The Qaidam Basin(QB)is a concentrated distribution area and chemical industrial bases of salt lakes in China.Lakes in the QB have been expanding during the past 20 years.Rapid lake expansion resulted in some considera...The Qaidam Basin(QB)is a concentrated distribution area and chemical industrial bases of salt lakes in China.Lakes in the QB have been expanding during the past 20 years.Rapid lake expansion resulted in some considerable scientific issues on the protection of salt lake resources and infrastructure,and monitoring of hydrological processes at the lake-basin scale.Although the spatial-temporal trends of lake changes on the Qinghai-Tibet Plateau(QTP)have been well documented,the underlying influencing mechanism and hydrogeological implications of rapid lake changes in the QB are not well understood.Three lakes in the northern QB were selected to investigate lake water level fluctuations on different time scales based on extensive in-situ monitoring and satellite observations.The influencing mechanism and hydrogeological implications of rapid changes of terminal lakes were discussed in combination with the reported increasing precipitation rate and mass balance of glaciers in the northern QTP.Results reveal the following:(1)the fluctuation pattern of Sugan Lake was asynchronous and out of phase with that of Xiao Qaidam and Toson lakes during the monitoring period;(2)Sugan Lake water rose gradually,and the rise interval was from late April to early July.In contrast,Xiao Qaidam and Toson lakes took on a rapid and steep rise,and the rise intervalwas from late July to September;(3)the influencing mechanisms for rapid lake fluctuations are controlled by different factors:glacier and snow melting with increasing temperature for Sugan Lake and increasing precipitation for Xiao Qaidam and Toson lakes;(4)in accordance with different intervals and influencing mechanisms of rapid lake expansions in the QB,hydrological risk precaution of lakes and corresponding river catchments was conducted in different parts of the basin.This study provided an important scientific basis for assessing the hydrological process and hydrological risk precaution,and protection of salt lake resources along with rapid lake expansions in the arid area.展开更多
The distribution of the Jurassic coal measures in the northern Qaidam Basin is obviously controlled by the regional structures. Based on the existing data of coalfield exploration and combined with the analysis of coa...The distribution of the Jurassic coal measures in the northern Qaidam Basin is obviously controlled by the regional structures. Based on the existing data of coalfield exploration and combined with the analysis of coalfield basement structures, features of the main faults, and the distribution of coal measures, this paper brings forward a scheme of coalfield tectonic divisional units and the definition of the coal-controlling structural styles in the northern Qaidam Basin. The structure control of the distribution of coal measures is further discussed. Several stages of regional tectonic activities since the Indosinian has led to the distribution of coal measures into the characteristics of zonation from the north to south and block from east to west. The results indicate that the structural deformations are the most intense in the front of the three uplifted belts, which are characterized by the combination of thrusts. The coal measures are uplifted to the shallow formations, and are easy to be exploited, but the scale of mines is small because of serious damages by the coal distribution. On the contrary, the stress and strain are weak in the three depressions, with the coal-controlling structural styles being mainly the thrust-fold and thrust-monocline combinations. The distribution of coals in the depressions is relatively stable. The shallower part of the depression will become the key areas for exploration and development of coal resources in the northern Qaidam Basin.展开更多
The uranium deposits in the Tuanyushan area of northern Qaidam Basin commonly occur in coal-bearing series. To decipher the U-enrichment mechanism and controlling factors in this area, a database of 72 drill cores, in...The uranium deposits in the Tuanyushan area of northern Qaidam Basin commonly occur in coal-bearing series. To decipher the U-enrichment mechanism and controlling factors in this area, a database of 72 drill cores, including 56 well-logs and 3 sampling wells, was examined for sedimentology and geochemistry in relation to uranium concentrations. The results show that coal-bearing series can influence uranium mineralization from two aspects, i.e., spatial distribution and dynamic control. Five types of uranium-bearing rocks are recognized, mainly occurring in the braided river and braided delta sedimentary facies, among which sandstones near the coals are the most important. The lithological associations of sandstone-type uranium deposits can be classified into three subtypes, termed as U-coal type, coal-U-coal type, and coal-U type, respectively. The coal and fine siliciclastic rocks in the coal- bearing series confined the U-rich fluid flow and uranium accumulation in the sandstone near them. Thus, the coal-bearing series can provide good accommodations for uranium mineralization. Coals and organic matters in the coal-bearing series may have served as reducing agents and absorbing barriers. Methane is deemed to be the main acidolysis hydrocarbon in the U-bearing beds, which shows a positive correlation with U-content in the sandstones in the coal-bearing series. Additionally, the 613C in the carbonate cements of the U-bearing sandstones indicates that the organic matters, associated with the coal around the sandstones, were involved in the carbonation, one important component of alteration in the Tuanyushan area. Recognition of the dual control of coal-bearing series on the uranium mineralization is significant for the development of coal circular economy, environmental protection during coal utilization and the security of national rare metal resources.展开更多
