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| Titel |
First discovery of dolomite and magnesite in living coralline algae and its geobiological implications |
| VerfasserIn |
M. C. Nash, U. Troitzsch, B. N. Opdyke, J. M. Trafford, B. D. Russell, D. I. Kline |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1726-4170
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| Digitales Dokument |
URL |
| Erschienen |
In: Biogeosciences ; 8, no. 11 ; Nr. 8, no. 11 (2011-11-15), S.3331-3340 |
| Datensatznummer |
250006203
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| Publikation (Nr.) |
 copernicus.org/bg-8-3331-2011.pdf |
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| Zusammenfassung |
| Dolomite is a magnesium-rich carbonate mineral abundant in fossil carbonate
reef platforms but surprisingly rare in modern sedimentary environments, a
conundrum known as the "Dolomite Problem". Marine sedimentary dolomite has
been interpreted to form by an unconfirmed, post-depositional diagenetic
process, despite minimal experimental success at replicating this. Here we
show that dolomite, accompanied by magnesite, forms within living crustose
coralline alga, Hydrolithon onkodes, a prolific global tropical reef species. Chemical
micro-analysis of the coralline skeleton reveals that not only are the cell
walls calcitised, but that cell spaces are typically filled with magnesite,
rimmed by dolomite, or both. Mineralogy was confirmed by X-ray Diffraction.
Thus there are at least three mineral phases present (magnesium calcite,
dolomite and magnesite) rather than one or two (magnesium calcite and
brucite) as previously thought. Our results are consistent with dolomite
occurrences in coralline algae rich environments in fossil reefs of the last
60 million years. We reveal that the standard method of removing organic
material prior to Xray Diffraction analysis can result in a decrease in the
most obvious dolomite and magnesite diffraction patterns and this may
explain why the abundant protodolomite and magnesite discovered in this
study has not previously been recognized. This discovery of dolomite in
living coralline algae extends the range of palaeo-environments for which
biologically initiated dolomite can be considered a possible source of
primary dolomite. |
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