| 1 | Formation mechanism of ferromagnetic minerals in loess of China:TEM investigation显示文摘The results of TEM investigation indicate that magnetite and maghemite are the major ferromagnetic minerals in loess-paleosol sequences. Primary magnetite has the similar morphology and surface characteristics as eolian detrital particles. The magnetite can be classified into two categories, high-titanium and low-titanium, which may be the indicators of magmatic rocks and metamorphic rocks, respectively. TEM investigation at nanometer scale shows that primary detrital magnetite of micron scale had been partially weathered to maghemite of 5~20 nanometer during the pedogenic process, which maintain the pseudomorphism of the aeolian debris. Some chlorite particles were also weathered to nanometer scale magnetite or maghemite in the pedogenic process. So weathering of the two minerals leads to formation of superparamagnetism, which may be the important mechanism of magnetic-susceptibility increase in paleosols. The magnetite or maghemite resulting from the weathering of chlorite contains a small amount of P and S, which is the signal of microbe-mineral interaction, and indicates that microbes may play a certain role in chlorite weathering and formation of superparamagnetic particles. | CHENTianhu XUHuifang JIJunfeng CHENJun CHENYang | 2003 | Chinese Science Bulletin2003，48，20： | 11 |
| 2 | Aragonite-calcite transfor-mation in fossil snail shells of loess sequences in Loess Plateau, Central China显示文摘The methods of X-ray diffraction (XRD) and ICP-AES are applied to analyzing the mineral composition of modern and fossil snail shells in Luochuan section and Xifeng section. The results show that the mineral phase of calcium carbonate in modern snail shells is aragonite, but for some fossil snail shells in certain layers of loess sequences, a part of aragonite is transformed into calcite. In Luochuan and Xifeng sections, the stratigraphic borderline of arago- nite-calcite transformation appearing obviously is between L5 and L6. Under the earth surface condition, the arago- nite-calcite transformation is influenced by the factor of temperature only in a long time scale. It seems that the pres- sure is not the factor influencing the aragonite-calcite trans- formation. The results also show that existing age of snail shells is possibly the dominant and principal factor for the aragonite-calcite transformation. To a certain extent, the degree of aragonite-calcite transformation in snail shell is controlled by the content of trace element, such as Mg2+. The trace element can improve the stability of snail shell arago- nite and impede the process of aragonite transforming into calcite. | SHENGXuefen CHENJun CAIYuanfeng CHENYang JIJunfeng | 2005 | Chinese Science Bulletin2005，50，9： | 0 |
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