonics, combining with the isotopic dating of ophiolite, igneous and volcanics, geochemical tests rare earth element analyze and seismic interpretation, this paper studies the pre-Carboniferous tectonics and sedimentary formation of the south edge of the Tarim Basin and proves that there exists the Kunlun Ocean under tensional tectonics during the Sinian and Cambrian in the south edge of the Tarim Plate. Statement that, due to the collision orogenesis, there formed the peripheral foreland basin in the south edge of Tarim; Reference to the fact that Upper Silurian and Devonian molasses sedimentary system superposed on the Sinian and Middle Silurian passive margin flysch sedimentary system and formed the bivariate structure of the foreland basin; Identification, based on the field geology and seismic interpretation, that the formation of the Silurian and Devonian have the character of half deposit which shows thick in the south area and thin in the north, and the pre-Carboniferous thrust compression tectonics remained in the foreland thrust belt, which further demonstrates that there existed the Silurian and Devonian peripheral foreland basin on the south edge of the Tarim Basin.

Reports that, based on the pore cast and cathodoluminescence thin sections, diagenesis process, source rock maturation history, structural evolution and reservoir quality characteristics, the points of view that the porosities of Paleozoic elastic eureservoirs in the platform of the Tarim Basin are mainly secondary, and the dissolution plays an unignorable role in the formation of eureservoirs, are put forward. Presentation in this paper of a series of criteria for the recognition of the secondary porosities; Introduction of the occurrence extent and classification of secondary porosity; Discovery of three kinds of dissolution mechanism–the aluminosilicate dissolution, the silicon dioxide dissolution and the carbonate dissolution—to generate the secondary porosity; Statement that the formation, distribution, preservation and disappearance of eureservoirs are controlled by the paleostructural framework and evolution, and hydrocarbon filling and discharging; Reference to the fact that paleostructural framework manipulate the migration path and direction of the acid fluid so as to determine the position and extent of the dissolution; Statement that the paleostructure highs and continuous paleouplifts are in favor of developing the secondary porosity; Potential for the hydrocarbon filling to preserve the secondary porosities; Ability of the hydrocarbon discharging t let the secondary porosities be filled by later calcite or quartz overgrowth cements; Suggestion that paleostructure highs and continuous paleouplifts during the maturation period of Cambrian, Ordovician and Carboniferous source rocks (corresponding to S, P and K) are main areas for eureser volts developing.

Reports that, based on detailed studies, this paper proposes that in the Tarim Basin, hydrocarbon reservoirs widespread either in vertical sequences or in plane and high-porosity and high-permeability reservoirs are developed all over the basin. Claim that obvious difference and heterogeneity exist among different kinds of reservoirs; Statement that the lithologic characteristics, reservoir space types and reservoir properties in various strata have been probed; Result indicating that although the Paleozoic carbonates have been deeply buried for a long period, high-quality reservoirs with the porosity of up to 5% -8% (12% as the maximum) and the permeability of 10x10&sup-3;–100x10&sup-3; µm² (1000x10&sup-3; µm² as the maximum) can be found in certain areas; Inclusion of the area with the development of reefs and carbonate beaches, the weathered-crust buried-hill belts that have undergone the long-term exposure, weathering and leaching, the area with the development of dolomitization, and those areas that have experienced the resolution of carbonic acid and organic acid generated by the maturity of the organic matter; Thorough investigation of the genesis of the high-porosity and high-permeability reservoirs in deep-buried conditions (with the depth more than 3500 m).

Tar mats were firstly discovered and determined accurately in terrestrial oil and gas reservoirs associated with Lower Tertiary sandstone reservoirs in the Yaha field of the Tarim Basin, China, by thin-layer chromatography-flame ionization detector (TLC-FID) and Rock-Eval analysis. The relative content of asphaltene in gross composition of tar mat extracts accounts for more than 30%, that in the corresponding oil leg less than 20%. In the geochemical description profile of oil and gas reservoirs, drastic changes in asphaltene contents between tar mats and oil legs could be discovered. This is an important marker to determine tar mats. Distribution characteristics of saturated and aromatic hydrocarbons from reservoir core extracts and crude oils in the Yaha oil and gas reservoirs in the Tarim Basin are described systematically in this paper, and the results show there are similarities among n-alkane distribution characteristics, biomarker distribution characteristics and their combined characteristics of saturated hydrocarbons, and the geochemical characteristics of aromatic hydrocarbons for tar mats, oil leg, asphaltic sand and crude oil. These characteristics suggest the hydrocarbons in these samples were originated from the common source rocks. However, the geochemical characteristics of tar mats revealed that the mechanism of formation of tar mats is the precipitation of asphaltene from crude oils in petroleum reservoirs caused by increased dissolved gas in oil legs (gas injection). [ABSTRACT FROM AUTHOR]

