The Xining Basin, located on northeastern Qinghai-Xizang Plateau, is adjacent to the Qaidam Basin and Gobi-desert. Therefore, thick, integrated deposits of loess or paleo-sol sequence were well developed. As is well k...The Xining Basin, located on northeastern Qinghai-Xizang Plateau, is adjacent to the Qaidam Basin and Gobi-desert. Therefore, thick, integrated deposits of loess or paleo-sol sequence were well developed. As is well known, there is much paleo-environmental information recorded in loess and paleo|sol. So if we deal with paleo-environmental index from different angles, especially from loess geochemistry, some important and detailed paleo-environmental evolutional information will be acquired. Based on this, the authors determined the contents of Sr and Ca contained in acid-soluble fraction from the bottom to the top of the Panzishan section. This section was obtained through making a well about 17 m in depth, including S-1 paleo-sol that was developed during the last interglacial period. According to the results, it is found that variations in contents of Sr and Ca are well correlated with conversion of loess and paleo-sol. In loess deposits, the contents of Sr and Ca are higher than those in paleo-sol deposits. It is known that loess was deposited under cold-dry climate conditions and paleo-sol was developed during warm-humid climate episodes. It is concluded that due to their mobile behaviors, under cold-dry climate conditions, Sr and Ca are stagnant during weak weathering, but under warm-humid climate conditions, Sr and Ca are easily leached and transported in aqueous solution. Therefore, they can be utilized as indicators of climate changes. Moreover, variations in contents of Sr and Ca are more sensitive than susceptibility. The mobile behaviors of Sr and Ca contained in acid-soluble fraction can serve as a new quantitative index to evaluate paleo-environmental changes on the plateau.展开更多
Optically stimulated luminescence (OSL) dating for polymlneral fine-grained loess samples, collected in Laoguantai (LGT) section on the south of the Chinese Loess Plateau, was made by application of single-aliquot...Optically stimulated luminescence (OSL) dating for polymlneral fine-grained loess samples, collected in Laoguantai (LGT) section on the south of the Chinese Loess Plateau, was made by application of single-aliquot regenerative-dose (SAR) protocol. A 'Double-SAW procedure in which aliquots are subjected to both infrared (IR) and blue stimulations was used and two sets of equivalent dose (De) determinations were produced and assumed to relate predominantly to feldspathic and quartz fine grain populations respectively, The OSL ages estimated from IRSL signals are smaller than those estimated from [post-IR] OSL signals due to the anomalous fading of feldspar IR signals, based on fading experiment, The young ages of the samples near ground surface may be originated from the post-depositional disturbance by the intensifying humanity's cultivation since 3.0 ka BP in the Guanzhong Basin, south of the Chinese Loess Plateau. Based on OSL dating, as well as field observations and stratigraphic correlation, we determine the chronology of the LGT Ioess-paleosol sequence. In combination with climate proxy records, it is indicated that aeolian loess deposition and pedogenesis underwent polyphase changes during the Holocene, likely to have been driven by shifts in the East Asian monsoon. This suggests that aeolian loess deposition is episodic and highly variable, with contributions from non-aeolian processes such as alluvial deposition found in the area.展开更多
We report the finding of the Wolitu Pb-Zn deposit in Inner Mongolia, China, through a series of geochemical surveys. The Wolitu area, located in the loess-cover area in the Hure Banner, Tongliao City,Inner Mongolia, a...We report the finding of the Wolitu Pb-Zn deposit in Inner Mongolia, China, through a series of geochemical surveys. The Wolitu area, located in the loess-cover area in the Hure Banner, Tongliao City,Inner Mongolia, and neighboring the Horqin Sandy Land to the north, had no previous history of Pb-Zn mining or record of Pb-Zn mineralization. Our study identified a large Pb-Zn anomaly with potential zones of mineralization by stream sediment survey. Random rock sampling reveals limonitization at sporadic outcrops in the gullies. The high concentrations of Pb in the residual debris provided guidelines to fix the position for exploratory trench. Oxidized concealed orebodies were identified by trenching.Blind orebodies in veins hosted within the structural zone between slates and marbles of the upper Carboniferous Shizuizi Formation and the Permian granite were discovered by drilling. It is computed that the ore reserve may reach up to 540,000 tones with Pb grade of 1.27% and Zn of 1.9%. This case study is an excellent example for identifying potential polymetallic deposits in loess covered terrains using geochemical exploration.展开更多
