Magnetic fabric of Bulgarian loess sediments derived by using various sampling techniques

The anisotropy of low field magnetic susceptibility has been studied for seven outcrops of loess sediments in North-Eastern Bulgaria. Different sampling methods were applied in order to choose the best technique for obtaining the primary magnetic fabric of such unconsolidated sediments. AMS results show significant changes in the petrofabric of samples collected by the first technique which disturbs the original sedimentary fabric. The second applied technique does not cause such a strong deformation but some disturbance of the magnetic fabric is probable. Typical sedimentary fabric is obtained from hand samples and it is therefore concluded that this represents the best method for obtaining reliable AMS results from soft sediments

Transformations of magnetic mineralogy in rocks revealed by difference of hysteresis loops measured after stepwise heating: theory and case studies

International audienceA new approach for tracking mineralogical alterations during laboratory stepwise heating experiments is proposed. It uses the hysteresis loop obtained as a difference between the loops measured after thermal treatment at two different consecutive temperatures. Depending on the nature of the mineralogical alterations (the formation of a new ferrimagnetic phase from a paramagnetic one, the thermal transformation of the originally present ferrimagnetic phases, grain size variation) and on their relative intensities, it is possible to distinguish between different cases. The examples shown reveal the significant alteration of magnetic carriers at low temperatures (up to 200°C) which usually is not identified by thermomagnetic analysis of magnetic susceptibility. The low temperature alteration of the remanence carriers has important consequences for the reliability and suitability criteria of palaeointensity determinations

EVALUATION OF SOIL CONTAMINATION DEGREE IN THE REGION OF MARITZA-EAST THERMAL POWER PLANTS USING MAGNETIC METHODS

Pilot study on soil contamination degree around the Maritza East thermal power plants, evaluated through applying magnetic methods, is presented. The magnetometry method is based on the well-established fact that anthropogenically contaminated with fly ashes soils display enhanced magnetic susceptibility, as well as other specific magnetic characteristics. Results from the magnetic investigations carried out in our study evidence significant soil contamination near the pollution sources and decreasing degree of anthropogenic load further away. The method applied is economically more efficient compared to classical physical and chemical methods for evaluation of soil contamination

Emplacement and fabric-forming conditions of plutons from structural and magnetic fabric analysis: A case study of the Plana pluton (Central Bulgaria)

International audienceThe relationship between intensity parameters, such as the corrected anisotropy degree P‧ and mean susceptibility Km for plutons with similar magnetic mineralogy, yields a criterion to determine the origin of their magnetic fabric: for a same mineralogy, the higher the P‧ values for the same mean susceptibility Km (irrespective of its absolute value) the higher tectonic effect was possible. Using this criterion, comparison of the magnetic fabric of the Upper Cretaceous mid- to shallow crustal level Plana pluton with that of other small Upper Cretaceous plutonic bodies in Sredna Gora Zone (Central and Southeast Bulgaria) highlights the structural evolution of the Plana pluton. The central part of Plana pluton and its southwest, west and east margins have preserved their emplacement fabric. Along its northern contact the pluton is affected by the last movements within the Okol Shear Zone where high-temperature S/L mylonites developed. The fabric of the pluton at its southeastern border was disturbed during the intrusion of the neighboring Gutsal pluton. The similarity in the orientation of magmatic and magnetic structures preserved in the central and southern parts of the Plana pluton and the transition from magmatic to high-temperature superimposed foliations and lineations at its north contact point to a composite superimposed shear-induced and emplacement-related magmatic magnetic fabric. Nearly vertical orientation of magnetic and magmatic foliations and lineations from the undeformed parts of the pluton shows a process of vertical magma rising and emplacement. The sub-vertical high-temperature solid-state mylonitic foliation and dip-parallel stretching lineation in the pluton along its northern contact reveals the transpression nature of the deformation in the vicinity of Okol Shear Zone with a strong pure shear component. The smooth transition between the deformed and undeformed parts of Plana pluton reveals the syn-kinematic character of the emplacement

Holocene palaeoenvironmental conditions in NE Bulgaria uncovered by mineral magnetic and paleomagnetic records of an alluvial soil

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Relations between the emplacement and fabric-forming conditions of the Kapitan-Dimitrievo pluton and the Maritsa shear zone (Central Bulgaria): magnetic and visible fabrics analysis

International audienceThe Kapitan-Dimitrievo pluton was emplaced within the 15 km wide Maritsa shear zone during the Late Cretaceous. It has well-known U-Pb zircon age (78.54 ± 0.13 Ma) and appears as a late-syntectonic intrusion that marked the last ductile deformation in the Maritsa shear zone. Magnetite is believed to be the main carrier of the magnetic fabric in this pluton, and crystallized mainly late, after the main rock-forming minerals. Two fabrics are recorded, a visible syn-magmatic fabric (due to magma flow) and magnetic late-magmatic fabric (related to regional stresses). Although different, both are mainly related to the shearing along this shear zone. These results constrain in age the dextral strike-slip controlled emplacement and evolution of the Late Cretaceous plutons from Central Bulgaria