Geochemical analysis of 64 oils sampled from an Ordovician carbonate reservoir in the Tuoputai region was undertaken to study the composition of molecular markers. All the oils have similar geochemical characteristics and belong to a single oil family. They are presumed to derive from the same source kitchen and have similar oil charging history. A histogram of homogenization temperatures ( T ) of aqueous inclusions in reservoir rocks shows a bimodal distribution pattern, indicating that the Ordovician reservoir has been charged twice. Coupling the measured T (°C) with the burial and geothermal histories reconstructed using 1D basin modeling, we relate the homogenization temperature to the relevant geological ages: i.e., 425-412 and 9-4 Ma, corresponding to the Middle to Late Silurian and the Miocene to Pliocene, respectively. The oil filling orientation and pathways are traced using molecular indicators related to alkyldibenzothiophenes and benzo[ b]naphthothiophenes. The oil charging orientation is from south to north generally. It can be predicted that the Ordovician reservoirs were sourced from a kitchen located to the south of the Tuoputai region, most probably between the Awati and Manjiaer Depressions. Traps located in the southern side of the Tuoputai region, along the oil charging pathways, should therefore be preferred oil exploration targets. [ABSTRACT FROM AUTHOR]

Background and aims: The encroachment of halophytic shrubs including tamarisk into saline meadows is accelerating with global warming in the northern Tarim Basin, Xinjiang, China. However, the role of tamarisk in the spatial heterogeneity of soil resources in different desertification stages remains unclear. Methods: The influences of tamarisk on soil resources were assessed via soil salinity and soil organic matter (SOM) measurements under tamarisk canopies and in interspaces. Geostatistical methods were applied to compare the spatial heterogeneity of these soil properties in three regions representing different desertification stages: 1) a meadow with shrubs, 2) a shrubland and 3) shrub duneland. Results: The highest coefficient of variation (CVs) of the soil analytes and most developed 'resource islands' were observed in the shrubland. The overall variation of most of the soil variables was lower in the shrub duneland than in the shrubland and similar to that in the meadow with shrubs. The distribution of SOM and most soil salinity ions were moderately spatially dependent in the meadow with shrubs but highly spatially dependent in the shrubland and shrub duneland. The autocorrelation distances of the most of soil salinity ions were approximately 6- to 15- fold and 2- to 4-fold highest than the tamarisk shrub size in the meadow with shrubs and shrubland, respectively. In contrast, the distribution range of total soil salinity (TSS) and soil K, Na and Cl in the shrub duneland were 1/5 ~ 2/3 of the tamarisk size. Conclusions: 1) Compared with the effect of tamarisk on soil resource heterogeneity in the meadow with shrubs, that in the shrubland was enhanced due to the larger shrub size and more open and scattered canopy in the latter.2) Although the largest shrub size were observed in the shrub duneland, the role of tamarisk in redistributing soil resources was overriden by those of physical processes due to the loose canopy. 3) The spatial heterogeneity of soil resources is determined by not only tamarisk but also environmental factors, such as the connectivity of bare areas and topography. [ABSTRACT FROM AUTHOR]

The impacts of the summer plateau monsoon (PM) over the Tibetan Plateau on summer rainfall over the Tarim Basin in northwest China are investigated, based on the observed rainfall data at 34 stations and the NCEP/NCAR reanalysis data during 1961 to 2007. Results showed that the PM is well correlated to the summer rainfall over the Tarim Basin. Process analysis shows that strong PM corresponds to an anomalous cyclone over the Tibetan Plateau in the middle troposphere and an anomalous anticyclone in the upper troposphere over northwest part of Tibetan Plateau. They result in cold air moving from high latitudes into Central Asia over the western part of Tibetan Plateau. The concurrences of the cooling in the middle-upper troposphere over Central Asia leads to an anomalous cyclone over Central Asia at 500 hPa and the anomalous descending motions prevailing over the cooling region. Associated with this anomaly, there are enhanced southerly winds and corresponding ascending motion over the Tarim Basin located in the east of the cooling region. These processes lead to more summer rainfall over the Tarim Basin. [ABSTRACT FROM AUTHOR]