The Northern Qaidam Basin is located at the northeastern part of the Qinghai-Tibetan Plateau. It contains very thick Cenozoic terrestrial clastic sediments, which records the formation of the northern Qaidam Basin due...The Northern Qaidam Basin is located at the northeastern part of the Qinghai-Tibetan Plateau. It contains very thick Cenozoic terrestrial clastic sediments, which records the formation of the northern Qaidam Basin due to compressional deformation during the Indo-Asian collision. In this paper, we used detrital apatite fission-track thermochronology, including 4 sandstones and 2 conglomerates samples from the Lulehe section, to reveal the Cenozoic evolution of the northern Qaidam Basin. Fission-track dating indicated the source region of the Lulehe section has experiencedimportant cooling and uplifting in the Late Cretaceous(at ~85.1 Ma and ~65 Ma) and the Eocene(~52 Ma), respectively. The AFT age distribution on the section suggested that the provenance of Lulehe section sediments were mainly derived from the south Qilian Shan(Qilian Mountains) and Altun Shan(Altun Mountains), and two significantly provenance changes may occur at 43.4-46.1 Ma and ~37.8 Ma, respectively. The results may have strong constrains on the Cenozoic deformation and tectonic evolution of the northern Qaidam Basin and Qinghai-Tibet Plateau.展开更多
The Late Cretaceous tectonic upheaval was an important event during the evolution of the Qaidam Basin, resulting in the omission of the Upper Cretaceous in the whole basin and unconformities between the Paleogene sequ...The Late Cretaceous tectonic upheaval was an important event during the evolution of the Qaidam Basin, resulting in the omission of the Upper Cretaceous in the whole basin and unconformities between the Paleogene sequence and pre-K2 strata. Inte-grating geological and geophysical data, two different groups of Late Cretaceous faults were recognized in the study area, one group consisting of E-W extending strike-slip faults (e.g., the Maxian and Yema-Jinan faults in the Mahai area, which caused an E-W omission zone of Mesozoic), while the other one has NW-SE thrust faults, resulting in NW-SE fold-and-thrust belts. Considering the different strikes and scale of these two groups, a simple-shear model has been employed to explain this structural phenomenon. The NW-SE thrust faults were thought to be subsidiary to the E-W strike-slip faults. Putting this into the framework of the Cretaceous paleogeographic environment of central Asia, it is inferred that this tectonic event of the Qaidam Basin is a response to the continuous northward drifting of the India plate.展开更多
Cenozoic climatic and environmental changes in the arid Asian interior, and their possible relations with global climatic changes and the Tibetan Plateau uplift, have been intensively investigated and debated over pas...Cenozoic climatic and environmental changes in the arid Asian interior, and their possible relations with global climatic changes and the Tibetan Plateau uplift, have been intensively investigated and debated over past decades. Here we present 40-Myr (million years)-long n-alkane records from a continuous Cenozoic sediment sequence in the Dahonggou Section, Qaidam Basin, northern Tibetan Plateau, to infer environmental changes in the northern basin. A set of n-alkane indexes, including ACL, CPI and Paq, vary substantially and consistently throughout the records, which are interpreted to reflect relative contributions from terrestrial vascular plants vs. aquatic macrophytes, and thus indicate depositional environments. ACL values vary between 21 and 30; CP1 values range from 1.0 to 8.0; and Paq values change from 〈0.1 to 0.8 over the past 40-Myr. We have roughly identified two periods, at 25.8-21.0 Ma (million years ago) and 13.0-17.5 Ma, with higher ACL and CPI and lower Paq values indicating predominant lacustrine environments. Lower ACL and CPI values, together with higher Paq values, occurred at 〉25.8 Ma, 17.5-21.0 Ma, and 〈13.0 Ma, corresponding to alluvial fan/river deltaic deposits and shallow lacustrine settings, consistent with the observed features in sedimentological facies. The inferred Cenozoic environmental changes in the northern Qaidam Basin appear to correspond to global climatic changes.展开更多
Previous studies of coal sequence stratigraphy have concentrated on coals associated with paralic depositional systems.Little attention has been paid to their counterparts in non-marine intra-mountain coal basins.The ...Previous studies of coal sequence stratigraphy have concentrated on coals associated with paralic depositional systems.Little attention has been paid to their counterparts in non-marine intra-mountain coal basins.The northern Qaidam Basin of northwestern China has been extensively developed with abundant oil and gas as well as coal resources in its Jurassic non-marine successions.A total of six sedimentary systems of the Early and Middle Jurassic展开更多
The Upper Paleogene lacustrine fine-grained sandstones in the hinterlands of the northern Qaidam Basin mainly contain two sweet spot intervals.Fracture/fault,microfacies,petrology,pore features,diagenesis,etc.,were in...The Upper Paleogene lacustrine fine-grained sandstones in the hinterlands of the northern Qaidam Basin mainly contain two sweet spot intervals.Fracture/fault,microfacies,petrology,pore features,diagenesis,etc.,were innovatively combined to confirm the controlling factors on the reservoir quality of shallow delta-lacustrine fine-grained sandstones.The diagenesis of the original lake/surface/meteoric freshwater and acidic fluids related to the faults and unconformity occurred in an open geochemical system.Comprehensive analysis shows that the Upper Paleogene fine-grained sandstones were primarily formed in the early diagenetic B substage to the middle diagenetic A substage.Reservoir quality was controlled by fault systems,microfacies,burial-thermal history,diagenesis,hydrocarbon charging events(HCE),and abnormally high pressure.Shallow and deep double fault systems are the pathways for fluid flow and hydrocarbon migration.Sandstones developed in the high energy settings such as overwater(ODC)and underwater distributary channels(UDC)provide the material foundation for reservoirs.Moderate burial depth(3000-4000 m),moderate geothermal field(2.7-3.2℃/100 m),and late HCE(later than E3)represent the important factors to protect and improve pore volume.Meteoric freshwater with high concentrations of CO_(2)and organic acids from thermal decarboxylation are the main fluids leading to the dissolution and reformation of feldspar,rock fragments,calcite and anhydrite cements.Abnormally high pressure caused by the undercompaction in a large set of argillaceous rocks is the key to form high-quality reservoirs.Abnormal pressure zones reduced and inhibited the damage of compaction and quartz overgrowth to reservoir pores,allowing them to be better preserved.A reservoir quality evaluation model with bidirectional migration pathways,rich in clay minerals,poor in cements,superimposed dissolution and abnormally high pressure was proposed for the ODC/UDC finegrained sandstones.This model will facilitate the future development of fine-grained sandstone reservoirs both in the Upper Paleogene of the Qaidam Basin and elsewhere.展开更多
