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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.
Acknowledgements
We are indebted to the Natural History Museum, Oslo, which provided a vehicle for the fieldwork. SMB thanks the David Bruton family for their great hospitality during the fieldwork. We are indebted to Tõnu Meidla for information about his sampling at the Gullhögen Quarry and to Alan Owen for useful manuscript comments. The laboratory work on the isotope samples was carried out by Bjørn Buchardt and Bo Petersen at the Stable Isotope Laboratory, Institute of Geography and Geology, University of Copenhagen. Useful comments by two anonymous reviewers and by Jan Bergström and Mikael Calner led to manuscript improvements.