New palaeobotanical data from Carboniferous Culm deposits in the eastern Pyrenees constrain the age of the Variscan deformation in low-grade rocks.

C. Martín Closas, S. Trias, J. M. Casas

Abstract


The pre-Variscan rocks of the Pyrenees exhibit a polyphase deformation linked to the Variscan crustal shortening and a low-pressure–high-temperature metamorphism. There is scarce chronostratigraphic evidence of this Variscan deformation in the Pyrenees. In low-grade metamorphic domains, data are provided by the synorogenic Carboniferous Culm deposits, although the age of these deposits is difficult to ascertain directly. In medium- to high-grade metamorphic areas, the geochronological ages of the Variscan regional metamorphism or intrusive magmatic bodies constrain the age of the main Variscan deformation structures. However, these data usually provide a minimum age. Here, we present new palaeobotanical data that assign a Namurian age to the base of the Culm deposits of La Cerdanya in the eastern Pyrenees. This dating is based on the co-occurrence of the sphenopsids Archaeocalamites radiatus, Mesocalamites cistiiformis and the seed Cardiocarpus sp. The plant remains were found in sandstone facies produced by high–density turbidity flows of a deep-sea fan system. This shows the usefulness of sphenophytes and the associated flora of allochthonous assemblages from turbidites in elucidating the biostratigraphy of flysch facies, which usually lack coeval fossil remains. The new biostratigraphic information obtained constrains the age of the Carboniferous succession and sheds new light on the age of the Variscan deformation in the low-grade metamorphic rocks of the Pyrenees.

Keywords


Paleobotany; Structural geology; Variscan; Biostratigraphy

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DOI: http://dx.doi.org/10.1344/%25x

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Geologica Acta (ISSN-1695-6133)
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