Paleomagnetism and paleogeography of the northern calcareous Alps (Austria)

Abstract

Prefolding magnetization components have been resolved at 38 sites of Liassic “Adnet” limestones in the central Northern Calcareous Alps (NCA) and at one site in the Drauzug. The site mean directions are northeasterly and down, and are closer to coeval European directions than to Southern Alpine “African” directions. The western end of both the NCA and of the Drauzug yield different site mean directions and negative fold tests indicating remagnetization. The sampling localities have been rotated relative to one another during thrusting, however, comparison of paleomagnetic poles with the European apparent polar wander path implies an average clockwise rotation of about 30° for the NCA relative to Europe. Larger‐scale clockwise rotations in excess of 80°, relative to the Southern Alps, are implied by comparison with the Southern Alpine (African) polar wander path. Facies analysis of Jurassic and Lower Cretaceous basinal sediments in the central part of the NCA suggests that Liassic subsidence was related to presently E‐W sinistral strike‐slip faults, whereas Malm‐Berriasian subsidence was controlled by presently E‐W south‐dipping normal faults. Both paleomagnetic and facies data tend to indicate that the NCA did not undergo the “African” rotation seen in Southern Alpine paleomagnetic data. This implies the existence of a short‐lived tract of Triassic?‐Jurassic ocean floor between the NCA and the Southern Alps, which linked the Pindos Ocean to the Ligurian trough and allowed Adria to rotate independently from the NCA during the Late Jurassic. Eo‐Alpine deformation and metamorphism are associated with the Early Cretaceous closure of this “Hallstatt” trough.