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1

Hazardous radioactivity levels and heavy mineral concentrations in beach sediments of Lake Peipsi, northeastern Estonia

Järvelill J.-I., Koch R., Raukas A., Vaasma T.

Geologos

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2018

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Vol. 24, No. 1

1--12

EN

The present study discusses results of heavy mineral analyses and radioactivity of beach sediments of Lake Peipsi. Such analyses are commonly done globally, but had not yet been conducted for the fourth largest lake in Europe. The average heavy mineral content in Lake Peipsi beach sediments along the northern and western coast is higher than usual for Estonian coastal and Quaternary sediments. Concomitantly, elevated radioactivity levels have been measured in several places, with the highest concentrations observed at Alajõe (1885.5 Bq/kg), which is over five times more than the recommended limit. The aim of the present study is to find sites with higher radioactivity levels, because the northern coast of Lake Peipsi is a well-known recreational area.

2

Quaternary deposits and weathered bedrock material as a source of dangerous radon emissions in Estonia

Petersell V., Jüriado K., Raukas A., Shtokalenko M., Täht-Kok K.

Geologos

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2015

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Vol. 21, No. 2

139--147

EN

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/m3). In such high radon-risk areas the concentration of radon in soil-contained air ranges from 50 to 400 kBq/m3, in a few cases reaching up to 2,100 kBq/m3 exceeding the permitted level for residential areas. The situation is particularly 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 radioactive elements and they are weaker sources of radon.

3

Dating of the reo site (Island of Saaremaa, Estonia) with silicate and iron microspherules points to an exact age of the fall of the Kaali meteorite

Moora T., Raukas A., Stankowski W. T. J.

Geochronometria

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2012

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Vol. 39, no. 4

262-267

EN

Pollen analyses and radiocarbon dates from the bottom sediments in the Kaali main crater suggested that the crater group is at least 4000-5000 years old. Investigations of silicate impact micro-spherules in surrounding mires (Raukas et al. 1995) put the age about 7500-7600 yr BP. Recently we found both silicate and iron microspherules from organic sediments below well-dated beach ridge in Reo site what supports the conclusions that the most realistic age of the Kaali craters is 7600š50 14C BP (8335-8537 cal BP) and the meteorite fall was from SSE to NNW.

4

Chronology of the last deglaciation in the south-eastern Baltic Region on the basis of recent OSL dates

Raukas A., Stankowski W. T. J., Zelčs V., Šinkunas P.

Geochronometria

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2010

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Vol. 36

47-54

EN

The study of the deglaciation chronology in the south-eastern Baltic Region belonging to the outer zone of the last Pleistocene glaciation has a long history. The Finnish investigator H. Hausen (1913) who worked in the north-western portion of the East-European Plain at the beginning of the 20th century was the first to attempt a reconstruction of the course of glacial retreat during the last glaciation. At that time investigators had no physical dating methods and the time scale based on varvometric method, introduced by the Swedish geologist G. de Geer (1912) who divided the deglaciation history of Scandinavia into Daniglacial, Gotiglacial and Finiglacial, each of which had different palaeoglaciological conditions. During last decades different dating methods, including 14C, ESR, luminescence methods and 10Be techniques have been used, but they could not help essentially improve the existing stratigraphical charts and many problems of topical interest in the history of deglaciation have not been solved yet. During last years the first two authors have studied the suitability of OSL method for the geochronological purposes, paying the most attention to the waterlaid sediments. In the first step they have found the most promising genetical varieties of glaciofluvial sediments (glaciofluvial deltas and sandurs) and in this paper they widened the study area to all three Baltic states with close cooperation with Latvian and Lithuanian colleagues. The obtained results demonstrated, that not all mineral grains in the uppermost glaciofluvial and glaciolacustrine sediments were fully bleached during the last deglaciation. Probably the older sediments also influenced to the luminescence results. It means, that stratigraphic conclusions based on single dates or their small sets are inadmissible and in each case luminiscence dating requires a verification using other methods.

5

Luminescence dating of the Morasko (Poland), Kaali, Ilumetsa and Tsoorikmäe (Estonia) meteorite craters

Stankowski W. T. J., Raukas A., Bluszcz A., Fedorowicz S.

Geochronometria

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2007

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Vol. 28

25-29

EN

The TL dating of sinter crust of Morasko meteorites proves that the extraterrestrial matter fell about 5000 yr BP. Similar data were obtained for the Kaali impact. The OSL analyses show incomplete bleaching of old rock material especially in the Estonian craters. Almost all data obtained for the immediate impact area indicate ages younger than the Quaternary morphogenesis. The method used seems promising for determining the age of impacts and the origin of small depressions of unknown genesis.

6

Influence of sedimentological composition on OSL dating of glaciofluvial deposits : examples from Estonia

Raukas A., Stankowski W.

