Abstract The Ordovician of Scandinavia (i.e. Denmark, Norway and Sweden) has been investigated for over two centuries and, through time, various chronostratigraphic schemes have been introduced, facilitating regional correlation. However, a modern chronostratigraphy has never been proposed. Here, we delineate ten regional stages for the Ordovician of Scandinavia, comprising, in ascending order, the Slemmestadian, Ottenbyan, Billingenian, Volkhovian, Kundan, Segerstadian, Dalbyan, Moldåan, Jerrestadian and Tommarpian. We propose to discontinue the use of the term Hunnebergian Regional Stage despite its Scandinavian origin; this interval is included in the new Ottenbyan Stage. The base of each stage, as (re)defined here, is selected to coincide with the appearance of a characteristic fossil taxon and delimited at the top by the base of the overlying stage. The stage boundaries generally coincide with or approximate to significant changes in the depositional environment that are recognizable across Scandinavia from the carbonate platform to the foreland basin. Local efficacy has been the primary criterion for the recognition of Scandinavian stage boundaries rather than approximating to the global or East Baltic stage boundaries. It is proposed to abolish the Baltoscandian regional series and subseries, as correlation with the global series is sufficiently precise to make these higher rank regional schemes redundant.

Abstract This paper summarizes recent knowledge on the palaeontology, biostratigraphy, correlation, sea-level and climate history and isotopic geochemistry of the Ordovician rocks in the western and central parts of the East European Craton, in the area extending from the southern margin of the Fennoscandian Shield to the western margin of the Ukrainian Shield. The regional chronostratigraphic standard is briefly summarized and its correlation to the global standard of the Ordovician is addressed. A two-part correlation chart of 10 areas with unique local Ordovician successions is aligned with the most recent international correlation standard of the Ordovician System and presented against the regular timescale. An updated summary of the evolution of the marine assemblages is provided, the principal gaps in the existing extremely rich palaeontological database are identified and the main bioevents are discussed.

Abstract The Early Palaeozoic Icehouse (Late Ordovician–Early Silurian, c. 455–425 Ma) was a remarkable event in the Earth’s climatic history, marked by extensive glaciations occurring at a time of elevated atmospheric CO 2 . The oceanography of the Early Palaeozoic Icehouse was markedly different from that of modern oceans, with frequent episodes of oceanic anoxia and high concentrations of CO 2 which may have acidified the oceans and restricted carbonate burial. Thus, the marine organic carbon reservoir may have more strongly influenced long-term changes in atmospheric CO 2 than at present. We suggest that deposition of black shales represented a major sink for atmospheric carbon. Sequence stratigraphy reveals that widespread black shale deposition occurred in transgressions, whereas regressions are characterized by deposition of bioturbated facies, allowing changes in lithofacies and deep-water redox conditions to be related to the Early Palaeozoic carbon cycle. Assuming increased temperature is a function of increased atmospheric CO 2 , and that glacioeustatic sea-level can serve as a proxy for temperature due to changing ice volume, we infer that the deposition of transgressive black shales may have acted as a negative feedback mechanism, drawing down CO 2 and preventing the onset of runaway greenhouse conditions.