The accumulation processes of loess in northeastern(NE)China record the varying characteristics of the East Asian Monsoons(EAM)and the evolution of the local environment.In this study,grain size end-member analysis of...The accumulation processes of loess in northeastern(NE)China record the varying characteristics of the East Asian Monsoons(EAM)and the evolution of the local environment.In this study,grain size end-member analysis of the Dajiugang(DJG)section deposited since the Last Glacial in Chifeng City,NE China was used to reveal the dynamic depositional characteristics of loess and environmental evolution of NE China.Results showed that the Chifeng loess comprises three grain size end-members(EM),EM1(7.38μm),EM2(49.4μm)and EM3(90.00μm),indicating the three transport dynamics of dust delivered to the region.The EM1 represents atmospheric dust as the background.The EM2,mainly derived from relatively distant-sources deposition,and EM3,material transported over a short distance,correspond to the intensity of southwesterly winds and the East Asian Winter Monsoon(EAWM),respectively.Results of climate reconstruction,combined with other records,showed that the climate was generally cold and dry with a strong EAWM and a weak East Asian summer monsoon(EASM)during the stadial-period[Marine Isotope Stage(MIS)4 and MIS 2 stage].The climate was predominantly warm and humid,with weak EAWM and surface winds and strong EASM in interstadial-period(MIS 3 and MIS 1 stage).Comparisons between indicators,e.g.,EM3,the LR04 benthicδ18O stack and summer insolation at 65°N suggest that the strong EAWM is induced by increasing the Northern Hemisphere ice volume and reduced summer solar radiation.展开更多
Nitrogen deposition will alleviate the nitrogen limitation in terrestrial ecosystems and greatly affect vegetation growth,thereby soil erosion.It is important to clarify the effects of nitrogen addition to the plant r...Nitrogen deposition will alleviate the nitrogen limitation in terrestrial ecosystems and greatly affect vegetation growth,thereby soil erosion.It is important to clarify the effects of nitrogen addition to the plant roots and soil properties on the soil erosion process.A nitrogen addition experiment was conducted in the grassland dominated by Bothriochloa ischaemum(Linn.)Keng(BI),which has received 0,2.5,5,and 10 g N m^(-2) yr^(-1)(N_(0),N_(2.5),N_(5)and N_(10),respectively)for three consecutive years.Then,a total of 150 undisturbed soil samples were collected(including bare soil control)and subjected to flowing water to test their soil detachment capacities under six shear stress levels(10.2 Pa to 29.9 Pa).Three-year nitrogen addition increased the soil bulk density,soil cohesion and nitrate nitrogen while decreasing the saturated hydraulic conductivity,soil water-stable aggregates,soil organic carbon,total nitrogen and ammonium nitrogen.The root mass density and root diameter decreased with nitrogen addition.And the root length,surface area and volume density of the N_(0) and N_(5) treatments were larger than those of the other treatments,while the plant roots were significantly inhibited by N_(10).Additionally,the soil detachment capacity(D_(c))and rill erodibility(K_(r))of the N_(0) and N_(5) treatments were significantly less than those of the N_(2.5) and N_(10)treatments,of which the Dc(0.020 kg m^(-2) s^(-1))of the N_(0) treatment was 69.0%,24.3%and 66.8%less than that of the N_(2.5),N_(5) and N_(10) treatments,respectively.The Kr of the N_(0) treatment was 0.0012 s m^(-1),which was 72.1%,25.0%and 70.0%less than that of the others.This study implies that an increase in nitrogen addition likely exacerbates soil erosion in the early(approximately 2.5 g N m^(-2) yr^(-1))and late phases(more than 10 g N m^(-2) yr^(-1)).However,when the nitrogen addition rate is approximately 5 g m^(-2) yr^(-1),soil erosion may be inhibited because of the responses of the plant roots and soil to nitrogen addition.展开更多
