The Permian–Triassic transition and the onset of Mesozoic sedimentation at the northwestern peri-Tethyan domain scale: Palaeogeographic maps and geodynamic implications

The main aim of this paper is to review Middle Permian through Middle Triassic continental successions in
European. Secondly, areas of Middle–Late Permian sedimentation, the Permian–Triassic Boundary (PTB) and
the onset of Triassic sedimentation at the scale of the westernmost peri-Tethyan domain are defined in order
to construct palaeogeographic maps of the area and to discuss the impact of tectonics, climate and sediment
supply on the preservation of continental sediment.
At the scale of the western European peri-Tethyan basins, the Upper Permian is characterised by a general
progradational pattern from playa-lake or floodplain to fluvial environments. In the northern Variscan Belt
domain, areas of sedimentation were either isolated or connected to the large basin, which was occupied by
the Zechstein Sea. In the southern Variscan Belt, during the Late Permian, either isolated endoreic basins
occurred, with palaeocurrent directions indicating local sources, or basins underwent erosion and/or there
was no deposition. These basins were not connected with the Tethys Ocean, which could be explained by a
high border formed by Corsica–Sardinia palaeorelief and even parts of the Kabilia microplate. The palaeoflora
and sedimentary environments suggest warm and semi-arid climatic conditions.
At the scale of the whole study area, an unconformity (more or less angular) is observed almost everywhere
between deposits of the Upper Permian and Triassic, except in the central part of the Germanic Basin. The
sedimentation gap is more developed in the southern area where, in some basins,Upper Permian sediment does not
occur. The large sedimentary supply, erosion and/or lack of deposition during the Late Permian, as well as the
variable palaeocurrent direction pattern between theMiddle–Late Permian and the Early Triassic indicate a period of
relief rejuvenation during the Late Permian. During the Induan, all the intra-belt basins were under erosion and
sediment was only preserved in the extra-belt domains (the northern and extreme southern domains). In the
northern domain (the central part of the Germanic Basin), sediment was preserved under the same climatic
conditions as during the latest Permian, whereas in the extreme southern domain, it was probably preserved in the
Tethys Ocean, implying a large amount of detrital components entering themarinewaters. Mesozoic sedimentation
began in the early Olenekian; the ephemeral fluvial systems indicate arid climatic conditions during this period.
Three distinct areas of sedimentation occur: a northern and southern domain, separated by an intra-belt domain.
The latter accumulated sediments during the Early–Middle Permian and experienced erosion and/or no-deposition
conditions between the Middle–Late Permian and the beginning of Mesozoic sedimentation, dated as Anisian to
Hettangian. At the top of the Lower Triassic, another tectonically induced, more or less angular unconformity is
observed: the Hardegsen unconformity, which is dated as intra-Spathian and is especially found in the North
European basins. This tectonic activity created new source areas and a new fluvial style, with marine influences at
the distal part of the systems. During the Anisian and Ladinian, continental sedimentation was characterised by a retrogradational trend. In other words, the fluvial system evolved into fluvio-marine environments, attesting to a
direct influence of the Tethys Ocean in the southern and northern domains. Both at the end of the Olenekian
(Spathian) and during the Anisian, the presence of palaeosols, micro- andmacrofloras indicate less arid conditions
throughout this domain

Field of study: Environmental science, Geography