Northern Junggar Basin Research Articles

Spatiotemporal evolution law and driving mechanism of production–living–ecological space from 2000 to 2020 in Xinjiang, China

Xinjiang is located in the northwest of China, with a vast territory and abundant resources, which holds an important strategic position for China. However, the climate in the region is arid and the ecological environment is fragile. In recent years, with the growth of population and the improvement of economic development level, construction and agricultural land in Xinjiang have gradually expanded, and ecological land has been extensively occupied. The competition between land resources is becoming increasingly fierce, leading to some ecological and environmental problems in the region. In this context, understanding the spatiotemporal changes and driving factors of Xinjiang's production space, living space and ecological space (PLES) is of great practical significance for promoting sustainable development in the region, and can also provide reference for the research of PLES in other arid areas at home and abroad. At present, most of the research on PLES is focused on small-scale areas such as urban agglomerations, rural areas, and watersheds, or non arid areas with relatively superior natural conditions, with less research on large-scale arid areas. In this study, the transfer matrix, the center of gravity movement trajectory, Moran's I and the spatial conflict measurement model were used to illustrate the spatial–temporal evolution of PLES in Xinjiang, and the correlation coefficient was used to determine the main factors affecting the change of PLES. Results show that (1) Xinjiang is dominated by ecological space, which accounts for more than 90% of the total area of Xinjiang and has significant continuity. They are mainly distributed in Tarim, Turpan, and the northern Junggar Basin. The production space area accounts for about 5% of the total area of Xinjiang and is distributed in the vicinity of the Tianshan and Kunlun Mountains. Living space accounts for about 1% of Xinjiang's total area and is scattered around cities. (2) From 2000 to 2020, the change degree of PLES in Xinjiang in the last decade is higher than that in the first decade, most of which is the transformation from ecological space to production space. The three types of spaces influence and restrict each other in the development process. (3) Population, crop sown area, natural conditions, policy and the development level of agricultural science and technology are the main factors affecting the spatial distribution of production. Environmental factors such as altitude, soil erosion and temperature have a great influence on ecological space. Population, the output value of various industries and total retail sales of consumer goods are the main factors affecting residential space. The evolution of Xinjiang PLES is the result of multiple factors. (4) The medium spatial conflict dominates, mainly distributed in Tarim Basin and Junggar Basin. The weak and strong space conflicts are concentrated in the oases in the north of the Tianshan and Kunlun Mountains, and the number is small. From 2000 to 2020, the increasing degree of spatial conflicts in Xinjiang is due to land desertification.

Fission-track thermochronological evidence for the Yanshanian tectonic evolution of the northern Junggar Basin, northwest China

The Junggar Basin is a multicycle intracontinental sedimentary basin developed on the pre-Mesozoic deformed basement. For a long time, the Junggar Basin and its adjacent Altai orogeny have been a focus of debate for geologists studying the opening and closing history of the Paleozoic Asian Ocean and Cenozoic intracontinental deformation. However, there has been no detailed research on the intracontinental tectonic activities of northern Xinjiang since the Mesozoic, particularly the Yanshanian tectonic activities in the northern Junggar Basin. Fission-track (FT) dating was conducted on 15 apatite samples and eight zircon samples obtained from the northern Junggar Basin to better understand the Yanshanian tectonic evolution. The results showed that apatite FT (AFT) ages ranged from 131 to 42 Ma and zircon FT ages ranged from 205 to 132 Ma. Based on the AFT track thermal history modeling and the regional geological data, we proposed that the northern Junggar Basin underwent three tectonic thermal events during 165–161, 93–81, and 72–66 Ma. The thermal events of 165–161 Ma may indicate magmatic activity during the Yanshanian, while the 93–86 and 72–66 Ma events reflect Late Cretaceous uplift and cooling. This study has confirmed the tectonic evolution of the Yanshanian in the northern Junggar Basin from the perspective of thermochronology. It has also revealed that the Yanshanian orogeny, a regional tectonic event, may have also occurred in northwest China.