Thick loess is deposited on the platform in the piedmont zone of Muling-Xingkai Plain(Muxing Plain),but the genesis of the Muxing loess is still unclear.The aims of this study are to analyze the grain size characteris...Thick loess is deposited on the platform in the piedmont zone of Muling-Xingkai Plain(Muxing Plain),but the genesis of the Muxing loess is still unclear.The aims of this study are to analyze the grain size characteristics of Muxing loess collected from the cores of a typical borehole(ZK1)in the piedmont zone of Muxing Plain,and to verify its genesis.The Muxing loess is mainly composed of the particles with diameter less than 50μm,with an average content of 92.48%.The coarse silt particles with diameter of 10-50μm are the basic composition of aeolian sediments,and their average content is 44.34% for the Muxing loess,which is the mode class among the particles with different diameters.The grain size parameters and frequency curves are similar to those of the typical aeolian sediments.The distribution characteristic of the Muxing loess in the C-M scatter diagram is consistent with that of the Xi Feng loess.In addition,the discriminant analysis shows the Muxing loess mostly consists of aeolian sediments.Therefore,it can be concluded that the Muxing loess mainly resulted from aeolian deposition based on the grain size characteristics.Muxing Plain is dominated by the monsoon climate,and the wind-blown dusts are gradually deposited after being transported over long distances.展开更多
The wind system responsible for transporting dust onto the Chinese Loess Plateau during the late Miocene and Pliocene is still unknown and recent investigations highlight many controversies. This report aims to invest...The wind system responsible for transporting dust onto the Chinese Loess Plateau during the late Miocene and Pliocene is still unknown and recent investigations highlight many controversies. This report aims to investigate spatiotemporal changes in grain-size and sedi- mentation rate of the Neogene Red Clay deposits in north China and to explore palaeoclimatic changes during the late Miocene and Pliocene, in particular the palaeowind system that trans- ported dust. Samples were collected from eight Red Clay sections on the Loess Plateau. Meas- urement and analysis show that there is a clear southward decrease in the mean grain-size index and in the coarse particle fraction (>20 μm). At Jiaxian site on the northern Loess Plateau, the average mean grain-size is around 20 μm, while at Lantian site in the south, the mean is around 9 μm. The coarse particle fraction >20 μm makes up 24.4% and 5.6%, at the two sites respec- tively. This distinct diversity of grain-size in the aeolian Red Clay deposit between the north and south indicate that the palaeodust was transported mainly by northerly low-level winds. The grain-size variations in the Red Clay deposits can also be divided into three stages (the lower, the middle and the upper interval): grain-size of the lower stage is significantly coarser than that of the middle stage, but finer than that of the upper stage. As a consequence, the intensity of pa- laeowind and desiccation of the dust source region during the late Miocene and Pliocene can be divided into three stages: 6.2―5.4 Ma, 5.4―3.5 Ma and 3.5―2.6 Ma. Strength of the palaeowind during the middle stage (5.4―3.5 Ma) is weaker than that of the previous and subsequent stages and the intensity of palaeowind during the latest stage (3.5―2.6 Ma) is stronger than that of the early time (6.2―5.4 Ma). Variations in the sedimentation rate of the Red Clay deposit can also be divided into three stages: the earlier, the middle and the later interval. The sedimentation rate of the earlier stage is higher than during the middle stage, but lower than during the later one. This is a clear indicator of changes in the palaeowind intensity and aridity in the dust source region and may be linked with global ice volume changes during the late Miocene and the Pliocene.展开更多
The loess-paleosol sequence in China records abundant and valuable information on the global and regional climate changes. Biological record from the loess sequence is the most direct evidence on variation in pattern ...The loess-paleosol sequence in China records abundant and valuable information on the global and regional climate changes. Biological record from the loess sequence is the most direct evidence on variation in pattern of paleo-atmospheric circulation and changes in winter and summer monsoon. A new record of climatic instability, which occurred in the Loess Plateau during the late glacial period, is presented. Through the study of terrestrial mollusks from three loess sequences, the authors intend to characterize the biological response process to rapid climate change and to learn the mechanisms driving the instable climate changes and the possible linkage in different regions. The result shows the striking consistent variability in the ratio records of three mollusk sequences of the late glacial, indicating apparent rapid climate fluctuations. Correlation of our three mollusk records with the oxygen isotopic records from Greenland ice cores and foraminiferal records from the Northeast Pacific Ocean展开更多
