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Abstract  Polarity zones of sedimentary sections reflect a pattern of alternating polarity of the geomagnetic field recorded by the remanent magnetization of rocks. Unfortunately, this pattern can have been modified by the variable sedimentation rate, which complicates the identification of polarity zones against the reference geomagnetic polarity time scale. To avoid this obstacle, the present paper suggests a transform applied to both the sequence of levels of polarity reversal horizons and the sequence of ages of polarity reversals before computing their cross-correlation. This transform usually reduces the impact of the variable sedimentation rate so that a sequence of more than eight polarity reversal horizons may be identified without biostratigraphic constraints. Numerical experiments involving random processes to simulate both the duration of polarity reversals and the sedimentation rate proved, however, that not all the parts of a hypothetical stratigraphic section spanning the past 165 Ma would be equally suitable for dating by magnetic polarity stratigraphy. A program performing both the compilation of polarity zones from the directions of the primary magnetization sampled along a section and subsequent identification of these polarity zones is made available online. [ABSTRACT FROM AUTHOR]

Abstract: Neotectonic crustal deformation in central Japan is described quantitatively on the basis of paleomagnetic measurements and numerical modeling. The welded part of the earliest Quaternary Nyukawa Pyroclastic Flow Deposit (NPFD) preserves stable remanent magnetization. Detailed paleo-/rock magnetic experiments reveal that remanence of the NPFD near the Takayama Basin resides in unimodal titanomagnetite and comprises a component of thermoremanent magnetization (TRM) and three components of thermoviscous remanent magnetization (TVRM). Scatter in the untilted declinations of the syn-depositional TRM component represents differential rotation about vertical axes related to Quaternary activity of three faults (Enako, Makigahora and Harayama) associated with the Takayama Basin. The normal and reversed TVRM components, probably acquired by warm water circulation near the active faults during the Jaramillo Subchron, record a complicated rotational sequence since ca. 1 Ma. Dislocation modeling successfully simulates the spatial distribution of rotation and the uplift/subsidence pattern around the Takayama Basin assuming strike–slip motion on the Enako and Makigahora Faults along the basin margin and vertical displacements on the Harayama Fault within the basin. Temporal changes in rotational motions recorded in the TVRMs of near-fault sites can be modeled by considering transition of active segments of the three faults, which is geologically constrained. [Copyright &y& Elsevier]

Magnetic measurements were performed on apparently deformed igneous rocks of 23 sites from the southeastern part of the Taimyr Peninsula. Rock magnetism and reflected light microscopy analyses reveal that fine-grained titanomagnetites up to pure magnetites mainly carry the majority of magnetic fabrics in the sills, and that the slightly coarser Ti-poor or -medium titanomagnetites carry most magnetic fabrics in the basaltic flows. Magnetic anisotropies were determined by applying anisotropy of low-field magnetic susceptibility (AMS) on 180 unheated samples and 128 samples that had been previously heated to 600°C during a paleomagnetic study to detect heating effects on the anisotropy of magnetic susceptibility (AMS) properties of volcanic rocks. Laboratory heating significantly affects anisotropy variations of these igneous rocks corresponding to the mineralogical changes during the heat treatment. [ABSTRACT FROM AUTHOR]

Abstract  In the Carolina de Michilla district, northern Chile, stratabound copper mineralization is hosted by Jurassic volcanic rocks along the trace of the Atacama fault system. In this study, we present the overall effects of hydrothermal alteration on the magnetic properties of rocks in this district. Two types of metasomatic alteration associations occur, one of regional extent and the other of local hydrothermal alteration associated with copper mineralization (e.g., Lince–Estefan�a–Susana). Regional alteration is interpreted as a low-grade “propylitic association” characterized by an epidote–chlorite–smectite–titanite–albite–quartz–calcite association. The local hydrothermal alteration is characterized broadly by a quartz–albite–epidote–chlorite–calcite mineral assemblage. The most pervasive alteration mineral is albite, followed by epidote and, locally, actinolite. These minerals contrast sharply against host rock minerals such as chlorite, calcite, zeolite, prehnite, and pumpellyite, but alteration is constrained to mineralized bodies as narrow and low contrast alteration halos that go outwards from actinolite–albite to epidote–albite, to epidote–chlorite, and finally to chlorite. Hydrothermal alteration minerals, compared to regional alteration minerals, show iron-rich epidotes, a lower chlorite content of the chlorite–smectite series, and a nearly total albite replacement of plagioclase in the mineralized zones. Opaque minerals associated with regional alteration are magnetite and maghemite, and those associated to hydrothermal alteration are magnetite, hematite, and copper sulphides. We present paleomagnetic results from nine sites in the Michilla district and from drill cores from two mines. Local effects of hydrothermal alteration on the original magnetic mineralogy indicate similar characteristics and mineralogy, except for an increase of hematite that is spatially associated with the Cu–sulphide breccias with low magnetic susceptibilities. Results indicate that it is impossible to magnetically differentiate mineralized bodies from unmineralized lavas, except for pyrite-rich hydrothermal breccias. In conclusion, for stratabound copper deposits of the Michilla type, the overall effect of hydrothermal alteration on the paleomagnetic properties of rocks is of low contrast, not clearly discernable even at a small scale. From an exploration point of view, magnetic exploration surveys should not discern mineralized bodies of Cu–sulphide breccias except in detailed ground surveys due to the small size of contrasting bodies. Unoriented drill cores with primary ore mineralization record a characteristic remanent magnetization of reverse polarity. Taking into account the azimuth and dip of the drill cores, we were able to compare the magnetization of the mineralized bodies with the characteristic directions from sites drilled in situ from Late Jurassic–Early Cretaceous intrusives mostly. The characteristic direction recorded by the Pluton Viera is similar to the magnetization of the ore bodies of the Estefania mine. If copper mineralization mostly postdates the tilt of the volcanic flows, the low paleomagnetic inclinations suggest an age for the mineralization near 145 Ma, the time of the lowest paleolatitude for the South American plate during the Mesozoic. [ABSTRACT FROM AUTHOR]

Abstract: We present a detailed study of natural remanence and rock magnetic properties of eight sediment cores from a South–North profile across the subtropical front (STF) in the South Atlantic, which previously have been combined into a stratigraphic network. Based on these measurements, we construct a first relative paleointensity (RPI) stack for the central South-Atlantic (SAS-300) covering the last 300 ka. The degree of down-core homogeneity of magnetic mineral concentration as well as magnetic mineral content and grain sizes vary between all cores and are quantified by high-resolution rock magnetic measurements. In the cores north of and close to the STF, the magnetic remanence is mainly carried by magnetite. The cores in the south also contain a high coercive mineral fraction. Based on a linear model of the sediment matrix, we propose to apply principal component analysis (PCA) of natural remanent magnetization (NRM), anhysteretic, and isothermal remanent magnetization (ARM and IRM) to determine a homogeneity interval, where remanences are only affected by a single environmental signal. This reduces lithologic and climatic influence upon the relative paleointensity record. For our data set PCA indicates that all remanences in the 30 mT to 80 mT demagnetization interval are dominated by a single environmental influence. Single core RPI estimates are then obtained by normalizing the NRM fraction in this homogeneity interval with respect to either IRM, ARM in the same interval, or by κ. By direct averaging, we obtain the stack SAS-300, which is compared to other paleointensity series such as Sint-800, or the RPI records from ODP Sites 1089 (Subantarctic South Atlantic) and 983 (Gardar Drift). The detailed documentation of environmental influences combined with the presentation of seven different recordings of the same geomagnetic signal allows to connect southern and northern hemisphere RPI data, also with respect to possible common environmental distortions. [Copyright &y& Elsevier]

