Permian–Triassic boundary magnetostratigraphy from the Southern Alps (Italy)

Abstract

Palaeomagnetic investigations of Permian–Triassic boundary sections in the Dolomites provided a magnetostratigraphy for the uppermost part of the Permian Bellerophon Formation to the Lower Triassic Werfen Formation. Magnetite was the dominant magnetic component in most of the samples, while the presence of hematite was characteristic for the Tesero horizon, which is regarded as the immediate Permian–Triassic boundary layer. The palaeomagnetic results are consistent with earlier studies of Permian and Triassic sediments and volcanites in the Southern Alps. The mean characteristic remanence directions indicate deposition and remanence acquisition at a shallow northerly palaeolatitude and a counterclockwise rotation. A zone of reversed polarity occurs at the top of the Permian sequence and a polarity change from reverse to normal polarity shortly above the base of the Werfen Formation. The onset of a tectonically controlled sedimentary cycle marks the beginning of the basal Triassic normal polarity zone, which corresponds to most of Griesbachian time. The record of geomagnetic polarity across the Permian–Triassic boundary confirms the apparent continuity as found by sedimentologic biostratigraphic investigations which emphasise a gradual lithic transition with no evidence for a time gap at the boundary.