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We present new results of geochronological, rock magnetic, paleomagnetic and paleointensity studies of the olivine gabbro dyke located at the northern part of the Murmansk craton, NE Fennoscandia (the Kola Peninsula). According to its geochemistry, petrographic and geochronology features, the dyke belongs to the 2.68 Ga dyke swarm, as confirmed by Sm-Nd mineral isochron. We find a significant difference in the rock magnetic and paleomagnetic characteristics of the central and marginal parts of the dyke, which is independently supported by petrography and geochemistry. It is shown that the rocks of the central part of the dyke retained not only their primary mineral composition, but also the primary component of the natural remanent magnetization. We use its direction to determine the 2.68 Ga virtual geomagnetic pole for the Murmansk craton: Slat = 68.64292° N, Slong = 37.7945° E, N = 41 specimens, Plat = –73.5°, Plong = 138.9°, dp/dm = 3.2°/3.4°, paleolat = –65.9°. We also obtain reliable estimates (17 samples) of the Earth's magnetic field intensity at ca. 2.68 Ga: VDM value is found to be 1.85 × 1022 A m2 corresponding to the geomagnetic field several times weaker than the present-day field. [ABSTRACT FROM AUTHOR]

Abstract—The concept of Alfvén waves plays a key role in the theory of ultralow-frequency (ULF) electromagnetic oscillations of extraterrestrial origin. This article is dedicated to the 80th anniversary of the discovery of Alfvén waves. It focuses on the ionospheric Alfvén resonator (IAR). IAR excites ultralow-frequency oscillations in the Pc1 range (0.2–5 Hz). When computing the oscillation spectrum within the standard model, it is assumed that the IAR is an autonomous dynamical system. In contrast, in this paper, IAR is treated as a specific subsystem of the general system of Alfvén oscillations of geomagnetic field lines. In other words, we proceed from the idea that IAR, in general, is not an autonomous oscillatory system. The problem about IAR spectrum is discussed in the context of the general problem on the spectrum of magnetohydrodynamic oscillations of the Earth's magnetosphere. The corresponding Sturm–Liouville problem is formulated. Analytical solutions of the problem are considered in the Wentzel–Kramers–Brillouin approximation. It is pointed out that the problem of IAR spectrum has to be solved by numerical methods due to the rather complicated distribution of the Alfvén velocity along the geomagnetic field lines. [ABSTRACT FROM AUTHOR]

Abstract—The paper presents the results of rock magnetic studies and relative paleointensity determinations from sediments of Lake Shira, Khakassia. Carrier minerals of natural remanent magnetization (NRM) were identified through hysteresis loop parameter measurements, thermomagnetic and X-ray diffraction (XRD) analyses. The sediment age was determined by radiocarbon dating; according to age estimates, the studied sediment sequence covers approximately the past 9100 years. To obtain high-quality relative paleointensity results, the determinations were made on linear segments of the pseudo-Arai‒Nagata diagrams. The quality was assessed by the criteria of the number of points in the calculations of slope, quality criterion (q), NRM fraction destroyed in the paleointensity determination interval, and relative paleointensity determination error (σ). According to the rock magnetic studies and XRD analysis, the magnetic carriers are mainly single-domain (SD) and pseudo-single-domain (PSD) magnetite and hematite. The comparison of the obtained relative paleointensity data with model paleointensities calculated for the Shira coordinates from the various models (CALS10K.1b (Korte et al., 2011), PFM9k.1 (Nilsson et al., 2014), HFM.OL1.AL1, CALS10k.2 ARCH10k.1 (Constable et al., 2016)), with absolute paleointensities and with the collection of results from the studies of sedimentary and igneous rocks and archaeomagnetic objects has shown that these data are in good agreement and share common trends. This provides grounds for applying this approach to paleointensity determination from bottom sediments of modern lakes using the pseudo-Thellier method. [ABSTRACT FROM AUTHOR]

Abstract—Ground-based magnetometers and vertical ionospheric sounding stations were used to record specific variations in the geomagnetic field, caused by the perturbation in the lower ionospheric current systems, and specific variations in the upper ionospheric electron density after a strong volcanic eruption in Kamchatka, Russia, on April 10, 2023. The analysis of the measurements from two series of explosions has shown that the impact on the lower ionosphere is realized via both seismic Rayleigh waves (which are a source of acoustic waves propagating into the ionosphere), and atmospheric internal gravity waves generated by explosions. At distances up to a thousand km from the source, a repeatability of the pattern of ionospheric perturbations after each of the six volcanic explosions is discovered. At larger distances, signals from acoustic waves caused by the Rayleigh waves are clearly recorded in the ionosphere, whereas separation of the signals from atmospheric internal waves is difficult due to the influence of perturbations from other external sources. [ABSTRACT FROM AUTHOR]

Abstract—A complex of archaeomagnetic and rock magnetic studies is conducted to compare the archaeomagnetic intensity determined by the Thellier–Coe and Wilson methods with the known "true" value of the geomagnetic field during the firing of the ceramic samples manufactured on February 21, 2017 in the town of Myshkin (Yaroslavl oblast, Russia). The results obtained show two different values of archaeomagnetic intensity corresponding to two temperature intervals. The archaeomagnetic intensity estimated from the low-temperature interval (~150–350°C) are approximately 13 μT lower than the true value, while the values obtained in the interval of ~350–600°C are fairly close to the "true" ones. The cause of the phenomenon is likely due to the presence of small magnetic grains in the ceramic under study, which are close in size to superparamagnetic ones and can resume their growth upon heating and reaching a particle size in a single-domain state. The results of rock magnetic studies suggest that thermoremanent magnetization in the studied ceramics is carried by grains of oxidized magnetite, hematite, and possibly ε-Fe2O3. [ABSTRACT FROM AUTHOR]

Abstract—To describe secular geomagnetic variation on geological timescales, statistical models have been widely used in recent decades. Currently, the most popular among these is the TK03 model (Tauxe and Kent, 2004). As other statistical models, TK03 numerically characterizes the amplitude of secular geomagnetic variation and the shape of the distribution of paleomagnetic directions which are thought to directly reflect the directions of the geomagnetic field on the considered interval of geological time. For this purpose, three main parameters are used: the scatter Sb (or S) of the virtual geomagnetic poles, the elongation E of the distribution of paleomagnetic directions, and the elongation direction of the distribution of paleomagnetic directions. The correct use of these parameters to describe paleosecular variation requires the fulfillment of certain, sometimes rather strict conditions. These conditions for parameters Sb and E were considered in a number of previous publications, while the limits and conditions of application of have not been studied in detail so far. The results of mathematical modeling presented in this paper allow us to evaluate the stability of the calculated parameter values as a function of sampling latitude, the number of samples used to determine this parameter, the length of the time series from which this parameter is estimated, as well as the inclination shallowing and the degree of averaging if is estimated from sedimentary rocks. We also consider the extent to which the parameter can be sensitive to the presence and characteristics of the equatorial dipole component in the total geomagnetic field. [ABSTRACT FROM AUTHOR]