Abstract: The effects of shock waves on the natural remanent magnetization and the intrinsic magnetic properties of geological materials remain poorly known. Still, hypervelocity impact phenomena are of primary importance in the evolution of many extraterrestrial bodies and of Earth. We present new experiments in which four rocks with different lithology and magnetic mineralogy (titanomagnetite, magnetite, monoclinic pyrrhotite, titanohematite) were shocked using a high-order explosive (penthrite) that provided maximum pressure of about 30GPa. The shock wave was modelled numerically and we studied the effects on the natural remanent magnetization as well as on the intrinsic magnetic properties of the shocked rocks as a function of the distance to the explosion. The intrinsic magnetic properties of the rock are permanently modified by the shock wave. The shock wave was able to superimpose a new fabric (with a minimum susceptibility axis parallel to the direction of shock) to the original magnetic fabric of the rock. Magnetite-, titanomagnetite- and pyrrhotite-bearing rocks show a noticeable increase of coercivity for pressure above 10GPa. These changes are attributed to fracturing and/or dislocations of the ferromagnetic grains. These results show that the magnetic properties of meteorites, which are commonly shocked to pressures well above 10GPa (e.g. Martian meteorites), may not be representative of the magnetic properties of their parent body. Natural remanent magnetization appears to be much more resistant to shock than isothermal remanent magnetization, probably because it is carried by grains with higher coercivity. For titanomagnetite-bearing rocks, we observe both a partial shock demagnetization of the original thermoremanent magnetization and the appearance of a shock magnetization. The demagnetizing effect of the shock wave depends closely on the coercivity spectrum of the grains carrying the original remanence, and the shock-remagnetizing effect depends on the presence of low-coercivity magnetic grains. With an impact occurring in an ambient magnetic field of similar intensity to the original magnetizing field, the post-shock magnetization may be higher or lower than the pre-shock magnetization depending on these two factors. The magnetic anomalies observed above impact basins are often used as a proxy to the presence or absence of an active dynamo at the time of impact. Our results show that the magnetic anomalies associated to shocked rocks can be misleading, so that the only decisive clue to the presence or absence of a dynamo at the time of impact is the possible thermoremanence carried by the volume of rock heated above blocking temperatures during the impact. [Copyright &y& Elsevier]

The Strzegom-Sobótka Variscan Massif (Fore-Sudetic Block, NE Bohemian Massif) consists of various post-kinematic Variscan granitoids emplaced into Palaeozoic low grade metamorphic rocks. Biotite from five samples representing the homblende-biotite monzogranite, biotite monzogranite and biotite granodiorite has been dated using the K-Ar method for two size-fractions (0.25–0.35 and 0.35–0.5 mm). Finer fractions show more intense chloritization and therefore the results for them were rejected in further discussion. Coarser fractions with higher potassium content were accepted as yielding a maximum estimate approaching the true K-Ar biotite cooling ages. The results are clustered in two groups. The older age group (308.8±4.6 Ma and 305.5±4.3 Ma) comprises results obtained from the biotite granodiorites. They are generally consistent with the zircon crystallization age of 308.4±1.7 Ma reported by Tumiak el al. (2005) and imply rapid cooling of the biotite granodiorite from magmatic temperatures down to the closure temperature of K-Ar isotopic system in biotite. The younger group is defined by 29 1.0±4.4 Ma and 298.7±5.2 Ma ages for the hornblende-biotite monzogranite and 294.2±4.3 Ma age for the biotite monzogranite. In the absence of precise U-Pb or Pb-Pb zircon data further geochronological studies are needed to decipher precisely the cooling history of the monzogranites. [ABSTRACT FROM AUTHOR]

Abstract: Reliable measurements of the intensity of the palaeomagnetic field are notoriously difficult to obtain. The approach generally taken is to produce multiple estimates per rock unit and assume that those which meet certain minimum standards of technical quality will combine to produce an accurate mean. However, here, using results produced from a package of 20th century basaltic lava flows from Mount Etna in Sicily, we demonstrate that this approach can fail. In this case, the application of typical sets of selection criteria actually introduces bias into the mean determination that we measure. We demonstrate that this is caused by two types of non-ideal behaviour acting in combination. The first is a result of the multidomain grains that the samples contain and the second is caused by differences in the natural and laboratory cooling rates. We discuss means of avoiding these sources of error in future palaeointensity studies performed on ancient rocks. We also develop a new, more general reliability criterion which is effective here and which we argue should be applied wherever possible in future palaeointensity studies in conjunction with standard criteria. It requires two distinct types of materials which both produce some good-quality palaeointensity measurements and uses their range of overlap to constrain the true palaeointensity. Both the application of this criterion and general reliability considerations require that future palaeointensity studies should measure many samples per cooling unit and that these should be as diverse in terms of their rock magnetic properties and cooling histories as possible. [Copyright &y& Elsevier]

Detailed magnetostratigraphic investigations were carried out on five sediment cores obtained from three sites on the northwestern shore of the Dead Sea, Israel. The sediments are heterogeneous, composed of fine clastic layers alternating with authigenic aragonite. The magnetic remanence is carried by Ti-magnetite and greigite, reflecting a detrital as well as an authigenic phase. Directions of the characteristic remanent magnetization were obtained from stepwise AF-demagnetization of the natural remanent magnetization and subsequent principle component analysis. The acquisition of a gyroremanent magnetization in a noticeable amount of the samples could be linked to core disturbances. The depth–age models, based on AMS 14C datings on plant remains, yielded an age of 10.04 ka cal. BP for the base of the longest profile from site Ein Gedi, a continuous lacustrine sediment sequence. The profiles from the two other sites representing near shore sedimentation are interrupted by a hiatus in sedimentation. Comparison of the inclination and declination records from all Dead Sea cores and nearby sited lakes suggest that low frequency variations documented in the Dead Sea sediments are likely of geomagnetic origin. [ABSTRACT FROM AUTHOR]

Laminated evaporitic sediments from the Dead Sea, Israel, were subjected to detailed rock magnetic investigations including the analysis of laboratory induced magnetizations and high temperature runs of the saturation magnetization. Ti-magnetite and greigite were identified as the main magnetic carrier minerals. The variations in concentration, grain size and coercitivity depended parameters reflect the varying amount of greigite with respect to Ti-magnetite. Samples with a high greigite concentration are characterized by S-ratios close to 1 in combination with low JARM/ JSIRM ratios. The results of a hierarchical agglomerative cluster analysis of the rock magnetic data presented in form of scatter plots allow for a qualitative identification of greigite-indicative parameters/parameter ratios and thus semi-quantitative estimation of the greigite content. The samples from the Dead Sea are distributed along a mixing line between the end members pure greigite and low Ti-magnetite. Determination of hysteresis parameters revealed that the greigite dominated samples show SD-behaviour whereas the Ti-magnetites plot in the PSD-range. [ABSTRACT FROM AUTHOR]

Abstract: Rock magnetic properties have been measured in a loess–paleosol sequence in the Gorina Quarry, which previously have been suggested to contain records of the Brunhes and part of the Matuyama polarity chrons. Lowest susceptibility values (below 50×10−8 m3/kg) are generally related to intensive weathered horizons, whereas highest values are obtained in loess layers (250×10−8 m3/kg) as a result of the greater ferromagnetic content in the parent material. The frequency-dependent part of susceptibility ranges between 0.5% and 6.8%; the higher value was obtained in B horizons of paleosols, which can be attributed to superparamagnetic contributions. Hysteresis loops indicate that the differences in ferrimagnetic and paramagnetic content in the sequence reflect the degree of pedogenesis. The same conclusion can be drawn with isothermal remanent magnetization. This point is relevant for determining past climatic changes because the wind-blown titanomagnetites from Cordillera de Los Andes during glacial periods were altered during interglacial periods. The mode of pedogenesis appears not only to control such alterations but also to produce other magnetic minerals. [Copyright &y& Elsevier]

