BOREAL–TETHYAN CORRELATION OF THE UPPER BERRIASIAN–VALANGINIAN: CONTRIBUTION OF NEW δ13C AND 87Sr/86Sr CHEMOSTRATIGRAPHIC DATA FROM ARCTIC SIBERIA

This study contributes to the development of C, O, and Sr isotope chemostratigraphy of the upper Berriasian–Valanginian of Arctic Siberia and to the improvement of the Boreal–Tethyan correlation scheme based on it. Results of an isotope–geochemical study of belemnite carbonate material from the Anabar and Boyarka river sections and the Nordvik Peninsula section (Ryazanian–lower Hauterivian) are presented. The following three phases of the global Weissert event are identified: a rapid increase in δ13C at the turn of the early and late Valanginian, stabilization of δ13C in the late Valanginian, and a smooth decrease in δ13C since the end of the Valanginian to the earliest Hauterivian. It is suggested by the δ18О data from the Neocomian formations of Siberia that the climate cooling associated with the Weissert event is negligible. The resulting 87Sr/86Sr values for the Boyarka and Nordvik sections in combination with bio- and magnetostratigraphy indicate that the base of the upper Berriasian falls into the middle part of the Hectoroceras kochi ammonite Zone of the Ryazanian Stage. It is revealed that the top of the Ryazanian is located below the base of the Valanginian. The interval between these boundaries in Siberia corresponds to the lowermost part of the Neotollia klimovskiensis ammonite Zone. The age of the ammonite zones of the Boreal (Siberian) standard of the lower Valanginian is clarified. It is reliably determined that the Homolsomites bojarkensis ammonite Zone belongs to the lower Hauterivian rather than upper Valanginian, which resolves the issue that has been the subject of lengthy discussions.