Geologos, 2015, 21, 2


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    Quaternary deposits and weathered bedrock material as a source of dangerous radon emissions in Estonia
    (Instytut Geologii UAM, 2015-06) Petersell, Valter; Jüriado, Krista; Raukas, Anto; Shtokalenko, Mihkel; Täht-Kok, Krista
    The risk of dangerous radon emissions in Estonia is high, being among the highest in Europe. In almost 33 per cent of Estonian land area, the content of radon in soil-contained air exceeds the safe limit for unrestricted construction (50 kBq/m 3 ). In such high radon-risk areas the concentration of radon in soil-contained air ranges from 50 to 400 kBq/m 3 , in a few cases reaching up to 2,100 kBq/m 3 exceeding the permitted level for residential areas. The situation is particu -larly serious in the northernmost part of the country, where uranium-rich graptolite argillite (Dictyonema shale) and the Obolus phosphorite are close to ground surface and their particles are constituent parts of Quaternary deposits. Radon emissions from bedrock have been investigated in detail, but to date Quaternary strata as a source of radon emissions are poorly studied. According to our measurements the highest concentrations of radon are related to tills containing clasts and fines of graptolite argillite and phosphorite. Glacial deposits include also granitoidal material, containing U, Th and K, which have been transported by glaciers from the outcrop areas of crystalline basement rocks in Finland and the Gulf of Finland. Due to weathering, outwash and repeated redeposition other genetic types are poorer in radioac -tive elements and they are weaker sources of radon.
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    Transport conditions of mountain-surging glaciers as recorded in the micromorphology of quartz grains (Medvezhiy Glacier, West Pamir)
    (Instytut Geologii UAM, 2015-06) Muzińska, Agnieszka
    In order to reproduce the conditions under which sediments were transported in surging glaciers, samples were taken from the margin and foreland of the surge Medvezhiy Glacier situated in West Pamir (Tajikistan). They were subjected to an analysis of rounding and frosting of quartz sand grains (0.8–1.0 mm) and of grain surface micromorphology under scanning electron microscope (SEM). Results obtained showed intense chemical weathering occurred in the majority of quartz grain surfaces, marked in the form of etching and precipitation. Frequencies of microstructures of glacial or -igin were low; individual microstructures were visible on single grains. A predominance of the crushing process over abrasion in transformation of quartz grains was noted. The commonest microstructures connected with a surge-glacier environment were large and small conchoidal fractures. However, grains with primary features not connected with a glacial environment were equally common. The majority of the grains examined showed features of multiple cycles of mechanical and chemical weathering forming a microtexture under various conditions (overprinting). Common features of grains from surging glaciers are also breakage blocks of >10µm, which depend of the phase of separation of the grain from the rock or on thermal changes in the glacier’s foreland.
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    Roundness and matt degree of quartz grain surfaces in (fluvio-)glacial deposits of the Pomeranian Stage (Weichselian) in northeast Germany
    (Instytut Geologii UAM, 2015-06) Górska-Zabielska, Maria
    Glacial tills and fluvioglacial sediments deposited by the ice-sheet during the Pomeranian Stage (Weichselian) in north -east Germany have been examined in terms of the degree of abrasion, rounding and frosting of quartz grain surfaces in order to determine the conditions and processes that occurred in the alimentation environment of the fine-grained material, as well as during transport. Strata in the glaciomarginal zone and the hinterland of the Pomeranian Stage in the area represent diverse lithofacies, but have similar textural features. These features illustrate mainly that a high-en -ergy aquatic environment had reacted with glacial deposits prior to their inclusion into the ice mass and deposited in the area covered by the Odra lobe. The lack of regional diversification in the character of quartz grain surfaces in glacial deposits between the German part of the Odra lobe and the remainder of the area analysed is recorded solely in the morphological dimension, i.e. the outlet fragment of the ice-front’s course, but not in textural features of the sediments.
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    Reconstruction of sediment provenance and transport processes from the surface textures of quartz grains from Late Pleistocene sandurs and an ice-marginal valley in NW Poland
    (Instytut Geologii UAM, 2015-06) Woronko, Barbara; Pisarska-Jamroży, Małgorzata; van Loon, A.J. (Tom)
    During the Pomeranian phase of the Weichselian glaciation (~17–16 ka), the Toruń-Eberswalde ice-marginal valley (NW Poland and easternmost Germany) drained water from the Pomeranian ice sheet, while intensive aeolian process -es took place across Europe in the foreland of the Scandinavian ice sheet (‘European Sand Belt’). The micromorphology of the quartz grains in the Toruń-Eberswalde ice-marginal valley shows no traces of these aeolian processes, or only vague signs of aeolian abrasion. This is unique among the aeolian sediments in other Pleistocene ice-marginal valleys in this part of Europe. The study of the surfaces of the quartz grains shows that the supply of grains by streams from the south was minimal, which must be ascribed to the climate deterioration during the Last Glacial Maximum, which resulted in a decrease of the discharge of these extraglacial rivers to the ice-marginal valley.
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    Climate evolution during the Pleniglacial and Late Glacial as recorded in quartz grain morphoscopy of fluvial to aeolian successions of the European Sand Belt
    (Instytut Geologii UAM, 2015-06) Woronko, Barbara; Zieliński, Paweł; Sokołowski, Robert Jan
    We present results of research into fluvial to aeolian successions at four sites in the foreland of the Last Glacial Maxi-mum, i.e., the central part of the “European Sand Belt”. These sites include dune fields on higher-lying river terraces and alluvial fans. Sediments were subjected to detailed lithofacies analyses and sampling for morphoscopic assessment of quartz grains. Based on these results, three units were identified in the sedimentary succession: fluvial, fluvio-aeolian and aeolian. Material with traces of aeolian origin predominate in these sediments and this enabled conclusions on the activity of aeolian processes during the Pleniglacial and Late Glacial, and the source of sediment supply to be drawn. Aeolian processes played a major role in the deposition of the lower portions of the fluvial and fluvio-aeolian units. Ae -olian material in the fluvial unit stems from aeolian accumulation of fluvial sediments within the valley as well as parti -cles transported by wind from beyond the valley. The fluvio-aeolian unit is composed mainly of fluvial sediments that were subject to multiple redeposition, and long-term, intensive processing in an aeolian environment. In spite of the asynchronous onset of deposition of the fluvio-aeolian unit, it is characterised by the greatest homogeneity of structural and textural characteristics. Although the aeolian unit was laid down simultaneously, it is typified by the widest range of variation in quartz morphoscopic traits. It reflects local factors, mainly the origin of the source material, rather than climate. The duration of dune-formation processes was too short to be reflected in the morphoscopy of quartz grains.
Uniwersytet im. Adama Mickiewicza w Poznaniu
Biblioteka Uniwersytetu im. Adama Mickiewicza w Poznaniu
Ministerstwo Nauki i Szkolnictwa Wyższego