According to variations of 137Cs and clay contents, 44 flood couplets were identified in a profile of res- ervoir deposit with a vertical length of 28.12 m in the Yuntaishan Gully. Couplet 27 at the middle of the prof...According to variations of 137Cs and clay contents, 44 flood couplets were identified in a profile of res- ervoir deposit with a vertical length of 28.12 m in the Yuntaishan Gully. Couplet 27 at the middle of the profile had the highest average 137Cs content of 12.65 Bq·kg?1, which indicated the 1963s' deposits, then 137Cs content decreased both downward and upward in the profile. The second top and bottom couplets had average 137Cs contents of 2.15 Bq·kg?1 and 0.92 Bq·kg?1, respectively. By integrated analysis of reservoir construction and management history, variations of 137Cs contents over the profile, sediment yields of flood couplets and rainfall data during the period of 1958-1970, individual storms related to the flood couplets were identified. 44 floods with a total sediment yield of 2.36×104 m3 occurred and flood events in a year varied between 1 and 10 times during the period of 1960-1970. 7-10 flood events occurred during the wet period of 1961-1964 with very wet autumn, while only 1-2 events during the dry period of 1965-1969. Average annual specific sediment yield was 1.29×104 t·km?2·a?1 for the Yuntaishan Gully during the period of 1960-1970, which was slightly higher than 1.11 ×104 t·km?2·a?1 for the Upper Yanhe River Basin above the Ganguyi Hydrological Station and slightly lower than 1.40 ×104 t·km?2·a?1 for the nearby Zhifang Gully during the same period. Annual specific sediment yields for the Yuntaishan Gully were correlated to the wet season's rainfalls well.展开更多
Aeolian loess deposits contain abundant information about the evolution of the paleoenvironment.For example,paleoclimate changes recorded in Chinese loess area obtained significant achievement in the past few decades....Aeolian loess deposits contain abundant information about the evolution of the paleoenvironment.For example,paleoclimate changes recorded in Chinese loess area obtained significant achievement in the past few decades.Compared to Chinese loess,research on Indian loess is lacking.Currently,most studies focus on the Kashmir area located in the southern Himalayas,and studies on other areas are rare.However,field observations demonstrate that the sediments around the New Delhi-Agra-Jaipur Plain are similar to Chinese loess-paleosol sequences.For example,the boundary between two strata is transitional and without horizontal bedding.Moreover,obvious pedogenic horizons developed among sediment sequences,probably indicating unrecognised aeolian deposits in the Indo-Gangetic Plain(IGP).To confirm this,pilot samples were obtained from the IGP and detailed indoor measurements conducted.The results indicate that the distribution patterns of particle size and rare earth elements(REE) of the pilot samples are similar to Chinese loess.Furthermore,the scanning electronic microscopy(SEM) images of pilot samples show obvious conchoidal fractures,dash-shaped concavities,and abundant small pits that usually form through mechanical impact.These are typical characteristics of aeolian particles.In addition,environmental and rock magnetic measurements indicate that the dominant magnetic minerals in the pilot samples are magnetite and maghemite,and that they likely contain small amounts of hematite.Furthermore,conventional magnetic parameters are comparable with Chinese loess.Based on this,aeolian loess deposits are widely distributed in the IGP,which may have promoted the development of Indian farming and contributed towards the prosperity of ancient Indian civilisation.This study also provides a new and valuable record for the research on paleoclimate changes in the study area in the future.展开更多
淤地坝作为黄土丘陵沟壑区水土流失治理的重要工程措施之一,其坝系优化布局、相对稳定性及坝地效益等受到广泛关注,但对其淤积过程研究甚少。该文通过对黄土高原淤地坝进行调查,典型坝淤积过程剖面的观测及取样分析,结合库容曲线和每个...淤地坝作为黄土丘陵沟壑区水土流失治理的重要工程措施之一,其坝系优化布局、相对稳定性及坝地效益等受到广泛关注,但对其淤积过程研究甚少。该文通过对黄土高原淤地坝进行调查,典型坝淤积过程剖面的观测及取样分析,结合库容曲线和每个淤积层的淤积厚度求出分层淤积量。根据暴雨产沙过程原理及淤积过程降雨资料,反演淤地坝各淤积层所对应的次侵蚀性降雨,建立层淤积量与相应次侵蚀性降雨指标的相关方程。研究结果表明:坝地淤积物中层淤积量和次侵蚀性降雨的降雨侵蚀力呈幂函数关系,层淤积量和次侵蚀性降雨的最大30 m in降雨强度呈指数函数关系,经检验结果良好。展开更多
