Terminal Ordovician stratigraphy of the Siljan district, Sweden

Integration of new isotopic data and earlier biostratigraphic information from eight sections through the terminal Ordovician (Pirgu and Porkuni stages) of the Siljan district, Sweden, allows a more precise correlation of sections in terms of biostratigraphy and carbon isotope dating. Four levels with positive δ¹³C excursions are identified (from bottom) – the Moe, an unnamed excursion, Paroveja and Hirnantian Carbon Isotope Excursion (HICE). The δ¹³C values through the Boda Limestone are 1–2‰ higher than usual in Baltica, only the values for the HICE remains within what is expected. Background values increase from 1.5‰ in the bottom of the core of the Boda Limestone up to 3‰ in the top of it. The HICE is identified in five of eight sections and the main peak falls according to inferred correlation within the <i>Metabolograptus persculptus</i> Biozone, at or close to the <i>Hindella</i> beds in the Upper Boda Member. The late Katian (Pirgu) age of <i>Holorhynchus</i> in the Siljan district is clear and its co-occurrence with the chitinozoan <i>Belonechitina gamachiana</i> in Estonia supports a Katian age for this zone. The base of the <i>Ozarkodina hassi</i> Biozone may occur within units B–C of the Upper Boda Member and in the upper part of the Loka Formation and most likely is correlated with the <i>M. persculptus</i> Biozone. The <i>Hirnantia</i>–<i>Dalmanitina</i> faunas reported from the lowermost part of the Loka Formation and units B–D of the Upper Boda Member seem to range through all the Hirnantian, but detailed morphological studies allow to distinguish an older ( = <i>extraordinarius</i>) and a younger ( = <i>persculptus</i>) fauna.