Abstract—A theoretical formalism has been developed to calculate the electromagnetic fields generated in the atmosphere–ionosphere system by a finite-length underground horizontal current source. A numerical model with a realistic profile of the ionosphere in a vertical geomagnetic field has been constructed based on this theory. It is shown that the apparent impedance of the electromagnetic field produced by an underground source on the Earth surface is an order of magnitude higher than the Earth impedance; this can be used to discriminate perturbations from seismogenic sources. The presented results of numerical modeling allow us to relate perturbations created by a large-scale underground source in the magnetic field of the Earth surface and in the electric field in the ionosphere. Based on these model estimates, it is concluded that many of the ULF electric field perturbations detected in satellite data prior to earthquakes cannot be attributed to direct emission from seismogenic sources. [ABSTRACT FROM AUTHOR]

Abstract—It has been observed that strong earthquakes and volcanic eruptions are sometimes followed by geomagnetic oscillations with frequencies of 3.5–4.0 mHz. This paper describes the theoretical study of the probable cause of these phenomena, which is related to the vertical acoustic resonance between the Earth's surface and the thermosphere, produced by the propagation of the atmospheric wave corresponding to the acoustic branch generated by surface displacements. The propagation of two-dimensional (2D) harmonic acoustic wave is analyzed in a plane layered model of the atmosphere and ionosphere with oblique geomagnetic field. The altitude of the reflecting atmospheric layer corresponds to the region of a sharp temperature change in the vicinity of the thermosphere boundary ~80–90 km. The calculated fundamental resonant frequency is close to the observed oscillations. The obtained solution is used to calculate currents and electromagnetic perturbations in the atmosphere and ionosphere. Assuming thin-layer approximation for the ionospheric E-layer, we derive formulas describing the geomagnetic disturbances (GMD) in the ionosphere and on the Earth's surface. The GMD spectrum has a sharp peak at the frequency corresponding to the acoustic resonance. According to the calculations, close to the resonance frequency, the power spectral density of GMD on the ground can reach 5–30 nT2/Hz, which is consistent with the results of ground-based measurements. [ABSTRACT FROM AUTHOR]

The paleodirection and paleointensity of the geomagnetic field are determined from seven andesibasalt–basalt samples of three lava flows (L1–L3) from the Avachinskii (Avacha) volcano. Based on the sample from the recent lava flow TFE-50 (Tolbachik Fissure Eruption), the reliability of the Thellier–Coe method for geomagnetic field paleointensity determination is demonstrated: the deviation of the calculated Han from the IGRF12 values is at most 3% with a quality factor q > 13. The age of lava flows L1–L3 is refined using paleomagnetic data. Flows L1, L2 of the Molodoi Cone were formed in 1827 and 300–600 years ago, respectively, and the age of flow L3 at the crest of the somma is determined at 30–32 ka, which agrees with the known age estimate of the debris avalanche associated with the catastrophic destruction of the Avachinskii volcano 29 900 ± 37 900 14C years ago. [ABSTRACT FROM AUTHOR]

Abstract—In 394 samples characterizing 266 stratigraphic levels in four Turonian–Santonian sections of the Southwestern Crimea, characteristic remanent magnetization components (ChRM) acquired at the stage of diagenesis are identified. The obtained data fix the record of the paleosecular geomagnetic variation of high amplitude (root mean square deviation S = 25.9° with a fixed cut-off angle of 45°, which is about twice as high as the model S for this latitude) in the sediments formed during ~5–6 Myr and is interpreted as anomalous behavior of the geomagnetic field in the Turonian, Coniacian, and Santonian. [ABSTRACT FROM AUTHOR]

Abstract—In contrast to reversals, geomagnetic field excursions can occur at lower convection intensity in the Earth's core. Since in such geodynamo regimes the magnetic field behavior is still quasi regular, a reduction in the dipole field during excursion may indicate a global failure in the dynamo process. As a consequence, it is possible that during the excursion, not only the dipole component, but also higher harmonics of the field decrease. This hypothesis is tested in a 3D (3D) dynamo model. [ABSTRACT FROM AUTHOR]

Abstract—The paper reports petromagnetic and archeomagnetic studies of ceramic fragments of the Late Bronze and Early Iron ages from archeological sites of the Grishinskii Istok III, Tyukov gorodok, and Shishkino hillfort, which are located in the Oka River basin, Ryazan district, Russian Federation. In total, 43 determinations of geomagnetic field intensity were obtained for the time interval of 1500–400 B.C., including 10 determinations for ceramics of the Grishinskii Istok III, 11 determinations for ceramics of the Tyukov gorodok, and 22 determinations for ceramics of the Shishkino hillfort. The investigated time interval is characterized by the elevated values of the geomagnetic field intensity of 55–59 μT, which are much higher than the average field intensity for the Russian Plain in the IV–first half of III millennium B.C. Obtained VADM values for the central Russian Plain fall in a wide range of values obtained on the Georgian archeological sites located in the same longitudinal sector. A large scatter of data can be related both to the large error in 14C determination, which is comparable with the duration of the time intervals under investigation, and with the high velocity of magnetic field variations within this time interval. [ABSTRACT FROM AUTHOR]

Abstract—Ground-based magnetometers and ionospheric radio probing by means of GPS were used to analyze and interpret specific variations of the geomagnetic field and the total electron content of the ionosphere during strong catastrophic earthquakes in Turkey on February 6, 2023. It is shown that the ionospheric responses to these earthquakes recorded at distances of 1200–1600 km from the epicenter in the lower ionosphere and at distances of up to 500 km from the epicenter in the upper ionosphere can be interpreted in terms of the propagation of the Rayleigh seismic wave and atmospheric waves—shock, acoustic and internal, that is, those waves that are generated by the earthquake itself. The energy of seismic events was estimated from the ionospheric response. [ABSTRACT FROM AUTHOR]

