Publication: Palaeogeographical significance of clay mineral assemblages in the
Permian and Triassic sediments of the SE Iberian Ranges,
eastern Spain
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Publication Date
1997
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Elsevier
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Abstract
The evolution of the palaeogeography of the SE Iberian Basin during the Permian and Triassic represents a general
evolution from continental to marine environments. It has been recently studied from the sedimentological,
stratigraphical, tectonic and palaeontological points of view. In spite of these results, many aspects of this
palaeogeography are still a matter of discussion. In this study, clay mineralogy analysis complements previous studies
representing a new aspect for understanding the evolution of the sedimentary environment and the palaeogeography
of the Iberian Basin during the periods in question and thus of the palaeogeography and the location of the major
high areas in the westernmost border of the Tethys sea.
In spite of late diagenetic transformations the original clay mineral associations of the Permian-Triassic sediments
of the SE Iberian Ranges can be reconstructed. Seventy-seven samples of siliciclastic and carbonate sediments of these
ages have been studied (SEM and XRD), revealing six new aspects that help to precise the palaeogeographical
interpretation of the area:
(1) Two major mineral assemblages have been found: illite+ kaolinite +pyrophyllite in the continental facies and
illite + chlorite + vermiculite + mixed-layer clays in the marine facies.
(2) The Mg-rich clay minerals are here considered to be of marine origin.
(3) Active phases of basin boundary faults are marked in the sediments by the presence of pyrophyllite, derived
directly from the Palaeozoic metamorphic basement.
(4) Unconformities separating major depositional sequences also separate formations with different clay mineralogy.
(5) Different groups of clay minerals can be separated clearly coinciding with the different palaeogeographical
stages also distinguished in the westernmost border of the Tethys sea.
(6) The clay mineral associations back up the data of a previous hypothesis of a humid climate for the end of the
Permian in the study area just prior to the first incursion of the Tethys sea.