Based on an extensive borehole survey of the Middle Jurassic coat-bearing sequences in the Saishiteng coalfield, northern Qaidam Basin (NQB), a total of 20 rock types and 5 sedimentary facies were identified, includ...Based on an extensive borehole survey of the Middle Jurassic coat-bearing sequences in the Saishiteng coalfield, northern Qaidam Basin (NQB), a total of 20 rock types and 5 sedimentary facies were identified, including braided river, meandering river, braided delta, meandering river delta, and lacustrine facies. The distribution of rock types and sedimentary facies contributed to the reconstruction of three periods' sedimentary facies maps of the Middle Jurassic in the Saishiteng coalfield, namely, the Dameigou age, the early Shimengou age and the late Shimengou age. That also provided the basis for the development of a three-stage depositional model of the Middle Jurassic in the NQB, indicating the lacustrine basin of the NQB in the Dameigou age and early Shimengou age were corresponding to an overfill basin, and that in the late Shimengou age was related to a balanced-fill basin. The analysis of the stability and structure of coat seams based on sedimentary facies maps showed that the preferred coal-forming facies in the Saishiteng coalfield were inter-delta bay and interdistributary bay of lower delta plain in the Dameigou age. In particular, the swamps that developed on the subaqueous pataeohigh favored the development of thick coat seams. Thus, ruinable coal seams may also be found along the Pingtai pataeohigh in the western part of the Saishiteng coalfield.展开更多
Knowing the rotation and paleo-stress history in Qaidam Basin is a fundamental parameter to quantify the mechanism of intracontinental deformation in Tibetan Plateau.However,few studies have been conducted on tectonic...Knowing the rotation and paleo-stress history in Qaidam Basin is a fundamental parameter to quantify the mechanism of intracontinental deformation in Tibetan Plateau.However,few studies have been conducted on tectonic rotation and stress evolution over long timescales in the Qaidam Basin.Here,we report new magnetic declination and the anisotropy of magnetic susceptibility(AMS)from a~52–7 Ma sequence of fluvial and lacustrine sediments in the Dahonggou(DHG)section in the northern Qaidam Basin.The magnetic declination revealed that the northern Qaidam Basin underwent a clockwise rotation 25.1°±8.6°during~33–17 Ma,followed by a counterclockwise rotation 16.9°±6.8°during~17–13.5 Ma.The AMS results showed that the“earliest deformation”fabrics were interrupted by the“pencil structure”fabrics in the intervals of~52–45 and~21–15 Ma.The interruption,synchronous with the marked deceleration of the India-Asia convergence rate,indicates pulse of strong tectonic compressive stress.In addition,the AMS results documented a transition in stress direction from S-N to SW-NE at~15 Ma,suggesting a kinematic shift in the northeastern TP.Our constraints on the rotation and stress from the northern Qaidam Basin support the two-stage evolution of the Altyn Tagh Fault(ATF).The fast-rate slip motion on the ATF during the early Oligocene caused the clockwise rotation in the northern Qaidam Basin;the second stage with enhanced thrusting since the middle Miocene caused extensive crustal shortening and dispersive NW-trending folds and faults in the Qaidam Basin and the northeastern TP.展开更多
Whether benthic macroalga can be an important type of bio-precursor of source rocks is a contentious issue in source-rock studies,and has not been well understood.This paper represents a case study of Jurassic mudston...Whether benthic macroalga can be an important type of bio-precursor of source rocks is a contentious issue in source-rock studies,and has not been well understood.This paper represents a case study of Jurassic mudstone source rocks from the northern Qaidam Basin,northwestern China,in which the benthic macro red algae were recognized for the first time based on combined organic petrological and biomarker works.We found not only cystocarps in the algae,representative of rhodophyta,but also diahopanes,which are diagnostic biomarkers of such algae.Thus,as many reservoired oils in the northern Qaidam Basin contain abundant diahopanes,it may indicate that the red algae have contributed to hydrocarbon accumulation.This was confirmed by integrated geological and geochemical analyses.Hence,this study provides new evidence for macroalga-generated hydrocarbons.展开更多
We investigate the growth of the northern Tibetan Plateau and associated climate change by applying oxygen and carbon isotopic compositions in Cenozoic strata in the southwestern Qaidam basin. The X-ray diffraction an...We investigate the growth of the northern Tibetan Plateau and associated climate change by applying oxygen and carbon isotopic compositions in Cenozoic strata in the southwestern Qaidam basin. The X-ray diffraction and isotopic studies reveal that the carbonate minerals are mainly authigenic and they do not preserve any evidence for detrital carbonate and diagenesis. The isotope data show large fluctuations in the δ^(18)O and δ^(13)C values in the middle-late Eocene, indicating relatively warm and seasonal dry climate.The positive correlation of the δ^(18)O and δ^(13)C values in the Oligocene and the positive shift of the δ^(13)C values from the Eocene to Oligocene suggest that the climate changed to arid in the Oligocene. However,the δ^(18) values show negative shift, which is closely related to the global cooling event. During the Miocene, the δ^(13)C values vary between-2‰ and-4‰, whereas the δ^(18)O values show continuous negative shift. The mean δ^(18) values decrease from-8.5‰, in the early Miocene to-10.0‰, in the late Miocene. The stable isotope-based paleoaltimetry results suggest that the elevation of the southwestern Qaidam basin was approximately 1500 m in the middle-late Eocene and Oligocene. Subsequently, during Miocene the crustal uplift process started and the elevation reached approximately 2000 m in the early Miocene and 2500 m in the late Miocene, which suggests large-scale growth of the northern Tibet Plateau during the Miocene.展开更多
