Hulterstad brachiopods and associated faunas in the Vormsi stage (upper ordovician, Katian) of the Lelle core, Central Estonia

Abstract

Integrated palaeontological and sedimentological study of the Upper Ordovician Vormsi Stage in the Lelle drill core section, Central Estonia, revealed an association of shelly fauna containing the endemic saukrodictyid brachiopod Hulterstadia cor (Wiman), which is otherwise known only from erratic boulders close to Hulterstad in the southeastern area of the Island of Öland, Sweden. In the Lelle core this fauna occurs in the uppermost Fungochitina spinifera chitinozoan Biozone of mid-Vormsi age. Cyclic changes in the content of siliciclastic material in the carbonate section, and in the predominance of shallower- and deeper-water scolecodonts in the interval of the distribution range of H. cor, suggest sea-level oscillations during mid-Vormsi time. Upper Vormsi strata, corresponding to the Tanuchitina bergstroemi chitinozoan Biozone, including the Acanthochitina barbata Subzone, are characterized by common occurrence of sponge remains. Lithologies of the uppermost part of the Lelle section indicate sedimentation in channel environments. Taxonomic composition of the macrofauna in the core differs considerably from that of North Estonia, but has some similarity with the deeper-water Ashgill faunas in other regions (e.g. Fosse Formation of Belgium and Portrane Limestone of Ireland). The Estonian specimens of Hulterstadia cor are described.