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At the Permian/Triassic boundary, terrestrial as well as marine life was seriously decimated. The drastic reduction was possibly due to a global event. In order to demonstrate this, sections at great distance from one another need to be correlated, which is a difficult task, especially between marine and land sections. One of the methods, which is independent of the environment, is magnetostratigraphic correlation. It was intended to apply this method for precise dating to Permian/Triassic boundary sections from the Bükk Mts, which include strata with high concentrations of magnetospherules. Since the Paleozoic-Mesozoic rocks of the Bükk Mts are anchimetamorphosed and intensively tectonized, it was decided to carry out a pilot paleomagnetic study on samples from two sections with different dips, before collecting a large number of samples for the intended magnetostratigraphy survey. The results of this study can be summarized as follows. The rocks of the sections possess remanences of pre-tilting age, and the magnetic fabric does not show any evidence of strong deformation. Nonetheless, the magnetization can not be primary since the measured inclinations are far too steep for the Permian/Triassic boundary. The estimated age of the acquisition of the paleomagnetic signal is Late Cretaceous. Although the results are negative in terms of magnetostratigraphy, they deserve attention from a tectonic point of view. The observations suggest that either the studied localities or the entire range of the Bükk Mts was involved in a post-Cretaceous (but pre-Miocene) counterclockwise rotation of about 40°

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Abstract

Paleomagnetic measurements were carried out on 163 independently oriented samples from 19 sites of the Bükk Mts and their northern, western and southern forelands. The aim was to correlate the sites with one of three Miocene rhyolite tuff horizons using the combination of paleomagnetic marker horizons (rotational events) and traditional magnetostratigraphy.

In contrast to the results of earlier studies in the southern Bükk foreland, which yielded only reversed polarity magnetizations, nearly half of the presently obtained paleomagnetic directions are of normal polarity. By their declinations they mostly belong to the middle tuff horizon, and only one belongs to the upper.

The paleomagnetic age assignment of the studied sites sometimes supports one or both of the classifications of Balogh (1964) and Pelikán et al. (2005). However, about one-third of the sites classified by these authors as upper or lower tuffs were shown to belong to the middle tuff complex.

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Acta Geologica Hungarica
Authors: Emő Márton, Davor Pavelić, Bruno Tomljenović, Péter Márton, and Radovan Avanić

This paper summarizes the paleomagnetic results that have been obtained for the Neogene of the Croatian part of the Pannonian Basin since 1995. The paleomagnetic investigations were carried out almost exclusively on sediments, which were deposited in widely differing environments. Most of the paleomagnetic directions can be considered as of pre-folding age, but some were clearly acquired diagenetically or even after deformation. This means that any future magnetostratigraphic study in the southern Pannonian Basin must be carried out with utmost care. Fortunately, the tectonic interpretation of the data is favorably affected by the fact that magnetizations of pre and post-folding ages show the same angles of declinations. They suggest that the entire Croatian part of the Pannonian Basin rotated counterclockwise, by about 30°, after the Early Pontian and before the Holocene. It is also remarkable that Ottnangian data from the Slavonian Mts do not indicate a Tisia-type clockwise rotation during the mid-Miocene.

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New K/Ar ages and paleomagnetic data connected with volcano-tectonic observations detected three intermediate (andesitic) and three acidic (dacitic-rhyolitic) magmatic phases. Cserhát magmatic activity occurred between 21-12 Ma. The timing of the initial and final acidic and intermediate phases may be connected with the Mátra volcano situated to the east. During the Badenian (15-14 Ma) the volcano-tectonic evolution was relatively independent in the Cserhát Mts. The third acidic and intermediate volcanic phases, which developed in the Lower Sarmatian, show similar features as the final phases of the Mátra volcano. Based on the major and trace element geochemistry the acidic rocks result from partial melting of the lower crust. Most of the intermediate volcanic rocks were generated from a rather homogeneous fluid-modified source (lithospheric), as triggered by an important heat transfer event. Initial melts sometimes experienced mixing or contamination in the lower or upper crust. This was a period of strong extensive tectonics. The rock of the second and third intermediate phases suggests minor fractional crystallization in the intermediary magma chamber(s).

