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RESEARCH PRODUCT

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

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International audience; Late Carboniferous to Permian basins of western Europe (~Gzhelian to Artinskian), developed during thelate stages of the Variscan orogeny in equatorial paleolatitudes. The stratigraphic context of most of thesebasins 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 withinternationally 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 theCarboniferous-Permian sedimentary successions of the Aumance and Decize-La Machine (DLM) basins. U-Pbdating 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 theshort time-intervals recorded in these basins, correlating them with other late Carboniferous to Permian basinsof western Europe requires the use of high-precision chemical abrasion – isotope dilution thermal ionizationmass spectrometry (CA-ID-TIMS), as successfully initiated in the neighboring Autun Basin by Pellenard etal. (2017). We therefore, we selected grains previously dated by LA-ICP-MS for analysis by CA-ID-TIMSto obtain more precise ages. The tonstein dated in the Aumance Basin (Lien Vert sample) together with thetwo tonsteins dated in the DLM Basin (LY-F well) provided ages with 2σ internal uncertainties of ± 0.35 Myrthat straddle the Carboniferous-Permian boundary. In the DLM Basin, the new ages, delimiting a 151 m-thickinterval (including coal, sandstones and conglomerates), suggest an outstanding sedimentation rate estimatedat ~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 atthat time. In fine, our new age model would also permit to refine the chronology and timing of the substantialCO2 storage in sedimentary organic matter at these paleolatitudes, which is usually underestimated in climatemodels.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 continentalseries 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 forexplosive volcanism calibrating the NW European continental Autunian stratotype. Gond. Res., 51, 118-136.