Sergey Popov

Abstract Volcanic ash layers (tephras) dispersed over large areas may offer important time markers in the geological record provided their age and geochemical fingerprint can be established. Accurately dated and geochemically characterized tephras are essential in correlation of temporally and spatially discontinuous geological records, which is key for paleoenvironmental, paleoclimatic, and paleogeographic reconstructions. Here we report geochronological and geochemical data for the Gorelka tephra (southwestern Russia) – a prominent tephra of uncertain age and origin that provides a key time marker for the largest marine transgression of the Eastern Paratethys Sea in the Miocene. Coupled U-Pb and (U-Th)/He dating of zircon crystals constrains the eruption age of the Gorelka tephra, and hence the age of the highest stand of Eastern Paratethys in the Miocene, to 11.5±0.5 Ma. Geochemical characteristics in combination with the new eruption age and tephra volume estimates suggest a magnitude ∼7.4 eruption from a volcanic source in the Transcarpathian region. The Gorelka tephra was transported ∼1,500 km ENE from its source by westerly winds, which were typical for the atmospheric circulation regime within the Ferrel cell in Central Europe during Sarmatian times. Based on the results presented here, the Gorelka tephra provides a reliable tie-point for paleoenvironmental and stratigraphic correlations across southeastern Europe.

The paper discusses a revised interpretation of the Late Messinian malacofaunas of Piedmont, namely the bivalves of the subfamily Lymnocardiinae (family Cardiidae), which are kept at the Museo Regionale di Scienze Naturali of Turin and the Museo Civico Archeologico e di Scienze Naturali "Federico Eusebio" of Alba (Cuneo). The historical Bellardi and Sacco collection in Turin contains various specimens of Lymnocardiinae that F. Sacco collected from various sites in the provinces of Cuneo and Alessandria (Piedmont) at the end of the 19th century. The Alba museum holds several species that O. Cavallo and G. Repetto found in the Alba area in the 1980-1990s. The authors of the paper deemed it necessary to reinvestigate the above-mentioned material, in spite of its non-optimal conservation status, because it testifies the high specific diversity of the Late Messinian “lago-mare” molluscan assemblages of Piedmont, whose original deposits are often no longer accessible. Both Ponti...

The anatomical structure of the bivalve mantle, which is responsible for the formation of the carbonate shell, ontogenetic features of growth, and formation of rhythmical and casual layers are described. Different types of microstructure seen under an optical and electron microscope are illustrated by block-diagrams. Based on the material of different taxonomic groups of Bivalvia, the possibilities of microstructure characters for systematics are discussed.

Transgressive stages in the Eastern Paratethys history are established on the base of facial analyses and following of the ancient coastal lines on the northern platform shelf zone. They are correlated with the first part of the early Oligocene, beginning of the late Oligocene, beginning of the Miocene, beginning of the Chokrakian, Karaganian, and Sarmatian during the Middle Miocene, the Upper Sarmatian and Early Pontian during the Late Miocene, the Akchagilian in the Caspian part in the Pliocene. Regressive phases are fixed based on deep river cuts, which allows to value time and amplitude of erosion basis downfalls. The maximal cuts are dated by terminal Eocene, second part of the Solenovian, end of the Maykopian in the Early Miocene, and early Pliocene in the Caspian Basin.
Seismic data allows watching the major discontinuities in deposition in result of water level downfalls and tectonic reasons, which are followed as in shalves, as in deepwater depressions. At least three erosional phases ranging from Paleogene to Pontian time: at the terminal Eocene, terminal Maykopian, and at the Sarmatian – Maeotian boundary. Moreover, intra-Pontian erosional surface is clearly identified.
The Eastern Paratethys stratigraphic scale stability during more then 100 years is determined by boundaries, which correlate with tectonic and lithologic-facial reorganizations and main water level downfalls and reflect not only paleontological events. Units, which based on faunistic data mainly, often are not well distinct out of stratotypic area and facial zone. We have these problems with units of the Maykopian second part (Upper Oligocene – Lower Miocene), late Chokrakian – Karaganian and Maeotian – Pontian boundaries.

