Abstract: The black shale samples from the Niutitang Formation in the Yangtze Block were sequentially treated using organic solvent extraction and wet chemical oxidation. The organic matter (OM) in the shales includes physically mobile OM (PmOM), chemically mobile OM (CmOM), and stable OM (StOM). The CmOM has the strongest CH4 adsorption capacity because it has the largest volume of micropores and mesopores. In contrast, the PmOM has a very negative effect on the CH4 adsorption because it is poreless. The XD shale is a siliceous shale, in which the quartz particles wrap partly OM, preventing extraction and oxidation. The SL shale is an argillaceous shale, in which most of the OM is combined with clay minerals to form organo-clay composites. In both the SL and XD shales, the OM that is extractable via organic solvents is distributed among the mineral particles and is interconnected. The conceptual model of marine black shale in different environments needs to be perfected in the future because quantitative and qualitative methods should be combined to clarify the relationship between the known OM types (e.g., pyrobitumen, solid bitumen, and solid kerogen) and the OM types identified in this study.
Abstract: Population growth and expanding urbanization have caused persistent shortages and contamination of groundwater resources in Mali, Africa. The increase in groundwater salinity makes it more difficult for residents to obtain drinking water, it is necessary to clarify the causes and control factors of groundwater mineralization in Gao region, northern Mali. Based on the analysis of the hydrochemical composition of groundwater in 24 boreholes, Piper and Schöeller diagrams, principal component analysis (PCA) and hierarchical cluster analysis (HCA) are used to carry out multivariate statistical analysis on the main ions. The results show that the groundwater samples are weakly alkaline, with pH values ranging from 5.83 to 8.40, and the average values of boreholes are 7.50, respectively. The average electrical conductivity (EC) value is 354.4 (µS/cm), and the extreme value is between 124.0 and 1247 (µS/cm). Water is usually mineralized and presents nine types of water phase. The three principal components explain 84.42% of the total variance for 13 parameters. The factor F1 (58.85%), the factor F2 (16.88%) and the factor F3 (8.69%) present for the majority of the total data set. In addition, multivariate statistical analysis confirmed the genetic relationship among aquifers and identified three main clusters. Clustering related to groundwater mineralization (F1), clustering related to oxide reduction and iron enrichment (F2), and clustering of groundwater pollution caused by nitrate and magnesium (F3). We found that agriculture, weathering activities and dissolution of geological materials promote the mineralization of groundwater. Groundwater quality in the Gao region is becoming less and less potable because of increasing salinity.
Abstract: Mineralogical data are presented for the peridotite xenoliths from Miocene (~19Ma) Qingyuan basalts in the eastern North China Craton (NCC), with the aim of constraining on property of the sub-continental lithospheric mantle (SCLM) beneath the northern Tan-Lu Fault zone (TLFZ) during the Cenozoic. The Qingyuan peridotites are dominated by spinel lherzolites with moderate-Mg# olivines (89.4 to 91.2), suggesting that the regional SCLM is mainly transitional and fertile. Light rare earth element (LREE)-depleted, slightly depleted and enriched clinopyroxenes (Cpx) are identified in different peridotites. Chemical compositions of the LREE-enriched Cpx and the presence of phlogopite suggest that the Qingyuan SCLM has experienced silicate-related metasomatism. The synthesis of available mineral chemical data of the mantle xenoliths across the NCC confirms the SCLM beneath the NCC is highly heterogeneous in time and space. The Mesozoic-Cenozoic SCLM beneath the TLFZ and neighboring regions are more fertile and thinner than that beneath the region away from the fault zone. The fertile and refractory peridotite xenoliths experienced varying degrees of silicate and carbonatite metasomatism, respectively. The spatial-temporal lithospheric mantle heterogeneity in composition, age and thickness suggest that the trans-lithosphere fault zone played an important role in heterogeneous replacement of refractory cratonic lithospheric mantle.
Abstract: In order to decipher element mobility in UHP meta-sedimentary rocks in the continental subduction zone, major and trace element compositions are investigated for a continuous profile from a representative UHP region in the Dabie Mountains. Among the lithologic contact zone, contents of K, Ca, LREE, and LILE exhibit varying degrees of downward trends in both marble and eclogite toward the contact zone, indicating that marble and their associated eclogite can release a large amount of K, Ca, and a small amount of LILEs and LREEs. Titanite is the main Ti phase in both marble and eclogite. Titanite rims around rutile can occasionally be seen in eclogite. Contents of Ti and HFSE exhibit a well-coupled relation among marble and eclogite, indicating that substantial Ti and HFSEs were migrated from eclogite to marble, in accord with the capacity of a melt medium. Rutiles and titanites in marble exhibit a relatively limited variation in Nb/Ta ratios (12.9-16.2), similar to those of titanites in eclogite (14.2-16.7), which demonstrates that rutiles and titanites in marble were sourced from eclogite because of short-distance migrations of Ti and HFSEs. According to the P-T path and the temperature and pressure conditions of the peak metamorphism reported by previous studies, the eclogite associated with marble may not form supercritical fluids in the subduction zone because of the addition of carbonate minerals.
Abstract: The groundwater (GW) in the floodplain riparian area frequently interacts intensely with surface water (SW). Heat as a tracer is one of the hot research fields in investigating GW-SW interactions, and analytical approaches have been proposed for the calculation of exchange flow velocity. However, few studies have considered the effects of very dynamic flow conditions and monitoring instrumentation on the calculation with field measured data. Herein, taking the middle reaches of the Heihe River as the study area, different types of monitoring wells were constructed under the riverbed and near the river, and multiple methods (Darcy’s law, heat tracing, and isotopic mixing methods) were employed to trace the exchanges between the river and groundwater. The results indicate that different methods demonstrate diverse information with obvious unevenly distributed flux along the vertical direction. And the combination of multiple methods has an important role in studying the interaction between GW and SW. Fully screened wells produce intraborehole flow and disturb the heat transport, which is relevant to flow velocity, and further affects the temperature distribution, impacting the temperature-based flow velocity calculation. Dynamic flow conditions aggravate riverbed sediment disturbances, e.g., scour and deposition, and additionally affect the interaction and monitoring data.
Abstract: Fluid–rock interaction plays a critical function in physical and chemical processes associated with the formation and evolution of oil and gas reservoir space. In the diagenetic stage of shallow burial, the dissolution of carbonate rocks by acidic fluids is conducive to the development of secondary pore space in reservoirs. In contrast, the free drift experiment based on water bath instrument can simulate the dissolution process of carbonate rocks in shallow burial environment effectively. In order to study the shallow burial dissolution mechanism of carbonate rocks in different acid solutions, 14 samples of typical carbonate rocks of Sinian, Cambrian, Ordovician, Permian and Triassic ages in the Tarim and Sichuan Basins, China were used. The dissolution experiments on carbonate rocks in sulfuric acid, acetic acid, hydrochloric acid, silicic acid and carbonic acid at shallow burial temperature (30℃≤T≤90℃) were carried out using a water bath instrument. The PHREEQC software was used to simulate the dissolution of carbonate minerals, in order to compare the results of constant temperature water bath experiment. The results show that acid solutions have significant dissolution effect on shallow burial carbonate rocks when T = 50–60℃, which corresponds to the burial depth of 1500–2000 m in the Tarim Basin and 1110–1480 m in the Sichuan Basin. However, there were obvious differences in the dissolution and reformation of carbonate rocks in different acids. In particular, sulfuric acid solution produced by thermochemical sulfate reduction can significantly promote the dissolution of carbonate rocks, especially dolomitic limestone. Moreover, the dissolution of limestone reservoirs is stronger than that of dolomite reservoirs in shallow burial. The results will provide new insights into the study of dissolution laws and influencing factors of carbonate reservoir space and the evaluation and prediction of carbonate reservoir in China.
Abstract: Zircon U–Pb ages, major and trace elements and Sr–Nd–Hf isotope data of the diabase in the Zhangjiakou district were studied to investigate its derivation and tectonic implications. Zircon U–Pb ages indicate that the diabase was emplaced at ~130 Ma or younger, and captured zircons cluster at ~147 Ma, ~240 Ma, ~430 Ma and ~465 Ma. The diabase is characterized by minor variations in SiO2 (49.35–52.10 wt.%), TiO2 (1.65–1.77 wt.%), Al2O3 (17.00–18.26 wt.%), MgO (4.28–4.93 wt.%), CaO (6.69–7.90 wt.%) and Mg# (48–54). It has no significant Eu anomaly and displays enrichment in large ion lithophile elements (Rb, Ba and Sr) and depletion in high field strength elements (Nb, Ta, P and Ti). The diabase exhibits homogeneous Sr ((87Sr/86Sr)i = 0.70606–0.70701) and Nd (εNd(t) =–13.6 to –13.2) isotopic compositions. These features suggest that the parental magma was derived from partial melting of the ancient lower crust, relating to mantle upwelling that triggered by stagnant slabs or lithospheric detachment associated with the westward subduction of the Paleo-Pacific Plate. The Early Paleozoic inherited igneous zircons in the diabase suggest that the northern margin of the North China Craton (NCC) likely underwent southward subduction of the Paleo-Asian Ocean.
