Early diagenetic influences on iron transformations in a freshwater lake sediment   总被引：4，自引：0，他引：4  

Paul Wersin  Patrick H  hener  Rudolf Giovanoli  Werner Stumm 《Chemical Geology》1991,90(3-4):233-252

Iron transformations in a calcium carbonate rich fresh-water sediment were studied by analyzing the relevant constituents of both interstitial water and solid matter. Analysis of interstitial water shows that the observed redox sequence NO⁻₃/NH⁺₄, MnO₂/Mn(II), FeOOH/Fe(II), SO²⁻₄/S(−II) is roughly in agreement with that predicted by the Gibbs Free Energy for the corresponding reactions. In contrast to marine sediments, these redox transitions occur in the uppermost sediments, i.e., at depths of 0–4 cm.

Deeper in the sedimentary sequence, the depth profile for dissolved iron exhibits a steady non-linear increase up to 400 μmol dm⁻³. In this anoxic zone, according to thermodynamic predictions, iron (II)-minerals such as iron sulfide, siderite, and vivianite should precipitate while Fe(III) oxides should be completely dissolved. However, microscopic analysis showed that Fe(III) oxides were present throughout the studied sediment. Furthermore, scanning electron microscope/energy dispersive spectroscopy analysis suggests the presence of iron sulfide could be verified but not that of siderite or vivianite. These observations indicate kinetic control of iron transformations.

We have investigated the importance of kinetic control of iron distribution in anoxic sediments using a diagenetic model for dissolved iron(II). A rough estimate of time scales for dissolution and precipitation rates was made by imposing limiting boundary conditions. Using the calculated rate constant, we established that more than 1000 years would be required for the complete dissolution of Fe(III) oxides, which is agreement with our observations and experimental data from the literature. Calculated precipitation rates of Fe(II) for a given mineral phase such as siderite yield a maximum value of 3 μg_(FeCO3) g⁻¹_{(dry sediment)} yr⁻¹. Such low rates would explain the absence of siderite and vivianite.

Finally, it can be inferred from the Mn_T/Fe_T ratio in the sediments that this ratio depends on the redox conditions of the sediment-water interface at the time of deposition. Thus, this ratio can be used as “paleo-redox indicator” in lacustrine sediments.  相似文献   

Correlations among the reflectances of vitrinite, chitinozoans, graptolites and scolecodonts     

Rudolf Bertrand 《Organic Geochemistry》1990,15(6)

Paleozoic marine sequences sampled in outcrops and wells of northeastern Gaspe Peninsula (Quebec Appalachians) yield kerogen composed in part of vitrinite and zooclasts (chitinozoans, scolecodonts and graptolites) on which reflectance measurements were made.The comparison between means of random measurements show that reflectance of chitinozoans is similar to that of telinite (vitrinite with a cellular texture) and that the reflectance of scolecodonts is significantly lower than that of telinite in the lower range of studied values. At higher reflectivities differences decrease but, at the end of the condensate gas zone reflectancea are not yet identical. As shown by previous studies, reflectance of graptolites is slightly less than that of telinite.Pyrobitumen reflectance is related to the lithology of the host-rock and no generalized correlation can be established between the reflectance of pyrobitumen and that of vitrinite.  相似文献   

Age and evolution of scheelite-hosting rocks in the Felbertal deposit (Eastern Alps): U-Pb geochronology of zircon and titanite     

Roland Eichhorn  Urs Schärer  Rudolf Höll 《Contributions to Mineralogy and Petrology》1995,119(4):377-386

