High‐Resolution Tracking of Baltica's Northward Drift in the Ordovician

Ahanin, Nastaran ; Gilder, Stuart A. (2025): High‐Resolution Tracking of Baltica's Northward Drift in the Ordovician. Geophysical Research Letters, 52 (7): e2024GL114. ISSN 0094-8276

Abstract

We investigated the paleogeography of Baltica via a paleomagnetic study of 471-454 Ma limestones from the Siljan (Sweden) impact structure. Stepwise thermal demagnetization isolated a well-defined magnetization component that unblocks up to the Curie temperature of magnetite and passes fold and reversal tests, indicative of a primary magnetization. Paleolatitude data show that Baltica experienced an initial stationary phase at approximately 55°S from 471 to 467 Ma, followed by a rapid northward drift (∼35 cm/yr) after 467 Ma. This motion slowed to ∼15 cm/yr at ∼463 Ma until 454 Ma when Baltica reached 33°S. A notable correlation was found between Baltica's latitude and the relative proportion of magnetite and hematite in the carbonates; they are relatively hematite rich at 55°S and magnetite rich by 33°S. Our results provide a high-precision model how Baltica moved in the Ordovician with potential environmental implications regarding the oxidation state of the ocean at that time.

Plain Language Summary
We studied the paleogeography of the Baltica plate by analyzing magnetic signals in 471–454 million-year-old limestones from the Siljan impact structure in central Sweden. Magnetic minerals in the rocks recorded the direction of Earth's magnetic field when the rocks formed, allowing us to track Baltica's position over time. Our findings reveal that Baltica remained near 55°S latitude during the early Mid Ordovician, then began moving rapidly northward at a rate of about 35 cm/yr. This pace slowed as Baltica reached 33°S. We also found a link between Baltica's latitude and the types of magnetic minerals within the limestones. At higher latitudes (∼55°S), the rocks contained more hematite, while at lower latitudes (∼33°S), magnetite became more dominant. Our results define Baltica's motion in the Ordovician and potentially indicate how ocean chemistry changed through that time.

• Doc-Type: Article (LMU)
• Organisational unit (Faculties): 20 Geosciences > Department of Earth and Environmental Sciences
• DFG subject classification of scientific disciplines: Natural sciences
• DFG: Funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) - 491502892