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Geomagnetic field reversals are relatively common events, occurring 4-5 times/Myr over the last 10 Ma. However, there are two well-documented periods, called superchrons, when no reversal occurred for >30 Myr in the Cretaceous and Permo-Carboniferous. A third superchron has been proposed in the Ordovician when the field was in a reversed polarity state. Here, we report high-resolution, Middle to Late Ordovician magnetostratigraphic data from carbonate rocks spanning 471 to 454 Ma collected in the Siljan district, central Sweden. The Siljan record correlates well with Ordovician sequences from Baltoscandia, Siberia and Poland. In Siljan, a flip from reversed to normal polarity at 466.1±0.9 Ma clearly identifies the termination of the Ordovician Reversed Superchron (ORS), thereby constraining its duration to 13.9±2.2 Myr. To evaluate the statistical significance of this interval, we compiled a geomagnetic polarity timescale spanning the last 493 Myr and analyzed chron length distributions using a robust interquartile range method. The ORS is a clear statistical outlier that exceeds a critical 6.8 Myr threshold, corroborating its classification as a bona fide superchron. Our chron length analyses support the view that superchrons represent rare, stable dynamo regimes, rather than merely the tail of a continuous reversal rate distribution.

The last 1.2 million years have witnessed fundamental changes in global climate, including substantial intensification of global glaciations and a shift from obliquity-to eccentricity-paced glacial-interglacial cycles. However, the effect of these changes on prevailing wind direction and mineral dust transport pathways remains enigmatic. Here, we utilize anisotropy of magnetic susceptibility (AMS) of Tajik loess over the last 1.2 Ma to constrain past wind regimes in the Afghan-Tajik Basin of southern Central Asia. The area is located at the intersection of the Siberian High pressure system, the Mid-Latitude Westerlies, and the Indian Summer Monsoon, and acts as one of the largest dust-emitting regions globally. AMS measures the magnetic fabric of loess, a function of dust transporting wind directions and post-depositional processes, and here we apply the technique to three different loess-palaeosol sections on the Khovaling Loess Plateau, Tajikistan. In addition to constraining post depositional reworking, we show through comparison to modern modelled and observed wind regimes that AMS does indeed reflect the directions of dust-transporting winds that, while partly affected by meso-scale and local topography, are ultimately driven by regional wind systems. Our results demonstrate that the directions of these dust-transporting winds have remained stable for the last 1.2 million years. This remarkable resilience of the dust transporting wind regime suggests a stability of the wider synoptic wind field despite major global climate transitions and regional orogenic uplift.

We report a comprehensive study of the temperature-dependent structural, magnetic, vibrational, and dielectric properties of Al-substituted M-type hexaferrites SrFe_12-xAlxO₁₉. Neutron powder diffraction and Mössbauer spectrometry show that Al³⁺ preferentially replaces Fe³⁺ at spin-up octahedral sites (2a, 12k), disrupting the exchange coupling with the spin-down 4f tetrahedral sites and leading to a progressive reduction of site-specific magnetic moments and a systematic decrease in the Curie temperature, supported by temperature-dependent susceptibility measurements. Raman spectroscopy reveals pronounced phonon anomalies near T_C, particularly in modes associated with bipyramidal Fe-O vibrations, reflecting the weakening of both 4e-12k and 4e-4f exchange pathways. However, the coercive field exhibits a dramatic increase, reaching μ₀H_C ∼1.2 T for SrFe_9.6Al_2.4O₁₉, among the largest values reported for this class. Susceptibility measurements suggest that Al substitution, while weakening the superexchange network, contributes to the stabilization of single-domain behavior.

Understanding the initiation, propagation and evolution of water injection-induced fractures is essential for geo-energyapplications. Hydromechanical stimulation experiments were conducted in a deep borehole drilled into crystalline bedrockto gain insights into these processes, involving simultaneous in-situ measurements of three-dimensional fracture displace-ments, injection flow rates, and water pressure in 2.4-m isolated borehole sections at 500-m depth. Three distinct sectionswere tested in the COSC-1 borehole (Sweden): a section of intact rock, a section with a hydraulically conductive fractureand a section with nonconductive fractures. Acoustic televiewer measurements conducted before and after the experimentsconfirmed the generation of new fractures. Accurate positioning of measurement tools was ensured through gamma log pro-filing and an innovative FFEC-based method for detecting flowing fractures. The tests revealed several transitional pressurevalues associated with mechanical events, with intact rock requiring the highest pressure to induce fracturing, followed bythe nonconductive fracture section and the initially conductive fracture section. Following fluid injection, transient pressuredecays were observed that were associated with leakage from newly generated fractures, providing insights into fracturebehaviour under stimulation. Vertical displacements were predominant across the different tests, with measured displacementstypically ranging from 10 to 100 μm. Fracture activation modes primarily involved the normal opening of subhorizontalfractures that were parallel to the metamorphic foliation, with some irreversible slip at higher pressures. However, a morecomplex scenario was observed in the test interval with previously nonconductive fractures, involving competition betweenthe opening of subhorizontal fractures and reverse shearing of a steeply dipping fracture.

