Estudio textural e isotópico de los sulfuros diseminados en los sedimentos de la Cuenca de Cameros (La Rioja, España)
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1
Universidad de Huelva
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2
Universidad Complutense de Madrid
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3
University of Leeds
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ISSN: 0214-2708
Year of publication: 1999
Volume: 12
Issue: 2
Pages: 241-250
Type: Article
More publications in: Revista de la Sociedad Geológica de España
Abstract
Pyrite and pyrrhotite have been found in small quantities scattered in the lutitic sediments of the Cameros Basin. The sedimentary pyrite appears as framboids, euhedral crystals and replacing fossil shells. Occasionally, together with the sedimentary pyrite it is possible to find pyrrhotite generated by the thermal breakdown of the sedimentary pyrite during the metamorphism. The sulphur isotopic signature of the pyrrhotite is always higher than the pyrite in the same sample, ranging from 4.5 to 57.7 ‰. The sedimentary pyrite was generated by the bacterial reduction of sedimentary sulphates. The isotopic composition of the pyrites varies depending on the zone of the basin considered. On one hand, in the east sector, the isotopic compositions are positive and very variable ranging from 2.6 to 19.7 ‰. On the other hand, in the west sector the δ34S values are always negative and quite constant (≈-18 ‰). These differences are related with two factors: a) variations in the subsidence rate between both sectors, and b) transformation reactions of pyrrhotite to pyrite during the retrogressive metamorphism.