The chemical leaching method is used for a systematic analysis of distribution characteristics of acid-soluble and acid-insoluble REE and other trace elements from the Luochuan loess deposits. The study shows that the...The chemical leaching method is used for a systematic analysis of distribution characteristics of acid-soluble and acid-insoluble REE and other trace elements from the Luochuan loess deposits. The study shows that the acid-insoluble phase in loess and palaeosol is a stable component of old aeolian dusts and is characteristic of the provenance; the acid-soluble phase is the unstable component in the weathering pedogenic process and reflects rock-forming features after accumulation of aeolian dusts. The acid-insoluble REE and acid-soluble Sr and Pb can be used as geochemical indicators respectively to trace the provenance characteristics and the weathering pedogenic process.展开更多
Palaeosols are one of the architectural elements of sedimentation in the Siwalik Foreland Basin holding a record of long term climate changes for the past 18 Ma.Systematic study of palaeosols,and associated non-pedoge...Palaeosols are one of the architectural elements of sedimentation in the Siwalik Foreland Basin holding a record of long term climate changes for the past 18 Ma.Systematic study of palaeosols,and associated non-pedogenic materials,along with their parent rock is important for understanding pedogenic processes and environments,which in turn gives insight into the interrelation between climate,topography and ecosystem.The fossil soils have a special value as they remains in the place of their formation展开更多
Since continental sediments (in addition to the marine geological record) offer important means of deciphering environmental changes, the sediments hosted by the successive flows of the continental flood basalt prov...Since continental sediments (in addition to the marine geological record) offer important means of deciphering environmental changes, the sediments hosted by the successive flows of the continental flood basalt provinces of the world should be treasure houses in gathering the palaeoclimatic data. Palaeosols developed on top of basalt flows are potentially ideal for palaeoenvironmental reconstructions because it is easy to determine their protolith geochemistry and also they define a definite time interval. The present paper summarizes the nature of the basalt-hosted palaeosols formed on the flood basalts provinces from different parts of the ~lobe havin~ different ages.展开更多
Palaeosols of the Siwalik Group are associated with fluvial and lacustrine deposits that occur as thick multiple pedocomplexes. The bright red color of the palaeosol beds has been earlier interpreted as a result of ho...Palaeosols of the Siwalik Group are associated with fluvial and lacustrine deposits that occur as thick multiple pedocomplexes. The bright red color of the palaeosol beds has been earlier interpreted as a result of hot and arid palaeoclimate. However, as against this view, our investigations of the bright red palaeosol beds of the Lower Siwaliks suggest that the climate was cool and subhumid, instead of hot and arid during the deposition of these beds. Since cold climate is not very conducive to impart red coloration, further research is needed to explain the cause of these red beds. For this, the micromorphological study of soil thin sections was done which showed the presence of features such as dissolution and recrystallisation of quartz, feldspar and mica, compaction, slickensides, presence of calcite spars, subrounded and cracked nature of quartz grains, microfabric, complex patterns of birefringence fabrics, pigmentary ferric oxides, thick cutans and cementation by calcite. These features indicate that diagenesis took place on a large scale in these sediments. The positive Eh and neutral-alkaline pH of soils also suggest that the conditions were favorable for the formation of diagenetic red beds. During burial diagenesis of sediments, the hydroxides of ferromagnesian minerals got converted into ferric oxide minerals (hematite). During deep burial diagenesis smectite was converted into illite and the preponderance of illite over smectite with increasing depth of burial also indicates the diagenesis of sediments. Thus, the red color of the Lower Siwalik palaeosols seems to be due mainly to the burial diagenesis of sediments and does not appear to be due to the then prevailing climatic condition.展开更多
Based on weathering characteristics of the fifth palaeosol layer (S5) of four sections in Guanzhong Plain, the thickness of the weathered profile of the paleosol is determined to be greater than the ordi- nary soil, a...Based on weathering characteristics of the fifth palaeosol layer (S5) of four sections in Guanzhong Plain, the thickness of the weathered profile of the paleosol is determined to be greater than the ordi- nary soil, a weathered and leached loess layer thicker than 2 m. The distribution depth of the red argil- lans, the weathered and leached loess layer, Fe2O3, CaCO3 and Sr content under the S5 all indicate that the precipitation in Guanzhong Plain was over 900 mm at that time. The distribution depth of gravity water zone reached 4.2 m at least, and the soil moisture