The C–O Isotope Geochemistry and Chemostratigraphic Correlation of Ordovician Deposits of the Lisino-10 Borehole Section, Northwestern Russian Plate

The borehole “Lisino-10” was drilled on the Izhora Upland, approximately 90 km southwest of St. Petersburg. This study presents the first continuous carbon and oxygen isotope curves obtained from Ordovician carbonate rocks (Latorp–Rakvere regional stages) in the northwestern part of the Russian Plate. Despite relatively small deviations in δ13C values (from –2.5‰ to 1.8‰), two positive carbon isotope excursions are clearly identified in the borehole section: (1) the MDICE (Middle Darriwilian Isotopic Carbon Excursion), with a peak δ13C value of 1.0‰ in the Loobu Formation, and (2) the GICE (Guttenberg Isotopic Carbon Excursion) at the Sandbian–Katian boundary, with a peak δ13C value of 1.8‰ at the boundary between the Vruda and Izvara formations. In addition to these positive excursions, two negative carbon isotope events are also recognized: (1) the BDNICE (Basal Dapingian Negative Isotopic Carbon Excursion), with a minimum δ13C value of –2.5‰ in the lower part of the Volkhov Formation, and (2) the LSNICE (Lower Sandbian Negative Isotopic Carbon Excursion), with a minimum δ13C value of –1.0‰ in the upper part of the Viivikonna Formation. These results enable carbon-isotope chemostratigraphic correlation of the Lisino-10 section with other regional sections and establish it as a reference section for the Ordovician paleobasin of the Russian Plate.