文摘The Xining Basin, located on northeastern Qinghai-Xizang Plateau, is adjacent to the Qaidam Basin and Gobi-desert. Therefore, thick, integrated deposits of loess or paleo-sol sequence were well developed. As is well known, there is much paleo-environmental information recorded in loess and paleo|sol. So if we deal with paleo-environmental index from different angles, especially from loess geochemistry, some important and detailed paleo-environmental evolutional information will be acquired. Based on this, the authors determined the contents of Sr and Ca contained in acid-soluble fraction from the bottom to the top of the Panzishan section. This section was obtained through making a well about 17 m in depth, including S-1 paleo-sol that was developed during the last interglacial period. According to the results, it is found that variations in contents of Sr and Ca are well correlated with conversion of loess and paleo-sol. In loess deposits, the contents of Sr and Ca are higher than those in paleo-sol deposits. It is known that loess was deposited under cold-dry climate conditions and paleo-sol was developed during warm-humid climate episodes. It is concluded that due to their mobile behaviors, under cold-dry climate conditions, Sr and Ca are stagnant during weak weathering, but under warm-humid climate conditions, Sr and Ca are easily leached and transported in aqueous solution. Therefore, they can be utilized as indicators of climate changes. Moreover, variations in contents of Sr and Ca are more sensitive than susceptibility. The mobile behaviors of Sr and Ca contained in acid-soluble fraction can serve as a new quantitative index to evaluate paleo-environmental changes on the plateau.
基金National Natural Science Foundation of China, No.40571154 No.40471119
文摘Optically stimulated luminescence (OSL) dating for polymlneral fine-grained loess samples, collected in Laoguantai (LGT) section on the south of the Chinese Loess Plateau, was made by application of single-aliquot regenerative-dose (SAR) protocol. A 'Double-SAW procedure in which aliquots are subjected to both infrared (IR) and blue stimulations was used and two sets of equivalent dose (De) determinations were produced and assumed to relate predominantly to feldspathic and quartz fine grain populations respectively, The OSL ages estimated from IRSL signals are smaller than those estimated from [post-IR] OSL signals due to the anomalous fading of feldspar IR signals, based on fading experiment, The young ages of the samples near ground surface may be originated from the post-depositional disturbance by the intensifying humanity's cultivation since 3.0 ka BP in the Guanzhong Basin, south of the Chinese Loess Plateau. Based on OSL dating, as well as field observations and stratigraphic correlation, we determine the chronology of the LGT Ioess-paleosol sequence. In combination with climate proxy records, it is indicated that aeolian loess deposition and pedogenesis underwent polyphase changes during the Holocene, likely to have been driven by shifts in the East Asian monsoon. This suggests that aeolian loess deposition is episodic and highly variable, with contributions from non-aeolian processes such as alluvial deposition found in the area.
基金granted by the China's National Mineral Resources Investigation Program (Grant No.1212011220598) the Inner Mongolia Mineral Survey Fund(Grant No.KD-05-09)
文摘We report the finding of the Wolitu Pb-Zn deposit in Inner Mongolia, China, through a series of geochemical surveys. The Wolitu area, located in the loess-cover area in the Hure Banner, Tongliao City,Inner Mongolia, and neighboring the Horqin Sandy Land to the north, had no previous history of Pb-Zn mining or record of Pb-Zn mineralization. Our study identified a large Pb-Zn anomaly with potential zones of mineralization by stream sediment survey. Random rock sampling reveals limonitization at sporadic outcrops in the gullies. The high concentrations of Pb in the residual debris provided guidelines to fix the position for exploratory trench. Oxidized concealed orebodies were identified by trenching.Blind orebodies in veins hosted within the structural zone between slates and marbles of the upper Carboniferous Shizuizi Formation and the Permian granite were discovered by drilling. It is computed that the ore reserve may reach up to 540,000 tones with Pb grade of 1.27% and Zn of 1.9%. This case study is an excellent example for identifying potential polymetallic deposits in loess covered terrains using geochemical exploration.
