This study examined the applicability of R. Fischer’s approach to the analysis of sample directions in the flow of eruptive rocks. A test of the hypothesis that all samples share a common direction of the ancient field was proposed.

In this article, the results of the rock-magnetic measurements (magnetic susceptibility and its anisotropy before and after the heating of rocks, magnetic saturation) and paleomagnetic studies of the Lower Syzran Subformation (Paleocene) in the Peschanyi Umyot section (Saratov, Russia) are discussed. The section is composed of weakly magnetic silicites and has the paleomagnetic parameters that are suitable for magnetostratigraphic purposes. The presence of a magnetic zone with predominantly reverse polarity, which is an analogue of either chron C27 or C26 or their combination, was found in the section. The results obtained, along with previously collected data from coeval sections in the south of the Saratov right bank and the city of Saratov, made it possible to draft a magnetostratigraphic chart for the Paleocene of the Volga region, provide a detailed correlation of the Syzran Formation, estimate the duration of the pre-Paleogene erosion, and more accurately date the age of deposits.

Giant mafic dykes are the key markers of the Earth’s evolution in the Precambrian and have been the subject of extensive research. This article presents the results of the paleomagnetic, rock-magnetic, and paleointensity B_anc studies of the Great Dyke of the Kola Peninsula (2.68 Ga). The mean paleomagnetic  direction of the characteristic magnetization component and the paleomagnetic pole of the Murmansk craton were calculated using the data from 5 sites (n = 41 samples): D = 117.6°, I = 77.1°, K = 40.9, α₉₅ = 12.1°, slat = 69.265°, slong = 34.35447°, plat = 51.5°, plong = 70.7°, dp/dm = 21.1°/22.6°, and paleolat = 65°. The rocks under study were thoroughly examined for their thermomagnetic properties, revealing that the main carriers of remanent magnetization are single-domain or small pseudo–single-domain (group A) or multidomain (group B) magnetite. The paleointensity values B_anc = (6.16 ± 0.92) μT were obtained for 12 samples from group A by the Thellier–Coe method. The corresponding mean virtual dipole moment VDM_2.68Ga = (0.85 ± 0.13)×10²² Am² was determined. These new findings align with previous results on the Archean and Proterozoic objects, indicating that the Earth’s magnetic field was remarkably weak in the Late Archean.

Detailed petrographic, electron-microscopic, and paleomagnetic studies were conducted on flatbedded synsedimentary carbonate breccias from three blocks of rocks (one block from Minyar, two blocks from Katav-Ivanovsk) to verify the ideas about the time of formation of the high-temperature component (HTC) of natural remanent magnetization (J_n) of limestones from the Upper Riphean Katav Formation, Southern Urals. Petrographic and electron-microscopic observations revealed that the composition of pebbles corresponds to that of the host matrix rocks, thus enabling the use of an intraformational conglomerate test. In all the studied blocks, the distribution of paleomagnetic directions for pebbles is generally chaotic, with the concentration parameter not exceeding 3. These test results meet the Graham criterion. The pebbles’ average J_n have a larger confidence oval and differ significantly from the matrix’s directions with a much smaller confidence oval. The Hodges-Ajne test was applied to the blocks from Katav-Ivanovsk. The Rayleigh test was used for the block from Minyar. The results obtained at this stage indicate that the HTC of magnetization of the Katav limestones may have a primary origin. If this is confirmed, the Katav Formation would be a good paleomagnetic record of the Earth’s Neoproterozoic history and provide valuable insights into the geomagnetic field behavior in the Late Precambrian.

This article reports on some preliminary findings of a study on the seismoacoustic profiling of the basin of Lake Turgoyak (Southern Urals) and the magnetic properties of its bottom sediments. In the eastern depressions, the lake sediments are up to 8 m thick. The radiocarbon dating of the sediment samples suggests that the lake is at least 25 000 years old. The seismoacoustic data reveal that the lower part of the section, which is composed of the dense Neopleistocene sediments, accumulated when the water level was lower. The Holocene sediments are poorly consolidated silts up to 4 m thick. The magnetic properties of the sediments were found to be indicative of the environmental conditions and fluctuations in the lake level. The high-amplitude variations in the scalar magnetic values of the sediments point to frequent changes in the sedimentation conditions. The sediments with the highest magnetic susceptibility (χ), natural remanent magnetization (NRM), coercive force (B_c), coercivity of remanence (B_cr), saturation magnetization (M_s), and magnetization remanence (Mrs) are likely to have formed during the periods when sedimentary material was transported by ice, often with a significant influence from wind.

