Analyse facio-séquentielle par diagraphies du trias du Centre-Ouest du bassin de Paris : apports à la reconstitution de l'environnement de dépot

Abstract : The well logging analysis of the Triassic of the west-center part of the Paris Basin (Donnemarie Sandstones, Intermediate Clays and Chaunoy Sandstones) was carried out for fifteen wells. The lithology textural and structural characterization of the facies conjointly to the recognition of their sequential evolution have enabled the reconstitution of the depositional environments of these formations. The Donnemarie Sandstoncs and the Intermediate Clays exhibit a general evolution from sandstone-like facies at the bottom 10 clayes facies at the top. One or the other of these formations lays directly onto the basement and marks the beginning of the Triassic sedimentation in the study area. The filling up of the basement paleotopographies by sandstone-like facies and the progressive on lap of these deposits by clays originated from Germanic Basin are pointed out (anhydritic clays, showing confinement sequence of shale-anhydrite type, over lied by sandstone-dolomilic clays). An uranium enriched level characteristic of a condensed section marks the tàp of the Intermediate Clays or their sandstone like equivalents. This level can be correlated with the radioactive level recognized above the Beaumont Dolomite in the eastern part of the Paris Basin and with the "Lehrberg Bänke" cf the eastern Germanic Basin. Then, the sandstone-dolomitic clays is supposed to be the lateral equivalent of the Beaumont Dolomite. The sandstone-like facies laterally evolve into the anhydritic clays which probably correspond to the "Grès à roseaux". The Chaunoy Sandstones characterize a continental depositional environment. The dolomitie facies are attributed to a pedologic duricrust. This formation is referred to an alluvial fan sedimentation, with WSW-ENE striking axis. The terrigenous deposits are WSW originated and become less important at the top of the formation, whereas the dolomitic paleosols arc generalized and display locally a very important thickness (21 m). This observations show evidence of a positive megasequence of sandstone-paleosol type. In the Sommital Clays, correlations are difficult because of the enlarged boreholes. However, the sandstone second unit recognized in this formation (western part of the studied zone) would be an equivalent of the Rhaetian Sandstones of the eastern part of the Paris Basin.
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Sylvie Bourquin. Analyse facio-séquentielle par diagraphies du trias du Centre-Ouest du bassin de Paris : apports à la reconstitution de l'environnement de dépot. Sciences de la Terre. Université Henri Poincaré - Nancy 1, 1991. Français. ⟨NNT : 1991NAN10155⟩. ⟨tel-01748583⟩

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