Showing papers in "Geochimica et Cosmochimica Acta in 1996"

TL;DR: A mathematical framework for quantitative evaluation of alpha-stopping effects on (U-Th)/He ages has been developed in this paper, and the results are useful for identifying the size and shape of grains which are best suited for (UTh/He) dating and provide the basis for correcting ages when ejection effects are significant.

TL;DR: In this article, an analysis of ochreous sediments and associated solutions from twenty-eight mine drainage sites showed that precipitates formed at pH 6.5 or higher were composed of ferrihydrite (nominally Fe5HO8 · 4H2O) or a mixture of ferria and goethite (α-FeOOH), whereas those precipitated from waters having pH values in the range of 2.8 to 4.5 were predominantly schwertmannite (ideally Fe8O8(OH)6SO4) with trace

TL;DR: In this paper, a survey was made of framboid size distributions in recently deposited sediments from euxinic (Black Sea; Framvaren Fjord, Norway; Pettaquamscutt River Estuary, Rhode Island, USA), dysoxic (Peru Margin), and oxic (Wallops Island, Virginia, USA; Great Salt Marsh, Delaware, USA) environments.

TL;DR: In this paper, the Mg concentrations within single chambers of the planktic foraminifer Globigerinoides sacculifer (BRADY) maintained under controlled laboratory conditions were measured at variable temperatures (19.5-29.5 °C) and constant salinity and (2) at variable salinity (22-45

TL;DR: In this article, the authors introduce the concept of a geochemical switch, in which HS- transforms the marine behavior of a conservative element to that of a particle reactive element, and the action point of the HS- switch is calculated to be, a(HS)- = 10(-3.6) - 10(-4.3).

TL;DR: In this article, the authors show that tortuosity is accurately correlated to readily measured porosity values, φ, through the simple relation: θ 2 = 1 − l n ( φ 2 ).

TL;DR: In this article, the isotopic compositions of aubrites coincide with the Earth and Moon, and also with the enstatite chondrites, and they also support the following genetic associations: (1) winonaites and IAB-IIICD irons, (2) acapulcoites and lodranites, and (3) ureilites and dark inclusions of C3 chondites.

TL;DR: In this paper, a generalized model was developed for the prediction of animal body water and phosphate δ18O to incorporate these factors quantitatively, and a moderate dependence of animal ǫ on humidity is predicted for drought-tolerant animals, and the correlation between humidity and North American deer bone composition as corrected for local meteoric water is predicted within the scatter of the data.

TL;DR: In this article, a range of precipitation rates was used to study the nonequilibrium and equilibrium partitioning behaviors of minor metal ions to calcite (CaCO3(s)) in natural waters.

TL;DR: In this article, the authors studied the distribution of rare earth elements in hydrogenetic marine ferromanganese (Fe-Mn) crusts from the Central Pacific Ocean and found that the rare earth properties of the seafloor are similar to those of the terrestrial environment.

TL;DR: The (U-Th)/He system for low-temperature thermochronometry was investigated in this article, where the authors measured helium ages on Durango fluorapatite and on apatites from a gabbro and two tonalites from the Peninsular Ranges Batholith.

TL;DR: This article determined the hafnium and neodymium isotopic compositions of thirty-two Precambrian granites and rhyolites from diverse suites of crustally derived magmatic suites.

TL;DR: In this article, the authors used the partial equilibrium approach to explain the simultaneous occurrence of Fe(III) and sulfate reduction, observed in several field studies, and showed that, depending on the stability of the iron oxides, simultaneous reduction of Fe (III), sulfate, and methanogenesis is thermodynamically possible under a wide range of sedimentary conditions.

TL;DR: Pyrite formation has been investigated at 70°C and pH 6-8 by aging precipitated, disordered mackinawite, Fe9S8, and greigite in solutions containing aqueous H2S, HS, Sx2−, S2O32−, SO32− and colloidal elemental sulfur as discussed by the authors.

TL;DR: In this article, a numerical model of sedimentary early diagenetic processes that includes oxic and anoxic mineralization is presented to reproduce the cycling of carbon, oxygen, and nitrogen along the ocean margin.

TL;DR: In this paper, X-ray diffraction and electron microscopic analyses indicated that the Fe-rich material collected was predominantly ferrihydrite and poorly crystallized lepidocrocite, while the Mn-rich mixture was a mixture of poorly crystallised Mn oxyhydroxides.

TL;DR: In this paper, an analysis of the phyllites from the Archean Buhwa Greenstone Belt, Zimbabwe, were deposited on a stable cratonic platform and the results indicated that the source dominantly consisted of tonalite with less common occurrences mafic volcanic rocks and granite.

TL;DR: In this paper, the authors investigated the photoreactivity of biologically refractory DOM in the Amazon River system and found that 15% of the DOM was photoreactive and that bacterial growth and respiration were not significantly inhibited during periods of sunlight exposure.

TL;DR: In this article, the authors used Born solvation theory for surface proton, electrostatic interactions of the adsorbing proton with a surface oxygen and an underlying metal, and an intrinsic binding of the proton to the surface.

TL;DR: The Steadsed1 as discussed by the authors model is a multicomponent reactive transport code for steady-state early diagenesis which fully incorporates the reaction couplings among the elements, C, O, N, S, Fe, and Mn.

TL;DR: The applicability of laser probe analysis of tooth enamel for δ18O has been verified, and the method has been applied to different modern herbivores in East Africa as discussed by the authors.

TL;DR: In this article, the chemical composition of the different phases carried in the Congo rivers and is followed by a companion paper, devoted to the modelling of major and trace elements, is presented.

TL;DR: In this paper, the authors analyzed the inter-REE(III) relationships and found that the heavy rare earth elements (REEs) behave virtually conservatively and are suitable as tracers of water masses.

TL;DR: A wide range of novel diagenetic and catagenetic products of the diaromatic carotenoid isorenieratene, a pigment of the photosynthetic green sulphur bacteria Chlorobiaceae, has been identified in a number of sedimentary rocks ranging from Ordovician to Miocene.

TL;DR: This paper used coupled measurements of the oxygen isotope composition of structural carbonate and phosphate from horse tooth enamel, and estimated the apparent fractionation factor between structural carbonates and body water is 1.0263 ± 0.0014.

TL;DR: The Pliocene (7 Ma) Nb-enriched arc basalts of the Valovayam Volcanic Field (VVVF) in the northern segment of Kamchatka arc (Russia) host abundant xenoliths of spinel peridotites and pyroxenites.

TL;DR: In this paper, a numerical model was proposed to predict aluminosilicate dissolution rates as a function of changes in residual mineral abundance, grain size distributions, and mineral surface areas with time.

TL;DR: In this article, the solubility of gold has been measured in aqueous sulphide solutions at temperatures between 150°C and 500°C, and pressures of 500-1500 bar over a wide range of pH and total dissolved sulphur concentrations.

TL;DR: In this paper, three parameters are proposed to determine the relative extent of alteration in CM chondrites: the mineralogic alteration index monitors the relative progress of coupled substitutions in the progressive alteration of cronstedtite to Mg-serpentine and increases with increasing alteration.