Fifty years ago, Pullaiah et. al (1975) derived temperature-dependent relaxation curves for single-domain (SD) magnetite, which have since been widely applied to a range of paleomagnetic problems. However, ideal SD behaviour is restricted to a narrow particle-size range. Most of the stable geological remanence carried by magnetite is instead held by vortex-state particles, for which SD theory fails to provide an adequate description. This study presents new numerical results for micromagnetically determined, temperature-dependent relaxation curves for submicron oblate, prolate and equidimensional cuboctahedral magnetite particles from 45-200 nm, with varying elongations. MERRILL was used to compute local energy-minimum (LEM) states over the full temperature range from 20 to 579 °C, and the nudged elastic band (NEB) method was employed to obtain energy barriers for use in Néel–Arrhenius estimates of relaxation times. The resulting relaxation curves are analysed and compared with the classical Pullaiah curves, highlighting the implications for interpreting paleomagnetic records carried by vortex-state particles.
How to cite: Donardelli Bellon, U., Williams, W., Nagy, L., and Muxworthy, A. R.: Micromagnetic constraints on Pullaiah curves for magnetite, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-1428, https://doi.org/10.5194/egusphere-egu26-1428, 2026.
In this study, we present the first full palaeointensity protocol based on quantum diamond microscope (QDM) measurements of the vertical magnetic field component (bz ) above thin sections of an archaeological ceramic. A key advantage of the QDM approach is that it enables the identification, isolation, and tracking of individual magnetic sources within a thin section, allowing ideal palaeomagnetic recorders to be analysed while excluding poorly behaved contributors that dominate bulk measurements. We invert magnetic moments associated with both near-surface and subsurface magnetic sources from QDM maps, and follow their response to alternating-field demagnetisation and anhysteretic remanent magnetisation (ARM) acquisition. Mean directions derived from these selectively inverted sources closely match bulk measurements obtained using a cryogenic rock magnetometer. We quantify the effects of filtering sources based on inversion quality and magnetic behaviour, and demonstrate that for well-separated dipole-like particles, pseudo-Arai slopes constructed from fitted ARM acquisition and AF demagnetisation curves yield palaeointensity estimates that agree, within uncertainty, with double-heating absolute palaeointensity determinations on sister samples. When combined with micro magnetic modelling constraints on the relationship between ARM and thermoremanent magnetisation, these results demonstrate that QDM-based palaeointensity methods offer a promising route toward high-precision, carrier-selective micropalaeomagnetic analysis at the thin-section scale.
How to cite: Williams, W., Bellon, U., de Souza-Junior, G., Muxworthy, A., Uieda, L., Fu, R., and Trindade, R.: Microscale pseudo-Thellier palaeointensity using a Quantum Diamond Microscope, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-4440, https://doi.org/10.5194/egusphere-egu26-4440, 2026.
Absolute paleointensity reconstructions provide critical constraints on the dynamics and long-term evolution of the geodynamo. Yet, a high failure rate persists in paleointensity experiments due to limitations inherent to bulk measurement techniques. As a result, measurements are often compromised by mineralogical alteration, multidomain behavior, magnetic interactions, and the presence of non-ideal remanence carriers that cannot be spatially isolated or individually evaluated. We present a new approach to absolute paleointensity determination based on Quantum Diamond Microscopy (QDM), enabling direct observation of thermoremanent magnetization (TRM) acquisition and decay at the sub-millimeter scale. We apply this technique to natural basalt and archaeological ceramic samples subjected to controlled laboratory TRM inductions, providing an opportunity to investigate magnetic recording processes at the level of localized anomalies. Experimental tests of TRM acquisition demonstrate that the direction of the applied laboratory field can be recovered from the magnetic vectors obtained from several hundred individual anomalies. For bias fields exceeding 2μT, the recovered vectors closely match the bulk direction, with minimal angular misfits across the population of carriers. This result provides direct physical validation, at the grain scale, of fundamental paleomagnetic recording assumptions that are traditionally inferred from statistical behavior in bulk measurements. This directional fidelity establishes the physical basis for extending micro-scale observations to quantitative paleointensity analysis. Using QDM, we implemented a full Thellier-style zero-field/in-field (ZI) protocol, monitoring both the thermal decay of natural remanent magnetization (NRM) and the acquisition of partial TRM (pTRM) on an anomaly-by-anomaly basis. This allows the identification and isolation of ideal magnetic recorders while excluding poorly behaving carriers, and enables the construction of localized Arai diagrams with a level of selection and quality assessment unattainable in conventional bulk techniques. The ceramic sample shows highly consistent paleointensity estimates, highlighting the robustness of the method. In contrast, paleointensity estimates for the basalt sample show larger variability, reflecting the influence of non-ideal magnetic carriers and local mineralogical heterogeneity. However, when rigorous spatial quality criteria are applied, including high Arai diagram linearity and vectorial decay constraints, the resulting paleointensity estimates converge toward the laboratory field with substantially improved accuracy and reduced uncertainty compared to bulk magnetometer results. Our results demonstrate that absolute paleointensity can be reliably determined at the micro-scale through the controlled ensemble analysis of magnetic anomalies. This approach represents a significant methodological advance in paleomagnetism, opening new perspectives for high-precision paleointensity studies of magnetically heterogeneous, minute, or rare materials, including meteorites, archaeological artifacts, and single crystals.
How to cite: F. Souza-Junior, G., Uieda, L., I. F. Trindade, R., D. Bellon, U., S. de Moraes, C., and Fu, R.: Absolute Paleointensity Through Quantum Diamond Microscope Measurements, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-16059, https://doi.org/10.5194/egusphere-egu26-16059, 2026.
