Investigating the duration and termination of the Early Paleozoic Moyero Reversed Polarity Superchron: Middle Ordovician paleomagnetism from Estonia

Flat-lying Early and Middle Ordovician limestones exposed along the northern 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 Reversed Polarity Superchron (MRPS). 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 400 oriented core samples spanning the stratigraphic interval from the Volkhov Stage, into the Uhaku Stage (Dapingian and Darriwillian, Middle Ordovician), expand upon the results of previous work. We isolated a stable characteristic magnetization of reversed polarity and the presence of an interval of magnetically Reversed polarity lasting into the Middle Ordovician. The interval begins in the Dapingian and is interrupted by a short normal period in the mid-Darriwillian (concurrent with the Yangtzeplacognathus protoramosus conodont Subzone) before returning to Reversed polarity. In addition, we recognize a magnetic overprint of apparent normal polarity held in antiferromagnetic phases.