This paper is devoted to the 80th anniversary of the discovery of Alfven waves, which play an important role in physics, radiophysics, astrophysics, and Earth physics. The emphasis is on the ponderomotive redistribution of plasma in the Earth's magnetosphere under the action of Alfven and ion-cyclotron waves. At relatively small distances from the Earth, the ponderomotive force is buoyant, i.e., is directed upwards, regardless of whether an Alfven wave propagates towards the Earth or away from it. In the near-equatorial zone of the central regions of magnetosphere, waves in the Pc 1 range push the plasma to the minimum of geomagnetic field, so that a maximum of plasma density arises on the equator at sufficiently high wave intensity. A bifurcation occurs at the magnetosphere's periphery, and the maximum is split into two maxima, the distance between which increases while moving away from the Earth. The polar wind, acceleration of heavy ions, and fictitious nonlinearity of the surface impedance of the Earth's crust are also briefly discussed. [ABSTRACT FROM AUTHOR]

Abstract—During a series of destructive earthquakes in Turkey on February 6, 2023, in particular, two strong earthquakes with magnitudes 7.8 and 6.7 immediately following each other, the results of instrumental observations of microbaric and geomagnetic variations made in the surface layer of the atmosphere, as well as variations of the electric field and the critical frequency of the regular F2 layer of the ionosphere are presented. It is shown that the earthquakes were accompanied by variations of magnetic and electric fields, generation of infrasound waves recorded at a considerable distance from the sources, as well as variations of the critical frequency f0F2. [ABSTRACT FROM AUTHOR]

The magnetic effects of two similar underwater earthquakes with magnitudes of 6.0 and 7.3, which occurred on March 16, 2022, were considered in (Adushkin et al., 2023). According to the data of INTERMAGNET magnetic observatories, these earthquakes were found to be accompanied (with a delay of ~55 min) by variations in the Earth's magnetic field in the form of a train of quasi-periodic oscillations with an amplitude of ~2–8 nT and a period of ~30 min at distances of ~210 to ~3000 km from the epicenter. It was suggested in the aforementioned study that this magnetic effect is caused by a disturbance of the geodynamo as a result of the impact of seismic waves propagating deep into Earth. This interesting hypothesis requires a detailed discussion from different points of view. A more detailed analysis of the pattern of geomagnetic field disturbance at all latitudes, performed by us, leads to a conclusion that the found quasi-periodic disturbance is a mid-latitude response to auroral electrojet variations and is not related to the earthquake. According to our estimates, variations with a source at the core–mantle interface on a time scale less than one year cannot manifest themselves on the Earth's surface at all. [ABSTRACT FROM AUTHOR]

The magnetic effects of strong earthquakes are considered using the example of a unique event: two underwater earthquakes of magnitude 6.0 and 7.3 that occurred on March 16, 2022 at close times (at 14:34 and 14:36 UTC, respectively) with a distance between sources of ~11 km. With the use of data from the Mikhnevo geophysical observatory of the IDG RAS (MHV) and a number of magnetic observatories of the INTERMAGNET international network, it is shown that in the absence of global geomagnetic disturbances, earthquakes were accompanied by characteristic variations of the Earth's magnetic field recorded as a train of alternating geomagnetic field oscillations with an amplitude of ~2–8 nT and a period of ~30 min almost simultaneously at ~15:30 UTC by all magnetic observatories located at distances from 210 to ~13 000 km, as well as by variations in the periods of passage of the seismic and infrasonic signal in the MHV. [ABSTRACT FROM AUTHOR]

Abstract—Estimating the time of formation of the Earth's solid inner core is a first-order problem in the thermal evolution of the Earth as a planet, which can be solved in particular by paleointensity (Banc) determinations. For this purpose, we have studied a collection of ~1380 Ma rocks sampled in the Udzha River valley within the Udzha aulacogen from the dolerite sill near the Khapchanyr River. The sill is an intrusion 5–7 m thick that cuts through the siltstones and carbonates of the Udzha Formation. To obtain reliable paleointensity (Banc) determinations, magnetic and thermomagnetic properties of the studied rocks have been investigated, and their X-ray diffraction patterns and electron-microscopic images have been collected. It is shown that the carriers of the characteristic component of natural remanent magnetization are single-domain (SD) and small pseudo-single-domain (PSD) magnetite grains. Two methods have been used to determine the Banc: the Thellier–Coe procedure including reheating to lower temperatures (the pTRM checkpoints procedure) and the Wilson express method. Paleointensity determinations have been obtained for 9 samples (30 duplicates) that met the selection criteria. The mean value of Banc is extremely low and amounts to 4.54 ± 0.49 μT; the corresponding calculated value of the virtual dipole moment (VDM) is (11.1 ± 1.2) × 1021 Am2, which is almost an order of magnitude lower than the mean VDM in modern epoch (≈80 × 1021 Am2) and more than six times lower than the mean VDM in the Cenozoic (6.44 × 1022 Am2). The VDM data over the 350–3500 Ma interval presented in the world paleointensity database (WPD), Borok, have been analyzed. An alternation of periods of low and high paleointensity is observed in the Precambrian and Paleozoic, which indicates a large variability in the operation mode of the geomagnetic dynamo regardless of the existence or absence of an inner solid core of the Earth. It is important to note that the number of reliable VDM values over such a long interval, 350–3500 Ma, is too small for a complete statistical analysis to single out any time interval as the most probable for the formation of the inner core. [ABSTRACT FROM AUTHOR]

Abstract—The paper presents the results of paleomagnetic, rock magnetic, and cyclostratigraphic studies of continental red beds that compose the Permian-Triassic boundary interval of the Staroe Slukino section in the Vladimir Region, Russia. Based on the directions of the characteristic components of the natural remanent magnetization of the studied rocks in the sampled stratum, the intervals of normal and reversed polarity related to the regional magnetozones r2RnP, r3RnP, and N3P-T were identified. Within the r3RnP zone, there is an interval of anomalous paleomagnetic directions, which has similar characteristics to those identified earlier in the coeval intervals of the Nedubrovo, Zhukov Ravine, and Okskiy Siyezd sections. Revising the biostratigraphy allows us to assume that the two zones of anomalous paleomagnetic directions in the composite magnetic polarity scale of the upper Permian of the Russian Platform are a reflection of the same epoch of an anomalous geomagnetic field configuration. It is estimated by the cyclostratigraphic method that the studied 16 m interval of the Staroe Slukino section took 900 ± 20 thousand years to accumulate, which limits the duration of the geomagnetic field anomalous state near the Permian-Triassic boundary to ~110 thousand years. A new Permian-Triassic (~252 Ma) paleomagnetic pole of the East European Platform is calculated: plat = 36.3°; plong = 155.0°; dp/dm = 2.8°/4.8°. [ABSTRACT FROM AUTHOR]

