A 87Sr/86Sr, δ18O and δ13C record of Turonian-Santonian belemnites from lower Volga region of the East European Platform: Stratigraphic significance and palaeoenvironmental reconstructions

We present the first strontium, carbon and oxygen isotope data on belemnites from the Upper Cretaceous (Turonian-Santonian) strata of the Lower Volga region, located between Saratov and Volgograd. The Sr-isotope evidence confirms the regional biostratigraphic data, indicating a deep erosion at the Coniacian-Santonian boundary, which suggests that some belemnitellid rostra from the lower Santonian so-called “Sponge horizon” of the Ozerki, Pudovkino and Mizino-Lipshinovka sections were redeposited from middle and upper Coniacian deposits and that the first representatives of the genus Belemnitella are thought to be late Coniacian in age. This study provides the first evidence of the Cenomanian-Coniacian Sr-isotope minimum from the East European (Russian) Platform, likely related to underwater Caribbean basaltic volcanism. New data suggest that the initial phase of Caribbean volcanism coincided with the temperature maximum and development of oceanic anoxic conditions (OAE 2), but the peak of the assumed volcanic activity in the late Turonian (90.8 Ma) was probably accompanied by a decrease in temperature and phytoplankton productivity. The problem of the regional Coniacian-Santonian oceanic anoxic event 3 (OAE 3) and global end-Cretaceous cooling is also touched upon.