This contribution, the third part of a monographic series, deals with the biogeography of the Tethys and Paratethys sea basins in the Late Oligocène and Early Miocene and includes reviews of the stratigraphy and paleogeography of the Paratethys, descriptions of the biogeographic distribution of planktonic foraminifers, nanno-and organic-walled phytoplankton, benthos (benthic foraminifers, ostracodes, and mollusks), and the ich-thyofauna, and provides biogeographic zonation based on these groups. The final section deals with the evolution of the main biochores in the western Eurasian basins during the second half of the Paleogene and Miocene.

ABSTRACT
The type section of the Oligocene to Lower Miocene Maikop Group, considered the main source rock in the Eastern Paratethys, has been studied using geochemical proxies to gain insights into depositional setting and hydrocarbon potential.
The Maikop Group at the type section is about 600 m [2000 ft.] thick. Deposition commenced after a major Late Eocene sea level drop and a subsequent Early Oligocene sea level rise. The Maikop Group is composed mainly of carbonate-free pelitic rocks. Calcareous rocks are limited to the Lower Oligocene Pshekha Formation, the Polbian Bed forming a basin-wide marker horizon deposited during a time with significantly decreased salinity (“Solenovian event”), and the Upper Morozkina Balka Formation. Anoxic conditions prevailed and were interrupted for longer times only during deposition of the lower part of the Pshekha Formation, the Polbian Bed and the Lower Miocene Olginskaya Formation.
TOC contents range up to 3.5 wt.%. HI values are typically below 300 mgHC/gTOC, but reach 420 mgHC/gTOC in black shales overlying the Polbian Bed (Lower Morozkina Balka Fm.). Organic richness of this level, about 10 m [33 ft.] thick, is controlled by low salinity and high bioproductivity.
The Maikop Group could generate approximately 2.0 t HC/m² surface area. A significant part (0.45 t/m²) comes from the Lower Morozkina Balka Formation, which generates a paraffinic-naphthenic-aromatic mixed oil with high wax and low sulphur contents. The Pshekha, Upper Morozkina Balka and Batalpashinsk formations would generate low-wax oil or condensate. The hydrocarbon generation potential of the overlying formations is minor.

Abstract—The Taman sections, reference for the Neogene of the Eastern Paratethys, are investigated thor oughly paleontologically and stratigraphically, with levelbylevel description of four sections, correlated in detail with each other; fossil remains coming from them are examined conjointly, with uniform binding to the sections. The composition of malacofaunas and foraminifers allowed the recognition of all regional stages and substages from the Upper Chokrakian to Middle Kimmerian, their boundaries, and correlation with the Kerch stratotypes. The study of the taxonomic composition of ostracods improved the boundaries of strati graphic ranges of particular species. The complete and continuous sequence of Karaganian–Konkian depos its has provided the data improving the volume and boundaries of the Konkian Regional Stage and showing that it is divided into three units. Investigation of these groups provided the stratigraphical basis for pioneer studies of phytoplankton; the taxonomic composition and distribution in the sections of nannoplankton, dia toms, and organicwalled phytoplankton are investigated completely for the first time; the points of penetra tion of marine water into the basin are recognized. The most reliable tool for correlation of deposits in a semi closed basin is distribution of “ecologically plastic” groups that are able to tolerate a wide range of salinity and variation of the gas regime, such as mollusks, benthic foraminifers, and, among phytoplankton, diatoms and dinocysts. The appearance of stratigraphically significant diatom and nannoplankton species in Konkian, Sarmatian, and Maeotian deposits allowed the comparison of intervals of their presence with the oceanic zones where these index species are provided with absolute dating. The levelbylevel palynological charac teristics of the beds is reported, providing the basis for reconstruction of climatic changes in this region.