BOREAL-TETHYAN CORRELATION OF THE UPPER BERRIASIAN–VALANGINIAN:
THE CONTRIBUTION OF NEW δ13C AND 87Sr/86Sr CHEMOSTRATIGRAPHIC DATA
FROM ARCTIC SIBERIA
V.D. Efremenko1, O.S. Dzyuba1, B.N. Shurygin1, A.B. Kuznetsov2, A.N. Pyryaev3
Keywords: Lower Cretaceous, belemnites, carbon isotopes, oxygen isotopes, strontium isotopes, integrated stratigraphy, Weissert event
Abstract
The paper contributes to the development of C-, O-, Sr-isotope chemostratigraphy for the Upper Berriasian–Valanginian of Arctic Siberia and, on this basis, to the improvement of Boreal–Tethyan correlations. Results of isotope and geochemical study of carbonate matter in belemnite rostra from sections of the Anabar and Boyarka rivers and the Nordvik Peninsula (Ryazanian–basal Hauterivian) are presented. Three phases of the global Weissert event are recognized, namely: of rapid increasing in δ13C across the Early–Late Valanginian boundary, stabilization in δ13C during the Late Valanginian, and a smooth decrease in δ13C at the Valanginian–Hauterivian transition. Judging by the δ18O data, recorded from the “Neocomian” of Siberia, the climate cooling associated with Weissert event was not strong. The 87Sr/86Sr values obtained for the Boyarka and Nordvik sections, in combination with bio- and magnetostratigraphy, indicate that the base of the Upper Berriasian falls in the middle part of the Ryazanian Hectoroceras kochi ammonite Zone. It has been established that the top of the Ryazanian is located below the base of the Valanginian. In Siberia, the interval between these boundaries corresponds to the lower part of the Neotollia klimovskiensis ammonite Zone. The age of ammonite zones in the Boreal (Siberian) standard of the Lower Valanginian have been clarified. The Homolsomites bojarkensis ammonite Zone has been reliably confirmed as belonging to the Lower Hauterivian rather than the Upper Valanginian, resolving a long-debated issue.
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