排序方式: 共有4条查询结果,搜索用时 875 毫秒
1
1.
Budakoglu Murat Unluer Ali Tugcan Doner Zeynep Kocaturk Huseyin Kaya Mustafa Kumral Mustafa Kirikoglu M. Sezai 《中国地球化学学报》2021,40(6):926-944
Acta Geochimica - In the last five decades, Rare Earth Elements (REE) are mostly produced from carbonatite complexes and alkaline magmatic environments. In this respect, pyroclastic flows produced... 相似文献
2.
Ronald G. Amundson Oliver A. Chadwick Janet M. Sowers Harvey E. Doner 《Quaternary Research》1988,29(3)
The relationship between the stable C-isotope composition of the soil environment and modern climate and vegetation was determined empirically along a present-day climatic transect in the eastern Mojave Desert. The δ13C of the soil CO2 and carbonates decreased with increasing elevation and plant density, even though plant assemblages at all elevations were isotopically similar. Several factors, including differences in the ratios of pedogenic of limestone calcite and differences in past vegetation, were considered as explanations of this trend, However, it appears that in the sparsely vegetated Mojave Desert, the δ13C of pedogenic carbonate is controlled by differences in plant density and biological activity. This relationship may provide a tool for assessing past vegetational densities, as long as the vegetation is isotopically homogeneous. 相似文献
3.
Heterogeneity effects often limit the accuracy of synchrotron X-ray fluorescence microprobe elemental analysis data to ± 30%. The difference in matrix mass absorption at Kα and Kβ fluorescence energies of a particular element can be exploited to yield information on the average depth-position of the element or account for heterogeneity effects. Using this technique, the heterogeneous distribution of Cu in a simple layered sample could be resolved to a 2 × 2 × 10 (x, y, z, where z is the depth coordinate) micrometer scale; a depth-resolution limit was determined for the first transition metal series and several other elements in calcite and iron oxide matrices. For complex heterogeneous systems, determination of average element depth may be computationally limited but the influence of heterogeneity on fluorescence data may still be assessed. We used this method to compare solid-state diffusion with sample heterogeneity across the Ni-serpentine/calcite boundary of a rock from Panoche Creek, California. We previously reported that Ni fluorescence data may indicate solid state diffusion; in fact, sample heterogeneity in the depth dimension can also explain the Ni fluorescence data. Depth heterogeneity in samples can lead to misinterpretation of synchrotron X-ray microprobe results unless care is taken to account for the influence of heterogeneity on fluorescence data. 相似文献
4.
Little Shingobee Lake and Fen are part of the extensive network of lakes and wetlands in the Shingobee River headwaters of
northwestern Minnesota, designed to study the interactions between surface and ground waters. Prior to about 11.2 cal. ka,
most of these lakes and wetlands were interconnected to form glacial Lake Willobee, which apparently formed when a debris
flow dammed the Shingobee River. Between 11.2 and 8.5 cal. ka, the level of Lake Willobee fell as a result of breaching of
the dam, transforming the deep lake into the existing lakes and wetlands. Analyses of a 9-m core from Little Shingobee Lake
(LSL-B), and lacustrine sediments under 3.3 m of peat in a 17-m core from Little Shingobee Fen (LSF-10), show that the dominant
components are allogenic clastic material, and endogenic CaCO3 and organic matter. In both cores almost all of the iron (Fe) and manganese (Mn) are incorporated in endogenic minerals,
presumed to be X-ray amorphous oxyhydroxide minerals, that occur in significant quantities throughout the cores; almost no
Fe and Mn are contributed from detrital aluminosilicate minerals. This suggests that, for most of the Holocene, the allogenic
watershed contributions to lake chemistry were minor compared to the dissolved mineral load. In addition, prior to 3.5 cal.
ka, pollen zone boundaries coincide with large changes in lake-sediment mineralogy, indicating that both landscape and climate
processes were linked to early- and mid-Holocene lake chemistry. The pollen time series, with sequential domination by spruce,
pine, sagebrush-oak, birch-oak and, finally, white pine is typical of the region and reflects the changing location of the
prairie-forest transition zone over time. These changes in vegetation had some profound effects on the geochemistry of the
lake waters. 相似文献
1