The Tunguska airburst occurred on June 30, 1908 and it was most likely caused by the impact of the Tunguska cosmic body (TCB). It is not clear what the origin of the TCB was as no impact craters or possible body remains have been found to date. We studied the possible molten fragments of the TCB found in lacustine sediments of Zapovednoe Lake, a water body which is located ~60 km west from the airburst epicentre. Lake sediment cores which were retrieved from the lake contained an event layer dated to 1908–1910 CE. This layer included microscopical molten fragments and anomalous composition. Three short cores (ZP1, ZP2, ZP3) were extracted in the central part of Zapovednoe Lake using a Kajak gravity corer. We used an X-ray fluorescence spectroscopy (XRF) and Scanning Electron Microscopy (SEM) for lake sediment characterization. Magnetic spherules (MSPs) and other magnetic grains were extracted from ZP1 by standard magnetic separation technique and all MSPs were identified with SEM and characterized using elemental microanalysis. We performed XRF analyses of 2 or 5 mm thick slices of the sediment cores and evaluated the concentrations and ratios of individual elements. Sediment samples of ZP2 were used for core dating, using gamma spectrometry for the specific activity of 210Pb, 137Cs, and 226Ra isotopes similar to the record from nearby Suzdalevo Lake. Radioisotope activities revealed the age consistent with the year 1908 CE. The gamma spectrometry results were in good agreement with the XRF measurements, where the event layer had increased concentrations of lithogenic elements, such as Mg, Al, Si, S, K, Ca, Ti, Fe, Cu and Mn. The SEM analysis revealed that molten fragments were indeed found among the potential MSPs extracted from the event layer and adjacent layers. These spherical melts were rich in iron and most of them were found at depth corresponding to the event layer. Only a small portion of MSPs was found in the adjacent layers. Our results revealed the presence of the TCB airburst event layer. The anomalous event layer resulted from increased erosion in the Zapovednoe Lake catchment. However, massive tree falls and subsequent wildfires from the airburst likely contributed to the anomalous elemental composition of the lake sediment as well. We found for the first time in lake sediments preserved MSPs which come from the melts produced by the TCB airburst and may contain an extraterrestrial material.

Here we present paleomagnetic investigations on sediments from Upper Toporowy Lake (local name: Toporowy Staw Wyżni), an infilled lake located on the Polish side of the Tatra Mountains. The sampling was done using a peat corer. A total of 49 paleomagnetic samples were acquired in two parallel sediment cores (~50 cm each). Characteristic remanent magnetizations of the samples from the first core have shallower inclinations while the second have values near the expected geocentric axial dipole model. We note correlation of our inclination data with published records from Southern Europe records of an Early Holocene age sediment. Since a Holocene paleomagnetic master curve is absent for Central Europe, the data of this study represent a first step in constructing a master curve that will contribute to global magnetic models and dating of sediments.Acknowledgments: The research was supported by the Charles University Grant Agency (project no. 265321).

In 1908, a massive explosion known as the Tunguska Event (TE) occurred in Central Siberia. However, its origin remains widely discussed and environmental impacts are not known in detail. We investigated evidence of the TE in sediments of Suzdalevo Lake, which is located near the explosion epicenter. According to local nomads (Evenkis), Suzdalevo Lake did not exist before the TE and was considered as a possible impact-origin water body. However, apart from oral testimony, there is no evidence of the lake formation process. Two short sediment cores (SUZ1 and SUZ3) were retrieved from the lake and dated using 210 Pb and 137 Cs. The sedimentary record was characterized using magnetic susceptibility, X-ray fluorescence, and the screening for melted magnetic microspherules. To study possible effects of the TE on the lake ecosystem, we performed diatom and freshwater fauna remains analyses. Results indicate that the lake contains sediments that originated before the TE and thus its formation was not related to the impact. Also, the depth to diameter ratio of the lake basin is too low (<1/100) for a young impact crater. In one of the two cores (SUZ1), we documented distinct changes in the lake-catchment ecosystem that occurred within a 5-cm-thick depth interval calculated for the best fit depths for the year 1908 using three alternative age-depth models (CRS, CIC, CFCS), namely, increases in terrestrial matter input (abundant fine plant macroremains, peaks in magnetic susceptibility and the Sr to Rb ratio) and taxonomic diversity and relative abundance of benthic taxa. The shifts in aquatic biota assemblages were likely caused by nutrient supply and improved water column mixing following a catchment disturbance. Nevertheless, precise timing of the observed abrupt changes in relation to the TE is not clear due to uncertainty of the 210 Pb dating method and absence of melted magnetic microspherules or an event layer. The disturbance signals in the proxy data may postdate the TE. Our results demonstrate potential usefulness of the paleolimnological approach to understand the possible environmental consequences of the TE and similar events elsewhere.