The Tarim Basin in western China has been receiving continuous marine to lacustrine deposits during the Cenozoic as a foreland basin of the Qinghai-Tibetan Plateau (QTP). Clay mineralogy and geochemical proxy data from these sedimentary archives can shed light on climate and tectonic trends. Here we report on an abrupt mineralogical and weathering shift at 17 Ma ± 1 Myr in the Miocene Qimugan section in the northwestern part of the Qinghai-Tibetan Plateau. The rapid shift involves decreasing trends of chemical weathering indices, Rb/Sr and Ba/Sr ratios, and of minor and immobile elements with respect to upper crust composition as well as increasing trends of Na/Al and Na/Ti ratios, smectite, chlorite, and calcite contents. We ascribe these trends to changing source rocks due to uplift of the northern part of the QTP leading to exposures of younger intrusive bodies and older gneisses, schists, and carbonate-rich rocks. These uplifts potentially caused regional aridification reducing chemical weathering. The dating is indirect via magnetostratigraphically dated ostracod biostratigraphy and detrital zircon chronology and currently not good enough to compare the shift accurately in time with the onset of the global middle Miocene Climate Optimum (MMCO) at 16.5 Ma. Nevertheless, regional tectonics seem to have dominated over global climate as the warmer MMCO is expected to have increased weathering indices and decreased Na/Al and Na/Ti, rather than the observed reverse trends. [ABSTRACT FROM AUTHOR]

A detailed correlation of Hetianhe condensates versus typical source rocks from the Tarim Basin was established. Moreover, the genetic relationship between the condensates and their associated gases was also studied based on their geochemical compositions and fluid inclusion data. Hetianhe condensates are characterized by high pristine/phytane (Pr/Ph) ratios, high relative abundances of C regular steranes, C-C triaromatic steroids, and triaromatic dinosteranes, and relatively heavy stable carbon isotopic compositions. They geochemically correlate well with the Cambrian source rocks, indicating that these condensates are derived from the Cambrian rocks. Based on several molecular maturity parameters, the condensates are recognized as being moderately to highly mature, which are too low in maturity to extensively crack into gases. The gases and condensates of the Hetianhe Field are derived from the same source rocks and the gases are from oil-cracking; however, clear evidence indicates that the gases were not cracked from their associated condensates and that the gas generation from oil-cracking did not occur in the present reservoirs. The liquid condensates produced from wellheads were likely dissolved in their associated gases underground and carried into the reservoirs by the gases. [ABSTRACT FROM AUTHOR]

Accurately estimating the changes in glacier mass balance and water storage in lakes and reservoirs is critical to studying the water cycle in the inland river basin in northwest China. We used high-resolution satellite images to analyze the changes in water surface area of lakes and reservoirs in Tarim Basin, and used the ICESat-GLAS altimeter data to estimate their water level changes and the glacier mass balance change, over the period 2003-2009. The results showed the average glacier thinning in the entire basin was at a rate of 0.34 ± 0.25 m w.e./year equivalent height of water, which means that the glacier mass balance occurred −6.8 ± 1.2 km water equivalent over the study period. However, the mean water level of nearby lakes decreased by 0.41 ± 0.2 m even with the influx of glacial melt water, indicating that the lake level declines were caused by the withdrawal of lake water for human activities. [ABSTRACT FROM AUTHOR]

The extremely arid Tarim Basin in northwestern China is an important cotton and fruit production region. However, extensive agricultural land reclamation combined with unreasonable water use in recent decades resulted in degradation of ecosystems along the Tarim River. With declining water availability, it is becoming increasingly important to utilize this essential resource more efficiently. Water pricing is considered an effective way to advance water allocation and water conservation. To identify whether a strong increase in water price may lead to a wiser agricultural water use along Tarim River, 128 farmers were interviewed with structured questionnaire in different parts of the Basin. Multinomial logistic regression was employed to explain the factors influencing farmers' reaction towards a strong increase in water price. The results show that under increased water price less than half of the interviewed farmers would opt for decisions that lead to improved water use efficiency. Moreover, the price increase might lead to a further expansion of groundwater exploitation in the region. Fruit farmers, as well as farmers with less land and less cash income are reluctant to adopt advanced irrigation technology or improve their crop production in reaction to increased water price. It was furthermore revealed that the experience of slight water shortage in the past created awareness by farmers to use water more wisely. It is concluded that the sole increase of water price is not a viable option; an integrated approach is necessary, in which creation of awareness and improving agronomic skills of farmers play a key role to overcome the tight water situation and realize a more efficient use of water. [ABSTRACT FROM AUTHOR]

