The high-quality laminated source rock organic matter(OM)originated from planktonic algae,and its sedimentation was affected by global climate change significantly in the upper Xiaganchaigou Formation of the western Q...The high-quality laminated source rock organic matter(OM)originated from planktonic algae,and its sedimentation was affected by global climate change significantly in the upper Xiaganchaigou Formation of the western Qaidam Basin.However,coupling research on the paleoenvironment change and OM enrichment during the sedimentation period of the source rock is still lacking.This study from the aspects of sedimentary petrology,geochemistry and paleontology palynology,the paleoenvironment of source rock is restored and the OM enrichment model is established in the study area.Firstly,kerogen maceral identification indicates that the kerogen maceral is mainly composed of Botryococcus,accompanied with amorphous organic matter and plant debris.Secondly,arid climate and relatively active tectonic were observed during the deposition of the source rock.The water column was received felsic source from the continental island arc tectonic background,and has the environmental characteristics of relatively saline,shallow depth,medium low productivity,fast sedimentation rate and anoxic reduction and so on.Lastly,the first-order controlling factors for the OM enrichment are anoxic water conditions and suitable sedimentation rate,and the secondary controlling factor is paleoproductivity.Through the coupling study of paleoclimate,paleoenvironment and OM enrichment,the paleoclimate high frequency alternating evolution was the root cause of sedimentary environment change and OM enrichment of the laminated shale in the Upper Xiaganchaigou Formation.The study on the OM enrichment mechanism of algae in Qaidam provides a good model for understanding the coupling relationship between the algae bloom in the saline lake basins and the environments,and provides important theoretical basis for predicting shale oil“sweet spot”and production well sites arrangement for the continental saline lacustrine basins.展开更多
Numerous Indosinian igneous rocks in the North Qaidam(NQ)provide crucial insights into the tectonic evolution of the Paleo-Tethys Ocean.This paper presents a comprehensive study of the petrography,mineralogy,geochemis...Numerous Indosinian igneous rocks in the North Qaidam(NQ)provide crucial insights into the tectonic evolution of the Paleo-Tethys Ocean.This paper presents a comprehensive study of the petrography,mineralogy,geochemistry,zircon U-Pb geochronology,and Hf isotope composition of dioritic rocks from the eastern NQ.Zircon U-Pb dating results indicate that the dioritic rocks were formed during the Middle Triassic(244-240 Ma).The rocks exhibit high-K calc-alkaline characteristics with variable SiO_(2)(55.25-65.39 wt%)and elevated K_(2)O+Na_(2)O(4.81-6.94 wt%)contents.They show enrichment in LILEs(Rb,Ba,K)and depletion in HFSEs(Nb,Ta,Ti),with slight negative Eu anomalies(Eu/Eu*=0.89-0.97).Zirconε_(Hf)(t)values(−20.93 to+5.60)and T_(DM2)ages(0.85-1.72 Ga)suggest mixed sources.Petrographic and mineralogical analysis reveals that the plagioclase phenocrysts exhibit disequilibrium textures(including reverse zoning),primarily composed of andesine and labradorite,with a small amount of oligoclase.The clinopyroxenes are all augites and have high crystallization temperatures(1111-1151℃).These features,particularly the reverse zoning of plagioclase,support a petrogenetic model involving mantle-derived magma underplating that induced melting of ancient lower crust,followed by mixing of underplated basaltic magma with crust-derived felsic magma.Our results indicate formation in a back-arc extensional setting during subduction of the Zongwulong Paleo-Tethys Ocean.展开更多
As shallow salt lake resources are increasingly exploited,deep confined brine has become a strategic alternative due to its widespread distribution and significant reserve potential.However,unfavorable reservoir chara...As shallow salt lake resources are increasingly exploited,deep confined brine has become a strategic alternative due to its widespread distribution and significant reserve potential.However,unfavorable reservoir characteristics,particularly low permeability and poor recovery efficiency,have historically rendered these deposits uneconomic,restricting their utilization.Taking the Mahai Salt Lake in the Qaidam Basin as a representative case,this study investigates the structural controls on brine enrichment through an integrated approach.Previous long-term metallogenic studies and exploration data indicate occurrences of an extensional fault zone favorable for brine accumulation.Therefore,we applied InSAR deformation analysis to assess coseismic and postseismic surface responses.Combined with radon-222 emanation mapping,our findings reveal a strong spatial correlation between high-productivity brine boreholes and active fault systems.The existence of active faults enhance brine migration and storage,provided that the target reservoirs have substantial halite thickness and maintain relatively low clay-silt content.展开更多
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 proven...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 East Kunlun Mountain.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 PaleoTethys 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 East Kunlun Mountain is significantly different from that in the South Qilian Mountain but is similar to that in the Altyn Tagh Mountain.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 East Kunlun Mountain and South Qilian Mountain in the formation and evolution process.展开更多
Territorial spatial ecological restoration is a crucial prerequisite for optimizing the territorial spatial patterns,enhancing the ecosystem functions,and achieving sustainable development at the regional scale.The Qa...Territorial spatial ecological restoration is a crucial prerequisite for optimizing the territorial spatial patterns,enhancing the ecosystem functions,and achieving sustainable development at the regional scale.The Qaidam Basin,located in the alpine arid region of the Qinghai–Xizang Plateau,China,is experiencing desertification,biodiversity loss,soil erosion,and environmental pollution.Selecting the Qaidam Basin as the study area,we identified 9 ecological sources in the region using the Morphological Spatial Pattern Analysis(MSPA)method and the landscape connectivity assessment,and extracted 10 significant corridors and 26 general corridors using the Minimum Cumulative Resistance(MCR)and Gravity models.Then,we determined 114 ecological"pinch points"and 42 ecological barrier points by employing the Circuit Theory,thereby constructing the ecological security pattern of the area.Further,we evaluated the ecosystem health of the Qaidam Basin during 2003–2023 using the Vitality–Organization–Resilience–Service(VORS)model.Finally,we integrated ecosystem health assessment and ecological security pattern to comprehensively identify the key areas for ecological restoration in the Qaidam Basin.The results revealed that the ecosystem in the basin fluctuated toward a healthier state from 2003 to 2023.The average ecosystem health index(EHI)for the basin decreased from 0.34 in 2003 to 0.28 in 2013,followed by a substantial recovery to 0.36 in 2023.Higher EHI values were found in the northeastern,southeastern,and southwestern fringes and lower values were located in the basin interior and northwestern region.During 2003–2023,the areas that exhibited a decrease in EHI were primarily located in the interior and northwestern regions of the basin,while those that exhibited an increase in EHI were located in the northeastern,southeastern,and southwestern fringes,demonstrating expanded spatial differences.This may be attributed to the fact that once an eco-environment is damaged,the ecological recovery of the vulnerable areas within the eco-environment will be slow and difficult.This study identified four types of ecological restoration areas,including corridor connectivity,artificial restoration,ecological recovery,and ecological enhancement zones,covering a total area of 6034.7 km2,and proposed targeted ecological restoration strategies according to these different categories.Our findings can serve as a valuable reference for optimizing the territorial spatial patterns,enhancing the ecosystem functions,and promoting sustainable development in the Qaidam Basin.展开更多