Detailed rock magnetic investigations were carried out on two 23-m-long sediment cores from Erlongwan maar lake, NE China. The completely laminated sediment sequence of the lake is interrupted by 410 graded layers with thicknesses between 0.1 and 150 cm. Magnetite of PSD-size was identified as the main magnetic carrier mineral by temperature-dependent measurements of the saturation magnetization and determination of hysteresis parameters. The minerogenic components in the laminated sediments and the graded layers are nearly identical, and their rock magnetic characteristics reflect the prevailing conditions, anoxic or oxic, during deposition. The most reliable criteria for estimating the availability of oxygen is whether an increase in minerogenic influx is linked to a shift in the magnetic grain size spectrum to coarser (oxic) or finer (anoxic) grains. Comparison of different rock magnetic parameters indicative for magnetic grain size and coercitivity revealed, that the S-ratio which is known to reflect the presence of high coercive minerals, is grain size indicative in sediments with a monomineralic magnetic composition. [ABSTRACT FROM AUTHOR]

We examine rockfall susceptibility of folded strata in the Sevier fold-thrust belt exposed in American Fork Canyon in north-central Utah. Large-scale geologic mapping, talus production data, rock-mass-quality measurements, and historical rockfall data indicate that rockfall susceptibility is correlated with limb dip and curvature of the folded, cliff-forming Mississippian limestones. On fold limbs, rockfall susceptibility increases as dip increases. This relation is controlled by several factors, including an increase in adverse dip conditions and apertures of discontinuities, and shearing by flexural slip during folding that has reduced the friction angles of discontinuities by smoothing surface asperities. Susceptibility is greater in fold hinge zones than on adjacent limbs primarily because there are greater numbers of discontinuities in hinge zones. We speculate that susceptibility increases in hinge zones as fold curvature becomes tighter. [ABSTRACT FROM AUTHOR]

In order to better define the dependence of the mineral texture on flow, anisotropy of magnetic susceptibility (AMS) and microscopic observations have been performed on calcite-rich precipitations occurring in a horizontal pipe where the flow direction is clearly defined. A total of 65 cubes were cut from five slices, magnetic studies identified-pseudo-single domain magnetite as the major AMS carrier. Horizontal foliation characterizes the magnetic fabrics and the lineation is parallel to the pipe axis, that is, the flow direction. The origin of this lineation is discussed and is interpreted to be mainly the consequence of elongated pseudo-single domain magnetite. To complete the magnetic fabric studies, shape preferred orientation statistics were performed on 563 calcite sections in the (0001) calcite plane. It shows elongated shapes with a general orientation parallel to the pipe axis. The mean shape orientation is the average of two distinct subpopulations that deviated slightly from the pipe axis. Observation on calcite shapes and the direction of the magnetic lineation are coherent, suggesting that it is possible to track hydrothermal palaeocirculation using magnetic lineation and petrographic fabrics. [ABSTRACT FROM AUTHOR]

The microwave palaeointensity technique has been used to determine palaeointensity during the R3–N3 geomagnetic field reversal, using lavas from the Esja region of southwestern Iceland. The resulting intensity determinations have been compared to two previous studies which used the Shaw and Thellier techniques. Both reported low field intensities during the reversal except for four flows that produced high values (20.4–36.8 μT) using the Shaw technique compared to a single maximum intermediate value of 15.9 μT using the Thellier method. In this paper, an average microwave transitional palaeointensity of 6.95 ± 2.07 μT is found for samples used in the Shaw technique study, and of 7.80 ± 1.61 μT for samples used in the Thellier study, demonstrating that there is no evidence for strong fields during this reversal. [ABSTRACT FROM AUTHOR]

Sediments deposited in three fjord systems latitudinally spanning the northeast Gulf of Alaska coastline have distinctive rock magnetic characteristics that are derived from glacially eroded accreted terranes. Ideal conditions exist in coastal Alaska to preserve primary rock magnetic properties within the sediment record because of the dominance of glacial erosion and rapid sediment transportation and burial. In temperate glacially dominated marine settings, terrigenous sediment is not diluted by biogenic material and diagenetic alteration is minimal. The juxtaposition of temperate glaciers on the northwest-trending accreted terranes of the southern Alaska continental margin provides magnetic provenance tracers of sediment derived from this region that can aid in the interpretation of glacial, paleoclimate, and tectonic proxy records from marine sediment. Holocene sediment deposited in Glacier Bay is eroded from the Craig subterrane of the Alexander terrane; it is characterized by high-volume magnetic susceptibility and coarse-grained, pseudosingle-domain (PSD) and multidomain (MD) magnetite. In Yakutat and Disenchantment bays, farther to the north, glaciers also erode the Yakutat and Chugach terranes. There, sediment contains slightly finer-grained PSD and MD magnetite, which is chemically distinct from that of Glacier Bay. In the northern-most sector, sediment is eroded from the Chugach terrrane in Harriman and College fiords, adjacent to Prince William Sound. These sediments have low magnetic susceptibility and contain micron-size pyrrhotite. [ABSTRACT FROM AUTHOR]

Abstract: Knowledge of palaeointensity variation is required for determining the full vector variation of the geomagnetic field as a function of geological time. This provides essential constraints for numerical geodynamo models. To date, most palaeointensity determination methods are laborious, characterised by rather low success rates, and demand substantial processing time. The rocks under investigation must obey stringent criteria to yield faithful palaeointensities: the magnetic particles must be single domain, the natural remanent magnetisation must be a thermoremanent magnetisation, and during the successive heating steps in the laboratory no chemical alteration should occur. Here, we describe a new method that allows all magnetic domain states to be processed, i.e. it does not require single domain particles. The method makes use of the linearity of partial thermoremanent magnetisation (pTRM) with the applied laboratory field. Multiple specimens are used so that every sample is exposed only once to a laboratory field, warranting that all samples experienced the same magnetic history. Through the limited number of thermal steps alteration effects are reduced as well. The laboratory pTRM and natural remanent magnetisation (NRM) of the specimens are oriented parallel to minimise the effects of high-temperature tails that affect multidomain minerals. The pTRM acquisition temperature is selected below the temperature at which chemical alteration sets in and above the temperature trajectory where secondary viscous NRM components occur. The procedure requires a lower number of steps than any other palaeointensity method, reducing significantly the total time needed per rock unit. We propose to name the new protocol ‘multispecimen parallel differential pTRM method’. It provides the correct answer to ∼5% for artificial samples and natural rocks containing multidomain magnetic particles that were given a laboratory TRM of known intensity. Application to the Paricutin September–December 1943 lava flow (three sites, 7 specimens per site) yields a weighted mean of 45.9±1.25 μT, within uncertainty margin of the expected value of 45.0 μT. [Copyright &y& Elsevier]

Abstract: Two models, derived in very different ways but both incorporating the symmetry constraints outlined in the previous paper, are developed for use in simulating Thellier-type palaeointensity experiments. These are then tested against experimental data which endorse them both as powerful tools. They predict that non-ideal behaviour due to MD grain content is sensitive not only to the protocol employed and the vector difference between the partial thermoremanent magnetisations (pTRMs) imparted in the laboratory and the natural remanent magnetisation (NRM), but also to the spacing of the temperature steps and the type of pTRM imparted during the remagnetisation stages. Consistent with experimental studies, the models predict that pTRM checks may fail despite no alteration occurring and that any double-stage experimental protocol will produce non-ideal results to some degree provided that MD grains are present. A single-heating (perpendicular or high-angle single heating) protocol is predicted to remove non-ideal effects provided that the grains obey the symmetry constraints perfectly. However, this remains to be experimentally tested and does not allow for the use of pTRM checks. Five straightforward recommendations for future palaeointensity studies to follow are outlined. These are designed to minimise non-ideal behaviour due to MD grains as far as possible while retaining the capacity to detect and reject those samples which will nonetheless produce significant errors. [Copyright &y& Elsevier]

