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Abstract

The Triassic System is divided into 3rd-order sequences along a west to east transect on the western Peritethyan margin in the Ardéche (South-East France Basin). The transect displays abrupt lateral variations, from proximal-continental to distal-marine environments, and marine ingressions have been recognized in clastic, carbonate and evaporitic facies. Biostratigraphic data in clastic series, provided by ichnofauna, microfossils and palynomorphs, enable us to characterize Anisian, Ladinian, Carnian and Rhaetian stages and to place the Ladinian/Carnian boundary. Abrupt variations in thickness and facies were controlled by synsedimentary faulting. Despite these features, major boundaries and successions of backstepping and forestepping systems tracts enable correlations between 3rd-order sequences in Ardéche and other domains in western Europe, in particular in the German Basin. The main characteristics of the Ardéche series are wide onlaps over the crystalline basement during the Ladinian stage, despite the thinness of the series and occurrence of thick interbedded coarse-grained clastic and evaporitic highstands in the Upper Triassic strata.

2nd-order sequences have been identified following 4 marine ingressions in the transect. The proposed Ladinian peak transgression is characterized by open-marine microfossils despite a clastic facies. Eustatic variations caused broad onlaps of backstepping series over a weakly subsiding Variscan Massif Central until late Ladinian time. In the Late Triassic Epoch, from the Carnian age onwards, mainly forestepping, thick clastic/evaporitic series were controlled by a more active tectonic subsidence.

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