基金supported by the National Natural Science Foundation of China(No:41771245).
文摘The accumulation processes of loess in northeastern(NE)China record the varying characteristics of the East Asian Monsoons(EAM)and the evolution of the local environment.In this study,grain size end-member analysis of the Dajiugang(DJG)section deposited since the Last Glacial in Chifeng City,NE China was used to reveal the dynamic depositional characteristics of loess and environmental evolution of NE China.Results showed that the Chifeng loess comprises three grain size end-members(EM),EM1(7.38μm),EM2(49.4μm)and EM3(90.00μm),indicating the three transport dynamics of dust delivered to the region.The EM1 represents atmospheric dust as the background.The EM2,mainly derived from relatively distant-sources deposition,and EM3,material transported over a short distance,correspond to the intensity of southwesterly winds and the East Asian Winter Monsoon(EAWM),respectively.Results of climate reconstruction,combined with other records,showed that the climate was generally cold and dry with a strong EAWM and a weak East Asian summer monsoon(EASM)during the stadial-period[Marine Isotope Stage(MIS)4 and MIS 2 stage].The climate was predominantly warm and humid,with weak EAWM and surface winds and strong EASM in interstadial-period(MIS 3 and MIS 1 stage).Comparisons between indicators,e.g.,EM3,the LR04 benthicδ18O stack and summer insolation at 65°N suggest that the strong EAWM is induced by increasing the Northern Hemisphere ice volume and reduced summer solar radiation.
基金supported financially by the National Natural Science Foundation of China(Grant Nos.41771555,41530858)the CAS"Youth Scholar of West China"Program(Grant No.XAB2019A04)the Innovation Capability Support Program of Shaanxi(Grant No.2022PT-23)。
文摘Nitrogen deposition will alleviate the nitrogen limitation in terrestrial ecosystems and greatly affect vegetation growth,thereby soil erosion.It is important to clarify the effects of nitrogen addition to the plant roots and soil properties on the soil erosion process.A nitrogen addition experiment was conducted in the grassland dominated by Bothriochloa ischaemum(Linn.)Keng(BI),which has received 0,2.5,5,and 10 g N m^(-2) yr^(-1)(N_(0),N_(2.5),N_(5)and N_(10),respectively)for three consecutive years.Then,a total of 150 undisturbed soil samples were collected(including bare soil control)and subjected to flowing water to test their soil detachment capacities under six shear stress levels(10.2 Pa to 29.9 Pa).Three-year nitrogen addition increased the soil bulk density,soil cohesion and nitrate nitrogen while decreasing the saturated hydraulic conductivity,soil water-stable aggregates,soil organic carbon,total nitrogen and ammonium nitrogen.The root mass density and root diameter decreased with nitrogen addition.And the root length,surface area and volume density of the N_(0) and N_(5) treatments were larger than those of the other treatments,while the plant roots were significantly inhibited by N_(10).Additionally,the soil detachment capacity(D_(c))and rill erodibility(K_(r))of the N_(0) and N_(5) treatments were significantly less than those of the N_(2.5) and N_(10)treatments,of which the Dc(0.020 kg m^(-2) s^(-1))of the N_(0) treatment was 69.0%,24.3%and 66.8%less than that of the N_(2.5),N_(5) and N_(10) treatments,respectively.The Kr of the N_(0) treatment was 0.0012 s m^(-1),which was 72.1%,25.0%and 70.0%less than that of the others.This study implies that an increase in nitrogen addition likely exacerbates soil erosion in the early(approximately 2.5 g N m^(-2) yr^(-1))and late phases(more than 10 g N m^(-2) yr^(-1)).However,when the nitrogen addition rate is approximately 5 g m^(-2) yr^(-1),soil erosion may be inhibited because of the responses of the plant roots and soil to nitrogen addition.
