The Hunneberg Stage (Ordovician) in the area east of St. Petersburg, north-western Russia

The bio- and lithostratigraphy of the poorly known early Ordovician (Arenig) Hunneberg Stage is described from the area east of St. Petersburg (Putilovo Quarry and Lava river), where the Lakity Beds (Leetse Fm.) consist of glauconitic sands and silty clays. The described fauna includes graptolites, conodonts, brachiopods, acritarchs, foraminifers, and several problematic groups. The Lakity Beds are unique within the lower Ordovician sequence of the East Baltic in the abundance of graptolites, co-occurring with conodonts. The conodonts from the lower part of the Lakity Beds belong to the uppermost subzone (Oelandodus elongatus — Acodus deltatus deltatus) of the Paroistodus proteus Zone, coinciding with the lower part of the Tetragraptus phyllograptoides Zone. This suggests that there is a hiatus between the Lakity Beds and the underlying Nazya Formation. The lower Lakity Beds also contain the brachiopods Leptembolon lingulaeformis and Eosiphonotreta cf. acrotretomorpha, which suggest that they may be correlated with the Joa Member of the Leetse Formation in North Estonia. In the upper part of the Lakity Beds, conodonts of the Prioniodus elegans Zone co-occur with graptolites indicating the upper subzone of the Tetragraptus phyllograptoides Zone in the Scandinavian sections. There are still problems of defining and correlating the base of the Billingen Regional Stage, which are outside the scope of this paper.