Marko Kohv

The Osmussaar Breccia in Northwestern Estonia — Evidence of a ~475 Ma Earthquake or an Impact?

The Osmussaar Breccia occurs in beds of the ~475 Ma basal Middle Ordovician (Arenig and Llanvirn series) siliclastic-carbonate rocks of northwestern Estonia. The Breccia consists of fragmented and slightly displaced (sandy) limestones, which are penetrated by veins and bodies of strongly cemented, breccia-like, lime-rich sandstone injections. The rocks above (horizontally-bedded, hard limestone) and below (weakly cemented silt and sandstone) are undisturbed and do not contain the sediment intrusions. Osmussaar Breccia is found over an area of more than 5000 km2 and is distributed in a west- east oriented elliptical half-circle centred approximately at Osmussaar Island (59°18′ N; 23°28′ E). The thickness of the brecciated unit ranges from 1-1.5 m on Osmussaar to a few (tens of) cm at ~70 km east of the island. Arenitic sandstone of the sediment injections contains quartz grains with planar deformation features (PDF). Several hypotheses concerning the origin of the Osmussaar event have been proposed: catastrophic earthquake, regional tectonic movements, tectonic movements occurring simultaneously with coastal processes, and an impact event. The latter hypothesis was suggested in connection with the discovery of the nearby-situated Neugrund impact structure. However, the sediment intrusions are stratigraphically ~60 Ma younger than the impact structure. Osmussaar Breccia does not correspond to any known impact structure of this age in Baltoscandia. Also, results of a seabed geophysical survey in the Baltic Sea for the search of a possible undiscovered feature did not identify any large structure in the area of the Osmussaar Breccia. Consequently, we suggest that a devastating ~475 Ma earthquake with an epicentre close to Osmussaar split the sea floor. It initiated underwater mud-flows eroding the primary Neugrund crater ejecta and/or crater rim walls, thus reworking the impact materials into the sedimentary injections, which is suggested by rounded morphology of the shocked quartz grains found in breccia matrix.

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.

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.

Interpreting Estonian mires: common perceptions and changing practices.

Over the centuries mires have been considered to be mostly useless, even dangerous places. Adopting a landscape semiotic perspective the article delineates the current common perceptions of Estonian mires based upon 767 questionnaires. Today the mire is commonly perceived as undisturbed wilderness offering possibilities for various recreational as well as traditional activities. The image of mires in popular consciousness is predominantly based on touristic experience of protected areas. The history of the most widespread practices in the mires over the 20th century reveals three general paradigmatic frames of reference: traditional where mire appears to be liminal; industrial where it is encultured; and ecological where mire is aestheticized. In its orientation towards aesthetic and emotional values the common perspective diverges from the landscape ecological definition. Tourism to non-protected, partly meliorated mires should be encouraged to give a more realistic perspective of the mires to non-professionals.

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.