High-field magnetic measurements and procedures, such as hysteresis, first-order reversal curves (FORC), and alternating-field (AF) demagnetization, are foundational methods in rock and paleomagnetic studies. Interpreting these data can be challenging and often requires an understanding of the particle scale contributions to these signals. This requires a numerical approach using micromagnetic models along with the inclusion of thermal fluctuations, which result in time dependent relaxation in experimental observations. This is a challenge that requires knowledge of all stable domain states, their connectivity, and energy barriers that partition the energy landscape that results from the field strength and orientation of each particle. This typically requires considerable user input and analysis, making this an unfeasibly time-consuming endeavor.
We are developing a method that calculates exact energy surfaces for uniformly magnetized particles and approximate energy surfaces for single vortex (SV) particles, akin, to software tools such as the Singe Domain Comprehensive Calculator (SDCC; Cych et al., 2025, doi: 10.1093/gji/ggaf149). This technique is integrated into the micromagnetic software package MERRILL and readily identifies minimum energy domain states, their connectivity, and (using the nudged elastic band method), can calculate the energy barriers between states. This automated process dramatically reduces user input and analysis at the cost of additional computational time resulting in high-field energy landscapes (HELs) which can then be used to simulate a wide range of thermally activated experiments, including hysteresis loops, FORC diagrams, anhysterestic remanent magnetization (ARM) acquisition and AF demagnetization. Additional computational resources are not, however, significant, since our method runs in a matter of minutes to hours on a modern laptop computer. This new approach will take the rock and paleomagnetic community one step closer to incorporating micromagnetic tools as a part of the standard analytical repertoire used to interpret the behavior of natural samples and reconstruct the signals they carry.
How to cite: Paterson, G., Cych, B., Nagy, L., and Williams, W.: Towards Thermally Activated High-Field Micromagnetism, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-10591, https://doi.org/10.5194/egusphere-egu26-10591, 2026.
First-order reversal curves (FORC) are gaining increasing popularity as an effective tool for characterizing magnetic minerals in rocks and sediments. The associated two-dimensional representation of hysteretic magnetization processes, known as FORC diagrams, enables the identification of specific fingerprints associated with magnetic grain size and mineralogy, and, in certain cases, the separation of magnetic components with widely overlapping coercivities, thus reducing the ambiguity of other magnetic characterization techniques. Recent progress in micromagnetic calculations also enable to calculate FORC diagrams for given magnetic mineral assemblages with enough statistical relevance to enable direct comparisons with real counterparts. Yet, interpretation ambiguities cannot be totally excluded, due to the different magnetization processes underlying each point of the FORC diagram. The additional measurement of zero-field hysteresis measurements to the original measurement protocol (Zhao et al., 2017) enables the separation of reversible and irreversible magnetization processes on a non-local basis, yielding different types of diagrams for each contribution. A local solution, which works for every point along a magnetization curve, is proposed here. It consists in the repeated measurement of Rayleigh loops in the applied field of the classic FORC protocol, as if low-field susceptibility would be instantaneously measured on the top of magnetometric measurements. Adequate processing of this modified measurement protocols divides the slope of magnetization curves into four contributions originating from (1) irreversible, (2) reversible, (3) viscous, and (4) aftereffect magnetization processes. Selected examples show the additional information that can be extracted from these measurements, as well as the disambiguation of not yet explained FORC features associated with the pseudo-single-domain and multidomain signatures of magnetite particles.
How to cite: Egli, R.: FORC-Rayleigh: A new measurement protocol for investigating the origin of magnetization changes in first-order reversal curves, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-11730, https://doi.org/10.5194/egusphere-egu26-11730, 2026.
Framboidal pyrrhotite, in sharp contrast to framboidal pyrite, has been rarely reported, and its formation remains poorly understood. Here we report its clear identification in a shale‐gas well core and explore its potential as a proxy for diagenesis or low‐grade metamorphism of organic-rich sediments. A range of complementary results including petrography, geochemistry, rock magnetism and paleomagnetism, collectively support the identification of framboidal pyrrhotite, whose coexistence with other framboidal minerals indicates pseudomorphic replacement of framboidal pyrite. A strong correlation between total organic carbon and natural remanent magnetization, together with its restriction to organic-rich layers, highlights organic matter's role in its genesis. Paleomagnetic and vitrinite reflectance data further link its formation to magmatic heating (∼274°C). We therefore propose hydrothermal replacement of framboidal pyrite by framboidal pyrrhotite, involving heating and organic matter. This study highlights its diagnostic features, key conditions, and proxy potential for hydrothermal alteration and low‐grade metamorphism in organic-rich sediments.
How to cite: Zhang, Y., Wang, Y., and Muxworthy, A.: Identifying Framboidal Pyrrhotite: A Proxy for hydrothermal alteration of Organic-Rich Sediments, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-2019, https://doi.org/10.5194/egusphere-egu26-2019, 2026.
Remagnetization in sedimentary basins is commonly regarded as “noise” that overprints primary remanence. However, if its acquisition timing and underlying mechanism can be constrained, remagnetization can instead be exploited as a physical archive of burial history, tectonic deformation, clay-mineral transformation, and hydrocarbon-related fluid activities. With the growing importance of hydrocarbon resource evaluation, magnetization resetting associated with organic-matter maturation and hydrocarbon migration has gradually become a major focus of remagnetization studies. To explore the relationship between remagnetization and hydrocarbon activity, we targeted the Upper Ordovician Zhaolaoyu Formation in the Fuping area along the southern margin of the Ordos Basin and carried out an integrated investigation combining petrographic observations, rock-magnetic experiments, paleomagnetic analyses, and organic geochemical measurements.
