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Lacustrine and marine sediments are one of the main sources of information in constructing Holocene global geomagnetic field models. The use of sediment records, however, leads to the question whether the compaction of sediments leads to a systematic biasing of inclination. We evaluate 78 sedimentary records worldwide for inclination flattening using the Elongation–Inclination (E/I) method; 20 records indicate flattening. The uncorrected and corrected values for inclination are compared to global geomagnetic field models. The results suggest that the uncorrected values agree better with the predictions from global geomagnetic field models based on sediment and archaeomagnetic data, but also with a model independent of sediment data. The 20 sites are located in mid-latitudes where inclination anomalies are predicted both in the Holocene and throughout the Brunhes epoch. Our results demonstrate that shallow inclination may not only result from compaction but may reflect the structure of the geomagnetic field on short timescales. This suggests that secular variation is not averaged out over a time period that covers the Holocene. [ABSTRACT FROM AUTHOR]

We report on a palaeomagnetic study from Mesozoic sedimentary and volcanic rocks from the conjugate areas of the Western Black Sea Basin; that is, the Crimean Peninsula in the north and the Western and Central Pontides in the south, to better constrain their palaeogeographic relationships within the southern margin of Eurasia.From the study of 87 sites in Crimea, we found that Triassic to Lower Jurassic sandstones and siltstones from the Tavric series, and Middle–Upper Jurassic sandstones, siltstones and limestones exhibit remagnetization. Both fold and conglomerate tests confirm a widespread remagnetization in Crimea. Comparison of palaeopoles with the expected reference apparent polar wander path (APWP) of Eurasia and results from conglomerate tests suggest that the remagnetization occurred in the Early Cretaceous. In the Central Pontides, no reliable palaeomagnetic results can be obtained from Triassic–Upper Jurassic rocks, however, a negative fold test in Upper Jurassic–Lower Cretaceous rocks from the Western Pontides shows that the palaeolatitude agrees with Lower Cretaceous data from Crimea. Our new palaeomagnetic results indicate a pervasive remagnetization in Crimea and the Western Pontides that could be attributed to the rifting phase of the Black Sea Basin during Lower Cretaceous. [ABSTRACT FROM AUTHOR]

Inclination shallowing of detrital remanent magnetization in sedimentary strata has solely been constrained for the mechanical processes associated with mud deposition and shallow compaction of clay-rich sediment, even though a significant part of mud diagenesis involves chemical compaction. Here we report, for the first time, on the laboratory simulation of magnetic assemblage development in a chemically compacting illite shale powder of natural origin. The experimental procedure comprised three compaction stages that, when combined, simulate the diagenesis and low-grade metamorphism of illite mud. First, the full extent of load-sensitive mechanical compaction is simulated by room temperature dry axial compression. Subsequently, temperature controlled chemical compaction is initiated by exposing the sample in two stages to amphibolite or granulite facies conditions (temperature is 490 to 750°C and confining pressure is 170 or 300 MPa) both in the absence (confining pressure only) and presence of a deformation stress field (axial compression or confined torsion). Thermodynamic equilibrium in the last two compaction stages was not reached, but illite and mica dehydroxylation initiated, thus providing a wet environment. Magnetic properties were characterized by magnetic susceptibility and its anisotropy (AMS) in both high- and low-applied field. Acquisition of isothermal remanent magnetization (IRM), stepwise three-component thermal de-magnetization of IRM and first-order reversal curves were used to characterize the remanence-bearing minerals. During the chemical compaction experiments ferrimagnetic iron-sulphides formed after reduction of magnetite and detrital pyrite in a low sulphur fugacity environment. The degree of low-field AMS is unaffected by porosity reduction from 15 to ∼1 per cent, regardless of operating conditions and compaction history. High-field paramagnetic AMS increases with compaction for all employed stress regimes and conditions, and is attributed to illite transformation to iron-bearing mica. AMS of authigenic iron-sulphide minerals remained constant during compaction indicating an independence of ferrimagnetic fabric development to chemical compaction in illite shale powder. The decoupling of paramagnetic and ferrimagnetic AMS development during chemical compaction of pelite contrasts with findings from mechanical compaction studies. [ABSTRACT FROM AUTHOR]

Elevated levels of airborne particulate matter (PM) are a current problem for air quality in many major metropolitan areas. Many European cities have tightened the PM limits in the air, due to advances in monitoring PM levels. In order to establish guidelines for monitoring and curbing anthropogenic PM output, a better understanding of its origin, composition and diffusion is required. Biomonitoring of magnetic properties of tree leaves has been suggested previously to be a good approach to measure pollution levels in cities both in space and time. We report on a magnetic biomonitoring study of PM in the city of Rome, conducted from 2005 October to December. We collected approximately 180 different sample sets of tree leaves of Quercus ilex, an evergreen oak widely distributed in Rome, at 112 different locations. Specific magnetic susceptibility χ of the leaf is used as a fast, easy and cost-effective proxy to assess levels of primary anthropogenic airborne PM pollution. Highly polluted areas correlate with high traffic areas, with an average susceptibility value of χ= 3.2 × 10−7 m3 kg−1. Low traffic zones are characterized by values more than an order of magnitude lower at χ= 1.4 × 10−8 m3 kg−1, and the background magnetic susceptibility is around χ= 2.6 × 10−9 m3 kg−1. The data show that distance dependence from the source is the most significant factor for the concentration of magnetic PM, and that pollution levels and sources can be reliably delineated by measuring magnetic susceptibility values on tree leaf samples of Q. ilex. A new protocol for magnetic susceptibility measurements is proposed, in order to account for changes due to water evaporation in the leaves as a function of time after collection of the samples. Additional magnetic analyses, such as acquisition of artificial remanences and hysteresis properties, were used to characterize the mineralogy and grain size of the magnetic PM. The results indicate that the population of ferrimagnetic phases have a homogenous composition and grain size throughout the investigated area. [ABSTRACT FROM AUTHOR]

In this study, the contribution of the paramagnetic, ferrimagnetic and haematite components to the magnetic anisotropy is separated by means of high-field torque magnetometry. Torque measurements at different fields, which are high enough to saturate the ferrimagnetic minerals, however, still low enough that the torque resulting from the haematite is linear with field, allow for the separation of the three magnetic anisotropy components. The method has been applied to haematite single crystals in which no paramagnetic or ferrimagnetic components have been found contribute to the torque signal. The mean direction of the poles to the crystallographic basal plane in the haematite single crystals is subparallel to the minimum-susceptibility direction measured in low-field. The separation analysis has also been applied to highly deformed red beds from the Lower Glarus nappe complex (Switzerland). No ferrimagnetic phases are present in the rocks and, therefore, they cannot contribute to the anisotropy of magnetic susceptibility. The magnetic fabric arises from a paramagnetic subfabric carried by the phyllosilicate minerals and haematite, in which the basal planes of both phases are in the cleavage plane. The measured magnetic lineation seen in low-field anisotropy of magnetic susceptibility appears to be an apparent lineation that arises from a weak girdling of haematite and the paramagnetic minerals conforming the rock. [ABSTRACT FROM AUTHOR]