Abstract: We present experimental evidence that partial thermal demagnetisation and remagnetisation treatments produce effects to the measured thermoremanent magnetisation (TRM) of an assemblage of multidomain (MD) ferromagnetic grains that are symmetrical to first order. Just as for assemblages of single domain (SD) grains, measured TRM is affected by a partial thermomagnetic treatment to an extent dependent only on the difference of the magnetic field vectors between that used to impart the TRM and that used in the partial treatment and is insensitive to the absolute field intensity. The only difference between MD and SD TRM is that the effect of a partial treatment in the former partly comprises a non-reciprocal component which cannot easily be erased. The results suggest a new paradigm for MD TRM whereby a full TRM is regarded as a background state rather than a string of partial TRMs and thermal demagnetisation treatments may be considered as overprinting the TRM rather than erasing it. The symmetrical behaviour can be explained through a simple kinematic model incorporating a temperature-dependent domain structure. This model, although greatly oversimplified, also exhibits numerous other observed traits of MD TRM behaviour including the additivity of pTRMs, the exponentially decreasing progressive effects of iterated treatments, and the concave-up Arai plots produced by a Thellier palaeointensity experiment. We argue that the conventional domain wall-pinning process is only dominant in highly stressed grains and may be responsible for a preference for MD grains to be demagnetised and consequently for a loss of symmetry which is barely discernable in this study. [Copyright &y& Elsevier]

Heavy metals in urban topsoils have been shown to be very useful tracers of environmental pollution. Thus, their detailed studies are of great importance. Apart from expensive and time-consuming chemical methods, several simple, rapid and cheap proxy methods have been developed recently, one of them being based on rock-magnetic parameters. This examines the use of rock-magnetic methods designed to assess the degree of heavy-metal pollution of urban topsoils from the city of Xuzhou (China). The aim was to identify the magnetic properties and to link the “magnetic pollution” to the concentrations of the heavy metals. Since a strong correlation has been found between saturation isothermal remanent magnetization (SIRM) and the heavy metals, namely, Fe, Se, Ti, Sc, Ba, Bi, Pb, Cu, Zn, Cr and Mo, an anthropogenic contamination origin is thought to be the cause. The present study shows that SIRM is a fast, inexpensive and non-destructive method for the detection and mapping of heavy-metal-contaminated urban topsoils. [ABSTRACT FROM AUTHOR]

Systematic studies conducted between 15°N and 40°N over ridge segments along the slow-spreading Mid-Atlantic Ridge (MAR) have shown that segment characteristics are related to the thermal state of the segments and gradually vary with their length. This paper presents further developments of a 3-D model, based on the presence of a hot zone located under the segment centres ( Gac et al. 2003 ), to (1) quantify the thermal structures and the geophysical signatures of segments of various lengths, considered as representative of the various MAR segments; (2) test if a simple and single model of thermal evolution can account for the characteristics of all segments and (3) explain the past evolution of the segmentation, as is observed off-axis along the MAR. The modelled thermal structure and three simulated geophysical outputs [crustal structure, along-axis variations of the earthquake maximum depth and the mantle Bouguer gravity anomalies (MBA)] are found to be directly controlled by the shape (geometry and dimensions) of the hot zone. A consistent fit between model outputs and along-axis variations of the geophysical observables over the various segments is obtained by varying solely the length of the hot zone. This result shows that segments of different length may in fact constitute the different stages of a single evolution process: the axial geophysical characteristics of the segment would progressively evolve from those of shorter segments to those of longer ones, as the hot zone lengthens along-axis. A subsequent shortening of the segment would result from a simultaneous shortening of the hot zone, segment characteristics reverting back from those of longer segments to those of shorter ones. Three geophysical fields (topography, gravity and magnetic anomalies) are simulated as the results of the thermal evolution of aligned and offset segments the length of which evolves through time. These simulations succeed in fitting observations for the entire range of observed axis offsets between adjacent MAR segments. The segment evolution produces peculiar off-axis isostatic topography and gravity anomaly (MBA), the rhomb-shaped patterns. Our simulations, which model adjacent offset segments having evolved through several cycles of lengthening and shortening, yield a good fit to the isostatic topography and MBA patterns observed in the off-axis region. Finally, the distribution of magnetization depends on the magnetic properties of each type of rocks and on the petrological structure of the lithosphere, which, in turn, results from its thermal structure and evolution. Modelled magnetic anomalies are shown to be in good agreement with off-axis observations along the N21°40′ segment (TAMMAR) of the MAR. [ABSTRACT FROM AUTHOR]

In order to isolate magnetic signals carried by single-domain (SD) ferrimagnetic (FM) minerals from multi-domain (MD) FM minerals, we developed a few parameters using partial anhysteretic remanent magnetization (pARM). Because MD fraction contains only soft (easy to be demagnetized) coercivity spectrum, pARM(>20 mT) was sensitive in eliminating MD contributions. Ratio of pARM(5 mT, 10 mT)/pARM(0, 5 mT) is useful in quantifying a relative abundance of mass ratio between SD and MD fractions. These new proxies can quickly characterize the details of grain size distribution of magnetic minerals in paleoclimatic and paleomagnetic studies. [ABSTRACT FROM AUTHOR]

For a successful palaeointensity experiment a sample should only consists of non-interacting single domain (SD) particles. As this cannot be completely guarantied for natural samples we applied two different interaction methods (ΔM plots and FORC-diagrams) on basaltic samples from Fernando de Noronha, Brazil, in order to determine the degree of interaction and estimate their use as a preselection tool for palaeointensity experiments. An independent classification of the samples in terms of SD/MD contribution and the occurrence of partial self-reversals is obtained by rockmagnetic means, Thellier-like experiments and continuous thermal demagnetization. The samples show a variable amount of mean interaction fields, which tends to be higher for samples with partial self-reversal. Nevertheless, high mean interaction fields can also be present in samples of successful palaeointensity experiments with high mean coercivities. This suggests, that the recording potential of a sample depends on the interplay of magnetic interaction and its mean coercivity, i.e. samples of higher mean coercivity resist higher mean interaction fields. As this is difficult to assess by normal rockmagnetic means, interaction measurements, especially the ΔM plot derived parameters ΔM 1 and 2, provide a fast tool for preselection. [ABSTRACT FROM AUTHOR]

It has been proposed that paleoclimatic changes and tectonic events strongly affect hominoid evolution. The Zhupeng section at Yuanmou Basin, southwestern China, with the hominoid-bearing fluvial-lacustrine sediments, is an ideal natural laboratory to test this hypothesis. This study provided an integrated magnetic study, including low-frequency susceptibility, the anisotropy of magnetic susceptibility, temperature-dependent susceptibility, hysteresis loops, isothermal remanent magnetization, and anhysteretic remanent magnetization, on samples from the Baozidongqing section at Zhupeng. Results show that the dominant magnetic carrier is hematite, with minor amount of magnetite. Both the composition and concentration of magnetic minerals strongly correlate with the lithostratigraphy. At least eight short-term events defined by higher concentrations of magnetite were identified. These short events reflect that the subtropical dry-hot climate is similar to today's climate. Basing on the lithostratigraphic and rock magnetic results, we suggest that Yuanmou Basin was in a steady deposition environment from about 11 to 7 Ma, which is characterized by alternating of long-term torrid-humid climate and short-term dry-hot climate. Our study provides invaluable environment information for understanding the climate shift and the relationship between paleoenvironment and hominoid evolution in southwestern China during late Miocene. [ABSTRACT FROM AUTHOR]

