THE LOWER AND MIDDLE DEVONIAN OF THE SOUTH-EASTERN BALTIC SEA

Abstract

In the Baltic region, Devonian sedimentary bedrock is exposed in a wide area extending from north-eastern Estonia through Latvia to the south-eastern Baltic Sea. Westwards in the Baltic Sea, the outcrop terminates against a presumably Permian fault, which extends southwards from Gotland. In the southernmost part of the Baltic Sea, the Devonian sedimentary bedrock was eroded during the Permian-Carboniferous uplift event. The Devonian sedimentary bedrock of the investigated area southeast of Gotland, consists of near-shore marine deposits, namely sandstone, siltstone, clay, dolomite, dolomitic marl, and limestone. Gypsum and anhydrite deposits occur frequently in the lower parts. The Silurian-Devonian boundary is marked by a stratigraphic break across the presently investigated offshore area. All regional stages of the Lower and Middle Devonian are present in exposures in the area. In the north-eastern part, offshore Latvia, the basal Devonian Gargždai deposits follow ontop of the Silurian sedimentary bedrock. Further to the south-west, the Gargždai beds are missing, and deposits of the next younger Kemeri Stage rest directly on the Silurian. In the Middle Devonian, the Pärnu Stage contains widespread sandbars, which are locally deeply truncated. This may indicate a shallow nearshore environment. Within the Old Red Sandstone facies of the late Middle Devonian Aruküla-Burtnieki complex, several discontinuity surfaces are present. The reflectors exhibit a mound-like pattern, which again may indicate a shallow nearshore environment with rapid deposition, erosion, and redeposition.