Determining the spatio-temporal distribution of the deformation tied to the India-Eurasian convergence and the impact of pre-existing weaknesses on the Cenozoic crustal deformation is significant for understanding how...Determining the spatio-temporal distribution of the deformation tied to the India-Eurasian convergence and the impact of pre-existing weaknesses on the Cenozoic crustal deformation is significant for understanding how the convergence between India and Eurasia contributed to the development of the Tibetan Plateau. The exhumation history of the northeastern Tibetan Plateau was addressed in this research using a new apatite fission track （AFT） study in the North Qaidam thrust belt （NQTB）. Three granite samples collected from the Qaidam Shan pluton in the north tied to the Qaidam Shan thrust, with AFT ages clustering in the Eocene to Miocene. The other thirteen samples obtained from the Luliang Shan and Yuka plutons in the south related to the Luliang Shan thrust and they have showed predominantly the Cretaceous AFT ages. Related thermal history modeling based on grain ages and track lengths indicates rapid cooling events during the Eocene-early Oligocene and since late Miocene within the Qaidam Shan, in contrast to those in the Cretaceous and since the Oligocene-Miocene in the Luliang Shan and Yuka region. The results, combined with published the Cretaceous thermochronological ages in the Qaidam Shan region, suggest that the NQTB had undergo rapid exhumation during the accretions along the southern Asian Andean-type margin prior to the India-Eurasian collision. The Cenozoic deformation initially took place in the North Qaidam thrust belt by the Eocene, which is consistent with the recent claim that the deformation of the northeastern Tibetan Plateau initiated in the Eocene as a response to continental collision between India and Eurasia. The immediate deformation responding to the collision is tentatively attributed to the preexisting weaknesses of the lithosphere, and therefore the deformation of the northeastern Tibetan Plateau should be regarded as a boundary-condition-dependent process.展开更多
The geochemical analysis and experimental simulation are comprehensively used to systematically study the hydrocarbon generation material,organic matter enrichment and hydrocarbon generation model of Paleogene source ...The geochemical analysis and experimental simulation are comprehensively used to systematically study the hydrocarbon generation material,organic matter enrichment and hydrocarbon generation model of Paleogene source rock in the Western Qaidam Depression,Qaidam Basin,NW China.Three main factors result in low TOC values of saline lacustrine source rock of the Qaidam Basin:relatively poor nutrient supply inhibits the algal bloom,too fast deposition rate causes the dilution of organic matter,and high organic matter conversion efficiency causes the low residual organic carbon.For this type of hydrogen-rich organic matter,due to the reduction of organic carbon during hydrocarbon generation,TOC needs to be restored based on maturity before evaluating organic matter abundance.The hydrocarbon generation of saline lacustrine source rocks of the Qaidam Basin is from two parts:soluble organic matter and insoluble organic matter.The soluble organic matter is inherited from organisms and preserved in saline lacustrine basins.It generates hydrocarbons during low-maturity stage,and the formed hydrocarbons are rich in complex compounds such as NOS,and undergo secondary cracking to form light components in the later stage;the hydrocarbon generation model of insoluble organic matter conforms to the traditional“Tissot”model,with an oil generation peak corresponding to Ro of 1.0%.展开更多
Typical reefs in the Paleogene and early Neogene strata of the Qaidam Basin, Tibetan Plateau, China, reveal their internal structures and sedimentation environments and consist mainly of algal reef, stromatolite reef ...Typical reefs in the Paleogene and early Neogene strata of the Qaidam Basin, Tibetan Plateau, China, reveal their internal structures and sedimentation environments and consist mainly of algal reef, stromatolite reef and thrombolite reef with distinct reef structures, fore-reef, back-reef and reef-plateau. The fore-reef is characterized by a combination of pinnacle reef, thrombolite and algal reef. The back reef is composed of stromatolite reef and algal reef. The pinnacle reefs (micro-atoll), most of which are several tens of centimeters in diameter (whereas some exceptionally big ones are over 200 cm in diameter), and several tens of centimeter to 2 m in height, are situated on the far front-edge of the reef; the pinnacle reef is also often of recumbent form with a gravel-filled circular hole in the center. The algal reef is in the form of dome and irregular beds, and filled with algal detritus, ostracodes, spirorbis fossils, ooid and terrigenous debris, and worm traces; cavities and scour marks are often developed. The algal reef is gray commonly when fresh and weathers to a brown color. The lacustrine thrombolite in the Qaidam Basin is light gray or deep gray when fresh, white-gray or brown when weathered, dense and homogeneous with abundant pores filled by oil and bitumen. Observed under the microscope, the thrombolite consists mainly of brown or brown-black clots with a little algal debris, ooid, pellet, ostracodes, spirorbis fossils and terrigenous debris, in some cases, terrigenous debris, even gravel, is abundant. Many features of the thrombolite suggest that it is formed in a high-energy envkonment. The stromatolite reefs developed on the lacustrine algal reef in the Qaidam Basin are very complex whether in shape or in internal structure. The simplest ones form laminated layers and the most complex ones have intensely branching structures. The size is also variable.展开更多
The timing of onset of deposition of the Lulehe Formation is a significant factor in understanding the genesis of the Qaidam basin and the evolution of the Tibetan Plateau. Here, we describe a detailed magnetostratigr...The timing of onset of deposition of the Lulehe Formation is a significant factor in understanding the genesis of the Qaidam basin and the evolution of the Tibetan Plateau. Here, we describe a detailed magnetostratigraphic and magnetic fabric study of the middle and lower parts of the Lulehe Formation. A total of 234 samples were collected from 117 sites throughout a thickness of almost 460 m of fluvial and lacustrine deposits at the Xitieshan section in the northeastern Qaidam basin. Out of these sites, 94 sites yielded well-defined characteristic remanent magnetization components by stepwise thermal demagnetization and were used to establish the magnetostratigraphy of the studied section. Based on correlation with the geomagnetic polarity timescale, the studied section spans the period from 53.8 Ma to 50.7 Ma. Our results show a three-fold decrease in sedimentation rates as well as marked change in facies from braided river to delta and shore-shallow lake around 52.6 Ma, which suggests tectonic uplift of the northeastern Qaidam basin margin ridge was rapid at the onset of formation of the Qaidam basin and subsequently weakened after 52.6 Ma. The anisotropy of magnetic susceptibility results indicate that tectonic compression stress had reached the northeastern Tibetan Plateau by the early stages of Indo-Eurasian plate collision and that the direction of stress in the study area was NE-SW. Furthermore, a weakening of tectonic compression stress around 52.6 Ma is consistent with sedimentary records. The age of initial deposition of the Qaidam basin （around 53.8 Ma） was almost synchronous with that of the Qiangtang, Hoh Xil, Xining, and Lanzhou basins, which implies that stress was transferred rapidly through the Tibetan Plateau during or immediately after the onset of Indo-Eurasian collision.展开更多
Based on the systematic study of aromatic hydrocarbons in over 100 crude oil samples collected from the Tabei and Tazhong uplifts in the Tarim Basin,the western depression area in the Qaidam Basin and the Tabei depres...Based on the systematic study of aromatic hydrocarbons in over 100 crude oil samples collected from the Tabei and Tazhong uplifts in the Tarim Basin,the western depression area in the Qaidam Basin and the Tabei depression in the Turpan Basin,the geochemical characteristics of the marine（Tarim Basin）,saline lacustrine（Qaidam Basin）,and swamp（Turpan Basin） oils were investigated.The marine oils from the Tarim basin are characterized by relatively low abundance of diaromatic hydrocarbons such as biphenyl and naphthalene,and relatively high abundance of triaromatic hydrocarbons including phenanthrene,dibenzothiophene and fluorene.In contrast,the swamp oils from the Turpan Basin are dominated by the highest relative abundance of diaromatic hydrocarbons and the lowest relative abundance of triaromatic hydrocarbons in all the oil samples in this study.The relative abundance of diaromatic and triaromatic hydrocarbons in the saline lacustrine oils from Qaidam Basin is between that in Tarim oils and Turpan oils.Aromatic parameters based on the isomer distributions of dimethylnaphthalenes（DMN）,trimethylnaphthalenes（TMN）,tetramethylnaphthalenes（TeMN） and methylphenanthrenes（MP）,i.e.,1,2,5-trimethylnaphthalene（TMN）/1,3,6-TMN ratio,1,2,7-TMN/1,3,7TMN ratio,（2,6-＋2,7-）-dimethylnaphthalenes（DMN）/1,6-DMN ratio,1,3,7-TMN/（1,2,5-＋1,3,7-）TMN,1,3,6,7-TeMN/（1,3,6,7-＋1,2,5,6-＋1,2,3,5-）-TeMN ratio and MP index,may reflect the diversity of organic source input,thermal maturity and depositional environments.In addition,the dibenzothiophenes（DBTs）/fluorenes（Fs） and dibenzofurans（DBFs）/Fs ratios were found to the very useful and effective in determining genetic types of crude oils for the marine,saline lacustrine,and swamp depositional environments,and for oil-oil correlations.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