This study revisits seismic reflection data from the Central Scandinavian Caledonides, initially acquired during campaigns in the late 1980s and early 1990s. Previous analyses faced challenges in merging and imaging due to varying trace spacing and data gaps, particularly in the western parts. To address these limitations, we spatially resampled the data to a consistent trace spacing, carefully merged segments, and migrated the entire merged section. This approach resulted in a revised seismic profile, with notable changes in the western section where the image reveals key differences compared to earlier interpretations. The updated profile indicates near-continuous reflections across merged segments, resolving issues of abrupt breaks present in some prior publications. Enhanced imaging in the western section unveils new structural details, including collapsed diffractions and shorter reflective segments, offset from one another. These reflecting segments in the Skard & ouml;ra antiform are interpreted as representing dolerite sills that were once continuous over a larger area but have been offset by normal faulting. This reinterpretation suggests a significantly thinner upper allochthon in the west than in previous interpretations. These results emphasize the importance of careful data integration and migration for seismic interpretation, shedding new light on the structural complexity of the western Scandinavian Caledonides. The study contributes to refining geological models and advancing understanding of the region's tectonic history.

Seismic surveys are essential for studying the Earth's subsurface. However, the interpretation of seismic surveys requires a link between field data and rock physical properties by linking laboratory-derived data from drill core samples with borehole information and seismic images. Here, we study the seismic properties of the second "Collisional Orogeny in the Scandinavian Caledonides" borehole (COSC-2), which intersects parautochthonous turbidites, highly deformed black shales (Alum Shale), autochthonous sediments, and the underlying Baltic basement. We selected six core samples of the major lithologies (graywacke, lithic arenite, Alum Shale, arkosic arenite, porphyry, and dolerite) to measure ultrasonic P- and S-wave velocities ( and ) under dry conditions at confining pressures of 10-240 MPa. For anisotropic sedimentary samples, we measured and in three mutually perpendicular sub-samples oriented relative to foliation and lineation. Combining our measurements with theoretical concepts of elasticity, we estimated key influences on seismic properties. Our results show: (a) Pressure solution seams in arenites have little effect on seismic anisotropy. (b) Strongly anisotropic graywacke and Alum Shale samples have orthorhombic or lower symmetry, challenging the common transverse isotropy assumption for clay-rich rocks. Accounting for laboratory-derived anisotropy may improve the reflectivity in seismic surveys. (c) Organic matter in Alum Shale reduces seismic velocities, enhances seismic anisotropy, and causes Alum Shale to be a prominent reflector. (d) Despite the low porosity, microcracks in the dolerite cause velocities to be significantly higher under saturated conditions than under dry conditions, which must be considered when interpreting the reflectivity of dolerites intruded into porphyries.

Interpretation of palaeomagnetic data requires the detection of magnetofossils in sedimentary rocks and an understanding of their influence on magnetic properties. Subsamples collected from IODP site M0061 lost up to 90 per cent of their initial bulk magnetic susceptibility (MS) during cold-room storage of 5 months, which was attributed to the alteration of single-domain magnetosomal greigite (Fe3S4). To test if the magnetic susceptibility loss affected the anisotropy of MS (AMS) we resampled site M0061 with a Kullenberg piston corer (3 cores), took palaeomagnetic subsamples and undertook time-dependent AMS measurements over 1 yr in a controlled cool, humidified environment and exposed to air. Most subsamples possessed an initial normal oblate AMS fabric predicted for laminated sediments (horizontal with respect to the bedding plane) but we also detected a negative trend between the degree of anisotropy (Pj) and MS. In accordance with previous observations, MS decreased over 1 yr, which we accredit to oxidation of magnetosomal greigite and conversion into a less magnetic phase (probably FeO(OH)) that does not make a detectable contribution to AMS. These results allowed us to isolate, through application of an AMS tensor subtraction routine, the fabric of the magnetosomal greigite component that had decayed. In subsamples with the largest MS loss over one year, the decayed component had a prolate, inverse AMS fabric (defined as the principal susceptibility axis perpendicular to the bedding place) but relatively low Pj. We conclude that the initial (in-situ) AMS ellipsoid consisted of a mixture of a typical normal, oblate sedimentary fabric and the prolate, inverse magnetosomal fabric. The mostly inverse nature of the separated fabric indicates that the long axis of the magnetosomal greigite (as individual single-domain magnetofossils or chains) must be oriented parallel to the bedding plane, which implies that the magnetosomal greigite was deposited from the water column and contributes to a depositional remanent magnetization (DRM). Our results indicate that greigite magnetofossils can (i) explain the inverse AMS fabrics that have been reported in similar sedimentary environments and (ii) carry DRM with a median destructive field (MDF) of approximately 20 mT, although this remanence is transient under ambient laboratory conditions and is prone to oxidation.

