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Groundwater discharge from natural springs commonly involves gas emissions, providing valuable insights into the origin of spring and subsurface geology. Here, we report substantial carbon dioxide (CO2) emissions, instead of methane (CH4), from Aiken Spring, which is located in a desert region of the western Qaidam Basin, a Mars-analog environment within the Tibetan Plateau. The CO2 fluxes from the spring water surface reach up to 43.7 g/m2/h, with the estimated total emissions from the entire spring reaching at least 207 tons in the summer (90 days). The carbon (C) isotopic composition of the CO2 released from the spring is − 8.9 ± 1.6‰, which corresponds to an estimated value for dissolved inorganic carbon (DIC) of − 4.6 ± 1.6‰ in the original spring water, suggesting a mixture of mantle-derived CO2 and sedimentary carbonates. The mantle-derived CO2 at Aiken Spring may indicate active subsurface magmatic degassing within the intersection of the Altyn Tagh Fault and the Kunlun Fault, but it is more likely linked to a subsurface CO2 reservoir from ancient magmatic activity. Overall, our results indicate that Aiken Spring provides insights into deep subsurface geological processes and potentially the terrestrial subsurface biosphere. [ABSTRACT FROM AUTHOR]

Reconstructing the growth model of the Northeastern Qinghai–Tibet Plateau is of significant importance in understanding its tectonic evolution through time. We present 20 new zircon fission track data on samples collected from the Chakabeishan-Shaliuquan district in the North Qaidam Tectonic Belt (NQTB) to constrain its Mesozoic mineralization and exhumation history. Sample ages and characteristics are differentiated by regional thrust fault systems. The mineralized pegmatite ages with high U concentrations can be divided into two groups of 170–168 Ma and 149–137 Ma, recording exhumation and hydrothermal mineralization events, with average cooling and exhumation rates of 0.074 mm/y and 2.305°C/Ma, respectively. Two ZFT ages groups characterized by low U concentrations at the deposit periphery of 125–106 Ma and 99–80 Ma, respectively, are associated with accelerated cooling and exhumation, with mean values of 7.662°C/Ma and 0.245 mm/y. We suggest that the NQTB was positioned in the high background thermal field in the Triassic, and subsequent tectonic extension resulted in the unroofing, cooling and mineralization of the region. The transition from extensional to contractional deformation in the Cretaceous tectonic setting has reactivated regional thrust fault systems and reset the Jurassic ZFT ages, and this exhumation event was influenced by the closure of the Middle-Tethys and Mongol-Okhotsk Oceans, consistent with the double-sided subduction model. [ABSTRACT FROM AUTHOR]

To deepen the comprehension of the geochemical behaviour of salt-forming elements (K, Li, B, Ca, Mg, Sr) and distribution patterns in the primary lithium-rich salt lake region of Qaidam Basin, 31 river and lake surface sediments from various hydrogeological settings spanning high mountain to terminal salt lake regions were gathered from the Nalenggele River, the primary feeder river of the lithium-rich salt lakes. Through sequential extraction procedure, we identified notable variances in the chemical speciation of elements across various hydrological environments. Excluding elements bound to the residual fraction, all other chemical speciation content of salt-forming elements show distinct regional variations, suggesting a predominant influence of evaporation and hydrodynamic and the inherent chemical properties of elements are also very important in determining their chemical speciation distribution characteristics. Meanwhile, we have found that in addition to being absorbed and fixed by secondary clay minerals, Li bound to Fe–Mn oxides may also play a crucial role in Li isotope fractionation from the river to the terminal salt lake brine and the precipitation of evaporation salt minerals could influence the B isotope fractionation to a certain extent. Furthermore, The Li and B lost to sediments during the migration process have potential utility and there is scope for enhanced exploitation in the future. Therefore, the results obtained from the sequential extraction procedure of sediments evidently serve as a valuable method for understanding the geochemical behaviour of salt-forming elements in the epigenetic environment. [ABSTRACT FROM AUTHOR]

The Tataleng River (TTR), as an important tributary of the Da Qaidam Salt Lake (DQSL) and Xiao Qaidam Salt Lake (XQSL) in the Qaidam Basin (QB), has an exceptionally high B content. However, the solute sources and the provenance of B in the TTR are still unclear, which significantly hinders a deeper understanding of the source–sink processes of the boron deposits in the QB. In this study, water samples were collected from tributaries, mainstreams, mud volcanoes, hot springs, and rainwater in the TTR area. Through hydrochemical analysis, forward modeling, and B isotope geochemistry methods, combined with the previous research results, some findings were obtained. The hydrochemical type of TTR is Ca–Mg–Cl, and the major mechanism of controlling chemical composition is rock weathering. The solute sources in the TTR are mainly from dissolution of evaporites (75.9%), atmospheric precipitation (20.8%), and a minor contribution from carbonates (3.1%) and silicates weathering (0.6%). The higher B content (0.89–4.30 mg/L, mean = 2.13 mg/L) and lower δ11B value (0.79‰–4.71‰, mean = 4.17‰) of the TTR indicate that the B sources are mainly from mixture of mud volcanic waters (56.19–199.98 mg/L, mean = 113.51 mg/L, − 1.26‰–2.22‰, mean = 0.85‰) in the upper reaches, and the deep groundwater near the Indosinian granite in the lower reaches. The significant difference in boron resources between the two lakes may be due to the enrichment of B in the late Pleistocene in the DQSL, which received exceptionally rich soluble B carried by the ancient TTR during an active tectonic period, while the weakening of tectonic activity and the diversion of the ancient TTR resulted in the supply of B with significantly reduced content to the XQSL. These results are helpful for a deeper understanding of the ore-forming mechanisms of the boron deposits in salt lake. [ABSTRACT FROM AUTHOR]

Brine groundwater in Quaternary salt lakes is widely exploited to extract potassium, lithium, and boron; the complex hydrogeological parameters of brine aquifers could cause significant difficulties in brine resource assessment and exploitation. However, the origin and porosity of brine aquifers remain unclear. This study presents an approach that utilizes geochemical indicator analysis with paleogeographic reconstruction to better assess porosity in salt lake aquifers. We identified 15 representative boreholes in Mahai Salt Lake, and the lithology, porosity, and chloride contents of their respective sediments, the pore porosity of each borehole in the study area ranges from 38.17 to 0.51%, the average chloride content of each borehole ranges from 26.63 to 38.74%, found that the vertical porosity fluctuations of halite deposits were significantly larger than those of detrital deposits, the sediments in the boreholes consisted predominantly of halite-containing debris or fine-debris-containing halite, reflecting the paleoenvironmental signatures of the salt lake. According to lithology and sedimentary environment, four brine aquifers were classified and the chloride and porosity distribution characteristics in the I–IV brine aquifers were further illustrated. Based on information of paleolake evolution in Qaidam Basin, we established a conceptual model to identify the impact factors for the porosity distribution pattern in the I–IV brine aquifers. [ABSTRACT FROM AUTHOR]