Abstract—A new method for analytical description of time-dependent signals of different nature based on local and regional versions of the method of linear integral representations in spaces of different dimensions is proposed. The inverse problem of finding the field sources is reduced to solving ill-conditioned systems of linear algebraic equations with an approximate right-hand side. The results of a mathematical experiment on finding elements of nonstationary gravity and magnetic fields of the Earth are presented. [ABSTRACT FROM AUTHOR]

Abstract—The model of variations in the Earth's magnetic field with random Gaussian coefficients is considered. It is shown that at small amplitudes of random nondipole field component σ, the scatter of the direction of the virtual geomagnetic pole grows with increasing latitude. At large σ, the scatter does not change much and its maximum is located at middle latitudes. [ABSTRACT FROM AUTHOR]

Abstract—The results of calculations of the magnetic field structure in the kinematic approximation are presented, testifying to the consistency of the constructed numerical model with the structure of the flows of a conducting liquid: the instability of the convective process in a rotating spherical shell is reflected in the evolution of the magnetic field, manifesting itself in the pulsation regime of the field. It is shown that the features of the field evolution in the calculations are most clearly pronounced at high latitudes and have analogs in the behavior of the real geomagnetic field. [ABSTRACT FROM AUTHOR]

Abstract—The magnetic properties and mineralogy of titanomagnetite in the Red Sea pillow-basalt at different distances from the contact surface with water were studied. It was revealed that the composition of titanomagnetite in the pillow basalt changes from the crust deep into the pillow: the titanium content in titanomagnetite increases, while the magnesium and aluminum content decreases. Titanomagnetite in the surface layer of pillow basalt (0–2 cm) is single-phase oxidized, with a maximum oxidation degree of 0.13, and at more than 3 cm from the crust has stoichiometric composition. According to the increase in magnetic susceptibility from 0.2 up to 1.8 × 10–2 SI, saturation magnetization from 0.026 to 0.895 A m2/kg and residual saturation magnetization from 0.014 to 0.296 A m2/kg, decrease in coercivity (Hc from 90 to 15 mT, Hcr from 153 to 20 mT), as well as by observations of electron and magnetic force microscopy, it is shown that the concentration of titanomagnetite in basalt and the grain size from single-domain state to pseudo-single-domain state increase with distance from the crust. The magnetic hardness of titanomagnetite grains was found to correlate with the maximum cooling rate of basalt. The NRM of basalt varies non-monotonically with distance from the pillow surface: up to a depth of about 3 cm its growth caused by the growth of titanomagnetite concentration was revealed, then a decrease caused by a decrease in the magnetic hardness of the grains. In spite of a rather strong variation of the magnetic properties in the 0–7 cm layer of pillow basalt, the experiments by the Thellier-Coe method for all layers showed close values of the geomagnetic field paleointensity (62.5–66.0 μT) with a high value of quality coefficient q (11–45). No regularity in the value of paleointensity with distance from the cushion surface was detected. [ABSTRACT FROM AUTHOR]

Abstract—The use of a special technique for processing variations of the geomagnetic field at several mid-latitude observatories allowed us to identify a series of jerks over a 17-year period, from 2004 to 2020. To interpret the our experimental results showing that jerks follow with a quasi period of 3‒4 years, a probable mechanism of the occurrence of rapid changes in the geomagnetic field caused by unstable processes in the Earth's core is proposed. [ABSTRACT FROM AUTHOR]

This study addresses the problems and shortcomings of the traditional field geomagnetic diurnal variation reduction method, the single-observatory reference method, by applying the Taylor polynomial model to establish a spatial reference field for diurnal variation reduction based on geomagnetic network data and comparing the results of the two methods. The findings are as follows: 1. The Taylor polynomial spatial reference field method can effectively describe the spatial distribution pattern of the geomagnetic field, and its results are more accurate and reliable than those of the single-observatory reference method. 2. The results obtained by the proposed method are more uniform and stable than those obtained by the single-observatory reference method, and they are closer to the theoretical shape of Earth's crustal magnetic field changes. 3. While applying the proposed method on earthquakes, it optimizes the display of seismomagnetic information and has good application values. [ABSTRACT FROM AUTHOR]

Abstract–In order to determine the paleointensity of the geomagnetic field in the Precambrian, a collection of rocks from 83 samples of 19 sites selected from the Mesoproterozoic (1133 Ma) dikes of the Bunger Oasis (East Antarctica) was studied. The magnetic and thermomagnetic properties of rocks have been studied in details, the domain structure of magnetic grains, carriers of natural remanent magnetization, has been evaluated, and micromagnetic and X-ray studies have been carried out. It is shown that the carriers of the characteristic component of natural remanent magnetization are single- and/or small pseudo-single-domain grains. Paleointensity was determined by the Thellier-Coe method with the check-points procedure and, in addition to it, the express Wilson method. For 11 sites, low to extremely low values of paleointensity Banc were obtained, which meet modern reliability criteria, the main array of Banc determinations by sites is grouped around (1.5–5) μT. The calculated values of the virtual dipole moment VDM vary from 3 to 8 (×1021 Am2), which is an order of magnitude (and more) less than the current VDM value. Such low values of paleointensity do not agree with the hypothesis of an increased intensity of the geomagnetic field in the Middle Proterozoic and testify against the hypothesis of the formation of the Earth's inner core in the time interval from 1.5 to 1 Ga ago. An analysis of the VDM values presented in 2022 in the world database over the interval of 3600–500 Ma showed that the behavior of the geomagnetic field in the Precambrian is characterized by the alternation of long periods of low and high intensity with a tendency to its gradual weakening from the Archean to the Neoproterozoic. A linear approximation of such a dependence of the VDM value on time has a correlation coefficient of 0.22 at a confidence level of 0.98. The noted features of the behavior of the intensity of the geomagnetic field in the Proterozoic and Paleozoic testify in favor of the hypothesis of the origin of the Earth's solid core not earlier than the Late Neoproterozoic. [ABSTRACT FROM AUTHOR]

