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Titolo:
The occurrence of phosphate minerals in lacustrine clayey diatomite deposits, Thessaly, Central Greece
Autore:
Stamatakis, MG; Koukouzas, NK;
Indirizzi:
Natl Univ Athens, Dept Geol, Sect Econ Geol & Geochem, Athens 15784, Greece Natl Univ Athens Athens Greece 15784 eol & Geochem, Athens 15784, Greece Ctr Solid Fuels Technol & Applicat, Athens 15310, Greece Ctr Solid Fuels Technol & Applicat Athens Greece 15310 ens 15310, Greece
Titolo Testata:
SEDIMENTARY GEOLOGY
fascicolo: 1, volume: 139, anno: 2001,
pagine: 33 - 47
SICI:
0037-0738(20010101)139:1<33:TOOPMI>2.0.ZU;2-B
Fonte:
ISI
Lingua:
ENG
Soggetto:
DIAGENESIS;
Keywords:
phosphate; clayey diatomite; Upper Miocene; lake sediments; Greece;
Tipo documento:
Article
Natura:
Periodico
Settore Disciplinare:
Physical, Chemical & Earth Sciences
Citazioni:
38
Recensione:
Indirizzi per estratti:
Indirizzo: Stamatakis, MG Natl Univ Athens, Dept Geol, Sect Econ Geol & Geochem, Athens 15784, Greece Natl Univ Athens Athens Greece 15784 Athens 15784, Greece
Citazione:
M.G. Stamatakis e N.K. Koukouzas, "The occurrence of phosphate minerals in lacustrine clayey diatomite deposits, Thessaly, Central Greece", SEDIMENT GE, 139(1), 2001, pp. 33-47

Abstract

Irregular masses, veins and leaf replacements composed of the phosphate minerals vivianite, mitridatite, anapaite and hydroxylapatite occur in the Sarantaporo-Elassona Upper Miocene lacustrine basin, Thessaly, central Greece. They are hosted in clayey diatomite, Grey to dull green irregular veins of anapaite up to 40 cm thick and spherical concretions up to 2 cm in diameter sporadically occurred at shallow depths. Minor hydroxylapatite rims anapaite masses. Mitridatite occurs in the near surface as greenish-brown veins5 cm thick, cutting the diatomite or oriented sub-parallel to bedding. Themitridatite veins are rimmed by, and grade into, iron oxides-hydroxides atthe surface. In borehole samples, at depths greater than 40 m, bluish vivianite frequently replaces leaves and faecal pellets up to 2 cm in diameter. Conditions permitting the precipitation of phosphate minerals in the basinwere the deposition of organic matter, a highly reducing environment at depth (possibly in the lake water but certainly in the bottom sediment), and a low availability of calcium during sedimentation, but its subsequent moderate enrichment in groundwater. The kind of phosphate formed depended on the diagenetic microenvironment. The diagenetic environment was slightly alkaline (8 > pH > 7). The Ca2+/Fe2 and Ca2+ phosphates (i.e. anapaite and hydroxylapatite) that occur at shallow burial depths, most likely formed at the expense of the originally formed Fe2+-phosphate vivianite. The progressive substitution of Fe by Ca is attributed to the action of Ca-rich groundwater. The alteration of the ferrous phosphate anapaite to the ferric phosphate mitridatite, plus amorphous iron hydroxides and goethite at the surface, is an indicator of strongly oxidising conditions. The Fe2+ ions of the phosphates were derived from the leaching of the ultrabasic and schist basement rocks. The absence of calcite in the diatomite reflects the low calcium content of the lake water during sedimentation. Thepresence of smectite and vermiculite promoted the adsorption of phosphate ions in the sediments of the basin. The accumulation of Fe indicates of the presence of a eutrophic lake environment. The phosphate minerals further suggest stagnant bottom waters and high biological productivity that was promoted by warm-humid conditions. (C)2001 Elsevier Science B.V. All rights reserved.

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Documento generato il 23/10/20 alle ore 05:54:39