Results are presented of a high-resolution study of foraminifers, ostracods and marine palynomorphs from the continuous succession of Middle Volgian-Lower Valanginian (Upper Jurassic to Lower Cretaceous) deposits of the Nordvik section (NE Siberia). Six foraminiferal and six dinoflagellate cyst (dinocyst) zones and subzones have been identified. Volgian foraminiferal assemblages (Dorothia tortuosa JF51 zone and Ammodiscus veteranus, Evolutinella emeljanzevi JF52 zone) may be regarded as correlative markers for Arctic regions as they are also observed in Barents Sea shelf sediments and different regions of Siberia. Marine palynomorph assemblages provide a reliable correlation with northern areas of Western Europe and Canada at three stratigraphic levels: (a) the base of the Upper Volgian, (b) the middle of the Berriasian and (c) the lowermost Valanginian. The stratigraphic position of foraminiferal and dinocyst zones has been analyzed taking into consideration two alternative horizons for the Jurassic-Cretaceous boundary (A-base of the Upper Volgian, B-base of the Boreal Berriasian). Remarkable changes in foraminiferal assemblages and the first occurences of stratigraphically important taxa occur at the base of the Gaudryina gerkei, Ammobaculites gerkei KF 1 zone, slightly higher than horizon B. The base of the Ammodiscus veteranus, Evolutinella emeljanzevi JF52 zone (slightly below horizon A) is marked by a significant turnover of the characteristic species and dominant taxa. The strongest changes in dinocyst assemblages occur near the base of the Paragonyaulacysta ?borealis, Dingodinium ?spinosum zone (horizon A). The analysis of published macrofauna data and new microfossil information indicates palaeoenvironments ranging from the middle sublittoral to the lower sublittoral.

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Oxygen isotope compositions of bone phosphate (δO) were measured in broiler chickens reared in 21 farms worldwide characterized by contrasted latitudes and local climates. These sedentary birds were raised during an approximately 3 to 4-month period, and local precipitation was the ultimate source of their drinking water. This sampling strategy allowed the relationship to be determined between the bone phosphate δO values (from 9.8 to 22.5‰ V-SMOW) and the local rainfall δO values estimated from nearby IAEA/WMO stations (from -16.0 to -1.0‰ V-SMOW). Linear least square fitting of data provided the following isotopic fractionation equation: δO = 1.119 (±0.040) δO - 24.222 (±0.644); R = 0.98. The δO-δO couples of five extant mallard ducks, a common buzzard, a European herring gull, a common ostrich, and a greater rhea fall within the predicted range of the equation, indicating that the relationship established for extant chickens can also be applied to birds of various ecologies and body masses. Applied to published oxygen isotope compositions of Miocene and Pliocene penguins from Peru, this new equation computes estimates of local seawater similar to those previously calculated. Applied to the basal bird Confuciusornis from the Early Cretaceous of Northeastern China, our equation gives a slightly higher δO value compared to the previously estimated one, possibly as a result of lower body temperature. These data indicate that caution should be exercised when the relationship estimated for modern birds is applied to their basal counterparts that likely had a metabolism intermediate between that of their theropod dinosaur ancestors and that of advanced ornithurines.

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