The Structure and Formation Conditions of the Bedenekir Formation Deposits (Thithonian Stage) of Mountainous Crimea

The composition and origin of the Bedenekir Formation deposits of Mountainous Crimea are detailed on the basis of our work results and analysis of both published and unpublished data.     

Gravity and magnetic field interpretation based on transformations of horizontal gradients in the VECTOR system

A method of potential field processing based on the transformation of vectors of the total horizontal gradient in windows of various sizes is considered. The gradients are calculated at the centers of triangles, whose vertices are points of observations, as a rule, of gravity and magnetic fields. Averaging of horizontal gradients of the field rather than initial values of the field is the main distinction of this approach from the known methods. This procedure, referred to in this paper as vector scanning of the field, makes it possible to obtain layer distributions of field sources in a 3-D diagram that is a quasi-density model of the study medium within the framework of certain model concepts. The paper presents a model example demonstrating the possibility of separating the fields produced by two sources located on a vertical line and an example illustrating the application of this method to the interpretation of the gravity field in the zone of the geodynamic influence of the Urals.     

The Early Cretaceous Anoxic Basin of the Russian Plate: Sedimentology and Geochemistry

The profile comprising a series of lower Aptian sections from Ul'yanovsk to Saratov in the Russian Plate has been studied. It is shown that the unit of organic-rich rocks is characterized by the lack of bioturbation and elevated concentration of many chemical elements. The petrography and geochemistry of organic matter (OM) indicate the prevalence of basinal OM in carbonaceous sediments, while continental OM dominates in host rocks. Sedimentological, biotic, and geochemical data testify to the deposition of organic-rich sediments under anoxic conditions. The anoxic environment in the Aptian basin of the Russian Plate correlates with the global OASE-1a anoxic event. The mechanism of Aptian carbonaceous sedimentation is discussed.     

Stratigraphy and paleoenvironmental interpretation of the Paleocene-Eocene transition in the Eastern Crimea

The study of nannofossils and dinoflagelate cysts from the Paleocene-Eocene transition in the Nasypnoe section, Eastern Crimea identified the bed corresponding to the global event referred as the Paleocene-Eocene Thermal Maximum (PETM). The assemblages of both groups of microphytoplankton display significant changes including the appearance of Rhomboaster spp., Discoaster anartios and D. araneus nannofossils and Apectodinium augustum and Wilsonidium pechoricum dinocysts featured for this event and major variations in the ratio of taxa resulted in domination of eutrophic and warm-water species. The paleoecological interpretation of nannofossil and dinocyst distribution suggests a drastic sea-level fall preceded the PETM and occurrence of two transgressive episodes during it.     

Microbiota and stratigraphy of lower Paleogene deposits of the Urma Plateau,Central Dagestan

The study of nannofossils, dinocysts, and foraminifera from Paleogene deposits of the Urma Plateau of Central Dagestan revealed the Paleocene-Eocene age of the Gray Formation, to apply zonations based on of all three groups of microplankton, and to correlate the regional dinocyst and planktonic foraminifer zonations to the standard nannofossil scale. Nannofossil zonation of O. Varol’s (1989) is shown to be successfully applied for subdivision of Danian deposits. The large foraminifer assemblage found in the lower Eocene deposits is correlated to the NP12-NP13 zones of the nannofossil scale.     

Sedimentary environments and geochemistry of Upper Eocene and Lower Oligocene rocks in the northeastern Caucasus

Upper Eocene and Lower Oligocene rocks in the northeastern Caucasus were examined in the most representative Chirkei section (Sulak River basin). Sharp lithogeochemical distinctions between them were revealed. The results of the study of nannoplankton demonstrated that the Eocene/Oligocene interface occurs slightly below the boundary between the Belaya Glina and Khadum formations. The studied section revealed a series of nannoplankton bioevents facilitating its stratigraphic subdivision. It has been established that organic matter (OM) in rocks of the Khadum Formation is characterized by a relatively high degree of maturity. Probably, the material of mainly marine genesis contains a terrigenous OM admixture. Positive oxygen isotope anomaly in the upper part of the Belaya Glina Formation reflects global climate changes (cooling) near the Eocene/Oligocene interface. Limitation of the anomaly by the upper boundary of the Belaya Glina Formation is likely related to changes in water salinity variations in the Early Oligocene basin and intense early diagenetic processes in rocks therein. Lithological, geochemical, and paleoecological data suggest that the Khadum paleobasin was depleted in oxygen. Such environment was unstable with periodic intensification or attenuation. Paleoecology in the Belaya Glina basin was typical of normally aerated basins.     

Mesozoic and Early Cenozoic Paleoecological Events in the Sedimentary Record of the NE Peri-Tethys and Adjacent Areas: An Overview

Lithology and Mineral Resources - Manifestations of short-term global and subglobal events have been recognized in the Mesozoic and Cenozoic sedimentary record of the North Caucasus:...     

Sequence-stratigraphic analysis of the Aptian deposits in the valley of the Mzymta River

In this work, based on the example of a well drilled in the valley of the Mzymta River (Northwest Caucasus) the possibilities of the sequence-stratigraphic method are demonstrated for the first time. This method allows us to clarify the natures of numerous repetitions in the same interval of the geological sequence (modern, ancient landslide or syn-sedimentary-landslide, and tectonic or eustatic). In addition, the geochemical characteristics of bituminous sediments are given. The sequence that was studied in the well shows the complex polygenetic evolution of sediments since Aptian time and the oceanic anoxic event-1.     

Middle Eocene to early Oligocene nannofossils and palynomorphs from the Landzhar section,southern Armenia: Zonal stratigraphy and paleoecology

The results of the study of nannofossils and palynomorphs from the Landzhar section in southern Armenia were used to correlate bioevents of two groups of microorganisms, recognize zonal subdivisions, and identify variations in the assemblage compositions reflecting changes in the hydrology and sedimentation regime in the basin during the middle Eocene to early Oligocene.     

New age data from the Lesnaya Group: A key to understanding the timing of arc-continent collision, Kamchatka, Russia

Abstract The Lesnaya Group is part of a thick, poorly dated turbidite assemblage that sits in the footwall of a regionally extensive collision zone in which the Cretaceous–Paleocene Olutorsky island arc terrane was obducted onto continental margin basin strata. Nannoplankton from 18 samples from the upper part of the Lesnaya Group yield Paleocene through Middle Eocene assemblages. Detrital zircons from nine sandstone samples have a young population of fission-track ages that range from 43.7 ± 3.4 to 55.5 ± 3.5 Ma (uppermost Paleocene to Middle Eocene). The deformed footwall rocks of the Lesnaya Group and the overlying thrusts of the Olutorsky arc terrane, are unconformably overlain by neoautochthonous deposits which are Lutetian (lower Middle Eocene) and younger. Together, these new data indicate that thrusting, which is inferred to have been driven by collision of the Cretaceous–Paleocene island arc with north-eastern Asia, took place in the mid-Lutetian, at about 45 Ma.