基金This study was financially supported by the China Geological Survey’s project(No.DD20160311)National Natural Science Foundation of China(No.41602268).
文摘Thick loess is deposited on the platform in the piedmont zone of Muling-Xingkai Plain(Muxing Plain),but the genesis of the Muxing loess is still unclear.The aims of this study are to analyze the grain size characteristics of Muxing loess collected from the cores of a typical borehole(ZK1)in the piedmont zone of Muxing Plain,and to verify its genesis.The Muxing loess is mainly composed of the particles with diameter less than 50μm,with an average content of 92.48%.The coarse silt particles with diameter of 10-50μm are the basic composition of aeolian sediments,and their average content is 44.34% for the Muxing loess,which is the mode class among the particles with different diameters.The grain size parameters and frequency curves are similar to those of the typical aeolian sediments.The distribution characteristic of the Muxing loess in the C-M scatter diagram is consistent with that of the Xi Feng loess.In addition,the discriminant analysis shows the Muxing loess mostly consists of aeolian sediments.Therefore,it can be concluded that the Muxing loess mainly resulted from aeolian deposition based on the grain size characteristics.Muxing Plain is dominated by the monsoon climate,and the wind-blown dusts are gradually deposited after being transported over long distances.
基金supported by the National Natural Science Foundation of China(Grant Nos.49902009 and 40202005)the Outstanding Overseas Chinese Scholars Fund of the Chinese Academy of Sciences(Grant No.2003-1-7).
文摘The wind system responsible for transporting dust onto the Chinese Loess Plateau during the late Miocene and Pliocene is still unknown and recent investigations highlight many controversies. This report aims to investigate spatiotemporal changes in grain-size and sedi- mentation rate of the Neogene Red Clay deposits in north China and to explore palaeoclimatic changes during the late Miocene and Pliocene, in particular the palaeowind system that trans- ported dust. Samples were collected from eight Red Clay sections on the Loess Plateau. Meas- urement and analysis show that there is a clear southward decrease in the mean grain-size index and in the coarse particle fraction (>20 μm). At Jiaxian site on the northern Loess Plateau, the average mean grain-size is around 20 μm, while at Lantian site in the south, the mean is around 9 μm. The coarse particle fraction >20 μm makes up 24.4% and 5.6%, at the two sites respec- tively. This distinct diversity of grain-size in the aeolian Red Clay deposit between the north and south indicate that the palaeodust was transported mainly by northerly low-level winds. The grain-size variations in the Red Clay deposits can also be divided into three stages (the lower, the middle and the upper interval): grain-size of the lower stage is significantly coarser than that of the middle stage, but finer than that of the upper stage. As a consequence, the intensity of pa- laeowind and desiccation of the dust source region during the late Miocene and Pliocene can be divided into three stages: 6.2―5.4 Ma, 5.4―3.5 Ma and 3.5―2.6 Ma. Strength of the palaeowind during the middle stage (5.4―3.5 Ma) is weaker than that of the previous and subsequent stages and the intensity of palaeowind during the latest stage (3.5―2.6 Ma) is stronger than that of the early time (6.2―5.4 Ma). Variations in the sedimentation rate of the Red Clay deposit can also be divided into three stages: the earlier, the middle and the later interval. The sedimentation rate of the earlier stage is higher than during the middle stage, but lower than during the later one. This is a clear indicator of changes in the palaeowind intensity and aridity in the dust source region and may be linked with global ice volume changes during the late Miocene and the Pliocene.
