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THE BEGINNING OF MESOZOIC SEDIMENTATION OF THE NORTH AND EAST OF FRANCE: PALAEOENVIRONMENTAL RECONSTRUCTIONS AND IMPLICATIONS ON GEODYNAMIC EVOLUTION OF THE TRIASSIC IN NW EUROPE

Abstract : The beginnings of Mesozoic sedimentation in north and east of France are located in three presentday areas: the Paris Basin, the Rhine Graben and the Bresse-Jura Basin. If the relations between Paris and German basins are exposed in recent papers, especially for the Early Triassic, the relation with BresseJura Basin is less understood even it is considered as a sub-basin connected with German and Paris Basin. The aim of this paper is, from new data and correlations in the northern part of France, (1) to reconstruct isopach and palaeogeographic maps, and (2) to discuss the geodynamic evolution of the north-west European domain during the Triassic. The Triassic series mainly crop out in the eastern part of France and only well-log data can provide a continuous record. By studying outcrops, core data and a complete set of wells, we can carry out correlations of the Triassic series between basement and Early Jurassic deposits. Around 600 wells are correlated using the principles of high-resolution sequence stratigraphy to establish the 2-D and 3-D geometries. The use of geomodeller Gocad allow to produce palaeogeographic and isopach maps. At the scale of the whole study area, an unconformity is observed between Permian and Triassic systems. Mesozoic sedimentation began during the Olenekian; the ephemeral fluvial systems indicate warm and arid climatic conditions. At the top of the Lower Triassic series, another tectonically induced unconformity is observed: the Hardegsen unconformity, which is intra-Spathian in age. That leads to the development of a new sedimentation area to the west. This tectonic activity creates new source areas and a new fluvial style, with marine influences at the distal part of the systems. Both during the end of the Olenekian and the Anisian, the presence of palaeosols, micro-and macrofloras indicates less warm conditions throughout the region. During the Anisian and Ladinian, continental sedimentation is characterized by a retrogradational trend. In other words, the fluvial system evolves towards fluvio-marine environments, attesting to a direct influence of the Tethys Ocean in the eastern domain. The maximum flooding episode is Ladinian and corresponds to wellextend Muschelkalk facies to the west. The progradational trend is characterized by evaporite sedimentation in the eastern domain and alluvial fan deposits in the western part. The sediment supply comes from the Armorican Massif and the climate conditions are warm and humid. The sedimentation is controlled by faults creating subsiding areas where salt series are preserved. During the Middle Carnian, the climate becomes more humid, without evaporite and the fluvial systems come from the north. This episode marks the beginning of a new retrogradational cycle that end in Early Jurassic. After this humid episode, more warm conditions occur with evaporite deposits and alluvial fan sediments preserved only in the western part. An intra-Norian unconformity, i.e. Early Cimmerian unconformity, allows the separation of two basins, i.e. the Paris Basin and Bresse-Jura Basin. Above the unconformity, an acceleration of the retrogradational trend occurs with transition from dolomitic sebkha, to marine Rhaetian sandstone and then to Liassic limestones.
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Submitted on : Tuesday, February 27, 2018 - 8:47:34 AM
Last modification on : Friday, April 5, 2019 - 8:17:58 PM

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  • HAL Id : insu-01718002, version 1

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Sylvie Bourquin, Christian Le Carlier de Veslud, Marc Durand. THE BEGINNING OF MESOZOIC SEDIMENTATION OF THE NORTH AND EAST OF FRANCE: PALAEOENVIRONMENTAL RECONSTRUCTIONS AND IMPLICATIONS ON GEODYNAMIC EVOLUTION OF THE TRIASSIC IN NW EUROPE. International Meeting of Sedimentology 2017, Oct 2017, Toulouse, France. pp.126, 2017, Abstract book. ⟨insu-01718002⟩

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