There is limited research on the variations in brine element changes and the factors that influence them during large-scale exploitation. The Xitaijnar Salt Lake in the Qaidam Basin is a large brine lithium deposit. In this study, we investigated the variations in chemical composition and the factors that influence intercrystalline brine at different time periods. Hydrochemistry, mineralogy, and hydrogeochemical simulation methods were employed to understand the brine evolution. Our results indicate that after nearly 20 years of exploitation, the intercrystalline brine still belongs to the magnesium sulfate subtype, with only slight variations in salinity. The concentrations of Na, K, and SO4 showed a slight increase, while the content of Mg and Cl decreased slightly. The concentrations of B and Li exhibited minor fluctuations. The provenance, water level, and hydraulic connection had minimal influence on the chemical composition of the intercrystalline brine. By contrast, the dynamic dissolution and precipitation of sulfate minerals and halite, as well as drastic changes in hydrological conditions (such as floods), were identified as the main factors affecting the chemical composition of brine. With the large-scale extraction of intercrystalline brine, the content of elements in the salt lake showed a decreasing trend. This can be attributed to the fact that intercrystalline brine is formed through long-term evaporation and concentration. Therefore, during the exploitation process, it is crucial to monitor the hydrochemical variations of intercrystalline brine and understand the controlling factors. The results of this study may prove useful for the sustainable development and utilization of salt lake resources worldwide. [ABSTRACT FROM AUTHOR]

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Copyright of Acta Scientiarum Naturalium Universitatis Pekinensis is the property of Editorial Office of Acta Scientiarum Naturalium Universitatis Pekinensis and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The climate change in the Qaidam Basin has significant impacts on local humans and ecological environment. However, the humidity variation and relationship between climate factors in the Qaidam Basin remain insufficient. Here we study the modern climate change in the Qaidam Basin. The mean annual temperature in the Qaidam Basin has increased rapidly by 0.5 °C/10a between 1959 and 2022, exhibiting cycles of 9.1 a and 3.2 a. Concurrently, the pattern of precipitation variations has displayed an upward trend, with a rate of increase amounting to 9.2 mm/10a and a cycle of 2.5 a. The Qaidam Basin has witnessed a considerable increase in temperature since 1977, as indicated by the Mann–Kendall mutation test. Within the Qaidam Basin, the mutation point at which precipitation transitioned from a lesser amount to a more volume occurred in 2001. Furthermore, a reduction in the variation of evaporation was observed between 1959 and 2003, possibly attributed to decreased sunshine and wind speed within the basin. The moist coefficient (precipitation/evaporation) and absolute humidity serve as direct indicators of the level of humidity in the environment. The moist coefficient has displayed an upward trend, accompanied by a corresponding increase in absolute humidity. The lake area and vegetation coverage are indirect indicators that reflect the level of humidity in the environment. In the Qaidam Basin, the lakes have expanded in surface area and there has been a noticeable increase in vegetation coverage. Collectively, these indicators unambiguously show that the Qaidam Basin is undergoing a process of increased moisture levels. Thus, it can be deduced that the modern Qaidam Basin is both experiencing warming and becoming wet. [ABSTRACT FROM AUTHOR]

Copyright of Arid Zone Research / Ganhanqu Yanjiu is the property of Arid Zone Research Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

For insight into the productive and storage mechanisms of biogas in the Qaidam Basin, efforts were made to investigate the groundwater recharge and the processes of hydrocarbon generation by CDOM-EEM (fluorescence excitation-emission matrix of Chromophoric dissolved organic matter) spectrum, hydrogen and oxygen isotopes, and geochemical characters in the central depression of the Qaidam Basin, China. The samples contain formation water from three gas fields (TN, SB, and YH) and surrounding surface water (fresh river and brine lake). The results indicate that modern precipitation significantly controls the salinity distribution and organic matter leaching in the groundwater system of the central depression of the Qaidam Basin. Higher salinity levels inhibit microbial activity, which leads to organic matter degradation and to gas generation efficiency being limited in the groundwater. The inhabitation effect is demonstrated by the notable negative correlation between the extent of organic matter degradation and its concentration with hydrogen and oxygen isotopes. The conclusion of this study indicated that modern precipitation emerges as a crucial factor affecting the biogas production and storage in the Qaidam Basin by influencing the ultimate salinity and organic matter concentration in the formation, which provides theoretical insight for the maintenance of modern gas production wells and the assessment of gas production potential. [ABSTRACT FROM AUTHOR]

Objective Well C902, located in the Ganchaigou area of the western Qaidam Basin, achieved a breakthrough in shale oil exploration as indicated by the high-production oil flow in the Ⅳ-Ⅵ layers of the Upper Member of the Palaeogene Xiaganchaigou Formation. However, ambiguities in evaluation criteria and resource potential limit the efficiency of shale oil development in the Upper Member of the Xiaganchaigou Formation in the Ganchaigou area. Methods Thus, the exploration potential of shale oil in the Ⅳ-Ⅵ layers of the Upper Member of the Xiaganchaigou Formation in the Ganchaigou area was comprehensively evaluated by comparing the lithology, physical properties, pore structure, and organic geochemistry between Well C902 and other wells. Results The complicated lithofacies of laminar/lamellar dolostone, laminar/lamellar limestone, laminar clay shale, and lamellar mudstone suggest the mixed carbonate and siliciclastic deposition of the Ⅳ-Ⅵ layers. The high brittleness index implies the good fracability of the Ⅳ-Ⅵ layers. The intergranular pores and laminar fractures, with a total proportion of 85% in the pore system, were dominant in the Ⅳ-Ⅵ layers that can be roughly classified as low-porosity and ultralow-permeability reservoirs. The organic matter, dominated by type Ⅰ-Ⅱ1, shows an average TOC content of more than 0.9% in the Ⅳ-Ⅵ layers. Both chloroform asphalt "A" and S1+S2 indicate a high hydrocarbon generation capacity. Conclusion Summarily, the widely deposited the Ⅳ-Ⅵ layers of the Upper Member of the Xiaganchaigou Formation have the characteristic of source-reservoir integration and show not only good quality of source rock but also strong fracability of the shale oil reservoir. The excellent source-reservoir-caprock assemblage is also widely developed, which ensures good sealing ability and favors improving oil and gas recovery after fracturing. This study can theoretically improve the development efficiency of shale oil in the Ganchaigou area.

Objective The composition and degradability of dissolved organic matter (DOM) play a critical role in evaluating biogenic gas production during shale gas exploration. A simple and effective method needs to be developed to assess the composition, functional groups and microbial activity of DOM, which will provide crucial valuable information concerning the gas production mechanism in the field of biogenic shale gas. Methods Shale samples were collected from depths of 1 219 m to 1 309 m from the ST1 exploration well located at the edge of the Sebei No.1 gas field in the Qaidam Basin. According to the 3D fluorescence of the extraction and emission matrix (EEM) and the UV visible absorption spectrum characteristics of chromophoric dissolved organic matter (CDOM), the composition, functional group and degradation characteristics of CDOM were analysed to determine the distribution of methanol formation substrates. Results The DOM in the samples mainly consisted of the small molecular tryptophan-like fluorescent components C1 and C3, which are readily degradable by biotic processes and account for 70.54% of the total fluorescence intensity. The fluorescence components, fluorescence parameters (HIX, BIX), and absorbance ratios (E253/E203, SUVA254) confirmed that the core layers at depths of 1 219-1 222 m and 1 285-1 301 m were potential effective gas-generating formations. These layers contain low amounts of humified organic matter, weak aromaticity and high amounts of methanol functional groups. The active gas-generating formations are generally consistent with those in previous reports. Conclusion The results indicated that the CDOM spectrum is a valuable method for exploring the methanol formation substrate distribution and microbial activity. The CDOM-EEM method has the potential to serve as an effective indicator of the methanol formation characteristics of DOM in mud shale and provides an effective and essential way to assess geochemical-based gas production capacity in hydrocarbon source rocks.