Abstract: The connectivity of shale pores and the occurrence of movable oil in shales have long been a focus of research. In this paper, samples from Wells BX7 and BYY2 in the Eq34-10 cyclothem of Qianjiang Formation in the Qianjiang Depression, were analyzed. A double mercury injection method was used to distinguish between invalid and effective connected pores. The pore characteristics for occurrence of retained hydrocarbons and movable shale oil were distinguished based on comparison of pore changes in low temperature nitrogen adsorption and high pressure mercury injection experiments before and after extraction and the change in the mercury injection amounts in the pores between two separate mercury injections.. The results show that less than 50% of the total connected pores in the Eq34-10 cyclothem samples are effective. The development of effective connected pores affects the mobility of shale oil but varies with different lithofacies. The main factor limiting shale oil mobility in Well BX7 is the presence of pores with throat sizes less than 15nm. In Well BYY2, residual mercury in injection testing of lamellar dolomitic mudstone facies was mainly concentrated in pores with throats of 10~200 nm, and in bulk argillaceous dolomite facies it was mainly concentrated at 60~300nm. The throats of hydrocarbon-retaining pores can be 5nm or even smaller, but pores with movable shale oil in the well were found to have have throat sizes greater than 40nm. Excluding the influence of differences in wettability, the moveability of shale oil is mainly affected by differences in lithofacies, the degree of pore deformation caused by diagenesis, the complexity of pore structures, and the connectivity of pore throats. Dissolution and reprecipitation of halite also inhibit the mobility of shale oil.
Abstract: In-situ fluid phase behavior is important in determining hydrocarbon contents and the multiphase flow through shale reservoirs. The gas-to-oil ratio (GOR) has been recognized as the critical indicators of fluid types. However, little is known about the impact of fluid phase variation across the thermal maturity on shale oil/gas production (e.g., estimated ultimate recovery, EUR). According to the specific gravity ratio of oil/gas, the producing GOR was converted and normalized into a mass fraction of gas in total hydrocarbons (MGOR) to compare North American shale oil/gas plays with Chinese shale oil and hybrid gas-condensate plays. A correlation between MGOR, the fluid phases and production data was established to identify five phase stages of flow. MGOR varies systematically with the different production zones, which shows promise in rapidly indicating the well production performance and high-production stages of shale oil/gas plays. The hybrid shale gas-condensate index, Tmax, total gas contents were integrated to present the fluid types and maturity of shale gas-condensates, which indicates fluid phase and production variation across thermal evolution. The results offer a unique perspective on the shale oil reservoir producibility based on the impact of GOR on fluid phases and EUR from the global dominant oil/gas plays.
Abstract: Abstract: Most knowledge about the Cretaceous-Paleogene strata in the Tarim Basin is mainly inferred from the outcrops at the basin’s margin，but first time in the basin. The formation mechanism of the Paleocene basal conglomerate was determined using geochemical isotopes of the breccia from well PBX1 in the southwestern Tarim Basin. The results showed that the global K/Pg (i.e., Cretaceous/Paleogene) clay layer boundary was located in the middle of the Paleocene basal conglomerate at the depth of 7066.75m in well PBX1. In the Late Cretaceous, associated with volcanic activities and earthquakes, the caldera in the PBX1 well block formed an annular depression with large elevation differences in response to the Pamir block collision. As a result, the collapsed breccia with storm tide genesis deposited at the periphery and inside of the depression, characterized by syn-sedimentary deformation. During the Paleocene, multiple sets of interbedded carbonate and collapsed breccia deposited in response to multi-phased transient transgression-regression cycles. The transportation of breccia exhibited near-source accumulation/extremely close or in-situ rapid accumulation. The studied region is located in the eastern end of the Tethys Sea, the Late Cretaceous-Early Paleocene breccia is of great significance for reconstructing the paleogeography of the Tarim basin in Tethys.
Key words: South-western Tarim；Paleogene system；Breccia；Attribution and genesis
Abstract: It has long been recognized that garnet has the capacity to preserve the trace element and isotopic signature of distinct metamorphic growth zones because of its high closure temperature. Combined with the large size of certain garnet porphyroblast, this allows investigating variations in metamorphic conditions such as pressure, temperature, deviatoric stress, and fluid composition, which occur during subduction-related metamorphism. Here, one garnet porphyroblast of 6 cm diameter was sampled from the Yardoi schists of Tibet, and the major-, trace-, and Li-Mg isotopic compositions of distinct growth zones were determined in situ. The δ7Li values range from +6.0 ‰ to +4.1 ‰ and follow ‘S-shape’ patterns on both sides of the garnet’s core, revealing a two-stage growth process corresponding to the fluid-assisted sequential recrystallization of chlorite and micas during prograde metamorphism. By contrast, once corrected for the overprinting by retrograde metamorphism, the δ26Mg values vary monotonously from -1.73 ‰ in the core to -1.32 ‰ in the outer rim, reflecting a single-step process interpreted to result from increasing temperature and the solid-state recrystallization of chlorite-biotite during prograde metamorphism. This different behavior of Li and Mg isotopes is interpreted to result from the fact that Li is more fluid-mobile than the major element Mg.
Abstract: Iron pyrite has been reported as a kind of potential material for arsenic (As) removal from the groundwater because it exhibits a strong attraction in groundwater for both arsenite and arsenate species. In this study, batch adsorption experiments were carried out to determine the optimum conditions for As adsorption by the iron pyrite adsorbent, including the initial concentration, adsorbent dosage ratio, pH, temperature and stirring rate. Precisely characterization methods were employed to identify the mechanism of As removal. Maximum removal efficiency for As(III) was observed 93% at pH=7, and for As(V) was 95% observed at pH=5. Langmuir model resulted in the maximum adsorption capacity (qm) for As(III) and As(V) were 571.7 μg/g and 671.1 μg/g respectively, as well as the experiments were found to be favorable as separation factor RL < 1. The value of "n" 2.68 and 2.47 for As(III) and As(V) obtained by Freundlich model (n > 1) indicates favorable adsorption. The pseudo-first and second-order kinetic models also fitted well. The addition of oxalate on the adsorbent surface plays an important role for the recycling of Fe(II)/Fe(III) to minimize the arsenic concentration. Specific surface area, ion exchange mechanism and structure of adsorbent confirmed that addition of oxalate could enhance the surface area of adsorbent.
Abstract: During the late Paleozoic–early Mesozoic era, the sediment transport system and tectonic regime in the southeastern margin of the South China Block (SESCB) all changed, significantly affected by the Paleo-Pacific subduction. This study uses detrital zircon geochronology to discuss the Late Triassic source-to-sink system in the SESCB and provides some references for the Paleo-Pacific subduction process. The paleogeography and similarity of detrital zircon age distribution reveal three sinks in the SESCB during the Late Triassic: 1. the Yangchun–Kaiping–Gaoming area, comprising major age ranges of 260–220, 460–400, and 1,200–800 Ma, which might be sourced from the Yunkai Terrane; 2. the Jiexi–Kanshi–Nanjing area, characterized by the significant age component of 2,000–1,800 Ma, which corresponded to the Wuyi Terrane; 3. the Xinan area, consisting of significant age groups of 290–250 Ma and 380–320 Ma, which might be sourced from the magmatic rocks formed by the Huinan Movement and Paleo-Pacific subduction. The Upper Triassic strata contain many 290–250 Ma zircons, and their trace elements suggested a magmatic arc existed near the SESCB during the 290–250 Ma. Thus, we propose that the Paleo-Pacific subduction might have begun in the Early Permian.
Abstract: The large-scale implementation of the Gully Stabilization and Land Reclamation (GSLR) project induces various failures of loess slopes due to excavation in Yan'an, China. However, the deformation and failure behavior of these excavated loess slopes have not been fully understood. In this study, field investigation was undertaken for analyzing the distributions and failure features of excavation-induced loess slope failures. It is found that plastic failure mainly occurs in Q3 loess layers and brittle failure in Q2. To understand the underlying failure mechanism, a series of triaxial shear tests were conducted on intact Q3 and Q2 loess samples that with different water contents, namely natural water content (natural), dry side of the natural value (drying 5%), and wet side (wetting 5%). The characteristics of stress-strain curves and failure modes of the samples were analyzed. Results show that the stress-strain curves of Q2 samples are dominated by strain-softening characteristics, while Q3 samples mainly exhibit strain-harden features except in the drying state. Correspondingly, shear failures of Q3 specimens are mainly caused by shear crack planes (single, X or V-shaped). For Q2 loess, the dominance of tensile cracks is observed on the surface of damaged specimens. These disclose the different failure modes of excavated slopes located in different strata, that is, the arc sliding failure of Q3 loess slopes and the stepped tensile failure of Q2 loess slopes, and are helpful in the design and management of the ongoing GSLR projects in the Loess Plateau.
