The Permian-Triassic effusive traps in the Kotui River valley (Siberian Platform) were studied in detail by a paleomagnetic method, resulting in a summarized magnetic stratigraphic section of the stud

A complex study is carried out for the collection of trap rocks sampled from two sequences in the geographically distant regions of the Siberian trap province: the Ergalakh section (Norilsk region) and Tyvankitskii and Delkanskii formations (Maymecha-Kotuy region). The magnetic and thermomagnetic properties are studied, petrographic and microscopic investigations are carried out, the paleointensities are determined, and the domain structure of ferromagnetics is assessed using the Day diagram and the thermomagnetic criterion. It is shown that small single-domain and/or pseudo-single-domain grains are the carriers of remanent magnetization. The absolute paleointensities H _anc are determined by the Thellier-Coe method with test heating of the samples to lower temperatures (check-point procedure). The paleointensity estimates that meet the modern reliability criteria are obtained in more than 130 samples. The mean H _anc values in the lava flows from the Ergalakh section and the TyvankittskiiFormation, as well as in samples from the Delkanskii Formation, vary within 2.1–24.6 mkT, which is considerably lower than the present magnetic field at the sampling site (∼ 50 mkT). The corresponding mean VDM values in these sites vary within (0.54–3.2) × 10²² Am² (with a dispersion of ∼0.9 × 10²² Am²), which is far lower than the mean VDM value (∼8 × 10²² Am²) in the Late Cenozoic. The agreement of low H _anc and VDM determined in the Ergalakh section, Tyvankitskii, and Delkanskii formations with the previous similar data on the traps (Solodovnikov, 1994; Heunemann et al., 2004; Shcherbakova et al., 2005; 2013) supports the Mesozoic Dipole Low (MDL) hypothesis. In the Ergalakh section, low and extremely low H _anc (11.2 and 2.7 mkT) are determined in two pulses (five flows) of the Ivakinskii Formation, which precedes the geomagnetic reversal. This probably indicates that these flows recorded a sharp decrease in H _anc prior to the geomagnetic reversal (or at its beginning), which occurred at the earliest stage of the Norilsk tuff-lava sequence formation. The abnormal values of paleodirections and paleointensities in the group of the flows of the Tyvankitskii Formation suggest that they could have been formed during the anomalous nonstationary state of the geomagnetic field such as the excursion.

The Siberian Traps Large Igneous Provinces (LIP) emplacement is considered as one of possible triggers for the end-Permian global biotic crisis. However, relative timing of the onset of extinction and the main phase of the magmatic activity are not yet accurately constrained. We present the detailed paleomagnetic data for the thickest composite section of the Siberian Traps volcanics, located in the Maymecha-Kotuy region. The major part of the Maymecha-Kotuy section erupted in the beginning of Early Triassic period and postdate came the onset of the biotic crisis. However, the initial pulse of volcanic activity in this region took place at the end of the Permian period, and likely preceded the extinction event, being nearly coeval to the lowest part of tuff-lava sequence of Norilsk. The suggested correlation scheme of volcanic sections from different regions of the Siberian platform shows that explosive and extrusive events foregoing the onset of extinction can be identified in almost all regions of the Siberian Traps LIP. Finally, we estimate the total duration of magmatic activity in the Maymecha-Kotuy region as ~2 Myr and assume that this lasted after the termination of eruptions in other parts of the Siberian platform.

—The Permian–Triassic magnetostratigraphy of the central East European platform has been updated using evidence from the Zhukov Ravine, Slukino and Okskiy Siyezd reference continental redbed sequences. The new data reveal five rather than four polarity subzones in magnetozone R₃P, which thus can be ranked up to orthozone RnP. The upper Permian strata of the Zhukov Ravine and Okskiy Siyezd sections contain intervals of anomalous paleomagnetic directions similar to those revealed earlier in roughly coeval rocks from the Nedubrovo section in the Vologda region. The anomaly may be of regional extent and may correspond to quite a long (thousands of years) span of geomagnetic field stability near the Paleozoic–Mesozoic boundary, which fits the subequatorial dipole field in the first approximation. The paleomagnetic results were used to constrain the position of three new Permian–Triassic paleomagnetic poles of the East European platform, corrected for inclination shallowing: PLat = 54.8°, PLong = 173.6°, dp/dm = 2.6°/4.0° (Zhukov Ravine); PLat = 47.6°, PLong = 164.3°, dp/dm = 3.0°/4.8° (Slukino); PLat = 52.7°, PLong = 153.6°, dp/dm = 3.7°/5.4° (Okskiy Siyezd).

Выделенная сравнительно недавно недубровская пачка - предмет неутихающих споров в связи с неопределенностью возраста слагающих ее отложений. Проведенные различными исследователями многочисленные определения фауны и флоры позволяют относить недубровские отложения, с одной стороны, к терминальной перми, с другой - к нижнему триасу. Уникальность недубровской пачки определяется также отсутствием известных возрастных аналогов в пределах Московской синеклизы. В настоящей статье даны результаты комплексных палеомагнитных и магнитно-минералогических исследований предположительно наиболее древних недубровских слоев нижнего триаса Московской синеклизы, вскрывающихся в нижнем течении р. Кичменьги (Вологодская обл.) и залегающих на глинах вятского яруса верхней перми. Детальные температурные магнитные чистки позволили выявить в большинстве образцов наличие монополярной стабильной компоненты естественной остаточной намагниченности (ЕОН). Среднее направление характеристической компоненты намагниченности изученных красноцветов (slat = 60,04521°, slong = 45,74047°, N = 142, D = 246,3°, I = -6,6°, K = 10,0, α95 = 3,9°) значительно отличается от ожидаемых позднепермских-раннетриасовых палеомагнитных направлений и с высокой степенью вероятности может быть аномальным. Мы полагаем, что аномальная намагниченность сформировалась во время продолжительного, порядка первых тысяч лет, отклонения конфигурации магнитного поля Земли от поля центрального осевого диполя. Имеющиеся свидетельства присутствия соответствующих интервалов с аномальными палеомагнитными направлениями в осадочных и вулканических разрезах верхней перми Западной Сибири указывают на возможность их использования в качестве маркеров для проведения региональных и глобальных магнитостратиграфических корреляций, а также позволяют косвенно предполагать верхнепермский возраст недубровских отложений. палеомагнетизм, магнитная стратиграфия, пермь, триас, Русская плита, недубровская пачка