The results showed that magnetite was the dominant magnetic carrier, and stepwise demagnetization isolated a stable characteristic remanent magnetization. The corresponding paleomagnetic pole matched the Early–Middle Triassic segment of the apparent polar wander path of the North China Block, indicating a Triassic remagnetization. Anisotropy of magnetic susceptibility results indicated a primary sedimentary compaction fabric, and together with previous high-resolution Sr-isotope studies showing no signature of tectonically derived fluids in the section, these observations effectively ruled out remagnetization driven by subsequent tectonic fluids. Optical microscopy showed heterogeneous iron-oxide infillings within microfractures, and SEM further revealed spherical magnetite developed within microfractures; fluorescence microscopy also indicated that organic matter was predominantly hosted within microfractures. Collectively, these microscopic observations suggested that the spatial distribution of authigenic magnetite may be linked to the presence of organic matter. Notably, based on the commonly used parameter (NRM–TOC), natural remanent magnetization (NRM) showed a significant positive correlation with total organic carbon (TOC), further supporting an association between remagnetization in the Zhaolaoyu Formation and hydrocarbon activity. Meanwhile, we introduced the hydrocarbon generation potential (Pg) and the ratio of effective specimen number to total specimen number (N₀/N), and established quantitative relationships between Pg and NRM, as well as between N₀/N and TOC to evaluate the relationship between magnetic records and organic matter. Both relationships showed positive correlations.
In summary, the Zhaolaoyu Formation records an Early–Middle Triassic chemical remagnetization event associated with organic-matter maturation. This interpretation is consistent with previous hydrocarbon-generation modeling results for the study area. This study provides key constraints on the hydrocarbon-generation evolution of Ordovician source rocks along the southern margin of the Ordos Basin and, for the first time in the Ordos Basin, verifies the feasibility and applicability of using remagnetization as a tool to constrain hydrocarbon activity. In addition, the two parameter sets proposed in this study (NRM–Pg and N0/N–TOC) provide new quantitative metrics that can be applied to explore similar remagnetization mechanisms in other stratigraphic intervals and sedimentary basins.
How to cite: Lan, S., Cheng, X., and Wu, H.: Hydrocarbon-linked chemical remagnetization in the Upper Ordovician Zhaolaoyu Formation, southern margin of the Ordos Basin: constraints from paleomagnetism and geochemistry, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8962, https://doi.org/10.5194/egusphere-egu26-8962, 2026.
Measurements of magnetic susceptibility on the soil surface are routinely used for, e.g., assessment of distribution of atmospherically deposited dust particles rich in iron oxides. In general, the data obtained using Bartington MS2D coil integrate signal from a depth down to about 10 cm, with non-linear response function. Therefore, it is believed that the iron oxides in this layer may be due to atmospheric deposition, weathering of lithogenic rocks, and pedogenic processes occurring directly in the soil. In order to assess the significance of these sources, as well as to observe the stratification of the soil column, shallow vertical soil cores, usually down to 30 cm, are used. However, there is no comprehensive comparison of the vertical distribution of magnetic susceptibility, projected on the surface, with the values actually measured on the soil surface. In our contribution, we use the known response function, defining the weight of magnetic susceptibility with depth, to obtain the total model susceptibility projected on the soil surface, and compare it with the real data measured in the field. Our results show that good agreement between the measured and modelled surface values is not a general rule. Thus, the use of shallow vertical distribution of susceptibility in terms of interpreting the data measured on the surface is subject to ambiguities and doubts.
How to cite: Petrovsky, E., Magiera, T., Jankowski, M., Szuszkiewicz, M., Grison, H., Sykula, M., Bucko, M., Zawadzki, J., Fabijanczyk, P., and Stejskalova, S.: Relationship between surface-soil magnetic susceptibility and its shallow vertical distribution, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-6469, https://doi.org/10.5194/egusphere-egu26-6469, 2026.
Along Sicily's southeastern coast, sandy barriers and geological features isolate coastal lagoons known locally as "pantani." This study examines the anisotropy of magnetic susceptibility (AMS) in 69 oriented samples from the Pantano Morghella wetland, north of Portopalo. Collected in 2 cm³ plastic cubes from a single trench ~700 m from the present shoreline, samples follow two parallel profiles (alternated by 1 cm) spanning 134 cm of stratigraphic sequence. This includes sediments from one of antiquity's most devastating tsunamis, which struck offshore Crete on July 21, 365 CE (Gerardi et al., 2012, https://doi.org/10.5194/nhess-12-1185-2012).
The basal tsunami deposit at the trench site consists of a ca. 5 cm thick yellowish bioclastic sandy layer, whose abrupt and probably erosive lower boundary is at about 101.5 cm stratigraphic depth. The rest of the analysed stratigraphic sequence consists of massive grey to blackish muds and grey to pale brown muds, respectively below and above the tsunami sand.
Magnetic susceptibility profiles and AMS data divide the sequence into six zones, revealing distinct depositional environments.
Zone VI (134–101.5 cm): Lowest susceptibility (~500 × 10⁻⁶ SI) and oblate fabric, with a minimum susceptibility axis (kmin) close to the vertical and the maximum (kmax) and intermediate (kint) susceptibility axes scattered in the horizontal plane. This indicates undisturbed, low-energy lagoon/wetland deposition.
Zone V (101.5–94 cm): The sandy tsunami layer, with only three samples showing scattered AMS axes, reflecting chaotic high-energy deposition.
Zone IV (94–63 cm): High susceptibility (1000–2500 × 10⁻⁶ SI), prolate fabric, clustered E-W horizontal kmax, and kint and kmin axes scattered in the N-S vertical plane. This indicates deposition under the action of high-energy currents almost perpendicular to the coast.
Zone III (63–53 cm): Similar fabric to Zone IV but lower susceptibility, decreasing upward to ~500 × 10⁻⁶ SI, suggesting waning high-energy influence.
Zone II (53–35 cm): Returns to Zone VI-like low susceptibility and oblate fabric, typical of calm lagoon conditions.
Zone I (35 cm upward): High susceptibility (>2000 × 10⁻⁶ SI in top 20 cm) and triaxial fabric, linked to human salt pan activities – that started in the XIX century - altering sedimentation.