Abstract: The Wutonggou iron deposit is located in the well-known iron metallogenic belt in the eastern Tianshan, NW China, and has been regarded as a sedimentary iron deposit. Hydrothermal overprinting could play indispensable roles in the formation of high-grade iron ores in sedimentary iron deposits, thus the nature and evolution of hydrothermal fluids have important implications on the genesis of these deposits. Consequently, an integrated study of ore geology, H–O–C isotopes and 40Ar–39Ar dating, is conducted on the Wutonggou deposit, in order to reveal the features, source, and timing of hydrothermal mineralization. The studied deposit includes two mining sections namely the Jianshan and Wutonggou. The δ18O values of early magnetite from the Jianshan section range from +3.0‰ to +5.8‰ that nearly consistent with classic magmatic magnetite, while increase to 6.3‰–8.0‰ in the late stage. Quartz from the two sections shows comparable H–O isotopic compositions and identical fractionation trends, and is plotted in or periphery to the primary magmatic water area. Calcites from the two sections are broadly similar in carbon and oxygen isotopic compositions, and siderite from the Wutonggou section is plotted in the same region. Thus, comparable stable isotopic compositions and evolution trends indicate similar magmatic fluids contributed hydrothermal iron mineralization in the two mining sections. Moreover, water-rock interactions of varying degrees generated distinct mineralization styles in the Jianshan and Wutonggou sections, and caused the isotopic fractionation in late stages. Biotite extracted from a hydrothermal siderite ore yielded a 40Ar–39Ar plateau age of 299.5 ± 2.0 Ma, indicating the timing of hydrothermal iron mineralization is corresponding to the emplacement of vicinity granitoids. Taken together, the hydrothermal mineralization in the Wutonggou iron deposit was the product of remobilization and upgrading of early sedimentary iron ores, and ore-forming fluids were most probably originated from regional granitic magmatism.
Abstract: Since the 1950’s, 212 earth fissures have been discovered in the Wei River Basin. During a field survey in 2016, an additional 48 earth fissures were discovered in Anren area, northeast of the Wei River Basin. The characteristics and formation mechanisms of these fissures were studied through field investigations, measurements, trench excavation, and drilling. On-site investigations indicated that these earth fissures were distributed along a fault-controlled geomorphic boundary. Fissures trended at 60°–80° NE and were divided into five groups. Trenches revealed multiple secondary fissures, exposing severe soil ruptures in the shallow earth surfaces. Drilling profiles revealed that earth fissures dislocated several strata, and resembled synsedimentary faults. Seismic reflection profiles revealed buried faults beneath the earth fissures. The Anren area fissures formed in the following three stages: regional extension that initially generated multiple buried faults; seismic activity rupturing multiple strata, resulting in multiple buried fractures; and finally, erosion processes that propagated the buried fractures to the surface, forming the current earth fissures.
Abstract: The Xing’an–Inner Mongolia Orogen is a critical tectonic unit for constraining the evolution of the Paleo-Asian Ocean. However, the location and time for the closure of the Paleo-Asian Ocean are still debated. Here, we select a representative basin in Dashizhai in northeastern China, using U-Pb zircon geochronology and geochemistry to analyze the sedimentary facies, depositional ages, and provenance. The results show that the age of the Dashizhai Formation range from 400 to 347 Ma, the Shoushangou Formation range from 400 to 348 Ma, the Zhesi Formation range from 307 to 252 Ma, and the Linxi Formation range from 299 to 241 Ma. The Dashizhai Formation is composed of metamorphic andesite and clastic rocks. The Shoushangou Formation comprises siltstone, rhyolite, and argillaceous siltstone. The Zhesi and Linxi Formations are composed of mudstone and argillaceous siltstone. Geochemical data shows that these rocks are enriched in light rare earth elements and depleted in Eu with various La/Sc, Th/Sc, and La/Co ratios. The Permian Dashizhai Basin is from Permian volcanic and felsic igneous rocks from the Ergun, Xing’an, and Songliao blocks. The absence of the Late Carboniferous strata in the Dashizhai Basin indicates an extension setting during this period. Furthermore, we suggest the Xing’an–Inner Mongolia Orogen was an uplifting process associated with evolution the Paleo-Asian Ocean during the Late Permian.
Abstract: Chen Lake has been seriously modified by reclamation to expand the residential and agricultural area. Lake reclamation can decrease water quantity, cause water quality problems, and degrade water ecological function. To clarify the interaction between groundwater and lake water influenced by reclamation, water level and hydrochemical characteristics of five groundwater nests and three lake sites were monitored. Results emphasize that the seasonal fluctuations of lake water level is an important factor for both recharge and maintaining groundwater levels in study area. Groundwater in reclaimed farmland have seasonal patterns following lake water with a lag time. Noteworthy, the lag time of porewater in reclaimed farmland is one month longer than confined water. HCA showed that lake water and groundwater samples in same cluster were characterized by high δD, δ18O, Cl- and K+, suggesting the provision of lake to groundwater systems and the transfer of chemical signature. Other Cluster was dominated by reclaimed farmland groundwater samples and enriched in Ca2+, HCO3-, Si. This finding interpreting that water-rock interaction is the predominant process in reclaimed farmland. As a result, there is a high degree of connectivity between lake water and underlying groundwater. However, porewater hydrodynamic conditions gradually weaken and groundwater recharge in reclaimed farmland is modified after large-scale reclamation.
Abstract: The unique desertification under alpine climate and ecosystem on Tibetan Plateau could provide critical clues on the natural and anthropogenic impacts on desertification. This study used the Landsat data to investigate the distributions of desertification from 1990 to 2020 in two areas (Shannan and Mainling), within the Yarlung Zangbo River Basin. The results show not only different spatial distributions but also various temporal changes of desertification. In Shannan, aeolian sand is distributed in wide areas from valley floor to mountain slope, while in Mainling, it is distributed sporadically at the footslope. The aeolian sandy land expanded at first, followed by a long-term shrinkage in Shannan. While in Mainling, it steadily expanded and then followed by a fast decrease. These changes are attributed to climate change and anthropogenic factors. The increase in temperature causes desertification expansion in Shannan, while favorable climate along with decreasing human activity promotes desertification reversal. However, both the expansion and shrinkage of desertification are sensitive to human activity in Mainling. This show diverse responses of desertification to natural and anthropogenic impacts on different backgrounds of climatic and vegetation coverage. A threshold of climatic conditions could control the dominant factor in desertification from natural to anthropogenic elements.
Abstract: This paper introduces the use of point cloud processing for extracting 3D rock structure and the 3DEC -related reconstruction of slope failure, based on a case study of the 2019 Pinglu rockfall. The basic processing procedure involves: (1) computing the point normal for HSV-rendering of point cloud; (2) automatically clustering the discontinuity sets; (3) extracting the set-based point clouds; (4) estimating of set-based mean orientation, spacing, and persistence; (5) identifying the block-forming arrays of discontinuity sets for the assessment of stability. The effectiveness of our rock structure processing has been proved by 3D distinct element back analysis. The results show that SfM modelling and rock structure computing provides enormous cost, time and safety incentives in standard engineering practice.
Abstract: In Southwestern China, the development of karst landforms and the planation surfaces is closely related to local tectonics, fluvial incision and base level change, as well as climate change. While researches on when these karst landforms and planation surfaces formed and how they evolved along drainage development are scarce. Fortunately, horizontal caves with numerous fluvial deposits in high karst mountains can be used as time markers in landform evolution. Here we select large horizontal caves to perform studies of geomorphology, sedimentology and geochronology. Field work shows that more than 25 km long horizontal cave passages are perched 1500 m higher than the local base level, but filled with several phases of fluvial sediments and breakdown slabs. The first phase of fluvial gravels and related cave drainage were dated back to 6.4 Ma using cosmogenic nuclide burial dating, and the stalagmite covering the cave collapse was dated by the U-Pb method , older than 1.56 Ma. These results show that the continuous horizontal cave drainage system and the planation surface were developed prior to the Late Miocene. The lowering process of the base level as a result of the sharp fluvial incision and water level lowering, along with the regional uplift, led to the abandonment of the horizontal cave and the elevated planation surface at the Late Miocene . After that, the phase of cave collapse , thick fluvial sand and clay sediments in the caves from the recharge of the cave deposited at around 1.6 Ma and during the Middle Pleistocene, respectively. Subsequently, speleothems widely deposited on the collapse and clay sediment during the period from 600 to 90 ka ,whereas the deposition of cave fluvial sediments terminated suddenly. The tectonic could control the denudation of surface caprock and the development of karst conduits prior to the Late Miocene, whereas the river incision acted as the main driver for the base level lowering and the destruction of the horizontal cave drainage at high altitude. In addition, the rapid incision and the retreat of Silurian gorges finally caused the formation of karst mesa in the Middle Pleistocene.