The distribution of Girvanella within the Yijianfang Ordovician reef complexes of the Bachu area, western Tarim Basin, is elucidated in order to reveal the effects of Girvanella on the formation of potential reservoirs. Three categories of Girvanella include rafts, intraclasts, and crusts. Both Girvanella rafts and intraclasts have been transported, whereas Girvanella crusts are preserved in situ. Each category has been preserved mainly in fore-reef and back-reef outer shoals, and in upper slope deposits. Trends in the abundance of in situ Girvanella are inversely proportional to the abundance of Calathium and bryozoans. In situ Girvanella is abundant primarily in comparatively low-energy deposits, whereas Calathium and bryozoans occur commonly in higher-energy deposits, inferring that the faunal variations within the reef complexes are highly controlled by the original sedimentary conditions. The abundance of Girvanella is inversely correlated with both porosity and permeability. This may be due to effects associated with Girvanella including: (1) Girvanella rafts and intraclasts composed of micrite are well preserved, and the micrite envelopes associated with Girvanella crusts may protect the skeletal grains, preventing them from being dissolved; (2) Activities of Girvanella may block up primary pores. Results of this study will be useful for understanding the relationship between microbes and sedimentary environments and provide critical information about the genesis of potential reservoirs within the Ordovician reef complexes. [ABSTRACT FROM AUTHOR]

This article aims to analyze the main controlling factors of development, distribution and evolution of the fault systems in the Tarim Basin. Based on the seismic profile interpretation, comprehensive analysis of the drilling and geologic data, six fault systems maybe recognized in the Tarim Basin, they are the foreland fault system of the South Tianshan Mountain, the northern Tarim uplift fault system, North Tarim depression fault system, central fault system, Southwest Tarim fault system, and Southeast Tarim fault system. It is indicated that the main differences exist at the development, evolution and distribution of the fault systems in the Tarim Basin. The sub-fault systems can be recognized according to the differences of the fault development and distribution in the interior of the fault system. It is characterized that the multi-level differential development and distribution of the fault systems exist in the Tarim Basin. The fault belt developed in the Paleozoic strata mainly distribute at the paleo-uplift and paleo-slope in the interior of the Tarim Basin, and the fault belt occurred in the Meso-Cenozoic beds mainly develop at the peripheral foreland depressions. Zonal and segment differential development and distribution of the fault systems also exist in the Tarim Basin. The formation and distribution of the Tarim fault systems is of complex controlling mechanisms. Poly-phase structural movement and tectonic transition controls the multi-phase differential development and distribution of the fault systems in the Tarim Basin. Multi-level differential development and distribution is controlled by multi-level detachment belt and regional unconformities. Zonal and segment differential development and distribution of the Tarim fault systems maybe controlled by pre-existed basement structural texture. The major direction of the fault systems in the Tarim Basin is controlled by the later stage basin-mountain coupling. [ABSTRACT FROM AUTHOR]

Based on the analysis of sedimentary facies and chemical index of alteration (CIA) in Nanhua and Ediacaran Systems in the southwest of Tarim Block, some features of glacial records in Neoproterozoic become more clear. Six sedimentary facies have been divided in the study area, including alluvial fan facies, lacustrine facies, glacial facies, littoral facies, neritic facies, and lagoonal facies, showing that this area underwent a process from continent to marine, with mainly littoral and neritic sedimentation. Two cold events have been recognized by analysis of CIA values in the study area, called Bolong and Yutang glaciation, respectively. They present as thick-layer tillite deposition in the Bolong Formation and thin-layer tillite deposition in the Yutang Formation, respectively. The Bolong glacial period in the study area can be correlated to the Yulmeinak glacial period in Aksu area, Tereeken glacial period in Qurugtagh area, and the Nantuo glacial period in South China, which is equivalent to the universally acknowledged Marinoan glacial period. The Yutang glacial period can be correlated to the Hankalchough glacial period in Qurugtagh, which is equivalent to Gaskers glaciation in Newfoundland. [ABSTRACT FROM AUTHOR]