Eclogites have been recently discovered in the Xitieshan area in the middlesegment of the northern margin of the Qaidam basin. These eclogites, together with those recognizedearlier in the Yuka area of the western seg...Eclogites have been recently discovered in the Xitieshan area in the middlesegment of the northern margin of the Qaidam basin. These eclogites, together with those recognizedearlier in the Yuka area of the western segment of the northern margin of the Qaidam basin and inthe Dulan area of the eastern segment of the northern margin of the Qaidam basin, form an eclogitebelt with a length of 350 km. A comparison of the eclogites from the Yuka and Xitieshan areassuggests that they show different country rocks, microtextures, mineral assemblages, and especially,different peak temperatures, PT paths during decompression and isotopic features. Eclogites fromthe Yuka area bear evidence of prograde metamorphism, such as prograde mineral relics in garnet andgrowth zoning of garnet, and hairpin-shaped PT paths with coincidence of the baric and thermal peaksof metamorphism, which reflect rapid burial and uplift. Sm-Nd isotopic determination shows obviousSm-Nd disequilibrium, and no isochron ages of Early Paleozoic metamorphism was obtained. On thecontrary, the Xitieshan eclogite was subjected to metamorphism of higher eclogite-facies andpost-eclogite-facies temperatures, showing an obvious granulite-facies overprint. A tentative PTpath for the Xitieshan area suggests that the baric peak preceded the thermal culmination. Wholerock-garnet-omphacite Sm-Nd isotopic data give an isochron age in the Early Paleozoic. Thedifferences between the two eclogites imply their different tectonic-thermal history during theirburial and uplift.展开更多
Palaeodrainage basin,as an important component of the source-to-sink system,contains critical information on provenance and palaeoenvironment.Previous studies indicate that the scaling relationships of source-to-sink ...Palaeodrainage basin,as an important component of the source-to-sink system,contains critical information on provenance and palaeoenvironment.Previous studies indicate that the scaling relationships of source-to-sink system components generally follow power laws,and channel-belt thickness represents a reliable first-order proxy for the drainage area.In this study,a database of borehole cores and geophysical well logs of the Jurassic coal measures from Saishiteng area in the northern Qaidam Basin was used to reconstruct the palaeogeography,and to identify single-story channel-belts.Three palaeochannels,namely,River A,River B and River C,were identified which were persistent throughout the Dameigou and Shimengou Formations during the Middle Jurassic.The mean channel-belt thicknesses of River A,River B and River C in the Dameigou Formation were 9.8 m,8.9 m and 7.9 m,respectively,and those in the Shimengou Formation were 7.4 m,6.2 m and 5.4 m,respectively.We estimate the drainage area of three major rivers by using scaling relationships between drainage area and channel-belt thickness.The drainage areas of River A,River B and River C in the Dameigou Formation were 63.0×10~3 km^2,50.1×10~3 km^2 and 37.7×10~3 km^2,respectively,and those in the Shimengou Formation were 32.3×10~3 km^2,21.2×10~3 km^2 and15.3×10~3 km^2,respectively.The drainage basin lengths of River A,River B and River C in the Dameigou Formation were 300.4 km,239 km and 180.2 km,respectively,and those in the Shimengou Formation were 154.3 km,101.3 km and 73.1 km,respectively.For both the Dameigou and Shimengou Formations,River A showed the largest scale,followed by River B and River C succeedingly,which was mainly determined by the stretch direction of provenance in the southern Qilian Mountains.The variations of channel-belt thickness,drainage area and drainage basin length between Dameigou and Shimengou Formations are the response of source-to-sink system to the transformation from extension to compression depression during the Middle Jurassic in the northern Qaidam Basin.展开更多
The current study tested the gas component and carbon isotopic composition of gas samples from 6 oilgas fields at the northern margin of Qaidam Basin, and established a chart to quantitatively identify the mixing rati...The current study tested the gas component and carbon isotopic composition of gas samples from 6 oilgas fields at the northern margin of Qaidam Basin, and established a chart to quantitatively identify the mixing ratio of source-mixed gas. Besides, this research quantitatively investigated the natural gas generated by different types of organic matter. The results show that different ratios of source-mixed gas exist in the 6 oil-gas fields at the northern margin of Qaidam Basin. Among them, Mabei has the highest mixing ratio of coal-type gas, followed by Nanbaxian, Mahai, Lenghu-4, Lenghu-3 and Lenghu-5, with the ratios of coal-type gas 91%, 87%, 83%, 66%, 55% and 36%, respectively. Lenghu-3 and Lenghu-4 oil-gas fields were mainly filled by coal-type gas earlier. For Lenghu-3, the gas was mainly generated from low matured source rocks in lower Jurassic Series of Lengxi sub-sag. For Lenghu-4, the gas was mainly generated from humus-mature source rocks in lower Jurassic Series of the northern slope of Kunteyi sub-sag. Gas in Lenghu-5 was mainly later filled oil-type gas, which was generated from high matured sapropelics in lower Jurassic Series of Kunteyi sub-sag. Earlier filled coal-type gas was the main part of Mahai, Nanbaxian and Mabei oil-gas fields. Gas source of Mahai was mainly generated from high mature humics in lower Jurassic Series of Yibei sub-sag; for Nanbaxian, the gas was mainly generated from high matured humics in middle-lower Jurassic Series of Saishiteng sub-sag; for Mabei, the gas was mainly generated from humus-mature source rocks in middle Jurassic Series of Yuqia sub-sag.展开更多
We investigated the geological factors associated with unsuccessful exploration wells in the northern margin of the Qaidam basin to better understand their cause.The structural situation,the hydrocarbon accumulation m...We investigated the geological factors associated with unsuccessful exploration wells in the northern margin of the Qaidam basin to better understand their cause.The structural situation,the hydrocarbon accumulation mechanism and unsuccessful well data collected from 1996 to 2005 were studied.The results show that the main geological factors associated with unsuccessful exploration wells are a lack of effective source rocks and a lack of effective traps,as well as the migration-accumulation conditions that exist in this area.The basin was reformed by Meso-Cenozoic tectonic evolution.Multi-stage tectonic activities have both positive and negative effects on hydrocarbon accumulation.Source rocks distribution,effective migration channels,effective traps and the tectonic evolution effects on hydrocarbons should be the key objects for further studies.展开更多
基金Supported by the Second Tibetan Plateau Scientific Expedition and Research Program(No.2019 QZKK 0805)the National Natural Science Foundation of China(No.U 21 A 2018)the Foundation of Department of Qinghai Science&Technology(No.2020-ZJ-T 06)。
