Lower Katian (Upper Ordovician) δ13C chemostratigraphy, global correlation and sea-level changes in Baltoscandia

Abstract

A long-standing problem in the Ordovician stratigraphy of south-eastern Norway has been to the relations between the Mjøsa Formation in the Lake Mjøsa region and coeval strata in the Oslo region. The recent discovery of the globally distributed Guttenberg δ13C excursion (Guttenberg Isotopic Carbon Excursion) in the Mjøsa region provided the impetus to search for this excellent chemostratigraphic marker in the classical Oslo region succession, where it was found in the Frognerkilen Formation. Another positive δ13C excursion, which we identify as the Kope excursion, was discovered in the Solvang Formation. The new data show that the lower Katian δ13C chemostratigraphy in the Oslo region is closely similar to that from south-eastern and southern Estonia. This permits detailed correlations across Baltoscandia, which are useful for recognising the Baltic stage boundaries in the Oslo region succession. Both the Lake Mjøsa and Oslo regions study successions can be chemostratigraphically correlated with those in North America and eastern Asia. The newly established stratigraphic relations in the Oslo region are also used for a re-assessment of lower Katian local and eustatic sea-level changes.