ИСТИНА

In terms of completeness of the geological record, the Ordovician key section of the Moyero River valley (North of the Siberian Platform) until recently was considered to be one of the best Ordovician sections of Northern Eurasia. However, until now only the interval from Arenigian (Floian) to Ashgillian (Katian) part of the section have been thoroughly studied. Our new data indicate the occurrence in this section the Cambrian-Ordovician boundary and existence of several hundred meters thick Tremadocian sequence. All this taken together bring this section to the number of the best Ordovician sections of the world. Although a significant part of this section contains primary paleomagnetic record, there are also numerous layers of different lithology, which are completely or partly remagnetized by Permian-Triassic traps, represented in this area by sills sporadically intruded into the sedimentary strata. In this report, we present the data indicating that numerous sedimentary rocks outcropped in the vast area expanding over tens of kilometers along the Moyero river valley had been remagnetized during a very short remagnetization event which duration barely exceeded several hundred years. We consider the origin of this remagnetization and show that it is not due to simple heating or to thermoviscous processes but linked rather with fluid migration ejected to the rocks during the trap intrusion emplacement. This case of very fast magnetization indicates that paleomagnetic directions derived from remagnetized rocks should be used with caution to calculate the position of paleomagnetic poles. This work is supported by RSF #20–17–00198