文摘The Qaidam Basin(QB)is a concentrated distribution area and chemical industrial bases of salt lakes in China.Lakes in the QB have been expanding during the past 20 years.Rapid lake expansion resulted in some considerable scientific issues on the protection of salt lake resources and infrastructure,and monitoring of hydrological processes at the lake-basin scale.Although the spatial-temporal trends of lake changes on the Qinghai-Tibet Plateau(QTP)have been well documented,the underlying influencing mechanism and hydrogeological implications of rapid lake changes in the QB are not well understood.Three lakes in the northern QB were selected to investigate lake water level fluctuations on different time scales based on extensive in-situ monitoring and satellite observations.The influencing mechanism and hydrogeological implications of rapid changes of terminal lakes were discussed in combination with the reported increasing precipitation rate and mass balance of glaciers in the northern QTP.Results reveal the following:(1)the fluctuation pattern of Sugan Lake was asynchronous and out of phase with that of Xiao Qaidam and Toson lakes during the monitoring period;(2)Sugan Lake water rose gradually,and the rise interval was from late April to early July.In contrast,Xiao Qaidam and Toson lakes took on a rapid and steep rise,and the rise intervalwas from late July to September;(3)the influencing mechanisms for rapid lake fluctuations are controlled by different factors:glacier and snow melting with increasing temperature for Sugan Lake and increasing precipitation for Xiao Qaidam and Toson lakes;(4)in accordance with different intervals and influencing mechanisms of rapid lake expansions in the QB,hydrological risk precaution of lakes and corresponding river catchments was conducted in different parts of the basin.This study provided an important scientific basis for assessing the hydrological process and hydrological risk precaution,and protection of salt lake resources along with rapid lake expansions in the arid area.
文摘The distribution of the Jurassic coal measures in the northern Qaidam Basin is obviously controlled by the regional structures. Based on the existing data of coalfield exploration and combined with the analysis of coalfield basement structures, features of the main faults, and the distribution of coal measures, this paper brings forward a scheme of coalfield tectonic divisional units and the definition of the coal-controlling structural styles in the northern Qaidam Basin. The structure control of the distribution of coal measures is further discussed. Several stages of regional tectonic activities since the Indosinian has led to the distribution of coal measures into the characteristics of zonation from the north to south and block from east to west. The results indicate that the structural deformations are the most intense in the front of the three uplifted belts, which are characterized by the combination of thrusts. The coal measures are uplifted to the shallow formations, and are easy to be exploited, but the scale of mines is small because of serious damages by the coal distribution. On the contrary, the stress and strain are weak in the three depressions, with the coal-controlling structural styles being mainly the thrust-fold and thrust-monocline combinations. The distribution of coals in the depressions is relatively stable. The shallower part of the depression will become the key areas for exploration and development of coal resources in the northern Qaidam Basin.
基金supported by the Major National Science and Technology Program of China (grants No. 2016ZX05041004)the National Natural Science Foundation of China (grant No. 41572090)High-level Talent Recruitment Project of North China University of Water Resource and Electric (grant No. 40481)
文摘The uranium deposits in the Tuanyushan area of northern Qaidam Basin commonly occur in coal-bearing series. To decipher the U-enrichment mechanism and controlling factors in this area, a database of 72 drill cores, including 56 well-logs and 3 sampling wells, was examined for sedimentology and geochemistry in relation to uranium concentrations. The results show that coal-bearing series can influence uranium mineralization from two aspects, i.e., spatial distribution and dynamic control. Five types of uranium-bearing rocks are recognized, mainly occurring in the braided river and braided delta sedimentary facies, among which sandstones near the coals are the most important. The lithological associations of sandstone-type uranium deposits can be classified into three subtypes, termed as U-coal type, coal-U-coal type, and coal-U type, respectively. The coal and fine siliciclastic rocks in the coal- bearing series confined the U-rich fluid flow and uranium accumulation in the sandstone near them. Thus, the coal-bearing series can provide good accommodations for uranium mineralization. Coals and organic matters in the coal-bearing series may have served as reducing agents and absorbing barriers. Methane is deemed to be the main acidolysis hydrocarbon in the U-bearing beds, which shows a positive correlation with U-content in the sandstones in the coal-bearing series. Additionally, the 613C in the carbonate cements of the U-bearing sandstones indicates that the organic matters, associated with the coal around the sandstones, were involved in the carbonation, one important component of alteration in the Tuanyushan area. Recognition of the dual control of coal-bearing series on the uranium mineralization is significant for the development of coal circular economy, environmental protection during coal utilization and the security of national rare metal resources.
基金funded by the Natural Science Foundation of China (Grants No. 41501209 and 41571177)the Fundamental Research Funds for the Central Universities (862457, lzujbky-2016-22)
文摘The Northern Qaidam Basin is located at the northeastern part of the Qinghai-Tibetan Plateau. It contains very thick Cenozoic terrestrial clastic sediments, which records the formation of the northern Qaidam Basin due to compressional deformation during the Indo-Asian collision. In this paper, we used detrital apatite fission-track thermochronology, including 4 sandstones and 2 conglomerates samples from the Lulehe section, to reveal the Cenozoic evolution of the northern Qaidam Basin. Fission-track dating indicated the source region of the Lulehe section has experiencedimportant cooling and uplifting in the Late Cretaceous(at ~85.1 Ma and ~65 Ma) and the Eocene(~52 Ma), respectively. The AFT age distribution on the section suggested that the provenance of Lulehe section sediments were mainly derived from the south Qilian Shan(Qilian Mountains) and Altun Shan(Altun Mountains), and two significantly provenance changes may occur at 43.4-46.1 Ma and ~37.8 Ma, respectively. The results may have strong constrains on the Cenozoic deformation and tectonic evolution of the northern Qaidam Basin and Qinghai-Tibet Plateau.