To solve the problems in restoring sedimentary facies and predicting reservoirs in loose gas-bearing sediment, based on seismic sedimentologic analysis of the first 9-component S-wave 3D seismic dataset of China, a fourth-order isochronous stratigraphic framework was set up and then sedimentary facies and reservoirs in the Pleistocene Qigequan Formation in Taidong area of Qaidam Basin were studied by seismic geomorphology and seismic lithology. The study method and thought are as following. Firstly, techniques of phase rotation, frequency decomposition and fusion, and stratal slicing were applied to the 9-component S-wave seismic data to restore sedimentary facies of major marker beds based on sedimentary models reflected by satellite images. Then, techniques of seismic attribute extraction, principal component analysis, and random fitting were applied to calculate the reservoir thickness and physical parameters of a key sandbody, and the results are satisfactory and confirmed by blind testing wells. Study results reveal that the dominant sedimentary facies in the Qigequan Formation within the study area are delta front and shallow lake. The RGB fused slices indicate that there are two cycles with three sets of underwater distributary channel systems in one period. Among them, sandstones in the distributary channels of middle-low Qigequan Formation are thick and broad with superior physical properties, which are favorable reservoirs. The reservoir permeability is also affected by diagenesis. Distributary channel sandstone reservoirs extend further to the west of Sebei-1 gas field, which provides a basis to expand exploration to the western peripheral area.

Abstract In the late stage of underground brine mining in salt lakes, the method of injecting fresh water is often used to extract the salt from the brine storage medium. This method of freshwater displacement breaks the original water–rock equilibrium and changes the evolution process of the original underground brine. To explore the mechanism of salt release in saline water-bearing media under conditions of relatively fresh lake water dissolution, this paper analyzes the changes in the chemical parameters of brine from 168 sampling points in the Mahai salt lake in the Qaidam Basin at three stages (before exploitation, during exploitation, and late exploitation) by correlation analysis, ion ratio analysis, and other methods and investigate the variations in porosity and the evolution laws of brine. The results show that the changes in the main ion content and brine mineralization during the exploitation process are small. The changes in Ca2+ content are significant due to the low solubility of calcium minerals, the precipitation of gypsum during the mixing process, and the adsorption of cations by alternating with Ca2+. Primary intergranular pore skeletons are easily corroded to form secondary pores, which increase the geological porosity. Na+ and Cl- are the dominant ions in the brine in the study area, but the concentration of Ca2 + decreased significantly under the influence of mining, by 41.7% in the middle period and 24.5% in the late period. The correlation between Ca2+ and salinity changes significantly in different mining stages, and the reason for the decrease of Ca2+ may be due to the influence of mineral dissolution, mixing, and anion-cation exchange. The porosity of the layer in the study area showed the opposite trend of Ca2+, and the porosity increased first and then decreased. The innovation of this paper lies in analyzing the reasons and mechanisms of the disturbance of artificial dissolution mining on stratum structure by comparing the hydrochemical characteristics and porosity of underground brine storage media in three different mining stages. The research in this paper provides a theoretical basis for the calculation of brine resource reserves and the sustainable development of underground brine in salt lake areas.

The Paleogene-Neogene strata in the Western Depression of the Qaidam Basin represent a primary focus for oil and gas exploration and development. Influenced by both terrigenous clastic influx and endogenic carbonate deposition, these strata exhibit significant variation in sedimentary systems and reservoir characteristics. This study comprehensively examines the depositional patterns and reservoir properties of the Paleogene-Neogene sequence across the inner, middle, and outer belts of the basin, employing core analysis, thin section petrography, and physical property assessment of reservoirs. Key findings include 1) The development of a concentric sedimentary system in the Western Depression during the Paleogene-Neogene period, characterized by increased carbonate mineral content and decreased clastic material from the periphery to the center of the basin. 2) Varied sedimentary facies associations across different zones, with the outer belt dominated by fan delta and braided river delta deposits, and the middle and inner belts characterized by near- shore shallow lacustrine carbonates and algal mat deposits, and offshore semi-to deep-lacustrine fine sediments, respectively. 3) The outer belt exhibits reservoirs with favorable physical properties and connectivity, while the inner and middle belts show high heterogeneity, indicating potential for lithological traps and shale oil exploration. These insights offer scientific guidance for further investigation into the depositional systems of lacustrine basins in the Western Depression of the Qaidam Basin and for identifying promising reservoirs. [ABSTRACT FROM AUTHOR]

The low nutrient content of soil in desert ecosystems results in unique physiological and ecological characteristics of plants under long-term water and nutrient stress, which is the basis for the productivity and stability maintenance of the desert ecosystem. However, the relationship between the soil and the plant nutrient elements in the desert ecosystem and its mechanism for maintaining ecosystem stability is still unclear. In this study, 35 sampling sites were established in an area with typical desert vegetation in the Qaidam Basin, based on a drought gradient. A total of 90 soil samples and 100 plant samples were collected, and the soil's physico-chemical properties, as well as the nutrient elements in the plant leaves, were measured. Regression analysis, redundancy analysis (RDA), the Theil–Sen Median and Mann–Kendall methods, the structural equation model (SEM), and other methods were employed to analyze the distribution characteristics of the soil and plant nutrient elements along the drought gradient and the relationship between the soil and leaf nutrient elements and its impact on ecosystem stability. The results provided the following conclusions: Compared with the nutrient elements in plant leaves, the soil's nutrient elements had a more obvious regularity of distribution along the drought gradient. A strong correlation was observed between the soil and leaf nutrient elements, with soil organic carbon and alkali-hydrolyzed nitrogen identified as important factors influencing the leaf nutrient content. The SEM showed that the soil's organic carbon had a positive effect on ecosystem stability by influencing the leaf carbon, while the soil's available phosphorus and the mean annual temperature had a direct positive effect on stability, and the soil's total nitrogen had a negative effect on stability. In general, the soil nutrient content was high in areas with a low mean annual temperature and high precipitation, and the ecosystem stability in the area distribution of typical desert vegetation in the Qaidam Basin was low. These findings reveal that soil nutrients affect the stability of desert ecosystems directly or indirectly through plant nutrients in the Qaidam Basin, which is crucial for maintaining the stability of desert ecosystems with the background of climate change. [ABSTRACT FROM AUTHOR]

Early diagenetic nodules with low permeable and weather-resistant structures are considered to be favorable for biosignature preservation. Numerous nodular structures forming in neutral-to-alkaline and saline diagenetic fluids were previously identified at Gale Crater on Mars, yet their astrobiological significance remains poorly understood. In the Mars-like western Qaidam Basin, China, there are a multitude of carbonate nodules which can be analogous to those found at Gale Crater on Mars in terms of their formation backgrounds and post-depositional processes. In this study, we combine microscopic, spectroscopic, and geochemical methods to characterize the biosignature preservation of the Qaidam nodules. Carbonaceous materials, including an organic annulus inferred to be a fossil spore or algal filament microfossil, are observed in the Qaidam nodules. The total organic carbon contents of the Qaidam nodules are slightly higher than those of the surrounding fluvio-lacustrine deposits, suggesting that early diagenesis of the Qaidam nodules might facilitate the rapid entombment of biomass within magnesium carbonate or aragonite matrixes before complete degradation. The carbonate matrix showing alternating micritic and sparry layers as well as enrichment of 13C could have a physicochemical origin though the possibilities of biomineralization and organomineralization cannot be entirely ruled out. The 1-1350/1,600 distribution of carbonaceous materials implies the existence of carbon precursors of various subcellular components or coexisting organisms in pore waters. Organic carbon isotopes indicate the carbon fixation pathways such as the Calvin cycle or the Wood-Ljungdahl pathway utilized by organisms in pore waters. The findings of this study shed light into the taphonomy and detection of biosignatures in terrestrial playa nodules, with potential applications for biosignature exploration on Mars. [ABSTRACT FROM AUTHOR]

