Drainage and environmental evolution across the Permo–Triassic boundary in the south‐east Germanic Basin (north‐east Bavaria)

Abstract

AbstractThe identification of the factors triggering continental environmental changes at the Permian–Triassic transition is of general interest as they allow a better understanding of the most controversial mass extinction of the Phanerozoic. This study investigates the environmental response to external forcings on continental successions at the south‐east‐margin of the Central European Basin System in Germany. Studies from this area are scarce, and its evolution is poorly understood. This work integrates high‐resolution core‐logging and quantitative sedimentary petrography of Middle Permian–Early Triassic successions recovered from the wells Obernsees‐1 and Lindau‐1. The sedimentological investigation reveals major vertical variations in the depositional settings marked by changes in grain‐size trends and facies associations: (i) the progradation of mass flow/fluvial fans over sandflat environments denotes the Guadalupian–Lopingian; (ii) sabkha to shallow‐marine conditions occur during the uppermost Permian; (iii) the onset of braided fluvial sequences marks the Permian–Triassic boundary; (iv) changes in fluvial style, reflecting increased river sinuosity, and aeolian deposition characterize the remaining Triassic. Environmental changes are accentuated by variations in sediment composition. Proximal deposits (for example, alluvial fan) are lithic arkoses, while more distal associations reveal arkosic composition. Detrital modes point to: (i) a high‐grade metamorphic source feeding the drainage of Lindau‐1 (metamorphic index, MI 441–500); and (ii) a mixed low‐grade and high‐grade metamorphic source (MI 277–395) feeding the Permian of Obernsees‐1, passing upward to high‐grade metamorphic (MI 441–500) and subordinate granitoid sources. Compositional signatures and environmental changes suggest distinct drainage evolutions regulated by upstream climate and tectonic controls. The higher plutonic clast content coeval to the onset of fluvial sedimentation and coarse‐grained influxes reflects local tectonic perturbations attributed to the Early Triassic reactivation of Variscan faults. The evidence of perennial fluvial systems during the lowermost Triassic reflects wetter climate conditions in the upstream catchment area, which contradicts the common view of increased aridity at the Permian–Triassic boundary.