Archaeomagnetic intensity in Finland during the last 6400 years: problems in measurement techniques, dating errors or evidences for a non-dipole field

Archaeomagnetic intensity in Finland has been determined for the past 6400 years with the Thellier technique of bricks, potsherds and baked clays. The normalized intensity shows an increase from -4360 BC to the maximum at AD 500–AD 900, after which it decreases to the present value. The peak at AD 500–AD 900 is not a consequence of the applied Thellier technique since we are able to reproduce the known field values in the laboratory, and some of the bricks yield values which are in broad agreement with the observatory data. We have shown that variations in grain size of the magnetic carriers, cooling rate, fabrik or magnetic refraction are unlikely to cause systematic errors in intensity larger than ten percent. Previously we have demonstrated that the high intensity at AD 500 in Finland can be modelled by a non-dipole field producing enhanced latitude-normalized values at higher latitudes (Finland) and relatively weaker fields at lower latitudes (Bulgaria), and that extrapolation of the present field (IGRF 1990) back in time shows similar behaviour. However, the new Bulgarian smoothed archaeointensity curve by Daly and Le Goff (1996) shows a maximum in Bulgarian curve at ~AD 630 (i.e., 130 years later than in Finland) and another maximum at AD 950 (i.e., 50 years later than in Finland) , and the new relative intensity data of Finnish lake sediments (Saarinen, 1996) reveals a peak at ~AD 870 corresponding roughly with the second maximum. These new curves are somewhat controversial but they east doubt on the previous datings of the Finnish archaeomagnetic materials of the first millennia AD. Here we show that a better match of the Finnish and Bulgarian intensity data with the Finnish lake sediment data can be obtained if the Finnish ages of the first millennium are slightly younger than previously thought. However, the Finnish intensities are still significantly higher than the coeval Bulgarian intensities so that a non-dipole field enhancement may have also been operative

Fennoscandia Paleomagnetics Meeting

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95029/1/eost8757.pd

Physical properties of 368 meteorites: Implications for meteorite magnetism and planetary geophysics

Petrophysical studies (susceptibility, intensity of natural remanent magnetisation (NRM) and dry bulk density) of 368 meteorites are reviewed together with magnetic hysteresis data for 50 achondrites and chondrites. The relationships between dry bulk density, metallic FeNi-content and porosity will be discussed in the case of L-chondrites. Using the petrophysical classification scheme the meteorite class and the petrologic group of a sample can be determined in most of the cases providing a rapid means for determining a preliminary classification of a new sample. In addition, the petrophysical database provides a direct source of basic physical properties of the small bodies in the solar system. Paleointensity determinations with Thellier technique will be presented for 16 meteorites representing different chondrite groups. The results yield high paleofield values ranging from 51μT to 728μT for the magnetically hardest meteorites consistent with previous studies. However, these values must be looked with caution, because of possible physico-chemical or mineralogical alterations during heating

Rock Magnetic Studies of the Neuschwanstein EL6 Chondrite : Implications on the Origin of its Natural Remanent Magnetization

Peer reviewe

Palaeomagnetism of Middle Ordovician Carbonate Sequence, Vaivara Sinimaed Area, Northeast Estonia, Baltica

The hill range of Vaivara Sinimaed in northeast Estonia consists of several narrow east-to northeast-trending glaciotectonic fold structures. The folds include tilted (dips 4-75 degrees) Middle Ordovician (early Darriwilian) layered carbonate strata that were studied by mineralogical, palaeomagnetic, and rock magnetic methods in order to specify the post-sedimentational history of the area and to obtain a better control over the palaeogeographic position of Baltica during the Ordovician. Mineralogical studies revealed that (titano) magnetite, hematite, and goethite are carriers of magnetization. Based on data from 5 sites that positively passed a DC tilt test, a south-easterly downward directed component A (D-ref = 154.6 degrees +/- 15.3 degrees, I-ref = 60.9 degrees +/- 9.7 degrees) was identified. The component is carried by (titano) magnetite, dates to the Middle Ordovician (Plat = 17.9 degrees, Plon = 47.3 degrees, K = 46.7, A95 = 11.3 degrees), and places Baltica at mid-southerly latitudes. Observations suggest that in sites that do not pass the tilt test, the glaciotectonic event has caused some rotation of blocks around their vertical axis.Peer reviewe

Advancing Precambrian palaeomagnetism with the PALEOMAGIA and PINT(_QPI) databases.

