late cretaceous

In the structure of modular organization of the Late Cretaceous hexactinellid sponges, the terminal position is assigned to colonial forms, with skeletons peculiar for complex, intricate structures. Primitive (primary) and genuine (secondary) colonies have been revealed. Skeletons of the primary forms, generally with multiple numbers of equivalent modules and oscula, differ morphologically from the genuine colonies in undeveloped module connecting elements, such as junctions and wall closures, and in the lack of ostia

The authors consider the compound of the late cretaceous deposits opened up in the bore hole number 13, 62 at the Gremyachinsk field of the potassium soils in the Volgograd region. According to the sediment basins evolution from the epicontinental basins (cenoman, turon-cognacian) to the subpelagic basins (cenonian) the lithotipe which form in the late cretaceous level the regular repeated layers of the terrigenous, carbonate, argillaceous-siliceous deposits are characterized

Tendencies of morphogenesis in the Late Cretaceous modular forms contributed to formations of complexly structured secondary (genuine) colonies. Skeletons of genuine colonial sponges differ not just in numerous and diversely arranged equivalent oscula-carrying modules, but in the presence of the module connecting elements – junctions, as well. Characteristic elements of genuine colony skeletons – ostia – have been recognized between the modules and the junctions.

Partial and complete regeneration phenomena, cases of skeleton habitus restoration have been recorded in representatives of the Late Cretaceous hexactinnelids. Regeneration incidences are in many ways associated with the ability of silicon-producing cells responsible for constructing skeleton-generating elements, spicules, to transform, to rearrange their functions in response to the changes of the organism position on the substrate surface and/or upon the changes of the aquatic environment parameters.

Guettardiscyphia skeletons are peculiar for thin walls and highly dense apo- and prosopores. Wall mobility was conductive to formation of conical lobate skeletons of various, occasionally geometrically regular outlines. Substantial number of fossil samples from variously composed rocks from all the Upper Cretaceous intervals has made it possible to trace skeleton transformations in sponge ontogenesis and depending on their environmental conditions.

Basic structure types have been specified in hexacinellids with soldered spicule lattice. The fossils of those occur as skeletal forms. Certain tendencies in Lychniscosa and Hexactinosa morphogenesis were identified as conductive to shaping the spectrum of skeleton archetypes. The increase of sponge morphological diversity was in many ways predetermined by thickness reduction of the skeleton-forming walls, associated with reduction of the irrigation system elements. That has brought about forms of complicated tubular labyrinth habits.

On the base of spectral Fourier analysis of magnetic susceptibility time series of nearly 10 000 measurements of rock samples in the turonian-maastrihtian sediments, exposed near Nizhnyaya Bannovka village (Volga River Right Bank, Southern Saratov Region) there were detected long and short eccentricity cycles. Petromagnetic variations, correlated with different variants of eustatic curves detected the presence of well known sequences.

The Ventriculitidae representatives used to hold noticeable and occasionally dominant position within the Coniacian – Maastrichtian sponge assemblages. Relatively simple skeleton construction in the representatives of the family among the Late Cretaceous hexactinellids has made it possible to trace variations in skeleton morphology, changes in the goblet habitus and in the structure of irrigation system depending on the width variations of the skeleton-building wall.

Among the Late Cretaceous Ventriculitidae, with the most simply constructed pariform skeleton, representatives characterized by unusual neoplasms were identified. On the paragastric surface after the lapel of these sponges (Contubernium), cone-shaped submodules are regularly based, the appearance of which is associated with incomplete blastogenesis. Paragastra of submodules are not associated with the atrium, therefore, Contubernium is considered as a perifrontal organism, occupying an intermediate position between single and modular forms of spongia.

Study of the skeletal morphology of a new representative of the Leptophragmidae family, with no suboscula in its structure, provides support for the earlier specified regularities in generation of Hexactinellida modular forms. Good preservation state of a major colony has made it possible to specify the aspects of paleoecology and taphonomy in the later representatives of the Middle Coniacian – Early Santonian succession of siliceous sponges.