SOME QUESTIONS IN THE HISTORY OF THE GEOMAGNETIC FIELD AT THE END OF THE MIDDLE PALEOZOIC AND IN THE UPPER PALEOZOIC

Abstract : From paleomagnetic work on the Russian and North American Platforms and their mountainous borderlands, in the second half of the Paleozoic Era, two regular characteristics in the development of the geomagnetic field: long duration of the zones of reverse magnetization; close grouping of the paleomagnetic poles of each epoch for each of the different continents. The considerable durations of the reversely magnetized zones make it possible, on the basis of stratigraphic interconnections, to effect a comparison and alignment of (magnetic) zones on an inter-regional (supraregional) scale; also to tie in the paleomagnetic pole determinations with definite zones, and thus exclude, in comparing poles, error due to differing ages of the rocks studied. These facts, together with the clear separation of the Recent and Paleozoic pole positions, give us grounds for considering the upper half of the Paleozoic as the most convenient interval in which to test and demonstrate basic paleomagnetic hypotheses. The work here reported, which was carried out on Paleozoic cross-sections in the intermontane basins of the Sayan-Altai folded region, constitutes only a part of the research that is being conducted throughout the Asiatic part of the USSR with the object of group-by-group comparison of paleomagnetic sections. (Author)