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Fibrous clays in the Almazan Basin (Iberian Range, Spain): genetic pattern in a calcareous lacustrine environment

Published online by Cambridge University Press:  09 July 2018

F. Lopez-Aguayo
Affiliation:
Dpto. Cristalograftía y Mineralogía, Estratigrafía, Geodinàmica y Petrología y Geoquímica, Facultad Ciencias del Mar. Universidad de Cádiz, Apdo. 40, 11510 Puerto Real, Cádiz, Spain
J. M. Gonzalez Lopez
Affiliation:
Dpto. Ciencias de la Tierra, Facultad de Ciencias, Universidad de Zaragoza, Plz. S. Francisco, s/n 50009 Zaragoza, Spain

Abstract

The Tertiary sediments of the southern part of Almazán basin (Province of Soria) exhibit two different facies with a sharp transition between them: (1) a coarse detrital facies; and (2) a lutite and carbonate facies. The vertical evolution of these facies in the different sections and boreholes is made up of several retrograde depositional sequences which evolve from proximal alluvial fans to carbonate lacustrine systems associated with the most distal fan sediments.

The variation of the mineralogical association (carbonates, quartz, detrital clay minerals, palygorskite and, occasionally, sepiolite and smectites) allows four ‘mineralogical facies’ to be established. Each facies has a distinctive mineralogy related to the main genetic processes: (1) detrital facies; (2) transitional facies; (3) ‘chemical dolomite-palygorskite’ facies and (4) ‘chemical calcite’ facies. Although the carbonates (calcite and dolomite) are always the most abundant minerals, fibrous clay minerals are also important. The main mechanism of mineral authigenesis in this basin is chemical precipitation; the presence and distribution of carbonates and fibrous clay minerals is controlled by the relative concentrations of [Mg2+], [Ca2+], pCO2, pH and [SiO4H4]. Palygorskite occurrences, in these conditions, are related to dissolution-precipitation mechanisms of pre-existing detrital material.

Type
Research Article
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1995

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