content was generally more than 20% within the range of 4.2 m. At that time there was sufficient soil moisture and no dried earth layer developed in Guanzhong Plain, suitable for the forest to develop. When this soil developed, the mean annual pre- cipitation was more than the annual soil moisture evaporation. The value of soil moisture balance was positive and the atmospheric precipitation could supply the underground water normally. Soil water was weak acidic in the middle and late stages when S5 developed in Guanzhong Plain. It was a kind of subtropical climate and even more humid and warmer than the northern edge of the subtropical climate zone in Guanzhong Plain when the S5 developed. At that time the subtropical climate was prevailing over the northern side and southern side of Qingling Mountains, showing the Mountains no longer to be the boundary between the subtropical zone and the temperate zone in China. The summer monsoon acted intensely and could go over Qingling Mountains frequently bring abundant precipitation.展开更多
Particle size analysis for samples from three last glacial cycle loess_palaeosol profiles along a northwest_southeast transection on the Chinese Loess Plateau has been carried out. The paleoclimatic significance of gr...Particle size analysis for samples from three last glacial cycle loess_palaeosol profiles along a northwest_southeast transection on the Chinese Loess Plateau has been carried out. The paleoclimatic significance of grain size indices has been obtained by analyzing the fraction content variations and their comparisons with global ice volume and solar radiation variations. The results show that (i) paleoclimatic significance of the grain size indices of loess_palaeosol deposit is different with grain size fraction content and sampling points in Chinese Loess Plateau; (ii) the sub_coarse grain fraction is a good proxy index of East Asia winter monsoon strength and therefore can be used to detect the global climate changes; (iii) the content of sub_fine and fine grain fractions is influenced by both the input of sub_coarse grain fraction and pedogenesis; (iv) the sub_coarse fraction exhibits a negative relationship with the sub_fine and fine fraction.展开更多
To understand climate changes recorded in the Luochuan loess-palaeosols, Shaanxi province, northwes- tern China, clay mineralogy was studied using X-ray diffraction (XRD), high-resolution transmission electron micro...To understand climate changes recorded in the Luochuan loess-palaeosols, Shaanxi province, northwes- tern China, clay mineralogy was studied using X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), and scanning electron microscopy (SEM) methods. XRD results show that clay mineral compositions in the Luochuan loess-palaeosols are dom- inantly illite, with minor chlorite, kaolinite, smectite, and illite-smectite mixed-layer clays (US). Illite is the most abundant species in the sediments, with a content of 61%- 83%. The content of chlorite ranges from 5%-22%, and the content of kaolinite ranges from 5%-19%. Smectite (or US) occurs discontinuously along the loess profile, with a content of 0-8%. The Kfibler index of illite (IC) ranges from 0.255°-0.491°, and the illite chemical index (ICI) ranges from 0.294-0.394. The CIA values of the loess- palaeosols are 61.9-69.02, and the R3+/(R3+ + R2+ + M+) values are 0.508-0.589. HRTEM observations show that transformation of illite to illite-smectite has occurred in both the loess and palaeosol, suggesting that the Luochuan loess-palaeosols have experienced a certain degree of chemical weathering. The Luochuan loess-palaeosols have the same clay mineral assemblage along the profile. However, the relative contents of clay mineral species, CIA, ICI, and IC values fluctuate frequently along the profile, and all these parameters display a similar trend. Moreover, climate changes suggested by the clay index are consistent with variations in the deep-sea 6180 records and the magnetic susceptibility value, and thus, climate changes in the Luochuan region have been controlled by global climate change.展开更多
本次研究得出了2.5 Ma BP以来洛川剖面黄土-古土壤序列的酸不溶物^(87)Sr/^(86)Sr、Rb/Sr、磁化率和沉积速率的变化曲线。黄土和古土壤酸不溶物^(87)Sr/^(86)Sr、Rb/Sr和磁化率的变化具有类似的阶段性和周期性,这与晚新生代以来古气候...本次研究得出了2.5 Ma BP以来洛川剖面黄土-古土壤序列的酸不溶物^(87)Sr/^(86)Sr、Rb/Sr、磁化率和沉积速率的变化曲线。黄土和古土壤酸不溶物^(87)Sr/^(86)Sr、Rb/Sr和磁化率的变化具有类似的阶段性和周期性,这与晚新生代以来古气候的主要变化以及行星轨道参数相一致。研究证明,黄土和古土壤酸不溶物^(87)Sr/^(86)Sr值是化学风化强度的替代指标,沉积速率是物理风化强度的替代指标。自2.5 Ma BP以来在喜马拉雅山的北面风化强度的变化分为两个阶段,其界限在约1.2 Ma BP。自2.5 Ma BP以来化学风化强度在总体上呈下降趋势,而物理风化强度呈上升趋势。物理风化强度总的增长可能是导致海水^(87)Sr/^(86)Sr迅速上升的主要原因。展开更多
文摘The chemical leaching method is used for a systematic analysis of distribution characteristics of acid-soluble and acid-insoluble REE and other trace elements from the Luochuan loess deposits. The study shows that the acid-insoluble phase in loess and palaeosol is a stable component of old aeolian dusts and is characteristic of the provenance; the acid-soluble phase is the unstable component in the weathering pedogenic process and reflects rock-forming features after accumulation of aeolian dusts. The acid-insoluble REE and acid-soluble Sr and Pb can be used as geochemical indicators respectively to trace the provenance characteristics and the weathering pedogenic process.
