# The Brecy depocenter as part of a new northern Massif Central Carboniferous-Permian Basin (France)

Laurent Beccabetto, Sylvie Bourquin

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Laurent Beccabetto, Sylvie Bourquin. The Brecy depocenter as part of a new northern Massif Central Carboniferous-Permian Basin (France). 29 ème édition de la réunion des sciences de la Terre (RST 2025), Société Géologique de France (SGF), Oct 2025, Montpellier, France. pp.662314. insu-05350581

HAL Id: insu-05350581

https://insu.hal.science/insu-05350581v1

Submitted on 6 Nov 2025

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# The Brécy depocenter as part of a new northern Massif Central Carboniferous-Permian Basin (France)

Laurent Beccaletto*¹ and Sylvie Bourquin²

¹Bureau de Recherches Géologiques et Minières – Bureau de Recherches Géologiques et Minières – France

²Géosciences Rennes – Université de Rennes, Institut National des Sciences de l'Univers, Centre National de la Recherche Scientifique – France

## Résumé

The late Carboniferous-Permian is a period of large-scale geodynamic reorganization, with the final accretion of Pangea and the beginning of its breakup (NeoTethys opening), coeval with the acme of the Late Paleozoic Ice Age, constituting a turning point in the climate regimes of the Paleozoic.

From the end of the Carboniferous onwards, the over-thickened and hot Variscan crust collapsed, triggering the rise of high-grade metamorphic domes and the development of thick post-orogenic coal basins.

We present here the structural pattern, thickness, tectonic evolution and depositional environments of the late Carboniferous-Permian Brécy depocenter (SW Paris Basin), as revealed by the reprocessing and interpretation of 115 km of vintage seismic lines combined with deep well data.

The present-day geometry of the Brécy depocenter is controlled by seven major and eleven minor eastward dipping normal faults. All these faults were active during the Meso-Cenozoic period, and some of them were possibly connected to deep detachments active during the late Carboniferous-Permian history. The maximum thickness of the Brécy depocenter is estimated to be 3900 m.

The filling indicates a thick late Carboniferous-early Permian syn-rift stage overlain by a thin early to middle post-rift stage, comparable to the tectonic evolution of basins in Lorraine and Germany. The facies generally characterize lake environments, with occurrences of fluvial, alluvial and delta fan deposits. They mainly display a retrogradational-progradational pattern during the syn-rift stage, and a retrogradational pattern during the post-rift stage. The Brécy area is therefore the thickest depocenter known in the northern Massif Central by far. We propose that it was part of a larger basin during the latest Carboniferous-early Permian times, with a roughly W-E trend spanning more than four hundred kilometers in length in the northern Massif Central region. Strictly speaking, all the other so-called outcropping basins (Aumance, Decize-La-Machine, etc.) should be considered as depocenters, as they belong to a wider scale basin, i.e. the northern Massif-Central Carboniferous-Permian Basin.

<footnote>*Intervenant</footnote>
Our work highlights that these late-orogenic basins were much wider and thicker than pre-
viously expected, with potential effective impacts on the understanding of the late Variscan
tectonic and climatic evolution in France and western Europe.

**Mots-Clés:** France, Late Variscan basins, Permian, Carboniferous, seismic processing and interpretation