Paleomagnetism of Ordovician and Devonian sedimentary rocks in the northwest of the Russian platform: New constraints on the Baltica kinematics in the Paleozoic and the remagnetization in the Permian-Triassic

摘要

A detailed paleomagnetic study of profiles of Ordovician (Arenigian-Llanvirnian) and Upper Devonian (Frasnian) carbonate and terrigenous rocks in the Leningrad region (the Putilovo and Syas River sections) revealed two groups of ancient components of the natural remanent magnetization (NRM) denoted as the P, PD, and S components. The conglomerate test is positive for the high temperature PD component in terrigenous rocks of the Upper Devonian. The P component is identified in carbonate beds showing no visible traces of secondary alterations, and we also classified it as primary. Comparison of the corresponding positions of paleomagnetic poles, (10.8 degrees N, 133.6 degrees E; dp = 2.2 degrees, dm = 4.5 degrees) for the Late Devonian, (29.1 degrees N, 48.4 degrees E; dp = 11.5 degrees, dm = 13.0 degrees) for the Llanvirnian, and (24.7 degrees N, 57.6 degrees E; dp = 4.1 degrees, dm = 4.9 degrees) for the Arenigian, with the apparent polar wander path (APWP) from Baltica indicates the normal polarity of the geomagnetic field in the studied interval of the Frasnian and the reversed polarity in the Arenigian and Llanvirnian. The S component of the NRM has the normal polarity in the Ordovician rocks and the reversed polarity in the Devonian rocks, and its paleomagnetic poles (58.4 degrees N, 164.3 degrees E; dp = 1.6 degrees, dm = 2.3 degrees) and (48.8 degrees S, 346.7 degrees E; dp = 2.1 degrees dm = 3.4 degrees) determine, respectively, Triassic and Permian ages of this component. A new version of the APWP of the paleomagnetic pole from Baltica in the Ordovician-Devonian interval is proposed on the basis of the paleomagnetic determinations of this study and the updated paleomagnetic database.