Magma reservoirs typically form through the incremental emplacement of smaller magma pulses over extended timescales. Pulsed reservoir growth significantly impacts a magma body's temperature evolution, chemical differentiation potential, and the probability, scale, and timing of volcanic eruptions. Moreover, the addition of thermal energy and magmatic fluids reheat and hydrothermally alter previously emplaced magma. Consequently, it may be difficult to distinguish individual magma pulses in exposed solidified intrusions (plutons), obscuring evidence of magma body construction and evolution. In this study, we employ geological mapping combined with petrofabric and Anisotropy of Magnetic Susceptibility (AMS), Anisotropy of Anhysteretic Remanent Magnetization (AARM), hysteresis, First-Order Reversal Curves (FORCs) and susceptibility versus temperature analyses to investigate pulsed magma emplacement and its consequences in terms of fabric overprinting and hydrothermal alteration within the Slaufrudalur pluton in Southeast Iceland. The field mapping documents distinct emplacement styles, including magma ascent in marginal zones, subhorizontal sheet emplacement, and bulk intrusion below the sheets. The AMS fabrics show high K-m values (similar to 1 x 10(-2) SI), but overall weak degrees of anisotropy (P-j < 2%). The weak magnetic fabrics reflect the destructive interference between the magnetite fabric and the fabric of hematite and iron hydroxides. Later, pulses of magma are less oxidized, which indicates that the alteration was caused by volatile release from magma that intruded below already emplaced magma. Our results demonstrate that rock magnetic data provide a novel approach to detecting magma pulse interactions and associated alteration in plutons, offering insights into magma body dynamics.

Magma reservoirs typically form through the incremental emplacement of smaller magma pulses over extended timescales. Pulsed reservoir growth significantly impacts a magma body's temperature evolution, chemical differentiation potential, and the probability, scale, and timing of volcanic eruptions. Moreover, the addition of thermal energy and magmatic fluids reheat and hydrothermally alter previously emplaced magma. Consequently, it may be difficult to distinguish individual magma pulses in exposed solidified intrusions (plutons), obscuring evidence of magma body construction and evolution. In this study, we employ geological mapping combined with petrofabric and Anisotropy of Magnetic Susceptibility (AMS), Anisotropy of Anhysteretic Remanent Magnetization (AARM), hysteresis, First-Order Reversal Curves (FORCs) and susceptibility versus temperature analyses to investigate pulsed magma emplacement and its consequences in terms of fabric overprinting and hydrothermal alteration within the Slaufrudalur pluton in Southeast Iceland. The field mapping documents distinct emplacement styles, including magma ascent in marginal zones, subhorizontal sheet emplacement, and bulk intrusion below the sheets. The AMS fabrics show high Km values (∼1 × 10−2 SI), but overall weak degrees of anisotropy (Pj < 2%). The weak magnetic fabrics reflect the destructive interference between the magnetite fabric and the fabric of hematite and iron hydroxides. Later, pulses of magma are less oxidized, which indicates that the alteration was caused by volatile release from magma that intruded below already emplaced magma. Our results demonstrate that rock magnetic data provide a novel approach to detecting magma pulse interactions and associated alteration in plutons, offering insights into magma body dynamics.

Environmental magnetism, including the use of magnetic susceptibility (MS), has formed the backbone of analyzing past terrestrial climate dynamics recorded in loess deposits world-wide. However, the nature of MS signal response and frequency dependence (χ_FD) varies between loess sequences, which can limit the applicability of the approach. Here, we explore how measuring MS using multiple alternating-current field frequencies can transform our understanding of the past climate record in loess. We compare loess MS data measured at 15 different frequencies from diverse environments across the Northern Hemisphere, and provide high-resolution data for a late Quaternary loess-paleosol section in Tajikistan. Additionally, we study the magnetic mineral composition in selected Tajik loess samples using rock magnetic methods and Raman spectroscopy and assess the usefulness of calculating superparamagnetic nanoparticle (SP) size distributions from multi-frequency magnetic susceptibility. Our results demonstrate that using this approach to determine χ_FD has several advantages over widely used dual-frequency approaches: (a) Inclusion of a wider grain size range of magnetism-bearing SP particles in measuring χ_FD, allowing for a more complete analysis of the environmental drivers behind the MS signal; (b) Higher sensitivity of the χ_FD palaeoclimate proxy to climatic changes; and (c) Increased statistical meaningfulness of the χ_FD proxy by allowing quantification of uncertainty. Our approach is particularly beneficial for understanding sites characterized by low-susceptibility samples and potentially diverse processes of magnetic enhancement. However, we advocate its routine use even in more typical loess sequences due to its greater sensitivity to climatic changes and better understanding of inherent proxy uncertainties.