in progress in the Autun basin. The palaeontological richness of this basin allowed at the time to define the Autunian as a reference stage for the continental Lower Permian of Europe. According to modern stratigraphy, the Margenne site belongs to the Millery Formation which is one of the youngest formations of the Autun basin. It corresponds to the upper part of the Autunian of the ancient authors. Based on plant, invertebrate, and amphibian fossils, the Autunian was considered to be an age equivalent to the global marine stages of the late Gzhelian, Asselian, Sakmarian, and Artinskian. Since the end of the 2010s, radiometric dating of volcanic ash (altered in tonsteins) intercalated in the sedimentary layers of several geological formations constituting the Autunian of the Autun basin revealed that the Autunian corresponded almost exclusively to the Asselian of the international geological time scale. The lower Autunian is represented by the Igornay and Muse formations. The middle part of the Igornay Formation is dated at 299.9 ± 0.38 Ma and represents the late Gzhelian (latest Carboniferous), confirming the first age estimates of the oldest Autunian levels. The Lally oil shale bed in the lower part of the Muse Formation is dated at 298.91 ± 0.08 Ma, which corresponds, at ± 100,000 years, to the Carboniferous-Permian boundary set in the marine strata in the Ural Mountains. The upper part of the Muse oil shale bed is dated between 298.05 ± 0.19 and 298.57 ± 0.16 Ma. These dates demonstrate that the lower Autunian corresponds to the late Gzhelian and early Asselian, and therefore encompasses the end of the late Carboniferous and the base of the early Permian. Two other levels of volcanic ash present at the top of the Muse Formation (lower-upper Autunian boundary) and in the upper part of the Millery Formation gave ages of 298.39 ± 0.09 Ma and 297.7 ± 0.08 Ma, the latter indicating an early-middle Asselian age. These dates indicate that the upper Autunian (represented by the Surmoulin, Millery, and Curgy formations) probably did not exceed an Asselian age. Thus, these dates prove that the five geological formations of the Autun basin which defined the Autunian represent a geological duration of less than 2.5 million years and include the Carboniferous-Permian boundary. This duration is significantly shorter than the 10 million years of deposits previously estimated. Thus, the genus Callibrachion from the Millery Formation, whose age was successively considered