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Abstract—A paleomagnetic study of the Okhotsk–Chukotka belt volcanics exposed in the region of the Kupol field (~66.9° N, 170.1° E) has been carried out. The studied rocks were formed between 85 and 95 Ma during the Cretaceous Normal Superchron (CNS). In most of the studied samples, the characteristic magnetization component is isolated. Its primary origin is supported by the positive fold test, magnetic mineralogy data, and similarity of the calculated paleomagnetic pole with that of coeval rocks from the same region. It is shown that the studied rocks were formed in high polar latitudes close to 80° N. The amplitude of paleosecular variation (PSV) of the geomagnetic field during CNS has been estimated. Depending on the calculation method, the estimates (and their confidence intervals) for ~81° N are Sb = 22.1° (19.5°; 24.7°) in case of using a fixed cut-off angle of 45° and Sb = 23.1° (20.3°; 25.7°) in case of the cut-off angle calculated by the Vandamme method. The obtained estimates generally support the existing models of PSV latitudinal dependence for CNS. At the same time, the estimates are less consistent with the model (McFadden et al., 1991) where PSV values are low at the equator and sharply increase with latitude than with the model (Biggin et al., 2008) predicting higher PSV values at the equator and their more gentle increase towards polar latitudes. Irrespective of the calculation method, the obtained estimates almost perfectly fit the PSV latitudinal dependences for the last 5 Ma. This means that the amplitude of secular geomagnetic variation during CNS, at least at high latitudes, was the same as it was during the last 5 Ma. The obtained result does not support the hypothesis that geodynamo regimes change at the transition from the periods of frequent geomagnetic reversals to superchrons (e.g., (Gallet and Pavlov, 2016)), which suggests, in particular, that the modern numerical models are not fully adequate to the real processes of generation of the geomagnetic field. [ABSTRACT FROM AUTHOR]

Abstract—Paleomagnetic studies of several Late Cretaceous volcanic sections of the Okhotsk–Chukotka volcanic belt have been carried out in the Bilibino region of the Chukotka Autonomous Okrug and along the Pevek–Egvekenot road. Extensive collections have been acquired and analyzed. The laboratory experiments isolated the ancient characteristic magnetization component reflecting the direction of the geomagnetic field at the time of formation of the studied rocks (~85 Ma ago). The primary character of the revealed characteristic magnetization component is supported by the positive regional fold test and by the coincidence of the paleomagnetic pole calculated from this component with that previously obtained for Chukotka from the rocks of similar age (Stone et al., 2009). The paleomagnetic pole calculated from the combination of the previous and our newly obtained data (Plat = 69.3°, Plong = 180.7°, N = 99, A95 = 5.1°) indicates that the sampled rocks were formed in the immediate vicinity of the geographic pole. The reliability of the existing Late Cretaceous paleomagnetic poles for Eurasia and North America is analyzed, and the refined poles are calculated for these plates for the time of ~85 Ma. The reconstruction of the Chukotka–Kolyma–Omolon block's position relative to Eurasia and North America allowing for the paleomagnetic poles calculated for that time is proposed. The reconstruction implies that from the formation time of the studied rocks up to the present, the Chukotka–Kolyma–Omolon block has undergone relatively small (tens to first hundreds of km) southward movements relative to the North American plate and has been noticeably shifted (by a few hundred km) relative to the Eurasian plate. Our reconstruction is close to that proposed in (Otofuji et al., 2015) but, in contrast to the latter, it does not require a collision between the Chukotka–Kolyma–Omolon block and Eurasia after 80 Ma ago. [ABSTRACT FROM AUTHOR]