The type, grain size and origin of ferrimagnetic minerals separated from red paleosols of Pleistocene Epoch (Q\-2) in eastern China, were studied by using mineral magnetic measurement, X\|ray powder diffraction and el...The type, grain size and origin of ferrimagnetic minerals separated from red paleosols of Pleistocene Epoch (Q\-2) in eastern China, were studied by using mineral magnetic measurement, X\|ray powder diffraction and electron microscopy. Results showed that the iron oxides in red paleosols were composed of hematite (α\|Fe\-2O\-3), maghemite (γ\|Fe\-2O\-3) and goethite(α\|FeOOH). Mineral magnetic parameters and X\|ray diffraction patterns indicated that maghemite was the dominant remanence carrier in red paleosols, which is characterized by superparamagnetic (SP) and stable single domain (SSD) grains. The variations of magnetic susceptibility (χ), anhysteretic magnetic susceptibility (χ\-\{ARM\}) and saturation isothermal remanent magnetization (SIRM) for red paleosols following heating to various temperatures showed two peak values at 700℃ and 900℃. The spherulitic magnetic particles measuring \{250-1000\}μm in diameter in red paleosols were separated by the magnetic separation method, indicating that these magnetic particles were an assemblage of superparamagnetic and stable single domain ferrimagnetic grains. It is suggested that the ferrimagnetic minerals of red paleosols be a pedogenic ferrimagnetic component under high temperature and high humid conditions in the Pleistocene Epoch (Q\-2). It is concluded that the magnetism characteristics of red paleosols can be used to evaluate the environmental changes of Quaternary in eastern China.展开更多
Core YSDP103 was retrieved in the muddy deposit under the cold eddy of the southeastern South Yellow Sea, and the uppermost 29.79 m core represents the muddy sediments formed in the shelf since about 13 ka BP. The low...Core YSDP103 was retrieved in the muddy deposit under the cold eddy of the southeastern South Yellow Sea, and the uppermost 29.79 m core represents the muddy sediments formed in the shelf since about 13 ka BP. The lower part from 29.79 to 13.35 m, called Unit A2, was deposited during the period from the post-glacial transgression to the middle Holocene (at about 6 14C ka BP) when the rising sea level reached its maximum, while the upper part above 13.35 m (called Unit A1) was deposited in a cold eddy associated with the formation of the Yellow Sea Warm Current just after the peak of post-glacial sea level rise. Rock-magnetic properties of the uppermost 29.79 m core were investigated in detail. The experimental results indicate that the magnetic mineralogy of the core is dominated by magnetite, maghemite and hematite and that, except for the uppermost 2.35 m, the magnetic minerals were subject to reductive diagenesis leading to significant decline of magnetic mineral content and the proportion of low-coercivity component. More importantly, ferrimagnetic iron sulphide (greigite) is found in Unit A2 but absent in Unit A1, suggesting the control of marine environmental conditions on the magnetic mineral diagenesis. Magnetic parameters show abrupt changes across the boundary between Units A1and A2, which reflects a co-effect of environmental conditions and primary magnetic components of the sediments on the diagenesis. Alternating zones of high and low magnetic parameters are observed in Unit A2, which is presumably due to periodic changes of the concentration and/or grain size of magnetic minerals carried into the study area.展开更多
Mineral magnetic measurements have been made on Quaternary Red Earth profilesfrom Zhejiang Province, Eastern China. Three distinctive magnetic stratigraphic horizons havebeen identified on the basis of magnetic suscep...Mineral magnetic measurements have been made on Quaternary Red Earth profilesfrom Zhejiang Province, Eastern China. Three distinctive magnetic stratigraphic horizons havebeen identified on the basis of magnetic susceptibility, anhysteretic remanent magnetization,saturation isothermal remanent magnetization and magnetization parameters measurements.Magnetic measurements revealed that there were great variations in ferrimagnetic mineralconcentration, mineralogy assemblages and grain size in Quaternary Red Earth profiles, suggestingthat these variations reflect pedogenic processes fluctuation and environmental changes. Thepreliminary results indicate that mineral magnetic measurement of Quaternary Red Earth is usefulfor studying the Quaternary environmental changes recorded in paleosols.展开更多