Several rock magnetic properties are reported for remagnetized biohermal carbonate rocks, platform carbonate rocks and siliciclastic rocks from the NE Rhenish massif, Germany. Thermal demagnetization of a triaxial isothermal remanent magnetization (IRM) applied at room temperature identifies a variety of magnetic minerals in the sample set. Magnetite is the predominant magnetic phase and carries a Late Palaeozoic remagnetization component and can be accompanied by haematite and pyrrhotite as the carrier of remagnetization. High haematite contents are characteristic for samples carrying a remagnetization of Triassic age. Zero field heating of remanence acquired at 10 K indicates significant contribution from magnetic material with blocking temperatures between 10 and 100 K. The Verwey transition at 120 K is much more pronounced in siliciclastic rocks than in carbonate rocks and is presumably related to the presence of detrital multidomain (MD) magnetite. Samples from biohermal carbonate rocks have hysteresis properties with highandratios similar to those from remagnetized carbonate rocks from North America. In those lithologies, the intensity decrease of a low temperature IRM during heating from 10 to 100 K combined with the absence of paramagnetic minerals, high hysteresis ratios, magnetic viscosity and frequency dependence of susceptibility give strong evidence for the presence of superparamagnetic (SP) magnetite. This supports the hypothesis of a chemical remagnetization event in the NE Rhenish massif during the Late Carboniferous. The rock magnetic properties of siliciclastic rocks are characterized by high amounts of paramagnetic material and MD magnetite. MD material obscures the contributions of other material to the bulk magnetic properties completely in most siliciclastic rocks and partly in platform carbonate rocks. [ABSTRACT FROM AUTHOR]

Abstract: We have developed a new three-axis vibrating sample magnetometer, which allows continuous high-temperature magnetization measurements of individual cylindrical ∼0.75 cm3 samples up to ∼650 °C and the acquisition of thermoremanent magnetization (TRM) in any direction and field intensity up to 200 μT. We propose a fast (less than 2.5 h) automated experimental procedure adapted from Boyd''s [Nature 319 (1986) 208–209] modified version of the Thellier and Thellier [Ann. Geophys. 15 (1959) 285–376] method which provides continuous intensity determinations over a large (typically 300 °C) temperature interval for each sample. This procedure allows one to take into account both the cooling rate dependence of TRM acquisition and anisotropy of TRM. Several examples of analyses of ancient magnetization demonstrate the quality and reliability of the data and illustrate the promising potential of this new instrument in paleo- and archeomagnetism. [Copyright &y& Elsevier]

Repeated heating and cooling cycles appear frequently in thermomagnetic experiments used to infer the palaeomagnetic field intensity. According to the fundamental assumptions used to interpret these measurements, a remanence acquired at some temperatureTis not influenced by subsequent heating and cooling cycles at lower temperatures. This presumption is tested for natural and synthetic multidomain particle ensembles in the case of the so-called tail of pTRM* (partial thermoremanent magnetization). This case is of special interest, since hitherto no theoretical explanation for the tail of pTRM* has been available. The experimental results for all samples show that repeating the acquisition process for the tail of pTRM* leads to an asymptotic saturation. This phenomenon can be explained in terms of a statistical theory of multidomain thermoremanence based on concepts of non-equilibrium thermodynamics. The presented experiments support the hypothesis that domain state stabilization by iterated thermal magnetization processes in multidomain particle ensembles is a statistical process. Iterative saturation of the tail of pTRM* can be interpreted using a combination of exponential saturation functions related to the subspectrum of the involved transition matrix. Its explanation does not require chemical alteration or irreversible after-effects. [ABSTRACT FROM AUTHOR]

Abstract: Long-wavelength and satellite magnetic anomalies require that some regions of the Earth''s crust contain minerals that are magnetic at lower crustal conditions. Studies of high-grade metamorphic rocks emphased multi-domain magnetite as a likely source. Members of the hematite–ilmenite series were not considered, because hematite commonly has a relatively weak magnetization and, though ilmenite compositions in the range Ilm 50–70 can be strong ferrimagnets, their low Curie T<260 °C makes them an unlikely source. However, recent investigations have described hematite–ilmenite magnetism and coercivity in terms of a new ferrimagnetic substructure related to interfaces between ilmenite and hematite in exsolution lamellae down to unit-cell thickness. In this “lamellar magnetism”, ferrimagnetism is coupled to principal AF moments of hematite and retains many properties of titanohematite, including high coercivity and thermal stability. If exsolution lamellae are the source of the magnetism, a temperature above that predicted for lamellar resorption should destroy it. To look at behaviour of lamellae at mid-to-lower crustal conditions, we selected a hemo-ilmenite sample, Ilm 84, on which detailed studies of microstructures, mineral chemistry and magnetic properties had been made. We designed experiments at 10 kbar as an analog for lower crustal conditions. After initial 5-day runs at 540, 685 and 950 °C, a temperature of 580 °C was chosen for 8- and 21-day runs. At one atmosphere, this T, for Ilm 84, is above that predicted for complete resorption of all lamellae to produce a homogeneous paramagnetic R3¯ ilmenite. In these experiments, exsolution lamellae coarsened. If these features were reproduced in the lower crust, hemo-ilmenite or ilmeno-hematite would retain a magnetic moment and higher than expected coercivity due to the microstructures. EMP and TEM analyses were used to understand the compositional differences between the natural sample, products of the experiments and one-atmosphere phase diagrams. If the experimental changes are interpreted as moving the compositions closer to equilibrium at 580 °C, 10 kbar, then a considerable widening of miscibility gaps as a function of pressure and the ∼20% geikielite component in the ilmenite, as well as an increase in Nèel temperature of hematite, is predicted. An alternate is to consider the response as Ostwald steps short of equilibrium. Experimental results indicate that exsolution microstructures play a key role in mineral magnetism, and that such microstructures, as well as coarse hematite, may be preserved at pressures and temperatures of the lower crust. [Copyright &y& Elsevier]

The article presents information on various minerals. Spinel is cubic, octahedral in shape. Spinel when pure, is colorless. Usually it is found in various shades of red, especially purplish red, blue, green, brown and black. Spinel with a trace of Carbon monoxide can show a color change from blue in daylight to violet in tungsten light. Magnetite is ferromagnetic and one of the few minerals strongly attracted to a magnet. It occasionally has induced polarity and is then known as lodestone. The latter when suspended from an unspun thread acts as a compass. Magnetite is the major contributor to the magnetic properties of rocks. It is a good conductor of electricity. Chromite is common as an accessory mineral in basic and ultramafic igneous rocks such as peridotites, dunites and serpentinites derived from such rocks.

