The change in the ecological environment in the arid core area is a critical issue in the context of global warming.To study the paleoclimate evolution,precise identification of minerals deposited in Asia’s arid hint...The change in the ecological environment in the arid core area is a critical issue in the context of global warming.To study the paleoclimate evolution,precise identification of minerals deposited in Asia’s arid hinterland,Lop Nur Salt Lake,NW China was conducted.The hyperspectral data of the salt crust was sampled to identify the species and content of sedimentary minerals,and the multispectral photos were used to reconstruct the salt crust morphology using the unmanned aerial vehicles platform.The SUnSAL(sparse unmixing by variable splitting and augmented Lagrangian)method was employed to inverse the sedimentary mineral components along the shoreline.The heterogeneity of salt and clay minerals in bright and dark ear-shaped strips was evaluated.The paleoclimatic environment associated with salt lake extinction was reconstructed by analyzing paleoclimate records of sediments,spectral reflectance and morphology of the salt crust.Results show that:(1)the variations in the micro-geomorphology of the salt crust are obviously the reason for the formation of bright and dark ear-shaped strips and the differences in the species and relative content of the sedimentary minerals are the microscopic reason.The high ratio of sedimentary salt minerals to clay minerals(RS/C)contributes to the high reflectivity,and the salt crust presents a bright texture.The low RS/C results in the low reflectivity,salt crust presents a dark texture;(2)the bright and dark ear-shaped strips represent warm-arid and cold-humid climates.The shape of the Lop Nur Lake shoreline evolved due to alternating warm-dry and cold-humid paleoclimate changes.展开更多
The Lop Nur Salt Lake, located in the eastern part of the Tarim Basin, Xinjiang, China, has become a playa in the Quaternary. Rhombic in shape, the Lop Nur depression is mainly controlled by the NE-striking and nearly...The Lop Nur Salt Lake, located in the eastern part of the Tarim Basin, Xinjiang, China, has become a playa in the Quaternary. Rhombic in shape, the Lop Nur depression is mainly controlled by the NE-striking and nearly N-S-striking sets of faults. Since 1995, a superlarge brine potash deposit with potash resources of 2.50×108 t has been found in the Luobei subbasin in the northeastern part of the Lop Nur. We intensively studied the features and formation mechanism of faults inside the Lop Nur through satellite images, geomorphologic survey and continuous conductivity imaging and found seven subparallel graben faults formed under the action of nearly N 10o E principal compressional stress during deposition of the Lop Nur Salt Lake. These faults are up to >60 km long and 1–4 km wide and may extend downward for 1000 m or more. It is just under the action of these tensional faults that potash subbasins formed. The largest subbasin is the Luobei subbasin and the smaller ones are the Luoxi hollow, Erbei hollow and Tienan hollow. Investigation also indicates that the graben faults in the Lop Nur not only control the origin of the potash subbasins, but they themselves are also good brine reservoir structures, in which abundant potash-rich brines are stored. Therefore, The faults had played an important role in the potash formation of the Lop Nur.展开更多
Potash deposits commonly accumulate in highly restricted settings at the final stage of brine evaporation. This does not mean that potash deposits are formed simply as a result of the evaporation concentration of seaw...Potash deposits commonly accumulate in highly restricted settings at the final stage of brine evaporation. This does not mean that potash deposits are formed simply as a result of the evaporation concentration of seawater or lake water, but rather as a coupling result of particular provenance, tectonics and climate activities. In this paper, we focus on the formative mechanism of the potash deposits of Lop Nur depression in Tarim Basin to interpret the detailed coupling mechanism among provenance, tectonics and climate. In terms of the provenance of Lop Nur Lake, the water of the Tarim River which displays "potassium-rich" characteristics play an important role. In addition, the Pliocene and Lower-Middle Pleistocene clastic beds surrounding Lop Nur Lake host a certain amount of soluble potassium and thus serves as "source beds" for potash formation. During the late Pliocene, the Lop Nur region has declined and evolved into a great lake from the previous piedmont and diluvial fan area. Since the mid Pleistocene, the great-united Lop Nur Lake has been separated and has generated a chain system consisting of Taitema