Reconstructing Baltica’s Ordovician paleogeography and pinning the end of the Ordovician Superchron: Paleomagnetic data from Siljan

We present a paleomagnetic study of 471–454 Ma (Dapingian to Sandbian) limestones from the Siljan (Sweden) impact structure, offering new insights into Baltica’s paleogeography and the Mid–Late Ordovician geomagnetic polarity timescale. Stepwise thermal demagnetization revealed a primary magnetization component that passes fold and reversal tests. Our data indicate Baltica’s initial stationary phase at ~55°S during the Dapingian–Early Darriwilian, followed by rapid northward drift (~35 cm/year) starting in the Middle Darriwilian and slowing to ~15 cm/year by the Sandbian (~33°S). Furthermore, we established a detailed polarity timescale and correlated it with Ordovician outcrops across Baltoscandia and the Siberian platform. Based on our magnetostratigraphic data, we defined the end of the Ordovician superchron at 465.7 Ma, further advancing its temporal resolution. Our findings align with prior studies, including normal polarity chrons in the Mid and Late Darriwilian stages, and limit the superchron's maximum duration to about 14 Myr.