Abstract: The Cenozoic source-to-sink history of the Qaidam Basin is crucial for understanding of the basin-filling architecture, mountain-building processes and even the dynamics of the Tibetan plateau growth. However, the provenance history of Cenozoic strata in the Qaidam Basin remains ambiguous, especially in the northern Qaidam Basin. This controversy highlights the importance of obtaining the spatial source-to-sink relationships between the Qaidam Basin and its surrounding mountain ranges. In this study, we investigated the detrital zircon U–Pb ages of modern fluvial systems draining the Eastern Kunlun Shan. Their detrital zircon age distributions fall into five age groups: 300-190, 530-360, 1000-560, 2000-1100 and 2650-2000 Ma. The dominant age groups are 530-360 and 300-190 Ma, which represent the successive subduction of the Proto-Tethys and Paleo-Tethys Oceans and the subsequent continental collisions, respectively. Combining these new detrital zircon U–Pb ages with available age datasets, we finally obtained complete detrital zircon age information for modern fluvial systems in the whole Qaidam Basin. The U–Pb age distributions of modern river sands reveal that the zircon age signature of basement rocks in the Eastern Kunlun Shan is significantly different from that in the South Qilian Shan but is similar to that in the Altyn Tagh Shan. Moreover, these zircon age observations were confirmed by the significant difference in the Nd isotopic signature of modern river sands, which reveals a significant difference between the Eastern Kunlun Shan and South Qilian Shan in the formation and evolution process.
Abstract: Many sandstone-type uranium mineralization sites have been identified along the northern margin of the Qaidam Basin in North China. Intense tectonism and multistage magmatism that occurred there have restricted the use of conventional techniques (petrogeochemistry) to deduce the sources of detritus and uranium in these sediments, and to further explore the sandstone-type uranium deposits. In this study, U–Pb geochronological and Hf isotopic analyses were conducted on detrital zircon grains collected from Jurassic to Paleogene sandstones exposed in the Yuqia area of the Qaidam Basin. The results indicated that the U–Pb ages of the analyzed zircon grains are clustered into four periods, 285–229, 498–401, 999–806, and 2520–2305 Ma. The εHf(t) of the analyzed zircon grains ranged from -21.9 to +10.5, with two-stage Hf model ages (TDM2) concentrated between 2.1 and 1.3 Ga. Based on paleocurrent studies and results of petrological, detrital zircon geochronology, and Hf isotopic analyses, the Jurassic sediments in the Yuqia area were likely derived from the tectonic belt along the northern margin of the Qaidam Basin, such as the Qilian Mountains and the Quanji block. In contrast, the Paleogene sediments were probably sourced from the northern margin of the Qaidam Basin and the Qilian Mountains. The uranium and thorium content and Th/U value of the rock mass and sedimentary strata in the source area show that the Indosinian Early Paleozoic uranium-rich granites and the Middle Jurassic uranium-rich strata of the northern margin of the Qaidam tectonic belt in the source area provide dual uranium sources for the Yuqia sandstone-type uranium mineralization. Therefore, the study area appears to be favorable for sandstone-type uranium mineralization and may have potential for uranium prospecting.
Abstract: Large benthic foraminifera are an integral component of shallow-water tropical habitats and like many marine calcifiers are susceptible to ocean acidification (OA) and ocean warming (OW). In particular, the prolific Symbiodiniaceae-bearing and high-magnesium calcite Marginopora vertebralis has a low threshold compared to several diatom-bearing and low-magnesium calcite species. In this multi-year mesocosm experiment we tested three RPC 8.5 climate change scenarios (i) present day, (ii) the year 2050, and (iii) 2100. To enable a realistic epiphytic association these experiments were uniquely conducted using natural carbonate substrate, living calcifying alga, and seagrass. In contrast to previous studies, we detected no reduction in surface-area growth under future climate conditions compared with present day conditions. In terms of calcification, M. vertebralis’ epiphytic association to primary producers (i.e., calcifying algae and seagrasses) potentially ameliorates the effects of OA by buffering against declines in boundary layer pH during periods of photosynthesis (i.e., CO2 removal). Importantly for population maintenance, we observed a strong reduction in asexual fecundity under the 2100 scenario. We propose the additional energy needed to maintain growth might be one reason for drastically reduced asexual reproduction. The other possibility could be due to the +2°C temperature increase, which interfered with the environmental synchronization that triggered asexual multiple fission. We conclude that the low levels of reproduction will reduce populations in a high CO2 environment and reduce a valuable source of CaCO3 sediment production.
Abstract: To investigate groundwater flow and solute transport characteristics of the karst trough zone in China, tracer experiments were conducted at two adjacent typical karst groundwater flow systems (Yuquandong (YQD) and Migongquan (MGQ)) in Sixi valley, western Hubei, China. High-resolution continuous monitoring was utilized to obtain breakthrough curves (BTCs), which were then analyzed using the multi-dispersion model (MDM) and the two-region nonequilibrium model (2RNE) with basic parameters calculated by CXTFIT and QTRACER2. Results showed that: (1) YQD flow system had a complex infiltration matrix with overland flow, conduit flow and fracture flow, while the MGQ flow system was dominated by conduit flow with fast flow transport velocity, but also small amount of fracture flow there; (2) they were well fitted based on the MDM (R2=0.928) and 2RNE (R2=0.947) models, indicating that they had strong adaptability in the karst trough zone; (3) conceptual models for YQD and MGQ groundwater systems were generalized. In YQD system, the solute was transported via overland flow during intense rainfall, while some infiltrated down into fissures and conduits. In MGQ system, most were directly transported to spring outlet in the fissure-conduit network.
Abstract: It is well known that the deformation and damage of reservoir colluvium landslides are often determined by the combined dynamics of reservoir water level change and rainfall. Based on the systematic analysis of the change law of reservoir water level, rainfall and displacements of reservoir colluvium landslide, this paper proposes the compound hydrodynamic action of rainfall and reservoir water as the unload-load parameter, and the landslide displacement as the unload-load response parameter. Based on this, a physical prediction model of the compound hydrodynamic unload-load response ratio of reservoir colluvium landslide was established, and the quantitative relationship between the compound hydrodynamic unload-load response ratio and its stability evolution was in-depth analyzed and determined. On the basis of the above research, taking Shuping landslide, a typical hydrodynamic pressure landslide as an example, the unload-load response ratio model is used to systematically evaluate and predict the stability evolution law and the change trend of the landslide under compound hydrodynamic action. The prediction result shows that the variation law of the compound hydrodynamic unload-load response ratio is consistent with the dynamic evolution law of its stability. Therefore, the above studies show that the compound hydrodynamic unload-load response ratio parameter is an effective displacement dynamic evaluation parameter for reservoir colluvium landslides, so it can be used in the prediction of the reservoir colluvium landslides.
Abstract: Single-sensor monitoring of flood events at high spatial and temporal resolutions is difficult because of the lack of data owing to instrument defects, cloud contamination, imaging geometry. However, combining multisensor data provides an impressive solution to this problem. In this study, 11 synthetic aperture radar (SAR) images and 13 optical images were collected from the Google Earth Engine (GEE) platform during the Sardoba Reservoir flood event to constitute a time series dataset. Threshold-based and indices-based methods were used for SAR and optical data, respectively, to extract the water extent. The final sequential flood water maps were obtained by fusing the results from multisensor time series imagery. Experiments show that, when compare with the Global Surface Water Dynamic (GSWD) dataset, the overall accuracy and Kappa coefficient of the water body extent extracted by our methods range from 98.8 % to 99.1 % and 0.839 to 0.900, respectively. The flooded extent and area increased sharply to a maximum between May 1 and May 4, and then experienced a sustained decline over time. The flood lasted for more than a month in the lowland areas in the north, indicating that the northern region is severely affected. Land cover changes could be detected using the temporal spectrum analysis, which indicated that detailed temporal information benefiting from the multisensor data is highly important for time series analyses.
Abstract: The complex plate collision process led the South Yellow Sea Basin (SYSB) to go through an intensity tectonic inversion during the early Cenozoic, which led to a regional unconformity surface development. As a petroliferous basin, SYSB saw intensity denudation and deposition process, making it hard to characterize their source-to-sink system(S2S), and this study provided a new sight to reveal them quantitatively. According to the seismic interpretation, it was found that two types of tectonic inversion led to the strata shortening process, which was classified according to their difference in planar movements, dip-slip faults, and strike-slip ones. As for dip-slip faults, the inversion structure was primarily formed by the dip-slip movement and many fault-related folds developed, which mainly developed in the North Depression Zone of the SYSB. The strike-slip ones, accompanying developed with some negative flower structures, are dominated in the South Depression Zone of the SYSB. Then, to reveal its source-to-sink system in the tectonic inversion basin, we speculated the sediments’ provenance area and their migration distance, referring to the zircon U-Pb data and heavy mineral assemblage. As for the North Depression Zone, it is shown that fewer distal sediments from the West Sulu Orogenic Belt are infilled, and proximal slump or fan delta are prominently developed during the tectonic inversion stage. The provenance rebuild in the South Depression Zone shows increasing sediments from the proximal area (Central Uplift Zone in SYSB and Wunansha Uplift) and the prograding delta long-axis parallel to these boundary faults during the tectonic inversion stage. Calculations were conducted on the coarse sediments content, faults displacements, catchment relief, sediments migration distance, and discussions about the impact factors to the Source-to-sink system developed in various strata shortening patterns with a statistical method. It was found that, within the dip-slip faults-dominated zone, the volume of the sediment routing system and the ratio of coarse-grained sediments merely has a relationship with the amount of sediment supply and average faults broken displacement. Compared with the strike-slip faults-dominated zone, the source-to-sink system shows a lower level of sandy sediment influx, and its coarse-grained content is mainly determined by the average faults broken displacement.