The trends of magnetic fabric are then compared to CT-scan data (X-ray microtomography) providing statistics of size, shape, and orientation of the sand grains. Overall, AMS analyses provide a robust proxy for paleoenvironmental reconstruction in Pantano Morghella. They distinguish intervals of undisturbed, low-energy sedimentation typical of a lagoon/wetland environment from those disrupted by natural catastrophes, such as the 365 CE tsunami, and later anthropogenic activities over the past two centuries.
How to cite: Sagnotti, L., Smedile, A., De Martini, P. M., Paris, R., and Lecuyer, C.: The magnetic fabric of fine-grained sediments laid from the Cretan 365 CE tsunami on the SE coast of Sicily, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5006, https://doi.org/10.5194/egusphere-egu26-5006, 2026.
The anisotropy of magnetic susceptibility (AMS) of pyrrhotite-bearing rocks (typically represented by ultramafic rocks) is often composite, carried not only by pyrrhotite, but also by magnetite and mafic silicates. In magnetic fabric studies, it is therefore desirable to separate the AMS component due to pyrrhotite from that due to the rest of the rock. This can be made, in addition to other techniques, by the anisotropy of the out-of-phase component of the AMS (opAMS). For comparative studies, it is vital to know quantitative relationship between opAMS and ipAMS, which is the aim of this paper. This knowledge is useful in interpreting the AMS of rocks in which pyrrhotite is important but not dominant magnetism carrier.
The out-of-phase susceptibility (opMS) of the pyrrhotite-bearing rocks investigated increases significantly with the field intensity within the field range between 10 A/m and 700 A/m. The increase is faster in very low fields (<100 A/m) than in stronger fields. The principal directions of the opAMS are virtually field independent in the entire low-field range used, being also very well parallel to the ipAMS directions. The degree of opAMS is also virtually field independent, but much higher than the degree of ipAMS. The shape parameter in opAMS is also field independent and resembles that in ipAMS.
The Rayleigh Law range, in which magnetization is linearly related to the field, is relatively narrow, less than 40 A/m. Theoretical quadratic relationship was suggested by Markert and Lehman (1996, GJI) between the tensor of initial ipMS and the tensor of Rayleigh coefficient characterizing the opAMS. The tensors are related by a constant c, which in general may or may not be direction independent. The direction independence would give rise to very simple relationship between the respective anisotropy degrees. Our investigations show that the constant c is in case of pyrrhotite direction independent. The tensor of the Rayleigh coefficient can be calculated from the opAMS measurement in one field, while the same tensor determined from field variation of ipAMS requires measurement in multiple fields (in two in minimum).
How to cite: Hrouda, F., Chadima, M., and Ježek, J.: Quantitative relationship between opAMS and ipAMS in some pyrrhotite-bearing rocks, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-13503, https://doi.org/10.5194/egusphere-egu26-13503, 2026.
Variations in the paleointensity of the Earth's magnetic field are intrinsically linked to the evolution of planetary interior dynamics and surface environmental conditions. However, the reliability of absolute paleointensity experiments is often compromised by the non-ideal magnetic behavior of multi-domain grains and alteration of magnetic minerals. To mitigate these challenges, besides conventional rock magnetic methods, this study also employs Visible and Near-Infrared Reflectance (VNIR) spectroscopy as a rapid screening tool to identify thermally unstable mineral phases that can distort experimental results. Systematic rock magnetic analyses reveal that samples with more pronounced single-domain-like magnetic properties achieve significantly higher success rates in paleointensity experiments. The implementation of VNIR-based screening increased the average success rate of analyzed samples by a factor of 1.9 compared to magnetic selection alone. We recommend using VNIR screening with Mrs/Ms ≥ 0.16 as the sample selection criterion, which can increase the success rate threefold while maintaining sufficient sample availability. By integrating VNIR spectroscopy with conventional rock magnetic methodologies, this study presents a robust approach to enhance the reliability and success rates of paleointensity determinations.
How to cite: Zhang, W., Jiang, Z., Zhao, X., Zheng, Z., and Liu*, Q.: Enhancing the Success Rate of Paleointensity Measurements by Integrating Visible and Near‐Infrared Reflectance Spectroscopy and Rock Magnetism, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-4319, https://doi.org/10.5194/egusphere-egu26-4319, 2026.
Quantum Diamond Microscopy (QDM) has opened new avenues for palaeomagnetism by enabling magnetic imaging at micrometre-scale spatial resolution, bridging the gap between bulk rock measurements and grain-scale magnetic observations. Micromagnetic Tomography (MMT) experiments integrate QDM data with micro- or nano-CT–derived grain geometries to determine magnetic moments of individual grains within a sample. Adding spatial information to the inversion problem makes it possible to calculate magnetic moments of individual iron-oxide grains even in samples with high grain concentrations, complex domain states, and overlapping magnetic signals. This enables the magnetic contribution of individual particles to be quantified, compared through consecutive (de)magnetization steps, and tested for stability. MMT therefore provides direct experimental access to grain-scale magnetic moments and goes beyond what bulk or surface-integrated measurements can reveal.
The goal of MMT has always been to isolate and select contributions of only the most reliable recorders in a rock sample. Nevertheless, MMT faces a fundamental challenge in spatial scales: wide-field QDM imaging achieves spatial resolutions of ~1 µm, while the practical resolution of micro- and nano-CT similarly limits the detection of magnetic particles to sizes of ~1 µm and larger. Magnetite and titanomagnetite grains in this size range are typically characterized by multidomain behaviour and are therefore often magnetically unstable, limiting their usefulness as reliable paleomagnetic recorders. As a result, current grain-scale approaches predominantly probe particles that are least suitable for preserving stable remanent magnetisations.
