верхний мел

The discovery of a tooth of the cow shark Hexanchus microdon (Ag., 1835) from carbonate deposits of the Karsun Formation in the ‘Krasny Oktyabr’ quarry (Volsk, Saratov Volga River Right Bank) is described. Based on the associated foraminifera complex, the stratigraphic position of the find was determined as Lower Maastrichtian, benthic foraminifera LC20 Falsoplanulina multipunctata Zone. It was calculated that the individual size of the described shark species H. microdon was 153–166 cm.

A representative complex of the Turonian-Santonian carbonate-producing invertebrates has been revealed. It comprised benthic foraminifers, diverse echinoderms, brachiopods, calcareous and siliceous sponges.

The paper presents detailed biostratigraphical division and lithological characteristics of the Turonian-Lower Santonian interval within the compiled Chukhonastovka section. The presence of the Lower Turonian deposits has been ascertained alongside with the unusual structure of the rock interval synchronous to the Lower Santonian “sponge” horizon.

Representatives of the genus Sororistirps, distinguished among the Ventriculites, have been detected in the Santonian – Maastrichtian rocks from the southeast of the Russian Plate. The structures of the skeletons and of the irrigation systems have been considered, the Sororistirps morphogenesis has been traced; the forms characteristic of the Santonian, Campanian and Maastrichtian spongiocomplexes have been determined.

In the course of this work we cast the light on the state of research of the Late Cretaceous sea urchins in the Volga region as well as the development of ideas about their distribution in the rocks of the Upper Cretaceous in the region. Resources used in the research include studies about this group of invertebrates since the beginning of the XIX century up to the present day. It was estab­lished that the vast majority of publications consist of fragmentary information containing mentions of echinoderm remnants findings.

A lithologically continuous Santonian and Campanian rock section has been examined; the character of rock interrelations has been determined as the one common to the junction area of the northern part of the Don-Medveditsa and the southern termination of the Rtishchevo-Balanda swells and the Karamysh depression.

The level with anomalous high values of natural remanent magnetization and Koenigsberger ratios was identify in the Upper Maastrichtian of Vol’sk depression (Saratov Volga Region). The microprobe studies of samples from this layer registered elevated concentrations of microparticles of iron, nickel, intermetallics and magnetite spherules of cosmic genesis. Similar petromagnetic anomaly was detect in the uppermost of Maastrichtian in the South Cis-Caspian (Aktolagay Plateau, Kazakhstan).

In the right-bank part of the Saratov Region, a section of terrigenous and carbonate rocks has been determined to underlie the ?sponge? horizon conventionally dated back to the Santonian. The maximum thickness of the marls, constituting a substantial portion of the section, occurs in the western part of the region.

On the base of spectral Fourier analysis of magnetic susceptibility time series of nearly 10 000 measurements of rock samples in the turonian-maastrihtian sediments, exposed near Nizhnyaya Bannovka village (Volga River Right Bank, Southern Saratov Region) there were detected long and short eccentricity cycles. Petromagnetic variations, correlated with different variants of eustatic curves detected the presence of well known sequences.

In the ?Ozerki? sections, in the terrigenous and carbonate rocks, a faunal complex has been determined – unusually diversified and relatively abundant for the right-bank part of the Saratov Region. Examination of the specified groups of fossil invertebrates has allowed to propose variants for biostratigraphic division and correlation of the sections under consideration. The carbonate rocks are supposed to belong to the Turonian-Coniacian and the underlying terrigenouscarbonate rocks are regarded as the Lower Turonian ones. Formation of the ?sponge?