Magnetostratigraphy of the Moyero river section (north-western Siberia): Constraints on geomagnetic reversal frequency during the early Palaeozoic

We present the magnetostratigraphy of the early Palaeozoic Moyero river section in north-western Siberia. The section investigated, which consists mainly of reddish limestones, marls and greyish limestones, extends from the upper Cambrian to the lower Silurian. Palaeomagnetic analyses reveal two magnetic components. One is interpreted as a remagnetization acquired during Siberian trap emplacement; the other is believed to be early diagenetic, consistent with the established lower Palaeozoic apparent polar wander path for Siberia. Reversed polarity dominates from the upper Cambrian to the middle Ordovician, while normal polarity dominates from the upper Ordovician to the lower Silurian. Only a few reversals, which are poorly defined, are observed through the section, in particular during the Llandeilo. These data are in agreement with previous magnetostratigraphic data from the Baltic platform and Siberia and indicate that magnetic reversal frequency was low during the Ordovician. Because of the time-delayed process of acquisition of the magnetization carried by haematite, we cannot clearly ascertain if a reversed superchron occurred during the lower to middle Ordovician. However, our results suggest that a 15 Myr-long reversed interval existed during the Arenig.