Accessing the information stored in smaller, submicron, vortex-state grains that are reliable recorders of the Earth’s magnetic field requires moving beyond wide-field QDM imaging. Improvements in spatial resolution of wide-field QDMs are fundamentally restricted by the optical diffraction limit, motivating a transition to Quantum Scanning Microscopy (QSM). In QSM, a single nitrogen-vacancy centre functions as an atomic-scale magnetometer, enabling nanometre-scale spatial resolutions that are ideal for magnetic imaging of vortex-state grains.
Here we present the first results of QSM stray-field imaging applied to a volcanic rock sample, in combination with slice-and-view FIB-SEM analysis of the same sample to characterise the particles’ geometries. These measurements demonstrate the feasibility of detecting magnetic signals at length scales inaccessible to wide-field QDM and current MMT techniques, while highlighting both the opportunities and technical challenges associated with pushing paleomagnetic observations into the nanoscale. Together, these developments provide a path forward towards resolving the magnetic behaviour of the particles that are most relevant for reliable paleomagnetic recording in rock samples.
How to cite: Klein Schiphorst, S., D’Astolfo, P., Cortés-Ortuño, D., and de Groot, L.: Towards nanometre-scale imaging of paleomagnetic recorders , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-6858, https://doi.org/10.5194/egusphere-egu26-6858, 2026.
Impact-generated shock waves can modify the remanence properties of magnetic minerals in target rocks, but their effects remain poorly understood. This study examines shock-induced modifications in the magnetic properties of both unshocked lithologies and impactites at the Dhala impact structure in India. The structure formed during the Paleoproterozoic (2.5–1.7 Ga) and lies within the Bundelkhand craton of the Indian Shield, with an original diameter of ~11 km. The unshocked target lithologies are primarily granitoid, while two types of impactites, impact melt rock and monomict breccia, are prominently exposed at the surface. Primary magnetic carriers are multidomain (MD) Ti-poor magnetite in unshocked rocks; pseudo–single-domain (PSD) Ti-magnetite with minor Ti-hematite and pyrrhotite in impact melt rock; and pseudo–single-domain to single-domain (PSD–SD) Ti-magnetite with minor Ti-hematite in monomict breccia (Pandey et al., 2026). To evaluate coercivity spectra, domain state, and remanence efficiency, alternating field (AF) demagnetization, isothermal remanent magnetization (IRM), and anhysteretic remanent magnetization (ARM) experiments were conducted on unshocked granitoid rocks and on impactites.
AF demagnetization results reveal distinct magnetic decay patterns among the lithologies. Unshocked rocks exhibit a peak in magnetization intensity at 10 mT, likely due to removal of a low-coercivity antiparallel component, followed by gradual decay, with median destructive field (MDF) values of ~20–60 mT and 65–90% loss of magnetization at 100 mT. Impact melt rocks exhibit smoother decay trends, with MDFs ranging from 10 to 40 mT, corresponding to 75–98% loss of magnetization at 100 mT. In contrast, monomict breccia displays the most unstable behavior with fluctuating magnetization intensity, often retaining >50% of remanence at 100 mT. The average mass-normalized saturation IRM1000mT values vary systematically among lithologies, with the lowest (4.18×10-3 Am2 kg-1) in monomict breccia, intermediate (1.11×10-2 Am2 kg-1) in impact melt rocks, and the highest (6.7×10-1 Am2 kg-1) in unshocked rocks. Average mass-normalized ARM values follow a similar trend, with the lowest (2.18×10-6 Am2 kg-1) in monomict breccia, intermediate (3.65×10-5 Am2 kg-1) in impact melt rocks, and the highest (1.03×10-2 Am2 kg-1) in unshocked rocks.
Together, these results demonstrate a progressive reduction in remanence acquisition capacity and magnetic stability from unshocked rocks to monomict breccia. Overall, the findings highlight that impact-generated shock waves significantly modify the domain state, coercivity spectrum, and remanence efficiency of the target rocks.
Reference: Pandey, A. K., Agarwal, A., Joshi, G., Sangode, S., & Venkateshwarlu, M. (2026). Shock demagnetization in an ambient magnetic field at the Dhala impact structure, India. Communications Earth & Environment. https://doi.org/10.1038/s43247-025-03164-6
How to cite: Pandey, A. K., Agarwal, A., Sangode, S. J., and Joshi, G.: Shock Effects on Magnetic Remanence in Rocks from the Dhala Impact Structure, India, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-587, https://doi.org/10.5194/egusphere-egu26-587, 2026.
The Galápagos Archipelago has been formed as the Nazca Plate moved over a volcanic hotspot. The islands' age increases from west to east, and they exhibit pronounced climatic zonation, ranging from arid lowlands to humid highlands. In this work, topsoil and parent material samples from four islands, Isabela, Floreana, Santa Cruz, and San Cristóbal, were analyzed to investigate iron mineralogy as a function of island age and climate. Samples were collected from six sites in the humid highlands on all four islands, as well as from two sites in very dry and dry zones on Floreana and San Cristóbal, respectively.
Room-temperature Mössbauer spectroscopy and magnetic measurements, including hysteresis loops (up to 3.0 T) and temperature-dependent magnetization (50 – 1000 K), were performed to identify and characterize the iron-bearing phases. Mössbauer spectra reveal the presence of Fe²⁺ and Fe³⁺ doublets attributed to iron silicates, as well as a sextet corresponding to hematite. In all samples, the relative contribution of the Fe²⁺ doublet decreases from parent material to topsoil, accompanied by an increase in the Fe³⁺ doublet contribution. Samples from the older islands (Santa Cruz and San Cristóbal), in addition to the presence of Fe3+, showed an important sexted associated with hematite in the topsoil and parent material samples. We cannot rule out the contribution of fine particle size and superparamagnetic goethite and/or ferrihydrite associated with the Fe3+ doublet.
