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Book Chapter

Origin of Phosphorites, Glauconites and Associated Facies Through Time: Case Studies

Published:
January 01, 2000

Abstract:

Study of the carbonate micrite phase of laminated pelletal phosphorites from various phosphate fields of the Negev reveals that this phase was largely formed in situ, and that bacterial mats are principally the frame-builders of this phase. These mats are composed of vertically stratified, calcite-mineralized assemblages of bacterial bodies of various shapes, sizes, and organizations. This biostratification is believed to represent the fossilized record of time-successive consumer bacterial populations that degraded planktonic detritus, and mats of filamentous and coccoid microphytes, which colonized the Mishash seafloor during phosphorite formation and were partly preserved in these rocks as apatitic sheaths and envelopes. Carbonate mineralization of the bacterial consumers probably took place during anaerobic degradation of the matted sediments, as indicated by low δ13C values in many of these carbonates. The diagenetic fate of the filamentous and coccoid Mishash bottom-dwelling microphytes (apatite mineralization versus turnover as bacterial carbonates) was dependent on the balance between the rate of organic matter accumulation and the extent of bottom sediment ventilation, which together controlled the redox conditions of organic matter decomposition and pore-water carbonate ion concentrations. This may explain why primary (pristine) apatite beds are common in condensed proximal Mishash sections around Negev Campanian highs, whereas they are more sporadic in basinal carbonate-rich Mishash sections. It might also explain why the coccoid and filamentous microphyte structures, which matted the Mishash seafloor and are now preserved in many of the Negev phosphorite rocks, were found to be mineralized only by phosphate and never by carbonate.

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SEPM Special Publication

Marine Authigenesis: From Global to Microbial

Craig R. Glenn
Craig R. Glenn
Department of Geology and Geophysics, University of Hawaii
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Liliane Prévôt-Lucas
Liliane Prévôt-Lucas
Centre de Géochimie de la Surface, Strasbourg
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Jacques Lucas
Jacques Lucas
Université Louis Pasteur, Institut des Sciences de la Teree, Strasbourg
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SEPM Society for Sedimentary Geology
Volume
66
ISBN electronic:
9781565761889
Publication date:
January 01, 2000

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