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 ...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.展开更多
基金This work was supported by the National Key Program for Basic Research(Grant No.2001 CCB00100)the Key Pro-gram of National Natural Science Foundation of China(Grant No:4033 1001)the National Basic Research Program of China(Grant No:2004CB720204).
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.
