The 'Avins event': a remarkable worldwide spread of corals at the end of the Tournaisian (Lower Carboniferous)

摘要

The "Avins event" is a widespread development of corals at the end of the Tournaisian due to a very high rise of the sea level. On the shallow water shelf of Belgium and northern France, it is marked by the development of oolitic limestones (Avins Member) which correspond to the top of the highstand systems tract of the third-order sequence 4. In Western Europe, it marks a shift between the Tournaisian coral faunas and the Visean faunas, and in the pattern of deposition of the third-order sequences, and is considered as heralding change to a Carboniferous climate with glaciations. The Avins event is characterized by the appearance of the earliest representatives of the genera Palaeosmilia, Merlewoodia, Dorlodotia and Amygdalophyllum, which marks the base of the RC4131 Coral Subzone. It is traced throughout Eurasia and as far as Australia mainly on the basis of its coral association and supported by the foraminifer zonation (assemblage C of the Cf4a1 Subzone). In some areas, the corresponding levels rest directly on an old basement and are the oldest Lower Carboniferous rocks recorded. The Avins event is followed by a strong fall in the sea level during which the common stock of corals gave rise by separate evolutions to endemic Lower Visean coral assemblages, with basins becoming more or less isolated.