Near 12,850 cal. yr. BP, the Younger Dryas cooling (YD) abruptly reversed the warming trend from the last glacial to the present interglacial at high northern latitudes. Subsequent YD-onset-related changes, including hydroclimate shifts, affected ecosystems and human societies worldwide. The main YD trigger – e.g., a massive meltwater input into the North Atlantic Ocean, volcanic gas aerosols from the cataclysmic Laacher See (LS) eruption in the Volcanic Eifel, Germany, or an extraterrestrial body impact or airburst – remains widely debated and unclear. We have obtained lake sediment cores from three sites located in the Bohemian Forest Mts., Czechia-Germany-Austria border area (distance of 450–470 km from the LS volcanic crater). The characteristic LS tephra glass shards were documented in all three cores using X-ray fluorescence scanning, magnetic susceptibility measurements, and direct observation by scanning electron microscopy, and their concentrations were quantified by a TESCAN Integrated Mineral Analyzer (TIMA). Our geochemical results show the closest match with the so-called MLST-B phreatomagmatic phase of the LS eruption. Moreover, a significant amount of LS-(crypto)tephra-related phosphorus (up to 0.15%), often the limiting nutrient in both terrestrial and freshwater ecosystems, was found in the sediments. The discovery of the LS volcanic ash in the Bohemian Forest points to a wider distribution of this (crypto)tephra than has been known so far (evident transport also in the eastern direction). It opens up new potential for tephrochronologically supported research of Late-glacial sediments in eastern Central Europe and exploring the role of the event in human prehistory. In addition to the LS cryptotephra, we observed magnetically extracted iron-rich microspherules with signs of high-temperature melting and quenching in all studied sediment cores. Their maxima (3–36 objects per 1 g of dry sediment) were situated 2.2–3.1 cm above peaks in the LS tephra shard concentrations. Such exotic objects were reported from numerous sites on several continents where more impact-related proxies were documented by proponents of the YD impact hypothesis. Based on this evidence, we hypothesize that the Allerød-Younger Dryas transition in Central Europe was likely affected by more than one extreme event. The LS eruption was followed by an event during which the iron-rich microspherules were formed. The ongoing study is supported by the Czech Grant Foundation (20-08294S – PROGRESS).

Near 12,850 cal. yr. BP, the Younger Dryas cooling (YD) abruptly reversed the warming trend from the last glacial to the present interglacial at high northern latitudes. Subsequent YD-onset-related changes, including hydroclimate shifts, affected ecosystems and human societies worldwide. The main YD trigger – e.g., a massive meltwater input into the North Atlantic Ocean, volcanic gas aerosols from the cataclysmic Laacher See (LS) eruption in the Volcanic Eifel, Germany, or an extraterrestrial body impact or airburst – remains widely debated and unclear. We have obtained lake sediment cores from three sites located in the Bohemian Forest Mts., Czechia-Germany-Austria border area (distance of 450–470 km from the LS volcanic crater). The characteristic LS tephra glass shards were documented in all three cores using X-ray fluorescence scanning, magnetic susceptibility measurements, and direct observation by scanning electron microscopy, and their concentrations were quantified by a TESCAN Integrated Mineral Analyzer (TIMA). Our geochemical results show the closest match with the so-called MLST-B phreatomagmatic phase of the LS eruption. Moreover, a significant amount of LS-(crypto)tephra-related phosphorus (up to 0.15%), often the limiting nutrient in both terrestrial and freshwater ecosystems, was found in the sediments. The discovery of the LS volcanic ash in the Bohemian Forest points to a wider distribution of this (crypto)tephra than has been known so far (evident transport also in the eastern direction). It opens up new potential for tephrochronologically supported research of Late-glacial sediments in eastern Central Europe and exploring the role of the event in human prehistory. In addition to the LS cryptotephra, we observed magnetically extracted iron-rich microspherules with signs of high-temperature melting and quenching in all studied sediment cores. Their maxima (3–36 objects per 1 g of dry sediment) were situated 2.2–3.1 cm above peaks in the LS tephra shard concentrations. Such exotic objects were reported from numerous sites on several continents where more impact-related proxies were documented by proponents of the YD impact hypothesis. Based on this evidence, we hypothesize that the Allerød-Younger Dryas transition in Central Europe was likely affected by more than one extreme event. The LS eruption was followed by an event during which the iron-rich microspherules were formed. The ongoing study is supported by the Czech Grant Foundation (20-08294S – PROGRESS).

