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The late Carboniferous–early Permian represents a key period in the Phanerozoic history, given the major global geodynamic and climate modifications. The aim of this work is to better understand the context and characteristics of the sedimentation recorded in the continental environments of eastern equatorial Pangea at this time, through the example of the Autun Basin (northeastern Massif Central, France). The Autun Basin contains the historical stratotype of the Autunian continental stage, and its stratigraphy was recently improved by accurate numerical ages. This basin formed in an extensional tectonic context during the latest stages of the Variscan orogeny, and it is essential to study its paleoenvironmental evolution to provide new insights into the sedimentary evolution of contemporaneous surrounding basins. Using field and subsurface data, we propose a refined sedimentological model for the Autun Basin, relying on updated facies interpretations, organic matter content fluctuations, and sequence stratigraphy concepts and correlations. The continental environments of the lower sedimentary succession of the Autun Basin, previously considered to be fluvial and lacustrine, are herein re-interpreted as mainly lacustrine, comprising fine-grained organic matter-rich deposits, and supplied by coarser-grained deltaic siliciclastic sediments, without preservation of strict fluvial sedimentation. The determination of the sequence stratigraphy cycles, strengthened by the quantification of the organic matter content, and reflected by the temporal succession of progradational and retrogradational trends, is used to determine new correlations between several sections, as well as to reconstruct the paleoenvironment evolution at the Carboniferous–Permian transition. This study provides evidence that the sedimentation area of the Autun Basin at the time of its filling was much larger than the preserved basin area, and suggests connections with contemporaneous neighboring French basins, pointing to a large sedimentary system in the northeastern Massif Central area rather than narrow and isolated basins. [ABSTRACT FROM AUTHOR]

The late Carboniferous-to-Permian coal-bearing Decize-La Machine Basin, and more specifically the Lucenay-lès-Aix area, located south of the Paris Basin, has been investigated to reassess the palaeoenvironmental evolution and the basin architecture. The detailed sedimentological study has been carried out based on core data and digitised old mining data, i.e., seismic profiles and well-logs. An interpretation of well-logs without core data is proposed, based on a palaeoenvironmental interpretation from cores and their respective well-log data, and three depositional environments have been defined: an alluvial plain, an alluvial-fan, and deltaic and lacustrine environments. Correlations between wells have been performed using markers identified in seismic profiles, paired with sequence stratigraphic interpretations from well-log and core data. An evolution in seven major progradational–retrogradational stratigraphic cycles is proposed based on the evolution of the depositional environment observed at the basin scale, leading to a reconstruction of palaeogeographic maps at the Carboniferous–Permian transition. This new viewpoint shows that through time, the deposits, proximal at the base of the succession with coal preservation, become more lacustrine with the delta prograding into the basin. In consequence, the basin evolution shows a general retrogradational trend with increasing lacustrine deposits at the top of the succession eroded by the Permian–Triassic unconformity. Therefore, the current borders of the basin in the Lucenay-lès-Aix area are not representative of those at the time of the sedimentary filling, and thus, this area could be part of a larger one, perhaps encompassing all north-eastern French Massif Central late Carboniferous-to-Permian basins. [ABSTRACT FROM AUTHOR]

The Carboniferous to Permian volcanic-sedimentary succession shown by the LY-F core from the Lucenay-lès-Aix area, in the northern part of the Massif Central, has been studied in order to obtain both landscape reconstructions (sedimentological analyses) and geochronological constraints (U-Pb dating on zircon and apatite). The lowermost part of the core consists mainly of lacustrine deposits with Gilbert-type delta and volcaniclastic-rich fan delta deposits including several altered volcanic ash layers (tonstein). In contrast, in the uppermost part of the core, playa-lake deposits dominate. LA-ICP-MS U-Pb analyses were performed on both zircon and apatite grains from interbedded tonsteins. This coupled U-Pb dating approach allows to assess potential reworking of volcanic material or the occurrence of non-volcanic grains, such as xenocrysts, in order to provide better evaluations for the depositional ages of the tonsteins. These investigations reveal that sedimentation took place between the late Gzhelian and the late Sakmarian (i.e., between c. 301 and 290 Ma). This sedimentary succession can therefore be compared to those from adjacent basins for which geochronological constraints are available (i.e., Autun and Lodève basins, resp. located north and south of the Massif Central). This study provides a reference section for future comparisons with similar sections from other Carboniferous to Permian basins, in France as well as elsewhere in Europe. • The LY-F section contains lacustrine deposits with interbedded tonstein layers. • The lower part of the core consists of Gilbert-type deltas deposits. • They are interbedded with volcaniclast-rich delta deposits. • The upper part of the core consists of playa-lake deposits. • The depositional age of the LY-F section is late Gzhelian to late Sakmarian. [ABSTRACT FROM AUTHOR]