The Upper Ordovician Lianglitag Formation carbonate rocks are important oil and gas reservoirs in the Tarim Basin, Northwest China, with obviously distinct reservoir properties among different oilfields. As a case area of the above carbonate reservoirs correlation, Tahe and Tazhong oilfields are chosen for the study through an integrated analysis of biostratigraphic isochronous framework, cores, thin sections, logs, and strontium isotopes. The research shows that the two areas were respectively attributed to different carbonate platforms during the Lianglitag Formation depositional phase. For the Lianglitag Formation, five fourth-order sequences may be divided in Tazhong, whereas only four fourth-order sequences are preserved in Tahe that correspond to the lower ones observed in Tazhong. The Lianglitag Formation carbonate platform in Tahe was characterized by ramp and/or weak rimmed types, with low depositional rates (37 μm/a), higher whole-rock clastic contents, and higher Sr/Sr isotope ratios of carbonate matrix, showing relatively deep-water environment and evident terrigenous input for carbonate deposition. However, a strongly rimmed carbonate platform was developed in Tazhong, with high depositional rates of 250 μm/a and less whole-rock clastic contents, indicating a high-energy depositional environment. Because of the sedimentary environment differences mentioned above, less high-energy facies but relatively intense syndepositional (early diagenetic) sea-water cementation of carbonates were developed in Tahe, and ubiquitous high-energy reef and shoal facies, with a frequent exposure to subaerial, and weak syndepositional sea-water cementation of carbonates in Tazhong. Therefore, fewer primary pores occurred in the Lianglitag Formation carbonate rocks of Tahe, whereas more primary pores were preserved in the same lithostratigraphic unit of the Tazhong (No. 1 fault zone). Available high-energy reef-shoal facies and early diagenesis, with more primary pores preserved, provided a key material basis for the Lianglitag Formation carbonate reservoirs that largely occurred in Tazhong. [ABSTRACT FROM AUTHOR]

U-Pb ages of Devonian detrital zircons from Tabei Uplift have been determined through LA-ICP-MS test technology. The results revealed that most zircon ages concentrate on 460-414 Ma, especially around 436-423 Ma, indicating possible occurrences of strong tectonic events at the northern margin of Tarim Basin during that period. Combined with previous researches on the basin marginal orogenic belts, intense tectonic activities developed at the northeast margin of Tarim Basin and its obvious sedimentary responses in basin during the end of Ordovician to Early-Middle Silurian are discussed. These include (1) several unconformities within the Late Ordovician-Silurian, showing truncation, erosion, and onlap characteristics, which reflected the local uplift formed during the surrounding extrusion process; (2) the Silurian fluvial delta system from northeast to southwest in Keping, Yingmaili, Hade, and Caohu areas, which reflected the partial uplift at the northeast margin and provided clastic supply to basin; and (3) as indicated by heavy mineral analysis, the Silurian sediments came mainly from the recycles of orogenic belts provenance, which indicated the compress tectonic setting. In addition, a wide range of red mudstone layer distribution in the upper part of the Silurian may be closely related to the surrounding tectonic uplift and the rapid decline of sea levels. [ABSTRACT FROM AUTHOR]

A typical ancient karst cave is found in the Yijianfang Formation of Ordovician at Liuhuanggou, North Tarim Basin. With an entrance of 4.8 m wide and 20 m high, the Liuhuanggou ancient karst cave extends to NW 315° and has been filled by sediments, which can be classified into three types according to their nature and origin: clastic sediments (gravels), chemical sediments (palaeotravertine), and mixed sediments. Among them, the Paleotravertine and gravels are most common. The palaeotravertine is laminated type and yellowish brown or black in color due to oil inside. When saturated with oil, the palaeotravertine is black. Under microscope, oil mainly accumulates in the cracks between calcite crystals. The filling period of the Liuhuanggou karst cave can be divided into three stages: mixed filling, chemical filling, and clastic (palaeotravertine breccia) filling. Numerous fractures are distributed on one side of the karst cave. The fractures can be as wide as 40 cm and over 40 m long. Fractures of different periods and sizes constitute a fracture network and are all filled with calcite veins. Oil can be found inside the fractures. In the chemical fillings, sulfur is also found, which can indicate the magma influence on karst caves. The existence of sulfur also confirms that the Liuhunggou karst cave was formed in ancient times rather than recently or nowadays. Different from normal sedimentary limestone, the ancient Liuhuanggou karst cave has a distinct isotope fractionation and the depletion of heavy carbon and oxygen isotope. Controlled by the northwest oriented vertical strike-slip shear fault, the karst cave is actually a dissolved vertical fault belt. [ABSTRACT FROM AUTHOR]

