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Tectonic movements formed several unconformities in the north-west margin of the Junggar basin. Based on data of outcrop, core, and samples, the unconformity is a structural body whose formation associates with weathering, leaching, and onlap. At the same time, the structural body may be divided into three layers, including upper layer, mid layer, and lower layer. The upper layer with good primary porosity serves as the hydrocarbon migration system, and also accumulates the hydrocarbon. The mid layer with compactness and ductility can play a role as cap rock, the strength of which increases with depth. The lower layer with good secondary porosity due to weathering and leaching can form the stratigraphic truncation traps. A typical stratigraphic reservoir lying in the unconformity between the Jurassic and Triassic in the north-west margin of the Junggar basin was meticulously analyzed in order to reveal the key controlling factors. The results showed that the hydrocarbon distribution in the stratigraphic onlap reservoirs was controlled by the onlap line, the hydrocarbon distribution in the stratigraphic truncation reservoirs was confined by the truncation line, and the mid layer acted as the key sealing rock. So a conclusion was drawn that “two lines (onlap line and truncation line) and a body (unconformity structural body)” control the formation and distribution of stratigraphic reservoirs.

Carbonate cemented zones are normally adjacent to the top overpressured surface in the central Junggar Basin, NW China. Stable carbon and oxygen isotopic compositions and petrological investigations of carbonate cements in the carbonate cemented zones indicate that: (1) carbonate cements are composed dominantly of ferrocalcite, ferroan dolomite, and ankerite; (2) carbonate cements are formed under a high temperature circumstance in the subsurface, and organic fluid migration has an important effect on the formation of them; and (3) carbon and oxygen ions in the carbonate cements migrate from the underlying overpressured system. This suggests that the occurrence of carbonate cemented zones in this region results from multiple phases of organic fluid expulsion out of the overpressure compartment through geological time. This study provides a plausible mechanism of the formation of carbonate cemented zones adjacent to the top overpressured surface in the clastic sedimentary basins, and has an important implication for understanding the internal correlation between the formation of carbonate cemented zones adjacent to top overpressured surface and geofluids expulsion out of overpressured system.

Oil and natural gas are important for energy supply around the world. The exploring, drilling, transportation and processing in oil and gas regions can release a lot of volatile organic compounds (VOCs). To understand the VOC levels, compositions and sources in such regions, an oil and gas station in northwest China was chosen as the research site and 57 VOCs designated as the photochemical precursors were continuously measured for an entire year (September 2014–August 2015) using an online monitoring system. The average concentration of total VOCs was 297 ± 372 ppbv and the main contributor was alkanes, accounting for 87.5 % of the total VOCs. According to the propylene-equivalent concentration and maximum incremental reactivity methods, alkanes were identified as the most important VOC groups for the ozone formation potential. Positive matrix factorization (PMF) analysis showed that the annual average contributions from natural gas, fuel evaporation, combustion sources, oil refining processes and asphalt (anthropogenic and natural sources) to the total VOCs were 62.6 ± 3.04, 21.5 ± .99, 10.9 ± 1.57, 3.8 ± 0.50 and 1.3 ± 0.69 %, respectively. The five identified VOC sources exhibited various diurnal patterns due to their different emission patterns and the impact of meteorological parameters. Potential source contribution function (PSCF) and concentration-weighted trajectory (CWT) models based on backward trajectory analysis indicated that the five identified sources had similar geographic origins. Raster analysis based on CWT analysis indicated that the local emissions contributed 48.4–74.6 % to the total VOCs. Based on the high-resolution observation data, this study clearly described and analyzed the temporal variation in VOC emission characteristics at a typical oil and gas field, which exhibited different VOC levels, compositions and origins compared with those in urban and industrial areas.

Empirical constraints on orbital gravitational solutions for the Solar System can be derived from the Earth’s geological record of past climates. Lithologically based paleoclimate data from the thick, coal-bearing, fluvial-lacustrine sequences of the Junggar Basin of Northwestern China (paleolatitude ∼60°) show that climate variability of the warm and glacier-free high latitudes of the latest Triassic–Early Jurassic (∼198–202 Ma) Pangea was strongly paced by obliquity-dominated (∼40 ky) orbital cyclicity, based on an age model using the 405-ky cycle of eccentricity. In contrast, coeval low-latitude continental climate was much more strongly paced by climatic precession, with virtually no hint of obliquity. Although this previously unknown obliquity dominance at high latitude is not necessarily unexpected in a high CO ₂ world, these data deviate substantially from published orbital solutions in period and amplitude for eccentricity cycles greater than 405 ky, consistent with chaotic diffusion of the Solar System. In contrast, there are indications that the Earth–Mars orbital resonance was in today’s 2-to-1 ratio of eccentricity to inclination. These empirical data underscore the need for temporally comprehensive, highly reliable data, as well as new gravitational solutions fitting those data. Significance Geological records of paleoclimate provide the only constraints on Solar System orbital solutions extending beyond the ∼50-Ma limit imposed by chaotic diffusion. Examples of such constraints are coupled high and low latitude, Triassic–Jurassic (∼198–202 Ma) sedimentary cyclicity in coal-bearing outcrops from the ∼60° N-paleolatitude Junggar Basin (Western China), and contemporaneous tropical basins. Analysis reveals climate variability dominated by obliquity-scale cyclicity in the Junggar Basin and precession-scale cyclicity in the tropics. Together, these geological records empirically constrain orbital solutions by providing joint g4 − g3 and s4 − s3 secular frequency estimates of the Earth–Mars orbital resonance. These results demonstrate the opportunity for developing a new class of solutions grounded by geological data extending hundreds of millions of years into the geologic past.

