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G. N. Baturin 《Doklady Earth Sciences》2006,407(1):330-334
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Morphology, microstructure, and chemical composition of the nodular fraction of phosphatic sand from the outer Namibia shelf are considered. The nodules are divided into three varieties: concretions, phosphatic casts of shells pelecipod and gastropod, and phosphatized sea lion coprolites. A part of nodules shows massive homogeneous structure, whereas other nodules contain sand-size phosphatic grains derived from the host phosphatic sand. All nodules display the same spectrum of microstructures, including colloform, granular-globular, and crystallomorphic ones. The crystallomorphic nodules are composed of scattered and aggregated crystallites of isometric, rod-shaped, and dumbbell-shaped forms, as well as crystallized shells on grains incorporated into nodules. Phosphatized remains of diatoms, foraminifers, and embryonic gastropods, as well as vermicular and filamentous bacterial forms occur among biogenic components of the nodules. Framboidal pyrite is present in all nodules. In terms of phosphate microstructure, character of organic remains, and chemical composition, the nodules are similar to phosphate grains of the host sand, recent phosphorites from the inner Namibia shelf, and some ancient phosphorites. 相似文献
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Doklady Earth Sciences - The relation of nonferrous metals and other elements to the main mineral phases in iron–manganese ore is a matter of interest in theoretical and practical terms and... 相似文献
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The geochemical study of the suspended matter in the waters of the Amazon River and its tributaries revealed that the chemical composition of this material ranges widely; however, generally, it is similar to the average composition of the suspended matter in the rivers and clayey sedimentary rocks around the world. Against this background, an essential regional Hg enrichment due to the anthropogenic factor is distinguished. The suspensions from the so-called clear waters from the tributaries of the Amazon River—Xingu and Trombetas—demonstrate the local enrichment in Pb, Sn, Zn, and organic carbon indicating the ore mineralization of the drainage basin, and points to the presence of metal-organic complexes. 相似文献
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A set of smoothed temperature gradient profiles around overshooting layers at the solar convective zone bottom is considered. In classical local theories of convection the one point defined according to the Schwarzschild criterion is enough to describe a convective boundary. To get a sophisticated picture of the overshooting we use four points to compute the transition overshooting functions. Analyzing the transition gradient profiles we found that the overshooting convective flux may be either positive or negative. A negative overshooting flux appears in nonlocal convective theories and causes a steep temperature gradient profile. But we propose an evenly smoothed gradient which corresponds to a convective flux positive everywhere. To outline the effect of the temperature gradient on the solar oscillations the squared Brunt–Väisälä frequency N 2 is calculated. In local convective theories the N 2 profile shows the discontinuity of the first derivative at the convective boundary, while all smoothed profiles eliminate the break. 相似文献
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Although diffusion is usually associated with equalizing of the chemical composition, the pressure and temperature gradients inside the Sun cause elemental diffusion segregation. While light hydrogen is flowing up to the solar envelope, helium and heavier elements are settling down to the core. The target of our simulation is an accurate estimation of the settling rate in solar plasma during the course of solar evolution. The rate of helium depletion in the envelope is a key parameter of the solar evolution and depends on position and conditions around the base of the convective mixing zone. The rate of heavy element settling is sensitive to the degree of ionization and interaction with the radiation flux. We estimate the effect of ion ionization on the settling rate for several heavy elements up to iron in the framework of the LTE assumption and the thermodynamic calculation according to SAHA-S EOS. 相似文献