Upper Cretaceous

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.

Arterial directions in formation of module organization of skeleton hexactinellids are caused by vegetative forms of reproduction. It is supposed that some tendency of selection of protozoa module forms can be traced in morphogenesis of separate generic types of late Cretaceous sponges. The concept “polyosculumic„ sponges is considered in vast context personally in reference to skeletons with some osculumics formed in the result of partial regeneration of organism

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.

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?

The representative data about magnetic susceptibility, its anisotropy before and after heating up to 500°C and other petromagnetic characteristics were received on two sections of carbonate sediments of Maastrihtian – Chahmahly and Takma, located in Bakhchysarai region of the Republic of Crimea. In the studied sections there were established the magnetozones of normal and anomalous polarity, the comparison of determined zones with Geomagnetic Polarity Time Scale was conducted.

The examination of the modular organization in fossil skeletal sponges (Hexactinellida) is mainly related to a study of their vegetative reproduction. The concepts of the reproductive forms for both Recent and Mesozoic hexactinellids can be ambiguous. Examples of the skeletons of fossil sponges from the Late Cretaceous of the Volga River basin, with morphologically detached and naturally distributed sprouts interpreted as buds, are shown. 

The section of campanian deposits of the south-west of the Ulyanovsk region characterized by a strata of “knotty” chalk is described. It was found relatively numerous faunal complex presented mostly by belemnites, bivalves and echinoids. The diversity of epibiontic organisms is described. The study of fauna has helped clarify stratigraphic position of the section within the scope of valid regional scheme.