The identification of the origin and source of natural gas is always a difficult and hot issue. Hereinto, the maturity identification is one of the most important scientific problems. Many empirical equations have been established to decipher the relationship between the maturity of gas source rocks and the carbon isotopic composition of natural gas. However, these equations proposed often fail to identify the maturity of the source rocks correctly, which in turn prevents the identification of genetic types and source rocks of the natural gas because the petroliferous sedimentary basins in China are complex and diverse, with multiple sets of source rocks and different thermal history. In this paper, the oil-associated gas from the Permian lacustrine source rocks and the coal-derived gas from the Jurassic source rocks in Junggar and Turpan-Hami basins have been investigated to decipher the relationship between the maturity (vitrinite reflectance) of gas source rocks and the carbon isotopic composition of methane. The equations established are δ 13 C 1 =25lg R o −42.5 for oil-associated gas, and δ13C 1 =25lg R o −37.5 for coal-derived gas. These new equations are suitable for the maturity identification of source rocks in most petroliferous basins, and favorable for the identification of the genetic type and source of natural gas, which is very important to improve the geological theory of natural gas.

In this study, the Xgboost method is employed for TOC estimation in mixed carbonate and siliciclastic shale from the Hashan area, Junggar Basin. The results show that this approach is effective for TOC estimation in this area although the model performance is not very excellent with a correlation coefficient of 0.54 between measured TOC and predicted TOC values, likely due to a small samples dataset. Therefore, the PCA method is applied to debase dimension of well log data from five dimensional to two-dimensional data, which enhances the correlation coefficient between the predicted and measured TOC from 0.54 to 0.68. Based on the model, the isopleth maps of TOC distributions in Fengcheng Formation were redrawn showing two shale oil exploration targets, which likely correspond to two depositional centers of this strata. All the same, the model in this work provides reliable data for shale oil evaluation in the study area and a good example under similar geological setting.

The 1 Gt oilfield discovery solidified the Mahu oilfield as the world’s largest conglomerate oil region, underscoring the exploration potential of these reservoirs. However, optimizing and selecting the target interval for hydraulic fracturing remains challenging due to the significant heterogeneity of the structure and composition of conglomerate reservoirs. This study addresses key gaps in understanding conglomerate reservoir characteristics and their impact on hydrocarbon production, focusing on the Baikouquan (T 1 b ) Formation (Fm) on the Mahu Depression’s northern slope. It introduces a new classification to better manage these complexities. In contrast to other classification methods, the proposed approach incorporates key factors influencing hydraulic fracture (HF) propagation, including grain size, cementation, supporting forms, and gravel composition, the latter of which is introduced for the first time. Based on core and test results, the conglomerate reservoirs are categorized into two main groups—fan delta front and fan delta plain conglomerates—and further divided into eight lithofacies types. Fan delta front conglomerates are subdivided into four types: A-1 (tuff, metamorphic, and magmatic rocks-dominated gravel-supported cobble-to-boulder lithofacies), A-2 (tuff and magmatic rocks-dominated matrix-supported pebble-to-cobble lithofacies), A-3 (tuff-dominated matrix-supported granule-to-pebble lithofacies), and A-4 (tuff-dominated gravel-supported granule-to-pebble lithofacies). Fan delta plain conglomerates are further divided into four types: B-1 (tuff and magmatic rocks-dominated gravel-supported granule-to-pebble lithofacies), B-2 (tuff and sedimentary rocks-dominated gravel-supported pebble-to-cobble lithofacies), B-3 (tuff-dominated gravel-supported cobble-to-boulder lithofacies), and B-4 (tuff, magmatic, and sedimentary rocks-dominated matrix-supported pebble-to-cobble lithofacies). The novelty of this classification method lies in its integration of both geological and engineering perspectives, particularly in optimizing hydraulic fracturing strategies. The study evaluates lithofacies from geological factors such as bedding, composition, and poroperm characteristics, as well as engineering considerations like fracturing potential and flow capacity. The results reveal that certain lithofacies types correlate strongly with higher fracturing success, providing insights that can guide more efficient hydraulic fracturing practices. By addressing the challenge of heterogeneity of the structure and composition in conglomerate reservoirs, this study offers a comprehensive framework for selecting optimal target intervals for hydraulic fracturing, which can significantly enhance hydrocarbon exploration and production strategies. This approach is expected to be valuable for similar complex conglomerate reservoirs worldwide.