Climate-dependent variations are also evident. Mössbauer spectroscopy data of topsoil samples from humid environments exhibit a higher hematite contribution (59%) compared to those from dry environments (49%). For parent materials, humid conditions yield a 54% hematite contribution, whereas samples from dry conditions show a 17% contribution from maghemite. The magnetic results are complemented by hysteresis loops, which indicate the presence of a high-magnetization phase, consistent with Ti-magnetite and/or Ti-maghemite. The absence of a Verwey transition near 120 K in low-temperature magnetization curves and a drop in magnetization near 580 °C in high-temperature magnetization curves further support the presence of Ti-magnetite. AC magnetic susceptibility curves exhibit a frequency dependency, which may indicate a broad distribution of particle sizes, due to the contribution of superparamagnetic iron phases.
How to cite: Berquo, T. and Zehetner, F.: Magnetic investigation of iron oxides of the Galápagos Archipelago and the relationship with island age and climate, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-4098, https://doi.org/10.5194/egusphere-egu26-4098, 2026.
In anoxic marine sediments, in steady state conditions, organoclastic sulfate reduction and anaerobic oxidation of methane release hydrogen sulfide to pore waters. Hydrogen sulfide, in turn, reacts with either solid-phase Fe(III) (oxyhydr)oxides or dissolved Fe2+ liberated by dissimilatory Fe(III) reduction to form iron sulfides with greigite as a precursor phase and pyrite as the end member of the reaction sequence. This process is characteristic for sulfate-methane transition zones (SMTZ). However, non-steady state conditions are common in marine sediments and the sequence described above may be disrupted. These conditions may lead to the preservation of early diagenetic greigite and/or to a late formation of greigite during burial enabled by reactivated biotic or abiotic processes. Site U1417 drilled during Integrated Ocean Drilling Program (IODP) Expedition 341 in the Gulf of Alaska has no shallow SMTZ and a deep inverse SMTZ at ~650 meters below sea floor, with a thick sulfate-free and methane-free zone above the deep inverse SMTZ, which makes non-steady state diagenetic conditions at this site unique. The deep inverse SMTZ is likely caused by tectonically-induced fluid circulation related to plate bending fractures. In this study, we aim to investigate how the inverse diagenetic zonation and related tectonically-induced fluid circulation impact the magnetic mineral assemblage and the paleomagnetic record in the sediment. We will pay special attention to the authigenic phases such as greigite which is responsible for secondary magnetizations. We will also assess the role of the diagenetic processes on the original detrital magnetic minerals, and their impact on the iron, sulfur, and carbon elemental cycles.
How to cite: Kars, M. and Zindorf, M.: Magnetic properties and mineralogy in non-steady state diagenetic conditions: Study in IODP Expedition 341 Site U1417 marine sediments, Gulf of Alaska, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5399, https://doi.org/10.5194/egusphere-egu26-5399, 2026.
The Namib Desert (Namibia) hosts giant dune fields whose sand color ranges from yellow to deep red. While provenance and grain composition contribute to these variations, a major control is the occurrence of Fe-bearing coatings (“varnish”) made of iron oxides and oxyhydroxides (e.g., magnetite, hematite, goethite) that surround sand grains. In this study, we analyze a set of 10 samples collected across various environments within a ~600 km perimeter in the northern Namib Desert. The mineralogical and textural nature of these coatings was investigated using a rock-magnetic approach. We combine bulk magnetic measurements, including magnetic susceptibility, hysteresis parameters, IRM acquisition, and thermomagnetic experiments, to identify the dominant magnetic carriers and assess the relative contributions of ferrimagnetic versus antiferromagnetic phases. These data are coupled with complementary mineralogical analyses (optical and scanning microscopy, Raman spectroscopy). Preliminary observations suggest that the magnetic phases are embedded in a clay-rich matrix and may be associated with microbial aggregates, raising questions about their origin and formation pathways. Furthermore, dune, terrace, and riverbed samples display distinct magnetic signatures, indicating the role of transport and/or in situ processes. By linking magnetic signatures to colorimetric variability and microstructural observations, this study aims to evaluate sand color as a potential environmental proxy for sediment transport pathways, weathering conditions, and hydroclimatic controls on iron oxide formation in arid environments.
How to cite: Carlut, J., Barrier, L., Perrenx, L., and Bruneau, O.: Rock magnetic and microstructural investigation of Fe-bearing coatings on sand grains from the Namib Sand Sea, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-13582, https://doi.org/10.5194/egusphere-egu26-13582, 2026.
Magnetic susceptibility is a widely used non-destructive proxy for soil characterisation. In this study, shallow vertical magnetic susceptibility profiles were analysed to explore their potential for soil discrimination across multiple locations representing different environmental settings. Magnetic susceptibility was measured in situ down to a depth of 30 cm, providing high-resolution vertical profiles.
The analysis focused on vertical patterns and variability of magnetic susceptibility along the soil profile. A combination of descriptive statistics and geostatistical parameters, as well as multivariate analysis, was applied to assess similarities and differences among soil profiles from different locations. The applied methodology aimed to evaluate the reliability and applicability of magnetic susceptibility as a proxy for comparative soil analysis.
The results show that shallow vertical magnetic susceptibility profiles exhibit substantial variability among profiles and locations, allowing for the identification of characteristic vertical patterns and differences between locations. Geostatistical parameters provided additional insight into the spatial organisation of magnetic susceptibility along the vertical axis, supporting the interpretation of profile variability.
The study demonstrates that shallow vertical magnetic susceptibility profiles can support comparative analysis of soils across multiple locations, while also highlighting the limitations of using magnetic susceptibility alone for soil discrimination.