文摘The Late Cretaceous tectonic upheaval was an important event during the evolution of the Qaidam Basin, resulting in the omission of the Upper Cretaceous in the whole basin and unconformities between the Paleogene sequence and pre-K2 strata. Inte-grating geological and geophysical data, two different groups of Late Cretaceous faults were recognized in the study area, one group consisting of E-W extending strike-slip faults (e.g., the Maxian and Yema-Jinan faults in the Mahai area, which caused an E-W omission zone of Mesozoic), while the other one has NW-SE thrust faults, resulting in NW-SE fold-and-thrust belts. Considering the different strikes and scale of these two groups, a simple-shear model has been employed to explain this structural phenomenon. The NW-SE thrust faults were thought to be subsidiary to the E-W strike-slip faults. Putting this into the framework of the Cretaceous paleogeographic environment of central Asia, it is inferred that this tectonic event of the Qaidam Basin is a response to the continuous northward drifting of the India plate.
基金partially supported by the National Basic Research Program of China (2010CB833406)National Natural Science Foundation of China (NSFC 41172008 and 41372002)+1 种基金Distinguished Young Scientist of Ministry of Land and Resources, China, and Hong Kong RGC (HKU 703809P)HKU research facility was supported by the Special Equipment Grant from the University Grants Committee of the Hong Kong Special Administrative Region, China (SEG_HKU01)
文摘Cenozoic climatic and environmental changes in the arid Asian interior, and their possible relations with global climatic changes and the Tibetan Plateau uplift, have been intensively investigated and debated over past decades. Here we present 40-Myr (million years)-long n-alkane records from a continuous Cenozoic sediment sequence in the Dahonggou Section, Qaidam Basin, northern Tibetan Plateau, to infer environmental changes in the northern basin. A set of n-alkane indexes, including ACL, CPI and Paq, vary substantially and consistently throughout the records, which are interpreted to reflect relative contributions from terrestrial vascular plants vs. aquatic macrophytes, and thus indicate depositional environments. ACL values vary between 21 and 30; CP1 values range from 1.0 to 8.0; and Paq values change from 〈0.1 to 0.8 over the past 40-Myr. We have roughly identified two periods, at 25.8-21.0 Ma (million years ago) and 13.0-17.5 Ma, with higher ACL and CPI and lower Paq values indicating predominant lacustrine environments. Lower ACL and CPI values, together with higher Paq values, occurred at 〉25.8 Ma, 17.5-21.0 Ma, and 〈13.0 Ma, corresponding to alluvial fan/river deltaic deposits and shallow lacustrine settings, consistent with the observed features in sedimentological facies. The inferred Cenozoic environmental changes in the northern Qaidam Basin appear to correspond to global climatic changes.
文摘Previous studies of coal sequence stratigraphy have concentrated on coals associated with paralic depositional systems.Little attention has been paid to their counterparts in non-marine intra-mountain coal basins.The northern Qaidam Basin of northwestern China has been extensively developed with abundant oil and gas as well as coal resources in its Jurassic non-marine successions.A total of six sedimentary systems of the Early and Middle Jurassic
基金supported by the National Major Science and Technology Projects of China(No.2016ZX05033-001002)the National Natural Science Foundation of China(No.41272155)the China Scholarship Council。
文摘The Upper Paleogene lacustrine fine-grained sandstones in the hinterlands of the northern Qaidam Basin mainly contain two sweet spot intervals.Fracture/fault,microfacies,petrology,pore features,diagenesis,etc.,were innovatively combined to confirm the controlling factors on the reservoir quality of shallow delta-lacustrine fine-grained sandstones.The diagenesis of the original lake/surface/meteoric freshwater and acidic fluids related to the faults and unconformity occurred in an open geochemical system.Comprehensive analysis shows that the Upper Paleogene fine-grained sandstones were primarily formed in the early diagenetic B substage to the middle diagenetic A substage.Reservoir quality was controlled by fault systems,microfacies,burial-thermal history,diagenesis,hydrocarbon charging events(HCE),and abnormally high pressure.Shallow and deep double fault systems are the pathways for fluid flow and hydrocarbon migration.Sandstones developed in the high energy settings such as overwater(ODC)and underwater distributary channels(UDC)provide the material foundation for reservoirs.Moderate burial depth(3000-4000 m),moderate geothermal field(2.7-3.2℃/100 m),and late HCE(later than E3)represent the important factors to protect and improve pore volume.Meteoric freshwater with high concentrations of CO_(2)and organic acids from thermal decarboxylation are the main fluids leading to the dissolution and reformation of feldspar,rock fragments,calcite and anhydrite cements.Abnormally high pressure caused by the undercompaction in a large set of argillaceous rocks is the key to form high-quality reservoirs.Abnormal pressure zones reduced and inhibited the damage of compaction and quartz overgrowth to reservoir pores,allowing them to be better preserved.A reservoir quality evaluation model with bidirectional migration pathways,rich in clay minerals,poor in cements,superimposed dissolution and abnormally high pressure was proposed for the ODC/UDC finegrained sandstones.This model will facilitate the future development of fine-grained sandstone reservoirs both in the Upper Paleogene of the Qaidam Basin and elsewhere.
