International Field Workshop on 'The Triassic of eastern France'

Figure IV.4: (A) Maps of retrogradational phase of the Carnian cycle. (B) Maps of progradational phase of the
Carnian cycle. See Figs. III.2 and IV.1 for key. After Bourquin et al., 2002.
4.2.4. Lower ‘Marnes irisées supérieures’ minor cycle or Norian Cycle
In the east and centre of the Paris Basin, the base of the ‘Marnes irisées supérieures’ consists of
anhydritic coastal sabkha deposits (called ‘Argiles de Chanville’ on outcrops). Landward, in the extreme
western part of the basin, the deposits consist of alluvial fan deposits of Chaunoy Sandstones (Figs. I.1 and
IV.1) exhibiting dolomitic palaeosols which are mainly well developed at the top (Bourquin et al., 1993,
1998). The alluvial fan axis is oriented WSW-ENE and the terrigenous sediments were introduced from the
WSW. To the east, these alluvial fan deposits pass progressively at their base into fan delta deposits in a
lacustrine environment, and are overlain by a braided fluvial system.
This minor cycle is characterized in the west by a base-level rise in the Chaunoy Sandstones. The
maximum of the base-level rise is characterized by extensive flooding of the alluvial fan by lacustrine
sediments. It is overlain by braided channel deposits or fluvio-lacustrine deposits. To the east, the base-level
rise is recorded within the anhydritic coastal sabkha sediments (Figs. III.2, IV.2). The base-level fall trend,
characterized in the central part of the basin by numerous well developped anhydritic strata, ends with an
erosional discontinuity.
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