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.