Numerical simulation of the process of remagnetization of small pseudo–single-domain magnetite particles (Т_c = 580°С) was performed. The particles are cylindrical in shape, with a height h of 60–350 nm and a height-to-diameter ratio of 1.29. This geometry enables preferential anisotropy of the shape, causing the magnetic moment of the particle to align along the cylinder’s axis in a stable state. As the size increases, the domain structure shifts from the single-domain state (60 nm) to the flower mode (h = 70–85 nm), and then to a vortex structure. Particles in the range of h = 75–250 nm are remagnetized through a vortex state, with the axis aligned along their diameter. In the range of h = 300–350 nm, at the top of the potential barrier, the domain structure transforms from a single vortex to a multi-vortex configuration. The blocking temperatures T_b of the particles vary from 520 to 580°C, while the dependence Тb(h) is non-monotonic and manifests a “pit” at h = 90–140 nm. At the same time, at h = 300–350 nm, T_b values differ from by Т_с  no more than 1°C. At h = 100 nm, the ratio of magnetic energy in the external field B of the order of the earth to thermal energy at T = T_b reaches 1. This suggests a strong nonlinearity of the TRM(B) dependence even in such small fields and particle sizes. The results obtained highlight the need to revise the existing micromagnetic models by taking into account the specific shape and deficiency of the crystal structure of particles in order to bring them in line with the properties of actual ferrimagnets present in rocks.

This article presents the results of a detailed paleomagnetic study of five sections of the Permian-Triassic sedimentary rocks from the southeastern part of the Volga-Ural anteclise in the East European Platform (Orenburg region, Russia): Boevaya Gora, Vyazovka, Sambulak, Krasnogor, and Vozdvizhenka. The magnetic fabric determined by magnetic susceptibility anisotropy indicates that the rocks accumulated under the conditions of intense hydrodynamic activity. This makes it possible to reconstruct a predominantly submeridional transport of detrital material. The rocks of the Boevaya Gora section have a bipolar distribution of the characteristic component of their remanent magnetization, while other sections show a reversed polarity. In the Vyazovka section, the E/I method was used to calculate the inclination shallowing coefficient of the rocks (f = 0.79). The regional fold test yielded positive results, suggesting that the rocks of the studied sections were displaced after the deposition. For each section, paleomagnetic poles were calculated, with the poles of the Boevaya Gora and Vyazovka sections being the most reliable. The mean paleomagnetic pole coordinates of the studied sections, except the Sambulak section, are as follows: slat = 51.7°, slong = 55.8°, n = 4, plat = 48.5°, plong = 173.4°, α₉₅ = 3.4°, paleolat = 23.4°.

The total energy of the potential geomagnetic field (up to the core-mantle boundary) is divided into dipole and non-dipole parts, which are determined by their evolution and frequency properties. The calculations presented here are based on the available and sufficiently reliable COV-OBS.x2 geomagnetic field model that covers the period of 1840–2020. The proposed approximations for longer periods are preliminary, as further work is required to estimate errors through comparison with other historical observational and paleomagnetic models of the geomagnetic field, as well as with numerical models of the geodynamo. The actual dipole energy (about 5 EJ) turned out to be only three times higher than the non-dipole energy, rather than the previously reported one order or more. It was found that the dipole energy decreases relatively slowly and monotonically, while the non-dipole part changes much faster and quasi-periodically. Therefore, the characteristic times are on the order of one thousand years for the dipole component and on the order of hundreds of years for the non-dipole component, respectively. If the quadrupole and octupole contributions to the geomagnetic field are only considered, which is a natural limitation for paleoand archaeomagnetologists, then the energy of such a “truncated” non-dipole part increases monotonically, and its evolutionary and frequency characteristics become different from the full (up to the 14th spherical harmonic) non-dipole part. The results show that the power or the time derivative of energy varies more significantly compared to the energy, being on the order of one hundred MW for both the dipole and non-dipole parts. Frequency values were obtained by analyzing the power/ energy ratios.

