Record Details

Miocene phosphorites from the Murray Ridge, northwestern Arabian Sea

DRS at CSIR-National Institute of Oceanography

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Title Miocene phosphorites from the Murray Ridge, northwestern Arabian Sea
 
Creator Rao, V.P.
Hegner, E.
Naqvi, S.W.A.
Kessarkar, P.M.
Ahmad, S.M.
Raju, D.S.
 
Subject Murray Ridge
REE and trace elements
Phosphorites
Microbial activity
 
Description Phosphorites from the Murray Ridge, NW Arabian Sea comprise nodules, bioclasts, and bone fragments. The nodules are made up of a homogeneous, light-colored phosphate nucleus consisting of Rivulariacean filamentous cyanobacteria and a thin dark-grey colored phosphate cortex showing abundant microbial filaments and microborings. The bioclasts comprise of approx. 14-14.5 Ma old planktonic foraminifers, accepted as the time of deposition. Spherical to ovoid-shaped apatite microparticles resembling fossil bacteria are distinct components in the bioclasts. Bone fragments exhibit apatite fillings. The nodules and bone fragments consist entirely of carbonate fluorapatite (CFA) with low Al, K, and Th concentrations suggesting absence of continental detritus. Shale-normalized REE patterns of the samples support a seawater-derived composition. The highly uniform initial Sigma sub(Nd) values of -4.8 to -5.1 are interpreted as the seawater value at the onset of phosphatization approx. 14 Ma ago. In contrast, sup(87) Sr / sup(86) Sr ratios show a large range of 0.709055 to 0.709124 corresponding to unusually young stratigraphic ages of approx. 1 to 3 Ma. The data are interpreted as evidence for post-depositional Sr exchange of the recrystallizing phosphorites with fluids isotopically not much different from modern seawater. It is concluded that the phosphorites formed under oxic, shallow-water conditions where microbial populations assimilated phosphorus primarily from seawater and mediated precipitation of CFA during early diagenesis at the sediment–water interface on different substrates.
 
Date 2008-05-01T06:56:34Z
2008-05-01T06:56:34Z
2008
 
Type Journal Article
 
Identifier Palaeogeography, Palaeoclimatology, Palaeoecology, vol.260(3-4); 347-358p.
http://drs.nio.org/drs/handle/2264/1060
 
Language en
 
Rights Copyright Elsevier [2008]. It is tried to respect the copyright. If it is brought to our notice that the rights are violated then the item would be withdrawn.
 
Publisher Elsevier