How to cite: Zawadzki, J., Fabijańczyk, P., Bućko, M., Grison, H., Jankowski, M., Magiera, T., Petrovsky, E., Podrázský, V., Sykuła, M., Szuszkiewicz, M., and Vacek, Z.: Shallow Vertical Magnetic Susceptibility Profiles for Exploring Soil Discrimination across Multiple Locations Using Statistical and Geostatistical Methods, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-4909, https://doi.org/10.5194/egusphere-egu26-4909, 2026.
This study examines the spatial variability of soil magnetic susceptibility measured on the soil surface across multiple sites in Poland and the Czech Republic. The investigated areas encompass a broad range of soil types, including Podzol, Gleysol enriched with iron ore, Rubic Arenosol, Ranker‑Cambisol, Cambisol, Luvisol, Brown acidic soil, and Podzolic brown soil. Surface magnetic susceptibility was measured with Bartington MS2D to capture both natural pedogenic patterns and potential anthropogenic magnetic enhancement. Spatial correlations were quantified using experimental variograms and their parameters to assess the scale and structure of spatial variability of soil magnetic susceptibility. Among these parameters, nugget effects varied substantially between soil types, indicating differences in micro-scale heterogeneity and surface disturbance.
The results demonstrate that surface magnetic susceptibility, combined with geostatistical analysis, is a sensitive indicator of both natural soil-forming processes and anthropogenic pollution.
How to cite: Fabijańczyk, P., Zawadzki, J., Bućko, M., Grison, H., Jankowski, M., Magiera, T., Petrovsky, E., Podrázský, V., Sykuła, M., Szuszkiewicz, M., and Vacek, Z.: Spatial Structure of Surface Soil Magnetic Susceptibility Measured with MS2D across Multiple Soil Types in Poland and the Czech Republic, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-4948, https://doi.org/10.5194/egusphere-egu26-4948, 2026.
Iron-bearing nano- and microparticles are ubiquitous in urban environments, often emitted by anthropogenic pollution sources. However, the occurrence of metallic iron (α-Fe) in non-reducing, near-surface environments is anomalous given the oxidizing nature of Earth’s atmosphere. Quantifying the magnetic changes associated with the oxidation kinetics of these particles allows for the determination of their atmospheric residence times. We conducted hysteresis measurements on synthetic iron powders of varying grain sizes (1-149 µm) at specific intervals following exposure to temperatures ranging from 200°C to 500°C. By plotting saturation magnetization (Ms), saturation remanent magnetization (Mrs), and coercive force (Hc) against oxidation time, we observed that oxidation is most likely diffusion-limited: it proceeds rapidly at the grain surface and decelerates as oxygen penetration becomes restricted by the oxide shell. Using MS decay as a proxy for oxidation progress, we constructed an Arrhenius plot to determine activation energies. This allows for the extrapolation of reaction rates to room temperature. Consequently, we present a method to estimate the time elapsed since particle emission. When combined with meteorological data, we can backtrack trajectories to pinpoint specific anthropogenic sources of α-Fe emission.
How to cite: Ostermeier, F., Gilder, S., Petersen, N., and Hess, K.-U.: Magnetic Characterization of α-Fe Oxidation Kinetics: Implications for Source Attribution in Urban Pollution., EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5424, https://doi.org/10.5194/egusphere-egu26-5424, 2026.
As of 2024, 100% of Parisian residents remain exposed to concentrations of fine particulate matter (PM₂.₅) that exceed the World Health Organization’s (WHO) guideline limit of 5 µg/m³. Despite gradual improvements in air quality, atmospheric pollution—particularly from fine particles and nitrogen dioxide (NO₂)—continues to pose a major public health challenge. Recent findings by the French association Respire revealed that 682 daycare centers and schools in Île-de-France (Administrative region of Paris) exceed WHO NO₂ thresholds, underscoring the urgent need for intervention and the increasing mobilization of local stakeholders.
In the Paris region, wood heating and road traffic are the primary sources of fine particulate matter. Ultrafine particles (<1 µm), often enriched in heavy metals and exhibiting magnetic properties due to their iron content, present significant health risks. Their high reactivity and association with toxic metals suggest a potential link to neurodegenerative diseases.
This study presents the first results from the interdisciplinary Nanomap project (based on the Ecorc’Air scientific protocol), launched in 2024 in Île-de-France. The project integrates researchers from social sciences, geosciences, and participatory science, collaborating with nine citizen associations. Its objective is to map fine and ultrafine metallic particles pollution near schools and daycare centers, with the aim of tracing and determining the variability of pollution sources in urban areas. Additionally, the project examines scientific practices and interactions between researchers and citizen groups.
The study employs plane tree bark as a passive pollution sensor, leveraging its annual renewal and widespread presence in cities (more than 42,000 plane trees in Paris) to enhance spatial and temporal resolution. In 2025, nearly 700 samples were collected by citizens, with half of which were situated near educational facilities. Magnetic susceptibility measurements revealed varying concentrations of metallic particles.
Samples collected near potential pollution sources (e.g., ring roads, high-traffic areas) are currently undergoing advanced chemical analysis (ICP-MS and spICP-MS) and detailed magnetic characterization. This integrated approach is essential for validating suspected sources before any public disclosure to the citizen groups involved in the Nanomap project.
How to cite: Isambert, A., Carvallo, C., Turcati, L., Sivry, Y., Junghans, G., Bontemps, E., Fluteau, F., Herran, N., Moizard, J., and Franke, C.: Mapping Sources of Fine Metallic Particles Near Schools in Greater Paris Using Passive Biocaptors: transforming environmental monitoring practices, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8031, https://doi.org/10.5194/egusphere-egu26-8031, 2026.
Airborne particulate matter (PM) is known to have serious effects on human health. Unfortunately, assessing spatial variability of PM at high resolution remains challenging due to limitations in the number of existing regulatory air quality stations in cities. As an alternative approach, biomonitoring using vegetation within cities has been proposed in recent years.
