Vol 27, No 4 (2019)

All current data on the Jurassic and Cretaceous climates of Siberia based on isotope, paleontological, and lithological proxies are summarized. The late Pliensbachian cooling episode, early Toarcian warming, promptly replaced by long-term Middle Jurassic cooling at the end of the Toarcian, and a long-term warm interval in the Late Jurassic are clearly recorded. From the end of the Ryazanian, a gradual cooling episode began, which apparently continued throughout the Early Cretaceous except for a brief warming episode in the early Aptian. At the beginning of the Late Cretaceous, the climate became warmer; the peak of warming is recorded at the Cenomanian–Turonian boundary. Then, the middle–late Turonian was marked by a relatively cold episode. Later, in the Coniacian–Campanian, the climate warmed again, but at the end of the Campanian another cooling episode occurred. New findings of marine reptiles are described from the Toarcian, Kimmeridgian, Volgian, and Santonian-Campanian deposits of north of Eastern Siberia. All existing records of marine reptiles known from the Jurassic and Cretaceous of Siberia are revised, and all the findings (from 51 localities) are positioned in relation to paleolatitudes. It is established that the majority of occurrences of these fossils were within the polar paleolatitudes (70°–87°). We found no direct correlation between climate fluctuations and the distribution of these organisms. Taking into account the newest data showing that representatives of the majority of Jurassic and Cretaceous large groups of marines reptiles were able to maintain a more or less constant body temperature and were also able to undertake large-scale seasonal migrations, it is reasonable to be cautious in interpreting the presence of remains of these animals as indicators of a warm climate.

This work presents the results of the integrated study of the sequence of Oligocene (Maikop) and underlying Eocene deposits uncovered in borehole 768 (362 m). This section can be regarded as the reference one as for Northern Ergeni, as for the entire northern part of the Eastern Paratethys. The data obtained on lithology, mollusks, and benthic foraminifers enabled us to subdivide the Oligocene interval of the Maikop Group into formations and subformations (Tsimlyanian, Solenovian, and Kalmyk), to correlate it with adjacent and remote areas of the Paratethys and with the scale of regional stages, and to reconstruct the main sedimentation conditions. On the basis of nannoplankton and dinocysts, these subdivisions are correlated with the zonal stratigraphic scale (Gradstein et al., 2012), and according to the palynological data, the evolution of climatic conditions at the Paratethys northern margin is reconstructed. The phytoplankton, foraminiferal, and paleomagnetic data show a significant reduction of the section in its Eocene interval. The latter includes only negatively magnetized intervals of the Keresta, Kuma, and Belaya Glina formations, separated by discontinuities, as well as the complete set of biotic and paleomagnetic zones of the Lower Oligocene. The lower subformation of the Solenovian Formation (50 m), eroded in most of the sections of Ciscaucasia, is characterized by unusual completeness. It is probable that the Kalmyk Formation in this section is incomplete and is represented only by the first half of the Chattian.