G. S. Iskül

Key section stratigraphy of the Middle Ordovician Kunda and Aseri stages of the Lava River (south of the Lake Ladoga region)

Abstract. The paper proposes a bed-by-bed description and new lithostratigraphic classification of the Middle Ordovician Kunda and Aseri stages of the Lava River. The Obukhovo Formation (Kunda Stage) includes the Voka, Lava, Il’yinskoye, Chernavino, and Simankovo members. The first two are also common in more western sections of the Baltic-Ladoga Klint (Loobu type), the others — with the eastern sections (Obukhovo type). The Lava Member is a new subdivision introduced to replace the Utria Member, which initially had a smaller volume and different identification principle. The upper “Oolite Bed” is not considered as an independent unit and refers to a local “facies” of the Chernavino Member and Lower Simankovo Member; with its appearance, the clay content of limestone can increase sharply. The Duboviki Formation (Aseri Stage) includes the Kavra, Mel’nitsa, Suosaari, and Zhikharevo members; the Lower Porogi-Valim Formation (top of the Aseri Stage and lower part of the Lasnamägi Stage) has the new Perevelje Member. The Kavra Member is developed only in the east of the Klint (south of the Lake Ladoga region) and the more carbonate Saksolovo Member replaces it to the west. The Mel’nitsa-Perevelje members are distributed over most of the Ingermanland Klint. A reinterpretation of the stratigraphy of five drillholes in the Putilovo Upland was carried out based on their correlation with the key section of the Lava River.

Keywords: Ordovician, carbonate deposits, stratigraphy, trilobites, brachiopods, Baltic-Ladoga Klint, Lava River