The Hardawu granites in the eastern segment of the ultrahigh-pressure metamorphic belt, the northern Qaidam Basin, were studied by whole-rock major and trace elements and in-situ zircon U-Pb geochronology and Hf isotopes to discuss the petrogenesis and tectonic evolution. Geochronological results show that the granites have a crystallization age of 401 ± 3 Ma, suggesting that they were formed in the Early Devonian. The granites have SiO2 contents of 75.32 wt.%–76.05 wt.%, total alkali contents of 8.23 wt.%–8.36 wt.%, and K2O/Na2O ratios of 1.62–1.91. They were rich in K2O, poor in TiO2, MnO, MgO, and P2O5, and have A/CNK values of 1.05–1.07, Rittmann index δ values of 2.05–2.14, and differentiation index (DI) values of 92.85–94.18. They are high potassium calc-alkaline, weak-peraluminum, and highly differentiated I-type granites. The granites also show enrichment of large ion lithophile elements (LILE) such as Rb, Ba, and Th, and depletion of high field strength elements (HFSE) such as Nb, Ta, and Ti. The total REE concentrations range from 169 ppm to 232 ppm, with enrichments of light rare earth elements and negative Eu anomalies (δEu = 0.39–0.55). The zircon εHf(t) values range from −0.65 to −2.29, and the two-stage model ages (tDM2) changed within a small range of 1.44 to 1.54 Ga, indicating that the magma of the Hardawu granites was originated from the partial melting of Mesoproterozoic lower crustal materials. Combined with previous studies, we suggest that the Hardawu granites were formed in the extensional tectonic setting after the collision between the Qaidam Block and the central and southern Qilian Block in the Early Devonian. [ABSTRACT FROM AUTHOR]

Fractures are widely developed in lacustrine carbonate reservoirs in the Oligocene Lower Ganchaigou Formation of the western Yingxiongling area and their distribution trend is unclear. Based on well logging, formation testing, rock mechanics parameters obtained by logging interpretation, and the paleotectonic stress obtained by acoustic emission experiments, finite element numerical simulation is used to restore the tectonic stress of the typical section and target layer plane models in the late Himalayan period in the study area. The fracture distributions of the section and the plane are quantitatively predicted and their distribution trends are summarized. The results show that the tectonic compression at the end of the Neogene was strong in the study area. Under the effect of the paleotectonic stress field, the fracture development degree of the upper member of the Lower Ganchaigou Formation is generally high. Fractures mainly developed in the fault zones and their surroundings, the hanging wall of the Shizigou fault, and the abnormally high-size area of tectonic stress intensity in the northern and middle tectonic zones of the presalt carbonate reservoirs. The fracture distribution is mainly affected by faults, lithology, structural parts, and tectonic stress intensity. The predicted favorable development areas of fractures can be considered favorable exploration positions in the deep layers of the study area. This study can provide a guide for the deep oil–gas exploration in the study area and a feasible method for predicting the sweet spots of this type of tight reservoir. Using the finite element numerical simulation, the geological models for the lacustrine carbonate oil reservoirs are established. The tectonic stress field of theirs is restored. Combined with the comprehensive fracture index evaluation, the fracture development degree parameters are constructed to realize the quantitative prediction of the fracture distribution. [ABSTRACT FROM AUTHOR]

To solve the problems in restoring sedimentary facies and predicting reservoirs in loose gas-bearing sediment, based on seismic sedimentologic analysis of the first 9-component S-wave 3D seismic dataset of China, a fourth-order isochronous stratigraphic framework was set up and then sedimentary facies and reservoirs in the Pleistocene Qigequan Formation in Taidong area of Qaidam Basin were studied by seismic geomorphology and seismic lithology. The study method and thought are as following. Firstly, techniques of phase rotation, frequency decomposition and fusion, and stratal slicing were applied to the 9-component S-wave seismic data to restore sedimentary facies of major marker beds based on sedimentary models reflected by satellite images. Then, techniques of seismic attribute extraction, principal component analysis, and random fitting were applied to calculate the reservoir thickness and physical parameters of a key sandbody, and the results are satisfactory and confirmed by blind testing wells. Study results reveal that the dominant sedimentary facies in the Qigequan Formation within the study area are delta front and shallow lake. The RGB fused slices indicate that there are two cycles with three sets of underwater distributary channel systems in one period. Among them, sandstones in the distributary channels of middle-low Qigequan Formation are thick and broad with superior physical properties, which are favorable reservoirs. The reservoir permeability is also affected by diagenesis. Distributary channel sandstone reservoirs extend further to the west of Sebei-1 gas field, which provides a basis to expand exploration to the western peripheral area. [ABSTRACT FROM AUTHOR]

As a Chinese endemic species, Nitraria tangutorum Bobr. distributes in Qaidam Basin undergo intensive environmental stress, especially in climate change. To investigate the distribution characteristic of simple sequence repeats (SSRs) and develop SSR marker for genetic diversity research, we developed SSRs based on transcriptome data and investigate the distribution characteristic of SSRs, and selected 23 pairs of for genetic diversity analyze. The result showed that the frequency of SSR site is 49.97%; AG/CT and AAG/CTT are the dominant repeat units. A total of 126 alleles were detected; the Ne, He, Ho and Shannon's index are 2.581, 0.588, 0.604 and 0.987, respectively, and the Fst and Nm are 0.039 and 6.243. About 5% of the variation come from population, and 95% of the variation came from individuals. Six populations are divided into two genetic clades which are different with Geographical distance distribution. Fragmentation of habitat is the main reason for the differentiation between populations, and human interference is the main reason for reducing population diversity. Therefore, the protection of this plant should minimize unreasonable human development and utilization, focus on in-situ protection, pay attention to its habitat protection and pest control, and actively carry out the collection and genetic improvement of germplasm resources. [ABSTRACT FROM AUTHOR]

Copyright of Plateau Meteorology is the property of Plateau Meteorology Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Plateau Meteorology is the property of Plateau Meteorology Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

[Objective] The Carboniferous system of the Ounan Depression in the eastern Qaidam Basin is a key area for oil and gas exploration in new regions and strata. Drilling and outcrops reveal significant differences in the sedimentary characteristics of the Upper Carboniferous strata across the plane. Previous research, mainly based on outcrop and drilling data, has focused on longitudinal sedimentary evolution and the overall sedimentary background, leaving the distribution characteristics of sedimentary facies unclear. This uncertainty affects the deployment of oil and gas exploration in the Upper Carboniferous of the eastern Qaidam Basin. [Methods] The article focuses on the Upper Carboniferous strata of the Ounan Depression. It predicts the distribution characteristics of sedimentary facies under the guidance of sedimentary model theory using a limited amount of drilling data and 2D seismic data. Utilizing 2D seismic data from the Ounan Depression, it also conducts a detailed study of the internal structure and external geometric features of seismic reflections using seismic facies identification technology. [Results] The comprehensive study identifies six types of seismic facies within the Upper Carboniferous of the Ounan Depression: parallel sheet, sub-parallel sheet, mounded, wedge-shaped, oblique foreset, and chaotic. A planar assemblage map of the seismic facies was developed. By integrating regional geological data, outcrops, well logs, and seismic data, and under the guidance of seismic sedimentology and continental shelf sedimentation theory, the relationship between seismic facies and sedimentary facies in the Upper Carboniferous of the Ounan Depression was established, and the distribution characteristics of sedimentary facies in the study area were predicted. [Conclusion] The results indicate significant differences between the seismic facies in the western and eastern regions of the Ounan Depression. Overall, the western part exhibits lower frequency and more continuous phases compared to the eastern region; the western region also has greater monolayer thickness and a more stable sedimentary environment. From east to west, the Ounan Depression develops a sequential fluvial-delta plain sedimentary system, delta front sedimentary system, and prodelta-deep water shelf sedimentary system. [Significance] The research findings provide a scientific basis for predicting favorable reservoir distribution areas and deploying exploration targets for Carboniferous oil and gas exploration in the eastern region of the Qaidam Basin. [ABSTRACT FROM AUTHOR]

