The bedrock relief below the Väinameri, in a shallow-marine branch of the central Baltic Sea offshore Estonia

Abstract

This paper represents one output of the extensive seismo-acoustic profiling performed by the Estonian Geological Survey in the Väinameri, the shallow sea in the West Estonian Archipelago, during the geological mapping conducted in 2019–2022. Based on recordings from boomer-type sound transmitters, this study describes and analyses the bedrock relief to assess a prior suggestion that there exists a NE–SW trending pre-Quaternary river valley traversing the Väinameri, extending across the central Baltic Sea. The bedrock relief map and 3D model reveal a valley-like structure with distinctive cuesta elements crossing the central Väinameri. The cuesta plateau, along with the cuesta escarpment (Silurian Klint) that emerges faintly in the Bay of Matsalu, has been substantially reshaped by Pleistocene glaciers around the Muhu depression in the very centre of the Väinameri and is best preserved between Saaremaa and Hiiumaa islands. The general drainage pattern also points towards a fluvial erosion component in shaping the bedrock depression below the Väinameri. Despite that, the age and genesis of this valley-like feature with the Silurian Klint below the Väinameri remain open. The hypothesis that a pre-Quaternary Eridanos River System might have eroded these bedrock structures contradicts the altitude of the klint base below the Baltic Sea, which remains far below the presently estimated reach of the Eridanos fluvial erosion. Further studies are needed to specify the possible genesis and age of the klints and buried bedrock valleys in Estonia, which, in many aspects, reveal the characteristics of pre-Quaternary fluvial denudation rather than Pleistocene glacial erosion.

Keywords

• central baltic sea
• bedrock relief
• west estonian archipelago
• väinameri
• river eridanos
• glacial erosion
• silurian klint