Geologists agree that the collision of the Indian and Asian plates caused uplift of the Tibet Plateau. However, controversy still exists regarding the modes and mechanisms of the Tibetan Plateau uplift. Geology has re...Geologists agree that the collision of the Indian and Asian plates caused uplift of the Tibet Plateau. However, controversy still exists regarding the modes and mechanisms of the Tibetan Plateau uplift. Geology has recorded this uplift well in the Qaidam Basin. This paper analyzes the tectonic and sedimentary evolution of the western Qaidam Basin using sub-surface seismic and drill data. The Cenozoic intensity and history of deformation in the Qaidam Basin have been reconstructed based on the tectonic developments, faults growth index, sedimentary facies variations, and the migration of the depositional depressions. The changes in the sedimentary facies show that lakes in the western Qaidam Basin had gone from inflow to still water deposition to withdrawal. Tectonic movements controlled deposition in various depressions, and the depressions gradually shifted southeastward. In addition, the morphology of the surface structures in the western Qaidam Basin shows that the Cenozoic tectonic movements controlled the evolution of the Basin and divided it into （a） the southern fault terrace zone, （b） a central Yingxiongling orogenic belt, and （c） the northern fold-thrust belt; divided by the XI fault （Youshi fault） and Youbei fault, respectively. The field data indicate that the western Qaidam Basin formed in a Cenozoic compressive tectonic environment caused by the India--Asia plate collision. Further, the Basin experienced two phases of intensive tectonic deformation. The first phase occurred during the Middle Eocene--Early Miocene （Xia Ganchaigou Fm. and Shang Ganchaigou Fro., 43.8- 22 Ma）, and peaked in the Early Oligocene （Upper Xia Ganchaigou Fro., 31.5 Ma）. The second phase occurred between the Middle Miocene and the Present （Shang Youshashan Fro. and Qigequan Fro., 14.9-0 Ma）, and was stronger than the first phase. The tectonic--sedimentary evolution and the orienta- tion of surface structures in the western Qaidam Basin resulted from the Tibetan Plateau uplift, and recorded the periodic northward growth of the Plateau. Recognizing this early tectonic--sedimentary evolution supports the previous conclusion that northern Tibet responded to the collision between India and Asia shortly after its initiation. However, the current results reveal that northern Tibet also experi- enced another phase of uplift during the late Neogene. The effects of these two stages of tectonic activity combined to produce the current Tibetan Plateau.展开更多
The eastern margin of the Qaidam Basin lies in the key tectonic location connecting the Qinling, Qilian and East Kunlun orogens. The paper presents an investigation and analysis of the geologic structures of the area ...The eastern margin of the Qaidam Basin lies in the key tectonic location connecting the Qinling, Qilian and East Kunlun orogens. The paper presents an investigation and analysis of the geologic structures of the area and LA-ICP MS zircon U-Pb dating of Paleozoic and Mesozoic magmatisms of granitoids in the basement of the eastern Qaidam Basin on the basis of 16 granitoid samples collected from the South Qilian Mountains, the Qaidam Basin basement and the East Kunlun Mountains. According to the results in this paper, the basement of the basin, from the northern margin of the Qaidam Basin to the East Kunlun Mountains, has experienced at least three periods of intrusive activities of granitoids since the Early Paleozoic, i.e. the magmatisms occurring in the Late Cambrian （493.1±4.9 Ma）, the Silurian （422.9±8.0 Ma-420.4±4.6 Ma） and the Late Permian-Middle Triassic （257.8±4.0 Ma-228.8＋1.5 Ma）, respectively. Among them, the Late Permian - Middle Triassic granitoids form the main components of the basement of the basin. The statistics of dated zircons in this paper shows the intrusive magmatic activities in the basement of the basin have three peak ages of 244 Ma （main）, 418 Ma, and 493 Ma respectively. The dating results reveal that the Early Paleozoic magmatism of granitoids mainly occurred on the northern margin of the Qaidam Basin and the southern margin of the Qilian Mountains, with only weak indications in the East Kunlun Mountains. However, the distribution of Permo-Triassic （P-T） granitoids occupied across the whole basement of the eastern Qaidam Basin from the southern margin of the Qilian Mountains to the East Kunlun Mountains. An integrated analysis of the age distribution of P-T granitoids in the Qaidam Basin and its surrounding mountains shows that the earliest P-T magmatism （293.6-270 Ma） occurred in the northwestern part of the basin and expanded eastwards and southwards, resulting in the P-T intrusive magmatism that ran through the whole basin basement. As the Cenozoic basement thrust system developed in the eastern Qaidam Basin, the nearly N-S-trending shortening and deformation in the basement of the basin tended to intensify from west to east, which went contrary to the distribution trend of N-S-trending shortening and deformation in the Cenozoic cover of the basin, reflecting that there was a transformation of shortening and thickening of Cenozoic crust between the eastern and western parts of the Qaidam Basin, i.e., the crustal shortening of eastern Qaidam was dominated by the basement deformation （triggered at the middle and lower crust）, whereas that of western Qaidam was mainly by folding and thrusting of the sedimentary cover （the upper crust）.展开更多
The Qaidam Basin, located in the northern margin of the Qinghai-Tibet Plateau, is a large Mesozoic-Cenozoic basin, and bears huge thick Cenozoic strata. The geologic events of the Indian- Eurasian plate-plate collisio...The Qaidam Basin, located in the northern margin of the Qinghai-Tibet Plateau, is a large Mesozoic-Cenozoic basin, and bears huge thick Cenozoic strata. The geologic events of the Indian- Eurasian plate-plate collision since -55 Ma have been well recorded. Based on the latest progress in high-resolution stratigraphy, a technique of balanced section was applied to six pieces of northeast- southwest geologic seismic profiles in the central and eastern of the Qaidam Basin to reconstruct the crustal shortening deformation history during the Cenozoic collision. The results show that the Qaidam Basin began to shorten deformation nearly synchronous to the early collision, manifesting as a weak compression, the deformation increased significantly during the Middle and Late Eocene, and then weakened slightly and began to accelerate rapidly since the Late Miocene, especially since the Quaternary, reflecting this powerful compressional deformation and rapid uplift of the northern Tibetan Plateau around the Qaidam Basin.展开更多
The Qarhan Salt Lake area is the Quaternary depocenter of the Qaidam Basin, and carries thick lacustrine sediments, as well as rich potassium and magnesium salt deposits. The abundant resources and thick sediments in ...The Qarhan Salt Lake area is the Quaternary depocenter of the Qaidam Basin, and carries thick lacustrine sediments, as well as rich potassium and magnesium salt deposits. The abundant resources and thick sediments in this lake provide an ideal place for the study of biogas formation and preservation, salt lake evolution, and the uplift of the Tibetan Plateau. In this study, we attempt to construct a paleomagnetic and ^(230)Th age model and to obtain information on tectonic activity and salt lake evolution through detailed studies on a 1300-m-long drill core(15DZK01) from the northwestern margin of the Qarhan Salt Lake area(Dongling Lake). Based on gypsum ^(230)Th dating, the age of the uppermost clastic deposit was calculated to be around 0.052 Ma. The polarity sequence consist of 13 pairs of normal and reversed zones,which can be correlated with subchrons C2r.1r-C1n of the geomagnetic polarity timescale(GPTS 2012)(from ~2.070 Ma to ~0.052 Ma). Sedimentary characteristics indicate that Dongling Lake witnessed freshwater environment between ~ 2.070 Ma and 1.546 Ma. During this period, the sedimentary record reflects primarily lakeshore, shallow-water and swamp environments, representing favourable conditions for the formation of hydrocarbon source rocks. Between 1.546 Ma and ~ 0.052 Ma, the Dongling Lake was in sulphate deposition stage, which contrasts with the central Qarhan Salt Lake area, where this stage did not occur in the meantime. During this stage, Dongling Lake was in a shallow saltwater lake environment, but several periods of reduced salinity occurred during this stage. During the late Pleistocene at ~0.052 Ma, the Dongling Lake experienced uplift due to tectonic activity, and saltwater migrated through the Sanhu Fault to the central Qarhan Salt Lake area, resulting in the absence of halite deposition stage. The residual saline water was concentrated into magnesium-rich brine due to the lack of freshwater, and few potassium salt deposits occur in the Dongling Lake area.展开更多