The upper member of the Lower Ganchaigou Formation (UMoLGF) is a highpotential hydrocarbon exploration area in the North margin of the Qaidam Basin (NMoQB). It represents a typical low-permeability sandstone reservoir. The current understanding of reservoir characteristics of the UMoLGF is poor, and the main controlling factors of high-quality reservoir development remaining unclear. This study, for the first time, integrated various factors to investigate the formation mechanism of high-quality reservoirs in the UMoLGF's low-permeability sandstone reservoirs. Results show three provenance systems developed in the study area: northwest, northeast, and east. The northwestern and northeastern areas share similar reservoir characteristics. The rock type is predominantly feldspar, with relatively poor particle sorting and rounding. Pore types are dominated by secondary dissolution pores. However, the northwestern area has more developed fractures and poorer pore structures than the northeastern. Meanwhile, in the eastern area, the rock fragment content was high, the rock type was mainly litharentie and lithic arkose, particles were well-sorted and well-rounded. Residual intergranular pores, with good structures, dominated the pore type. The UMoLGF has entered the eo-diagenesis B stage with minor progression into the meso-diagenesis A stage. Based on quantitive calculations, this study established porosity evolution models for the different study areas. The initial porosities in the northwestern, northeastern, and eastern areas were 30.8%, 30.4%, and 34.8%, respectively. Compaction and cementation are the major factors contributing to porosity reduction in the three areas, with the most significant impact in the northwestern area. Dissolution significantly improved the reservoir properties in the northwestern area, with little effect on the northeastern and eastern areas. The formation of high-quality reservoir in the UMoLGF was affected by provenance, diagenesis, and fractures, with the primary controlling factors varying by area. In the northwestern area, the formation of high-quality reservoirs benefited from strong dissolution and well-developed fractures. In the northeastern area, the high-quality reservoir was relied upon favorable provenance and dissolution. In the eastern area, provenance provided an excellent material basis for developing high-quality reservoirs, with dissolution and chlorite cementation further improving reservoir properties. This study provides a theoretical foundation for further exploration and development of UMoLGF and offers insights for exploring and developing similar low-permeability sandstone reservoirs. [ABSTRACT FROM AUTHOR]

In the late stage of underground brine mining in salt lakes, the method of injecting fresh water is often used to extract the salt from the brine storage medium. This method of freshwater displacement breaks the original water–rock equilibrium and changes the evolution process of the original underground brine. To explore the mechanism of salt release in saline water-bearing media under conditions of relatively fresh lake water dissolution, this paper analyzes the changes in the chemical parameters of brine from 168 sampling points in the Mahai salt lake in the Qaidam Basin at three stages (before exploitation, during exploitation, and late exploitation) by correlation analysis, ion ratio analysis, and other methods and investigate the variations in porosity and the evolution laws of brine. The results show that the changes in the main ion content and brine mineralization during the exploitation process are small. The changes in Ca2+ content are significant due to the low solubility of calcium minerals, the precipitation of gypsum during the mixing process, and the adsorption of cations by alternating with Ca2+. Primary intergranular pore skeletons are easily corroded to form secondary pores, which increase the geological porosity. Na+ and Cl- are the dominant ions in the brine in the study area, but the concentration of Ca2 + decreased significantly under the influence of mining, by 41.7% in the middle period and 24.5% in the late period. The correlation between Ca2+ and salinity changes significantly in different mining stages, and the reason for the decrease of Ca2+ may be due to the influence of mineral dissolution, mixing, and anion-cation exchange. The porosity of the layer in the study area showed the opposite trend of Ca2+, and the porosity increased first and then decreased. The innovation of this paper lies in analyzing the reasons and mechanisms of the disturbance of artificial dissolution mining on stratum structure by comparing the hydrochemical characteristics and porosity of underground brine storage media in three different mining stages. The research in this paper provides a theoretical basis for the calculation of brine resource reserves and the sustainable development of underground brine in salt lake areas. [ABSTRACT FROM AUTHOR]

The Qaidam Basin is the largest Cenozoic sedimentary basin on the northern part of Qinghai-Xizang Plateau, with a stratum thickness exceeding 10 km. By revealing the magnetic fabric information preserved in Cenozoic within the basin, it is possible to reconstruct the regional tectonic stress orientation, which is of great significance for exploring the tectonic deformation and dynamic mechanism in the northern part of Qinghai-Xizang Plateau. The anisotropy of magnetic susceptibility in various directions of Cenozoic strata samples from Lulehe section in the northern Qaidam Basin was measured. Subsequently, magnetic fabric information was obtained from 1 070 samples, and an analysis was conducted on the morphology of the magnetic fabric and its related parameters. The results show that the magnetic fabric of strata during 23.7-9.9 Ma in Lulehe section shows an initial deformation magnetic fabric, with its magnetic lineation indicating the direction of compression stress. The magnetic fabric of strata during 9.9-5.2 Ma is characterized by sedimentary fabric, and no obvious tectonic stress direction is recorded. After removing the effects of structural rotation using magnetic declination, variations are observed in the orientation of the compressive stress recorded by the magnetic fabric in Lulehe section over different periods, respectively. During 23.7-18.1 Ma, it gathers at ～25°, revealing that the northern Qaidam Basin suffers from near SN compression stress in the Early Miocene. During 18.1-15.2 Ma, the direction of compressive stress rotates counterclockwise from ～25° to ～-20°. During 15.2-9.9 Ma, the direction of compressive stress rotates clockwise from ～-20° to ～20°. These results reveal that the compression stress direction of the northern Qaidam Basin first rotates counterclockwise (18.1-15.2 Ma) and then rotates clockwise (15.2-9.9 Ma) in the Middle Miocene. Based on the surrounding tectonic framework and the previous analysis of tectonic deformation, it is considered that the rotation of tectonic stress on the northern margin of Qaidam Basin since the Middle Miocene may be closely related to the superposition of bidirectional compression stress from East Kunlun and Qilian Mountains [ABSTRACT FROM AUTHOR]

The northeastern periphery of the Qaidam Basin is a crucial region for comprehending the northeastward growth of the Tibetan Plateau, as it documents Late Cenozoic crustal deformation that elucidates the plateau's growth process. In this study, we reconstruct three stages of crustal deformation in the northeastern periphery of the Qaidam Basin during the Late Cenozoic based on interpretation of growth strata from five seismic profiles, structural mapping of the typical superimposed folds and detailed detrital zircon analysis within the study area. (1) During the Early Miocene to Late Miocene period (23–8.6 Ma), there was NW–SE extensional deformation in the northeast margin of the Qaidam Basin, which exerted control over the deposition of the Youshashan Formation. (2) The NW–SE shortening occurred during the Late Miocene period (8.6–8.1 Ma), subsequent to the deposition of the Youshashan Formation and preceding the deposition of the Shizigou Formation, resulting in a parallel unconformity between these two geological units. (3) The intense shortening of the NE–SW direction occurred during the Late Miocene and Pliocene epochs (8.1–2.5 Ma). The timing of this deformation aligns with the sedimentary age of the Shizigou Formation, suggesting that the initial deformation age may represent the onset of NE extrusion from the Tibetan Plateau towards the northeast margin of the Qaidam Basin. The present study not only delineates a Late Cenozoic structural dome resulting from two‐stage crustal shortening in the northeastern periphery of the Tibetan Plateau, but also provides a crucial evidence for reconstructing the Late Cenozoic intracontinental deformation process in this region. [ABSTRACT FROM AUTHOR]

