Upper Cretaceous

Tremabolites sponges known among the Middle-Late Cretaceous beds in Europe are reliably identifiable due to the numerous openings against the background of the skeleton smooth upper surface. The ideas of the level of organization in these sponges and of the species characteristics are far from being univocal. The paper deals with the species diversity of Tremabolites common in the Coniacian – Santonian rocks from the Volga Region. Examples of regeneration and budding in the representatives of the group are presented.

The morphological diversity of diosculumic sponges, known as Paracraticularia cylindrical, results from the fact that many fossils assigned to this species prove to be fragments of the apical segments of internodes (branches) from major colonies that are rarely encountered as totally preserved fossils. The structures of the branch apical segments and the oscula outlines reflect various manifestations of hexactinellida synchronous division conductive to morphological diversity of the descendants, the succeeding complicatedly structured colonial sponges.

The paper presents biostratinomical characteristics of the Cenomanian and the Turonian fossil complexes found in the Middle Turonian phosphorite horizon from the Senomanskaya Stenka section (Volgograd region, Zhirnovsk district) constituting the basis of the benthic colonies and nekton communities. Probable interpretations for the settings contributory to generation of the phosphorite inclusion clusters are provided.

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).