Abstract: The reservoir operation awakens numerous landslides with multiple sliding surfaces known as reservoir landslides, and the systematic stability analysis for such landslides is becoming increasingly urgent. Taking the Majiagou landslide as an example, this paper analyses the comprehensive performance of the landslide from a probabilistic point of view. Under a reservoir operation cycle, a series of numerical analyses are carried out to simulate the migration of the seepage field, then the dynamic stability of the landslide is quantified accordingly. Subsequently, the wetting-drying cycles test is used to model the weakening of strength parameters in hydro-fluctuation belt under the long-term reservoir operation. Considering the weakening effect of long-term reservoir operation on the hydro-fluctuation belt, the system reliability is evaluated using the Ditlevsen's bounds. The results suggest that the reservoir operation can affect the stability of the landslide by changing the seepage field. The system failure probability gradually rises as the number of wetting-drying cycles increases. Compared with conventional probabilistic analysis that calculates the failure probability of each sliding surface mechanically, analyzing the landslide in terms of system reliability can effectively narrow the failure probability range, which provides an insightful idea for evaluating the systematic stability of analogous reservoir landslides.
Abstract: Columnar jointed basalt (CJB) widely distributes in the dam site of the Baihetan Hydropower Station. The developments of CJB and fracture have a significant influence on the mechanical properties of the whole rock mass, and the mechanical properties of CJB are of great significance to the Baihetan hydropower project. Therefore, in situ direct shear tests were carried out on ten test adit at different locations in the dam site area to study the shear behavior of CJB. In this study, 21 sets of in situ direct shear tests were conducted for rock types of type Ⅱ2, type Ⅲ1 and type Ⅲ2, with horizontal and vertical shear planes and two different specimen sizes of CJB. Shear strength parameters of CJB were obtained by linear fitting of in situ direct shear test results based on the Mohr-Coulomb strength criterion. The results indicate that the shear strength parameters of CJB with horizontal shear plane increase as the increase of rock type grade. The shear strength parameters of CJB show obvious anisotropy and the friction coefficient of the horizontal shear plane is greater than the vertical shear plane. the friction coefficient in the horizontal direction of the shear plane is 1.27 times that in the vertical direction of the shear plane. With the increase of rock type grade, the difference of friction coefficient becomes larger. However, the cohesion changes little whether the shear plane is horizontal or vertical. In addition, the size effect of CJB in this area is significant. The shear strength parameters of large size (100cm x 100cm) specimens are lower than those of regular size (50cm x 50cm) specimens. The reduction of cohesion is greater than that of the friction coefficient. for rock type Ⅲ2, the cohesion of large-size specimens is 0.6370 of the regular-size specimens. the reduction percentage of the friction coefficient for type Ⅲ2 is 1.66 times that of type Ⅲ1. the reduction percentage of the cohesion for type Ⅲ2 is 1.27 times that of type Ⅲ1. the size effect decreases with the increase of rock type grade. The research results of this study can provide an important basis for the selection of rock mechanics parameters in the dam site area of Baihetan Hydropower Station and the stability analysis of the dam foundation and rocky slopes.
Abstract: The influence of different types of roots on the soil is complex and still remains unclear. Four in-situ extrusion tests were conducted on two types of root systems, namely fibrous and tap root system, for three plants (i.e. Eleusine indica, Potentilla anserine and Artemisia argyi), according to the classification in Botany, and the thrust–displacement curves and failure patterns of different samples were analysed by comparison to fill the aforementioned gap. Results reveal that the roots can reduce the characteristics of soil brittleness and enhance its capability to resist large deformation, and different root types contribute different effects on the strain-hardening behaviour of the root–soil mass. The contribution of the fibrous root system on strength is limited, whilst the tap root system substantially enhances strength and stiffness. Results of failure patterns show that fibrous and tap root systems affect soil solidification and surface cracking reduction. However, the effect of the tap root system depends on the composition of lateral and tap roots: long and rich lateral roots are effective for resisting the creation of cracks, but thick tap roots with few and thin lateral roots may lead to several surface cracks.
Abstract: Interactions between anchored slide-resistant piles and landslides with weak-hard interbedded bedrock have not yet been systematically studied. Physical models of landslides reinforced by anchored slide-resistant piles are investigated based upon the self-developed testing system. The landslide system evolution with increasing loading force is revealed; the internal force and deformation of anchored slide-resistant piles in weak-hard interbedded bedrock are analyzed. A single anchored pile in weak-hard interbedded bedrock is analyzed theoretically, and an optimized calculation method for the axial force of the anchor cable is proposed. The results show that (1) The landslide system evolves through four stages: creeping, coordinated deformation, uncoordinated deformation, and failure. (2) The thrust sharing ratio of the pile-anchor first increases, then decreases slightly, and finally stabilizes; the maximum thrust sharing ratio is 12.22. (3) The anchoring force provided by weak-hard interbedded bedrock is between those of homogeneous hard and homogeneous weak rocks. The horizontal displacement of the pile in homogeneous hard rock is small, but more thrust is borne by the pile, and vice versa. (4) The theoretical value for a single anchored pile calculated by the optimized method is close to the measured value. These findings provide a scientific basis for landslide control projects in areas with weak-hard interbedded bedrock.
Abstract: Aquifer connectivity could greatly affect groundwater flow and further control the contaminant transport in fractured medium. However, assessing connectivity of fractured aquifer at regional scales is still a challenge because such connectivity is difficult to measure directly. This study proposed a framework for assessing connectivity of a fractured aquifer, with Qitaihe area, Heilongjiang Province, northeastern China as an illustrating study area. The 3-D finite difference numerical models were established to interpret the results of three multi-well pumping tests and inversely estimate the distribution of hydraulic conductivity (K) in the fractured aquifer. A static connectivity metric of the minimum hydraulic resistance (MHR) was calculated, based on the optimized K-field, to evaluate the hydraulic connectivity in the aquifer, and the corresponding least resistance paths (LRPs) were identified. The results indicate that a better horizontal connectivity in the fractured aquifer in the northeastern and middle parts than in the southwestern part of the study area. The identified LRP indicated that the preferential flow channels at regional scales were controlled mainly by aquifer connectivity instead of local high-K zones.The results of this study can provide a method for aquifer connectivity estimation at regional scales.
Abstract: Mineral recognition and discrimination play a significant role in geological study. Intelligent mineral discrimination based on deep learning has the advantages of automation, low cost, less time consuming and low error rate. In this manuscript, characteristics of quartz, biotite and K-feldspar from granite thin sections under cross-polarized light were studied for mineral images intelligent classification by Inception-v3 deep learning convolutional neural network (CNN), and transfer learning method. Dynamic images from multi-angles were employed to enhance the accuracy and reproducibility in the process of mineral discrimination. Test results show that the average discrimination accuracies of quartz, biotite and K-feldspar are 100.00%, 96.88% and 90.63%. Results of this study prove the feasibility and reliability of the application of convolution neural network in mineral images classification. This study could have a significant impact in explorations of complicated mineral intelligent discrimination using deep learning methods and it will provide a new perspective for the development of more professional and practical mineral intelligent discrimination tools.
Abstract: The Yingshan Formation of the Lower-Middle Ordovician in the Tarim Basin (NW China) was mainly deposited in a shallow platform, which was intensely bioturbated with burrows filled with both dolomites and calcites. This study aims to figure out the controls on the dolomitization of burrow infills and the effects on petroleum reservoir quality based on petrographic examination, fluid inclusion microthermometry, and isotopic (C-O-Sr) geochemical analyses. The differentiation of burrow-associated carbonates (dolomites and calcites) was likely controlled by the interactions of sea-level oscillations of variable orders and depositional environments. The burrow-associated dolomites (BADs) were precipitated in a relatively restricted (i.e., lagoon) depositional environment during the lowstand of long-term sea level. In contrast, the burrow-associated calcites (BACs) were formed in a water circulation-improved lagoonal environment during the transgression of long-term sea level. Isotopic geochemical data indicate that the BADs in the Yingshan Formation were formed from slightly saline (i.e., mesosaline to penesaline) seawater, whereas the BACs were precipitated from nearly normal seawater. In addition to the anoxic condition, the presence of marine-sourced organic matter and sulfate-reducing bacteria, and a sufficient supply of dolomitizing fluids enriched in magnesium ions (Mg2+) and their Mg2+ concentration may have played a critical role in the formation of BADs. In the more permeable and disturbed burrow sediments as a result of burrowing, penetrating fluids with higher salinities and higher Mg2+ concentration relative to seawater favored dolomite precipitation. The fluids with seawater-like Mg2+ concentration, however, would lead to calcite precipitation. The progressive dolomitization of these burrowed sediments could have propagated the dolomitizing fronts and extended into ambient limestones, leading to the development of extensive dolomites. This dolomitization process can improve the petrophysical properties (porosity and permeability) and the potential as hydrocarbon reservoirs during the emplacement of hydrocarbons from underlying source rocks of the Cambrian to Lower Ordovician.
