Rare Earth Element Fractionation in Hydrogenetic Fe-Mn Crusts: The Influence of Carbonate Complexation and Phosphatization on SM/YB Ratios
E. Heinen De Carlo, X. Y. Wen, J. P. Cowen, 2000. "Rare Earth Element Fractionation in Hydrogenetic Fe-Mn Crusts: The Influence of Carbonate Complexation and Phosphatization on SM/YB Ratios", Marine Authigenesis: From Global to Microbial, Craig R. Glenn, Liliane Prévôt-Lucas, Jacques Lucas
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Hydrogenetic Fe-Mn crust layers accrete sequentially over millions of years and incorporate many trace elements by particle scavenging processes. By regulating the chemical environment at the aqueous/particle interface, conditions in the oceanic water column can thus influence the composition of Fe-Mn crusts. Because crusts are subject to much less diagenesis and post-depositional reworking than most other sedimentary deposits, they represent condensed stratigraphic sequences that reflect oceanic conditions through geologic time. Unfortunately many past efforts to reconstruct growth histories of crusts suffered from limitations inherent in dating techniques. Recently it has been demonstrated that Fe-Mn o ust laminae can be dated reliably using nannofossil biostratigraphy; and a combined approach using biostratigraphy and other dating methods now provides better chronological control on crust stratigraphy than previously available.
In this paper we present high-resolution (<3 mm) rare earth element (REE) profiles in hydrogenetic Fe-Mn crusts from two Pacific seamounts. We evaluate the concentrations of these trace elements in light of results of laboratory scavenging experiments and attempt to resolve the influence of solid-phase mineralogy and seawater chemistry on the extent of REE fractionation in growth layers of crusts. Because the chemistry of the REE in seawater is dominated by complexation with dissolved carbonate we hypothesize that temporal variations in REE fractionation in Fe-Mn crusts reflect primarily changes in the dissolved carbonate content of seawater. The use of the Sm/Yb ratio is proposed as a convenient measure of REE fractionation in Fe-Mn crusts and variations thereof are examined with respect to changes in oceanic carbonate content during the Cenozoic. Shale- normalized Sm/Yb ratios in nonphosphatized sections of crusts from the Pacific are believed to represent unaltered signals of conditions in the oceans at the time of accumulation and correlate inversely with the CCD throughout the Cenozoic.
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Marine Authigenesis: From Global to Microbial
This volume is a collection of 33 state-of-the-art papers focusing on various aspects of authigenic and diagenetic marine minerals and related global elemental cycling. The commingling of the various studies of authigenic minerals in this volume, including the most recent advances in knowledge concerning the occurrence and origins of phosphorites, glauconites, dolomites, siderites, manganese-iron associations, barites, ironstones, and other marine chemical sediments/sedimentary rocks of early authigenic/diagenetic origin, is partly the result of the increasing awareness that there are many overlaps, even direct co-associations, between different authigenic minerals, both in time, space, and genesis. Taken together, this compilation represents a holistic approach towards marine authigenesis that considers the integrated whole more than the simple sum of its parts.