INFLUENCE OF THE BEDROCK TOPOGRAPHY ON OIL SHALE MINING IN NORTH-EAST ESTONIA

Abstract

According to the zonation of the Estonian bedrock topography, presented on the basis of relative and absolute heights and taking into consideration the lithological composition of the bedrock, Estonian oil shale deposit is located in the Viru-Harju Plateau including the Pandivere Elevation and Ahtme Eminence. The plateau has a thin Quaternary cover, mainly a few metres in thickness. The oil shale basin is dissected by linear structures and ancient buried valleys, which complicate oil shale mining. The buried valleys are eroded into the commercial oil shale beds and serve as natural boundaries between mining and exploration fields. Ancient buried valleys were mainly formed in the Late Paleogene when the Earth’s crust was much higher than at present due to the riftogenesis in the North-Atlantic region. They were overdeepened in the Pleistocene by glaciers. Probably, some valleys are glacial in origin. There are seven bigger valleys (Loobu, Haljala, Selja, Kunda, Pada, Purtse and Vasavere) located in the study area. The valleys contain big reserves of building sand and gravel, and high-quality underground water. Tectonic features, human impact and karst phenomena play an essential role in the formation of the chemical composition of water, especially at local and regional scales.