We identified a Neogene rapid uplift-denudation event of the South Tianshan based on apatite (U-Th)/He and apatite fission track (AFT) ages in Tertiary rocks of the Tarim basin, using borehole samples. The (U-Th)/He thermochronology can be used to reveal the tectono-thermal events with lower temperature than that of AFT thermochronology and has not been used previously to study the uplift of the Tianshan Mountain. Using these data, we show the relationship between the uplift of the South Tianshan and the subsidence/deposition of the northern Tarim basin during the Neogene. The apatite helium ages reveal the migration of uplift, erosion and deposition in the northern Tarim basin. A rapid uplift of the South Tianshan during the Miocene and a corresponding rapid subsidence in the northern Tarim basin occurred. However, in the Pliocene, the Kuqa Depression and South Tianshan uplifted and eroded at the same time and in turn provided the detrital source rocks for the Northern Uplift of the Tarim basin. In contrast to earlier studies, we arrive at the conclusion that the South Tianshan experienced rapid uplift in the Miocene based on (U-Th)/He data of apatite obtained from borehole samples collected in the Tarim basin itself, and not from the bordering mountain chain. Combined apatite (U-Th)/He and fission track thermochronometry enables reconstruction of thermal histories of sedimentary rocks between 40 and 120°C, and this has implications for the generation of liquid hydrocarbon in the 65-120°C range in the basin. Thermal and burial histories of typical samples were also modelled to show the rapid uplift in our study. Our works not only provide a new evidence for the South Tianshan uplift but also indicate that there is a coupling between uplift and subsidence in the South Tianshan and adjacent northern part of the Tarim basin, which controlled hydrocarbon accumulation in the Kuqa Depression and Northern Uplift of the Tarim basin. [ABSTRACT FROM AUTHOR]

Ordovician black shales are widely distributed in the Tarim Basin and its peripheral regions, and some of them may serve as potential hydrocarbon source rocks. The present study of the Ordovician graptolite fauna from these shales, together with the yielded conodonts and chitinozoans etc., permits a refined correlation of the rocks. Based mainly on a new collecting of the graptolites and a study of the faunas in Kalpin and Kuruktag regions, and the successful identification of the new graptolite material from a few drill cores within the basin, we are able to update our knowledge of the Ordovician in the regions, and draw some conclusions: (1) The most widespread distribution of the black shales in the Tarim Basin and its peripheral regions, which correspond to the Nemagraptus gracilis Zone, may be related to a global sea-level rise during this time interval. (2) Black shales of Ordovician occur most frequently and extensively in the Kuruktag (also spelled as Quruq Tagh) region in eastern Tianshan Mountains, spanning Tremadocian to mid-Katian ( D. spiniferus Zone) temporally and extending southeastwards into Manjiaer Depression. The black shales of the D. spiniferus Zone may even extend into the central Tarim Basin. (3) Three different bio- and litho-facies belts (Bachu: carbonate platform and reef belt; Kalpin-Aksu: marginal platform and upper slope belt; Wushi: slope belt) are recognized in the northwestern Tarim Basin. (4) The internationally well-correlated Saergan black shale, which has been considered to possess high potential for hydrocarbon source rock, may possess a restricted distribution in the Kalpin and Aksu areas. [ABSTRACT FROM AUTHOR]

The structural framework and evolution processes of the giant superimposed Tarim basin in Paleozoic Era are controlled by three main factors: (1) features and structures of the basin basement; (2) deep mantle dynamics process (such as the Sinian rifting and the Permian plume-related magmatic activities); (3) the powerful regional compressional or compresso-shear stress regime generated by the orogenic movement from surrounding regions. The latter of which occurring in multiple episodes is the most important factor for the Paleozoic Tarim basin evolution. Under the above tectonic background, the underlying lithosphere of the Tarim basin had been flexed, and then the upper crust was folded. The paleo-uplifts (e.g., Tabei (塔北) and Tazhong (塔中)) and depressions occurred in both of the flexural and folding processes, which are different with the models of foreland basin in stable and large cratons in the world. During the early evolution stage in Cambrian-Early Ordovician, low-relief paleo-uplifts, and open carbonate platforms formed in center area, while during the Late Ordovician compressional tectonic regime, the belted uplifts and restricted platforms formed in the contemporaneous folding processes. Denudated stages occurred during the strong tectonic events marked by the unconformities and karstified weathered crusts formed on platforms. All the discovered giant-middle oilfields are closely related to the paleo-uplift and karstified crust evolution. There are two main types of oil reservoir: paleo-karst type and reef-bank type on the carbonate platform in paleo-uplift areas. In Permian, plume-related massive magmatic activities led to geo-temperature increase and the regional uplifting in this basin, ending the marine deposit filling sequences and starting the formation of terrestrial deposits-dominated sequences. With abundant supply from giant hydrocarbon generation depressions, the most important oil fields formed in Tabei and Tazhong areas. To reveal the multi-stage evolution processes and the structural framework of the paleo-uplifts may be helpful for the prediction of new hydrocarbon domains. The integrated study on coupling relationship between the basin and surrounding orogens can provide an important approach for the superimposed basin dynamic research. [ABSTRACT FROM AUTHOR]

