The Tournaisian-Viséan boundary in Eurasia : definition, biostratigraphy, sedimentology and early evolution of the genus Eoparastaffella (foraminifer)

The late Tournaisian to early Viséan interval (Lower Carboniferous) was a time of important changes. In Belgium, the Namur-Dinant Basin evolved from a carbonate ramp to a platform, benthic and nektobenthonic marine faunas changed significantly, and a major sea-level fall is recorded in the boundary interval. The precise timing and mechanism of that fall were, however, unclear, notably because of insufficient biostratigraphic resolution. Moreover, the present definition of the Viséan Stage has to be revised as decided by the Subcommission on Carboniferous Stratigraphy (SCCS). Despite this, some authors correlated the same sea-level fall worldwide, postulating a eustatic origin. In this work evidence (sedimentology, biostratigraphy) from the Namur-Dinant Basin are re-examined and sedimentary basins in Ireland, the Czech Republic, northern Iran and southern China are studied in detail. Benthic foraminifers and conodonts are used as primary dating and correlation tools. Investigated basins are then compared, and the results conflated with available published data on other basins worldwide. A new high-resolution biostratigraphic scheme for the Tournaisian-Viséan boundary interval, based on foraminifers and conodonts, and valid at the scale of Eurasia, is developed. A criterion to recognize the base of the Viséan based on an evolutionary lineage in the genus Eoparastaffella (foraminifer) is proposed, as well as a new stratotype section in southern China. Increased biostratigraphic resolution demonstrates that in Western Europe, the latest Tournaisian was characterized by HST conditions, and that a major and rapid sea-level fall occurred shortly before the base of the Viséan. Latest Tournaisian HST conditions are observed in many other areas across the globe, but the succeeding sea-level fall is not recorded in all regions investigated. Yet, the eustatic hypothesis cannot be ruled out because of the still relatively low amount of well-dated and correlated sections, and because of possible glacio-isostatic effects.Doctorat en sciences (sciences géologiques) (GEOL 3)--UCL, 200