Tiit Hang

A Late Weichselian geomagnetic record from Lake Tamula, SE Estoniah

Abstract A Late Weichselian palaeomagnetic record has been obtained from sediments deposited in Lake Tamula in SE Estonia, and detailed mineral magnetic studies have been undertaken to identify the carriers of remanence. The palaeomagnetic record can be compared to records from southern Sweden and Karelia in NW Russia. A westerly declination swing in the Swedish and Russian records, between 13,300 and 12,100 calender years BP is also found in the Lake Tamula sediments. Based on a floating varve chronology in the varved clay unit the deglaciation can be dated to 14,400 calender years or 12,600 radiocarbon years BP. The palaeomagnetic evidence supports the presently accepted deglaciation chronology of southeastern Estonia, which is based on radiocarbon dates of the Haanja and Otepaa ice‐marginal stages. Sandgren, P., Hang, T. & Snowball, I.F., 1997: A Late Weichselian geomagnetic record from Lake Tamula, SE Estonia. GFF, Vol. 119 (Pt. 4, December), pp. 279–284. Stockholm. ISSN 1103–5897.

Palaeogeographic Model for the SW Estonian Coastal Zone of the Baltic Sea

The authors combined geological, geodetic and archaeological shore displacement evidence to create a temporal and spatial water-level change model for the SW Estonian coast of the Baltic Sea since 13,300 cal. years BP. The Baltic Sea shoreline database for Estonian territory was used for the modelling work and contained about 1,200 sites from the Baltic Ice Lake, Ancylus Lake and Littorina Sea stages. This database was combined with a shore displacement curve from the Parnu area (in SW Estonia) and with geodetic relative sea-level data for the last century. The curve was reconstructed on the basis of palaeocoastline elevations and radiocarbon-dated peat and soil sequences and ecofacts from archaeological sites recording three regressive phases of the past Baltic Sea, interrupted by Ancylus Lake and Littorina Sea transgressions with magnitudes of 12 and 10 m, respectively. A water-level change model was applied together with a digital terrain model in order to reconstruct coastline change in the region and to examine the relationships between coastline change and displacement of the Stone Age human settlements that moved in connection with transgressions and regressions on the shifting coastline of the Baltic Sea.

Bedrock geology and topography of the Lake Peipsi depression, eastern Estonia

Abstract Seismic reflection profiling in the western part of Lake Peipsi, eastern Estonia, revealed two major units in the sedimentary bedrock, namely Devonian terrigenous rocks on top of Ordovician carbonate rocks. In the Ordovician sequence several subhorizontal reflectors and subvertical faults were recorded. The Ordovician-Devonian contact carries signs of erosion and has an inclination towards the south to southeast by 2-2.2 m per km in the northern and central parts and 4.5- 4.9 m per km in the southern part of the lake. The thickness of the Devonian terrigenous rocks increases rather abruptly in the southern part of the lake, approximately within the same zone where the inclination of the Ordovician-Devonian contact increases. Gently sloping depressions and elevations were distinguished at the bedrock surface, which dips towards the center of the lake. A buried valley in Devonian sedimentary bedrock was found in the northwestern part of the lake. The magnitude of the glacial erosion in the central part of the depression, as related to the altitude of the bedrock surface in the surrounding onshore areas, is estimated to at least 50-60 m. The glacial erosion has not been compensated by subsequent glacial accumulation and late- to postglacial lake sedimentation. Because of this, the main features of the bedrock topography are still traceable at the till surface as well as in the lake bottom topography.

Seismic stratigraphy of Quaternary deposits in Lake Peipsi, eastern Estonia

Abstract Shallow marine seismic reflection profiling in the western part of Lake Peipsi, eastern Estonia, has revealed new information about thickness, structure and distribution of the Quaternary deposits. Additional data from numerous drillings in the area around the lake have facilitated the interpretation of the seismic profiles. The thickness of the Quaternary deposits varies over a wide range, from a few metres in the northwestern part to over 50 m in the central part. Two seismic units have been subdivided in the Quaternary cover, interpreted as till followed by glaciolacustrine and postglacial lacustrine sediments. The till layer has in general a rather complicated structure. It reaches a thickness of about 33 m in the elongated bedrock depressions found in the western part of the lake, whereas within the flat bedrock areas, it has a more uniform structure and a thickness of 10–15 m. The till is only locally exposed in the lake bottom in the northwestern and northeastern areas. The glaciolacustrin...

