A. TRENCH, W. S. McKERROW, T. H. TORSVIK; Ordovician magnetostratigraphy: a correlation of global data. Journal of the Geological Society ; 148 (6): 949–957. doi: https://doi.org/10.1144/gsjgs.148.6.0949
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Palaeomagnetic studies where primary magnetizations are established from well-dated rocks have been compiled to construct a magnetostratigraphic time-scale for the Ordovician period. An excellent correlation of magnetozones is observed between independent studies of the Baltic and South Siberian platform sequences. Supplemental datasets from other continents concur with the Baltic and Siberian polarity data.
Early Ordovician times were mainly characterized by a reverse field. Rapid reversals then occurred during Llanvirn and Llandeilo times. Late Ordovician times were dominated by a normal polarity field.
Some gaps remain in the polarity record, notably for late Caradoc-early Ashgill and mid-Tremadoc times.