The magnetic properties of an icosahedral Cd–Mg–Tb quasicrystal were studied by dc magnetization and thermoremanent magnetization time decay measurements. An unusual temperature dependence of the susceptibility below freezing temperature can be attributed to the inhomogeneous sample structure. In addition to the quasicrystalline portion which exhibits a spin-glass transition at 12.5 K a part of the sample behaves like a paramagnet. During aging of the sample in air the spin-glass part transforms into the paramagnetic one. The linear M∝H dependence of the thermoremanent magnetization time decay on magnetic field is quite different as compared to canonical spin glasses. [Copyright &y& Elsevier]

Abstract: The aim of the present study is to obtain a detailed characterization of fly ashes and nearby anthropogenic soils from different Bulgarian power plants, by using integrated rock magnetic and classical microscopic methods. These combined techniques, which enable a better understanding of the complexity of anthropogenic magnetic phases, impose the need for application of an interdisciplinary approach in environmental studies. The combined use of both single grain and bulk hysteresis measurements, combined with thermomagnetic analysis and microscopic (optical, scanning electron microscopy observations and energy dispersive X-ray analysis) reveal the major factors which control the magnetic properties of the fly ashes. Optical microscope observations on polished sections show that the complex internal structure (dendritic exsolutions) and in particular surface morphology of the fly ash particles, are the reasons for the observed significant discrepancy between the estimated magnetic grain size and the physical grain size. Bulk magnetic extracts show hysteresis parameters typical for pseudosingle domain and single domain magnetic states that are a result of superposition of the magnetic response from particles with widely varying grain size distributions. Magnetic mineralogy deduced from the thermomagnetic analysis is dominated by a magnetite-like phase, but in some samples there is a significant contribution of a phase with a lower blocking temperature of 500 °C, probably indicating the presence of substituted ferrimagnetics. The magnetic mineralogy of the fly ashes is closely related to the type of coals used by different power plants. The results show a good correspondence between fly ash magnetic susceptibility and total Fe2O3 content which suggests the dominant role of strongly magnetic iron oxides. The magnetic behaviour of the anthropogenic soils is dominated by the magnetic signal from fly ash pollution, although contributions from pedogenic and lithogenic magnetite are also observed. [Copyright &y& Elsevier]

Abstract: Magnetic methods provide a fast tool for delineation of industrial pollution. Mineral magnetic studies of anthropogenic magnetic phases in road dust from the industrial zone of Visakhapatnam city (India) reveal the presence of large anthropogenic spherules with diameters up to ∼300 μm. Different internal structures of the spherules and a wide variation in size of the spherules, as well as the presence of melt-like particles and irregular shaped grains containing heavy metals, point to multiple sources of pollution, including different industries and heavy vehicle traffic. Magnetic mineralogy of the samples is dominated by a magnetite-like phase. Hysteresis parameters measured for magnetic extracts and single grains, are typical for pseudo-single domain magnetite. This is in disagreement with the large grain size of the single particles. Scanning electron microscopy images reveals a complex internal structure, showing an agglomeration of smaller grains and in-part, an extreme porosity of the spherules, probably related to fast cooling. The chemical composition determined by energy dispersive X-ray analysis is strongly variable and can also be very heterogeneous within a particle. First order reversal curve analysis indicates a spectrum of single domain, pseudo-single domain and multidomain properties. Values of saturation magnetisation suggest that the particles either consist of mainly similar ferrimagnetic sub-grains, whereas others are a mixture of ferrimagnetic and non-magnetic phases. Several irregular grains, showing a ferrimagnetic behaviour, contain a large amount of chromium (>50 wt%). The variations of the magnetic susceptibility along the three major roads in the industrial zone of Visakhapatnam are interpreted in terms of the relative degree of pollution. [Copyright &y& Elsevier]

Abstract: A high-resolution study of an active Fe2+/Fe3+ redox horizon has been carried out on sediments of the central equatorial Atlantic. The multidisciplinary approach combining geochemical and rock-magnetic parameters gives evidence of the interrelation of the redox horizon with the last change from glacial to interglacial conditions (T1). Distinct enrichments of redox-sensitive elements (Mn, Fe, V, and U) reveal a characteristic depth-sequence, indicating non-steady-state diagenetic conditions caused by a decrease in productivity and an increase in oxygen content in the bottom water during T1 and a reversal during the Holocene. Thus, the redox boundaries first moved down into the sediment and subsequently upwards. The movement of the redox boundaries led to the development of conspicuous double peaks for Fe and Mn. The reconstruction based on geochemical data is supported by susceptibility and magnetization measurements of the sediments displaying well-defined anomalies in the vicinity of active and paleo redox boundaries. The combination of geochemical and rock-magnetic parameters, like the ferrimagnetic susceptibility, and total Fe concentration (χf/Fe) are suitable for characterizing distinct zones of dissolution and precipitation of ferromagnetic mineral phases (e.g. magnetite). Moreover, the small scale movement of the Fe2+/Fe3+ redox-boundary, could be traced in detail by overlaying the peak-shape pattern of V/Al and of χf/χtot. [Copyright &y& Elsevier]

Abstract: This work focuses on the study of flow and propagation of magma using rock magnetic analyses along sections across the thick Jurassic dyke of Foum-Zguid (Southern Morocco). Thermomagnetic data show that Ti-poor titanomagnetite is the main magnetic carrier. Petrographic analysis shows that the main Ti phase (ilmenite) occurs either as lamellae within spinel (center of the dyke) or as isolated grains (dyke margin). Bulk magnetic properties display distinct behavior according to the distance to the dyke margin; grain size of the main magnetic carrier decreases towards the center of the dyke, while the natural remanent magnetization and the bulk magnetic susceptibility increase. Only the magnetic susceptibility ellipsoid close to the dyke margin corresponds to that usually found in thin dykes, with the magnetic foliation sub parallel to dyke margins. Maximum principal axis is in most cases either parallel or perpendicular to the intersection between the planes of magnetic foliation and dyke wall. Moreover, when this axis is perpendicular to the intersection it is associated with a more oblate magnetic susceptibility ellipsoid shape, indicating the presence of complex magnetic fabrics. The studied magnetic properties show that, in this 100 m wide thick dyke, flow structures related with dyke propagation are only preserved close to the quickly cooled dyke margins. [Copyright &y& Elsevier]

Abstract: The purpose of this study is to compare the magnetic properties of parent rocks with their weathering products (i.e., sands) in order to ultimately trace the transport pathways of magnetic particles into the ocean. Considering the high rate of alteration and the high magnetic content of volcanic rocks, we chose to study a volcanic island as a test area. We selected the small Martinique Island, which is characterized by a hot climate and important alteration of the lava flows. Martinique Island sample sites consist of andesitic rocks that range in age from 0.7–23 Ma. Sands were sampled in several riverbeds on the island while rocks were taken in the surrounding lava flows. Classical rock magnetic parameters with associated ratios, hysteresis loops and the monitoring of magnetic susceptibility during heating were used as indicators of magnetic mineralogy, grain size and concentration. We found that the parent rocks and their weathering products have similar magnetic properties, thereby demonstrating that rock magnetic parameters of the parent rocks are, to the first order, good tracers of sediment sources and transport in the ocean. However, small variations between rocks and sands are mostly due to mineralogical changes between the parent rocks and their weathered sands. A small amount of a second mineral, that could be pyrrhotite, was detected in sands but not in the parent rocks. These observations indicate that the iron oxides within lavas can be affected by chemical weathering during their alteration in situ or during transport. Reduction/oxidation processes have some (limited) effects on the magnetic particles. These results agree with previous geochemical studies, which show that the particles transported to the ocean are not simply crushed parent rocks but are slightly chemically different. We suggest here that similarly small differences may exist in magnetic mineralogy, but this does not affect the magnetic parameters enough to induce problems in their use as tracers of magnetic sources. [Copyright &y& Elsevier]

Abstract: The analysis of magnetization curves with model functions has been proposed independently in several works as a method to unmix and characterize magnetic minerals assemblages in sediments and sedimentary rocks. Unfortunately, a successful result of such analysis relies on time-consuming measurements and on the choice of appropriate model functions. However, once the magnetic properties of individual magnetic components have been determined on a small set of selected samples, a simpler and faster analysis of similar samples is possible. The fast analysis of a large number of samples allows investigation of the effect of natural processes on the properties of single magnetic components. The simplification of the unmixing problem proposed in this paper is based on an iterative linearization procedure, which considers the variability of magnetic components. Any simplification of the unmixing problem is limited by a minimum number of parameters, which are required to fully characterize a magnetic component. It has been shown that a combination of four parameters, so-called magnetic fingerprints, is sufficient for a complete characterization of the remanent magnetization of a component. The usefulness of magnetic fingerprints in tracking natural processes is demonstrated exemplarily for lake sediments. The response of Baldeggersee (Switzerland) to environmental changes has been investigated, with special regard to the role of bacterial magnetite in the iron cycle and its possible use as a sensitive paleoredox indicator. The relation between the magnetic properties of lake sediments on one hand, and climatic, tectonic- and human-driven environmental changes on the other, is strongly non-linear. Therefore, a classic correlation between so-called magnetic proxies and environmental signals should be considered with care. [Copyright &y& Elsevier]