Simulation of the hydrogeologic effects of oil-shale mining on the neighbouring wetland water balance: case study in north-eastern Estonia

The water balance of wetlands plays an integral role in their function. Developments adjacent to wetlands can affect their water balance through impacts on groundwater flow and increased discharge in the area, and they can cause lowering of the wetland water table. A 430 km2 area was selected for groundwater modelling to asses the effect of underground mining on the water balance of wetlands in north-eastern Estonia. A nature conservation area (encompassing Selisoo bog) is within 3 km of an underground oil-shale mine. Two future mining scenarios with different areal extents of mining were modeled and compared to the present situation. Results show that the vertical hydraulic conductivity of the subsurface is of critical importance to potential wetland dewatering as a result of mining. Significant impact on the Selisoo bog water balance will be caused by the approaching mine but there will be only minor additional impacts from mining directly below the bog. The major impact will arise before that stage, when the underground mine extension reaches the border of the nature conservation area; since the restriction of activities in this area relates to the ground surface, the conservation area’s border is not sufficiently protective in relation to underground development.RésuméLe bilan hydrique joue un rôle fondamental dans le fonctionnement des milieux humides. Des activités contigües peuvent impacter l’écoulement de la nappe, causer une décharge accrue et un abaissement de son niveau. Une zone de 430 km2 a été sélectionnée pour modélisation de nappe et évaluation de l’effet de l’exploitation souterraine sur le bilan hydrique d’une zone humide du Nord-Est de l’Estonie. Un périmètre naturel protégé (incluant la tourbière de Selisoo) se trouve à 3 km d’une exploitation d’huile de roche mère. Deux scénarios correspondant à différentes emprises de la future exploitation ont été simulés et comparés à l’état actuel. Les résultats montrent que la conductivité hydraulique verticale de sub-surface est critique vis à vis de l’assèchement potentiel de la zone humide conséquente à l’exploitation. Un impact significatif sur le bilan hydrique de la tourbière de Selisoo sera causé par l’approche de l’exploitation mais l’impact additionnel de l’exploitation sous la tourbière elle même sera mineur. L’impact majeur surgira avant ce stade, quand la mine souterraine atteindra la limite de la zone de protection naturelle ; comme la restriction des activités dans cette zone concerne la surface du sol, la conservation de sa bordure n’est pas une protection suffisante vis à vis du développement souterrain des travaux.ResumenEl balance de agua de los humedales juega un rol integral en su función. Los desarrollos adyacentes a humedales pueden afectar su balance de agua a través de impactos sobre el flujo de agua subterránea y el incremento de la descarga en el área, y ello puede causar el descenso del nivel freático del humedal. Un área de 430 km2 fue seleccionada para modelar del agua subterránea y evaluar el efecto de la explotación subterránea sobre el balance de agua de un humedal en el noreste de Estonia. Un área de conservación natural (que abarca el pantano de Selisoo) está dentro de un radio de 3 km de una mina subterránea de esquistos bituminosos. Se modelaron dos escenarios futuros de explotación con diferentes extensiones areales y se compararon con la situación actual. Los resultados muestran que la conductividad hidráulica vertical del subsuelo es de importancia crítica para el drenaje potencial del humedal como resultado de la explotación. Un impacto significativo sobre el balance de agua del pantano de Selisoo será causado por la aproximación a la mina, pero serán solo un impacto menor adicional proveniente de la explotación directamente debajo del pantano. El mayor impacto surgirá antes de esa etapa, cuando la extensión de la mina en el subsuelo alcance el límite del área de conservación natural; puesto que la restricción de actividades en este área se relaciona a la superficie del terreno, el límite del área de conservación no es lo suficientemente protectora en relación al desarrollo subterráneo.摘要湿地水平衡在其功能上页页着整体作用。比页湿地的页页通页页地 下 水流的影响和增加的页页可影响水平衡,可降低湿地水位。页页一个 430平方公里的区域页行地下水模页,页价地下页采页页沙尼页页北部湿 地水平衡的影响。自然保页区就页于地下油页岩页3公里之内。页不同区 域范页的两个未来页采方案页行了模页并与页在的情况页行了页比。页 果页示地下的垂直水力页水系数页页采中潜在的湿地排水至页重要。接近 页山就会页Selisoo沼页水平衡页生重要影响,但直接在沼页之下的页采只 有很小的页外影响。主要影响出页在页个页期前,即地下页山延伸到自然 保页区的页界。因页本地区的活页限制与地表有页,因此,保页区的页界 不能足页防页地下的页页。ResumoO balanço hídrico das zonas húmidas desempenha um papel fundamental na sua função. Desenvolvimentos adjacentes às zonas húmidas podem afetar o seu balanço hídrico através de impactes sobre o fluxo de água subterrânea e o aumento da descarga na área, podendo causar o rebaixamento do nível da água subterrânea na zona húmida. Foi selecionada uma área de 430 km2 para modelação das águas subterrâneas, a fim de avaliar o efeito da exploração mineira subterrânea no balanço hídrico da zona húmida, no nordeste da Estónia. A área de conservação da natureza (englobando o pântano Selisoo) fica a 3 km de uma mina subterrânea de xisto betuminoso. Dois cenários futuros de exploração mineira, com diferentes extensões de área de exploração, foram modelados e comparados com a situação atual. Os resultados mostram que a condutividade hidráulica vertical do subsolo é de importância crítica para a potencial secagem das zonas húmidas, como resultado da mineração. A aproximação dos trabalhos mineiros causará um impacte significativo sobre o balanço hídrico no pântano Selisoo, mas apenas existirão impactes adicionais menores da mineração diretamente por baixo do pântano. O maior impacte vai surgir antes dessa fase, quando a extensão subterrânea da mina atingir a fronteira da área de conservação da natureza; uma vez que a restrição de atividades nesta área se relaciona com a superfície do solo, a conservação da fronteira da área não é suficientemente protetora em relação ao desenvolvimento dos trabalhos subterrâneos.