Groundwater plays a critical water resources role in arid and semi-arid areas. Quantitative evaluation of groundwater recharge is crucial in hydrogeological investigations. Under the complex hydrogeological and climatic conditions in China’s arid and semi-arid regions, groundwater recharge shows significant spatio-temporal heterogeneity. Although there has been much research, including hydrochemical analysis, isotope tracing, in-situ tests and numerical simulations, accurate quantitative groundwater recharge is still a great challenge. This paper reviews the progress in research on groundwater recharge in arid and semi-arid regions of China, focusing on the principles and current applications of the main techniques, as well as the achievements in nine typical arid and semi-arid regions (Tarim Basin, Junggar Basin, Shule River Basin, Heihe River Basin, Yinchuan Plain, Badain Jaran Desert, Loess Plateau, Ordos Plateau, North China Plain). The paper reveals that the chloride mass balance method is a popular method to estimate groundwater recharge rate, whereas stable isotopes and hydrochemistry analyses, as well as the joint use of both, have been widely used in the understanding of groundwater recharge processes and mechanisms in the arid and semi-arid regions of China. Numerical modeling and remote sensing technology will become important approaches to quantify large-scale groundwater recharge. It is also suggested that various estimation methods should be used in combination, in order to improve the reliability of recharge estimates. Furthermore, this review shows that the theoretical research so far still cannot meet the needs of regional development, and the paper highlights some scientific problems that need to be further explored.

Zeolite cement dissolution pores, buried at a depth of over 3600 meters, are found well developed in clastic rocks of Permian in northwest of Junggar basin. Studying the controlling factors of zeolite cement dissolution pores have important meaning to predict the distribution of favorable reservoirs in deep oil and gas exploration of Permian. A comprehensive research method of thin slice analysis of 800 pieces of castings from 60 wells, core observation, scanning electron microscopy, and clay mineral analysis was adopted. It is believed that the dissolution pores of zeolite cements are mainly controlled by zeolite distribution, the scale and range of inorganic and organic acids. Firstly, different zeolite cement types appear a regular pattern that control dissolution pore types and their distribution scope. The study area are well developed three types zeolite cements: heulandite, analcite and laumontite. The heulandite cements are developed in basin edge, showing a belt-like distribution, and then the analcite distribution area. laumontite cements are distributed in basin central. Horizontally in basin edge, reservoir pore type is primary intergranular pore, and followed by analcite dissolution pore. In central basin, the major pore type is laumonitite dissolution pore, and followed by primary intergranular pore. No heulandite dissolution pores are found in study area. Secondly, analcite dissolution pores, formed by inorganic acid and distributed in basin edge, are controlled by the scale of stratigraphic unconformities and faults. Laumonitite dissolution pores, formed by organic acid and developed in central basin, are controlled by the scope of source rock. Thirdly, it is proposed that the meddle-belt of basin is the favorable zone for Permian reservoirs because it is located fan delta front where the laumontite cement is developed, close to the source rock, and in the updip direction of the three stages of organic acid migration. It is considered that central basin has favorable conditions to form laumontite dissolution pores, and pointed out that this zone is a favorable zone for the development of deep reservoirs in the Permian.

The North Xinjiang region (NW China) is an important part of the Central Asia Orogenic Belt, situated at the junction of Siberia, Tarim and Kazakhstan plates. It is an area characterized by multiple stages of Phanerozoic continental growth, during which several porphyry and epithermal systems were formed. The relationship of these mineral systems to the geodynamic evolution of the region has not yet been well understood. In this paper, we list the main geological characteristics of 21 significant epithermal precious and base metal deposits in North Xinjiang, and classify them into high-sulfidation and low-sulfidation styles, with the latter being predominant. We have selected seven epithermal deposits representing different styles formed under different tectonic regimes and discuss their geology and geochemistry in some detail. The deposit-scale geology and geochemistry of epithermal systems in North Xinjiang are essentially similar to those in other parts of the world. All epithermal deposits in North Xinjiang are hosted in volcanic rocks with ages ranging from Devonian to Triassic, with the Early Carboniferous volcanic sequences being the most important, followed by the Permian and Triassic. The Devonian–Early Carboniferous host rocks belong to the calc-alkaline series that developed in pre-collisional arc-back-arc basin systems; whereas the Permian–Triassic host volcanic rocks of shoshonite series formed in post-subduction regimes. Available isotopic ages of these epithermal systems cluster in two periods: Early Carboniferous (>320 Ma) and Late Carboniferous–Triassic (320–220 Ma), reflecting two metallogenic episodes that occurred during subduction-related accretion and post-subduction collision regimes, respectively. Accordingly, three groups of epithermal deposits in North Xinjiang can be recognized as (1) pre-collisional deposits without or with negligible collisional-related modification, (2) deposits formed in collision regime and (3) ore systems strongly overprinted by fluid flow in post-subduction collision regime.