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Lacustrine mixed carbonate/siliciclastic sediment is an important type of oil and gas reservoir with significant potential. Although previous studies have investigated the sedimentary characteristics of the mixed depositional system in numerous oil and gas-bearing basins worldwide, a detailed sedimentary architecture model is still lacking for guiding reservoir characterization at the hydrocarbon reservoir scale. In this paper, a typical lacustrine mixed carbonate/siliciclastic sedimentary system, preserved in the lower member of the ShangGanchaigou Formation, Neogene, in the western Qaidam Basin, Western China, was deeply investigated based on well logging data from 640 wells, 438 m of cores from 3 core wells, and outcrop studies. The results demonstrate that 1) seven types of architecture elements, namely, distributary channel, channel mouth bar, distal bar, sheet-like sand, shallow water mud, algal mound, and marl flat characterized by different lithofacies associations, were recognized based on core and well logging data. 2) The lacustrine mixed carbonate/siliciclastic depositional system can be divided into three facies belts. Along the lakeward direction, the proximal facies belt is dominated by delta front deposits and characterized by gradually downstream bifurcating distributary channels and associated lateral amalgamated delta lobes. The middle facies belt is characterized by isolated and small-scale delta lobes and inter-lobe deposits, including sheet-like sand, small-scale algal mounds, and marl flats, and the distal facies belt is a combination of large-scale algal mounds and marl flats. 3) Within a depression, short-term base-level cycles controlled the facies belt transition, and the proximal, middle, and distal facies belts formed under relatively low, middle, and high base-level conditions, respectively. 4) The scale and connectivity of reservoirs gradually decreased from the proximal to the distal belt.

Salinization is a severe threat to agriculture and the environment in many areas, and the same in Qaidam Basin, Qinghai Province, Northwestern China. Microorganisms have an important influence on regulating the biochemical cycles of ecosystems; however, systematic research exploring microbial diversity and interactions with saline-soil ecosystems’ environmental variables remains scarce. Thus, 16 S rRNA high-throughput sequencing was performed in this paper to characterize microbial diversity under different levels of salinized soils: non-salinized (NS, 2.25 g/L), moderately salinized (MS, 6.14 g/L) and highly salinized (HS, 9.82 g/L). The alpha diversity results showed that the HS soil was significantly different from the NS and MS soils. An analysis of similarity (ANOSIM) and a principal co-ordinates analysis (PCoA) indicated that NS and MS clustered closely while HS separated from the other two. Significant differences in microbial composition were observed at the taxonomic level. Proteobacteria (42.29–79.23 %) were the most abundant phyla in the studied soils. Gammaproteobacteria (52.49 and 66.61 %) had higher abundance in the MS and HS soils at the class level; Methylophaga and Pseudomonas were the predominant bacteria in the HS soil; and Azotobacter and Methylobacillus were abundant in the MS soil. Most genera belonging to Proteobacteria and Actinobacteria were detected via a linear discriminate analysis (LDA) effect size (LEfSe) analysis, which indicated that microbes with the ability to degrade organic matter and accomplish nutrient cycling can be well-adapted to salt conditions. Further analyses (redundancy analysis and Mantel test) showed that the microbial communities were mainly related to the soil salinity, electrical conductivity (EC1:5), total phosphorus (TP) and ammonia nitrogen (NH4+-N). Overall, the findings of the study can provide insights for better understanding the dominant indigenous microbes and their roles in biochemical cycles in different saline soils in the Qaidam Basin, Qinghai Province, China. The researches related to microbial community under typical poplar species should further clarify the mechanism of plant-microbial interaction and benefit for microbial utilization in salt soil remediation.

The characterization of pore systems in fine-grained carbonate rocks faces numerous challenges due to the significant complexity of microscopic features, including a variation of micro- and nanoscale pore sizes and the complex pore-throat distribution. In this work, digital core technology was adopted to characterize the pore systems of lacustrine fine-grained carbonate rocks in the Yingxi area of Qaidam Basin. The simulated results indicated that the pore types predominantly contain intercrystalline and dissolution pores. The former exhibit high porosity but extremely low permeability and are primarily developed in bedded dolostones. Conversely, the latter show relatively higher permeability, predominantly developed in bedded calcareous dolostones. The elevated dolomite content provides the material basis for the development of intercrystalline pores, while the extremely small throat radius constrains the fluidity of this pore system. In addition, the dissolution has a great impact on improving the permeable capability of intercrystalline pore system via increasing the radius and specific surface area of pores and throats. [ABSTRACT FROM AUTHOR]

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Copyright of Plateau Meteorology is the property of Plateau Meteorology Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Special Oil & Gas Reservoirs is the property of Special Oil & Gas Reservoirs Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

[Objective] Exploration practice of the Qaidam Basin show that the remaining petroleum in the Qaidam Basin is mainly concentrated in the western area, where relatively little exploration has been carried out due to the complex landform and the presence of typically low-permeability unconventional reservoirs. Accordingly, to increase petroleum exploration in the western Qaidam Basin. [Methods] A comprehensive study of the data from sedimentary structure observation, rock slices, X-ray diffraction whole-rock analyses and seismic data, among other techniques, was carried out on an interval of core from the Pliocene Xiayoushashan Formation in well Xiandong 1. [Results and Conclusions] The rock was found to comprise gray-black mudstone and shale interbedded with thin-to-medium massive fine-grained greywacke. The top and bottom of the sand bodies are in abrupt contact with the mudstone. The lower boundary of the sand bodies is obviously an uneven erosional surface, and the mudstone and shale beneath the erosion surface exhibits deformed bedding. The sand bodies are sandy debris flow deposits formed by re-transport. The dark-gray to gray black calcareous mudstone and shale contains interbeds of calcirudite bearing shell-terrigenous debris and siltstone, and a silty mass with obviously deformed bedding. These laminae are clearly seen and have an obvious deformation direction caused by clastic slump. The Pliocene Xiayoushashan Formation in well Xiandong 1 is mainly the dark gray-gray black mudstone and shale interbedded with siltstone bearing dolomite, calcite and clay. The mudstone and shale contains horizontal rhythmic bedding. The siltstone has developed slightly dipping cross-beds with more clay laminae, climbing-ripple lamination and coarsely interlayered bedding, which are mainly from semi- deep lake deposits interbedded with weaker bottom flow deposits derived from sediment gravity flows. In addition, the deeper-water areas of the Altun Mountain front appears to have developed slump-sediment gravity flow sedimentary reservoirs similar to well Xiandong 1 at a different period of basin development, but further research into this aspect is needed. [ABSTRACT FROM AUTHOR]

