A deformed wedge-top basin inverted during the collapse of the Variscan belt: the Permo-Carboniferous Lorraine Basin (NE France)

Abstract

<div> <div> <div> <p>A new structural model is presented for the Permo-Carboniferous Lorraine Basin (NE France), a major intramountain basin that developed during the latest stages of the Variscan orogeny (ca 315–270 Ma). This basin is buried in NE France below the Paris Basin but outcrops in southern Germany (Saar-Nahe Basin). Digitalized well logs and reprocessed seismic data were used to decipher the kinematic evolution of this basin located along the Rhenohercynian orogenic suture zone. The basin initiated during the late collision stage (Late Namurian-Westphalian) in a wedge- top position upon the Saxothüringian retrowedge. The syn-orogenic sequences are delimited to the north by the major SE-directed Metz Thrust, which is part of the backthrust system that propagated during Late Westphalian times. Seismic data provide evidence of negative tectonic inversion, allowing the formation of syn-rift depocenters (Stephanian-Early Permian) above the former anticlines. Erosion of these anticlines results in a major unconformity (base of Stephanian) marking the onset of post-orogenic collapse stage. The late Early Permian shortening (Saalian phase) reactivated former thrusts and normal faults, thus generating uplift of the basin. The post- orogenic phase is complex and diachronous at basin scale, and both compression and extension can be recorded in the same area over a short period (<10 Ma). The Late Carboniferous negative tectonic inversion along the Rhenohercynian suture zone is proposed to result from the lithospheric delamination of the Variscan orogenic roots. The associated upwelling of asthenospheric material is recorded by intense magmatic activity, and can be, in turn, considered as the main trigger for the subsequent thermal subsidence of the Paris basin.</p> </div> </div> </div>

The Brécy depocenter as part of a new northern Massif Central Carboniferous–Permian Basin (France)

“…The transition from a tectonic subsidence regime accommodated by discrete faults (syn-rift stage) to a regional subsidence regime (post-rift stage) through an uplift phase has not been documented yet in other French LOCPB, except in the Lorraine region (location in Figure 1). There, the latest Carboniferouslower Permian syn-rift deposits are also controlled by listric normal faults rooting downward in deep decollement levels [Hemelsdaël et al, 2023]. They are then eroded following their uplift and tilting, before the arrival of the early to middle Permian postrift sediments [Henk, 1993, Stollhofen, 1998].…”

“…They are then eroded following their uplift and tilting, before the arrival of the early to middle Permian postrift sediments [Henk, 1993, Stollhofen, 1998]. The latter are then themselves eroded (toplap geometries below the Triassic deposits) before the deposition of the first Triassic sediments, as in the Brécy area [Hemelsdaël et al, 2023]. Further east in Germany, the Upper Rotliegend units of the Saar-Nahe (eastward prolongation of the Lorraine Basin), Thuringian Forest and Saale basins may also record these postrift events [Hertle and Littke, 2000, Schäfer, 2011, Schneider and Romer, 2010].…”