In the framework of the Ecorc’Air citizen science project, a robust protocol has been developed based on the annual collection of plane tree bark, which serves as a passive airborne PM collector using magnetic susceptibility as a proxy parameter to estimate PM abundance in cities (Carvallo et al. 2024). This has been used to create annual maps showing the variations in magnetic particle concentrations. Since the project started in Paris (France) in 2016, there has been a growing participation of inhabitants, associations, and municipalities and it has recently grown beyond national borders.
In Germany, sampling took place downtown Cologne in spring 2025 as part of the DFG-funded project “Mapping the concentration of particles in the air in the city of Cologne using environmental magnetic techniques – a first step towards participation in the European science network Euro'Air”. In this presentation, we focus on the results obtained from analyzing the collected plane bark samples. We show the spatial distribution of magnetic susceptibility and frequence dependent magnetic susceptibility. Additionally, our preliminary results from attempts to characterize the particles by magnetic hysteresis parameters and first order reversal curves (FORC) as well as scanning electron microscopy (SEM/EDX) analyses. The outcome will be discussed with respect to the spatial distribution of the PM concentrations in Cologne.
How to cite: Franke, C., Scheidt, S., Carvallo, C., Isambert, A., Jung, K., Sivry, Y., and Turcati, L.: New results of the Ecorc’Air citizen science project: Biomonitoring of Vehicular Air Pollution in Cologne, Germany, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-12388, https://doi.org/10.5194/egusphere-egu26-12388, 2026.
The Mid-Norwegian margin hosts a thick volcanic succession of break-up–related basalts forming the seaward-dipping reflectors (SDRs). We investigated the magnetic fabric of basalts sampled from the feather edge of inner SDR packages. Azimuthally unoriented samples were collected during International Ocean Drilling Program (IODP) Expedition 396, from three sites along the margin from Kolga High in the south to the Skoll High in the north. Rock magnetic characterization suggests the presence of pseudo-singe domain Ti-magnetite as the main remanence carrier in the basalt. Our results show that the AMS in SDR basalt primarily reflects distribution anisotropy arising from subhedral/euhedral Ti-magnetite grains enclosed within an early-formed silicate framework.
The direction of natural remanent magnetization (NRM) preserved in the basalts is used to reorient the specimens into their in-situ orientation, allowing interpretation of the AMS fabric in a geographic coordinate system. Reoriented magnetic fabrics show systematic alignment with independent flow indicators.
Individual lava flows exhibit a strong zonation of magnetic fabric, characterized by oppositely dipping foliations in the top and basal parts. The opposing pair of foliations is attributed to flow-induced shear strain that is effective in the distal parts, away from the eruption centre, once a semi-solid / solid upper crust is developed. Imbricated magnetic foliations developed at the base of individual flows are used to decipher the lava flow direction, which indicates a consistently landward-directed lava transport towards the south. AMS-derived flow directions are also supported by seismic images, which show subvertical dyke swarms at the seaward edge of the inner SDR in the north, that likely served as feeders to the thick basaltic succession.
How to cite: Phukon, P., Agarwal, A., Varela, N., Venkateshwarlu, M., and Ferré, E. C.: Flow direction and internal structure of Seaward Dipping Reflectors along the Mid-Norwegian Volcanic Margin, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-449, https://doi.org/10.5194/egusphere-egu26-449, 2026.
Unlike anisotropy of magnetic susceptibility (AMS), which can be determined in a more or less simple way, the determination of anisotropy of magnetic remanence (AMR) is a relatively complex and laborious procedure involving a series of demagnetizations, directional magnetizations and measurements of the imparted directional remanence.
This complexity may logically imply larger errors in subsequent fitting of the AMR tensors compared to the AMS. The accuracy of the AMR determination primarily depends on the precision of imparting the directional remanence, the number of measuring directions, and the symmetry of the measuring design. The importance of the above control factors was investigated by means of mathematical modelling.
As shown in the previous model studies, the precision of the determination of the anisotropy of magnetic remanence (AMR) is directly proportional to the precision of the determination of the directional remanent magnetizations with respect to the degree of anisotropy. While the AMR imparted in weak to moderate fields is relatively commonly used in rock fabric studies (e.g., anisotropy of anhysteretic remanent magnetization), only a few attempts to determine the AMR in high fields (hfAMR) were reported most likely due to instrumental (insufficient precision in setting up the intensity of magnetizing field and its insufficiently homogeneity) or other methodological reasons.
Recently, a high-field impulse magnetizer has been developed (commercial name PUMA) that allows the standard palaeomagnetic specimen to be magnetized in a set of 18 predefined directions in the wide range of magnetic fields ranging from 1 mT to 5 T.
The elaborate design of this magnetizer allows precise setting of the pulse intensity and high homogeneity of the field over the entire specimen volume. To experimentally assess the precision of the hfAMR determination, the reproducibility in imparting the magnetic remanence in the same direction by the same magnetizing field was examined. We also investigated whether it was necessary to demagnetize the specimen between individual magnetizations to improve the remanence reproducibility despite the fact that each high field magnetization (“saturation”) should theoretically obliterate the previous remanence. The investigations were made on specimens having single mineral ferromagnetic fraction (magnetite, hematite, and pyrrhotite). The results helped us to decide whether the hfAMR is convenient to most rocks or only to strongly magnetic and strongly anisotropic ones.
In order to fit the AMR tensors, we present a simple, user-friendly toolbox which facilitates tensor fitting from an array of magnetic remanence vectors according the chosen magnetizing design (6, 9, 12, 15, 18 directions). This toolbox provides a graphical visualization of the intensity of measured remanence vectors and their directional comparison with the respective magnetizing directions.
How to cite: Chadima, M., Hrouda, F., and Ježek, J.: On the precision of anisotropy of magnetic remanence: Measuring designs, high-field experiments and tensor fitting toolbox, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-13427, https://doi.org/10.5194/egusphere-egu26-13427, 2026.
