U-Pb age constraints on Carboniferous-Permian French continental basins - implications for their depositional history and correlations with European basins

Mathilde Mercuzot (1) , Camille Rossignol (2) , Sylvie Bourquin (3) , J. Ramezani (4) , Céline Ducassou (3) , Marc Poujol (3) , Pierre Pellenard (1) , Laurent Beccaletto (5)

1 BGS - Biogéosciences [UMR 6282]
2 UniCa - Università degli Studi di Cagliari = University of Cagliari
3 GR - Géosciences Rennes
4 EAPS - Department of Earth, Atmospheric and Planetary Sciences [MIT, Cambridge]
5 BRGM - Bureau de Recherches Géologiques et Minières (BRGM)

Late Carboniferous to Permian basins of western Europe (~Gzhelian to Artinskian), developed during the late stages of the Variscan orogeny in equatorial paleolatitudes. The stratigraphic context of most of these basins remains poorly constrained, because mainly based on “continental stages” (e.g., Stephanian, Autunian, Saxonian and Thuringian) that are diachronous. Therefore, correlating these basins together and with internationally recognized stratigraphic marine stages requires precise radiochronologic ages. To the south of the Paris Basin (France), volcanic ash-fall layers (i.e., tonsteins) are interbedded in the Carboniferous-Permian sedimentary successions of the Aumance and Decize-La Machine (DLM) basins. U-Pb dating of zircon grains from these layers by laser ablation – inductively coupled plasma – mass spectrometry (LA-ICP-MS) confirmed a late Carboniferous to Permian age (~301-290 Ma; Ducassou et al., 2019). Given the short time-intervals recorded in these basins, correlating them with other late Carboniferous to Permian basins of western Europe requires the use of high-precision chemical abrasion – isotope dilution thermal ionization mass spectrometry (CA-ID-TIMS), as successfully initiated in the neighboring Autun Basin by Pellenard et al. (2017). We therefore, we selected grains previously dated by LA-ICP-MS for analysis by CA-ID-TIMS to obtain more precise ages. The tonstein dated in the Aumance Basin (Lien Vert sample) together with the two tonsteins dated in the DLM Basin (LY-F well) provided ages with 2σ internal uncertainties of ± 0.35 Myr that straddle the Carboniferous-Permian boundary. In the DLM Basin, the new ages, delimiting a 151 m-thick interval (including coal, sandstones and conglomerates), suggest an outstanding sedimentation rate estimated at ~453 ± 159 m/Myr. Beyond the improvement of the French basin stratigraphy and worldwide correlations, these new ages ultimately contribute to bring new insights on both the geodynamic and climatic setting at that time. In fine, our new age model would also permit to refine the chronology and timing of the substantial CO2 storage in sedimentary organic matter at these paleolatitudes, which is usually underestimated in climate models. Ducassou C., Mercuzot M., Bourquin S., Rossignol C., Pellenard P., Beccaletto L., Poujol M., Hallot E., Pierson- Wickmann AC., Hue C. & Ravier E. (2019) - Sedimentology and U-Pb dating of Carboniferous to Permian continental series of the northern Massif Central (France): Local paleogeographic evolution and larger scale correlations. Pal., Pal., Pal., 533, 109228. Pellenard P., Gand G., Schmitz M., Galtier J., Broutin J. & Stéyer JS. (2017) - High-precision U-Pb zircon ages for explosive volcanism calibrating the NW European continental Autunian stratotype. Gond. Res., 51, 118-136.

Mots clés: late Paleozoic; continental Pangea basins; Variscan orogeny

Domaines: Géochimie; Stratigraphie

Mathilde Mercuzot, Camille Rossignol, Sylvie Bourquin, J. Ramezani, Céline Ducassou, et al.. U-Pb age constraints on Carboniferous-Permian French continental basins - implications for their depositional history and correlations with European basins. CONGRESSO SGI-SIMP 2022, Sep 2022, Torino, Italy. , Abstract book, pp.1026, 2022. ⟨insu-03788196⟩