文摘Palaeosols are one of the architectural elements of sedimentation in the Siwalik Foreland Basin holding a record of long term climate changes for the past 18 Ma.Systematic study of palaeosols,and associated non-pedogenic materials,along with their parent rock is important for understanding pedogenic processes and environments,which in turn gives insight into the interrelation between climate,topography and ecosystem.The fossil soils have a special value as they remains in the place of their formation
文摘Since continental sediments (in addition to the marine geological record) offer important means of deciphering environmental changes, the sediments hosted by the successive flows of the continental flood basalt provinces of the world should be treasure houses in gathering the palaeoclimatic data. Palaeosols developed on top of basalt flows are potentially ideal for palaeoenvironmental reconstructions because it is easy to determine their protolith geochemistry and also they define a definite time interval. The present paper summarizes the nature of the basalt-hosted palaeosols formed on the flood basalts provinces from different parts of the ~lobe havin~ different ages.
文摘Palaeosols of the Siwalik Group are associated with fluvial and lacustrine deposits that occur as thick multiple pedocomplexes. The bright red color of the palaeosol beds has been earlier interpreted as a result of hot and arid palaeoclimate. However, as against this view, our investigations of the bright red palaeosol beds of the Lower Siwaliks suggest that the climate was cool and subhumid, instead of hot and arid during the deposition of these beds. Since cold climate is not very conducive to impart red coloration, further research is needed to explain the cause of these red beds. For this, the micromorphological study of soil thin sections was done which showed the presence of features such as dissolution and recrystallisation of quartz, feldspar and mica, compaction, slickensides, presence of calcite spars, subrounded and cracked nature of quartz grains, microfabric, complex patterns of birefringence fabrics, pigmentary ferric oxides, thick cutans and cementation by calcite. These features indicate that diagenesis took place on a large scale in these sediments. The positive Eh and neutral-alkaline pH of soils also suggest that the conditions were favorable for the formation of diagenetic red beds. During burial diagenesis of sediments, the hydroxides of ferromagnesian minerals got converted into ferric oxide minerals (hematite). During deep burial diagenesis smectite was converted into illite and the preponderance of illite over smectite with increasing depth of burial also indicates the diagenesis of sediments. Thus, the red color of the Lower Siwalik palaeosols seems to be due mainly to the burial diagenesis of sediments and does not appear to be due to the then prevailing climatic condition.
基金the National Natural Science Foundation of China (Grant No. 40672108)State Key Laboratory of Loess and Quaternary Geology, Chinese Academy of Sciences (Grant No. SKLLQ0605)
文摘Based on weathering characteristics of the fifth palaeosol layer (S5) of four sections in Guanzhong Plain, the thickness of the weathered profile of the paleosol is determined to be greater than the ordi- nary soil, a weathered and leached loess layer thicker than 2 m. The distribution depth of the red argil- lans, the weathered and leached loess layer, Fe2O3, CaCO3 and Sr content under the S5 all indicate that the precipitation in Guanzhong Plain was over 900 mm at that time. The distribution depth of gravity water zone reached 4.2 m at least, and the soil moisture content was generally more than 20% within the range of 4.2 m. At that time there was sufficient soil moisture and no dried earth layer developed in Guanzhong Plain, suitable for the forest to develop. When this soil developed, the mean annual pre- cipitation was more than the annual soil moisture evaporation. The value of soil moisture balance was positive and the atmospheric precipitation could supply the underground water normally. Soil water was weak acidic in the middle and late stages when S5 developed in Guanzhong Plain. It was a kind of subtropical climate and even more humid and warmer than the northern edge of the subtropical climate zone in Guanzhong Plain when the S5 developed. At that time the subtropical climate was prevailing over the northern side and southern side of Qingling Mountains, showing the Mountains no longer to be the boundary between the subtropical zone and the temperate zone in China. The summer monsoon acted intensely and could go over Qingling Mountains frequently bring abundant precipitation.
