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Calcretes, Palycretes and Silcretes in the Paleogene Detrital Sediments of the Duero and Tajo Basins, Central Spain

Published online by Cambridge University Press:  09 July 2018

M. Rodas
Affiliation:
Dpto. Cristalografía y Mineralogía, Fac. Geología, Universidad Complutense de Madrid, 28040 Madrid
F.J. Luque
Affiliation:
Dpto. Cristalografía y Mineralogía, Fac. Geología, Universidad Complutense de Madrid, 28040 Madrid
R. Mas
Affiliation:
Dpto. Cristalografía y Mineralogía, Fac. Geología, Universidad Complutense de Madrid, 28040 Madrid
M.G. Garzon
Affiliation:
Dpto. Cristalografía y Mineralogía, Fac. Geología, Universidad Complutense de Madrid, 28040 Madrid

Abstract

Three duricrust types (calcretes, palycretes and silcretes) have been distinguished in the Lower Paleogene arkosic materials from the margins of the Duero and Tajo basins (central Spain). In the calcretes the cements are composed of calcite plus palygorskite, whereas palygorskite is the only cement in the palycretes. In the silcretes, the cement consists chiefly of opal and chalcedony, with minor quartz. The important duricrust development in the Paleogene detrital materials can be correlated with a drastic climatic change towards colder and more arid conditions during this time, as inferred from the sedimentological features and the clay mineral evolution. The origin of calcretes and palycretes is related to the movement of alkaline phreatic waters generated from dolomitic rocks of Cretaceous age cropping out in the near surroundings. Silcretes originated from the vertical transfer of silica from supersaturated groundwaters, from the Hercynian granitic rocks, up to the surface. Silcretes are developed either on unconsolidated arkosic materials or replace previous calcrete or palycrete levels.

Type
Research Article
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1994

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