Abstract—The experiments have been carried out on the acquisition of thermochemical remanent magnetization (TCRM) in recent Kamchatka basalt containing grains of primarily magmatogene titanomagnetite (TM) with increased thermal stability by rapid heating of the initial samples in air to maximum temperatures of 500, 570 and 600°C followed by cooling at a rate of 1°C/h in the magnetic field of 50 μT. Thermal stability of single-phase oxidized TM fraction manifested itself in the appearance of a wide range of blocking temperatures from 270 to 540–570°C concentrated within two or three intervals of differently inclined linear segments on the Arai–Nagata diagrams. The integrated analysis of the results of this and our previous studies of TCRM acquisition in TMs has shown that when TCRM is created through the growth of the Curie temperature of the cells of TM oxy-exsolution structure as their composition approaches that of magnetite provided that their volume has been stabilized, TCRM proves to be close to the thermoremanent magnetization. This gives grounds to consider the paleointensity determinations obtained on these samples reliable. In other cases, the paleointensity determinations overestimate (for the low temperature segment (from 200 to 375–450°C) of the Arai-Nagata diagram) or underestimate the intensity of the magnetizing field. It is also concluded that the presence of a wide range of blocking temperatures may indicate thermochemical origin of remanent magnetization. [ABSTRACT FROM AUTHOR]

Abstract—The paper presents the results of analysis of the geoelectric (telluric) field variability during the Earth's magnetic field disturbances, caused by extreme space weather events. The area of the study is the territory of the Yenisei-Khatanga Regional Trough (YKRT) situated in the auroral zone, where geomagnetic disturbances are characterized by a high level of intensity. The economic development of the YKRT as a large oil and gas-bearing area in the Russian Arctic increases the relevance of the study of possible negative impacts of space weather on future infrastructure facilities. The most serious threat to conductive industrial structures in the polar region will be posed by geomagnetically induced currents (GIC) driven by geoelectrical responses to rapid geomagnetic field changes. The analysis of the variability of telluric fields and calculations of their extreme values in the YKRT area were made using a unique magnetotelluric impedance tensor database collected by Nord West Ltd. as a result of the regional phase of the geophysical study of the trough and adjacent areas. The geoelectric field spatial-frequency distributions on the Earth's surface were calculated on the basis of the impedance estimates and harmonic approximations of the external geomagnetic excitation. The obtained maps were correlated with geological data to find areas characterized by maximal distortions of the telluric field. Extreme amplitudes of geoelectrical responses at a series of representative locations in the YKRT were evaluated on the time series of telluric field variations, synthesized through the impedance dependences on frequency and magnetic field time series recorded during geomagnetic storms and substorms at the nearest stationary monitoring sites. The resulting estimates of amplitudes and directions of geoelectric fields during space weather disturbances can be used to account for possible destructive effects of GIC in design of pipelines, power transmission lines and railways. [ABSTRACT FROM AUTHOR]

Abstract—We present the results of studying the depths to lithospheric magnetic sources under the East Siberian Sea. The azimuthally-averaged Fourier power spectra of geomagnetic anomalies have been calculated from the global model EMAG2v3, which is the most current compilation of marine, aeromagnetic, ground, and satellite geomagnetic surveys. The depths to the centroid, the upper and lower boundaries of the magnetoactive layer have been calculated from the obtained spectra by the centroid method. The analysis of the results included comparing the depth distributions with known data on the thicknesses of sediments and the Earth's crust, the depths of regional earthquake hypocenters, the surface heat flow, and the tectonic structure of the study region. It has been concluded that the depth to the upper boundary of the magnetoactive layer varies from about 0.4 km under the De Long High to 7 km under the New Siberian and East Siberian sedimentary basins. The depth to the lower boundary of the lithospheric magnetic sources varies from about 25 km under the De Long massif and the Podvodnikov Basin to 43 km under the New Siberian-Chukchi fold belt. In the considered territory, the lithospheric magnetoactive layer is located entirely within the Earth's crust under the continent, the New Siberian Islands, the De Long High, and the western section of the East Siberian Sea shelf. The upper mantle is magnetic under the eastern section of the shelf and the Podvodnikov Basin. The obtained results indicate stronger warming of the lithosphere in the north of the study territory: under the Podvodnikov Basin and the De Long massif, characterized by suboceanic and continental crustal types, respectively. [ABSTRACT FROM AUTHOR]

Abstract—The intensification of geomagnetic variations due to a number of strong remote earthquakes is studied using a chain of ground-based midlatitude magnetic stations located a few thousand km away from each other. It is shown that the spectral peaks of the variations at periods between 5 and 13 min (the range of magnetic pulsations Pc5–Pc6) can be caused by the corresponding variations in the components of the interplanetary magnetic field. Geomagnetic variations with periods longer than 13 min are interpreted as the result of the propagation of slow magnetohydrodynamic (MHD) waves excited in the ionosphere by acoustic pulse after earthquakes or as the result of the passage of traveling ionospheric disturbances. [ABSTRACT FROM AUTHOR]

Abstract—The term "Big Data" has become very popular over the past decade. The frequency of its use in the research papers, reports, and broad press has been steadily increasing. This work describes the origin and development of the theory and practice of Big Data as a scientific discipline, outlines the main characteristics and methods for Big Data processing and analysis, discusses the formalism and family of Big Data V-characteristics, and presents the examples of the sources of the growing Big Data which have fundamental effect on the development of geophysics and related Earth sciences. The examples of the sources of Big Data in the Earth sciences are remote sensing, meteorology, geoecology (in terms of the global hierarchical network SMEAR (Stations Measuring Earth surfaces and Atmosphere Relations)), and seismic exploration. Besides, we discuss seismic monitoring data which can become Big Data when combined with other geophysical information and consider geomagnetic data which are not Big Data but nevertheless have a great scientific value. [ABSTRACT FROM AUTHOR]

Abstract—In response to the kind invitation of the Editorial Board of the journal "Izvestiya, Physics of the Solid Earth" to take part in the discussion concerning the methodology of statistical study of correlations between geophysical processes, we have done a small research and written this paper. Being predominantly geomagnetologists, we focused on the topical question of a correlation between the earthquakes and geomagnetic storms and briefly touched upon the connection of the earthquakes with seismic noise. The main result of our analysis is as follows. The correlation between the earthquakes and magnetic storms exists objectively. The problem deserves a further study using statistical hypothesis testing methods, and a special attention should be paid to clearly distinguishing between causal and acausal correlations. [ABSTRACT FROM AUTHOR]

