Conodont Biostratigraphy and Taxonomy of the Ordovician Shelf Margin Deposits in the Scandinavian Caledonides

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The Lower and Middle Ordovician (upper Tremadoc-lower Caradoc) succession in the Lower Allochthon of the Scandinavian Caledonides has been sampled with particular emphasis on the limestone intervals, most notably the Lower Ordovician (Arenig-Llanvirn) Stein Formation and the Middle Ordovician Elvdal Formation (Upper Llanvirn-Lower Caradoc).

Conodonts were examined in 133 samples from 15 localities situated along the Caledonian front from central south Norway (Valdres) to northwestern central Sweden (Jämtland). A total of 19,286 specimens were recovered, representing 398 morphotypes, which are referred to 45 genera and 102 species. Three genera and four species are new: the genera Costiconus, Minimodus, Nordiora and the species Microzarkodina corpulenta, Minimodus poulseni, Nordiora torpensis, and Triangulodus amabilis.

Because of its ocean-margin habitat, the conodont fauna of the Stein Formation contains several taxa that previously have not been reported from the Baltoscandian platform but are common in the marginal areas of North America. This makes the Stein Formation an effective link for biostratigraphical correlations across the Iapetus Ocean. The conodont fauna differs from the faunas that typify the more proximal, undeformed Baltoscandian platform, with respect to stratigraphic ranges and relative abundance. It is especially distinctive for the upper Arenig – lower Llanvirn time interval. As a consequence, seven new conodont zones have been established for the critical interval.

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