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      Geochemical evidence for major environmental change at the Devonian–Carboniferous boundary in the Carnic Alps and the Rhenish Massif

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      Palaeogeography, Palaeoclimatology, Palaeoecology
      Elsevier BV

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          The abundance of 13C in marine organic matter and isotopic fractionation in the global biogeochemical cycle of carbon during the past 800 Ma

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            Oxygen isotope variations in phosphate of biogenic apatites, I. Fish bone apatite—rechecking the rules of the game

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              An isotopic study of biogeochemical relationships between carbonates and organic carbon in the Greenhorn Formation.

              Carbon-isotopic compositions of total carbonate, inoceramid carbonate, micritic carbonate, secondary cements, total organic carbon, and geoporphyrins have been measured in 76 different beds within a 17-m interval of a core through the Greenhorn Formation, an interbedded limestone and calcareous shale unit of Cretaceous age (Cenomanian-Turonian) from the Western Interior Seaway of North America. Results are considered in terms of variations in the processes of primary production (which led to the biosynthesis of the molecular precursors of the geoporphyrins) and in secondary processes (those mediating the transformation of primary organic material into sedimentary total organic carbon). It is shown that the porphyrin isotopic record reflects primary isotopic variations more closely than the TOC isotopic record, and that, in these sediments, TOC is enriched in 13C relative to its primary precursor by 0.6 to 2.8%. This enrichment is attributed to isotope effects within the consumer foodweb and is associated with respiratory heterotrophy. Variations in this secondary enrichment are correlated with variations in the isotopic composition of marine carbonate. This correlation is attributed to effects of environmental changes on the marine foodweb. These may have included increased atmospheric oxygen associated with the Cenomanian-Turonian oceanic anoxic event. The isotopic fractionation associated with fixation of carbon by primary producers is observed to have varied by 1.5% during the interval of deposition. It is suggested that this change is due to a variation in the makeup of the community of primary producers and/or to a decrease in the atmospheric abundance of CO2 during the oceanic anoxic event.
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                Author and article information

                Journal
                Palaeogeography, Palaeoclimatology, Palaeoecology
                Palaeogeography, Palaeoclimatology, Palaeoecology
                Elsevier BV
                00310182
                October 2006
                October 2006
                : 240
                : 1-2
                : 146-160
                Article
                10.1016/j.palaeo.2006.03.048
                b7cdb915-7bf5-4998-8668-c8511d246615
                © 2006

                http://www.elsevier.com/tdm/userlicense/1.0/

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