The Spatiotemporal Characteristics and Driving Factors of Dust Emissions in East Asia (2000–2021)

The climate effect and environmental pollution caused by dust discharged into the atmosphere have attracted much attention. However, the driving factors of dust emissions have not been studied thoroughly. Here, spatiotemporal variations in dust emissions and the relationship between dust emissions and large-scale atmospheric circulation in East Asia from 2000 to 2021 were investigated using Modern-Era Retrospective Analysis for Research and Applications version 2, Cloud-Aerosol Lidar Pathfinder Satellite Observations, ERA5 reanalysis data, and climate indices. Results showed that the Taklimakan Desert in the Tarim Basin, the Gurbantonggut Desert in the Junggar Basin, the Turpan Basin, and the Gobi Desert in western Inner Mongolia and southern Mongolia are the main sources of dust emissions in East Asia. The period of strong dust emissions is from March to May, and emissions to the atmosphere were mainly distributed at 0–4 km in the troposphere. In the eastern and southwestern Tarim Basin, northern Junggar Basin, and parts of the Gobi Desert in southern Mongolia, dust emissions have significantly increased over the past 22 years, whereas in the southwestern Tibetan Plateau, southwestern Inner Mongolia, and a small part of the northern Mongolian Gobi Desert there was a significant decreasing trend. The winter North Atlantic Oscillation (NAO) and Arctic Oscillation (AO) were significantly negatively correlated with East Asian dust emissions the following spring. The various phases of the AO/NAO coupling have clear different effects on East Asian dust emissions in the spring. When the AO/NAO coupling was negative (positive), the East Asian trough and Siberian High were strengthened (weakened), the frequency of cold air activity increased (weakened), 800 hPa wind speed strengthened (weakened), and East Asian emissions increased (decreased). In AO−/NAO+ years, the Asian polar vortex was stronger to the south and the East Asian trough was stronger to the west. The Lake Baikal trough was in the deepening phase, which caused more polar cold air to move into East Asia, aggravating the intensity of dust activity. In the AO+/NAO− years, the Siberian High and East Asian trough weakened, which was unfavorable to the southward movement of cold air from Siberia. Therefore, the frequency of windy weather in East Asia decreased, partly weakening dust emissions. However, a positive geopotential anomaly in northeast China and a negative geopotential anomaly in South Asia triggered an anomalous enhancement in easterly wind in the tropospheric area over northwest China. Strengthening of the Balkhash trough provides favorable conditions for gale weather in northwest China. The frequency of gale weather increased, and dust emissions were enhanced in northwest China.

Quantitative characterization of fracture-pore distribution and effects on production capacity of weathered volcanic crust reservoirs: Insights from volcanic gas reservoirs of the Dixi area, Junggar Basin, Western China

Igneous hydrocarbon reservoirs worldwide are of significant importance to the petroleum industry for oil and gas exploration. The Carboniferous weathered volcanic crust reservoirs of the Dinan salient in the northern Junggar Basin are major exploration targets of PetroChina. The present study analyzes the geological, well logging, and production data to formulate development and distribution methods for quantitative characterization of weathered volcanic crust fractures and examine their fracture-pore distributions. The effects of the fracture-pore distribution on the productivity of various lithologies of weathered volcanic crust reservoirs were investigated. Various volcanic lithofacies demonstrate the lithological differences in their physical properties, fracture development, and distributions due to the conspicuous variations in weathering resistance among different volcanic rock types. The present study revealed the level of physical properties of volcanic rocks, which are ranked as follows: volcanic breccia > mafic lava > tuff > felsic intrusive rock. However, the degree of fracture development ranked differently from most developed to least developed as follows: felsic intrusive rock > mafic lava > volcanic breccia > tuff. The fracture distribution was primarily controlled by lithology, rock stratum thickness, degree of weathering and leaching, along with tectonism. Compared to other rock types, felsic intrusive rock and mafic lava were more prone to fracturing owing to different petrophysical properties. Additionally, fractures typically developed in single lithological bodies with a thickness of less than 15 m and were characterized by the “single-section” developing mode. For lithological bodies of thickness greater than 15 m, fracture development was more limited, primarily concentrated at the top and bottom of the lithological body and characterized by the “bi-section” or “tri-section” developing modes. These differences can be quantitatively characterized by the fracture development thickness, fracture layer density, and fracture development thickness ratio. Moreover, the influence of the degree of fracture development on the productivity of mafic lava and felsic intrusive gas reservoirs was higher than that of the porosity; however, volcanic breccia and tuff exhibited the opposite effect. The production capacity of weathered volcanic crust reservoirs is affected by the following factors in the order of degree of fracture development > porosity > lithology > thickness of a single lithological body > distance from the top surface of the weathered crust. These quantitative characterization methods can provide valuable technical support for optimizing favorable exploration targets.