Lake, Big Ear Lake and Luobei Lake which has turned into the deepest sag in Lop Nur Lake. Dry climate in Lop Nur region has increased since the Pliocene, and became extreme at the late Pleistocene. The study implies that potash formation in Lop Nur Lake depends on the optimal combination of extreme components of provenance, tectonics and climate during a shorter-term period. The optimal patterns of three factors are generally characterized by the long-term accumulation and preliminary enrichment of potassium, the occurrence of the deepest sub-depression and the appearance of an extremely arid climate in Lop Nur region. These factors have been interacting synergistically since the forming of the saline lake and in the later stages strong "vapor extraction" caused by extremely arid climate is needed to trigger large scale mineralization of potash deposits.展开更多
Since the middle Early Pleistocene (1.20 Ma B.P.), the desert steppe climate and environment have predominated in the Lop Nur area, Xinjiang, characterized by warm humid epochs interrupted by dry cold intervals. The g...Since the middle Early Pleistocene (1.20 Ma B.P.), the desert steppe climate and environment have predominated in the Lop Nur area, Xinjiang, characterized by warm humid epochs interrupted by dry cold intervals. The grain-size and magnetic susceptibility curves record 30 climatic oscillations, each with a ca. 40 ka cycle, in the area since 1.2 Ma B.P., which reflects the controlling effects exerted by the astronomic factor on the environment. The Quaternary sedimentary environment in the Lop Nur gradually changed from a fresh lake through a brackish lake to a saline lake, showing a spiral evolution, and finally it evolved into a playa.展开更多
Extremely saline soils are very harsh environments for the growth and survival of most plant species, however, halophytes can grow well. The underlying mechanism of halophyte to resist high saline is not well understo...Extremely saline soils are very harsh environments for the growth and survival of most plant species, however, halophytes can grow well. The underlying mechanism of halophyte to resist high saline is not well understood by us. This study was conducted at the potash mine near the Lop Nur, China, where the effects of the halophyte Suaeda salsa L. on the saline-alkaline soils and its growth and sustainability were investigated. Four plots(in which the salt encrustation layers were removed), with different soil treatments were evaluated:(1) undisturbed soil, with no additional treatment(T1);(2) the slag soil zone, in which a 40-cm layer of slag was placed on the undisturbed soil surface(T2);(3) slag+sandy soil, in which a 20-cm layer of slag was placed in the lower layer and 20 cm of sandy soil, taken from an area about 70 km away from Lop Nur potash mine, where Tamarix species were growing, was placed in the upper layer(T3); and(4) a 40-cm sandy soil layer taken from the area where Tamarix species were growing was placed on undisturbed soil(T4). Soil nutrient contents increased in the four treatments, but salt content only decreased in the T1 treatment. Salt content in the T4 treatment increased over the two-year period, which may be partly attributed to salt deposition from wind-blown dust within the mine and salt accumulation within the surface soil(0–20 cm) in response to high evaporative demands. The S. salsa plants exhibited greater improvements in growth under the T4 treatment than under the T1, T2, and T3 treatments, which demonstrated that low levels of salinity are beneficial for the growth of this species. The T1 treatment was sustainable because of its low cost and superior soil improvement characteristics. Therefore, S. salsa plants not only reduced soil salinity and increased soil nutrient levels, but also ameliorated the plant growth environment, which would be beneficial for both the ecological restoration of the Lop Nur area and similar areas throughout the world.展开更多
Many yellow silt layers have been identified in the Holocene sediments in the last lake of Lop Nur (playa),Xinjiang, northwestern China. Statistics of drill-hole cores have revealed more than one hundred layers, which...Many yellow silt layers have been identified in the Holocene sediments in the last lake of Lop Nur (playa),Xinjiang, northwestern China. Statistics of drill-hole cores have revealed more than one hundred layers, which exhibitregularity in time sequence. Study has further verified that these yellow silt layers were deposited through eolianprocesses. The time-frequency distribution diagram shows an obvious peak occurring at about 8200 a B.P., which isconsistent with the dry, windy and cold climate event occurring at 8200 a in other places around the world. Therefore, thisevent is regarded as a response to the global climate change.展开更多