Magnetism of outdoor and indoor settled dust and its utilization as a tool for revealing the effect of elevated particulate air pollution on cardiovascular mortality

International audienceSettled indoor and outdoor dusts in urban environment represent an important source of secondary pollution. Magnetic characteristics of the settled dust from six cities in Bulgaria are explored, allowing comparison on a national (country) scale. Monthly variations of the mass-specific magnetic susceptibilities (cindoor) and (coutdoor) and calculated dust loading rates for a period of 17 months do not show seasonal variability, probably due to the dominant role of traffic-related emissions and soil-derived particles in the settled dust. The main magnetic mineral is magnetite, present as spherules and irregular particles of pseudo-singledomain grain sizes. Systematically lower remanence coercivities are obtained for outdoor dusts when compared with the corresponding indoor samples, implying that penetration of smaller particles of ambient origin indoors is the main source of the indoor dust. Mean yearly values of the ratio (cindoor/coutdoor) for each city show statistically significant correlation with mortality due to cardiovascular diseases. This ratio reveals the source- and site-specific importance of the anthropogenically derived toxicogenic fraction. Heavy metal content of the settled dust is related to the contribution from several pollution sources (soil-derived, combustion and industrial), discriminated through analysis of principal components. SEM/EDX analyses reveal abundant presence of anthopogenic Fe-containing spherules, irregular particles and diesel exhaust conglomerates. High molecular weight polyaromatic hydrocarbons (PAH) dominate the total PAH content of the outdoor dust samples. The observed linear correlation between total PAH content, coercivity of remanence and the ratio Mrs/c suggest either adsorption of PAHs on iron oxide particles and especially magnetite, or emission related increase in total PAH concentration along with a decrease of effective magnetic grain size of the accompanying magnetic fraction

Geomagnetic field variations as determined from Bulgarian archaeomagnetic data. Part II:The last 8000 years

The knowledge about past secular variations of the geomagnetic field is achieved on the basis of archaeomagnetic researches of which the Bulgarian studies form an extended data set. In Part I (Kovacheva and Toshkov, 1994), the methodology used in the Sofia palaeomagnetic laboratory was described and the secular variation curves for the last 2000 years were shown. In Part II (this paper), the basic characteristics of the prehistoric materials used in the archaeomagnetic studies are emphasised, particularly in the context of the rock magnetic studies used in connection with palaeointensity determinations. The results of magnetic anisotropy studies of the prehistoric ovens and other fired structures are summarised, including the anisotropy correction of the palaeointensity results for prehistoric materials, different from bricks and pottery. Curves of the direction and intensity of the geomagnetic field during the last 8000 years in Bulgaria are given. The available directional and intensity values have been used to calculate the variation curve of the virtual dipole moment (VDM) for the last 8000 years based on different time interval averages. The path of virtual geomagnetic pole (VGP) positions is discussed

Early Neolithic settlement Yabalkovo (Maritsa valley, Bulgaria) in the context of archaeomagnetic studies: Раннонеолитното селище Ябълково (долината на Марица) в контекста на археомагнитно проучване

Five fired clay structures from the Northeast sector of the Early Neolithic settlement of Yabalkovo in the Maritsa valley, Bulgaria were a subject of an archaeomagnetic investigation. The results of the detailed rock-magnetic experiments carried out show that the collected materials are suitable for archaeomagnetic study and reliable determinations for past geomagnetic field elements can be obtained. According to the mean values calculated for the ancient geomagnetic field direction and intensity, two different periods of time can be undoubtedly distinguished for the investigated structures. This coincides exactly with the two chronological horizons suggested by the excavators. The archaeological observations point that the oven in sq. K36, the hearth in sq. F16 and the hearth in sq. H31 are related to Horizon II, while the hearths in sq. I31 and sq. F18 are connected with Horizon I.Based on the Bulgarian reference curves (latest version), the following archaeomagnetic dating intervals are received: Yabalkovo – Horizon II – (5685–5489 BC) and Yabalkovo – Horizon I – (5472–5427 BC). These results agree well with the archaeological data that structures from Horizon II are older than structures from Horizon I. The existing 14C dates (for materials taken mainly from the Southwest sector of the settlement) show considerably older dating intervals but they are not able to differentiate chronologically the different structures. The obtained archaeomagnetic determinations for Yabalkovo are compared with these available for other archaeomagnetically studied Early Neolithic sites from Bulgaria and Northern Greece. This comparison indicates that Horizon II of Yabalkovo can be synchronised with the younger layers of Kovatchevo (Karanovo I), Stara Zagora (Karanovo II) and Dobriniste. Horizon I of Yabalkovo is chronologically comparable with Horizons VII+VIII of Samovodene and Avgi (Nortern Greece)