Paléogéographie et répartition des faciès au Cénomanien dans le bassin rhodano-vocontien

Abstract

During the Cenomanian times, the paleogeography of the "Rhodano-Vocontian basin" was largely controlled by great faults trending SW-NE and SE-NW, probably inherited from the late Hercynian tectonic activity. These faults played a significant role in the sedimentation. To the West and to the North, coarse detrital materials were supplied by the "Massif Central" and its sedimentary cover : they were accumulated onto a platform, parted from the Hercynian landmass by the Cévennes faults and their northern tributaries. In between the Cévennes and Nîmes faults, there was a subsiding through ("sinus rhodanien") where fine-grained terrigenous deposits were accumulated, coming from the next platform. This trough was limited to the South by the "Du-rancian high" and the depending "Ventoux-Lure ridge". In the central and eastern parts of the basin, the sediments were more definitely pelagic (shales and argillaceous limestones). Slumpings and sudden variations in thickness eventually occur in this area, reflecting the influence of the Hercynian faults. During most of the Cenomanian time span, the sedimentation was quiet, but epirogenic movements took place in the Middle Cenomanian, causing local coarse detrital influx. To the West and to the North, coarse detrital materials were supplied by the "Massif Central" and its sedimentary cover : they were accumulated onto a platform, parted from the Hercynian landmass by the Cévennes faults and their northern tributaries. In between the Cévennes and Nîmes faults, there was a subsiding through ("sinus rhodanien") where fine-grained ter¬ rigenous deposits were accumulated, coming from the next platform. This trough was limited to the South by the "Du-rancian high" and the depending "Ventoux-Lure ridge". In the central and eastern parts of the basin, the sediments were more definitely pelagic (shales and argillaceous limestones). Slumpings and sudden variations in thickness eventually occur in this area, reflecting the influence of the Hercynian faults. During most of the Cenomanian time span, the sedimen¬ tation was quiet, but epirogenic movements took place in the Middle Cenomanian, causing local coarse detrital influx.