Baltoscandic conodont life environments in the Ordovician: Sedimentologic and paleogeographic evidence

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Abstract
Modern ecologic models for conodonts were extrapolated principally from experience with North American shallow-water subequatorial faunas. Further evidence can be derived from the calcareous lower part of the Swedish Ordovician. This succession among other things offers uniformity of facies, as well as long-ranging conodont genera. Paleomagnetic data indicate deposition at 60°S, i.e., relatively cool climate and fluctuations in air and shallow-water temperatures. The succession might represent a subantarctic shallow-water carbonate platform. Another interpretation favors depth of 100 to 500 m. The relative frequencies of long-ranging conodont genera were plotted against facies data. All data indicate complexity of interaction of depth, temperature, and current dependent factors that influenced the distribution of conodont genera, in particular during a regressive phase about the Arenigian-Llanvirnian transition. Microzarkodina, Periodon, and Protopanderodus had extended frequency minima during the regression. Paroistodus was abundant before the regression, then apparently disappeared from Europe. In a section at Skövde, formed perhaps in particularly deep water, Baltoniodus has a minimum and Drepanoistodus a maximum that might correspond to the peak of regression, but elsewhere the conditions are either ambiguous or reversed. At least Protopanderodus and Periodon probably were not epibenthic, since they occur with shelly fauna in carbonates as well as with graptolites in dark mudstones and with radiolarians in ophiolite-associated cherts (in Scotland). The importance of sorting by differential transport is stressed throughout the study.

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