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The late Silurian-Middle Devonian long-term eustatic cycle as a possible control on the global generic diversity dynamics of bivalves and gastropods

Ruban Dmitry A.

Geologos

2013

Vol. 19, No. 3

193--200

A long-term eustatic cycle (fall and subsequent rise of the global sea level) embraced the late Silurian-Middle Devonian time interval. Potentially, these sea-level changes could drive global biodiversity. The stratigraphic ranges of 204 bivalve genera and 279 gastropod genera included into the famous Sepkoski database allow reconstructing changes in the total diversity and the number of originations and extinctions of these important groups of marine benthic macro- -invertebrates during this interval. None of the recorded parameters coincided with the long-term global sea-level cycle. It cannot be not excluded, however, that the global sea-level changes did not affect the regions favourable for bivalve and gastropod radiation because of regional tectonic mechanisms; neither can it be excluded that the eustatic control persisted together with many other extrinsic and intrinsic controls. Interestingly, the generic diversity of gastropods increased together with a cooling trend, and vice versa. Additionally, the Ludlow, Eifelian, and Givetian biotic crises affected, probably, both fossil groups under study. There was also a coincidence of the relatively high bivalve generic diversity, initial radiation of gastropods and the entire biota, and the diversification of brachiopods with the Early Devonian global sea-level lowstand, and this may be interpreted as evidence of a certain eustatic control on the marine biodiversity.

Devonian palaeogeography of the Southern Urals

Mizens G. A.

Geological Quarterly

2004

Vol. 48, No 3

205--216

Devonian deep-water deposits of the Southern Urals are represented mainly by flysch and cherty units. The main sedimentary basins (marginal sea and back-arc basin) and their origin, evolution and principal depositional environments are characterised. The main sources of clastic material were the Uraltau microcontinent (especially in the Famennian, when a mountain range formed following collision with an island arc) and two island arcs: the Irendyk, at the end of the Early and at the beginning of the Mid Devonian; and the Magnitogorsk, in the Mid to Late Devonian. Comparison with transgressive-regressive cycles established in Devonian epicontinental basins worldwide indicates that these global sea level fluctuations were recorded also in the Southern Urals deep-water settings. This applies primarily to the Eifelian and Frasnian-Famennian transgressive-regressive cycles.