Поволжье

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.

The Gubkino Horizon (Turonian-Coniacian) in the Bolshoy Kamenny ovrag section (Zhirnovsk town, Volgograd Region) has not been purposefully studied so far. As a result of biostratigraphic and magnetostratigraphic researches the carbonate rocks of the Gubkino Horizon were first divided into zones based on benthic foraminifera complexes and characterized by geomagnetic polarity and rock-magnetism data. The most part of the Bolshoy Kamenny ovrag section is covered by the reverse polarity zone.

The first representatives of Cameroptychium on the territory of Russia, which are established in the rocks of the Upper Cretaceous of the Volga region, are described. The labyrinthine structure of the skeleton and the modular, colonial level of organization of these sponges are considered, which is typical for many Late Cretaceous Hexactinellids. The widespread manifestation of isomorphism indicates the finiteness of the formation of representatives of Hexactinellida. The origin of Cameroptychium is correlated with Santonian Plocoscyphia.

Among the numerous and diversiform Late Cretaceous siliceous sponges collected throughout the Volga region, several representatives of the genus Botryosella have been encountered, previously unknown for the area. Analysis of the skeleton morphology, peculiar for massive transverse outgrowths, confirms manifestations of isomorphism in Hexactinellids and the opinion of inaccuracies available in the descriptive terminology applied to the skeletal morphology of this Porifera group.