Vol 53, No 9 (2019)

Distribution of 57 ostracod species is investigated in the Quaternary sediment samples from the borehole RBH-16, drilled at the north-eastern Black Sea shelf edge off the town of Anapa. Among them, 52 species of the Caspian type and 5 species of the Mediterranean type were found. Four distinct assemblage zones are identified: the Caspian type one typical for Chaudian basin (Early Neopleistocene) (I) in interval 15.55–14.11 m; the Caspian type one dominating from the Late Pleistocene to the early Holocene (II), according to species composition closed to Khvalynian basin, at the depth 13.4–3.84 m (from 13.6 to 8.7 cal. ka BP), the mixed one of Caspian type and Mediterranean type species (III) in interval 3.84–0.95 m (younger than 8.7 cal. ka BP), and the assemblage with progressively increasing dominance of Mediterranean species (IV) in interval above 0.75 m (after 7.4 cal. ka BP).

Three most common Arctic foraminiferal species of the family Cassidulinidae from the Laptev Sea sediment cores were analyzed for paleoenvironmental reconstructions. This paleontological study is focused on morphological characteristics of apertural elements and the wall structure. The species Cassidulina neoteretis is considered an indicator of the Atlantic influence in contrast to the Arctic species Cassidulina reniforme and Islandiella norcrossi.

The Turtas Formation (the Upper Oligocene of Western Siberia), uncovered by the Zyryanka-1 Borehole, contain diverse assemblage of microfossils. The ecological composition (freshwater diatoms, spicules and gemmuloscleres of freshwater sponges, spores and pollen, as well as zygospores of Zygnematales algae) indicates the nonmarine nature of the Early Turtas Basin. In contrast to the assemblage of the Zhuravka horizon (southern regions of Western Siberia), the absence of Fagaceae and dinocysts of the genus Pseudokomewuia, as well as low numbers of Taxodiaceae–Cupressaceae and Betulaceae, are probably explained by local characteristics.

New data on the taxonomic diversity of radiolarians, calcareous dinocysts and nannoplankton associations in the Late Jurassic and Early Cretaceous of the Bazhenovo Formation of Western Siberia are presented. Analysis of the distribution of radiolarians in the Bazhenovo Formation confirms the possibility of its division into five biostratigraphic units. The upper part of the Bazhenovo Formation, according to the calcareous dinocysts, includes five biostratigraphic units at the rank of beds with microfauna. The presence of the genus Parvicingula confirms that the Bazhenov Sea was a marginal marine basin connected with the Paleo-Pacific Ocean.

The environments, favorable for the development of benthic microfauna were predominant in the Jurassic Sea in the northeastern part of the Ulyanovsk–Saratov Trough (Russian Platform). Such parameters as the distribution and the taxonomic composition of the assemblage of Jurassic benthic foraminifers, their abundance, generic and species diversity, the occurrence of new species, a ratio of species with agglutinating and calcareous shells serve as a basis for developing the paleobathymetric zonation of the basin. The tracing of the variations in these parameters through the section enables us to construct a quantity paleobathymetric curve for the Middle-Late Jurassic and to distinguish the sequence–stratigraphic elements.

Foraminifer assemblages from five massifs of the Triassic limestones of the Dalnegorsk District have been described for the first time, and images of these foraminifers are provided. Foraminifer associations are found here on all the known stratigraphic levels, except for the Rhaetian. In the massif of Mount Verkhnii Rudnik, four foraminifer assemblages have been recorded within the interval from the Carnian to the top of the Norian. The foraminifer assemblages in the Dalnegorsk limestones are comparable to the coeval foraminifer associations of the Carpathians and the Alps. The research results make it possible, for the first time, to compare the foraminifer assemblage composition between various limestone massifs and different stratigraphic levels.

The Kasimovian Stage is a stage in the Pennsylvanian Subsystem, originally recognized in Russia. Its type area, despite the stage name (which is after the town of Kasimov in the Ryazan Region), is in the vicinity of the Voskresensk Region in the lower reaches of the Moscow River for the Krevyakian and Khamovnikian regional substages and the former village of Dorogomilovo (Moscow Region) for the Dorogomilovian Regional Substage. The stratotypes of the subdivisions of the Krevyakinian and Khamovnikian regional substages were established in the Voskresensk Region and no longer exist. The conodont assemblages of the Krevyakian and Khamovnikian and the lower part of the Dorogomilovian were studied in the neostratotype of the Kasimovian Stage (Afanasievo Section) and the Perkhurovo Reference Borehole drilled near the town of Voskresensk.

The distribution features of foraminiferal assemblages in the Upper Viséan deposits of the reference wells 1 Melekess and 1 Buzuluk are investigated. According to the ratio of the structural components of rocks and their structural features 7 microfacies, characterizing the open shallow shelf and the coastal–marine depositional environments are distinguished in the carbonate sediments. The structure of benthic biota assemblages was revealed. The foraminiferal assemblages are described, taking into account the taxonomic diversity, frequency of occurrence and a degree of preservation.

Five types of scolecodont microornamentation are recognized: striate, regular, granular, rhombic, and columnar. The connection between the type of ornamentation and the position of the scolecodont element in the jaw is analyzed. The ability of scolecodonts to regenerate is examined based on material from the Devonian of the Voronezh Anteclise.