Abstract—Variations of the geomagnetic field and F2-layer critical frequency in the range of periods of planetary waves in winter season are analyzed. The measurements were conducted by a magnetometer and a vertical radio sounding ionosonde at the nearby Belsk and Warsaw stations and provided the records of the ionospheric current variations in the lower ionosphere and plasma density variations in the upper ionosphere, respectively. Spectral estimation is carried out for the winter seasons of 2018–2019 and 2014–2015 when solar activity was low and high, respectively. It is established that practically synchronous variations in the above range of period are present in the records by the ground magnetic station and in the ionosonde measurements of the F2 layer critical frequency. The spectra of the time variations of the geomagnetic field and F2-layer critical frequency in the period range of planetary waves in winter season contain the harmonic components associated with solar activity and with quasi-16-day and quasi-10-day planetary waves. The mechanism of the formation of the 16- and 10-day variations in the upper ionosphere is proposed. [ABSTRACT FROM AUTHOR]

Abstract—In order to determine the Earth's magnetic field intensity in the Devonian, a collection of rocks of the Baymak-Buribay formation of the Buribay volcanic complex in the West Magnitogorsk Zone—Southern Urals, Khvorostyanka section, has been studied. The complex dates back to the Late Emsian of the Early Devonian (D1e2, 408–393 Ma), based on the conodont fauna. A full set of experiments to study the magnetic and thermomagnetic properties of rocks and to assess the domain structure of magnetic grains have been performed; micromagnetic and X-ray studies have been carried out. It is shown that the carriers of the characteristic component of natural magnetization are single-domain and small pseudo-single-domain grains. The (Banc) paleointensity has been determined by the Thellier-Coe method and the Wilson express method. Ultra-low Banc values = (2.01–7.07) μT have been obtained in 8 samples (24 duplicates) from two sites. The average values of the virtual dipole moment (VDM) for both sites are close to each other and equal to ≈1×1022 Am2, which is almost an order of magnitude less than its current value of 8 ×1022 Am2. The new Banc determinations confirm the hypothesis that there was a period of very weak field in the Devonian, which again raises questions about the time of the Earth's solid core formation and the geometry of the geomagnetic field during periods of a very weak field intensity. The new Banc determinations are consistent with the already obtained data on paleointensity in the Devonian, indicating a high probability that there was a long period of a weak field at this time, the intensity of which is close to the intensity of the nondipole components of the current field. This fact raises the question about the actual geometry of the field at that time—was it dipole or multipole? [ABSTRACT FROM AUTHOR]

Abstract—The occurrence and evolution of plasma fluxes in the ionosphere is one of the factors that have a significant impact on the dynamics and state of the geophysical environment. The study of plasma and magnetohydrodynamic effects arising from the motion of plasma jets in real space is complicated by the scale of the phenomenon and the complex nature of the background environment, which is a non-stationary system of interacting neutral and partially or completely magnetized charged particles. The creation of theoretical models of this phenomenon is also completely unsolved scientific task. Under these conditions, controlled ionospheric plasma experiments are of great importance. The results of active rocket experiments obtained over the past few decades have made it possible to study the processes of magnetohydrodynamic interaction between a high-velocity plasma and the geomagnetic field, the generation of electromagnetic and MHD waves, optical radiation in the visible, UV and IR ranges, background gas ionization, the emergence of complex systems of electric fields and currents, the acceleration of charged particles, and other phenomena. The article discusses the current physical concepts developed from the analysis of the available experimental data, as well as the tasks and possibilities of new active experiments. [ABSTRACT FROM AUTHOR]

Abstract—The effects of the strong natural events on the acoustic fields in the atmosphere, geomagnetic field, and electrical characteristics of atmospheric surface layer—atmospheric current and electric field—are discussed. The extreme events analyzed in the paper are volcanic eruptions, earthquakes, and impacts of outer space bodies falling to the Earth. These natural phenomena are considered as local indicators of the enhancement of interactions between the geospheres in the lithosphere–atmosphere near-surface system with active involvement of the ionosphere. It is shown that in these cases, the induced effects in the geophysical fields are observed at quite a distance from an event source and have similar amplitudes, probably suggesting a special role of the ionosphere in a rapid long-distance transfer of the disturbances. The effect of the acoustic-gravity waves generated by the strong natural events in their epicentral zone is considered as the main excitation mechanism of the ionosphere. The objectives and tasks of the research aimed at establishing the main regularities and interaction mechanisms between the geospheres in the environment are formulated. [ABSTRACT FROM AUTHOR]

Abstract—Reconstructing the evolution of the geomagnetic field in the European part of Russia has been an extremely challenging problem due to the still limited data meeting the up-to-date quality criteria. The paper presents the results of archaeomagnetic studies for five groups of fragments of baked clay bricks from architectural monuments of the 18th to 19th centuries in the Yaroslavl region. Paleointensity of the samples was determined by the Triaxe method involving a series of continuous high-temperature measurements. The paleointensity determinations satisfying the up-to-date quality criteria are obtained from 71 samples of 19 fragments of five archaeomagnetic groups. The obtained paleointensity data are compared with the existing data for the European part of Russia and regional reference curves for Western and Eastern Europe. [ABSTRACT FROM AUTHOR]

Abstract—The results of geomagnetic studies in the Tashkent and Fergana geodynamic test sites, Uzbekistan, are presented. Detail analysis of anomalous geomagnetic variations caused by the processes occurring at different depths in the Earth's crust and upper mantle is conducted. By their linear size, variations are divided into regional (100 km and larger) and local (1 to 5 km and larger). Regional anomalous variations manifest themselves by sinusoidal, bay-like, and trend forms and last one to seven years. In the trend-type variations, the gradient is 0.5–2.0 nT/yr. Local anomalous variations typically have sinusoidal and bay-like shape. Bay anomalies have both positive and negative sign, and the change is reversible. The intensity of the anomalies ranges from 2 to 25 nT and the duration is from 10–15 days to three years or even longer. The local anomalous variations are neither precursory nor technogenic. Numerous anomalies of this type were for the first time revealed at the geodynamic test sites in Uzbekistan. The analysis of the data for the past 40–50 years has shown the absence of information on this type of anomalous variations. They can neither be explained by conventional mechanisms responsible for secular behavior of the geomagnetic field, nor by lithologic composition of the rocks, tectonics fetures, hydrogeological conditions, and geophysical fields of the studied territories. One of the peculiarities of local anomalous variations of this type is that they can change in time, in shape, in size of the area, in intensity, and in sign. The published data relevant to the anomalies in the secular variation of the geomagnetic field have been analyzed. However, unfortunately, these data provide almost no information on the origin of local anomalous variations discussed in our work. [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]

