Magnetic stratigraphy of the Samoedsky Formation, the upper part of the Siberian Traps LIP section in the Norilsk region

The question of the total duration of the Siberian Traps magmatic activity in the Siberian platform and its correlation with the Permian-Triassic boundary is still being contentious, remaining essential for a number of studies, especially for the possible links with the end-Permian global biotic crisis.

The aim of this work was to obtain for the first representative and reliable paleomagnetic data on the section of the Samoedsky Formation using the modern instrumental base of paleomagnetic studies to estimate the magmatic activity duration. The Samoedsky Formation lies at the top of the Permian-Triassic volcanic section of the Norilsk region. The major part of the Norilsk tuff-lava pile, except for the lowermost Ivakinsky Formation, corresponds to the normal magnetic polarity interval [1]. Although the paleomagnetic investigation of the Samoedsky Formation basalts was performed previously [1, 2], this interval still remains complicated and the issue of its relation to the normal or reverse polarity interval has not been resolved.

During the field work oriented samples were taken (233 samples from 11 sites) from the lava flows of the Samoedsky Formation in the Verkhnyaya Talovaya river valley (the Norilsk region). At the laboratory stage alternating field and thermal demagnetization were carried out using SQUID SRM, JR-6 (AGICO) magnetometers and MMTD80 thermal furnace.

Based on the results of calculations with the Enkin software package [3], it can be concluded that the three uppermost lava flows of the Samoedsky Formation are magnetized in reversed polarity, which confirms the latest data [1]. Other studied flows demonstrate the normal polarity. Thus, the emplacement of the Samoedsky Formation and consequently the entire lava sequence of the Norilsk region corresponds not only to the LT1n1n chron (the first normal polarity chron of the Lower Triassic), but also to the part of the reverse polarity chron LT1n1r [1], which also affects the correlation of the sections of the Siberian Traps LIP different regions.

References

1. Latyshev A.V., Fetisova A.M., Veselovskiy R.V. Linking Siberian Traps LIP Emplacement and End-Permian Mass Extinction: Evidence from Magnetic Stratigraphy of the Maymecha-Kotuy Volcanic Section // Geosciences. 2020. V. 10. № 8. P. 295.

2. Gurevitch, E.L., Heunemann, C., Rad’ko, V., Westphal, M., Bachtadse, V., Pozzi, J.P., Feinberg, H. Palaeomagnetism and magnetostratigraphy of the Permian-Triassic northwest central Siberian Trap Basalts // Tectonophysics. 2004. V.379. P. 211–226.

3. Enkin R.J. A computer program package for analysis and presentation of paleomagnetic data. Pacific Geoscience Centre, Geol. Surv. Can., 1994. P. 16.