Dinosaur taphonomy of the Jurassic Shishugou Formation (Northern Junggar Basin, NW China) – insights from bioerosional trace fossils on bone

Bioerosional trace fossils can offer invaluable insights into taphonomic processes, ecosystem dynamics and environmental conditions that are not obtainable by other lines of evidence. Here, we describe the first invertebrate trace fossils on dinosaur bone from the Upper Jurassic Shishugou Formation of the northeastern Junggar Basin. The traces occur as spherical holes in the bone, closely resembling boreholes attributed to either indeterminate insects or dermestid beetles and thus they are here likewise ascribed to feeding and/or pupation by necrophagous insects. Such bioerosional trace fossils have several taphonomical and palaeoecological implications for they are only inflicted on subaerially exposed tissues and preferentially when carcasses are desiccated. We, therefore, conclude that the dinosaur carcass was exposed for at least several weeks under a semi-arid and seasonal climate before it was buried by sediment. This supports the general palaeoclimatological and paleoenvironmental reconstructions for the Shishugou Formation from sedimentological data. Moreover, this is the first evidence for invertebrate–vertebrate interactions from the Late Jurassic of Asia, offering a novel glimpse into the diverse biotic relationships of this ancient Jurassic ecosystem.

The anthracotheres from northern Junggar Basin and their palaeoclimatic significance in relation to the Tibetan Plateau

Anthracotheres were an environmentally sensitive group that were thought to have become extinct from the middle-high latitudes of the northern hemisphere by the early Miocene. Hereby, the present author reports previously unpublished fossil bothriodonts, a group of anthracotheres, from the northern Junggar Basin, in China’s far northwest. An M3 of a small bothriodont Elomeryx sp., from the lower part of the Halamagai Formation, which is probably of the early middle Miocene age, is the only anthracothere record from the Neogene of northern China. More importantly, it is the latest anthracothere record from the middle-high latitudes of the northern hemisphere. The other teeth from Xiaerhete locality of the Irtysh River Formation, which is of the late Eocene age, are identified as Bakalovia sp. This poorly known genus was previously only reported from the middle or late Eocene of Southwest Europe. This study complements the sparse anthracothere fossil records of northwestern China. The present material, together with previous records, strongly suggests the occurrence of anthracothere interchanges between East Asia and both Europe and North America possibly from the middle or late Eocene to the early Oligocene. Anthracotheres declined remarkably in the Oligocene and Miocene in northern China, in contrast to their continued abundance in South and Southeast Asia at the same time, suggesting the existence of climate zonation and a faunal discontinuity in mammal distribution patterns between the northern and southern China. This zonation was probably related to the uplift of the Tibetan Plateau, which altered atmospheric circulation throughout Eastern Asia.

Small theropod teeth (Dinosauria) from the Upper Jurassic Qigu Formation of the southern Junggar Basin, NW China

Two small theropod teeth from the Qigu Formation of Liuhuanggou, Xinjiang Uygur Autonomous Region, People's Republic of China are described. They are compared to hitherto known finds of theropod teeth from both the northern and southern Junggar Basin. It is concluded that they cannot be confidently referred to any morphotype hitherto known from the Upper Jurassic of the Junggar Basin. Although the teeth agree well in principal measurements with material previously described and referred to basal tetanurans or basal tyrannosauroids (morphotype 4 of Han et al. 2011), they are both considerably smaller and show the distinctive feature of a lingually displaced mesial carina. The latter feature is shared with Dromaeosaurus albertensis and an unnamed dromaeosaur from the Lower Cretaceous of Spain and Denmark. It is therefore concluded that the material possibly represents a dromaeosaurid close to these taxa. It is the first record of putative dromaeosaurid theropods from the southern Junggar Basin. As dromaeosaurids have been previously announced from the Upper Jurassic of the northern Junggar Basin, this further underlines general similarity in the Upper Jurassic dinosaurian faunas between these areas.