Late Paleozoic to Early Mesozoic granites are widespread in the southern Qaidam Basin, northern margin of the eastern Kunlun orogenic belt. Their petrogenesis can provide us insights into the tectonic evolution and cr...Late Paleozoic to Early Mesozoic granites are widespread in the southern Qaidam Basin, northern margin of the eastern Kunlun orogenic belt. Their petrogenesis can provide us insights into the tectonic evolution and crustal growth process in the Qaidam Basin. This paper reports Permian–Triassic granites from the Kunbei area, southwestern Qaidam Basin. Detailed zircon LA-ICP MS U-Pb dating reveals that the granites from the four drilling cores（q404, q406, q1612-8, q1613-8） have identical ages of 251±3, 256±4, 247±2, and 251±6 Ma, respectively, these ages are identical with the Permian–Triassic granites from the eastern Qaidam Basin. Detailed geochemical analyses indicate that these granites display typical affinities of highly-fractionated I-type granites：（1） they have high SiO_2（up to 76.5 wt.%）, Na_2O＋K_2O（7.91 wt.% to 9.48 wt.%） contents and high FeO^T/MgO values of 4.7 to 9.3, suggesting significant fractional crystallization;（2） their low A/CNK values of 0.54 to 1.03, no normative Al-rich minerals, inconsistent with the per-aluminous S-type granites;（3） their low Ga（14.5 ppm to 20.7 ppm） and 10 000×Ga/Al（2.23 to 3.03, most of them 〈2.6） values are inconsistent with the A-type granites;（4） the high Rb（191 ppm to 406 ppm） contents and Rb/Sr（2.1 to 13.4） ratios, as well as the significant negative Eu anomalies（0.10 to 0.42） also indicate significant fractional crystallization of feldspars;（5） their low P_2O_5 contents（0.02 wt.% to 0.10 wt.%） suggest the limited solubility of phosphorus in primitive metaluminous melts. In combination with the geological background, we propose that the Permian–Triassic highly-fractionated I-type granites resulted from partial melting of intra-crustal mafic rocks, and the primitive I-type granitic melts underwent significant fractional crystallization of feldspars. The occurrence of highly-fractionated I-type granites in the southwestern Qaidam Basin suggests a Permian–Triassic active continental margin in the northern margin of the East Kunlun orogenic belt.展开更多
Clay mineralogy and bulk mineral composition of Tertiary sediments in Qaidam were investigated using X-ray diffraction （XRD） and scanning electron microscopy in order to better understand regional climate change res...Clay mineralogy and bulk mineral composition of Tertiary sediments in Qaidam were investigated using X-ray diffraction （XRD） and scanning electron microscopy in order to better understand regional climate change resulting from uplift of the Northeast Tibetan Plateau. Climate change in Qaidam since -53.5 Ma could be divided into four stages： a warm and seasonally arid climate between -53.5 and 40 Ma, a cold and arid climate from -40 to 26 Ma, a warm and humid climate between -26 and 13.5 Ma, and a much colder and arid climate from -13.5 to 2.5 Ma, respectively. The illite crystallinity and sedimentary facies suggested that uplift events took place around ＆gt;52–50, -40–38, -26–15, -10–8, and ＆lt;5 Ma inthe Qaidam region, respectively. The climate in Qaidam Basin could have been controlled by global climate prior to 13.5 Ma. As the Tibetan Plateau reached a significant elevation by -13.5 Ma, and the climate cycles of the East Asian monsoon might add additional influence.展开更多
The thick, Eocene to Pliocene, sedimentary sequence in Qaidam Basin at the northern margin of the Tibetan Plateau records the surface uplift history of the northeastern Tibetan plateau. In this study, we present detai...The thick, Eocene to Pliocene, sedimentary sequence in Qaidam Basin at the northern margin of the Tibetan Plateau records the surface uplift history of the northeastern Tibetan plateau. In this study, we present detailed geochemistry, heavy mineral, and clay mineralogy data of the well preserved sedimentary record in the Dahongou section in the northeast of the Qaidam Basin. The results suggest that the sedimentary sequence recorded a 30 Ma young uplift/unroofing event in the northern edge of the Qaidam Basin, which is characterized by high ZTR index value and chlorite content, and low CIW＇. The results are consistent with previous sedimentological studies of the Qaidam Basin, which indicated rapid increase of the accumulation rates around 30 Ma. Based on past thermochronological data from the mountains around the Qaidam Basin and the accumulation rates of the Cenozoic basins in the northeastern Tibetan Plateau, we infer a regional uplift and denudation event along the northeastern Tibetan Plateau during early Oligocene （-30 Ma）, indicating that the Tibetan Plateau had expanded north-eastward of the study area at that time.展开更多
Standardization is one of the important procedures in dendroclimatology. We used abundant Qilian juniper （Sabina przewalskii Kom.） tree-ring samples from the eastern margin of the Qaidam Basin to develop a new stand...Standardization is one of the important procedures in dendroclimatology. We used abundant Qilian juniper （Sabina przewalskii Kom.） tree-ring samples from the eastern margin of the Qaidam Basin to develop a new standardization method, i.e. total growth curve （TGC）. The samples that contained the complete pith and reached to the growing culmination around the 40th-60th year were used to fit TGC, and the generalized negative exponential function was used to fit the curve. Usually, most cores cannot reach the arboreal pith for some reasons and it is difficult to determine the arboreal cambial age. The empirical model of initial radial growth （IRG） was employed to estimate the number of rings missing from the pith by the same data and IRG model explained 90.9% of the variance. When developing the chronology, the cambial ages of cores that contained the complete pith were regarded as beginning from the first year and others were determined by the numbers of missing and included rings in the core. Standardization was accomplished by dividing each tree-ring series by corresponding TGC. The chronologies developed by TGC can retain more low-frequency variational information and TGC helps to develop more reliable tree-ring width chronology.展开更多
Due to the extremely arid climate in the western Qaidam Basin,the groundwater almost becomes the single water source for local residents and industrial production.It is necessary to know the reliable information on th...Due to the extremely arid climate in the western Qaidam Basin,the groundwater almost becomes the single water source for local residents and industrial production.It is necessary to know the reliable information on the groundwater cycle in this region for reasonable and sustainable exploitation of the groundwater resources with the further execution of recycling economy policies.This study focused on the recharge,the flow rate and the discharge of groundwater in the western Qaidam Basin through investigations on water chemistry and isotopes.Hydrological,chemical and isotopic characteristics show that the groundwater in the western Qaidam Basin was recharged by meltwater from new surface snow and old bottom glaciers on the northern slope of the Kunlun Mountains.In addition,the results also prove that the source water is enough and stable,and the rates of the circulation and renewal of the groundwater are relatively quick.Therefore,it can be concluded that the groundwater resources would guarantee the regional requirement if the meltwater volume of the mountains has not a great changes in future,moreover,water exploitation should be limited to the renewable amount of the groundwater reservoir in the western Qaidam Basin.展开更多
基金supported by the Joint Funds of the National Natural Science Foundation of China(No.2024DJ8702)the Science and Technology Research Project of the China National Petroleum Corporation(No.2024DJ87)+1 种基金the National Natural Science Foundation of China(No.42272029)the“Light of West China”Program of the Chinese Academy of Sciences(No.xbzglzb2022025)。
文摘The high-quality laminated source rock organic matter(OM)originated from planktonic algae,and its sedimentation was affected by global climate change significantly in the upper Xiaganchaigou Formation of the western Qaidam Basin.However,coupling research on the paleoenvironment change and OM enrichment during the sedimentation period of the source rock is still lacking.This study from the aspects of sedimentary petrology,geochemistry and paleontology palynology,the paleoenvironment of source rock is restored and the OM enrichment model is established in the study area.Firstly,kerogen maceral identification indicates that the kerogen maceral is mainly composed of Botryococcus,accompanied with amorphous organic matter and plant debris.Secondly,arid climate and relatively active tectonic were observed during the deposition of the source rock.The water column was received felsic source from the continental island arc tectonic background,and has the environmental characteristics of relatively saline,shallow depth,medium low productivity,fast sedimentation rate and anoxic reduction and so on.Lastly,the first-order controlling factors for the OM enrichment are anoxic water conditions and suitable sedimentation rate,and the secondary controlling factor is paleoproductivity.Through the coupling study of paleoclimate,paleoenvironment and OM enrichment,the paleoclimate high frequency alternating evolution was the root cause of sedimentary environment change and OM enrichment of the laminated shale in the Upper Xiaganchaigou Formation.The study on the OM enrichment mechanism of algae in Qaidam provides a good model for understanding the coupling relationship between the algae bloom in the saline lake basins and the environments,and provides important theoretical basis for predicting shale oil“sweet spot”and production well sites arrangement for the continental saline lacustrine basins.