文摘The type, grain size and origin of ferrimagnetic minerals separated from red paleosols of Pleistocene Epoch (Q\-2) in eastern China, were studied by using mineral magnetic measurement, X\|ray powder diffraction and electron microscopy. Results showed that the iron oxides in red paleosols were composed of hematite (α\|Fe\-2O\-3), maghemite (γ\|Fe\-2O\-3) and goethite(α\|FeOOH). Mineral magnetic parameters and X\|ray diffraction patterns indicated that maghemite was the dominant remanence carrier in red paleosols, which is characterized by superparamagnetic (SP) and stable single domain (SSD) grains. The variations of magnetic susceptibility (χ), anhysteretic magnetic susceptibility (χ\-\{ARM\}) and saturation isothermal remanent magnetization (SIRM) for red paleosols following heating to various temperatures showed two peak values at 700℃ and 900℃. The spherulitic magnetic particles measuring \{250-1000\}μm in diameter in red paleosols were separated by the magnetic separation method, indicating that these magnetic particles were an assemblage of superparamagnetic and stable single domain ferrimagnetic grains. It is suggested that the ferrimagnetic minerals of red paleosols be a pedogenic ferrimagnetic component under high temperature and high humid conditions in the Pleistocene Epoch (Q\-2). It is concluded that the magnetism characteristics of red paleosols can be used to evaluate the environmental changes of Quaternary in eastern China.
基金supported by the National Natural Science Foundation of China(Grant Nos.49976012 and 49736210).
文摘Core YSDP103 was retrieved in the muddy deposit under the cold eddy of the southeastern South Yellow Sea, and the uppermost 29.79 m core represents the muddy sediments formed in the shelf since about 13 ka BP. The lower part from 29.79 to 13.35 m, called Unit A2, was deposited during the period from the post-glacial transgression to the middle Holocene (at about 6 14C ka BP) when the rising sea level reached its maximum, while the upper part above 13.35 m (called Unit A1) was deposited in a cold eddy associated with the formation of the Yellow Sea Warm Current just after the peak of post-glacial sea level rise. Rock-magnetic properties of the uppermost 29.79 m core were investigated in detail. The experimental results indicate that the magnetic mineralogy of the core is dominated by magnetite, maghemite and hematite and that, except for the uppermost 2.35 m, the magnetic minerals were subject to reductive diagenesis leading to significant decline of magnetic mineral content and the proportion of low-coercivity component. More importantly, ferrimagnetic iron sulphide (greigite) is found in Unit A2 but absent in Unit A1, suggesting the control of marine environmental conditions on the magnetic mineral diagenesis. Magnetic parameters show abrupt changes across the boundary between Units A1and A2, which reflects a co-effect of environmental conditions and primary magnetic components of the sediments on the diagenesis. Alternating zones of high and low magnetic parameters are observed in Unit A2, which is presumably due to periodic changes of the concentration and/or grain size of magnetic minerals carried into the study area.
文摘Mineral magnetic measurements have been made on Quaternary Red Earth profilesfrom Zhejiang Province, Eastern China. Three distinctive magnetic stratigraphic horizons havebeen identified on the basis of magnetic susceptibility, anhysteretic remanent magnetization,saturation isothermal remanent magnetization and magnetization parameters measurements.Magnetic measurements revealed that there were great variations in ferrimagnetic mineralconcentration, mineralogy assemblages and grain size in Quaternary Red Earth profiles, suggestingthat these variations reflect pedogenic processes fluctuation and environmental changes. Thepreliminary results indicate that mineral magnetic measurement of Quaternary Red Earth is usefulfor studying the Quaternary environmental changes recorded in paleosols.