Reconstruction on regional paleo-drainage evolution in the northern Junggar Basin, China during the last ~27 myr from provenance analyses and its implications for uplift of the Altai Mountains

Tectonic activity and climate change are regarded as two important driving forces on the evolution of large-scale drainage. The evolution of the Irtysh River and Ulungu River, two large-scale drainage systems in the northern Junggar Basin, can provide a key constraint on the uplift of the Altai Mountains and Central Asian aridification. However, we know little about the evolution of these two large-scale rivers. This study presents new detrital zircon U–Pb data from the late Oligocene to late Miocene sedimentary sequences and modern river sediments to reconstruct Cenozoic paleo-drainage evolution in the northern Junggar Basin. The detrital zircon U–Pb results show a single major population at 460-360 Ma, which is mainly derived from the Altai Mountains, for late Oligocene and early Miocene sequences, but two populations at 460-360 Ma and 340-200 Ma, which are mainly from the Altai Mountains and East Junggar terrane, for middle and late Miocene sequences. Our provenance study argues that the Irtysh River and Ulungu River in their modern extent did not exist prior ~18 Ma when the Altai Mountains allowed southward-flowing rivers to transport sediments into the inner Junggar Basin directly. The provenance shift in northern Junggar Basin at 17–18 Ma represents the progressive drainage expansion of the Ulungu River, evolving from relatively small rivers confined to the eastern Junggar Basin to a near-modern large-scale drainage system, due to the rapid uplift in the East Junggar terrane and eastern Altai Mountains in early Miocene. After ~6 Ma, the Irtysh River experienced a progressive drainage expansion, captured the southward-flowing tributaries of the Ulungu River and formed modern drainage pattern. Our study supports the initiation of exhumation before late Oligocene and a local tectonic uplift in early Miocene in Altai Mountains, which imply a complex deformation process in the Central Asia.

The study of Yanshanian unconformity tectonic events in Northern Junggar Basin

Based on the background of Yanshanian tectonic activity in the northern Junggar basin, the temporal and spatial distribution characteristics of Yanshanian unconformity events in the northern Junggar basin are systematically studied through interpretation and comparison of outcrop profiles and seismic profiles. The study shows that Yanshanian stratigraphic unconformity in the northern part of Junggar Basin mainly manifests in the angle unconformity between Xishanyao formation and Toutunhe formation, Toutunhe formation and Tugulu group, which indicates that the study area mainly experienced three important periods of unconformity: the end of Xishanyao formation in middle Jurassic, the end of Toutunhe formation and the end of Tugulu group in early Cretaceous. From the analysis of the unconformity structure and its regional distribution characteristics, it can be concluded that the most prominent Yanshanian tectonic unconformity events occurred mainly in the late Jurassic and showed the unconformity distribution characteristics of the weak compression fold deformation under the background of strike-slip uplift.

Geochemistry, Petrology, and U–Pb dating of high‐K volcanic rocks in wells WC‐1 and Y‐2 from the northern Junggar Basin, northwestern China: Implications for the closure of the Keramaili oceanic basin during the Carboniferous

Carboniferous volcanic rocks are widely distributed in the Junggar Basin and may provide a unique insight into the tectonic history of this basin. In this paper, we focus on the tectonic evolution of the northern Junggar Basin (NJB) using geochronological and geochemical data to establish the diachronous closure model for the Keramaili oceanic basin. The Lower Carboniferous strata in the eastern part (well WC‐1) and the Upper Carboniferous strata in the western part (well Y‐2) of the NJB are composed of a mix of compositional and rock‐type forms. These volcanic rocks are mostly high‐K assemblages characterized by high K (1.73–6.48%), high alkali (Na2O + K2O = 5.04–7.45%), and low TiO2 (0.57–1.06%). They also exhibit various REE concentrations (68.44–168.19 ppm), an enrichment of LREE (LaN/YbN = 4.54–8.09), and small negative Eu anomalies (δEu = 0.74–0.90). The depletion of HFSE and relevant tectonic setting discrimination diagrams demonstrate that these two volcanic associations were formed in a subduction‐related environment. The data also indicate that the high‐K volcanic rocks are derived from a mix of melted subducted sediments and mantle metasomatized by silica‐rich fluids. Although these two sets of volcanic rocks formed in Early and Late Carboniferous, the similar petrographic and geochemical natures suggest similar magma source and tectonic setting. Along with different regional tectonic settings in the NJB during the Carboniferous, we propose an asynchronous subduction of Keramaili oceanic basin, resulting in the inconsistent temporal and spatial distribution of Upper Carboniferous volcanic rocks in the NJB.