文摘Particle size analysis for samples from three last glacial cycle loess_palaeosol profiles along a northwest_southeast transection on the Chinese Loess Plateau has been carried out. The paleoclimatic significance of grain size indices has been obtained by analyzing the fraction content variations and their comparisons with global ice volume and solar radiation variations. The results show that (i) paleoclimatic significance of the grain size indices of loess_palaeosol deposit is different with grain size fraction content and sampling points in Chinese Loess Plateau; (ii) the sub_coarse grain fraction is a good proxy index of East Asia winter monsoon strength and therefore can be used to detect the global climate changes; (iii) the content of sub_fine and fine grain fractions is influenced by both the input of sub_coarse grain fraction and pedogenesis; (iv) the sub_coarse fraction exhibits a negative relationship with the sub_fine and fine fraction.
基金This work was supported by the National Natural Science Foundation of China (Grant Nos. 41272053 and 41472041). C.W. acknowledges a postdoctoral science foundation of China (2015M582301), Fundamental Research Funds for the Central Universities, China University of Geosciences (Wuhan), and National Natural Science Youth Foundation of China (Grant No. 41602037). The authors wish to thank Dr. Yu J. S. for XRD analysis, Dr. Liu X. W, for HRTEM analysis and Dr. Yang H. and Dr. Yang Q. for SEM analysis.
文摘To understand climate changes recorded in the Luochuan loess-palaeosols, Shaanxi province, northwes- tern China, clay mineralogy was studied using X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), and scanning electron microscopy (SEM) methods. XRD results show that clay mineral compositions in the Luochuan loess-palaeosols are dom- inantly illite, with minor chlorite, kaolinite, smectite, and illite-smectite mixed-layer clays (US). Illite is the most abundant species in the sediments, with a content of 61%- 83%. The content of chlorite ranges from 5%-22%, and the content of kaolinite ranges from 5%-19%. Smectite (or US) occurs discontinuously along the loess profile, with a content of 0-8%. The Kfibler index of illite (IC) ranges from 0.255°-0.491°, and the illite chemical index (ICI) ranges from 0.294-0.394. The CIA values of the loess- palaeosols are 61.9-69.02, and the R3+/(R3+ + R2+ + M+) values are 0.508-0.589. HRTEM observations show that transformation of illite to illite-smectite has occurred in both the loess and palaeosol, suggesting that the Luochuan loess-palaeosols have experienced a certain degree of chemical weathering. The Luochuan loess-palaeosols have the same clay mineral assemblage along the profile. However, the relative contents of clay mineral species, CIA, ICI, and IC values fluctuate frequently along the profile, and all these parameters display a similar trend. Moreover, climate changes suggested by the clay index are consistent with variations in the deep-sea 6180 records and the magnetic susceptibility value, and thus, climate changes in the Luochuan region have been controlled by global climate change.
文摘本次研究得出了2.5 Ma BP以来洛川剖面黄土-古土壤序列的酸不溶物^(87)Sr/^(86)Sr、Rb/Sr、磁化率和沉积速率的变化曲线。黄土和古土壤酸不溶物^(87)Sr/^(86)Sr、Rb/Sr和磁化率的变化具有类似的阶段性和周期性,这与晚新生代以来古气候的主要变化以及行星轨道参数相一致。研究证明,黄土和古土壤酸不溶物^(87)Sr/^(86)Sr值是化学风化强度的替代指标,沉积速率是物理风化强度的替代指标。自2.5 Ma BP以来在喜马拉雅山的北面风化强度的变化分为两个阶段,其界限在约1.2 Ma BP。自2.5 Ma BP以来化学风化强度在总体上呈下降趋势,而物理风化强度呈上升趋势。物理风化强度总的增长可能是导致海水^(87)Sr/^(86)Sr迅速上升的主要原因。