ИСТИНА

For the Cretaceous reconstructions we suggest to use the extinction of planktonic foraminifers (PF)which lived in the water column like their modern representatives and were controlled by similarenvironmental factors: water temperature, water-mass structure, amount of nutrients, and stability or instability of oceanographic conditions.The climate during the Cretaceous had been globally warm, although from low to high latitudes it was less contrasted than in modern oceans. During the important Cretaceous radiations PF increased in size and acquired very special morphologies. PF evolved rapidly in some intervals (punctualism), slower in others (gradualism), allowing to construct a biostratigraphic scale at high resolution especially at low latitudes (Crimea-Caucasus area). Biostratigraphic scales for high latitudes have very low resolution (Russian Platform). The early PF assemblages consisted of small-sized opportunistic taxa (r-strategists); r/k intermediate taxa started to evolve in the Aptian, while specialized, orphologically complex keeled taxa evolved in the late Albian and persisted, although with different genera, until the end of the Cretaceous (kstrategists). These general evolutionary trends were interrupted in the Late Cretaceous by one minor event at the C/T boundary (rotaliporids extinction). The other feature, obvious for this interval, is the prevalence of non-keeled small forms belonging to Whiteinella, Hedbergella, Schackoina and Heterohelix (r-strategists). The perforate, elongated chambers and tubulspinines schakoinids may represent the best survivorship tool to achieve better oxygen and nutrient uptake (Coccioni et al., 2007). The next turnover coincides with the Santonian-Campanian boundary when replacement of marginotruncanids by globotruncanids was related to a cooling episode (Petrizzo, 2002; Huber et al., 2002).These events were parallel to palaeoenvironmental changes. All these changes are clearly recorded in the Crimea-Caucasus area. Low taxonomic diversity of lanktonic foraminifers in the Russian Platform’s epicontinental basins does not allow hem to date exactly. However, the cold boreal water influence is recognized along the north-eastern margin of the Russian Platform (Baraboshkin et al.,2002; Naidin et al.,2007). Late Maastrichtian warming is also well recognized.PF diversity decreases rom the tropics to high latitudes, from the Crimea-Caucasus area to theRussian Platform sedimentary basins. Species disappearance toward high latitudes affects the largersized,more-ornamented k-strategists. All k-strategists taxa are practically absent in the Russian Platform. Intermediate morphotypes occupy intermediate habitats, the most ornamented ones arecloser to the tropics and subtropics (Ukrainian and Polish-Lithuanian depressions). The occurrence of k or k/r-strategists at higher latitudes indicates the expansion of warmer conditions at a given time, for example, “elegans transgression” in the late Maastrichtian on the Russian Platform. Increases in diversity, size and morphological complexity through time identify an increasing number of trophic niches within the mixed layer and the onset of at least a weak thermocline. This work was supported by Russian Foundation for Basic Research, projects no 15-05-04099a, 15-05-03004a and IGCP project 609.