Aeolian landforms provide valuable insights into the planetary surface environment and its evolutionary history. In this study, the formation and evolution of megaripples in the Qaidam Basin and their relationship with the development environment are analyzed. By quantifying the wind environment, morphology, grain‐size distribution, sedimentary structure, and luminescence age of megaripples, we propose for the first time that there are multiple megaripple evolution modes. Investigation revealed that three evolution modes were responsible for forming megaripples in different equilibrium states: transient, stable, and metastable. Well‐sorted coarse sand grains accumulate on ridges and overlay poorly sorted fine sand grains to form transient megaripples. Stable megaripples have alternating sedimentary bedding of coarse and fine sand grains. Metastable megaripples have a secondary ripple formation on the surface. Throughout their formation, coarse and fine sand grains undergo regrouping. The response of coarse grains to the change in wind speed lags behind that of fine grains. This process controls the erosion and accumulation of megaripples and affects their size and sedimentary structures. The evolution mode, scale, and sedimentary structure of megaripples are influenced by the grain‐size range under the same wind conditions. The luminescence ages of the coarse‐grained megaripple sediments are less than 700 years. This study provides a fresh perspective on the coexistence of various sand ripples and transverse aeolian ridges found on Mars. Plain Language Summary: Megaripples are intermediate‐scale landforms between sand ripples and dunes, with heights of tens of centimeters and wavelengths of up to 20 m. Megaripples contain valuable environmental information. This makes them important for understanding the planetary environment and evolution. Fieldwork in the Qaidam Basin has shown that megaripples of varying shapes and sizes are formed through diverse evolution modes. We identified and elaborated on three models of megaripple formation by studying the wind patterns, shape, grain‐size distribution, sedimentary structure, and age of megaripples at three sites in the Qaidam Basin. Transient megaripples consist of coarse sand grains on their upper half and poorly sorted fine sand grains on their lower half. Stable megaripples have alternating layers of coarse and fine sand grains that correspond to different aeolian sand‐transport intensities, and metastable megaripples have secondary sand ripples on the surface due to transient strong wind causing the saltation of coarse sand grains. Changes in the wind strength regroup the fine and coarse sand, which drives the bimodal distribution of the sand grains, and the sediment grain size controls the evolution mode, sedimentary structure, and scale. This provides insights into the spatial pattern of ripple‐like aeolian landforms on Mars. Key Points: Megaripples have various evolution modesDuring the formation of megaripples, coarse and fine sand grains undergo regroupingThe grain‐size range plays a crucial role in facilitating the coexistence of multi‐scale megaripples [ABSTRACT FROM AUTHOR]

As the largest intermontane basin in the northeastern Tibetan Plateau (TP), the Qaidam Basin provides unique insight into paleoclimatic change and its relationship with global change and uplift on the TP. In this study, based on morphological comparison, fossil fruit of Cyclocarya from the Early Oligocene Shangganchaigou Formation in the Qaidam Basin is assigned as Cyclocarya cf. weylandii. The discovery of Cyclocarya cf. weylandii demonstrates the occurrence of Cyclocarya in the Oligocene sediment in Qaidam Basin. This is the first record of Cyclocarya fossil of Early Oligocene Age in China and indicates that Cyclocarya has existed on the northeastern TP since at least the Early Oligocene. The living analogues of the current fossil now lives in sub-tropical China, where the East Asian Monsoon is prevalent. Integrating the new fossils and previously reported fossil remains of plants and fishes, it can be inferred that the Early Oligocene Qaidam Basin was primarily influenced by westerly circulation and had a relatively warm and humid climate, which was in sharp contrast to the present-day climate in Qaidam Basin. [ABSTRACT FROM AUTHOR]

Studying the lacustrine microbialites in the Western Qaidam Basin in the northeastern margin of the Qinghai–Tibetan Plateau may provide clues to the sedimentary record, the depositional model, and the hydrocarbon potential. Based on geological, geochemical, and seismic data, the sedimentary characteristics and hydrocarbon potential of Eocene lacustrine microbialites in Western Qaidam Basin are estimated. Three microbialites are identified In the Eocene lacustrine system of the Qaidam Basin, including the thick thrombolites in relatively high-energy near-shore settings, the small-scale stromatolites and thrombolites in extremely shallow water environment, and the laminates in relatively deep water of intrabasinal environments. Three sedimentary models have been established, including the marginal steep slope zone, the marginal gentle slope zone, and the intrabasinal deep-water zone, respectively. The framework pores, intergranular pores, dolomite intercrystalline pores, dissolved pores and interlayered fractures commonly composed the pore spaces of microbialites. The Fossil Group of Botryococcus (a lipid-rich algae) contributed the main source of hydrocarbons particularly in saline water in Western Qaidam Basin. The development of Eocene lacustrine microbialites on the northeastern Qinghai–Tibetan Plateau provides a new perspective to explore the complex mineralization processes and hydrocarbon potential of microbialites. [ABSTRACT FROM AUTHOR]

Previous research shows that the origin and distribution of formation overpressure are governed by several dominant factors including disequilibrium compaction, hydrocarbon generation, tectonic compression and diagenesis, influenced by salt components and their concentration, but it is unclear how salts affect formation overpressure in saline lacustrine basins. This paper investigated the effect of salts on formation overpressure based on organic geochemistry, rock mineralogy, logging curve comparison and wave velocity-density cross-plot by combining the sedimentary and structural background. In the Western Qaidam Basin, the proportion of abnormally high pressures rises from the Neogene to the Paleogene. The top surface of the overpressure is between 2300 and 2500 m deep. As the subsidence and sedimentary centers of the basin moved eastward, the centers of the overpressure migrated from west to east. In the Upper Oligocene, the overpressure is developed in the deep and semi-deep lacustrine facies, and the pressure coefficient is 1.8–2.0. Disequilibrium compaction is the primary control factor with a contribution rate of more than 60% in the intersalt and subsalt strata, followed by tectonic compression with a contribution rate of 20–30%. Fracture reducing by salt filling and fluid volume expanding by gypsum dehydration increase the fluid volume in the formation, which promotes formation overpressure. The gypsum salt rocks also have strong plasticity and sealing effect, thus providing a closed environment for the formation overpressure. Through providing the primary migration driven force and sealing conditions for oil and gas, the overpressure is meaningful to petroleum accumulation and preservation in saline lacustrine formation of the Paleogene and Neogene in the Western Qaidam Basin, NW China. [ABSTRACT FROM AUTHOR]

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The Paleogene-Neogene strata in the Western Depression of the Qaidam Basin represent a primary focus for oil and gas exploration and development. Influenced by both terrigenous clastic influx and endogenic carbonate deposition, these strata exhibit significant variation in sedimentary systems and reservoir characteristics. This study comprehensively examines the depositional patterns and reservoir properties of the Paleogene-Neogene sequence across the inner, middle, and outer belts of the basin, employing core analysis, thin section petrography, and physical property assessment of reservoirs. Key findings include 1) The development of a concentric sedimentary system in the Western Depression during the Paleogene-Neogene period, characterized by increased carbonate mineral content and decreased clastic material from the periphery to the center of the basin. 2) Varied sedimentary facies associations across different zones, with the outer belt dominated by fan delta and braided river delta deposits, and the middle and inner belts characterized by near-shore shallow lacustrine carbonates and algal mat deposits, and offshore semi-to deep-lacustrine fine sediments, respectively. 3) The outer belt exhibits reservoirs with favorable physical properties and connectivity, while the inner and middle belts show high heterogeneity, indicating potential for lithological traps and shale oil exploration. These insights offer scientific guidance for further investigation into the depositional systems of lacustrine basins in the Western Depression of the Qaidam Basin and for identifying promising reservoirs.