Located in the eastern part of the Tarim basin, Xinjiang, the Lop Nur was an ultimate water catchment area of the Tarim basin during the Quaternary. Through nearly ten years of investigation and research, the authors ...Located in the eastern part of the Tarim basin, Xinjiang, the Lop Nur was an ultimate water catchment area of the Tarim basin during the Quaternary. Through nearly ten years of investigation and research, the authors have found a superlarge brine potash deposit in the Luobei subbasin—a secondary basin of the Lop Nur depression. The deposit has been mined now. On that basis, the authors propose new theories on the genesis of the potash rock deposit. In the tectonic and geomorphologic contexts, the Tarim basin lies in a "high mountain-deep basin" environment. At the beginning of the Quaternary, influenced by the neotectonic movement, the Lop Nur evolved into a "deep basin" in the Tarim basin. At the end of the middle Pleistocene, neotectonic migration began to take place in the interior of the Lop Nur and a new secondary deep basin—the Luobei subbasin—formed gradually. Despite its small area, it is actually the deepest subbasin in the Lop Nur depression, where brines of the Lop Nur Salt Lake gather and evaporate, thus providing materials for the formation of a superlarge brine potash rock deposit. With respect to the phenomenon of brine concentration and change with deepening of the lake, the authors propose a model of "high mountain-deep basin" tectonic migration for potash concentration. In the sedimentological context, the honeycomb-shaped voids developed in glauberite rock in the subbasin are good space for potash-rich brine accumulation. Study indicates that the deposition of glauberite requires recharge of calcium-rich water. In the Tarim area the calcium-rich water might come from deep formation water or oilfield water, and the river water recharging the Lop Nur Salt Lake was rich in sulfate radicals and other components; in addition, the climate in the area was very dry and the brine evaporated steadily, thus resulting in deposition of substantial amount of glauberite, potash accumulation in intercrystal brine and final formation of the potash deposit. Generally, potash formation in a salt lake undergoes a three-stage process of "carbonates—?sulfates (gypsum and glauberite)—^chlorides (halite etc.)", but in the study area there only occurred a two-stage process of "carbonates—>sulfates (gypsum and glauberite)". The authors call this new geological phenomenon the "two-stage potash formation" model. In conclusion, the superlarge Lop Nur potash deposit is the result of combined "high mountain-deep basin" tectonism and "two-stage potash formation".展开更多
The causes of the disappearance of the ancient town of Loulan in Xinjiang, China have been generally agreed to derive from two factors: human activities and natural factors (environmental variations). In this paper, t...The causes of the disappearance of the ancient town of Loulan in Xinjiang, China have been generally agreed to derive from two factors: human activities and natural factors (environmental variations). In this paper, the Muzart Glacier was selected as an example, and found that the length of the glacier has been gradually decreasing and the snow line has been retreating to a higher altitude, both results contributing to a decrease in river flow below the Muzart Glacier. From the distribution of moraines in the Tianshan Mountains and adjacent areas in different periods, the paper speculates that there have been four minor glacial periods since the Quaternary. Although the durations and scales of the four minor glacial periods were different, they all indirectly influenced the formation and disappearance of the Lop Nur Lake. The events of the fourth minor glacial period are the important impact factors in the existence and disappearance of Loulan. Whether the disappearance of Loulan can be related to the events of the three previous minor glacial periods needs further investigation.展开更多