Abstract: The ocean crust remnants of the Proto-Tethys were preserved as the Kudi ophiolites in the West Kunlun Orogenic Belt (WKOB), and its evolutionary history was mainly constructed by research on igneous or metamorphic rocks in the WKOB. Sedimentary rocks in the WKOB received little attention in the past; however, they could provide important constraints on the evolution of the oceanic lithosphere. Here, a series of shales and greywackes found in the Kudi area of WKOB were studied to constrain their depositional ages and explore their significance in the evolution of the Proto-Tethys oceanic crust. U-Pb dating and europium anomaly (Eu/Eu*) were analyzed for detrital zircons from greywackes interlayers, while bulk rare earth elements and yttrium (REY) of the shales were measured. Detrital zircons U-Pb ages yielded a maximum depositional age of 436 Ma for the greywackes and black shales, while the REY distribution patterns of the black shales are similar to those of the Tarim Ordovician Saergan shales. Accordingly, the studied WKOB black shales were deposited in the Proto-Tethys Ocean during the Late Ordovician-Early Silurian period. The maximum depositional age at 436 Ma may represent a minimum closure time of the Proto-Tethys Ocean, which is also supported by the absence of increases in Eu/Eu* values during the Late Ordovician-Early Silurian. Besides, our Eu/Eu* values in detrital zircons indicate diminished orogenesis during the Archean to Mesoproterozoic, subduction-related accretion at the margins of the supercontinent Rodinia during the Neoproterozoic.
Abstract: The mafic-ultramafic intrusion in the XV anomaly area, which contains magmatic Fe-Ti oxide-(P) ore, is located in the Bafq mining district in the Central Iran. It consists of cumulate and layered Fe-Ti-bearing gabbros and pyroxenites. The mineral assemblages include clinopyroxene, Fe-Ti oxides, plagioclase, amphibole, apatite and sulfides (pyrite and chalcopyrite). The Fe-Ti oxides mainly consist of magnetite-titanomagnetite and ilmenite, which occur as disseminated, intergrowth, lamellae (trellis and sandwich textures) and inclusions. Magnetite in the gabbroic rocks is from the near end-member of Fe3O4 (<1 wt. % TiO2) to titanomagnetite containing up to 8 wt. % TiO2 (about 3.73 to 26.84 % Ulvospinel (XUsp)). Magnetite in pyroxenite rocks is characterized with TiO2 range from 0.46 to 3.14 wt. % (XUsp varied from 1.76 to 10.46 %). The abundances of V2O3 range from 0.03 to 1.29 and 0.24 to 1.00 wt. % for gabbro and pyroxenite, respectively. XUsp contents of magnetite show insignificant correlations with Al2O3 and MgO. The average XIlm in the ilmenite of gabbro is 92 %, whereas it is 90.37 % in the pyroxenite rocks. The MgO and V2O3 contents show a slightly positive correlation with TiO2 in ilmenite. The composition of clinopyroxenes in gabbro and pyroxenite rocks fall in the diopside to augite field with Mg# ranging from 67 to 98 and 74 to 96, respectively. In both rock types, amphiboles are mainly pargasite and rarely actinolite. Plagioclase in pyroxenite rocks are clustered in the labradorite to andesine fields with a compositional ranges of An46-69 and in gabboic rocks fall in two fields with compositional ranges of albite with An0.65-5.95 and labradorite with An50-63. The δ 34S isotopic values cover a limited range from +3.15 ‰ to +4.10 ‰ V-CDT consistent with magmatic origin. Fe-Ti mineralization are formed in two stages, minor inclusions of Fe–Ti oxide minerals in the pyroxene and plagioclase crystallized in the early magmatic stage, whereas interstitial oxides formed by fractional crystallization processes that accumulated by gravitational settling in the later stage as intercumulus phase. Gravitational settling process is supported by the observation of decreasing the amount of Fe-Ti oxides from Fe-Ti oxide- rich pyroxenite to weak mineralized gabbro (base to top). The high contents of H2O, phosphorate and high initial Ti-Fe in parental magma are the crucial factors controlling the Fe-Ti oxides enrichment and mineralization.
Abstract: china’s coalbed methane(cbm) industry is in an extremely important "climbing period" and "strategic opportunity period", which can be generally characterized by "three low and one small": low degree of exploration and development, low adaptability of main technology, low return on investment and small development scale. under the "carbon peak and neutrality" background, the development status of cbm industry is systematically combed. the resources, technology, management problems and reasons are analyzed. strategies and countermeasures to accelerate the industrial development are put forward according to the factors such as efficient development of resources, major technical breakthrough, talent team training, policy formulation and implementation, return on investment and so on. the existing problems are as follows: a)the overall occurrence conditions in china are complicated and the development is difficult compared with the other countries. b) the research precision accuracy of cbm resource conditions is not enough; c) the adaptability of technology is poor. d) the management mode is not suitable. in view of these problems, this paper puts forward the "two steps" development strategy and the technical and management countermeasures of "five in one". the corresponding "five in one" technology and management countermeasures are the formulation and implementation of relevant safeguard measures in accordance with the principle of collaborative innovation in five aspects: resources, technology, talents, policies and investment. through the above measures, the dream and grand blueprint of cbm industry shall be realized.
Abstract: lake level, area and volume are sensitive indicators of climate change. at present, many studies have focused on the interannual water balance of lakes, but lake level and area can change remarkably with seasons, especially for lakes with seasonal ice cover. zhari namco, a seasonal frozen lake, was selected as an example to investigate its seasonal water balance. multi-source altimetry and landsat data were used to obtain the seasonal lake level and area from 1992 to 2019, and seasonal lake volume variations were also estimated. the results indicated the average lake level, area and volume in autumn were the largest. the lake level, area, and volume experienced three turning points approximately in 2000, 2010, and 2016, and showed an overall increasing trend from 1992 to 2019, with slopes of 0.15 m/year, 2.17 km2/year, and 0.14 km3/year, respectively. the lake area expanded significantly in autumn, which was related to the abundant precipitation. delay time of land surface runoff, increased temperature, and evaporation may be the reason for the low lake level and volume in summer. the precipitation was the dominant factor of water balance, which explained 62.09%, 62.43%, and 62.10% of the variations in lake level, area, and volume, respectively.
Abstract: the eastern pontides orogenic belt (epob) represents a significant segment of the alpine–himalayan orogenic belt that evolved from the paleozoic to cenozoic periods. here we report new zircon u–pb ages, together with lu–hf isotopes, and whole-rock geochemical and sr–nd isotopic analyses of plutonic rocks from epob, northeastern turkey. our aim is interpret to magmatic evolution in which the granitoids formed. zircon u–pb dating of six samples yielded crystallization ages of ~134 ma; ~82 ma; ~39 ma, respectively. they show a wide range of 87sr/86sr(i) (0.7039–0.7109), and εnd(t) values varying from −9 to +4.6 , yielding model ages (tdm) from 520 to 1623 ma, suggesting a heterogeneous magma source. dated zircons show exlusively positive εhf(t) values (+12.4 to +1.4), yielding model ages (tdm) from 352 to 1059 ma, implying that are most likely derived from a juvenile lower crust rather than the mature continental crust. in this study, we suggested that the northward subduction of the neo-tethyan oceanic slab began from the early cretaceous and resulted in the late cretaceous magmatism. moreover, the middle eocene magmatism in the epob was related to the collision of the anatolide taurid platform (atp) with the pontides.
Abstract: mineral dissolution and mechanical deformation of granite are two main mechanisms that affect permeability evolution of rock fracture. in this study, two water flow-through experiments with large granite fractures were conducted at 200 °c with a constant flow rate for 24 h, under confining pressures of 5 and 10 mpa, respectively. water pressure and temperature were measured, fracture aperture and permeability were calculated, and chemical element concentrations in effluent water were tested for mechanism analysis. the permeability fluctuates up and down between 2.62×10-12 and 3.16×10-12 m2 at confining pressure of 5 mpa; while it decreased monotonously by 24% from 1.92×10-12 to 1.45×10-12 m2 at a confining pressure of 10 mpa. the heat transfer rates at both experiments stay stable at about 0.25 j/s. the mass concentration of ca, na, k, and si in effluent water are between 5 to 23 mg/l, indicating slight dissolution of ca-plagioclase, na-plagioclase, and k-feldspar, as well as possible precipitation of minor amount of kaolinite or qartz. the total amount of free-face dissolution and pressure dissolution are similar at 5 and 10 mpa. the geochemical reaction counts only small part of aperture change, and the mechanical deformation counts the major part of aperture change.