Abstract—The spectra of geomagnetic variations calculated in the period range close to planetary waves—5, 10, and 16 days—are analyzed. The records of the geomagnetic field at the Geophysical Observatory "Mikhnevo" of the Institute of Geosphere Dynamics of Russian Academy of Sciences are used. Spectral estimation based on parametric approach is carried out for the winter and summer periods of 2009 (low solar activity) and 2015 (high solar activity). For the first time, it is established that the harmonics directly related to the manifestation of the atmospheric planetary waves in the entire period range from 4 to 17 days are only observed in winter and, irrespective of solar activity; the changes in the atmospheric pressure are about a month ahead of the changes in the geomagnetic field. In the spectra of geomagnetic variations in the period range of 4–17 days, the harmonics of the 27-day geomagnetic periodicity and the harmonics associated with their modulation by the 11-year solar cycle, annual and semiannual variations are revealed. In the spectra for the period range from 12 to 17 days, harmonics with periods close to tidal waves Мf and Msf are identified. [ABSTRACT FROM AUTHOR]

Abstract—The paper addresses the variability properties of the intensity and direction of the magnetic field during a substorm as well as magnetically quiet periods. The main focus is on the properties of the variations in the time derivative of the magnetic field dB/dt which are a factor of particular importance for the problem of the geomagnetically induced currents. A method of two- (2D) and three-dimensional (3D) diagrams is proposed for visual representation of the directional variations of a vector field. As an example, the geomagnetic field variations during the isolated substorm of October 17, 2015 are analyzed with the use of the chain of the IMAGE network magnetic stations. It is confirmed that dB/dt in the horizontal plane has a much stronger variability than the geomagnetic field perturbation ΔВ. The proposed 3D diagrams show that the dB/dt polarization plane is inclined towards the Earth's surface, which is probably due to the irregularity of the field of geomagnetic fluctuations. [ABSTRACT FROM AUTHOR]

Abstract—The analysis of paleomagnetic data from Late Neoproterozoic complexes of Siberia and Australia is carried out. We show that the existing paleomagnetic datasets are in a disagreement with the concept of the axial-dipole configuration of the Late Neoproterozoic geomagnetic field: proposed non-actualistic models of the field do not reasonably explain the distribution of the paleomagnetic poles. We carried out analysis of paleomagnetic and virtual geomagnetic poles distribution based on simple geometric calculations. The analysis suggests that the configuration of the Late Neoproterozoic geomagnetic field was determined by the coexistence of a weak, long-lived source that was stably fixed in space, with a main dipole source that experienced sporadic multidirectional jumps within a certain preferred region of the Earth. Predominantly equatorial orientation of the main dipole source is substantiated by paleoclimate proxies. We propose a descriptive non-actualistic model of the Late Neoproterozoic geomagnetic field—the Devious Equatorial Dipole hypothesis, which brings paleomagnetic and paleoclimate data into accordance. [ABSTRACT FROM AUTHOR]

Various geodynamo models proposed recently in the different ways explain the processes of geomagnetic field generation and its evolution over the course of the geological history. The testing capabilities of these models are strongly limited, inter alia, by the scarcity of the reliable magnetostratigraphic data for the Paleozoic and more ancient eras of geologic time, especially for the time periods before the establishment of the Kiama and Moyero superchrons. In this work, we present the results of the magnetostratigraphic and geochemical studies of the top part of the Upper Cambrian section in the Chopko river valley, Norilsk region, which is one of the most complete Upper Cambrian reference sections in the Siberian Platform. Our studies have shown that in the Late Cambrian there has been an interval of the reversed magnetic polarity which lasted at least 1.5 million years. Together with the previous data obtained on the Upper Cambrian of the Kulumbe river section and on the Early Ordovician of the Kotuy river (Pavlov and Gallet, 1998; Pavlov et al., 2017), our result presented in this study means that between the mid-Cambrian epoch of the extremely frequent reversals (Gallet et al., 2019) and the Ordovician Moyero superchron of the reversed polarity (Pavlov et al., 2005), there intervened at least two magnetic polarity intervals (reversed and normal) whose duration was at least one million years. This conclusion quite definitely points to a low frequency of the reversals on the eve of the Ordovician superchron and supports the concept according to which a process preparing the onset of the superchron takes place at the core/mantle boundary. The data obtained in our study support the hypothesis of the existence of three geodynamo regimes with sharp, on the order of a few million years, transitions between them (Gallet and Pavlov, 2016). At the same time, overall, the quality and amount of the currently existing magnetostratigraphic data for the pre-Mesozoic and, in particular, for the Paleozoic are still insufficient for confident testing this hypothesis. [ABSTRACT FROM AUTHOR]

Abstract—The experiments on the determination of paleointensity Banc of the Earth's magnetic field by Thellier method on basalts of the Berd (Jurassic) and Paravakar (Cretaceous) collections sampled in the northeastern Armenia in 2006 revealed an anomalous behavior of the Arai–Nagata diagrams. The anomaly manifests itself by a sharp drop in the intensity of natural remanent magnetization (NRM) under heating of samples to about 400°C, which is accompanied by a very weak acquisition of partial thermoremanent magnetizations (pTRMs) in this temperature interval. The further increase in temperature leads to the opposite phenomenon—an unexpectedly sharp rise in pTRMs intensity with almost no decrease in NRM, which creates the L-shape of the Arai–Nagata diagram. A similar phenomenon of a steep decline during thermal demagnetization was also established for remanent saturation magnetization Mrs(T). We carried out a number of magnetomineralogical experiments from which we conclude that, consistent with the hypothesis suggested by (Kosterov and Prevot, 1998), the sharp drop in Mrs(T) and NRM(T) curves is caused by the transitions of the domain state from a metastable configuration to a more stable one. These transitions are initiated by the processes of single- and heterophase oxidations of primary titanomagnetites under the laboratory heating of samples to moderate temperatures. [ABSTRACT FROM AUTHOR]

