Vol 25, No 1 (2017)

The results of investigations of Upper Vendian‒Lower Cambrian deposits in the northeastern part of the Baltic monocline specify views on the evolution of depositional environments of sedimentary successions constituting the basal part of the sedimentary cover in inner areas of the northwestern East European Platform. It is shown that the Late Vendian and initial Cambrian were characterized by the consecutive influx of relatively mature terrigenous detrital material that originated from both the weathering crust of the Baltic Shield and new sources. Its deposition was interrupted by notable, although likely asynchronous, hiatuses, which are registered at the base of the Upper Vendian Vasileostrovskaya and Voronkovo formations and Lower Cambrian Lomonosov Formation. In the Late Vendian, sedimentary material was transported from the Baltic Shield, while beginning from the initial Early Cambrian the additional contribution to the formation of the sedimentary cover of the Baltic monocline was provided by coarse-grained sedimentary material from the Timan margin of the Baltica as follows from U‒Pb isotopic ages obtained for detrital zircons. At the same time, lithogeochemical parameters of fine-grained rocks experienced no substantial changes.

The integral investigation of the upper Campanian‒Maastrichtian section near the settlement of Nizhnyaya Bannovka (Krasnoarmeiskii district, Saratov oblast) included its detailed lithological description and the study of different organic remains (belemnites, benthic and planktonic foraminifers, radiolarian, calcareous nannofossils, dinocysts) with the analysis of their taxonomic composition and stratigraphic distribution and magnetostratigraphic (magnetic polarity and petromagnetic) properties. The belemnite findings indicate the presence of the upper Campanian Belemnitella langei Zone in the section, which comprises sediments previously attributed to the lower Maastrichtian Belemnitella lanceolata Zone. The analogs of magnetic polarity chrons 33n, 32r, and 31n (probably superposed chrons 31n and 30) are established. It is assumed that radiolarians offer the opportunity to define the middle Campanian substage by analogy with the standard (international) stratigraphic scale. On the basis of benthic foraminifers, calcareous dinocysts, and paleomagnetic data, the late Maastrichtian age of sediments previously dated back to the early Maastrichtian is substantiated. A large hiatus corresponding to the terminal Campanian‒early Maastrichtian is revealed in the section. The succession of sedimentological, biotic, and paleogeographic events is outlined for the late Campanian‒Maastrichtian interval. The obtained data make it possible to disclose paleobiogeographic connections between microfaunal communities of the Campanian and late Maastrichtian seas on the East European and West Siberian plates. It is established that the uppermost Maastrichtian sediments are enriched in extraterrestrial matter.

The paper reports on the micropaleontologcal (diatoms, silicoflagellates, radiolarians, and pollen flora) data substantiating the age and conditions of sedimentary cover formation of the submarine Ulleung Plateau (Krishtofovich Rise) in the Sea of Japan. Five rock complexes with different age and origin were distinguished on the basis of micropaleontological and petrographic data. Complex 1 (tuffites, tuffogenous siltstones) with numerous freshwater diatoms and pollen flora that prove the lacustrine genesis and the Early Miocene age occurs at the base of the sedimentary cover. Complexes 2–5 are composed of marine tuffogenous sedimentary deposits of end of Early Miocene–Pleistocene age. Stratigraphic unconformity between continental and marine deposits involves a short-time interval in the end of the Early Miocene and points to rather fast tectonic submersion of the Ulleung Plateau. Marine sedimentation in bathyal conditions dominated from the end of the Early Miocene. In the Late Miocene, in the northern part of the plateau, the region of the large rise was characterized by shallow-water conditions, indicating supposed existence of an island territory in this place.