A de-flat roundness method for particle shape quantitative characterization

Roundness is a simple but important shape characteristic. It can preserve a record of clasts wearing and deposit reworking. One of the previous methods was called percentage roundness, which could be known as the ratio of the particle’s area that holds to the area of a circle with the same perimeter Cox (J Paleontol 1(3):179–183, 1927). However, it is more likely expressed the degree of circularity rather than rounding due to the limit by its formula. In this paper, a new idea is proposed by modifying the percentage roundness in order to be associated with rounding more appropriately, which is called the de-flat roundness method. The method uses a de-flat algorithm based on image morphing, which is further designed to a software. The software provides the calculation of both percentage roundness and de-flat roundness. It also features other parameters like the area and perimeter of the measured one. To demonstrate its effectiveness, 81 sample grains of Krumbein’s roundness grade (J Geol 49(5):482–520, 1941) were measured. The correlation coefficient of de-flat roundness is 0.7183, with a 0.3416 increase than that of percentage roundness. An application of de-flat to intermittent and ephemeral braided paleochannel deposit in a Late Triassic fluvial fan from northern Junggar Basin, China, was conducted. Results show that two types of palaeoenvironment can be quantitatively distinguished by de-flat roundness, and the values match well with human perception. Therefore, de-flat method can be an effective idea in terms of roundness measurement for either geology or other research fields related to particle morphology.

准北哈山地区二叠系风城组云质岩储层特征及成因分析

准北哈山地区二叠系风城组云质岩储层特征及成因分析

Application of Gravel Roundness Quantitative Description in Conglomerates Reservoirs

In this paper, we focus on the quantitative roundness characteristics of drilling cores in conglomerates reservoir from the Triassic Baikouquan Formation in the Circum–Mahu Sag, northern Junggar Basin, Xinjiang Province in Northwestern China. Based on de–flat roundness measuring method, we try to use quantitative roundness analysis to distinguish different sedimentary microfacies of core images. As a result, two types of channels deposits gathering coarse-grained sediments are exampled. It reveals that ephemeral channels get a higher roundness value by 0.436–0.811, dominated by sub-rounded shape. Intermittent channels get a smaller roundness value by 0.387–0.678. Meanwhile, roundness variation of gravel in intermittent channel is lower than that of ephemeral channel. There’s good gravel roundness and diversified roundness type in the braided channel deposition developed in fan delta plain. The reason of worse roundness in intermittent channels might be the mix of hard-to-wear source rock gravels after in-lake.

A comparative study of free and bound bitumens from different mature source rocks with Type III kerogens

The complicated macromolecular structure of kerogen has made it difficult to extract chemical information on bound molecules. The hydropyrolysis (Hypy) technique, which can release considerable amounts of hydrocarbons from kerogen via the mild cleavage method, provides an opportunity to solve this problem. In this study, Type III kerogens with varying degrees of maturation from Lower Carboniferous source rocks in the northern Junggar Basin, China, were subjected to solvent extractions and Hypy experiments. A quantitative comparison of the amount and composition of free and bound bitumen reveals the precise cleavage process of bound molecules from kerogen. As maturation increases, free and bound aliphatic molecules, including biomarkers, decrease markedly as a consequence of continuous cracking and degradation. However, the bound 3-benzene ring compounds are initially enriched and then depleted, consistent with the evolution of the aromatic structure of kerogen. In the early-mature and mature stages, bound bitumen could be a reliable pool of biomarkers, and undoubtedly the bound biomarkers preserve more information about biological inputs. Moreover, due to the protection of the macromolecular structure of kerogen against extreme thermal stress, a few informative biomarkers, especially aliphatic moieties, can be released by Hypy from high-mature kerogens. The rearranged hopane Ts and diasteranes may be present in bound bitumen due to the incorporation of related molecules into the kerogen, possibly during the formation of kerogen. In contrast, C30 rearranged hopane (C30∗) only occurs in free bitumen due to the catalysis by acidic clays during the mature stage. Side chain and ring isomerization of free and bound hopanes and steranes occurring during maturation is more complicated. For example, the configuration changes from R-dominant, to equilibrium R and S configurations, and then to R configuration dominance again. These changes may be controlled by the generation and degradation processes affecting these compounds. However, most aromatic maturity parameters of the bound fractions increase with maturity (i.e. with increasing %Ro). As documented in the literature, kerogen severely suppresses the chiral isomerization of bound aliphatics, but our results show that it does not retard methyl transfer reactions in aromatic rings.