Abstract: sampling is usually scarce in geological modeling, and hence, complex and continuous geological phenomena are difficult to simulate when anisotropy changes locally. the current study aimed to present a method for modeling folded structures using transiogram with locally varying anisotropy in scarce data scenarios. based on the direction fields of locally varying anisotropy, a pathline-based algorithm was proposed to simulate the folds that are flattened and calculate the relative position of any two random points thereafter. compared to the traditional two-point spatial continuity measures (such as the variogram), the locally varying anisotropy transiogram could not only describe the high order markovian of the spatial distribution of geological bodies, but also do so with explicable physical implication. the report revealed that the locally varying anisotropy transiogram of horizontal strata can be directly obtained if the stratigraphic sequence and stratum thickness are known. in the case study, only one geological map was used in a real complex-fold area to successfully simulate the 3-d stratigraphic model.
Abstract: gastropods, as one of the most common invertebrates in shallow marine environments, were heavily impacted by the permian-triassic mass extinction (ptme), with severe loss of diversity and remarkable dwarfism of body size. here, we report a new gastropod fauna from the permian‒triassic carbonates of zuodeng, guangxi province, south china. five species belonging to five genera and two indeterminate taxa are identified. the zuodeng fauna is dominated by paleozoic holdover taxa, including holopea teres, protostylus sp., and wannerispira shangganensis although most of them are found in the basal triassic microbialites. three gastropod communities have been recognized by cluster analysis. further morphological analyses show that the changing pattern of disparity, with diversity decreasing from community ⅱ to ⅲ, fits the interior-reduction model. in addition, the morphospace of community in microbialites is higher than those in non-microbialite bearing beds at zuodeng, shedding new light on the ecological role of microbialites during the permian-triassic environmental stress.
Abstract: frequent ground collapses resulted by anthropogenic activities occur due to rapid urbanization. accurate susceptibility mapping is critical for disaster prevention and control. in this study, 1198 ground collapse cases were collected from 2017 to 2020 in shenzhen. after multicollinearity testing, eight effective factors (elevation, relief, clay proportion, average annual precipitation, distance from water, land use type, building density, and road density) were selected to construct an evaluation index system. ground collapse susceptibility was analyzed and mapped using the normalized frequency ratio (nfr), logistic regression (lr), and nfr-lr coupling models. finally, the rationality and performance of the three models were compared using the frequency ratio (fr) and receiver operating characteristic (roc) curve, respectively. all three models could effectively evaluate the ground collapse susceptibility (area under the roc curve (auc) > 0.7), though the result of nfr-lr model was more rational and had the highest performance (auc = 0.791) among the three models. shenzhen possessed ground collapses mainly in built-up areas, the greater the intensity of anthropogenic activity in a location, the higher the likelihood of a disaster. the high and very high susceptibility zones covered a total area of 546.76 km2 and involved the nanshan, luohu, and futian districts, as well as some areas of the baoan, guangming, and longgang districts.
Abstract: The Machari Formation ranges from the “upper Series 3” (Middle Cambrian) to Furongian (Upper Cambrian) in the Yeongwol area, Korea. It has been known to yield relatively diverse invertebrate fossils. Particularly trilobite biozones of the formation have been well defined. On the other hand, little has hitherto been studied on conodont microfossils for the formation. This paper reports a diverse and well preserved protoconodonts and paraconodonts of Series 3 from the formation in the Eodungol section, exposed along a southern mountain trail of Mt. Sambangsan, Yeongwol, Korea.
Five of the thirteen samples collected for conodont contain a rich protoconodont and paraconodont assemblage and numerous shelly fossils including trilobites, brachiopods, sponge spicules, hyolithids and incertae sedis. Sample Eo5 is extremely fossiliferous (465 elements, 96.5 % of total collection), and the most abundant species was Phakelodus elongatus (236 elements, 62 % of the Eo5 collection).
The preservation is relatively good, but some specimens are corroded and fragmentary. Some of protoconodonts are exfoliated. Relatively larger ones were commonly preserved as phosphatized internal molds, particularly in specimens of Furnishina bigeminata, Furnishina leei n. sp., Muellerodus pomeranensis, Nogamiconus sinensis and westergaardodids. Phakelodids were commonly preserved as clusters.
Among twenty species referable to nine genera, Furnishina bigeminata, Furnishina leei n. sp., Nogamiconus sinensis, Huayuanodontus tricornis, Proscandodus obliquus, and Westergaardodina grandidens were previously undescribed species in Korea. This assemblage is named herein as the Westergaardodina matsushitai Zone, which is new biozonal name replacing the old one i.e., Gapparodus bisulcatus-Westergaardodina matsushitai-Westergaardodina moessebergensis Assemblage. The W. matsushitai Zone corresponds to the Lejopyge armata trilobite Zone, and is well correlated with the upper Series 3 conodont biozones of the Westergaardodina matsushitai-Westergaardodina grandidens Zone of South China, and the Westergaardodina matsushitai Zone of North China, respectively. The present data allow a useful correlation to China and Baltica in relation to new subdivision of the Cambrian. Furnishina leei n. sp. is newly described.
Abstract: the occurrence of geological disasters can have a large impact on urban safety. protecting people's safety is the most important concern when disasters occur. safety improvement requires a large amount of comprehensive and representative risk analysis and a large collection of information related to geological hazards, including unstructured knowledge and experience. to address the relevant information and support safety risk analysis, a geological hazard knowledge graph is developed automatically based on computer vision and domain-geoscience ontology to identify geological hazards from input images while obeying safety rules and regulations, even when affected by changes. in the implementation of the knowledge graph, we design an ontology schema of geological disasters based on a top-down approach, and by organizing knowledge as a logical semantic expression, it can be shared using ontology technologies and therefore enable semantic interoperability. computer vision approaches are then used to automatically detect a set of entities and attributes, using the data from input images, and object types and their attributes are identified so that they can be stored in neo4j for reasoning and searching. finally, a reasoning model for geological hazard identification was developed using the neo4j database to create nodes, relationships, and their properties for modeling, and geological hazards in the images can be automatically identified by searching the neo4j database. an application on geological hazard is presented. the results show the effectiveness of the proposed approach in terms of identifying possible potential hazards in geological hazards and assisting in formulating targeted preventive measures.
Abstract: The U-Pb isotope system and uranium isotope composition (235U/238U and 234U/238U) were studied in a number of samples from the vertical section of the uranium ore body at the Vershinnoe sandstone-type deposit, Vitim uranium ore district, Russia. These parameters were determined to broadly vary. Deviations of the 234U/238U ratio from the equilibrium value indicate that the uranium ore was not completely conserved during the postore stage, and uranium was determined to continue mi‐grating at the deposit. Comparison of the U-Pb isotope age value and 234U/238U isotope ratio provides an insight into the migrate direction of uranium in the ore body. The broad variations (137.377–137.772) in the 238U/235U ratio over the vertical section of the ore body can be explained by the different settings of the samples relative to the ore deposition front and changes in the redox conditions when this front shifted. The fact that the δ238U and K234/238 values are correlated indicates that the transfer of the 234U iso‐tope into the aqueous phase may have been coupled with isotope fractionation in the 238U-235U system during the postformation uranium migration within the orebody.
Abstract: In the continental basins of Northern China (NC), a series of energy resources commonly co-exist in the same basin. As the three typical superimposed basins of different genesis in the NC, the Junggar, Ordos, and Songliao basins were chosen as the research objects. The favorable uraniumbearing structures are generally shown as a basin-margin slope or transition belt of uplifts with the de‐velopment of faults, which are conducive to a fluid circulation system. The Hercynian, Indosinian, and Yanshanian movements resulted in the development of uranium-rich intrusions which acted as the sig‐nificant uranium sources. The main hydrocarbon source rocks are developed in the Carboniferous, Permian, Jurassic and Cretaceous. The mature stage of source rocks is concentrated in the Jurassic–Cretaceous, followed by the multi-stage expulsion events. Influenced by the India-Eurasian collision and the subduction of the Pacific Plate, the tectonic transformation in the Late Yanshanian and Himala‐yan periods significantly influenced the sandstone-type uranium mineralization. The hydrocarbon reser‐voirs are spatially consistent with sandstone-type uranium deposits, while the hydrocarbon expulsionevents occur in sequence with sandstone-type uranium mineralization. In the periphery of the faults or the uplifts, both fluids met and formed uranium concentration. The regional tectonic movements moti‐vate the migration of hydrocarbon fluids and uranium mineralization, especially the Himalayan move‐ment.