基金supported by China Geological Survey Project(DD20190069 and DD20221636)Science and Technology Plan Project in Shaanxi Province,China(2023-JC-ZD-14,2023-JC-YB-236,2024JC-YBQN-0249,and 2022JQ-286).
文摘Numerous Indosinian igneous rocks in the North Qaidam(NQ)provide crucial insights into the tectonic evolution of the Paleo-Tethys Ocean.This paper presents a comprehensive study of the petrography,mineralogy,geochemistry,zircon U-Pb geochronology,and Hf isotope composition of dioritic rocks from the eastern NQ.Zircon U-Pb dating results indicate that the dioritic rocks were formed during the Middle Triassic(244-240 Ma).The rocks exhibit high-K calc-alkaline characteristics with variable SiO_(2)(55.25-65.39 wt%)and elevated K_(2)O+Na_(2)O(4.81-6.94 wt%)contents.They show enrichment in LILEs(Rb,Ba,K)and depletion in HFSEs(Nb,Ta,Ti),with slight negative Eu anomalies(Eu/Eu*=0.89-0.97).Zirconε_(Hf)(t)values(−20.93 to+5.60)and T_(DM2)ages(0.85-1.72 Ga)suggest mixed sources.Petrographic and mineralogical analysis reveals that the plagioclase phenocrysts exhibit disequilibrium textures(including reverse zoning),primarily composed of andesine and labradorite,with a small amount of oligoclase.The clinopyroxenes are all augites and have high crystallization temperatures(1111-1151℃).These features,particularly the reverse zoning of plagioclase,support a petrogenetic model involving mantle-derived magma underplating that induced melting of ancient lower crust,followed by mixing of underplated basaltic magma with crust-derived felsic magma.Our results indicate formation in a back-arc extensional setting during subduction of the Zongwulong Paleo-Tethys Ocean.
基金supported by the National Key Research and Development Program Projects(2023YFC2906502 and 2018YFC0604801)。
文摘As shallow salt lake resources are increasingly exploited,deep confined brine has become a strategic alternative due to its widespread distribution and significant reserve potential.However,unfavorable reservoir characteristics,particularly low permeability and poor recovery efficiency,have historically rendered these deposits uneconomic,restricting their utilization.Taking the Mahai Salt Lake in the Qaidam Basin as a representative case,this study investigates the structural controls on brine enrichment through an integrated approach.Previous long-term metallogenic studies and exploration data indicate occurrences of an extensional fault zone favorable for brine accumulation.Therefore,we applied InSAR deformation analysis to assess coseismic and postseismic surface responses.Combined with radon-222 emanation mapping,our findings reveal a strong spatial correlation between high-productivity brine boreholes and active fault systems.The existence of active faults enhance brine migration and storage,provided that the target reservoirs have substantial halite thickness and maintain relatively low clay-silt content.
基金supported by the Geological Survey of China(No.DD20221645)the National Natural Science Foundation of China(Nos.42171010,42072141,41702118)。
文摘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 East Kunlun Mountain.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 PaleoTethys 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 East Kunlun Mountain is significantly different from that in the South Qilian Mountain but is similar to that in the Altyn Tagh Mountain.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 East Kunlun Mountain and South Qilian Mountain in the formation and evolution process.
基金supported by the National Natural Science Foundation of China(41961045)the Shanxi Province Basic Research Program(202103021223253).
文摘Territorial spatial ecological restoration is a crucial prerequisite for optimizing the territorial spatial patterns,enhancing the ecosystem functions,and achieving sustainable development at the regional scale.The Qaidam Basin,located in the alpine arid region of the Qinghai–Xizang Plateau,China,is experiencing desertification,biodiversity loss,soil erosion,and environmental pollution.Selecting the Qaidam Basin as the study area,we identified 9 ecological sources in the region using the Morphological Spatial Pattern Analysis(MSPA)method and the landscape connectivity assessment,and extracted 10 significant corridors and 26 general corridors using the Minimum Cumulative Resistance(MCR)and Gravity models.Then,we determined 114 ecological"pinch points"and 42 ecological barrier points by employing the Circuit Theory,thereby constructing the ecological security pattern of the area.Further,we evaluated the ecosystem health of the Qaidam Basin during 2003–2023 using the Vitality–Organization–Resilience–Service(VORS)model.Finally,we integrated ecosystem health assessment and ecological security pattern to comprehensively identify the key areas for ecological restoration in the Qaidam Basin.The results revealed that the ecosystem in the basin fluctuated toward a healthier state from 2003 to 2023.The average ecosystem health index(EHI)for the basin decreased from 0.34 in 2003 to 0.28 in 2013,followed by a substantial recovery to 0.36 in 2023.Higher EHI values were found in the northeastern,southeastern,and southwestern fringes and lower values were located in the basin interior and northwestern region.During 2003–2023,the areas that exhibited a decrease in EHI were primarily located in the interior and northwestern regions of the basin,while those that exhibited an increase in EHI were located in the northeastern,southeastern,and southwestern fringes,demonstrating expanded spatial differences.This may be attributed to the fact that once an eco-environment is damaged,the ecological recovery of the vulnerable areas within the eco-environment will be slow and difficult.This study identified four types of ecological restoration areas,including corridor connectivity,artificial restoration,ecological recovery,and ecological enhancement zones,covering a total area of 6034.7 km2,and proposed targeted ecological restoration strategies according to these different categories.Our findings can serve as a valuable reference for optimizing the territorial spatial patterns,enhancing the ecosystem functions,and promoting sustainable development in the Qaidam Basin.
