Two Distinct Early Cambrian Paleomagnetic Poles but a Single Siberian Platform

The determination of the Early Cambrian paleomagnetic pole for the Siberian platform is of great importance, in particular to test the episode of Inertial Interchange True Polar Wander proposed by Kirschvink et al. (1997). Two very different paleomagnetic poles have been published so far, one by Kirschvink and Rozanov (1984 ; see also Kazanski et al, 2001, Spring AGU), which implies superfast paleomagnetic polar wander for Siberia during the Early Cambrian, and the second by Pisarevsky et al (1997), which on the contrary corresponds to « normal ¯ polar wander. In order to try and understand the reasons for this discrepancy, we carried out a paleomagnetic study of five Vendian to Early Cambrian sections from the Anabar block (northern part of the Siberian platform ; lat. 68 to 72 deg. North, long. 88 to 124 deg. East). One of these sections is close to that reported by Kazanski et al. Middle Cambrian sediments analyzed previously by Pavlov and Gallet (2001) yielded easily interpretable results. Both Early and Middle Cambrian are present in one of our sections (Khorbusuonka). Again the Middle Cambrian yields straightforward results, but most of the Early Cambrian rocks analyzed (three sections up to this date) show scattered directions, carried either by magnetite or by hematite, with evidence for both magnetic polarities. Some of these directions cluster close to both directions reported previously. At this step of our work, we do not know if this is due to unfavorable paleomagnetic behaviour of the studied rocks (alteration, partial remagnetization, multiple components with variable overlap.), or to unusual behaviour of the geomagnetic field during the Early Cambrian.