Paleomagnetism of the Lower Ordovician and Cambrian sedimentary rocks in the section of the Narva River right bank: For the construction of the Baltic Kinematic model in the Early Paleozoic

摘要

The paleomagnetic study of the Lower Ordovician and Cambrian sedimentary rocks exposed on the Narva River's right bank revealed a multicomponent composition of natural remanent magnetization. Among four distinguished medium- and high-temperature magnetization components, the bipolar component, which carries the reversal test, is probably the primary component and reflects the geomagnetic field direction and variations during the Late Cambrian and Early Ordovician. The pole positions corresponding to this component have coordinates 22A degrees N, 87A degrees E (dp/dm = 5A degrees/6A degrees) for the Late Cambrian, and 18A degrees N, 55A degrees E (dp/dm = 5A degrees/7A degrees) for the Early Ordovician (Tremadocian and Arenigian). Together with the recently published paleomagnetic poles for the sections of the Early Ordovician in the Leningrad Region and the series of poles obtained when the Ordovician limestones were studied in Sweden, these poles form new key frameworks for the Upper Cambrian-Middle Ordovician segment of the apparent polar-wander path (APWP) for the Baltica. Based on these data, we propose a renewed version of the APWP segment: the model of the Baltica motion as its clockwise turn by 68A degrees around the remote Euler pole. This motion around the great circle describes (with an error of A(95) = 10A degrees) both variations in the Baltic position from 500 to 456 Ma ago in paleolatitude and its turn relative to paleomeridians. According to the monopolar components of natural remanent magnetization detected in the Narva rocks, the South Pole positions are 2A degrees S, 351A degrees E (dp/dm = 5A degrees/9A degrees), 39A degrees S, 327A degrees E, (dp/dm = 4A degrees/7A degrees), and 42A degrees S and 311A degrees E (dp/dm = 9A degrees/13A degrees). It is assumed that these components reflect regional remagnetization events in the Silurian, Late Permian, and Triassic.