U-Pb isotope analyses of zircon and titanite extracted from different rocks of the Felbertal scheelite deposit yield the following information: (1) An age of 593±22 Ma (2) is obtained for zircon crystallization in the scheelite-bearing matrix of an eruption breccia in the western ore field. (2) Discordant zircons from an elongated, up to 8 m thick scheelite-rich quartzite body in the eastern ore field give an upper intercept age of 544±5 Ma. This quartzite contains a laminated, fine-grained scheelite mineralization. (3) Zircons from a small granitoid intrusion of the western ore field reveal an age of 336±16 Ma, and concordant titanites document an age of 282±2 Ma for Variscan amphibolite facies metamorphism. Both events, granitoid intrusion and later metamorphism caused ore re-mobilization, including the formation of yellowish fluorescent (molybdo-) scheelite porphyroblasts. (4) For a narrow lamprop-1hyric dike in the western ore field, a concordant titanite age of 283±7 Ma is obtained. This age is identical with the titanites from the amphibolite facies metamorphic intrusion. Tiny scheelite grains were tapped by the dike from pre-existing scheelite mineralizations in the truncated host rocks. (5) Alpine metamorphism at 31±4 Ma did not exceed lowermost amphibolite facies conditions, and it caused scheelite re-mobilization on a minor scale only, producing bluish fluorescent porphyroblasts in quartz veinlets and veins, as well as bluish fluorescent scheelite rims around older scheelite grains. Moreover, crosscutting Alpine fissure fillings show bluish fluorescent, inclusion-free scheelite. (6) The preservation of Variscan titanites, the absence of Alpine titanite growth, and the large degree of Variscan scheelite re-mobilization demonstrate that amphibolite facies metamorphism in the Felbertal area has a Variscan age. This result clearly documents Variscan tectono-metamorphism to be the dominant event, instead of the hitherto surmised Alpine metamorphism. This multi-stage evolution of the Felbertal ore bodies corroborates the view that tungsten deposits are conditioned by several succeeding thermal events, leading to a series of stages that ultimately produce high-grade scheelite concentrations. These high-grade ores predominately occur along shear zones of different age, accompanied by the formation of large volumes of low-grade scheelite mineralizations along host rock foliations and quartz veinlets and veins.  相似文献   

III. Bücher- und Zeitschriftenschau     

Bubnoff  Wilckens  Otto Wilckens  W. Obrutschew  Max Richter  R. Stickel  Rudolf Leutelt  Leuchs  Hans Frebold  W. Salomon-Calvi 《International Journal of Earth Sciences》1931,22(3-4):241-271

Ohne Zusammenfassung  相似文献   

Bücher- und Zeitschriftenschau     

Chudoba  Rudolf Leutelt  Wilckens 《International Journal of Earth Sciences》1929,20(6):458-461

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Bücher- und Zeitschriftenschau     

Leuchs  W. E. Schmidt  Bubnoff  H. Cl  Wilckens  W. Salomon  Donath  Wetzel  R. Stickel  Rudolf Leutelt 《International Journal of Earth Sciences》1930,21(5):314-338

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IV. Bücher- und Zeitschriftenschau     

Rudolf Hundt 《International Journal of Earth Sciences》1918,9(1-2):60-61

Ohne Zusammenfassung  相似文献   

Ferdinand von Wolff     

Dr. Rudolf Gaedeke 《Bulletin of Volcanology》1953,14(1):185-197

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Eine Methode zur Bestimmungdes wahren Winkelsder optischen Achsen und des mittleren Hauptbrechungsquotienten zweiachsiger Minerale im Dünnschliff     

Prof. Dr. Rudolf Mosebach 《Contributions to Mineralogy and Petrology》1951,2(5):432-436

Zusammenfassung Eine früher mitgeteilte Bestimmungsmethode des wahren Winkels der optischen Achsen und des mittleren Hauptbrechungsquotienten /ß mit Hilfe von Drehtischmessungen am Dünnschliff wird auf ihre Brauchbarkeit an Mineralien der Olivingruppe praktisch erprobt. Für senkrechten der nahezu senkrechten Austritt der Mittellinien werden einfache Berechnungsformeln abgeleitet und ihr Anwendungsbereich geprüft. An Olivinen verschiedener Herkunft wird der Fayalitgehalt optisch ermittelt und mit dem Ergebnis der quantitativen chemischen Analyse verglichen.Die Anwendbarkeit der Methode für ähnliche Bestimmungen an anderen, optisch zweiachsigen Mineralgruppen wird erwogen und in Ergänzung einer Methode von BuRRI besonders für rhombische Pyroxene vorgeschlagen.  相似文献   

Die Bestimmung des optischen Schwerpunktes von Glühlicht-Filter-Kombinationen     

Prof. Dr. Rudolf Mosebach 《Contributions to Mineralogy and Petrology》1951,2(5):437-442

Zusammenfassung Ein Verfahren zur mikroskopischen Bestimmung des optischen Schwerpunktes von Glühlicht-Filter-Kombinationen mit Hilfe von Drehkompensatoren wird entwickelt und praktisch erprobt. Bei genügend engem spektralen Durchlässig-keitsbereich (z. B. Lifa-Filter Nr. 215 rot und Nr. 391 blau) ist die Bestimmung der Schwerpunktswellenlänge () bis auf Bruchteile von m möglich. Das Verfahren kann prinzipiell auf alle Lichtquellen ausgedehnt werden; deren Wellenlängen sich in genügend engen Spektralbereichen halten. Erforderlich ist lediglich die genaue Kenntnis der Kompensatorkonstanten für Na-Licht, welche am besten durch Eichung mit einer Na-Dampflampe bestimmt wird.  相似文献