Twenty unconformities, primarily superimposed types, were identified based on interpretation of a 46 000 km seismic profile combined with data from over 40 drilling wells. These respectively correspond to the main tectonic evolution stages and the boundaries between those stages. Reconstruction of the original depths of eroded strata was conducted for the Middle Caledonian, Early Hercynian, Late Hercynian, Indosinian, Early Yanshanian and Late Yanshanian unconformities using the virtual extrapolation of seismic reflection. Eroded strata thicknesses were also calculated for individual periods and intervals. Based on the reconstructed data, in combination with data from research on sedimentary facies, a paleogeomorphological profile was constructed for different tectonic evolution stages of the basin during the Early Paleozoic. The profile indicates the presence of obvious regularity in the temporal and spatial evolution of these unconformities. Based on the characteristics of paleo-uplift evolution and post-layering reconstruction, the paleo-uplifts were divided into inherited (e.g., Tazhong (塔中)), residual (e.g., North Tarim) and active (e.g., Southwest Tarim and Bachu (巴楚)) types. The huge North Tarim uplift represents a typical form of residual paleo-uplift. The Paleozoic strata in the upper layers of the uplift is in poor condition for reservoir accumulation and preservation; however, the Upper Mesozoic-Cenozoic structural layer can form a secondary reservoir that is relatively rich in oil and gas. Furthermore, the flank slope area of the uplift is always a key source for oil and gas collection and the most advantageous position for the formation of the original reservoir. The Tazhong paleo-uplift has been stable since its formation in the Late Ordovician, where petroleum accumulation has been distributed not only in the uplift, but also in the deep and slope belts of the uplift. Important breakthroughs in petroleum exploration of the slope break in the North Tazhong area dating back to the Paleozoic have further confirmed the enrichment of oil and gas in this type of uplift. The Southwest Tarim paleo-uplift is a buried type, which has given it favorable properties for hydrocarbon migration over a long time. An open question is whether the large amount of oil and gas accumulated here was transported to the current Bachu uplift. [ABSTRACT FROM AUTHOR]

The Bachu (巴楚) uplift is one of the most active tectonic regions nowadays in the Tarim basin, which is also a faulted block uplift that was intensively active during the Cenozoic. This study was based primarily on the geological structure interpretation of seismic profiles, applying the theories and methods of basin dynamics, structural analysis and tectono-stratigraphic analysis, the geometry and kinematics features of the fault systems in the Bachu uplift were analyzed in detail. Our study shows that each fault belt is mainly characterized by compression and overthrusting, most of the faults initiated and activated during the Mid-Late Himalayan period, and that the general structural styles of the Bachu uplift were basement-involved pop-up thrust faulted block uplift, of which the southern margin was covered by the large-scale decollement fault system. The basement-involved structures widely developed in the higher position of the basement uplift, while decollement fault system developed mainly at the position with gypsum mudstone. The evolution process of Bachu uplift included back-bulge slope of the peripheral foreland basin in Mid-Late Caledonian, forebulge in Hercynian-Yanshanian and the latest compressional faulted block uplift in Mid-Late Himalayan. Meanwhile, the study also suggests that the formation, reconstruction and stabilization of the uplift were controlled by the development and evolution of fault systems clearly. In the early forebulge stage, it was mainly presented as flexural deformation without the developing of thrust faults in the Bachu area; to the late stage, under the influence of violent lateral compression deformation, the faulted block uplift formed finally. [ABSTRACT FROM AUTHOR]