基金supported by the National Natural Science Foundation of China(41030213, 41502108)the Major National Science and Technology Program of China(2011ZX05033-002)
文摘Based on an extensive borehole survey of the Middle Jurassic coat-bearing sequences in the Saishiteng coalfield, northern Qaidam Basin (NQB), a total of 20 rock types and 5 sedimentary facies were identified, including braided river, meandering river, braided delta, meandering river delta, and lacustrine facies. The distribution of rock types and sedimentary facies contributed to the reconstruction of three periods' sedimentary facies maps of the Middle Jurassic in the Saishiteng coalfield, namely, the Dameigou age, the early Shimengou age and the late Shimengou age. That also provided the basis for the development of a three-stage depositional model of the Middle Jurassic in the NQB, indicating the lacustrine basin of the NQB in the Dameigou age and early Shimengou age were corresponding to an overfill basin, and that in the late Shimengou age was related to a balanced-fill basin. The analysis of the stability and structure of coat seams based on sedimentary facies maps showed that the preferred coal-forming facies in the Saishiteng coalfield were inter-delta bay and interdistributary bay of lower delta plain in the Dameigou age. In particular, the swamps that developed on the subaqueous pataeohigh favored the development of thick coat seams. Thus, ruinable coal seams may also be found along the Pingtai pataeohigh in the western part of the Saishiteng coalfield.
基金supported by the National Natural Science Foundation of China(Grant Nos.42274105,41972208,42172251)the Geological Survey of China(Grant No.DD20190370)the National Oil and Gas Major Science and Technology Project(Grant No.2016ZX05003-006).
文摘Knowing the rotation and paleo-stress history in Qaidam Basin is a fundamental parameter to quantify the mechanism of intracontinental deformation in Tibetan Plateau.However,few studies have been conducted on tectonic rotation and stress evolution over long timescales in the Qaidam Basin.Here,we report new magnetic declination and the anisotropy of magnetic susceptibility(AMS)from a~52–7 Ma sequence of fluvial and lacustrine sediments in the Dahonggou(DHG)section in the northern Qaidam Basin.The magnetic declination revealed that the northern Qaidam Basin underwent a clockwise rotation 25.1°±8.6°during~33–17 Ma,followed by a counterclockwise rotation 16.9°±6.8°during~17–13.5 Ma.The AMS results showed that the“earliest deformation”fabrics were interrupted by the“pencil structure”fabrics in the intervals of~52–45 and~21–15 Ma.The interruption,synchronous with the marked deceleration of the India-Asia convergence rate,indicates pulse of strong tectonic compressive stress.In addition,the AMS results documented a transition in stress direction from S-N to SW-NE at~15 Ma,suggesting a kinematic shift in the northeastern TP.Our constraints on the rotation and stress from the northern Qaidam Basin support the two-stage evolution of the Altyn Tagh Fault(ATF).The fast-rate slip motion on the ATF during the early Oligocene caused the clockwise rotation in the northern Qaidam Basin;the second stage with enhanced thrusting since the middle Miocene caused extensive crustal shortening and dispersive NW-trending folds and faults in the Qaidam Basin and the northeastern TP.
基金Supported by National Natural Science Foundation of China (Grant Nos. 40602014, 40872086, 40638042)
文摘Whether benthic macroalga can be an important type of bio-precursor of source rocks is a contentious issue in source-rock studies,and has not been well understood.This paper represents a case study of Jurassic mudstone source rocks from the northern Qaidam Basin,northwestern China,in which the benthic macro red algae were recognized for the first time based on combined organic petrological and biomarker works.We found not only cystocarps in the algae,representative of rhodophyta,but also diahopanes,which are diagnostic biomarkers of such algae.Thus,as many reservoired oils in the northern Qaidam Basin contain abundant diahopanes,it may indicate that the red algae have contributed to hydrocarbon accumulation.This was confirmed by integrated geological and geochemical analyses.Hence,this study provides new evidence for macroalga-generated hydrocarbons.
基金supported by National Science and Technology Major Project (2011ZX05009-001)
文摘We investigate the growth of the northern Tibetan Plateau and associated climate change by applying oxygen and carbon isotopic compositions in Cenozoic strata in the southwestern Qaidam basin. The X-ray diffraction and isotopic studies reveal that the carbonate minerals are mainly authigenic and they do not preserve any evidence for detrital carbonate and diagenesis. The isotope data show large fluctuations in the δ^(18)O and δ^(13)C values in the middle-late Eocene, indicating relatively warm and seasonal dry climate.The positive correlation of the δ^(18)O and δ^(13)C values in the Oligocene and the positive shift of the δ^(13)C values from the Eocene to Oligocene suggest that the climate changed to arid in the Oligocene. However,the δ^(18) values show negative shift, which is closely related to the global cooling event. During the Miocene, the δ^(13)C values vary between-2‰ and-4‰, whereas the δ^(18)O values show continuous negative shift. The mean δ^(18) values decrease from-8.5‰, in the early Miocene to-10.0‰, in the late Miocene. The stable isotope-based paleoaltimetry results suggest that the elevation of the southwestern Qaidam basin was approximately 1500 m in the middle-late Eocene and Oligocene. Subsequently, during Miocene the crustal uplift process started and the elevation reached approximately 2000 m in the early Miocene and 2500 m in the late Miocene, which suggests large-scale growth of the northern Tibet Plateau during the Miocene.
基金the National Natural Science Foundation of China(49732070 ,49902018)the National Key Project for Basic Research on the Tibetan Plateau(G1998040805)the Key Project of the Ministry of Land and Resources of China(20010201).
