PALEOMAGNETISM OF VENDIAN ROCKS IN THE SOUTHWEST OF THE SIBERIAN PLATFORM

Abstract

Presented in this paper are paleomagnetic data for the Vendian sedimentary rocks of the southwestern region of the Siberian Platform, obtained during the study of the reference rock sequences of the Central and Biryusa areas of the Sayan region and of the Yenisey mountain range in the lower reaches of the Angara River and its tributaries. This study proved the wide development of metachronous pre- and synfolding magnetization components which originated after the deposition of the sedimentary rock sequences, yet, obviously not later than the Early Cambrian. All of the study rocks of the Nemakit-Daldynian age show two clearly distinguished paleomagnetic trends which seem to have formed during or soon after the deposition of the rocks. Earlier, we got similar results for the Late Vendian rocks of the Southwest Baikal and East Sayan regions and also for the transitional Vendian-Lower Cambrian rock sequences of the Siberian Platform. This allowed us to infer the anomalous behavior of the geomagnetic field at the end of the Vendian to the beginning of the Lower Cambrian. The results obtained in the study reported here prove the actual basis of this hypothesis. During our study of the older Ediacarian and Ediacarian-Nemakit-Daldynian rocks, we managed to distinguish stable high-temperature magnetization components, obviously reflecting the trend of the geomagnetic field that existed during the deposition of these rocks. The paleomagnetic poles corresponding to these components allowed us to reconstruct the late Vendian trend of the apparent migration of the pole and evaluate the character of the Siberian Platform movements during that time, which allowed us to chose the polarity for the Riphean paleomagnetic trends of Siberia.