Two bryozoan assemblages from the Ordovician of the Russian Arctic

Abstract

Two assemblages from the Ordovician rocks of the Arctic region contain exclusively trepostome bryozoans. The first assemblage from the Yunoyaga Formation (Middle Ordovician) of Maly Oleniy Island, Novaya Zemlya, contains Monticulipora mammulata d’Orbigny, 1850 and Nicholsonella vaupeliformis Modzalevskaya, 1955. Both species possess thick-branched ramose colonies characteristic for rather high energy environments. The second assemblage comes from two localities of the Stroinaya Formation (Upper Ordovician) of the October Revolution Island containing the single species Amplexopora angusta Astrova, 1965. The monospecific bryozoan fauna of branched, rarely encrusting growth forms and sedimentological characteristics of embedding rocks (floatstone) suggest low energy conditions in deeper environments, apparently accompanied by high salinity conditions.

Keywords:

• Bryozoa
• Ordovician
• Arctic
• taxonomy
• palaeoecology

Acknowledgements

Palaeontological material was collected during the SWEDARCTIC International expeditions to Severnaya Zemlya in 1999 and Novaya Zemlya in 2004. We are grateful to two anonymous reviewers for their helpful and constructive reviews.