Palaeoenvironmental reconstitutions at the Carboniferous–Permian transition south of the Paris Basin, France: implications on the stratigraphic evolution and basin geometry

Abstract

The late Carboniferous-to-Permian coal-bearing Decize-La Machine Basin, and more specifically the Lucenay-les-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-les-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.