Ichthyofaunal correlation of the Triassic deposits from the northern Cis-Caspian and southern Cis-Urals regions

Maxim G. MINIKH & Alla V. MINIKH

en Geodiversitas 19 (2) - Pages 279-292

Published on 24 June 1997

All the known data on the Triassic ichthyofauna from south-east European Russia are summarised. The material studied comes from thirty-nine localities from the Lower and Middle Triassic reference and stratotype sections of the South Cis-Urals and northern Cis-Caspian regions. Data on terrestrial vertebrates, ostracodes, and charae are used as well as paleomagnetic sampling results. A certain stratigraphic importance of the Triassic gnathorhiza and ceratods is demonstrated relative to lungfish, the one of hybodontids relative to squaliforms and that of saurichthiids among actinopterygians. Two super-ichthyocomplexes were revealed within the Triassic sections according to dipnoan distributions: those of gnathorhiza and ceratods. Their change in the region occurs in the middle of the Olenekian age and is associated with the rather short Akhtuba time in the Cis-Caspian and with the synchronous Fyodorovka time in the South Cis-Urals. Considering the data on other fish groups, three independent ichthyocomplexes are recognised in the Triassic ichthyofauna: the Vetlugian and Yarenian ones in the Early Triassic and another one in the Middle Triassic. The Yarenian ichthyocomplex comprises two clearly manifested groups of different ages (the Akhtuba and Bogdo ones in the Cis-Caspian and the Fyodorovka and Gamskaya ones in the South Cis-Urals). The Middle Triassic ichthyocomplex comprises the Donguz and Bukobaj fish groups. The regularities revealed in fish-taxa changes with time, are traced within the sections across the adjacent territories from the Cis-Urals to the Cis-Caspian. The Lower Triassic Akhtuba suite from the Cis-Caspian Bogdo section was correlated by fish with the lowermost part of the Petropavlovka suite, and the overlying Bogdo suite with the rest of the Petropavlovka section from Orenburg region. The Middle Triassic Donguz and Bukobaj suites from the Cis-Urals are stratigraphically analogous to the Elton and Inder suites from the Middle Triassic section in the northern Cis-Caspian. The succession revealed in the Triassic ichthyofauna development is maintained all over the territory of European Russia. It is traced in the adjacent regions and may serve as the basis for stratigraphic divisions and interregional correlations of different-facies marine and non-marine sections of the Triassic.

Keywords :

Ichthyofauna, Triassic, northern Cis-Caspian, southern Cis-Urals