Saline lakes are useful repositories for paleo-climatic records. In recent years, magnetic properties of saline lake sediments have been widely applied to establish paleo-climatic change. However,the influence factors...Saline lakes are useful repositories for paleo-climatic records. In recent years, magnetic properties of saline lake sediments have been widely applied to establish paleo-climatic change. However,the influence factors of magnetic properties in saline lakes have not been fully understood, which complicates the paleoenvironmental interpretation.Here, we present a rock magnetic analyses result of LOP_1 profile(40°26′09″′N, 90°21′23″E) from Lop Nur, a well-known saline lake, located in the eastern Tarim Basin in northwestern China. We combined the particle size, total organic content, and mineral characteristics analysis to assess the influence factors of magnetic properties in Lop Nur and its environmental significance. The results indicate that early diagenesis is the major influence factor on magnetic properties of Lop Nur saline sediments.Authigenic greigite and pyrite are identified within organic-rich sediments, which produce zones with high and low magnetic susceptibilities, respectively.The different authigenic iron sulfide contents in different layers are related to sedimentary environment changes. Sufficient supplies of organic matter and sulphate and low sedimentation rates favour the pyritization process. Moreover, if pyritization was constrained, intermediate greigite formed and was preserved. In oxidizing environments, sediment magnetic properties are consistent with those of source materials from Tarim Basin and are mainly controlled by particle size and hydrodynamic sorting of mainly detrital magnetite is largely unaffected by early diagenesis. Our study demonstrates that magnetic properties can provide a robust approach for studying depositional environment change in saline lake. In addition, the information obtained in this study would also provide insights into the geochemical processes of iron element in saline lakes.展开更多
A 10.35-m-long sediment core from the Luobei depression in Lop-Nur,Xinjiang,Northwest China,provides detailed information about environmental changes during the Late Pleistocene.The samples taken every 5 cm of the cor...A 10.35-m-long sediment core from the Luobei depression in Lop-Nur,Xinjiang,Northwest China,provides detailed information about environmental changes during the Late Pleistocene.The samples taken every 5 cm of the core were analyzed for 10 environmental proxies,including magnetic susceptibility,granularity,chroma,carbonate and loss on ignition(LOI),and pH value.The chronology data are provided by the uranium/thorium disequi-librium dates.The sediments of the section were deposited during the last 32000 years.The results of analysis of 10 proxies were examined using multivariate statistical analysis,and the principal components were calculated.According to the results,the Late Pleistocene sequence contains four climatic and environmental stages appearing in the cycles of cold-wet and warm-dry changes.During 10-9 ka BP,it was the earliest warm episode in the Holocene.Environmental changes in this district were restricted by global change,as suggested by the analysis of glacial-interglacial cycles.But it was different from the mutative trend of a monsoon region in East China because of its own characteristics,which was the situation of cold-wet and warm-dry climate-environment change.The candidate reason may be the uplift of the Tibet Plateau and the westerly wind circulation.展开更多
基金Supported by the National Natural Science Foundation of China(Nos.42071313,41571363)the Science and Technology Project for Black Soil Granary(No.XDA28080500)the Scientific Investigation of Natural and Cultural Heritage of Lop Nur Region(No.2014FY210500)。
文摘The change in the ecological environment in the arid core area is a critical issue in the context of global warming.To study the paleoclimate evolution,precise identification of minerals deposited in Asia’s arid hinterland,Lop Nur Salt Lake,NW China was conducted.The hyperspectral data of the salt crust was sampled to identify the species and content of sedimentary minerals,and the multispectral photos were used to reconstruct the salt crust morphology using the unmanned aerial vehicles platform.The SUnSAL(sparse unmixing by variable splitting and augmented Lagrangian)method was employed to inverse the sedimentary mineral components along the shoreline.The heterogeneity of salt and clay minerals in bright and dark ear-shaped strips was evaluated.The paleoclimatic environment associated with salt lake extinction was reconstructed by analyzing paleoclimate records of sediments,spectral reflectance and morphology of the salt crust.Results show that:(1)the variations in the micro-geomorphology of the salt crust are obviously the reason for the formation of bright and dark ear-shaped strips and the differences in the species and relative content of the sedimentary minerals are the microscopic reason.The high ratio of sedimentary salt minerals to clay minerals(RS/C)contributes to the high reflectivity,and the salt crust presents a bright texture.The low RS/C results in the low reflectivity,salt crust presents a dark texture;(2)the bright and dark ear-shaped strips represent warm-arid and cold-humid climates.The shape of the Lop Nur Lake shoreline evolved due to alternating warm-dry and cold-humid paleoclimate changes.
