Showing papers in "American Journal of Science in 1980"

Radium, thorium, uranium, and 210 Pb in deep-sea sediments and sediment pore waters from the North Equatorial Pacific

Abstract: Determination of radium, thorium, uranium isotopes, and /sup 210/Pb in sediments and sediment pore waters from North Equatorial Pacific deep-sea clay-silicous oozes shows that the radium and uranium isotopes are mobile in the pore water. The concentration-depth profiles of radium can be understood in terms of a diagenetic model which takes into account mixing of sediment particles by bioturbation, molecular diffusion in the pore water, adsorption onto particle surfaces, as well as radioactive production and decay. The /sup 234/U//sup 238/U activity ratios in several samples are higher than the seawater value, indicating some enrichment of /sup 234/U in the pore water. However, the absolute concentrations of /sup 238/U and /sup 234/U are 25% lower than those in seawater, suggesting that the sediments form a sink for uranium isotopes. /sup 210/Pb is present in the pore water at concentrations approx. 20% that of /sup 226/Ra. The origin of /sup 210/Pb in the pore water is uncertain and could be due either to its in situ mobilization in the sediments or subsequent production in the laboratory from the decay of /sup 222/Rn. /sup 230/Th is present in measurable concentrations in the pore waters, but its distribution does not show any systematic trendmore » with depth or other parameters. The most likely source of /sup 230/Th appears to be minute amounts of sediment particles collected in the pore waters during the squeezing operation.« less

Chemical interaction of aqueous solutions with epidote-feldspar mineral assemblages in geologic systems; 1, Thermodynamic analysis of phase relations in the system CaO-FeO-Fe 2 O 3 -Al 2 O 3 -SiO 2 -H 2 O-CO 2

Abstract: Simultaneous consideration of Moessbauer and/or experimental phase equilibrium data for epidote, andradite, and hedenbergite together with the thermodynamic properties of aqueous species, CO/sub 2/-H/sub 2/O fluids, and coexisting minerals permits comprehensive analysis of mineral stabilities and the effects of preferential site occupancy and solid solubility on hydrothermal solution compositions in the system CaO-FeO-Fe/sub 2/O/sub 3/-Al/sub 2/O/sub 3/-SiO/sub 2/-H/sub 2/O-CO/sub 2/ at high pressures and temperatures. Assuming substitutional order/disorder in epidote solid solutions to be independent of composition together with random mixing and equal interaction of cations on energetically equivalent sites in garnet and epidote solid solutions permits calculation of the extent of Al/sup 3 +/ and Fe/sup 3 +/ partitioning between coexisting garnet and epidote. The results of these calculations agree closely with published compositions of garnet and epidote solid solutions in skarn deposits, low-grade metamorphic rocks, and geothermal systems.

Calcite-seawater reactions in ocean surface waters

Abstract: The behavior of calcite in typical mixed-layer seawater supersaturated with respect to calcite and aragonite was investigated using saturometry techniques. Additions of reagent-grade calcite to this seawater produced surface films on the calcite, some of which are more soluble than calcite or aragonite. Correlation of film thickness and solubility with the solubilities of Mg calcites indicates that the Mg content of the surface films increases with the square root of film thickness, except for the thinnest films produced. The solubility of a given film decreases with age, a phenomenon originally described by Weyl. The aging process, as measured by diminution of the carbonate alkalinity of the seawater solutions, is approximately a logarithmic function of time. Current evidence indicates that high magnesium skeletal suspended sedimentary materials should dissolve in response to increased atmospheric CO/sub 2/.

The distribution of Fe (super 2+) and Mg between coexisting ilmenite and pyroxene with applications to geothermometry

Abstract: A process is disclosed for improving the oxidative resistance of amorphous carbon or graphite articles. The process comprises applying a solution of water; an oxide or hydroxide of a group 2 metal; a member of the group consisting of nitric acid; sodium nitrite and sodium carbonate; and boric acid or sodium tetraborate.