<Emphasis Type="Italic">Crescentiella</Emphasis>-microbial-cement microframeworks in the Upper Jurassic reefs of the Crimean Peninsula

In the Upper Jurassic reef successions of the Crimean Peninsula (Sudak and Jalta areas), the microencruster Crescentiella morronensis (Crescenti), microbialites, and multiple generations of cements, form microframeworks. They were observed in two stages of the carbonate platform evolution, in the Middle–Upper Oxfordian, and in the Upper Kimmeridgian–Tithonian. Generally, in both stages, the features of the microframeworks are similar and consist of densely packed Crescentiella associated with microbialites and branched colonies of the sclerosponge Neuropora lusitanica Termier. The difference between the occurrences of the two stages is the variable amount of nubecularid foraminifera and enigmatic tube-shaped structures forming the central cavities of Crescentiella. The Crescentiella-microbial-cement microframeworks formed under phreatic conditions in the upper slope and seaward marginal depositional settings where intensive synsedimentary cementation took place. They formed in the initial stages of long cycles of restoration and blooming of the reefs. The late Jurassic examples resemble the Permian algae-microbial-cement reefs as well as the Triassic Tubiphytes and cement crust-dominated reefs. Concurrently, all these examples formed a transitional facies zone between typical slope facies to shallow subtidal platform margin facies characterized by high taxonomic diversity of calcified sponges, corals, and microencrusters forming the principal part of the reefs.