基金funded by the National Science Foundation of China(Grant No.41102128,41330207,41372206,41472181,and 41402170)the National S&T Major Project(Grant No.2016ZX05008-001 and 2016ZX05003-001)+1 种基金Research Funds from Bureau of Education Zhejiang Province(Grant No.Y201019040)the Fundamental Research Funds for the Central Universities(Grant No.2016FZA3007)
文摘Determining the spatio-temporal distribution of the deformation tied to the India-Eurasian convergence and the impact of pre-existing weaknesses on the Cenozoic crustal deformation is significant for understanding how the convergence between India and Eurasia contributed to the development of the Tibetan Plateau. The exhumation history of the northeastern Tibetan Plateau was addressed in this research using a new apatite fission track （AFT） study in the North Qaidam thrust belt （NQTB）. Three granite samples collected from the Qaidam Shan pluton in the north tied to the Qaidam Shan thrust, with AFT ages clustering in the Eocene to Miocene. The other thirteen samples obtained from the Luliang Shan and Yuka plutons in the south related to the Luliang Shan thrust and they have showed predominantly the Cretaceous AFT ages. Related thermal history modeling based on grain ages and track lengths indicates rapid cooling events during the Eocene-early Oligocene and since late Miocene within the Qaidam Shan, in contrast to those in the Cretaceous and since the Oligocene-Miocene in the Luliang Shan and Yuka region. The results, combined with published the Cretaceous thermochronological ages in the Qaidam Shan region, suggest that the NQTB had undergo rapid exhumation during the accretions along the southern Asian Andean-type margin prior to the India-Eurasian collision. The Cenozoic deformation initially took place in the North Qaidam thrust belt by the Eocene, which is consistent with the recent claim that the deformation of the northeastern Tibetan Plateau initiated in the Eocene as a response to continental collision between India and Eurasia. The immediate deformation responding to the collision is tentatively attributed to the preexisting weaknesses of the lithosphere, and therefore the deformation of the northeastern Tibetan Plateau should be regarded as a boundary-condition-dependent process.
基金Supported by the PetroChina Science and Technology Project(2021DJ1808).
文摘The geochemical analysis and experimental simulation are comprehensively used to systematically study the hydrocarbon generation material,organic matter enrichment and hydrocarbon generation model of Paleogene source rock in the Western Qaidam Depression,Qaidam Basin,NW China.Three main factors result in low TOC values of saline lacustrine source rock of the Qaidam Basin:relatively poor nutrient supply inhibits the algal bloom,too fast deposition rate causes the dilution of organic matter,and high organic matter conversion efficiency causes the low residual organic carbon.For this type of hydrogen-rich organic matter,due to the reduction of organic carbon during hydrocarbon generation,TOC needs to be restored based on maturity before evaluating organic matter abundance.The hydrocarbon generation of saline lacustrine source rocks of the Qaidam Basin is from two parts:soluble organic matter and insoluble organic matter.The soluble organic matter is inherited from organisms and preserved in saline lacustrine basins.It generates hydrocarbons during low-maturity stage,and the formed hydrocarbons are rich in complex compounds such as NOS,and undergo secondary cracking to form light components in the later stage;the hydrocarbon generation model of insoluble organic matter conforms to the traditional“Tissot”model,with an oil generation peak corresponding to Ro of 1.0%.
文摘Typical reefs in the Paleogene and early Neogene strata of the Qaidam Basin, Tibetan Plateau, China, reveal their internal structures and sedimentation environments and consist mainly of algal reef, stromatolite reef and thrombolite reef with distinct reef structures, fore-reef, back-reef and reef-plateau. The fore-reef is characterized by a combination of pinnacle reef, thrombolite and algal reef. The back reef is composed of stromatolite reef and algal reef. The pinnacle reefs (micro-atoll), most of which are several tens of centimeters in diameter (whereas some exceptionally big ones are over 200 cm in diameter), and several tens of centimeter to 2 m in height, are situated on the far front-edge of the reef; the pinnacle reef is also often of recumbent form with a gravel-filled circular hole in the center. The algal reef is in the form of dome and irregular beds, and filled with algal detritus, ostracodes, spirorbis fossils, ooid and terrigenous debris, and worm traces; cavities and scour marks are often developed. The algal reef is gray commonly when fresh and weathers to a brown color. The lacustrine thrombolite in the Qaidam Basin is light gray or deep gray when fresh, white-gray or brown when weathered, dense and homogeneous with abundant pores filled by oil and bitumen. Observed under the microscope, the thrombolite consists mainly of brown or brown-black clots with a little algal debris, ooid, pellet, ostracodes, spirorbis fossils and terrigenous debris, in some cases, terrigenous debris, even gravel, is abundant. Many features of the thrombolite suggest that it is formed in a high-energy envkonment. The stromatolite reefs developed on the lacustrine algal reef in the Qaidam Basin are very complex whether in shape or in internal structure. The simplest ones form laminated layers and the most complex ones have intensely branching structures. The size is also variable.
基金supported by Foundation of Geological Survey of China(no.1212011121261)the National Natural Science Foundation of China (no.40902049)+1 种基金the Special Fund for Basic Scienctific Research of Central Colleges, China University of Geoscience (Wuhan) (no.CUGL09206)the State Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences(no.GBL11207)
文摘The timing of onset of deposition of the Lulehe Formation is a significant factor in understanding the genesis of the Qaidam basin and the evolution of the Tibetan Plateau. Here, we describe a detailed magnetostratigraphic and magnetic fabric study of the middle and lower parts of the Lulehe Formation. A total of 234 samples were collected from 117 sites throughout a thickness of almost 460 m of fluvial and lacustrine deposits at the Xitieshan section in the northeastern Qaidam basin. Out of these sites, 94 sites yielded well-defined characteristic remanent magnetization components by stepwise thermal demagnetization and were used to establish the magnetostratigraphy of the studied section. Based on correlation with the geomagnetic polarity timescale, the studied section spans the period from 53.8 Ma to 50.7 Ma. Our results show a three-fold decrease in sedimentation rates as well as marked change in facies from braided river to delta and shore-shallow lake around 52.6 Ma, which suggests tectonic uplift of the northeastern Qaidam basin margin ridge was rapid at the onset of formation of the Qaidam basin and subsequently weakened after 52.6 Ma. The anisotropy of magnetic susceptibility results indicate that tectonic compression stress had reached the northeastern Tibetan Plateau by the early stages of Indo-Eurasian plate collision and that the direction of stress in the study area was NE-SW. Furthermore, a weakening of tectonic compression stress around 52.6 Ma is consistent with sedimentary records. The age of initial deposition of the Qaidam basin （around 53.8 Ma） was almost synchronous with that of the Qiangtang, Hoh Xil, Xining, and Lanzhou basins, which implies that stress was transferred rapidly through the Tibetan Plateau during or immediately after the onset of Indo-Eurasian collision.
基金funded by the National Natural Science Foundation of China (Grant No. 40973041)
文摘Based on the systematic study of aromatic hydrocarbons in over 100 crude oil samples collected from the Tabei and Tazhong uplifts in the Tarim Basin,the western depression area in the Qaidam Basin and the Tabei depression in the Turpan Basin,the geochemical characteristics of the marine（Tarim Basin）,saline lacustrine（Qaidam Basin）,and swamp（Turpan Basin） oils were investigated.The marine oils from the Tarim basin are characterized by relatively low abundance of diaromatic hydrocarbons such as biphenyl and naphthalene,and relatively high abundance of triaromatic hydrocarbons including phenanthrene,dibenzothiophene and fluorene.In contrast,the swamp oils from the Turpan Basin are dominated by the highest relative abundance of diaromatic hydrocarbons and the lowest relative abundance of triaromatic hydrocarbons in all the oil samples in this study.The relative abundance of diaromatic and triaromatic hydrocarbons in the saline lacustrine oils from Qaidam Basin is between that in Tarim oils and Turpan oils.Aromatic parameters based on the isomer distributions of dimethylnaphthalenes（DMN）,trimethylnaphthalenes（TMN）,tetramethylnaphthalenes（TeMN） and methylphenanthrenes（MP）,i.e.,1,2,5-trimethylnaphthalene（TMN）/1,3,6-TMN ratio,1,2,7-TMN/1,3,7TMN ratio,（2,6-＋2,7-）-dimethylnaphthalenes（DMN）/1,6-DMN ratio,1,3,7-TMN/（1,2,5-＋1,3,7-）TMN,1,3,6,7-TeMN/（1,3,6,7-＋1,2,5,6-＋1,2,3,5-）-TeMN ratio and MP index,may reflect the diversity of organic source input,thermal maturity and depositional environments.In addition,the dibenzothiophenes（DBTs）/fluorenes（Fs） and dibenzofurans（DBFs）/Fs ratios were found to the very useful and effective in determining genetic types of crude oils for the marine,saline lacustrine,and swamp depositional environments,and for oil-oil correlations.
