GEOMAGNETIC POLARITY REVERSAL RATE FOR THE PHANEROZOIC

The recently updated Global Paleomagnetic Database provides an opportu nity to construct a preliminary model of long-term magnetic polarity r eversal behavior for the last 570 My. After filtering for quality, a s ub-set of data from this global database is used to estimate relative reversal frequency, and the results show the expected long intervals o f low reversal rate during the Cretaceous Normal and Permo-Carbonifero us Reversed Superchrons. In addition to the established superchrons, t hese new results indicate a long period of very low reversal rate in t he Ordovician, which may be a previously unidentified superchron, and an additional short period of anomalously low reversals at the Jurassi c/Triassic boundary. If the Ordovician reversal rate anomaly is a sing le polarity superchron, it represents the third major change in revers al rate within the Phanerozoic, with approximately 200 My between the CNS, the PCRS and the new Ordovician reversed interval.