State-of-the-art measurements of the direction and intensity of Earth's ancient magnetic field have made important contributions to our understanding of the geology and palaeogeography of Precambrian Earth. The PALEOMAGIA and PINT(QPI) databases provide thorough public collections of important palaeomagnetic data of this kind. They comprise more than 4,100 observations in total and have been essential in supporting our international collaborative efforts to understand Earth's magnetic history on a timescale far longer than that of the present Phanerozoic Eon. Here, we provide an overview of the technical structure and applications of both databases, paying particular attention to recent improvements and discoveries

Shock experiments in range of 10-45 GPa with small multidomain magnetite in porous targets

Peer reviewe

Magnetic susceptibility of Middle Ordovician sedimentary rocks, Pakri Peninsula, NW Estonia

Magnetic susceptibility (MS), its frequency-dependence and anisotropy of the Middle Ordovician Dapingian and Darriwilian sedimentary sequence from three sites (Uuga, Testepere and Leetse) in the Pakri Peninsula, NW Estonia are analysed in combination with the mineralogical composition. The study is based on 463 cores drilled at intervals of a few centimetres to a maximum of about 1 m. All the samples show low and positive MS, which suggests the presence of small quantities of paraand/or ferromagnetic minerals. The stratigraphic units of the three studied sites have a similar along-section appearance, which provides a base for a composite curve. The relatively higher susceptibilities are carried by secondary Fe-Ti oxides (Toila Formation), goethite ooids (Kandle Formation) and ferrous dolomite (Pae Member), whereas paramagnetic minerals are mostly responsible for the rest of the sequence. Considering the dependence of MS on regressive transgressive cycles (high/low MS within deposits of regressive/transgressive parts of the cycles, respectively), the MS data do not agree with sedimentologically derived sea-level compilations. The measured changes in MS in the Pakri Peninsula outcrops correlate at certain characteristic levels with those deposited in the deeper part of the palaeobasin (Viki core), indicating that the post-depositional iron mobilization within the sediments took place at least at a regional level. Because of post-depositional reorganization of ferromagnetic carrier minerals, the MS values may, however, not be used as a detrital proxy.Peer reviewe

Magnetic Nanoparticles in Human Cervical Skin

Magnetic iron oxide nanoparticles, magnetite/maghemite, have been identified in human tissues, including the brain, meninges, heart, liver, and spleen. As these nanoparticles may play a role in the pathogenesis of neurodegenerative diseases, a pilot study explored the occurrence of these particles in the cervical (neck) skin of 10 patients with Parkinson's disease and 10 healthy controls. Magnetometry and transmission electron microscopy analyses revealed magnetite/maghemite nanoparticles in the skin samples of every study participant. Regarding magnetite/maghemite concentrations of the single-domain particles, no significant between-group difference was emerged. In low-temperature magnetic measurement, a magnetic anomaly at similar to 50 K was evident mainly in the dermal samples of the Parkinson group. This anomaly was larger than the effect related to the magnetic ordering of molecular oxygen. The temperature range of the anomaly, and the size-range of magnetite/maghemite, both refute the idea of magnetic ordering of any iron phase other than magnetite. We propose that the explanation for the finding is interaction between clusters of superparamagnetic and single-domain-sized nanoparticles. The source and significance of these particles remains speculative.Peer reviewe

The long life of SAMBA connection in Columbia : A paleomagnetic study of the 1535 Ma Mucajai Complex, northern Amazonian Craton, Brazil

In recent years, there has been a significant increase in the paleomagnetic data of the Amazonian Craton, with important geodynamic and paleogeographic implications for the Paleo-Mesoproterozoic Columbia supercontinent (a.k.a., Nuna, Hudsoland). Despite recent increase of paleomagnetic data for several other cratons in Columbia, its longevity and the geodynamic processes that resulted in its formation are not well known. A paleomagnetic study was performed on rocks from the similar to 1535 Ma AMG (Anorthosite-Mangerite-Rapakivi Granite) Mucajai Complex located in the Roraima State (Brazil), in the northern portion of the Amazonian Craton, the Guiana Shield. Thermal and AF treatments revealed northwestern/southeastern directions with upward/downward inclinations for samples from twelve sites. This characteristic remanent magnetization is mainly carried by Ti-poor magnetite and in a lesser amount by hematite. Site mean directions were combined with previous results obtained for three other sites from the Mucajai Complex, producing the dual polarity mean direction: Dm = 132.2 degrees; Im = 35.4 degrees (N = 15; alpha(95) = 12.7 degrees; k = 10.0) and a paleomagnetic pole located at 0.1 degrees E, 38.2 degrees S (A(95) = 12.6 degrees; K = 10.2). The Mucajai pole favours the SAMBA (South AMerica-BAltica) link in a configuration formed by Amazonia and Baltica in Columbia. Also, there is geological and paleomagnetic evidence that the juxtaposition of Baltica and Laurentia at 1.76-1.26 Ga forms the core of Columbia. The present paleomagnetic data predict a long life 1.78-1.43 Ga SAMBA connection forming part of the core of the supercontinent. (c) 2019 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.Peer reviewe