Geographical and stratigraphical distribution of Devonian coral faunas in the USSR

Abstract Devonian marine deposits, with their included coral remains, are wide-spread over the USSR. The Lower Devonian is developed in the geosynclinal regions of the Urals, Taimyr, Central Asia, Kazakhstan, Altai, Salair, Transbaikal, the Far East, and the Northeast of the USSR. In the Middle Devonian, marine transgressions occurred in areas such as the Russian platform, Caucasus, and Transcaucasus. Upper Devonian seas covered the same regions. The study of the Devonian coral fauna of USSR has assisted materially in the Devonian correlations. On the basis of the coral faunas, the Russian Devonian divides naturally into six biostratigraphic units. The first, corresponding to the Lower Devonian, is characterised by the dominance of squamulate Favositidae, by Spongophyllidae, Tryplasmatidae, and Chonophyllidae. The second biostratigraphic unit corresponds to Lower Eifelian and is characterised by the development of Favistellidae, Columnariidae, Xystriphyllidae, Spongophyllidae, Acanthophyllidae, and a great expansion of Pachyfavosites. The third unit (Upper Eifelian) was a time of maximal coral development. Particularly abundant are Thamnoporidae, Alveolitidae, Coenitidae, Digonophyllidae, Zonophyllidae, Stringophyllidae and Heliophyllidae. The fourth unit (Givetian) is characterised by the predominance of Thamnoporidae, Alveolitidae, Disphyllidae, Thamnophyllidae, Heliophyllidae, Haliidae. It marks the disappearance of Heliolitidae, Favositidae, cystimorphs, Favistellidae, and the other old coral groups. The fifth unit (Frasnian) is marked by an expansion of Thamnoporidae, Alveolitidae, Disphyllidae, Thamnophyllidae, Halliidae and Macgeeidae. The end of this stage coincides with the disappearance of all Devonian coral families, which are absent in the final biostratigraphic unit, corresponding to the Famennian Stage. Considering the general development of corals we can establish regional complexes, which permit division of the territory of the USSR into several provinces: Ural-Tien Shanian, Altai-Sayanian, Djungar-Balchashian, Indigir-Colymian, and Mongol-Oehotian, Distinct coral assemblages are characteristic of each of the provinces and biostratigraphic units permitting correlation between the different regions.