The study of Cenomanian planktonic Foraminifera can be performed in great details in the subalpine chains of Southeastern France, owing to very good conditions of exposition and the richness of the sediments in megaand microfossils. This makes it possible to integrate the planktonic Foraminifera and Ammonites standard scales with a very good accuracy. A division into six assemblage zones, named Cn 1 to Cn 6, is proposed for the Cenomanian stage. Each of the three two zone-groupings can be correlated fairly well with one of the three major subdivisions of the Cenomanian, established by means of mega-fossils.
The boundary between Cenomanian and Turonian (upper Cretaceous) beds in the upper basin of the Esteron river (Alpes-Maritimes, France) is defined on the basis of ammonites and pelagic foraminifera. The rich faunas of these beds are especially important because Cenomanian and Turonian beds in southeastern France are normally very poor in fossils.
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.
New paleontologic data, especially the discovery of Globotruncana concavata (foraminifer) and an Inoceramus (I. sp. ex gr. muelleri) in the gray-blue upper Cretaceous limestones of Glandage-Creyers (Drome, French Prealps), indicate that the limestones are essentially Santonian, possibly extending upward into the lower Campanian. The underlying Gas conglomeratic complex is now assigned to the upper Turonian and, at the top, to the Coniacian. The Gas complex consists of two conglomerate layers separated by sandy limestones. Thus the so-called pre-Senonian orogeny apparently took place in at least two phases, one early Turonian (pre-Senonian), the other late Coniacian (early Senonian). The Coniacian, not the Turonian, is the major phase.
Upper Turonian-lower Senonian deposits in western Vercors, correlation with Diois deposits, Santonian and Campanian-Maestrichtian deposits in northeast Vercors, correlation with Senonian of Devoluy and Bochaine, pre-Santonian orogeny, subsidence, emergence, Cretaceous, France
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