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Book Chapter

Diagenetic Evolution of Seamount Phosphorite

By
Laura M. Benninger
Laura M. Benninger
Geology Department, University of California, Davis, California, 95616, USA
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James R. Hein
James R. Hein
U.S. Geological Survey, MS 999, 345 Middlefield Rd., Menlo Park, California, 94025, USA
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Published:
January 01, 2000

Abstract:

Phosphorite, limestone, basalt, and breccia/conglomerate occur on the flanks of central Pacific Cretaceous seamounts. Phospbatization occurred during the Tertiary, at or immediately below the sediment-water interface, within thin bodies of porous carbonate sediment and within all rock types that occur on the seamounts. The phosphorites are composed of carbonate fluorapatite (CFA), which lines pores and replaces carbonate and silicate protoliths; protolith fabric is locally preserved in fine detail. Phosphatization is typically most pervasive adjacent to pores, fractures, and the outer surfaces of samples.

In order of decreasing abundance, diagenetic minerals associated with seamount phosphorites (SMP) include: CFA, Fe-Mn oxyhydroxides, palagonite, smectite, phillipsite, and barite. This mineral assemblage indicates that CFA formed under conditions consistent with low-temperature, open-circulation seafloor alteration of basalt. The common association between CFA and precipitation of Fe-Mn oxyhydroxides indicates that SMP formed under oxic to suboxic conditions.

Phosphatization is characterized by mineralization fronts; the angular superposition of those fronts (successive mineralizing fluids coming from different directions) locally leads to irregularly shaped domains that differ in pervasiveness of phosphatization, degree of fabric preservation, and abundance of secondary minerals. Phosphatization is, therefore, controlled by a variety of factors including protolith mineralogy and fabric, degree of pore-fluid saturation with respect to CFA, rate of pore-fluid/seawater circulation (rock-water ratio), and number of previous episodes of phosphatization.

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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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