Early diagenetic nodules with low permeable and weather-resistant structures are considered to be favorable for biosignature preservation. Numerous nodular structures forming in neutral-to-alkaline and saline diagenetic fluids were previously identified at Gale Crater on Mars, yet their astrobiological significance remains poorly understood. In the Mars-like western Qaidam Basin, China, there are a multitude of carbonate nodules which can be analogous to those found at Gale Crater on Mars in terms of their formation backgrounds and post-depositional processes. In this study, we combine microscopic, spectroscopic, and geochemical methods to characterize the biosignature preservation of the Qaidam nodules. Carbonaceous materials, including an organic annulus inferred to be a fossil spore or algal filament microfossil, are observed in the Qaidam nodules. The total organic carbon contents of the Qaidam nodules are slightly higher than those of the surrounding fluvio-lacustrine deposits, suggesting that early diagenesis of the Qaidam nodules might facilitate the rapid entombment of biomass within magnesium carbonate or aragonite matrixes before complete degradation. The carbonate matrix showing alternating micritic and sparry layers as well as enrichment of 13C could have a physicochemical origin though the possibilities of biomineralization and organomineralization cannot be entirely ruled out. The I-1350/1,600 distribution of carbonaceous materials implies the existence of carbon precursors of various subcellular components or coexisting organisms in pore waters. Organic carbon isotopes indicate the carbon fixation pathways such as the Calvin cycle or the Wood-Ljungdahl pathway utilized by organisms in pore waters. The findings of this study shed light into the taphonomy and detection of biosignatures in terrestrial playa nodules, with potential applications for biosignature exploration on Mars.

The upper member of the Lower Ganchaigou Formation (UMoLGF) is a high-potential hydrocarbon exploration area in the North margin of the Qaidam Basin (NMoQB). It represents a typical low-permeability sandstone reservoir. The current understanding of reservoir characteristics of the UMoLGF is poor, and the main controlling factors of high-quality reservoir development remaining unclear. This study, for the first time, integrated various factors to investigate the formation mechanism of high-quality reservoirs in the UMoLGF’s low-permeability sandstone reservoirs. Results show three provenance systems developed in the study area: northwest, northeast, and east. The northwestern and northeastern areas share similar reservoir characteristics. The rock type is predominantly feldspar, with relatively poor particle sorting and rounding. Pore types are dominated by secondary dissolution pores. However, the northwestern area has more developed fractures and poorer pore structures than the northeastern. Meanwhile, in the eastern area, the rock fragment content was high, the rock type was mainly litharentie and lithic arkose, particles were well-sorted and well-rounded. Residual intergranular pores, with good structures, dominated the pore type. The UMoLGF has entered the eo-diagenesis B stage with minor progression into the meso-diagenesis A stage. Based on quantitive calculations, this study established porosity evolution models for the different study areas. The initial porosities in the northwestern, northeastern, and eastern areas were 30.8%, 30.4%, and 34.8%, respectively. Compaction and cementation are the major factors contributing to porosity reduction in the three areas, with the most significant impact in the northwestern area. Dissolution significantly improved the reservoir properties in the northwestern area, with little effect on the northeastern and eastern areas. The formation of high-quality reservoir in the UMoLGF was affected by provenance, diagenesis, and fractures, with the primary controlling factors varying by area. In the northwestern area, the formation of high-quality reservoirs benefited from strong dissolution and well-developed fractures. In the northeastern area, the high-quality reservoir was relied upon favorable provenance and dissolution. In the eastern area, provenance provided an excellent material basis for developing high-quality reservoirs, with dissolution and chlorite cementation further improving reservoir properties. This study provides a theoretical foundation for further exploration and development of UMoLGF and offers insights for exploring and developing similar low-permeability sandstone reservoirs.

In recent years, several small and rich lithologic oil and gas reservoirs have been discovered in the saline lacustrine beach bar sand in the Qaidam Basin. In order to expand the exploration scale of lithologic oil and gas reservoirs, find new exploration targets and zones, and increase storage and production of oilfields, based on coring, logging and seismic data, the controlling factors of oil and gas accumulation in lithologic reservoirs are defined, and some exploration succeeding fields of lithologic reservoirs are pointed out. The results show that: The southwestern Qaidam Basin has four favorable conditions for the formation of lithologic reservoirs. The first is the development of three stable ancient slopes, namely, the Qigequan-Hongliuquan, Shaxi-Yuejin, and Zahaquan-Wunan, which are inherited and conducive to the accumulation of oil and gas. The second is the proximity of two hydrocarbon generation centers, Hongshi and Zahaquan, with superior oil source conditions. The third is that the salt lake basin developed large braided river delta, widely distributed shoal-bar sand and algal hill-gray cloud flat deposits, forming two complementary types of reservoirs of clastic rock and carbonate rock. The fourth is the development of a variety of drainage systems, which can form several sets of oil-bearing strata vertically. Controlled by paleo-structural, sedimentary and diagenetic factors, there are four types of lithologic reservoirs in the southwestern Qaidam Basin: updip pinching out, sandstone lens, physical sealing and dolomitization trap. Lithologic reservoirs are controlled by three factors: paleo-structure, high-quality source rock and effective reservoir. Paleo-structure determines the type of lithologic traps and the direction of hydrocarbon migration. The high-quality source rock controls the distribution and scale of lithologic reservoirs and effective reservoir controls the accumulation of lithologic reservoirs. Comprehensive evaluation shows that the braided river delta front sand body is a favorable area for the exploration of lithologic reservoirs in the lower Ganchaigou Formation of the Lower Paleogene, mainly distributed in the basin dip end of Shaxi, Gasi, and Wunan. The dolomitization trap is a favorable area for exploration of lithologic reservoirs in the upper member of lower Ganchaigou Formation of Paleogene, mainly distributed around the Hongshi Sag. The widely distributed beach bar is a favorable area for lithologic oil exploration in the upper Ganchaigou Formation and lower Youshashan Formation of Neogene, mainly distributed in Yingxiongling, Gasi, Zhahaquan, Wunan, and other areas. This understanding supports a series of major breakthroughs in lithologic exploration, such as well Qietan 2 and the new series of Gasi, with important guiding significance for further exploration of lithologic reservoirs in the southwestern Qaidam Basin.

Understanding the paleoenvironment and phytogeographical history of the Tibetan Plateau, China relies on discovering new plant fossils. The Qaidam Basin has long been regarded as an ideal ‘field laboratory’ to investigate the paleoclimate and paleobiological evolution of the northern Tibetan Plateau. However, fossil angiosperms from the Qaidam Basin are rare, and our knowledge of its paleovegetation is poor. Here, we report fossil leaves and fruits of Betulaceae found from the Oligocene Shangganchaigou Formation of northwestern Qaidam Basin (Huatugou area). Comparative morphological analysis led us to assign the fruits to the Betula subgenus Betula and the leaves to Carpinus grandis. These findings, together with other reported fossil plants from the same locality, reveal a close floristic linkage between the Qaidam Basin and Europe during the Oligocene. The northern pathway of this floristic exchange may have crossed through the Qaidam Basin during the late Paleogene. This floristic linkage may have been facilitated by the continuous narrowing of the Turgai Strait and stronger westerlies, which transported moisture and provided favorable climatic conditions. Indeed, fossil plants collected from the Qaidam Basin suggest that during the Oligocene this region had warm and humid deciduous broad-leaf forest, which differs from the region’s modern vegetation and indicates that the Qaidam Basin may have been a suitable region for these plants to flourish and spread during the Oligocene.