A new tyrannosaurine specimen (Theropoda: Tyrannosauroidea) with insect borings from the Upper Cretaceous Honglishan Formation of Northwestern China

A large theropod ilium was recently collected from the Upper Cretaceous Honglishan Formation in the Sangequan area of the northern Junggar Basin, Xinjiang, China, which represents the first officially reported dinosaur fossil from this formation. Several morphological features, including robust supracetabular ridge, reduced supracetabular crest, concave anterior margin of the pubic peduncle, ventral flange on the pubic peduncle, converging dorsal surface of the iliac blades, laterally visible cuppedicus shelf, and ventral flange on the posterior surface of pubic peduncle, suggest that this specimen can be referred to Tyrannosaurinae, and furthermore, a few differences between this specimen and other tyrannosaurines in particular the contemporary Asian tyrannosaurine Tarbosaurus suggest that IVPP V22757 may represent a new tyrannosaurine species. However, in the absence of extensive data that would make it possible to properly evaluate these differences, we refrain from naming a new taxon based on this specimen. Some insect borings are also identified in this specimen, and are referable to the ichnogenus Cubiculum, which is interpreted as the insect pupichnia. This new fossil documents the presence of a gigantic theropod in the Upper Cretaceous of Junggar Basin, adding new information on its poorly studied ecosystems.

The basement property and evolution of the northern Junggar basin—evidence from zircon U–Pb chronology and trace element

Junggar basin is an important part of the Central Asian Orogenic Belt (CAOB) which is also one of the key areas of researches about formation and evolution of the CAOB. Recently, a question of whether the Junggar basin has a Precambrian basement is one of the hottest topics. We undertook LA-ICP-MS zircon U–Pb dating from Carboniferous pyroclastic rocks and Mesozoic sedimentary rocks in northern Xinjiang Province, NW China, with the aim of constraining the evolution and features of the basement of the north Junggar basin and adjacent areas. (1) The zircon U–Pb age analysis of the Carboniferous pyroclastic rock samples clustered in the 1447∼1410 Ma and 885∼559 Ma showed that the basement of the north Junggar basin was continental crust that formed 1.4 Ga ago. The zircon U–Pb ages clustered in the 536∼420 Ma, 401∼360 Ma, and 359∼303 Ma indicated a multiple evolution of basement. (2) The zircon trace element analysis of different age groups from the Carboniferous pyroclastic rock samples showed that the basement of the north Junggar basin was continental crust composed of acid rocks and intermediate-basic intrusive rocks, which were mainly the granitoids, syenite, basalt, dolerite, and larvikite. (3) The zircon U–Pb ages and trace element analysis of the Mesozoic sedimentary rock samples clustered in the 3022∼2102 Ma, 1747∼1202 Ma, 996∼915 Ma, 885∼544 Ma, 539∼420 Ma, 419∼356 Ma, and 354∼300 Ma revealed that not only 3.0-Ga continental crust existed in the north Junggar basin and adjacent areas but also multiple crustal material evolution that occurred during the formation of the basement. (4) The evolution of sedimentary cover experienced 299∼250 Ma, 210∼176 Ma, 175∼148 Ma, and 147∼132 Ma with the corresponding peak age of ca. 290, 180, 163, and 140 Ma, respectively, indicated that the sedimentary cover of the northern Junggar basin experienced a complex tectonic evolution from Permian.

Phylogeography of the arid shrub Atraphaxis frutescens (Polygonaceae) in northwestern China: evidence from cpDNA sequences.