Thickness distribution of quaternary deposits in the formerly glaciated part of the East European plain

A thickness map of Quaternary deposits in the south-eastern sector of the last Scandinavian Ice Sheet (SIS) and in areas of Middle Pleistocene Moscow (Warthe) and the Dniepr (Drente) stages of the Late Saalian glaciation on the East European Plain is presented (Main Map). The map of the thickness and related statistics of the Quaternary deposits were calculated from the difference between the current digital terrain model and the bedrock surface topography model. The distribution of Quaternary deposits shows that 29% of the mapped territory has sediments less than 25 m thick, 16% more than 100 m and 1.2% more than 200 m. Within the SIS area, the thickness of sediments in the southern sector exceeds threefold the sediment thickness in the eastern flank. This difference is attributed to the bedrock depression in the south-east of the Baltic Syneclise rather than to glacial dynamics. The calculated average thickness of the sediments within the SIS area is ca 50 m, in the formerly glaciated area outside the LGM it is ca 61 m and outside the glaciated area ca 14 m. Our study confirms that, in formerly glaciated areas, the spatial distribution of sediments did amplify the differences in glacial bed topography with the exception of the southern and eastern flanks of the Moscow glaciation area where exceptionally thick Quaternary deposits have inverted bedrock depressions into elevated areas in recent terrain. We suggest that the map presented improves existing knowledge of this area by adding detail and thus contributing to the on-going development of numerical ice-sheet models.

Glacial varves at Pärnu, south-western Estonia: a local varve chronology and proglacial sedimentary environment

A new varve chronology comprising 584 consecutive varve years, varve thickness changes and proglacial sedimentary environment are analysed across the Pandivere–Neva (>13 300 yr BP) belt of ice-recessional formations in coastal Estonia, eastern Baltic. Varved clays in the area have been deposited in the Baltic Ice Lake. All investigated sequences display a normal varve series with decreasing varve thickness upwards. According to the varve correlation, two groups of varve graphs could be distinguished: those representing sequences from the distal side and from the proximal side of the Pandivere–Neva ice marginal formations. Accumulation of varved clays started ca. 100 yr earlier in the distal part. A massive clay unit with corresponding 20 silty varves in some sequences precedes the beginning of varve formation at the proximal part of the basin and could therefore correspond to a ca. 20 yr long ice-stagnation period during the Pandivere–Neva Stade. Ice proximal conditions on both sides of the recessional formations (within 30 km distance) ceased simultaneously within a period of 10–15 yr, which is reflected in reduced total varve thickness accompanied with the beginning of winter layer dominance within a single varve. Because of post-sedimentary erosion, the length of the presented chronology underestimates the duration of proglacial conditions. Good visual correlation between the mean varve thickness graphs from the Pärnu area and from Lake Peipsi, eastern Estonia, indicate the possible regional causes of varve thickness changes and simultaneous varve formation in two basins.

Local clay-varve chronology in the Karlskrona-Hultsfred region, southeast Sweden

Abstract A local varve chronology from southeast Sweden between the town of Karlskrona in the province of Blekinge and Hultsfred in the province of Småland is presented. The chronology covers approximately 800 varve-years. The glaciolacustrine varves were deposited in the Baltic Ice Lake during the Late Weichselian deglaciation. The study includes 60 connected and 56 unconnected varve series and shows that the ice recession rates vary between 75–125 m/year and 250–340 m/year in the southern and northern parts of the area, respectively. An abrupt change from thin to thick clay varves was found in the northern part of the area. The change has been correlated with a similar change of silty varves in the bottom bed of one of the delta plains close to the highest shoreline. This change in the meltwater deposition has been hypothetically correlated with the transition between the Older Dryas (GI-1d) and Alleröd (GI-1c) chronozones, or around 13,750 GRIP years.

Pore Pressure Fluctuations Within Quasi-Stable Slopes in South-Western Estonia and Their Influence on Slope Stability

Pore pressure fluctuations within slopes are widely considered as one of the most common landslide triggers. Ten automatic piezometers were installed within two quasi-stable slopes in south-western Estonia in order to record fluctuating pore pressures during a 2-year period. Pore pressure values and meteorological and hydrological data were studied by non-parametric correlation and cluster analyses in order to quantify the influence of external parameters. Data from 51 groundwater monitoring wells, covering the period from 1960 to 2009, were analysed in order to evaluate long-term changes in the underlying artesian aquifer. The development, refilling and movement of the groundwater depression were recorded. The pore pressure field was modelled with the finite element model and used as an input for slope stability analyses. Significant changes in slope stability were revealed. The influence of the ongoing climate change on slope stability is discussed.