Abstract—The time scale of the geomagnetic polarity is the quintessence of our knowledge about the changes in the polarity of the Earth's magnetic field in the geological past. The pattern of the Earth's magnetic field polarity reversals is relatively well known for the Cenozoic, Mesozoic, and Late Paleozoic. However, our understanding of the behavior of geomagnetic polarity in the more ancient epochs is non-systematic and fragmentary. Obtaining the reliable high-quality information for the Lower and Middle Paleozoic should become the next important step.This paper compiles the main data yielded by recent studies on magnetic stratigraphy of the Lower Paleozoic (Cambrian and Ordovician) of the Siberian Platform and other regions conducted by our team and our colleagues. The synthesis of these data allows us to propose a working model of the Early Paleozoic magnetic polarity time scale which embodies the current knowledge about the character of changes in the geomagnetic field polarity on this interval of the geological time. The process of geomagnetic field polarity reversals in the Early Paleozoic is described by the following most important characteristics: (a) the existence of a superchron of reversed polarity during a significant part of the Early and Middle Ordovician (the third Phanerozoic superchron Moyero); (b) a high (probably peaking in the Phanerozoic) frequency of the geomagnetic reversals in the Middle Cambrian; (c) a decrease in the frequency of geomagnetic reversals in Late Cambrian and Tremadocian with the approach of the superchron; (d) the presence of anomalous period in the behavior of the geomagnetic field close to the Phanerozoic/Precambrian boundary; and (e) the absence of a double superchron in the Ordovician (Algeo, 1996). [ABSTRACT FROM AUTHOR]

Abstract—The archaeomagnetic study of ceramic material from Veksa III archaeological site (φ = 59°17′ N, λ = 40°10′ E) yield the data on the intensity of geomagnetic field in the V–III millennia B.C. in the Russian Plain. The combined results from the material of the Veksa III and Sakhtysh I sites (φ = 56°48′ N, λ = 40°33′ E) suggest that in the studied time interval, the intensity of the geomagnetic field mainly varied within 30 to 50 μT. The gradual changes in the intensity are superimposed by a variation with a characteristic time of approximately 1000 years. The results on the intensity of the geomagnetic field determined for the Russian Plain for the time interval V–III millennia B.C. add substantially to the magnetic field data during this time interval, which promotes better understanding of the variations in the ancient geomagnetic field. [ABSTRACT FROM AUTHOR]

Heteroclinic cycle is an invariant of a dynamical system comprised of steady states (or more general invariant subsets) and heteroclinic trajectories. The behavior of a dynamical system with a heteroclinic cycle is intermittent: a typical trajectory stays for a long time close to a steady state while the transitions between the states occur much faster. Intermittency is present in various physical phenomena, e.g., Earth's atmospheric circulation, climate variations considered on long time intervals, evolution of species, distribution of diseases, behavior of the Earth's magnetic field and many others. In this paper, we consider the examples of this natural system and the respective mathematical models possessing heterocliic cycles. [ABSTRACT FROM AUTHOR]

Abstract—We analyze the geomagnetic effect caused by the strong earthquakes using the data from the Geophysical Observatory "Mikhnevo" (MHV) of Institute of Geosphere Dynamics of Russian Academy of Sciences (IDG RAS) and from a number of observatories of the international INTERMAGNET network. It is shown that seismic events are accompanied by characteristic variations in the Earth's magnetic field. These induced geomagnetic variations contain a clearly pronounced short-period component with a period of ~0.5–0.8 min which is recorded during shallow earthquakes and a long-period component (~5–20 min) observed in the most cases. The maximum amplitudes of the induced geomagnetic variations are ~1.5–5 and ~2–20 nT for the short-period and long-period components, respectively. It is noted that the induced geomagnetic perturbations recorded by the observatories at significantly different distances from the source of the earthquake feature almost simultaneous and morphologically similar behavior. [ABSTRACT FROM AUTHOR]

Abstract—Paleo- and rock magnetic, sedimentological, and isotope geochemical study is carried out for the carbonate member of Late Neoproterozoic Nichatka Formation (Siberian Platform, western slope of the Aldan Shield) enclosed within glacial deposits corresponding to the hypothetical event of "Snowball Earth" global glaciation. Based on the sedimentological, rock magnetic, and geochemical indications it is established that sediments composing this member have varve-type seasonal stratification and, according to our estimates, have been accumulated for at most 13 thousand years. Obtaining the detailed paleomagnetic data for the Precambrian varves allowed us to reveal a linear trend in the distribution of the virtual geomagnetic poles and to link it with the peculiarity of secular variation of the geomagnetic field during the time span of the Nichatka Formation. The paleomagnetic record in the periglacial sediments of the Nichatka Formation testifies to their deposition close to the equator which might be considered as supporting the Snowball Earth hypothesis. However, the absence of annual temperature fluctuations within the equatorial belt makes the formation of seasonal deposits at low latitudes barely possible and completely excludes such a possibility in the conditions close to total glaciation. The contradiction between paleoclimatic and paleomagnetic data is not explained in the context of the actualistic model of the geomagnetic field. The peculiarities of the paleomagnetic record in the Nichatka Formation, similar to the record of the field during the reversal, suggest that the geomagnetic field in the Neoproterozoic could be determined by substantial contribution of the low-latitude non-axial-dipole component. This peculiarity of the Neoproterozoic geomagnetic field can explain the entire set of the worldwide paleomagnetic data implying low latitude glaciations in the Neoproterozoic. [ABSTRACT FROM AUTHOR]

The possibility of reconstructing geologic events by identifying patterns in variations of the geomagnetic field related to reversals is one of the fundamental applications of paleomagnetism. The most detailed records of reversal events, whose duration averages 1–10 thous. years, are known from studies of flood basalts of large igneous provinces. At the same time, there have been recent publications presenting facts interpreted as records of geomagnetic reversals in intrusive bodies. Specifically, such data were obtained for relatively thin dolerite sills of the Ergalakh complex in the Norilsk region of the Siberian trap province that supposedly recorded the Permian-Triassic "Ivakin-Syvermin" reversal. This interpretation is based on the hypothesis of a slowly cooling intrusion, in which its apical parts magnetized in the Ivakin epoch of reversed polarity and the central parts—after the reversal in the Syvermin epoch of normal polarity. In this paper, using results of mathematical modeling, we discuss the validity of such assumptions and the potential attractiveness of subvolcanic intrusions for studies of geomagnetic reversals. We demonstrate that the duration of their cooling, including the most probable interval of magnetization is several orders of magnitude less than the duration of reversal transitions, and that the most probable cause of the occurrence of both polarities is the self-reversal effect. [ABSTRACT FROM AUTHOR]