Climatic fluctuations during the Pleistocene are usually considered as a significant factor in shaping intraspecific genetic variation and influencing demographic histories. To well-understand these processes in desert northwest China, we selected arid adapted Atraphaxis frutescens as the study species. Two cpDNA regions (psbK-psbI, psbB-psbH) were sequenced in 272 individuals from 33 natural populations across the range of this shrub, and 10 haplotypes were identified. It was found to contain high levels of total gene diversity (H T = 0.858), and low levels of within-population diversity (H S = 0.092). Analysis of molecular variance (AMOVA) indicates that genetic differentiation primarily occurs among groups of populations. Based on BEAST (Bayesian Evolutionary Analysis Sampling Trees) analysis, we suggest that intraspecific differentiation of the species, resulting from isolated populations, accompanied enhanced desertification during the middle and late Pleistocene. The expansion of the Gurbantunggut and Kumtag deserts in this area appears to have triggered divergence among populations of the western, central, and eastern portions of the region and shaped genetic differentiation among them. Two possible independent glacial refugia were predicted, the Ili Valley and the northern Junggar Basin. Extensive development of arid habitats (desert margin and arid piedmont grassland) coupled with a more equable climate because the early Holocene are factors likely to have generated recent expansion of A. frutescens.

Large-scale thrusting at the northern Junggar Basin since Cretaceous and its implications for the rejuvenation of the Central Asian Orogenic Belt

The Wulungu Depression is the northernmost first-order tectonic unit in the Junggar Basin. It can be divided into three sub-units: the Hongyan step-fault zone, the Suosuoquan sag and the Wulungu south slope. The Cenozoic strata in the basin are intact and Mesozoic–Cenozoic deformation can be observed in the Wulungu step-fault zone, so this is an ideal place to study the Mesozoic–Cenozoic deformation. By integration of fault-related folding theories, regional geology and drilling data, the strata of the Cretaceous–Paleogene systems are divided into small layers which are selected as the subjects of this research. The combination of the developing unconformity with existing growth strata makes it conceivable that faults on the step-fault zone have experienced different degrees of reactivation of movement since the Cretaceous. Evolutionary analyses of the small layers using 2D-Move software showed certain differences in the reactivation of different segments of the Wulungu Depression such as the timing of reactivation of thrusting, for which the reactivity time of the eastern segment was late compared with those of the western and middle segments. In addition the resurrection strength was similarly slightly different, with the shortening rate being higher in the western segment than in the other segments. Moreover, the thrust fault mechanism is basement-involved combined with triangle shear fold, for which a forward evolution model was proposed.

A New Genus of Aplodontid Rodent (Mammalia, Rodentia) from the Late Oligocene of Northern Junggar Basin, China

A new genus and species of aplodontid rodent, Proansomys dureensis, from the late Oligocene of the northern Junggar Basin of China is described. The new genus is referred to as Ansomyinae because the ectoloph on the upper cheek teeth, although not fully crested, has attained the same characteristic bucket-handle-shaped configuration as other members of the subfamily. It represents the earliest record of the subfamily yet discovered in Asia and is more plesiomorphic than species of the genus Ansomys in having a partly crested ectoloph, a lower degree of lophodonty, and less complex tooth basins (lacking accessory lophules). Proansomys has transitional features between Prosciurus and Ansomys, suggesting that the Ansomyinae derived from a group of aplodontids related to Prosciurus, as did other advanced aplodontid rodents. This provides new light on the paleobiogeography of the Ansomyinae.

Late Cenozoic tectonic activity and its significance in the Northern Junggar Basin, Northwestern China

The Dingshan area located in the northern part of the Junggar Basin of northwestern China is a significant prospect area for sandstone-type uranium deposits in China, where mainly Cenozoic rocks were deposited. The Cenozoic strata can be divided into four units according to the prior data and our own field observation. Sedimentary studies indicate that most Cenozoic strata were deposited under a hot and arid climate in a continental environment. The sedimentary facies are alluvial-fan, meandering-fluvial, and fluvio-lacustrine. Field investigation and interpretation of satellite images suggest that Cenozoic tectonics in the area is characterized by reactivation of early deep-seated thrusts, resulting in extensional fractures and formation of many small depressions in the shallow crustal level. Measurement of joint orientations suggests that regional shortening direction trends in north–south in the middle Pleistocene as indicated by the ESR (Electronic Spin Resonance) age of 0.1–0.4 Ma obtained from fault gouge and gypsum deposits. A four-stage sedimentation-tectonic evolution model of the northern Junggar Basin during the Late Cenozoic can be established based on reconstruction of sedimentary filling processes and Cenozoic tectonic movements. We suggest that landform evolution and groundwater movement are controlled by active tectonics, indicating that Late Cenozoic tectonic activities may also play important roles in the formation of sandstone-type uranium deposits. Therefore, a new metallogenic model for sandstone-type uranium deposits is proposed.