As one of the major exploration objects of marine deposit in Tarim basin, Silurian has been paid more attention from oil/gas exploration and geologists. However, due to the widely deposit and later erosion, it is difficult to restore the original basin. The surrounding tectonic activity and provenance systems of Silurian Tarim basin have a lot of controversy. Aid of detrital zircons U-Pb dating data obtained from well drilling of Tabei (塔北) and Tazhong (塔中) areas and Sishichang (四十场) and Xiangyangcun (向阳村) outcrop profiles, integrated with other geological and geophysical data, the tectothermal evolution and provenance nature of Silurian deposit have been revealed. Zircons U-Pb dating shows Tarim basin has experienced 5-6 significant tectothermal events: 3 500-3 000 Ma Paleo-Mesoarchean, around 2 500 and 1 800 Ma Paleoproterozoic, around 1 000 and 800 Ma Neoproterozoic, and 500-400 Ma Eopaleozoic tectothermal events. These tectothermal events reflected the evolution of Tarim microplates and Tarim basin, respectively, corresponded to the forming and spilitting process of Ur supercontinent, Kenorland, Columbia and Rodinia supercontinent. Difference between the samples of Tazhong and Tabei areas indicated that North and South Tarim microplates were different in Paleo-Mesoarchean, and later evolutions were more synchronous after Paleoproterozoic. Integrated with seismic data and outcrop interpretation, the U-Pb dating results also revealed that the surrounding tectonic activities were still very active during Silurian, and indicated different regions had different source systems. At Tadong (塔东) and Manjiaer (满加尔) depressions, major source systems came from Ordovician Altyn orogenic belts. At Tabei area and northwest of Tarim basin, major source systems came from recycling orogenic zone (the activity of South Tianshan (天山) Mountain) and Precambrian stable basement (local paleo-uplifts at north of Tabei). The Ordovician uplift and orogenic zone at the south of Tarim basin and Precambrian granite basement provided lots of source systems to Tazhong area. [ABSTRACT FROM AUTHOR]

The two basalt flows in Kupukuziman (库普库兹满) Formation of Keping (柯坪) area are the typical products of Permian magmatism. Based on systematic field investigations, we carried out geochemical studies on representative Keping basalts. The results show that the SiO contents in basalts range from 44.69 wt.% to 51.68 wt.%, and the total alkalis range from 4.05 wt.% to 5.5 wt.%, belonging belonging to alkaline basalts. The Ti/Y=468.27-565.35 and TiO=(2.88-3.82) wt.% compared to those of the high-Ti basalts in Emeishan (峨眉山) large igneous province (LIP) (TiO=(3.58-5.21) wt.%, Ti/Y>500, Xiao et al., 2004). The contents of MgO and compatible elements Cr (12.9-18.6 ppm), Ni (13.7-22.7 ppm), and Co (39.6-50.2 ppm) are low, which suggest that the samples have undergone varying grades of fractional crystallization. All the samples have uniform REE and other trace element characteristics, with enriched LREE and LILE relative to HREE and HFS, similar REE patterns without Eu anomaly. The basalts are also show slightly depleted of Ta and Nb. They have higher initial Sr/Sr ratios (0.707 211-0.708 300), lower ɛ( t) values (−2.47 to −4.14), and a narrow range of (Pb/Pb)=37.535 2-38.297 7, (Pb/Pb)=15.435 7-15.517 0, and (Pb/Pb)=17.206 5-17.874 7 ratios. The Ce/Y versus Zr/Nb diagram shows that the parent magmas were originated from low-degree partial melting of the garnet-lherzolite. The analysis results based on geochemical studies seem all point to the same conclusion that the Keping basalts have formed as a product of the interaction between the plume-derived melts and the lithosphere. [ABSTRACT FROM AUTHOR]

The Carboniferous Karashayi (卡拉沙依) Formation of Tarim basin formed in the epicontinental sea shelf environment where the evolution of basins is pediocratic. As an important reservoir-forming combination, the Carboniferous Karashayi Formation consist of clastic rocks, carbonate rocks and gypsum rocks, which show clear sedimentary cyclicity. According to paleontology research and stratigraphic correlation, Karashayi Formation corresponds to Visean and Serpukhovian in international stratigraphic chart with a time limit about ±27 Ma. The sequence stratigraphic study for the Karashayi Formation is rough because of the difficulty to identify the unconformity surfaces. The current study mostly divides it into three or four 3rd sequences. However, this partition cannot meet the geological crossing correlation. At the theory aspect of sequence stratigraphy, the genesis of the 3rd sequence is also a disputed problem. Cyclostratigraphy study of the Natural Gamma-Ray Log, Spontaneous Potential Log and other logging curves has been taken out by spectrum analysis and wavelet analysis, etc.. For Well Shun6 and Well Zhong1 in Tazhong (塔中) and neighbouring area, combined core observation and base level analysis, the Karashayi Formation was divided into 9 or 11 sequence stratigraphic units. Continuous constraints of each sequence is about ±2.40 Ma, corresponding to astronomical cycle formed by three parameters of Earth orbit. Accompanied by the historical division of 3rd sequences, the formation mechanism of 3rd sequences was possibly forced by the 2.4 Ma astro-nomical eccentricity cycles. [ABSTRACT FROM AUTHOR]