Late Silurian reef development in the Baltic Sea

Abstract

In the Baltic Sea, reef structures are common in the Ordovician and Silurian sedimentary bedrock. Palaeozoic reef development culminated in the Silurian when several successive reef barriers developed. The present investigation has revealed new reef structures in the upper Silurian sedimentary bedrock. Two new biostromes, E1 and E2, have been found in the Ludlovian Eke Beds, east of Gotland. The biostromes trend in a more or less east-west direction and can be traced across the northern part of the Baltic Sea. In the Pridolian, two reef-like barriers, named B5 and B6, occur at the boundary to the Devonian. The lower barrier, B5, is found to the south of the younger B6 barrier. This indicates that a transgression occurred between the formation of the two barriers. A tentative reconstruction of the Pridolian bay suggests that the coast shifted from a more east-west direction in the Ludlovian to a more north-easterly to south-westerly direction in the Pridolian. Bioherms are commonly associated with the Eke biostromes and the upper Pridolian reef-like barriers. The bioherms occur on the seaward side of the larger reef structures, on the biohermal slope. Patch-reefs also occur on the biohermal slope but they are more common on the landward (lagoonal) side of the barriers.