Abstract: Intracrystalline distortions (like undulose extinction, dislocations, and subgrain boundaries) in olivine from naturally-deformed peridotites is generally taken as a sign of dislocation creep. However, similar features in olivine phenocrysts that were found in basaltic magmas are still not well understood. In particular, whether subgrain boundaries in olivine phenocrysts arise from plastic deformation or grain growth is still debated (In the latter case, they are essentially grain boundaries but not subgrain boundaries. Therefore, we used hereinafter subgrain-boundary-like structures instead of subgrain boundaries to name this kind of intracrystalline distortion). Here we carried out a detailed study on dislocations and subgrain-boundary-like (SG-like) structures in olivine phenocrysts from two Hawaiian basaltic lavas by means of petrographic microscopy, scanning electron microscopy, and transmission electron microscopy (TEM). Abundant and complex dislocation substructures (free dislocations, dislocation walls, and dislocation tangles) were observed in the decorated olivine grains, similar to those in olivine from peridotite xenoliths entrained by the Hawaiian basalts. The measured average dislocation density is 2.9 ± 1.3 × 1011 m-2, and is three to five orders of magnitude higher than that in laboratory-synthesized, undeformed olivine. TEM observations on samples cut across the SG-like structures by FIB (focused ion beam) demonstrated that this kind of structures is made of an array of dislocations. These observations clearly indicate that these structures are real subgrain boundaries rather than grain boundaries. These facts suggested that the observed high dislocation densities and subgrain boundaries were not resulted from crystal crystallization/growth, but were formed by plastic deformation. These deformation features do not prove that the olivine phenocrysts (and implicitly mantle xenoliths) were deformed after their capture by the basaltic magmas, but can be ascribed to a former deformation event in a dunitic cumulate, which was formed by magmatic fractionation, then plastically deformed, and finally disaggregated and captured by the basaltic magma that brought them to the surface.
Abstract: Metallogenic specialization of sedimentary cover in Central Asia is determined by its tec‐tonic setting that governs the hydrodynamic regime (exfiltrational or infiltrational) and as a consequence, the hydrogeochemical zonality (type of water and its gaseous and microcomponent composition). Hydro‐dynamic conditions (distribution of recharge and discharge areas) determine the direction of stratal water flow and location of mineralization resulted from the change in geochemical, thermodynamic, litholog‐ical, structural and other conditions. The exfiltrational regime suggests a dependence of the epigenetic mineralization upon the distribution and degree of preservation of hydrocarbon occurrences. Often, hy‐drocarbon matter serves as a reducing barrier and ore-concentrating factor during the formation of polymineral concentrations related to stratal oxidation zone. The supergene epigenetic ore-forming pro‐cesses are induced by the interaction between the Earth’s sedimentary cover and hydrosphere. Sedimen‐tary rocks themselves commonly serve as a source of ore materials. The ore deposition zones on geochemi‐cal barriers and ore material source are often located significantly apart from each other. The trend of these processes is determined by the position of ore-bearing depressions in large tectonic blocks.
Abstract: The active Sagaing Fault in Myanmar defines the boundary between the Indian Plate and the Eurasian Plate and causes seismic damage in the major cities of Myanmar. Small bodies of serpentinite occur along the fault. We for the first time investigated the highly sheared serpentinite bodies in the Sheinmagar area and Yega Inn area along the Sagaing Fault. Extensively sheared/brecciated serpentinites and related rocks, such as talc and/or chlorite-bearing rocks contains small rock fragments of serpentinites. Serpentine texture and mineral chemistry indicate that the protolith of these serpentinites were mainly harzburgite with minor amounts of dunite, some of which are cut by gabbroic veins. No shape-preferred orientation of the antigorite is present, indicating that the serpentinization was occurred under relatively static conditions. Protolith and serpentine minerals are similar to those of the jadeitite-bearing serpentinites in the north of the Sagaing Fault (the Jade Mine Belt). Chemical variations of spinels in the studied area are within the compositional range of forearc peridotites and those in the mantle section of nearby ophiolites. After the formation of antigorite serpentinite under static conditions, these serpentinites were subsequently, but locally deformed, probably due to the activity of the Sagaing Fault, resulting in the formation of serpentinite schist/brecciated rock. The presence of the less-deformed antigorite serpentinite in the sheared/brecciated zone indicates the strain localization mainly along the surrounding serpentine-talc (±chlorite) schistose rocks, which is probably formed by the reaction between serpentinite and country rocks. Further studies are needed to better understand whether the distribution of serpentinized peridotites cause variations in the activity of the Sagaing Fault.
Abstract: Many theoretical results on sandstone-type uranium mineralization in northern China obtained by the uranium research team of the Tianjin Center of Geological Survey in recent years are presented. From the source sink system of uranium-producing basins, sedimentary environment of uranium-bearing rock series, ore-forming fluid information, evolution of tectonic events, basin forma‐tion and development, we redefine and classify uranium orebodies, redox zoning, and ore-controlling structural styles. We then systematically propose a theoretical system of sandstone-type uranium depos‐its in northern China. We conclude that sandstone-type uranium deposits in northern China are main‐ly found in sedimentary environments such as rivers, deltas, and alluvial fans in the Mesozoic and Cenozoic lowstand systems tract and in gray sandstone layers in the vertical redox zoning. The orebodies are controlled by the tectonic slope belt, which is in the shape of a strip on the plane, and spreads in a layer or plate on the section. Vertical (ups and downs) tectonic movement triggers large-scale phreatic flow in the basin, which is the real driving force for controlling the ore-forming fluid. The theoretical system of sandstone-type uranium deposits in northern China should be based on global tectonic move‐ment and environmental changes and take into account factors such as basins as a unit to study miner‐alization background, ore concentration areas as objects to study mineralization, and the correlation between regional tectonic movement and metallogenic process as a breakthrough point to study tecton‐ic events and metallogenic events. It should also be based on different basin types to establish metallo‐genic models. The innovative research results and ideas are summarized with the aim of promoting the continuous improvement of sandstone-type uranium mineralization theory in northern China.
Abstract: Ores of infiltration sandstone-hosted uranium deposits in the sedimentary cover are ubiquitous composed of dispersed soot powder mineralization of black, brownish-black colour. Longterm studies of such loose U-ores by analytical transmission electron microscopy (ATEM) proved their polymineral nature. Uranium blacks are composed by at least three different U-mineral forms: oxide (uraninite), silicate (coffinite) and phosphate (ningyoite) which are present in various proportions of ore compositions. Such high dispersed friable uranium formations are difficult to diagnose by tradition‐al mineralogical methods (optical, XRD, IR and X-ray spectroscopy, etc.) which analyze total sample composition (phases mixture); their results characterize the dominant sample phase, omitting both sharply subordinate and X-ray amorphous phases. All research results are based on ATEM methods (SAED+EDS), which are optimal for crystallochemical diagnostics in the mineralogical study of such uranium ores. The article presents the diagnostic characteristics under electron microscope (EM) of uranous minerals from different sandstone deposits with their origin being discussed.
Abstract: Sandstone type deposits are the most common type of uranium deposits in the world. A large variety of sub-types have been defined, based either on the morphology of the deposits (e.g., tabu‐lar, roll front, etc), or on the sedimentological setting (e.g., paleovalley, paleochannel, unconformity), or on tectonic or lithologic controls (e.g., tectonolithologic, mafic dykes/sills), or still on a variety of others characteristics (phreatic oxidation type, interlayer permeable type, multi-element stratabound infiltra‐tional, solution front limb deposit, humate type, etc.), reflecting the diversity of the characteristics of these deposits, but making it difficult to have a clear overview of these deposits. Moreover, uranium de‐posits occurring in the same sedimentological setting (e.g., paleochannel), presenting similar morpholo‐gies (e.g., tabular), may result from different genetic mechanisms and thus can be misleading for explora‐tion strategies. The aim of the present paper is to propose a new view on sandstone-related uranium de-posits combining both genetic and descriptive criteria. The dual view is indeed of primordial importance because all the critical characteristics of each deposit type, not limited to the morphology/geometry of the ore bodies and their relationships with depositional environments of the sandstone, have to be taken into account to propose a comprehensive classification of uranium deposits. In this respect, several key ore-forming processes, like the physical-chemical characteristics of the mineralizing fluid, have to be used to integrate genetic aspects in the classification. Although a succession of concentration steps, potentially temporally-disconnected, are involved in the genesis of some uranium mineralization, the classification here proposed will focus on the main mechanisms responsible for the formation and/or the location of ore deposits. The objective of this paper is also to propose a robust and widely usable ter‐minology to define and categorize sandstone uranium deposits, considering the diversity of their origin and morphologies, and will be primarily based on the temperature of the mineralizing fluid considered as having played the critical role in the transportation of the uranium, starting from synsedimentary ura‐nium deposits to those related to higher temperature fluids.
Abstract: Research on recognition and causes of channel evolution is an important means to reshape the evolutionary history of river landform. This paper aims to study the channel evolution in the downstream of Yuan River in Hunan province, China in the Qing Dynasty via Landsat 8 satellite image data and relevant literature so as to establish the modes of channel evolution and discuss the significance of historical climate change. It is suggested that the paleochannel in the downstream of the Yuan River ware reflected in the late Ming Dynasty and the early Qing Dynasty, the Kangxi and Qianlong periods of the Qing Dynasty, the late Qing Dynasty, and World War II (1939-1945) and classified that the three main modes of river evolution. The research result shows a good correlation between channel revolution, flood events and climate change. Plenty of flood events that occurred from Late Qing Dynasty to the World War II(1939-1945) caused high frequency of channel revolution, which demonstrates the combined effects of climate change and human activities.