The signs of Palaeozoic volcanicity in Estonia

The present paper deals with the signs of volcanicity in the Estonian Palaeozoic. The core K-18 drilled from the epicentre of the Kärdla buried ring structure was subjected to the studies by the Geological Board of the Estonian SSR. The results obtained indicate the existence of explosive breccias on crystalline basement at depth of 360—423 from the earth’s surface. They are composed of strongly transformed bedrock particles, recrystallized acid lava, tuffites and tufosilts. In view of chemical composition the latter are rather close to acid volcanites. The occurrence of volcanic material in dictyonema shale is studied as well. The shape of quartz and K-feldspar grains and the degree of weathering give evidence of their tufogenic origin. The chemical composition of the terrigenous material comprised in dictyonema shale is rather similar to that of tuffites and tufosilts described from the core K-18. The occurrence of volcanic matter in the Estonian Palaeozoic has been insufficiently studied so far. Their geologico-structural position, composition and relations with the surrounding rocks arouse suspicion against meteoritic origin of the Kärdla structure and enable one to suppose that there are at least two genetically connected phases of Palaeozoic volcanicity.