Miidel, A., Noormets, R., Hang, T., Flodén, T. & Bjerkéus, M.
Bedrock geology and topography of the Lake Peipsi depression, eastern Estonia

Keywords
Seismic reflection profiling, Estonia, Lake Peipsi, bedrock geology, bedrock topography, Ordovician, Devonian, Quaternary, Weichselian glaciation

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.

Author info
A. Miidel & T. Hang, Institute of Geology, Tallinn Technical University, Estonia Ave. 7, EE-101 43 Tallinn, Estonia, miidel@gi.ee. R. Noormets, T. Flodén & M. Bjerkéus, Dept. of Geology and Geochemistry, Stockholm University, SE-106 91 Stockholm, Sweden. Present address for T. Hang: Dept. of Physical Geography and Quaternary Geology, Stockholm University, SE-106 91 Stockholm, Sweden.

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