Abstract
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.
Highlights
In the Tethyan realm and its margins, the Late Jurassic was a time of intensive growth of reefs
In the Upper Jurassic reef successions of the Crimean Peninsula, reef facies were observed where Crescentiella, microbial crusts and cements were prevailing components thereby forming microframeworks. Such structures have so far not been described in detail from the Crimea-Caucasus region
The basic difference between the Upper Oxfordian and the Upper Kimmeridgian–Tithonian specimens is the variable amount of nubecularid foraminifera and tube-shaped structures forming the central cavities
Summary
In the Tethyan realm and its margins, the Late Jurassic was a time of intensive growth of reefs. Unlike other Upper Jurassic reefs from both western and southern Europe, which have deserved a number of detailed studies, the reefs from the Crimea-Caucasus region have received less attention, as yet. For the Southern Crimea, Nikishin et al (2015a, b) presented a ternary plot showing the Late Jurassic reefbuilding communities of Crimean reefs based upon data from, among others, the Ai-Petri Massif (Krajewski 2008, 2010). In the Crimea Mts, the most spectacular Oxfordian coral reefs are reported from the Sudak area (e.g., Muratov 1973; Geister et al 2007; Nikishin et al 2015b) detailed studies on their facies and microfacies have so far not been published. A few papers with details concerning Upper Jurassic reefs were published from
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