Investigating the Death of the Early Paleozoic Moyero River Geomagnetic Superchron: Middle Ordovician Paleomagnetism from Estonia

Abstract

Flat-lying Early and Middle Ordovician limestones exposed on the North margin of Estonia provide key insights into the early Paleozoic biosphere and climatic history of the Baltic Platform, and potentially offer a site for calibrating the duration of the proposed Moyero River Reversed Superchron. Past paleomagnetic analyses on these rocks have been focused primarily on determining paleomagnetic pole positions and have been hampered by relatively weak remanent magnetizations. We therefore applied techniques of the Rock and Paleomagnetic Instrument Development (RAPID) consortium using thin-walled, low-noise quartz glass sample holders on an automatic system to enhance magnetostratigraphic resolution. Our results, based on over 300 oriented core samples spanning the stratigraphic interval from the Volkhov stage, up through the Lasnamagi stage, confirm previous work isolating a stable characteristic magnetization of reversed polarity, and furthermore confirm the presence of an interval of magnetically Reversed polarity spanning an interval of at least 15 million year duration. In addition, we recognize a magnetic overprint of presumed Normal polarity held in antiferromagnetic phases, of presumed Permian age, based on the apparent polar wander path given by (Plado et al., 2010).