文摘The Lop Nur Salt Lake, located in the eastern part of the Tarim Basin, Xinjiang, China, has become a playa in the Quaternary. Rhombic in shape, the Lop Nur depression is mainly controlled by the NE-striking and nearly N-S-striking sets of faults. Since 1995, a superlarge brine potash deposit with potash resources of 2.50×108 t has been found in the Luobei subbasin in the northeastern part of the Lop Nur. We intensively studied the features and formation mechanism of faults inside the Lop Nur through satellite images, geomorphologic survey and continuous conductivity imaging and found seven subparallel graben faults formed under the action of nearly N 10o E principal compressional stress during deposition of the Lop Nur Salt Lake. These faults are up to >60 km long and 1–4 km wide and may extend downward for 1000 m or more. It is just under the action of these tensional faults that potash subbasins formed. The largest subbasin is the Luobei subbasin and the smaller ones are the Luoxi hollow, Erbei hollow and Tienan hollow. Investigation also indicates that the graben faults in the Lop Nur not only control the origin of the potash subbasins, but they themselves are also good brine reservoir structures, in which abundant potash-rich brines are stored. Therefore, The faults had played an important role in the potash formation of the Lop Nur.
基金funded by the National Basic Research Program of China(No.2011CB403007)the State Key Program of National Natural Science of China(No.40830420)
文摘Potash deposits commonly accumulate in highly restricted settings at the final stage of brine evaporation. This does not mean that potash deposits are formed simply as a result of the evaporation concentration of seawater or lake water, but rather as a coupling result of particular provenance, tectonics and climate activities. In this paper, we focus on the formative mechanism of the potash deposits of Lop Nur depression in Tarim Basin to interpret the detailed coupling mechanism among provenance, tectonics and climate. In terms of the provenance of Lop Nur Lake, the water of the Tarim River which displays "potassium-rich" characteristics play an important role. In addition, the Pliocene and Lower-Middle Pleistocene clastic beds surrounding Lop Nur Lake host a certain amount of soluble potassium and thus serves as "source beds" for potash formation. During the late Pliocene, the Lop Nur region has declined and evolved into a great lake from the previous piedmont and diluvial fan area. Since the mid Pleistocene, the great-united Lop Nur Lake has been separated and has generated a chain system consisting of Taitema Lake, Big Ear Lake and Luobei Lake which has turned into the deepest sag in Lop Nur Lake. Dry climate in Lop Nur region has increased since the Pliocene, and became extreme at the late Pleistocene. The study implies that potash formation in Lop Nur Lake depends on the optimal combination of extreme components of provenance, tectonics and climate during a shorter-term period. The optimal patterns of three factors are generally characterized by the long-term accumulation and preliminary enrichment of potassium, the occurrence of the deepest sub-depression and the appearance of an extremely arid climate in Lop Nur region. These factors have been interacting synergistically since the forming of the saline lake and in the later stages strong "vapor extraction" caused by extremely arid climate is needed to trigger large scale mineralization of potash deposits.
基金This research was supported by Xinjiang Project 305 “Development and Utilization of Potash Resources of the Lop Nur,Xinjiang”(95-915-08-05).
文摘Since the middle Early Pleistocene (1.20 Ma B.P.), the desert steppe climate and environment have predominated in the Lop Nur area, Xinjiang, characterized by warm humid epochs interrupted by dry cold intervals. The grain-size and magnetic susceptibility curves record 30 climatic oscillations, each with a ca. 40 ka cycle, in the area since 1.2 Ma B.P., which reflects the controlling effects exerted by the astronomic factor on the environment. The Quaternary sedimentary environment in the Lop Nur gradually changed from a fresh lake through a brackish lake to a saline lake, showing a spiral evolution, and finally it evolved into a playa.
