морские ежи

The final, late Campanian – early Maastrichtian stage of development of echinoids Micraster and Isomicraster, was studied based on extensive material from the Upper Cretaceous sediments of the North Caucasus, Mangyshlak, Kopetdag, Volga and Transvolga regions. The changes in the complex of morphological characters in the youngest species, which are predominantly connected with variability in the structure of the oral surface of the test, considered in detail.

A first for the Volga region described two new species of echinoids and shows their stratigraphic position. Analyzed the relationship identified Maastrichtian sea urchins of the region coupled with synchronous complexes conjugate paleobiochores

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.

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.

The horizon enriched in glauconite and phosphorite was revealed at the carbonatic outcrops near Volsk in the Coniacian and Campanian stage deposits. The short descriptions of studying sections are presented. The spread of synchronous deposits within Khvalynsky district was traced. The Lower and Upper Santonian and the Campanian age deposits are proved by the presence of the inoceramids, belemnites and echinoides. Its vertical distribution was traced.