палеоэкология

The article describes examples of attachment of bivalves to the surfaces of skeletons of Late Cretaceous hexatinellid marine sponges. Attachment is associated with the adaptation of mollusks to living conditions in mobile laminar streams of bottom water masses carrying nutrient suspension, carbonate material and terrigenous components. The bottom population is represented mainly by marine sponges, hexatinellides, as well as bivalves adapted to the active dynamics of bottom waters.

The fouling of skeletons and shells of benthic organisms and the formation of multi-tiered skeletal formations are characteristic of carbonate-producing Porifera, which participated in the structure of reef communities during the Phanerozoic. The accretion of flint sponges, Hexactinellidas, to the solid elements of the substrate is a little-known phenomenon, since many representatives of this group were fixed on the sediment surface by rhizoid outgrowths.

As a result of the complex analysis of petromagnetic, micro- and macrofaunistic data of deposits on the Kallovian – Oxfordian boundary of Dubki section (Saratov), which is one of candidates for a role of a Global Boundary Stratotype Section and Point of Oxfordian boundary (GSSP), it is established significant correlation between magnetic susceptibility variations and changes of an abundance, a specific variety of ostracodes, foraminiferes and ammonites.

The analysis of the distribution of the Kimmeridgian–Volgian ostracods in the section near the village Valy made it possible to establish a sequence of eight communities, the change of which reflects changes in the ecological conditions in the basin. Changes in sea level fluctuations, the main physical and chemical parameters of the ostracod habitat – temperature, salinity of water, oxygen content in it, eutrophy and concentration of organic matter in sediment – are reconstructed. Information on the magnetic susceptibility and its increase after heating was obtained.

The paper analyzes the taxonomic composition and the habitat of the representatives of the Middle – Late Cenomanian and the Middle Turonian marine biota. The examined fossils have been isolated from the bulk sample obtained from the phosphorite horizon lying in the bottom of the Middle Turonian carbonate rocks in the Senomanskaya Stenka section (Volgograd Region, Zhirnovsk district).