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11.
Ammonium acetate dissolution experiments were performed on shell material of the modern bivalves, Crassostrea virginica (calcite) and Mercenaria mercenaria (aragonite). Their purpose was to determine the order of preferential dissolution of Sr, Mg and Ca; these results subsequently were compared with Sr, Mg and Ca data from other Recent as well as ancient mollusks.Results from these experiments suggest the following relative order of abundance of readily exchangeable Mg and Sr in biogenic carbonates: Mg(arag) > Mg(calc) > Sr(calc) > Sr(arag). It is apparent that incongruent dissolution of minerals with different solubilities cannot entirely explain the observed dissolution patterns for Sr, Mg and Ca in these biogenic carbonates. Secular changes in whole shell Mg and Sr concentrations for Recent and unrecrystallized fossil mollusks suggest an order of “ionic mobility” in diagenesis identical to the order of abundance for readily exchangeable ions found in the NH4Ac dissolution experiments. It is concluded that this “ionic mobility” is due to a post mortem, early diagenetic (pre-recrystallization) approach to equilibrium with the surrounding chemical environment. 相似文献
12.
Center-of-mass coordinates for 57 tracking sites participating in the GEOS-C mission are given in a unified system having
a common origin and scale. The positions were obtained either directly from analyses of satellite observations or from survey
ties to colocated sites with coordinates previously determined by various investigators from optical, laser of doppler data.
The uncertainty of the positions in nearly all cases is 5 m in each coordinate. Data reductions show that station coordinates
of this quality introduce a rapidly changing error into the altitude of a satellite unless global tracking constrains the
orbit. 相似文献