International Field Workshop on 'The Triassic of eastern France'

4.2.6. Upper ‘Marnes irisées supérieures’ - Rhaetian minor cycle or Norian-Rhaetian Cycle
This cycle started in the east with dolomitic playa deposits grading upwards into the restricted marine
deposits of the Rhaetian Sandstones which display some limited open marine influences within a
transgressive trend (Fig. III.2, IV.1). The base-level fall is recorded in the upper part of the Rhaetian,
characterized by the continental deposits of the ‘Argiles de Levallois’. Because of the intra-’Marnes irisées
supérieures’ stratigraphic discontinuity, this minor cycle lies directly upon the ‘Grès à roseaux’ - ‘Dolomie
de Beaumont’ minor cycle in the east (Fig. IV.1). Further west, the dolomitic coastal sabkha deposits grade
laterally into alluvial plain sediments with fluvio-lacustrine sandstones (‘Grès d'Egrenay’, ‘Grès de Boissy’,
‘Grès d'Etrechy’) where no classical Rhaetian facies are recognized (Fig. IV.6).
E-W correlations show that the ‘Rhaetian’ boundary is a diachronous facies boundary between a
coastal sabkha and a restricted marine environment within a base-level rise (Bourquin and Guillocheau,
1993; Bourquin and Guillocheau, 1996, Figs. III.2). In the southeast of the basin, the Rhaetian Sandstones
may have eroded the ‘Marnes irisées supérieures’ deposits locally.
Figure IV.6: (A) Maps of retrogradational phase of the Norian-Rhaetian cycle (denoted d, Fig. III.2). (B) Maps
of the base of the Rhaetian sandstones for the wells located in the eastern part of the basin to the top of the
Triassic (end of retrogradational phase and progradational phase of the Norian-Rhaetian cycle (denoted e,
Fig. III.2). See Figs. III.2 and IV.1 for key. After Bourquin et al., 2002.
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