Abstract: The characterization of individual magnetic components in sediments and sedimentary rocks is difficult, as these natural materials are often a complex mixture of magnetic mineral sources. The analysis of magnetization curves with model functions is the only practicable method of unmixing the magnetic components and characterizing their magnetic properties, if a priori information is not available. Unfortunately, such analyses rely on time consuming measurements and on the choice of appropriate model functions. The simplification of the unmixing problem is closely related to the number of parameters required to fully characterize a magnetic component, and the significance of these parameters in rock magnetic terms. A systematic analysis of synthetic and natural samples shows that a combination of four parameters, here called magnetic fingerprints, is sufficient for this purpose. The fingerprints of individual magnetic components isolated from a wide range of natural sediments and sedimentary rocks form well-defined groups with specific properties. These groups reflect common processes of formation, transport and dissolution of magnetic particles. A clear distinction can be made between two sorts of biogenic magnetite, atmospheric dust, urban pollution and ultrafine magnetite produced in soils and lacustrine/marine sediments. [Copyright &y& Elsevier]

We conducted a detailed rock magnetic study on upper 80 m of Jing'erwa core from the Nihewan basin. The results indicate that the sediments from Jing'erwa core are suitable for relative paleointensity study, and anhysteretic remanent magnetization (ARM) can be used as the normalization parameter of the natural remanent magnetization (NRM). Our relative paleointensity data of upper 80 m of Jing'erwa core provide a continuous record of the intensity variation during the last 0.8 Ma, which correlates well with the results from marine sediments cores in the Pacific Ocean. This means that the sediments records are reliable for relative paleointensity of Earth's magnetic field, and suggests that these sediments have recorded the real changes of geomagnetic field, which would provide a new method for regional stratigraphic correlation. [ABSTRACT FROM AUTHOR]

We report the results of a detailed rock-magnetic study of basaltic andesites for one of the best documented cases of the first occurrence of a new volcano, the 1943–1952 eruption of Paricutin in central Mexico. 102 oriented standard palaeomagnetic cores corresponding to 12 sites were collected from seven different lava effusion episodes, which cover the interval between 1943 September–December and 1946 March–August. Thermomagnetic investigations reveal that remanence is carried in most cases by Ti-poor titanomagnetite, resulting from oxy-exsolution that probably occurred during the initial flow cooling. Unblocking temperature and coercivity, point to ‘small’ pseudo-single domain magnetic grains for these (titano)magnetites. Thermal and alternating field demagnetization indicates that the lavas are characterized by univectorial or two-component magnetizations. Site-mean declinations and inclinations range from 331.9° to 32.3° and from 17.6° to 51.3°, respectively. The overall mean direction for 12 sites is: and . 23 samples were pre-selected for Thellier palaeointensity experiments because of their stable remanent magnetization and relatively low within site dispersion. Thellier palaeointensity experiments have yielded widely dispersed palaeointensity values from the historically observed geomagnetic intensity. Although, individual specimens yielded technically high quality palaeointensity results, the values obtained are significantly different from the expected value of approximately 45 μT. The palaeomagnetic record is dominantly characterized by shallower than expected site-mean inclinations as compared with data from the Teoloyucan Geomagnetic Observatory and estimates based on the International Geomagnetic Reference Field 1945 and 1950 models. Several alternative interpretations are examined, but no single factor resulting in abnormal shallow inclinations can be isolated. Direct field observations suggest that shallow inclinations and angular scatter can be associated with lava emplacement, in terms of internal viscous deformation and/or movement of parts of lava after cooling below the blocking temperatures during lava advance. Other factors analysed that could contribute to the shallow inclinations and angular scatter are high magnetic refraction effects and outcrop-scale to regional magnetic field anomalies. [ABSTRACT FROM AUTHOR]

Palaeomagnetic and rock magnetic studies were performed on a seaward transect of continental shelf sediments from sites 1071 and 1072 of Ocean Drilling Programme Leg 174A on the New Jersey margin. The sediments recorded a polarity change from reversed to normal, which was tentatively interpreted as the Matuyama–Brunhes boundary. The polarity boundary is closely correlated with the sequence boundary pp3(s), which is considered to have formed as an erosional unconformity during regression and subsequent transgression related to global eustacy. Rock magnetic analyses indicate that the sediment contains comparable amounts of magnetite and greigite (Fe3S4) with possible trace amounts of haematite. A marked change in rock magnetic properties is recorded at Site 1072 with an increase in greigite concentration at the polarity boundary (62.4 metres below seafloor), where the grain size does not change. At Site 1071, greigite is dominant from 2 m below pp3(s) to 0.8 m above it. These intervals are characterized by higher peak coercivities of remanence and subdued remanence in both the magnetite and greigite components. Palaeomagnetic analysis indicates that the intervals just below pp3(s) have dual-component magnetizations of reversed polarity and are considered to have been deposited during the Matuyama Chron (C1r.1r) and were possibly remagnetized during the Brunhes Chron through the formation of the pp3(s) surface. Detrital magnetite and early diagenetic greigite might have carried the reversed polarity magnetization. During the formation of pp3(s) in the Brunhes Chron, greigite might have formed at the oxidation front with ongoing downward formation due to oxidation of pyrite by percolating fresh water, which might be a cause of the remagnetization. Our study indicates that careful rock magnetic investigation is necessary for magnetostratigraphic studies of continental shelf deposits in order to recognize remagnetizations induced by sea-level changes. [ABSTRACT FROM AUTHOR]

The Stoer is the lowest of three groups comprising the Torridonian Supergroup, a clastic succession deposited late in Mesoproterozoic times on the (Lewisian) metamorphic foreland to the Caledonian Orogen in northwest Scotland. This study reports a palaeomagnetic, rock magnetic and magnetic fabric investigation through the full stratigraphic thickness of the succession. A primary magnetic fabric of sedimentary origin defines current flow from a westerly veering to northwesterly source. Rock magnetic studies identify the presence of both magnetite and hematite in these sediments. Magnetite is apparently of primary detrital origin whilst the hematite probably results mostly from early diagenesis in an environment of restricted chemical weathering. Palaeomagnetic study of sedimentary slumps shows that magnetic remanence post-dates deposition but was probably fixed by early dewatering and lithification because slumped blocks of Stoer in basal Torridon Group sediments preserve a primary remanence. Tilt adjustment, although inconclusive, also implies that magnetic remanence is older than pre-Torridian Group tectonic deformation. The lower part of the Stoer succession shows a progressive increase of magnetic inclination with shallower components resident in magnetite and steeper components in hematite. The succession above the Stac Fada Member has the steepest magnetic inclination and shows no significant difference between magnetite and hematite component directions. The inferred time sequence of palaeopoles coincides with the Gardar palaeomagnetic track (∼ 1250-1130 Ma) at 1180 Ma, conforming to a Pb-Pb determination of 1199 ± 70 Ma. The Stoer Group was fully lithified and deformed before deposition of the Torridon Group at ∼ 1030 Ma because it contains no vestige of the range of Caledonian and later overprints found extensively in the latter. Sedimentation and lithification of the Stoer Group are therefore linked with a phase of extensional tectonism... [ABSTRACT FROM AUTHOR]