This article overviews the results of a preliminary magnetic and mineralogical study of the bottom sediments of Lake Beloe (Southern Siberia, Russia). The magnetic and mineralogical properties of the sediments were examined. Their variations were correlated with geological factors. A comprehensive magnetic survey was performed: magnetic susceptibility of samples extracted from three sediment cores was measured; normal remanent magnetization in a continuously increasing external magnetic field of up to 1.5 T was calculated; differential thermomagnetic analysis was carried out based on induced magnetization and scanning electron microscopy (SEM) for certain samples. The magnetic component was divided into three subcomponents based on the normal magnetization curves: ferromagnetic, dia-/paramagnetic, and superparamagnetic. The contribution of each subcomponent to the total magnetization was determined. It was found that the magnetic susceptibility values correlate well across all the studied cores, thus making it possible to compare them. Magnetite and pyrite turned out to be the magnetic minerals distributed throughout almost the entire section. In the Day–Dunlop plot, the studied samples are represented by single-domain (SD) and pseudo–single-domain (PSD) grains. The magnetic components vary consistently along the section, suggesting that the depositional environment underwent substantial changes. Particles similar in composition and morphology to cosmogenic and volcanic spherules were discovered using the SEM method. Based on the obtained results, the boundary between the Pleistocene and Holocene deposits was defined.

A paleomagnetic study of volcanic rocks of the Okhotsk-Chukotka volcanic belt was performed to identify the scale and distribution pattern of orientation errors associated with the use of a magnetic compass, as well as to find how they influence the accuracy of calculated mean directions at both site and regional levels. The impact of these errors on the position of the final paleomagnetic pole and the dispersion of virtual geomagnetic poles, which is a common measure of the amplitude of paleosecular geomagnetic variations, was assessed. The alternative (non-magnetic compass) methods for orienting paleomagnetic samples were analyzed. Their advantages and disadvantages were outlined. A new method for orienting paleomagnetic samples using a theodolite equipped with a laser pointer was proposed. This method has a distinct advantage over previous alternatives as it is not limited by certain critical factors.

The bottom sediments of the Russian Arctic seas have been studied to varying degrees. The least attention has been paid to the East Siberian Sea, the Quaternary geology of which remains largely overlooked. This article summarizes the results of a comprehensive research on the East Siberian Sea, including the first paleomagnetic analysis of nine sediment cores collected during three cruise expeditions as part of the program “State Geological Mapping of the Territory and Continental Shelf of the Russian Federation at the Scale of 1:1 000 000”. The results obtained show that the processes and conditions of sedimentation vary in different parts of the East Siberian Sea.

This article discusses the Late Kungurian radioisotopic age (276.9 ± 0.4 Ma) of the middle part of the Starokuznetsk Formation (Kuznetsk Subgroup, Kolchugino Group) of the Kuznetsk Basin determined by chemical abrasion–isotope dilution–thermal ionization mass spectrometry (CA-ID-TIMS). The analysis of the biostratigraphic data confirms that the layer dated belongs to the interval in which the Balakhonka Flora (cordaitoid) was replaced by the Kolchugino Flora (fern-pteridosperm-cordaitoid). This indicates that the change from the Balakhonka Flora to the Kolchugino Flora in the low latitudes of Angaraland took place during the Late Kungurian. The data obtained were used for direct correlation of the lower part of the Kolchugino Group with the Upper Kungurian of the International Chronostratigraphic Chart. Similar sequences of non-marine bivalve assemblages in the Permian successions of Angaraland (giant Prokopievskia, Khosedaella-Redikorella-Palaeomutela, and dominant Palaeomutela) and Eastern Europe (giant Sinomya, Palaeomutela-Khosedaella-Redikorella, and dominant Palaeomutela) further support the validity of the correlation of the Kuznetsk Subgroup with the Ufimian Stage. The placement of the lower boundary of the Kolchugino Group in the upper part of the Kungurian Stage of the International Chronostratigraphic Scale raises the question of the continuation of the Ufimian Stage as an independent straton in the East European Stratigraphic Scale. Its lower boundary coincides with the beginning of the change in the Balakhonka and Kolchugino Flora in the low latitudes of Angaraland, as well as with the faunal exchanges between the Euramerican and Angarian non-marine bivalve assemblages.

This article outlines the results of the first-ever ichnological study of the Middle Devonian clastic succession in the South Tatar Arch. The analysis of the stratigraphic distribution of trace fossils in the boreholes revealed several levels with biogenic structures such as ichnofossils and bioturbation, which proved useful for the correlation of the boreholes. The boundary interval of the Pashyian and Timanian Horizons is made up by a succession of three layers: bioturbated siltstones with Spirophyton burrows, limestones, and mudstones with Lingulichnus burrows. The interval can be traced over the entire area of the South Tatar Arch and may serve as an additional marker for the boundary between the horizons.