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Systematic structural and anisotropy of magnetic susceptibility (AMS) measurements were carried out on Cenozoic clay-rich deposits from the Transdanubian Range, central part of the Alcapa Unit. The aim was to improve the knowledge of the Neogene tectonic evolution of the area and of the connection of the stress field and the magnetic fabric of the sediments. The measurements of AMS revealed dominant foliation with weak lineation for Middle Eocene-Lower Miocene sediments. The directions of AMS lineation are aligned either with the direction of NNE-SSW extension of a strike slip phase (30–19 Ma) or with the direction of NE-SW extension of the main rifting phase of the Pannonian Basin (19–14 Ma).The studied Late Miocene sediments have foliated AMS fabric, maximum and intermediate AMS directions are intermixed, and the AMS fabrics do not show any sign of tectonic deformation. In contrast, joints and faults were observed in the same rocks. Detailed structural analysis shows two extensional phases between ca. 10–4 Ma, with E-W to WNW-ESE and with NW-SE extension, respectively, and the youngest neotectonic strike-slip phase. The contrast between the presence of markers of brittle deformation and the absence of tectonically-induced AMS lineation is striking, since the same types of sediments in the South Pannonian basin show just the opposite. The explanation may be that northward-moving and CCW-rotating Adria caused strong compression in the southern Pannonian Basin, resulting in ductile deformation of the clay-rich sediments and systematic reorganization of AMS texture, while in our study area sediments of similar character and age were at a larger distance from the strongly deforming basin part.

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Abstract

Four paleosol layers indicating wet and moderate periods and five loess layers indicating dry and cold climate were separated by different methods. The following climate cycle model, based on the development of the sediment sequence created by the influence of climatic, geologic and geomorphologic phenomena, was established by detailed paleomagnetic studies (e.g. anisotropy of magnetic susceptibility (AMS), isothermal remanent magnetization (IRM), frequency dependence of magnetic susceptibility (κFD), etc.):

  1. A well-foliated magnetic fabric predominantly built up by multi-domain ferromagnetic minerals (magnetite, maghemite) was developed during the semi-arid (350–400 mm/y) and cold loessification period of the Pleistocene. The magnetic fabric can reflect the direction of dust deposition and/or the paleoslope.
  2. The accumulation period of dust was followed by the more humid (650 mm/y) pedogenic period indicated by the enrichment of superparamagnetic minerals and by the disturbed or inverse magnetic fabric developed during pedogenesis by different processes (e.g. leaching and/or bioturbation).
  3. The third period following the pedogenic period is the humid erosional phase indicated by the finely layered reworked loess. The magnetic fabric built up by multi-domain ferro- and superparamagnetic minerals is characterized by better-aligned directions of principal susceptibilities than in the wind blown material. Sheet wash and other waterlogged surface processes appeared in the fabric of these layers. This process is possibly connected to sudden, rare yet significant events with high precipitation and absence of vegetation.
  4. The cycle was closed by the beginning of the next dust accumulation period.
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Abstract

Ferromagnetic grains in airborne dust are important indicators of vehicle traffic, some industrial sources and combustion/heating. Settled dust consists mainly of diamagnetic material; therefore accessory ferromagnetic grains are readily indicated by magnetic measurements. In this paper settled dust samples collected on a monthly basis in the years 2008–2011 were studied. Non-destructive magnetic measurements were followed by geochemical and mineralogical analyses. In selected samples we identified airborne anthropogenic materials (e.g. silicate and magnetite spherules), minerals from the natural environment and organic material. Seasonally appearing materials (e.g. soot in winter, plant fragments and pollen in summer) increased the mass of the settled dust, but not the magnetic susceptibility. Thus, we realized that the generally interpreted mass susceptibility in environmental magnetic studies would not always appropriately characterize the magnetic pollution. In the interpretation we gave preference to total susceptibility because of its direct connection to the pollution, except in comparison with metal concentrations.

Trends in magnetic pollution were eventually analyzed for 19 sampling sites. Irrespective of the degree and source of the pollution the monthly variation curves of magnetic susceptibility exhibit a general maximum (March-April), followed by gradual decrease. A corresponding peak is observed in the amounts of dust. Both can be explained by re-suspension of dust settled in winter. The additional maxima in the mass of the dust (June and August, respectively) are probably due to contribution from vegetation and/or an artifact from algaecide. For three key sampling sites comparison was made between the concentrations of 12 metals and the respective mass susceptibilities and good linear correlation was found for Fe, Mn and Zn for all, for Cr, Cu, Pb, V, Ba, Sr and Zr for two sampling sites. Cd, which is enriched in all samples, does not correlate with the magnetic susceptibility.

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