基金supported by the Youth Innovation Promotion Association of Chinese Academy of Sciences (2017476)the National High-level Personnel Special Support Program+3 种基金Xinjiang Youth Science and Technology Innovation Leader Project (QN2016BS0162)the National Key Research and Development Program (2017YFSF03024105)the National Natural Science Foundation of China (31700423,31300449)the Xinjiang Uygur Autonomous Region Science and Technology Support Project (201433101)
文摘Extremely saline soils are very harsh environments for the growth and survival of most plant species, however, halophytes can grow well. The underlying mechanism of halophyte to resist high saline is not well understood by us. This study was conducted at the potash mine near the Lop Nur, China, where the effects of the halophyte Suaeda salsa L. on the saline-alkaline soils and its growth and sustainability were investigated. Four plots(in which the salt encrustation layers were removed), with different soil treatments were evaluated:(1) undisturbed soil, with no additional treatment(T1);(2) the slag soil zone, in which a 40-cm layer of slag was placed on the undisturbed soil surface(T2);(3) slag+sandy soil, in which a 20-cm layer of slag was placed in the lower layer and 20 cm of sandy soil, taken from an area about 70 km away from Lop Nur potash mine, where Tamarix species were growing, was placed in the upper layer(T3); and(4) a 40-cm sandy soil layer taken from the area where Tamarix species were growing was placed on undisturbed soil(T4). Soil nutrient contents increased in the four treatments, but salt content only decreased in the T1 treatment. Salt content in the T4 treatment increased over the two-year period, which may be partly attributed to salt deposition from wind-blown dust within the mine and salt accumulation within the surface soil(0–20 cm) in response to high evaporative demands. The S. salsa plants exhibited greater improvements in growth under the T4 treatment than under the T1, T2, and T3 treatments, which demonstrated that low levels of salinity are beneficial for the growth of this species. The T1 treatment was sustainable because of its low cost and superior soil improvement characteristics. Therefore, S. salsa plants not only reduced soil salinity and increased soil nutrient levels, but also ameliorated the plant growth environment, which would be beneficial for both the ecological restoration of the Lop Nur area and similar areas throughout the world.
基金supported by the Orientated Fund Project (DKD95-22)of the former Ministry of Geology and Mineral Resources of Chinathe"305"Project(96-916-08-05)of the Ministry of Science and Technology of China
文摘Many yellow silt layers have been identified in the Holocene sediments in the last lake of Lop Nur (playa),Xinjiang, northwestern China. Statistics of drill-hole cores have revealed more than one hundred layers, which exhibitregularity in time sequence. Study has further verified that these yellow silt layers were deposited through eolianprocesses. The time-frequency distribution diagram shows an obvious peak occurring at about 8200 a B.P., which isconsistent with the dry, windy and cold climate event occurring at 8200 a in other places around the world. Therefore, thisevent is regarded as a response to the global climate change.
基金the Oriented Foundation Proiect (DKD 95—22) the form er Ministry of Geology and Mineral Resources,State 305 Project(96-915—08—05)+2 种基金 the Ministry of Science Technology and Project 992025 the Ministry of Land and Resources.
文摘Located in the eastern part of the Tarim basin, Xinjiang, the Lop Nur was an ultimate water catchment area of the Tarim basin during the Quaternary. Through nearly ten years of investigation and research, the authors have found a superlarge brine potash deposit in the Luobei subbasin—a secondary basin of the Lop Nur depression. The deposit has been mined now. On that basis, the authors propose new theories on the genesis of the potash rock deposit. In the tectonic and geomorphologic contexts, the Tarim basin lies in a "high mountain-deep basin" environment. At the beginning of the Quaternary, influenced by the neotectonic movement, the Lop Nur evolved into a "deep basin" in the Tarim basin. At the end of the middle Pleistocene, neotectonic migration began to take place in the interior of the Lop Nur and a new secondary deep basin—the Luobei subbasin—formed gradually. Despite its small area, it is actually the deepest subbasin in the Lop Nur depression, where brines of the Lop Nur Salt Lake gather and evaporate, thus providing materials for the formation of a superlarge brine potash rock deposit. With respect to the phenomenon of brine concentration and change with deepening of the lake, the authors propose a model of "high mountain-deep basin" tectonic migration for potash concentration. In the sedimentological context, the honeycomb-shaped voids developed in glauberite rock in the subbasin are good space for potash-rich brine accumulation. Study indicates that the deposition of glauberite requires recharge of calcium-rich water. In the Tarim area the calcium-rich water might come from deep formation water or oilfield water, and the river water recharging the Lop Nur Salt Lake was rich in sulfate radicals and other components; in addition, the climate in the area was very dry and the brine evaporated steadily, thus resulting in deposition of substantial amount of glauberite, potash accumulation in intercrystal brine and final formation of the potash deposit. Generally, potash formation in a salt lake undergoes a three-stage process of "carbonates—?sulfates (gypsum and glauberite)—^chlorides (halite etc.)", but in the study area there only occurred a two-stage process of "carbonates—>sulfates (gypsum and glauberite)". The authors call this new geological phenomenon the "two-stage potash formation" model. In conclusion, the superlarge Lop Nur potash deposit is the result of combined "high mountain-deep basin" tectonism and "two-stage potash formation".
