The Lower and Middle Viruan Sequence in Two Borings in Östergötland, Central Sweden

The Viruan (Middle Ordovician) Aseri, Lasnamägi, and Uhaku Stages, and the overlying Dalby Limestone (Kukruse and Idavere Stages of the Estonian sequence) are described from two cores drilled in the northern part of the Cambro-Silurian area of Östergötland. For the local sequence the topo-stratigraphic and litho-stratigraphic divisions previously distinguished in southern Öland (Jaanusson, 1960) are used. Only the beds corresponding to the Folkeslunda Formation differ in Östergötland conspicuously from those of southern Öland, being formed mostly by fine-grained calcilutites with interealatians of mudstone instead of by calcarenites. The Aserian Segerstad Limestone and the Lower Lasnamägian Skärlöv Formation consist mainly of finely nodular limestones, and in northern Östergötland the thickness of these divisions exceeds that of the other Cambro-Silurian areas of Sweden. The thickness of the other divisions is of the same order of magnitude as in southern Öland, and, as far as the Dalby Limestone is concerned, as in the Siljan district. The sequence of the Aseri, Lasnamägi, and Uhaku Stages was previously unknown in Östergötland.