文摘Eclogites have been recently discovered in the Xitieshan area in the middlesegment of the northern margin of the Qaidam basin. These eclogites, together with those recognizedearlier in the Yuka area of the western segment of the northern margin of the Qaidam basin and inthe Dulan area of the eastern segment of the northern margin of the Qaidam basin, form an eclogitebelt with a length of 350 km. A comparison of the eclogites from the Yuka and Xitieshan areassuggests that they show different country rocks, microtextures, mineral assemblages, and especially,different peak temperatures, PT paths during decompression and isotopic features. Eclogites fromthe Yuka area bear evidence of prograde metamorphism, such as prograde mineral relics in garnet andgrowth zoning of garnet, and hairpin-shaped PT paths with coincidence of the baric and thermal peaksof metamorphism, which reflect rapid burial and uplift. Sm-Nd isotopic determination shows obviousSm-Nd disequilibrium, and no isochron ages of Early Paleozoic metamorphism was obtained. On thecontrary, the Xitieshan eclogite was subjected to metamorphism of higher eclogite-facies andpost-eclogite-facies temperatures, showing an obvious granulite-facies overprint. A tentative PTpath for the Xitieshan area suggests that the baric peak preceded the thermal culmination. Wholerock-garnet-omphacite Sm-Nd isotopic data give an isochron age in the Early Paleozoic. Thedifferences between the two eclogites imply their different tectonic-thermal history during theirburial and uplift.
基金supported by the National Natural Science Foundation of China(No.41572090)National Science and Technology Major Project(No.2016ZX05041004–003)
文摘Palaeodrainage basin,as an important component of the source-to-sink system,contains critical information on provenance and palaeoenvironment.Previous studies indicate that the scaling relationships of source-to-sink system components generally follow power laws,and channel-belt thickness represents a reliable first-order proxy for the drainage area.In this study,a database of borehole cores and geophysical well logs of the Jurassic coal measures from Saishiteng area in the northern Qaidam Basin was used to reconstruct the palaeogeography,and to identify single-story channel-belts.Three palaeochannels,namely,River A,River B and River C,were identified which were persistent throughout the Dameigou and Shimengou Formations during the Middle Jurassic.The mean channel-belt thicknesses of River A,River B and River C in the Dameigou Formation were 9.8 m,8.9 m and 7.9 m,respectively,and those in the Shimengou Formation were 7.4 m,6.2 m and 5.4 m,respectively.We estimate the drainage area of three major rivers by using scaling relationships between drainage area and channel-belt thickness.The drainage areas of River A,River B and River C in the Dameigou Formation were 63.0×10~3 km^2,50.1×10~3 km^2 and 37.7×10~3 km^2,respectively,and those in the Shimengou Formation were 32.3×10~3 km^2,21.2×10~3 km^2 and15.3×10~3 km^2,respectively.The drainage basin lengths of River A,River B and River C in the Dameigou Formation were 300.4 km,239 km and 180.2 km,respectively,and those in the Shimengou Formation were 154.3 km,101.3 km and 73.1 km,respectively.For both the Dameigou and Shimengou Formations,River A showed the largest scale,followed by River B and River C succeedingly,which was mainly determined by the stretch direction of provenance in the southern Qilian Mountains.The variations of channel-belt thickness,drainage area and drainage basin length between Dameigou and Shimengou Formations are the response of source-to-sink system to the transformation from extension to compression depression during the Middle Jurassic in the northern Qaidam Basin.
基金Financial support from the National Natural Science Foundation of China (No. 40730422)the Priority Academic Program Development of Jiangsu Higher Education Institutions of Chinadata provided by Jurassic Project Department in Research Institute of Petroleum Exploration and Development of China are gratefully acknowledged
文摘The current study tested the gas component and carbon isotopic composition of gas samples from 6 oilgas fields at the northern margin of Qaidam Basin, and established a chart to quantitatively identify the mixing ratio of source-mixed gas. Besides, this research quantitatively investigated the natural gas generated by different types of organic matter. The results show that different ratios of source-mixed gas exist in the 6 oil-gas fields at the northern margin of Qaidam Basin. Among them, Mabei has the highest mixing ratio of coal-type gas, followed by Nanbaxian, Mahai, Lenghu-4, Lenghu-3 and Lenghu-5, with the ratios of coal-type gas 91%, 87%, 83%, 66%, 55% and 36%, respectively. Lenghu-3 and Lenghu-4 oil-gas fields were mainly filled by coal-type gas earlier. For Lenghu-3, the gas was mainly generated from low matured source rocks in lower Jurassic Series of Lengxi sub-sag. For Lenghu-4, the gas was mainly generated from humus-mature source rocks in lower Jurassic Series of the northern slope of Kunteyi sub-sag. Gas in Lenghu-5 was mainly later filled oil-type gas, which was generated from high matured sapropelics in lower Jurassic Series of Kunteyi sub-sag. Earlier filled coal-type gas was the main part of Mahai, Nanbaxian and Mabei oil-gas fields. Gas source of Mahai was mainly generated from high mature humics in lower Jurassic Series of Yibei sub-sag; for Nanbaxian, the gas was mainly generated from high matured humics in middle-lower Jurassic Series of Saishiteng sub-sag; for Mabei, the gas was mainly generated from humus-mature source rocks in middle Jurassic Series of Yuqia sub-sag.
基金Project XQ-2004-01 supported by the National Oil Project of China
文摘We investigated the geological factors associated with unsuccessful exploration wells in the northern margin of the Qaidam basin to better understand their cause.The structural situation,the hydrocarbon accumulation mechanism and unsuccessful well data collected from 1996 to 2005 were studied.The results show that the main geological factors associated with unsuccessful exploration wells are a lack of effective source rocks and a lack of effective traps,as well as the migration-accumulation conditions that exist in this area.The basin was reformed by Meso-Cenozoic tectonic evolution.Multi-stage tectonic activities have both positive and negative effects on hydrocarbon accumulation.Source rocks distribution,effective migration channels,effective traps and the tectonic evolution effects on hydrocarbons should be the key objects for further studies.