The paleomagnetic results obtained in 23 sites from red beds of the northern border of the inverted Cameros Basin (northern Iberian Peninsula) prove a Cretaceous widespread remagnetization. Paleomagnetic and rock magnetic analyses indicate that the Natural remanent magnetization (NRM) is dominated by a stable and always normal polarity component carried by haematite. Two conglomerate test and five-fold test indicate that this component is a syn-tectonic overprint dated between Albian and Santonian times, most probably Albian, contemporary with a low-grade metamorphism. Remagnetization was acquired before compressional deformation and post-dates the main extensional stage of basin formation (Berriasian–Albian). Incremental fold tests provide best clustering solutions showing dispersed results and far from the expected direction. An alternative procedure to obtain fold test solution was applied considering asymmetric limb rotation. Mean directions obtained from these “asymmetric solutions” are consistent with the expected direction and yield a statistical value for significant grouping at the 95% confidence level in all fold tests performed. This reconstruction allows to determine the tilting of beds at the moment of acquisition of magnetization. These original dips were used to reconstruct the original geometry of the northern basin border, later modified during the Tertiary inversion stage. This extensional geometry can be characterised as a large-scale syn-sedimentary normal fault drag, with a minor roll-over anticline. The procedure developed in this paper should be tested in other inverted basins that also have undergone burial remagnetizations. [Copyright &y& Elsevier]

The Klodzko Metamorphic Complex (KMC) consists of Upper Proterozoic metaigneous and metasedimentary rocks forming a stack pile thrusted over the Givetian and overlain by Frasnian–Fammenian sediments. Magnetomineralogical experiments show that the magnetic minerals are secondary. The paleomagnetic experiments identified three components of the Natural Remanent Magnetization; labeled A1, A2 and M. The mean pole positions calculated in situ correspond with the Baltica Upper Devonian (A1: PlatS=−18°, PlongE=317°), Permo-Carboniferous (A2: PlatS=−39°, PlongE=2°) and Triassic–Jurassic (M: PlatS=−60°C, PlongE=308°) segments of the Apparent Polar Wander Path (APWP) for Baltica. This indicates that the region studied was situated close to the Baltica plate at least since the Upper Devonian and was not folded after this period. [Copyright &y& Elsevier]

Paleomagnetic measurements were made on samples from Silurian, Devonian, Carboniferous and Permian aged rocks from the Omulevka terrane, northeast Russia. The Omulevka terrane is a fragment of continental margin that forms a major component of the Kolyma–Omolon superterrane, a superterrane that constitutes the core of northeast Russia. All samples were collected from sites along the Taskan river, and all showed a very strong secondary overprint and in some cases more than one. With detailed thermal demagnetization, a component of magnetization that decayed towards the origin when viewed as an orthogonal plot was commonly present and showed better clustering of magnetization directions in stratigraphic coordinates. All of the sites sampled were tilted, but none had enough variation in bedding attitude to perform fold tests. Comparing data between localities was used as a pseudo fold test and indicates that in all but one case the characteristic remanent magnetization found represents a magnetization acquired very early in the history of the rock. Interpretation of these data in terms of both virtual pole positions and paleolatitude changes with time shows that the Omulevka terrane and the adjacent Omolon terrane were together at low latitudes in Silurian and Devonian time and until late Devonian their latitude was consistent with them being closely related to the Siberian Craton. Between Devonian and Permian times, the paleolatitudes of the terranes decreased and, when compared with equivalent reference paleolatitudes for the nearby Siberian platform, show a clear latitudinal separation. From Permian to Jurassic time, the Omulevka and Omolon terranes move steadily northwards, reducing the relative latitudinal separation from Siberia. By late Jurassic to early Cretaceous time, the observed and equivalent Siberian paleolatitudes are identical, indicating the accretion of the Kolyma–Omolon superterrane to the eastern Siberian continent. [Copyright &y& Elsevier]

Examines Cretaceous non-marine sedimentary rocks and volcanic rocks in the Gongju Basin, South Korea. Paleomagnetism; Rock magnetism; Age dating of the rocks; Clockwise rotation of the rocks.

Analyzes the theory of low-field anisotropy of magnetic susceptibility (AMS) of rocks. Measurement of field-independent susceptibility; Magnetization of multidomain materials in low fields; Comparison of magnetic susceptibility of magnetite, pyrrhotite, hematite and titanomagnetite.

Examines the thermal evolution of an orogen undergoing late-stage extension using rock magnetic properties of a suite of mafic dyke rocks. Components of natural remanent magnetization in the dykes; Isolation of the component of magnetization with highest blocking temperature; Constraints on the thermotectonic evolution of collapsing orogen.

We carried out an integrated paleomagnetic, rock-magnetic and paleointensity study of Miocene volcanic succession from the trans-Mexican volcanic belt (TMVB) north of Guadalajara. A total of 37 consecutive basaltic lava flows (326 oriented standard paleomagnetic cores) were collected at Lazo locality. Continuous susceptibility measurements with temperature and hysteresis experiments yield in most cases reasonably reversible curves with Curie points close to that of pseudo-single-domain magnetite. Two geomagnetic reversals were observed in the 300 m thick composite section. Paleosecular variation was lower than the one observed in general during Miocene. It appears that the volcanic units have been emplaced during a relatively short time span of about 1 Ma. The mean paleomagnetic directions obtained from this study do not differ significantly from that expected for the middle Miocene. The mean paleomagnetic direction calculated from all data is I=31.1°, D=354.6°, k=124 and α95=2.1°, N=37. Seventy-two samples with apparently preserved primary magnetic mineralogy and without secondary magnetization, mostly belonging to reverse polarity chron were pre-selected for Thellier paleointensity determination. The flow-mean paleointensity values are ranging from 22.4±3.4 to 53.8±6.0 μT and the corresponding virtual dipole moments (VDMs) are ranging from (5.4±0.8) to (12.0±1.4)×1022 A m2. This corresponds to mean value of (7.7±2.2)×1022 A m2, which is close to present day geomagnetic field strength. Altogether, our data suggest the existence of relatively high geomagnetic field strength undergoing low fluctuations. [Copyright &y& Elsevier]

Compares the results of the acid-ammonium-oxalate/ferrous-iron extraction method for natural samples with a directly related study into the dissolution behavior of synthetic samples, to see whether these behave in a similar way. Selective dissolution of pedogenic magnetic minerals from a loess-palaeosol transect.

The physical and chemical changes associated with the thermal maturation of organic-rich shale have affected the paleomagnetic and rock magnetic characteristics of the Devonian Duvernay Formation in the Western Canada Sedimentary Basin. This formation has several lithofacies that correspond to deposition in platform, slope and deeper water settings under varied redox conditions. Shale, laminated mudstone and some massive mudstone facies show evidence of magnetic changes associated with maturation but wackestone, packstone and some massive mudstone facies appear to be unaffected by the process. Rock magnetic evidence suggests that thermal maturation induces a change in the magnetization carrier from magnetite and hematite to solely magnetite.The packstone and wackestone facies commonly show a reversed characteristic magnetization with a paleopole at 194°E, 70°N (A95=13.2) of Late Cretaceous-age. Shale and laminated mudstone facies in immature areas of the basin have inclination-only characteristic remanent magnetization (ChRM) means that range from 55 to 67 °C, requiring a pre-Cretaceous magnetization age. Shale and laminated mudstone facies in mature areas of the basin have a much steeper ChRM in direction ranging from 77 to 83 °C. Their very steep nature suggests that step demagnetization has not completely removed a drilling-induced remanence in some wells. [Copyright &y& Elsevier]