Late Mesoproterozoic magnetostratigraphic results from Siberia: Paleogeographic implications and magnetic field behavior

We present a magnetostratigraphic study of the late Mesoproterozoic Malgina and Linok Formations, located along the southeastern (Uchur-Maya region) a nd northwestern (Turukhansk region) margins of the Siberian craton, respect ively. Biostratigraphic, radiometric, and chemostratigraphic data indicate that these formations are likely coeval between 1050 and 1100 Ma. Paleomagn etic analyses reveal a high-temperature component carried by magnetite and/ or hematite. This component yields positive fold and reversal tests, togeth er with a positive conglomerate test for the Malgina Formation, which indic ates that the magnetization was acquired during or soon after sediment depo sition. The mean paleomagnetic direction obtained from the Uchur-Maya regio n, which is unambiguously representative of the Siberian craton, indicates that it could not have been part of Rodinia at that time if Siberia was loc ated in the Southern Hemisphere and if we assume that Laurentia and Siberia were connected along their present northern shorelines. We emphasize that Siberia could have been part of Rodinia during the late Mesoproterozoic if southern Siberia was joined to the northern part of Laurentia as recently p roposed by Rainbird et al. [1998]. If true, placing the Siberian craton in the Southern Hemisphere implies that the magnetic polarity of the similar t o 1000 Ma Laurentian paleomagnetic poles must be switched. Our data also sh ow the occurrence of at least 15 symmetric geomagnetic field reversals, ind icating that the paleomagnetic results from the late Mesoproterozoic Keween awan lavas do not reflect a worldwide and persistent asymmetric field durin g the Proterozoic.