基金funded by National Basic Research Program of China (2010CB951003)Opening Fund of Key Laboratory of Oasis Ecology and Desert Environment, Chinese Academy of Sciences
文摘The causes of the disappearance of the ancient town of Loulan in Xinjiang, China have been generally agreed to derive from two factors: human activities and natural factors (environmental variations). In this paper, the Muzart Glacier was selected as an example, and found that the length of the glacier has been gradually decreasing and the snow line has been retreating to a higher altitude, both results contributing to a decrease in river flow below the Muzart Glacier. From the distribution of moraines in the Tianshan Mountains and adjacent areas in different periods, the paper speculates that there have been four minor glacial periods since the Quaternary. Although the durations and scales of the four minor glacial periods were different, they all indirectly influenced the formation and disappearance of the Lop Nur Lake. The events of the fourth minor glacial period are the important impact factors in the existence and disappearance of Loulan. Whether the disappearance of Loulan can be related to the events of the three previous minor glacial periods needs further investigation.
基金supported by the NationalNatural Science Foundation of China (Grant No.41701012)the project "ComprehensiveScientific Investigation of Natural and CulturalHeritage in the Lop Nur Region" (Grant No.2014FY210500)
文摘Saline lakes are useful repositories for paleo-climatic records. In recent years, magnetic properties of saline lake sediments have been widely applied to establish paleo-climatic change. However,the influence factors of magnetic properties in saline lakes have not been fully understood, which complicates the paleoenvironmental interpretation.Here, we present a rock magnetic analyses result of LOP_1 profile(40°26′09″′N, 90°21′23″E) from Lop Nur, a well-known saline lake, located in the eastern Tarim Basin in northwestern China. We combined the particle size, total organic content, and mineral characteristics analysis to assess the influence factors of magnetic properties in Lop Nur and its environmental significance. The results indicate that early diagenesis is the major influence factor on magnetic properties of Lop Nur saline sediments.Authigenic greigite and pyrite are identified within organic-rich sediments, which produce zones with high and low magnetic susceptibilities, respectively.The different authigenic iron sulfide contents in different layers are related to sedimentary environment changes. Sufficient supplies of organic matter and sulphate and low sedimentation rates favour the pyritization process. Moreover, if pyritization was constrained, intermediate greigite formed and was preserved. In oxidizing environments, sediment magnetic properties are consistent with those of source materials from Tarim Basin and are mainly controlled by particle size and hydrodynamic sorting of mainly detrital magnetite is largely unaffected by early diagenesis. Our study demonstrates that magnetic properties can provide a robust approach for studying depositional environment change in saline lake. In addition, the information obtained in this study would also provide insights into the geochemical processes of iron element in saline lakes.
基金supported by the NKBRSF Project Fund(2004CB720208)the National Natural Science Foundation of China(Nos.40599424 and 40473006)Institutions of Higher Learning Doctorate Foundation(No.20050358006).
文摘A 10.35-m-long sediment core from the Luobei depression in Lop-Nur,Xinjiang,Northwest China,provides detailed information about environmental changes during the Late Pleistocene.The samples taken every 5 cm of the core were analyzed for 10 environmental proxies,including magnetic susceptibility,granularity,chroma,carbonate and loss on ignition(LOI),and pH value.The chronology data are provided by the uranium/thorium disequi-librium dates.The sediments of the section were deposited during the last 32000 years.The results of analysis of 10 proxies were examined using multivariate statistical analysis,and the principal components were calculated.According to the results,the Late Pleistocene sequence contains four climatic and environmental stages appearing in the cycles of cold-wet and warm-dry changes.During 10-9 ka BP,it was the earliest warm episode in the Holocene.Environmental changes in this district were restricted by global change,as suggested by the analysis of glacial-interglacial cycles.But it was different from the mutative trend of a monsoon region in East China because of its own characteristics,which was the situation of cold-wet and warm-dry climate-environment change.The candidate reason may be the uplift of the Tibet Plateau and the westerly wind circulation.
