ИСТИНА

The geomagnetic polarity time scale over the last 150 million years was established from the study of oceanic magnetic anomalies as well as from numerous magnetostratigraphic studies. For older periods of the Phanerozoic, the magnetostratigraphic data can only be obtained from biostratigraphically well dated sections, which are not so abundant and thus provide incomplete and sometimes sketchy record of the time evolution of the geomagnetic field. Nevertheless, the available information confidently indicates that the frequency of geomagnetic reversals during the Phanerozoic varied significantly from almost zero, during the so-called superchron, to fairly high (7-8 reversals per Myr) values in the Miocene, Middle Jurassic and the Middle Cambrian [Pavlov and Gallet, 2005, Gallet et al., 2012, Opdyke and Channell, 1996]. To date, three Phanerozoic superchrons, lasting several tens of millions of years, have been established: the Ordovician Moyero [Pavlov and Gallet, 2005], the late Paleozoic Kiama [eg Opdyke and Channell, 1996] and the youngest - the Cretaceous superchron [Helsley and Steiner, 1968]. The question of why the process of rather frequent (on a geological scale) reversing of the geomagnetic field suddenly terminates for tens of millions of years in one of its two possible stationary states, is still unresolved. Main parameters of the geomagnetic field that can be used to study its evolution, are: the frequency of reversals, the intensity and the characteristics of secular variation. In this study we attempt to describe the behavior of geomagnetic field, based on geomagnetic secular variations, during the Cretaceous superchron. Data for this study was obtained using the unique collection of samples of successive volcanic flows from the Okhotsk-Chukotka volcanic belt (Chukotka, North-Eastern Russia), that effused 110-75 Ma ago and keep representative record of the Cretaceous superchron (121-83 Ma). This poster will present the first results of the paleomagnetic study of rocks of Okhotsk-Chukotka volcanic belt. These results will allow us to estimate the amplitude of the secular variations of the geomagnetic field during the Cretaceous superchron. This work is supported by the Russian Science Foundation under grant №19-47-04110.