Ordovician Reversed Superchron: Fact or Fallacy?

Geomagnetic field reversals are relatively common events, occurring 4–5 times/Myr over the last 10 Ma. However, there are two well-documented periods, called superchrons, when no reversal occurred for >30 Myr in the Cretaceous and Permo-Carboniferous. A third superchron has been proposed in the Ordovician when the field was in a reversed polarity state. Here, we report high‐resolution, Middle to Late Ordovician magnetostratigraphic data from carbonate rocks spanning 471 to 454 Ma collected in the Siljan district, central Sweden. The Siljan record correlates well with Ordovician sequences from Baltoscandia, Siberia and Poland. In Siljan, a flip from reversed to normal polarity at 466.1 ± 0.9 Ma clearly identifies the termination of the Ordovician Reversed Superchron (ORS), thereby constraining its duration to 13.9 ± 2.2 Myr. To evaluate the statistical significance of this interval, we compiled a geomagnetic polarity timescale spanning the last 493 Myr and analyzed chron length distributions using a robust interquartile range method. The ORS is a clear statistical outlier that exceeds a critical 6.8 Myr threshold, corroborating its classification as a bona fide superchron. Our chron length analyses support the view that superchrons represent rare, stable dynamo regimes, rather than merely the tail of a continuous reversal rate distribution.