文摘The loess-paleosol sequence in China records abundant and valuable information on the global and regional climate changes. Biological record from the loess sequence is the most direct evidence on variation in pattern of paleo-atmospheric circulation and changes in winter and summer monsoon. A new record of climatic instability, which occurred in the Loess Plateau during the late glacial period, is presented. Through the study of terrestrial mollusks from three loess sequences, the authors intend to characterize the biological response process to rapid climate change and to learn the mechanisms driving the instable climate changes and the possible linkage in different regions. The result shows the striking consistent variability in the ratio records of three mollusk sequences of the late glacial, indicating apparent rapid climate fluctuations. Correlation of our three mollusk records with the oxygen isotopic records from Greenland ice cores and foraminiferal records from the Northeast Pacific Ocean
基金Supported by CAS(Grant No.KZCX3-SW 422)NNSF(Grant Nos.90502002,40271015)+1 种基金ISWC(B105101-109)IAEA(12322/RO)
文摘According to variations of 137Cs and clay contents, 44 flood couplets were identified in a profile of res- ervoir deposit with a vertical length of 28.12 m in the Yuntaishan Gully. Couplet 27 at the middle of the profile had the highest average 137Cs content of 12.65 Bq·kg?1, which indicated the 1963s' deposits, then 137Cs content decreased both downward and upward in the profile. The second top and bottom couplets had average 137Cs contents of 2.15 Bq·kg?1 and 0.92 Bq·kg?1, respectively. By integrated analysis of reservoir construction and management history, variations of 137Cs contents over the profile, sediment yields of flood couplets and rainfall data during the period of 1958-1970, individual storms related to the flood couplets were identified. 44 floods with a total sediment yield of 2.36×104 m3 occurred and flood events in a year varied between 1 and 10 times during the period of 1960-1970. 7-10 flood events occurred during the wet period of 1961-1964 with very wet autumn, while only 1-2 events during the dry period of 1965-1969. Average annual specific sediment yield was 1.29×104 t·km?2·a?1 for the Yuntaishan Gully during the period of 1960-1970, which was slightly higher than 1.11 ×104 t·km?2·a?1 for the Upper Yanhe River Basin above the Ganguyi Hydrological Station and slightly lower than 1.40 ×104 t·km?2·a?1 for the nearby Zhifang Gully during the same period. Annual specific sediment yields for the Yuntaishan Gully were correlated to the wet season's rainfalls well.
基金supported by National Natural Science Foundation of China(Grant Nos.41210002,U1405231&41602185)
文摘Aeolian loess deposits contain abundant information about the evolution of the paleoenvironment.For example,paleoclimate changes recorded in Chinese loess area obtained significant achievement in the past few decades.Compared to Chinese loess,research on Indian loess is lacking.Currently,most studies focus on the Kashmir area located in the southern Himalayas,and studies on other areas are rare.However,field observations demonstrate that the sediments around the New Delhi-Agra-Jaipur Plain are similar to Chinese loess-paleosol sequences.For example,the boundary between two strata is transitional and without horizontal bedding.Moreover,obvious pedogenic horizons developed among sediment sequences,probably indicating unrecognised aeolian deposits in the Indo-Gangetic Plain(IGP).To confirm this,pilot samples were obtained from the IGP and detailed indoor measurements conducted.The results indicate that the distribution patterns of particle size and rare earth elements(REE) of the pilot samples are similar to Chinese loess.Furthermore,the scanning electronic microscopy(SEM) images of pilot samples show obvious conchoidal fractures,dash-shaped concavities,and abundant small pits that usually form through mechanical impact.These are typical characteristics of aeolian particles.In addition,environmental and rock magnetic measurements indicate that the dominant magnetic minerals in the pilot samples are magnetite and maghemite,and that they likely contain small amounts of hematite.Furthermore,conventional magnetic parameters are comparable with Chinese loess.Based on this,aeolian loess deposits are widely distributed in the IGP,which may have promoted the development of Indian farming and contributed towards the prosperity of ancient Indian civilisation.This study also provides a new and valuable record for the research on paleoclimate changes in the study area in the future.
文摘淤地坝作为黄土丘陵沟壑区水土流失治理的重要工程措施之一,其坝系优化布局、相对稳定性及坝地效益等受到广泛关注,但对其淤积过程研究甚少。该文通过对黄土高原淤地坝进行调查,典型坝淤积过程剖面的观测及取样分析,结合库容曲线和每个淤积层的淤积厚度求出分层淤积量。根据暴雨产沙过程原理及淤积过程降雨资料,反演淤地坝各淤积层所对应的次侵蚀性降雨,建立层淤积量与相应次侵蚀性降雨指标的相关方程。研究结果表明:坝地淤积物中层淤积量和次侵蚀性降雨的降雨侵蚀力呈幂函数关系,层淤积量和次侵蚀性降雨的最大30 m in降雨强度呈指数函数关系,经检验结果良好。