Geological Quarterly

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2005

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Vol. 49, No. 4

463--470

EN

We assess the suitability of luminescence (TL and OSL) dating techniques for establishing a precise Late Pleistocene chronology for the northern Baltic area, and show on the basis of the fine sand/coarse silt fraction of subaqueous deposits, how sedimentological composition influences the dates obtained. Turbidity, loading by fine suspended material, water depth, velocity of outwash streams and transport length, and also perhaps rapid night-time sedimentation and incorporation of older, unbleached particles are factors that variably influence the extent of bleaching of the luminescence signal, and thus, cause variability of dates obtained. Alongside reliable dates for "late-glacial" deposits between 11 000-15 000 OSL years BP, many entirely unreliable dates from 8 000 ±300 to 114 000 ±8 000 OSL years BP have been obtained. This means that the age determination of glaciofluvial deposits is extremely difficult in practice. This applies particularly to intermorainic sediments, the exact genesis of which is unknown. The paper is addressed to the investigators wishing to use luminescence dating techniques to establishing the Pleistocene chronostratigraphy of glaciofluvial deposits.

7

Sustainable management of mineral resources, soil cover and geosites in Estonia

Raukas A., Tavast E.

Polish Geological Institute Special Papers

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2004

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Vol. 13

191-197

EN

Nature conservation and protection of geological heritage have long traditions in Estonia. Already in 1910 the first nature reserve was established, and in 1935 the first nature protection law approved. In 1995, the Parliament of Estonia adopted the Act of Sustainable Development and in 1996, the Estonian Environmental Strategy was approved by the Government. Although small in area, Estonia is relatively rich in mineral resources (oil shale, phosphorites, peat, building materials, etc.), which together with large forested areas (about 50% of the territory) and high productivity agriculture have been and will be the basis for economy, and account for a substantial share in the Gross National Product. During the Soviet occupation, the soil cover of Estonia was subjected to severe degradation. About 1.9% of Estonian territory was used for military objects and these sites are still highly contaminated. Sharp increase in the exploitation of mineral resources has caused ever worsening impact on the environment. In the independent Republic of Estonia, nature conservation and mineral wealth protection gained importance of the first rate and the situation has improved.

PL

Konserwacja przyrody i ochrona dziedzictwa geologicznego mają już długą tradycję w Estonii. Pierwszy rezerwat przyrody został ustanowiony w 1910 r. W 1935 r. przyjęto pierwszą ustawę o ochronie przyrody. W 1995 r. parlament Estonii przyjął ustawę o zrównoważonym rozwoju, a w 1996 r. rząd zatwierdził Estońską Strategię Środowiskową. Chociaż niewielka, Estonia jest stosunkowo bogata w zasoby mineralne (łupki bitumiczne, fosforyty, torf, materiały budowlane itd.). Surowce te, wraz dużymi obszarami leśnymi (około 50% terytorium kraju) oraz wysoko produktywnym rolnictwem, będą podstawą gospodarki i wniosą duży wkład do dochodu narodowego. Podczas okupacji sowieckiej gleby Estonii poddane były poważnej degradacji. Około 1,9% terytorium Estonii wykorzystywane było na obiekty militarne. Tereny te są nadal silnie zanieczyszczone. Silny wzrost wydobycia surowców mineralnych także spowodował niekorzystny wpływ na środowisko. W niepodległej Republice Estonii konserwacja przyrody i ochrona bogactw mineralnych uzyskały pierwszorzędne znaczenie i ich sytuacja uległa poprawie.

8

The Holocene sedimentation history of Lake Vortsjärv, central Estonia

Raukas A., Tavast E.

Geological Quarterly

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2002

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Vol. 46, No 2

199-206

EN

Lake Vortsjärv is one of the biggest lakes in Eastern Europe and possesses a complex geological history. Bottom deposits consist mostly of fine sand and silt, accompanied with sapropel (up to 9 m thick) and lake marl (up to 8 m thick). In places, especially in the northern part where the bottom deposits are absent, varved clay or till are exposed in the lake basin. In the southern part of the lake the deposits are much thicker, indicating a gradual rise of water-level. Like the majority of lakes in the Northern Hemisphere, Lake Vortsjärv possesses a more open eastern and a more swampy and overgrown western bank. Shore types and the lithological composition of shore sediments are varied and highly controlled by the bedrock and glacial deposits. Long-shore transport of sediments is limited. The mineral composition of bottom sediments shows great qualitative and quantitative variability which relates to the grain-size and petrography of the parent deposits. Organic-rich sapropel can be used in agriculture and evidently also for medicinal purposes.

9

Application of the malacological method to solve stratigraphic and palaeogeographical problems on the example of the West Estonian coast

Tavast E., Raukas A.

Oceanological Studies

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1999

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Vol. 28, No. 3-4

45-57

EN

Subfossil mollusc shells are some of the most common remains in marine Quaternary sediments and can give precise information about the palaeogeographic conditions of palaeobasins. This is primarily due to their good preservation and the large number of species. They are widespread in nearly all biotopes and often occur in beach deposits, now lying at some distance inland above the present-day sea level. Molluscs are susceptible to the environment they inhabit and can therefore provide information about the substrata, water depth, salinity, temperature, isotopic composition of water and water-level fluctuations in ancient bodies of water. Molluscs can also be used in the stratigraphic subdivision and correlation of sediments. Conditions for the investigation of subfossil mollusc fauna in Estonia are extremely good. The bedrock in the coastal area consists mainly of limestones and dolomites, which are covered with carbonaceous till and limy aqueoglacial deposits. In Estonian offshore waters molluscs had suitable living conditions and sufficient material to build up the shells. In Estonia the Holocene mollusc fauna is much better preserved than in neighbouring countries.