CORRELATIONS BETWEEN THE EVOLUTION OF BENTHIC FAUNAL COMMUNITIES AND CONVERGENT MOVEMENTS OF LITHOSPHERIC BLOCKS FROM THE SILURIAN TO THE LATE DEVONIAN IN THE MIDPALEOZOIC URALIAN BASIN

The palaeogeographical interrelationships between benthic communities of middle Palaeozoic carbonate platforms from both sides of the Urals are compared. The evolution of endemism in time as well as of taxonomi c diversity and affinity trends in Silurian and Devonian brachiopods, tabulate corals and trilobites are investigated for the first time usi ng the internationally adopted standard of biozonation. Preliminary re sults indicate that, in all considered biotas, diversity and affinity rates were extremely low at the beginning of the Silurian. They increa se thereafter until the late Middle Devonian and the Late Devonian, wh ere a high degree of identity was reached. The observed overall increa se in biogeographic affinity is interpreted as being the result of con vergent plate movements between the eastern Uralian oceanic domain, wh ere platform carbonates were deposited either on island arcs or on mic roplates, and the passive East European margin. A certain delay in the progress of faunal relationships is observed in the early Middle Devo nian which may be related to the emplacement of the Magnitogorsk volca nic megazone at that time.