ИСТИНА

This study presents new stable isotope and trace element data from belemnite rostra from the Volgian-Hauterivian interval of the Izhma River, Russia (at a palaeolatitude of ~60°N) and from the Ryazanian-Hauterivian interval of the Boyarka River, Siberia (at a palaeolatitude of ~70°N). Well preserved belemnites of the Boreal Realm genera Acroteuthis, Cylindroteuthis, Lagonibelus and Pachyteuthis were investigated. A distinct Late Valanginian positive carbon isotope excursion is identified in the marine carbonate record from both successions. The excursion occurs at a time of relatively low sea-level in Russia and Siberia, and it also leads a marked cooling episode that is observed in the Izhma River data (as indicated by the significant increase in oxygen isotope values and concomitant decrease in Mg/Ca ratios). It seems likely, that a significant burial of sediments rich in organic carbon lead to a fall in atmospheric C02 concentration and to a subsequent drop in temperature (an 'inverse greenhouse' effect).