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co-supposed by the Knowledge Innovation Program of the Chinese Academy of Sciences(No.KZCX2-EW-ON112)Open Fund of Key Laboratory of Petroleum Resources Research of the Chinese Academy of Sciences(No.KFJJ2010-07)
文摘Geologists agree that the collision of the Indian and Asian plates caused uplift of the Tibet Plateau. However, controversy still exists regarding the modes and mechanisms of the Tibetan Plateau uplift. Geology has recorded this uplift well in the Qaidam Basin. This paper analyzes the tectonic and sedimentary evolution of the western Qaidam Basin using sub-surface seismic and drill data. The Cenozoic intensity and history of deformation in the Qaidam Basin have been reconstructed based on the tectonic developments, faults growth index, sedimentary facies variations, and the migration of the depositional depressions. The changes in the sedimentary facies show that lakes in the western Qaidam Basin had gone from inflow to still water deposition to withdrawal. Tectonic movements controlled deposition in various depressions, and the depressions gradually shifted southeastward. In addition, the morphology of the surface structures in the western Qaidam Basin shows that the Cenozoic tectonic movements controlled the evolution of the Basin and divided it into （a） the southern fault terrace zone, （b） a central Yingxiongling orogenic belt, and （c） the northern fold-thrust belt; divided by the XI fault （Youshi fault） and Youbei fault, respectively. The field data indicate that the western Qaidam Basin formed in a Cenozoic compressive tectonic environment caused by the India--Asia plate collision. Further, the Basin experienced two phases of intensive tectonic deformation. The first phase occurred during the Middle Eocene--Early Miocene （Xia Ganchaigou Fm. and Shang Ganchaigou Fro., 43.8- 22 Ma）, and peaked in the Early Oligocene （Upper Xia Ganchaigou Fro., 31.5 Ma）. The second phase occurred between the Middle Miocene and the Present （Shang Youshashan Fro. and Qigequan Fro., 14.9-0 Ma）, and was stronger than the first phase. The tectonic--sedimentary evolution and the orienta- tion of surface structures in the western Qaidam Basin resulted from the Tibetan Plateau uplift, and recorded the periodic northward growth of the Plateau. Recognizing this early tectonic--sedimentary evolution supports the previous conclusion that northern Tibet responded to the collision between India and Asia shortly after its initiation. However, the current results reveal that northern Tibet also experi- enced another phase of uplift during the late Neogene. The effects of these two stages of tectonic activity combined to produce the current Tibetan Plateau.
基金supports by the Basic Research Foundation of the Institute of Geomechanics,CAGS,China (DZLXJK200703)the National Natural Science Foundation of China(40342015)+1 种基金SinoProbe-Deep Exploration in China(SinoProbe-08)the National Science Foundation(USA) Instrumentation and Facilities Program (EAR-0443387)
文摘The eastern margin of the Qaidam Basin lies in the key tectonic location connecting the Qinling, Qilian and East Kunlun orogens. The paper presents an investigation and analysis of the geologic structures of the area and LA-ICP MS zircon U-Pb dating of Paleozoic and Mesozoic magmatisms of granitoids in the basement of the eastern Qaidam Basin on the basis of 16 granitoid samples collected from the South Qilian Mountains, the Qaidam Basin basement and the East Kunlun Mountains. According to the results in this paper, the basement of the basin, from the northern margin of the Qaidam Basin to the East Kunlun Mountains, has experienced at least three periods of intrusive activities of granitoids since the Early Paleozoic, i.e. the magmatisms occurring in the Late Cambrian （493.1±4.9 Ma）, the Silurian （422.9±8.0 Ma-420.4±4.6 Ma） and the Late Permian-Middle Triassic （257.8±4.0 Ma-228.8＋1.5 Ma）, respectively. Among them, the Late Permian - Middle Triassic granitoids form the main components of the basement of the basin. The statistics of dated zircons in this paper shows the intrusive magmatic activities in the basement of the basin have three peak ages of 244 Ma （main）, 418 Ma, and 493 Ma respectively. The dating results reveal that the Early Paleozoic magmatism of granitoids mainly occurred on the northern margin of the Qaidam Basin and the southern margin of the Qilian Mountains, with only weak indications in the East Kunlun Mountains. However, the distribution of Permo-Triassic （P-T） granitoids occupied across the whole basement of the eastern Qaidam Basin from the southern margin of the Qilian Mountains to the East Kunlun Mountains. An integrated analysis of the age distribution of P-T granitoids in the Qaidam Basin and its surrounding mountains shows that the earliest P-T magmatism （293.6-270 Ma） occurred in the northwestern part of the basin and expanded eastwards and southwards, resulting in the P-T intrusive magmatism that ran through the whole basin basement. As the Cenozoic basement thrust system developed in the eastern Qaidam Basin, the nearly N-S-trending shortening and deformation in the basement of the basin tended to intensify from west to east, which went contrary to the distribution trend of N-S-trending shortening and deformation in the Cenozoic cover of the basin, reflecting that there was a transformation of shortening and thickening of Cenozoic crust between the eastern and western parts of the Qaidam Basin, i.e., the crustal shortening of eastern Qaidam was dominated by the basement deformation （triggered at the middle and lower crust）, whereas that of western Qaidam was mainly by folding and thrusting of the sedimentary cover （the upper crust）.
基金co-supported by the President Fund and Innovation Program of Chinese Academy of Sciences(no.:kzcx2-yw-104)the Chinese National Science Foundation grants(no.:40334038)the Science and Technology Key Project of Ministry of Education of China(no.:306016).
文摘The Qaidam Basin, located in the northern margin of the Qinghai-Tibet Plateau, is a large Mesozoic-Cenozoic basin, and bears huge thick Cenozoic strata. The geologic events of the Indian- Eurasian plate-plate collision since -55 Ma have been well recorded. Based on the latest progress in high-resolution stratigraphy, a technique of balanced section was applied to six pieces of northeast- southwest geologic seismic profiles in the central and eastern of the Qaidam Basin to reconstruct the crustal shortening deformation history during the Cenozoic collision. The results show that the Qaidam Basin began to shorten deformation nearly synchronous to the early collision, manifesting as a weak compression, the deformation increased significantly during the Middle and Late Eocene, and then weakened slightly and began to accelerate rapidly since the Late Miocene, especially since the Quaternary, reflecting this powerful compressional deformation and rapid uplift of the northern Tibetan Plateau around the Qaidam Basin.
基金co-supported by the Geological Survey Project of China(Grant No. 1212331413023)the National Natural Science Foundation of China(Grant No. U1407207)
文摘The Qarhan Salt Lake area is the Quaternary depocenter of the Qaidam Basin, and carries thick lacustrine sediments, as well as rich potassium and magnesium salt deposits. The abundant resources and thick sediments in this lake provide an ideal place for the study of biogas formation and preservation, salt lake evolution, and the uplift of the Tibetan Plateau. In this study, we attempt to construct a paleomagnetic and ^(230)Th age model and to obtain information on tectonic activity and salt lake evolution through detailed studies on a 1300-m-long drill core(15DZK01) from the northwestern margin of the Qarhan Salt Lake area(Dongling Lake). Based on gypsum ^(230)Th dating, the age of the uppermost clastic deposit was calculated to be around 0.052 Ma. The polarity sequence consist of 13 pairs of normal and reversed zones,which can be correlated with subchrons C2r.1r-C1n of the geomagnetic polarity timescale(GPTS 2012)(from ~2.070 Ma to ~0.052 Ma). Sedimentary characteristics indicate that Dongling Lake witnessed freshwater environment between ~ 2.070 Ma and 1.546 Ma. During this period, the sedimentary record reflects primarily lakeshore, shallow-water and swamp environments, representing favourable conditions for the formation of hydrocarbon source rocks. Between 1.546 Ma and ~ 0.052 Ma, the Dongling Lake was in sulphate deposition stage, which contrasts with the central Qarhan Salt Lake area, where this stage did not occur in the meantime. During this stage, Dongling Lake was in a shallow saltwater lake environment, but several periods of reduced salinity occurred during this stage. During the late Pleistocene at ~0.052 Ma, the Dongling Lake experienced uplift due to tectonic activity, and saltwater migrated through the Sanhu Fault to the central Qarhan Salt Lake area, resulting in the absence of halite deposition stage. The residual saline water was concentrated into magnesium-rich brine due to the lack of freshwater, and few potassium salt deposits occur in the Dongling Lake area.