LAKE D. Vondrák, R. Kavková, B. Chattová, V. Goliáš, M. Takáč, E. Švecová, R. Štorc, G. Kletetschka, Institute for Environmental Studies, Charles University, Benátská 2, CZ-12801 Prague 2, Czechia, daniel.vondrak@natur.cuni.cz, Institute of Hydrogeology, Engineering Geology and Applied Geophysics, Charles University, Albertov 6, CZ-12843 Prague 2, Czechia, Department of Botany and Zoology, Masaryk University, Kotlářská 2, CZ-61137 Brno, Czechia, Institute of Geochemistry, Mineralogy and Mineral Resources, Charles University, Albertov 6, CZ12843 Prague 2, Czechia, Geophysical Institute, University of Alaska, Fairbanks, 903 N Koyukuk Drive, USA.

Geomagnetic fields interfere with the accumulation of iron in the human brain. Magnetic sensing of the human brain provides compelling evidence of new electric mechanisms in human brains and may interfere with the evolution of neurodegenerative diseases. We revealed that the human brain may have a unique susceptibility to conduct electric currents as feedback of magnetic dipole fluctuation in superparamagnetic grains. These grains accumulate and grow with brain aging. The electric feedback creates an electronic noise background that depends on geomagnetic field intensity and may compromise functional stability of the human brain, while induced currents are spontaneously generated near superparamagnetic grains. Grain growth due to an increase of iron mobility resulted in magnetic remanence enhancement during the final years of the studied brains.

The chemical variability, degree of radiation damage, and alteration of xenotime from the Písek granitic pegmatites (Czech Republic) were investigated by micro-chemical analysis and Raman spectroscopy. Dominant large xenotime–(Y) grains enriched in U, Th and Zr crystallized from a melt almost simultaneously with zircon, monazite and tourmaline. Xenotime is well to poorly crystalline depending on its U and Th contents. It shows complex secondary textures cutting magmatic growth zones as a result of its interaction with F,Ca,alkali-rich fluids during the hydrothermal stage of the pegmatite evolution. The magmatic xenotime underwent intense secondary alteration, from rims inwards, resulting in the formation of inclusion-rich well crystalline xenotime domains of near end-member composition. Two types of recrystallization were distinguished in relation to the type of inclusions: i) xenotime with coffinite-thorite, cheralite and monazite inclusions and ii) xenotime with zirconcheralite and zircon inclusions. Additionally, inner poorly crystalline U,Th-rich xenotime domains were locally altered, hydrated, depleted in P, Y, HREE, U, Si and radiogenic Pb, and enriched in fluid‐borne cations (mainly Ca, F, Th, Zr, Fe). Interaction of radiation-damaged xenotime with hydrothermal fluids resulted in the disturbance of the U–Th–Pb system. Alteration of radiation-damaged xenotime was followed by intensive recrystallization indicating the presence of fluids >200 °C. Subsequently other types of xenotime formed as a consequence of fluid-driven alteration of magmatic monazite, and Y,REE,Ti,Nb-oxides or crystallized from hydrothermal fluids along cracks in magmatic monazite and xenotime.

Texturni charakteristiky, chemicka variabilita a stupeň krystalinity xenotimu-(Y) z granitickeho pegmatitu Věžna I byly zkoumany mikrochemickou analýzou a Ramanovou spektroskopii.

Přispěvek prezentuje texturni, parageneticke a chemicke charakteristiky primarniho xenotimu-(Y) z albitove jednotky beryl-columbitoveho granitickeho pegmatitu Věžna I.

Xenotime-(Y) from the albite unit of the beryl-columbite Pisek granitic pegmatites (Czech Republic) have been studied with focus on contents of U and Th and degree of metamictization via Raman spectroscopy.

Xenotime-(Y) from the albite unit with abundant tourmaline of the beryl-columbite Pisek granitic pegmatites have been studied with focus on monitoring of the mineral assemblages, successional position, chemical variability of xenotime, the input of U, Th and REE elements in the structure of the xenotime and to determine their substitution mechanisms.

Xenotime-(Y) have been studied from Pisek granitic pegmatites at the following localities: “U Udražskeho obrazku” quarry, “U Noveho rybnika” quarry, and “Obrazek I.” quarry. Xenotime from the localities around Pisek have not been studied yet.