The Permian–Triassic boundary in Western Slovenia (Idrijca Valley section): magnetostratigraphy, stable isotopes, and elemental variations

Stable isotope analyses of carbonate (δ13Ccarb) and total organic carbon (TOC; δ13Corg), together with geochemical analyses of 54 major, minor, and trace elements and magnetic susceptibility measurements were carried out on whole rock samples of the undisturbed Permian–Triassic (P/Tr) limestone boundary sequence in the Idrijca Valley (W. Slovenia). At the P/Tr boundary, there is a 0.8-cm thick clayey marl layer (PTB) showing a characteristic magnetic susceptibility pulse and considerable enrichment in most major, minor, and trace elements. The P/Tr transition is characterized by (1) an abrupt decrease in sedimentation rate from 32 to 5 cm/100 ka, (2) a well known prominent negative excursion of δ13Ccarb and δ13Corg, reflecting global perturbations in the carbon cycle, and (3) the drastic disappearance of typically Upper Permian marine fauna. gh the shape of the δ13Ccarb curve indicates gradual long-term change across the P/Tr boundary, the sharp negative δ13Corg anomaly within an interval from 30 cm below to 6 cm above the boundary suggests an interruption of those gradual processes. servations for selected redox sensitive elements (Mo, U, V and Zn), abundances for organic carbon and sulphur and the rare earth elements (REE) distribution in the boundary sequence, as well as the shape of the Ce/Ce* curve suggest that oceanic anoxia was typical of the Upper Permian, and that the transition to oxygenated conditions occurred at the P/Tr boundary. Oxygenation at the P/Tr transition is coincidental with the terminal phase of the Upper Permian marine regression. The shape of the Ce/Ce* curve indicates that the redox environmental conditions changed again in the earliest Triassic, resulting once more in oxygen deficient conditions.