基金Financial support for this study was jointly provided by the National Natural Science Foundation of China (No.41102037)the foundation for the author of National Excellent Doctoral Dissertation of China (No.201324)+1 种基金the Foundation of Young Excellent Scientists of the Shaanxi Province (No.2014KJXX-60)the MOST Special Fund from the State Key Laboratory of Continental Dynamics
文摘Late Paleozoic to Early Mesozoic granites are widespread in the southern Qaidam Basin, northern margin of the eastern Kunlun orogenic belt. Their petrogenesis can provide us insights into the tectonic evolution and crustal growth process in the Qaidam Basin. This paper reports Permian–Triassic granites from the Kunbei area, southwestern Qaidam Basin. Detailed zircon LA-ICP MS U-Pb dating reveals that the granites from the four drilling cores（q404, q406, q1612-8, q1613-8） have identical ages of 251±3, 256±4, 247±2, and 251±6 Ma, respectively, these ages are identical with the Permian–Triassic granites from the eastern Qaidam Basin. Detailed geochemical analyses indicate that these granites display typical affinities of highly-fractionated I-type granites：（1） they have high SiO_2（up to 76.5 wt.%）, Na_2O＋K_2O（7.91 wt.% to 9.48 wt.%） contents and high FeO^T/MgO values of 4.7 to 9.3, suggesting significant fractional crystallization;（2） their low A/CNK values of 0.54 to 1.03, no normative Al-rich minerals, inconsistent with the per-aluminous S-type granites;（3） their low Ga（14.5 ppm to 20.7 ppm） and 10 000×Ga/Al（2.23 to 3.03, most of them 〈2.6） values are inconsistent with the A-type granites;（4） the high Rb（191 ppm to 406 ppm） contents and Rb/Sr（2.1 to 13.4） ratios, as well as the significant negative Eu anomalies（0.10 to 0.42） also indicate significant fractional crystallization of feldspars;（5） their low P_2O_5 contents（0.02 wt.% to 0.10 wt.%） suggest the limited solubility of phosphorus in primitive metaluminous melts. In combination with the geological background, we propose that the Permian–Triassic highly-fractionated I-type granites resulted from partial melting of intra-crustal mafic rocks, and the primitive I-type granitic melts underwent significant fractional crystallization of feldspars. The occurrence of highly-fractionated I-type granites in the southwestern Qaidam Basin suggests a Permian–Triassic active continental margin in the northern margin of the East Kunlun orogenic belt.
基金supported by the China Geological Survey(No.1212011121261)the National Natural Science Foundation of China(Nos.41272053and41072030)+1 种基金Specialized Research Fund for the Doctoral Program of Higher Education of China(No.20110145110001)the Independent Research Project Foundation of State Key Laboratory of Biogeology and Envi-ronmental Geology,China University of Geosciences,Wuhan(No.GBL11307)
文摘Clay mineralogy and bulk mineral composition of Tertiary sediments in Qaidam were investigated using X-ray diffraction （XRD） and scanning electron microscopy in order to better understand regional climate change resulting from uplift of the Northeast Tibetan Plateau. Climate change in Qaidam since -53.5 Ma could be divided into four stages： a warm and seasonally arid climate between -53.5 and 40 Ma, a cold and arid climate from -40 to 26 Ma, a warm and humid climate between -26 and 13.5 Ma, and a much colder and arid climate from -13.5 to 2.5 Ma, respectively. The illite crystallinity and sedimentary facies suggested that uplift events took place around ＆gt;52–50, -40–38, -26–15, -10–8, and ＆lt;5 Ma inthe Qaidam region, respectively. The climate in Qaidam Basin could have been controlled by global climate prior to 13.5 Ma. As the Tibetan Plateau reached a significant elevation by -13.5 Ma, and the climate cycles of the East Asian monsoon might add additional influence.
基金supported by the Foundation of Geological Survey of China (No.1212011121261)the National Natural Science Foundation (Nos.: 40921062 and 40830212)
文摘The thick, Eocene to Pliocene, sedimentary sequence in Qaidam Basin at the northern margin of the Tibetan Plateau records the surface uplift history of the northeastern Tibetan plateau. In this study, we present detailed geochemistry, heavy mineral, and clay mineralogy data of the well preserved sedimentary record in the Dahongou section in the northeast of the Qaidam Basin. The results suggest that the sedimentary sequence recorded a 30 Ma young uplift/unroofing event in the northern edge of the Qaidam Basin, which is characterized by high ZTR index value and chlorite content, and low CIW＇. The results are consistent with previous sedimentological studies of the Qaidam Basin, which indicated rapid increase of the accumulation rates around 30 Ma. Based on past thermochronological data from the mountains around the Qaidam Basin and the accumulation rates of the Cenozoic basins in the northeastern Tibetan Plateau, we infer a regional uplift and denudation event along the northeastern Tibetan Plateau during early Oligocene （-30 Ma）, indicating that the Tibetan Plateau had expanded north-eastward of the study area at that time.
基金National Natural Science Foundation of China, No.40371118National Natural Science Foundation of China, No.90502009
文摘Standardization is one of the important procedures in dendroclimatology. We used abundant Qilian juniper （Sabina przewalskii Kom.） tree-ring samples from the eastern margin of the Qaidam Basin to develop a new standardization method, i.e. total growth curve （TGC）. The samples that contained the complete pith and reached to the growing culmination around the 40th-60th year were used to fit TGC, and the generalized negative exponential function was used to fit the curve. Usually, most cores cannot reach the arboreal pith for some reasons and it is difficult to determine the arboreal cambial age. The empirical model of initial radial growth （IRG） was employed to estimate the number of rings missing from the pith by the same data and IRG model explained 90.9% of the variance. When developing the chronology, the cambial ages of cores that contained the complete pith were regarded as beginning from the first year and others were determined by the numbers of missing and included rings in the core. Standardization was accomplished by dividing each tree-ring series by corresponding TGC. The chronologies developed by TGC can retain more low-frequency variational information and TGC helps to develop more reliable tree-ring width chronology.
基金Under the auspices of National Natural Science Foundation of China (No 40603007)
文摘Due to the extremely arid climate in the western Qaidam Basin,the groundwater almost becomes the single water source for local residents and industrial production.It is necessary to know the reliable information on the groundwater cycle in this region for reasonable and sustainable exploitation of the groundwater resources with the further execution of recycling economy policies.This study focused on the recharge,the flow rate and the discharge of groundwater in the western Qaidam Basin through investigations on water chemistry and isotopes.Hydrological,chemical and isotopic characteristics show that the groundwater in the western Qaidam Basin was recharged by meltwater from new surface snow and old bottom glaciers on the northern slope of the Kunlun Mountains.In addition,the results also prove that the source water is enough and stable,and the rates of the circulation and renewal of the groundwater are relatively quick.Therefore,it can be concluded that the groundwater resources would guarantee the regional requirement if the meltwater volume of the mountains has not a great changes in future,moreover,water exploitation should be limited to the renewable amount of the groundwater reservoir in the western Qaidam Basin.
