Foraminiferal Evolution as A Basis for the Subdivision of the Middle Viséan in Europe

Abstract

Abstract First occurrences of selected foraminifers and their interpreted phylogenies in the uppermost Arundian Substage of the South Cumbria Shelf, northern England, allows the distinction of four biostratigraphic events. Event A1 is characterised by the occurrence of occluded Nodosarchaediscus, Consobrinellopsis, and Archaediscus krestovnikovi and is assigned to the ‘upper’ Cf4δ subzone. Event A2 is characterised by the first occurrence of Pojarkovella ketmenica and Archaediscus at concavus stage (including the first A. pauxillus) and is assigned to the base of the Cf5α subzone. Event A3 is characterised by Koskinotextularia aff. cribriformis, Koskinotextularia sp., Archaediscus moelleri, Endothyranopsis compressa, and Omphalotis minima and is assigned to the base of the Cf5β subzone. Event A4 is characterised by the first occurrence of Koskinotextularia cribriformis, Koskinotextularia bradyi, Koskinotextularia obliqua, and Pojarkovella nibelis morphotype 2. The base of the Cf5α subzone likely coincides with the base of the Livian in Belgium and Tulian in the Russian Platform, although the occurrence of hiatuses and facies barren in foraminifers leads to uncertainty in correlation. The Cf5β subzone is correlated with that part of the Livian and Russian Platform succession with preserved foraminifers and thus can be used for worldwide correlations. However, formally, it cannot be confirmed if this horizon is an isochronous level (due to hiatuses and hostile facies), and it is necessary to locate a slightly higher level of potential correlation that better displays the absence or presence of the successions, such as event A4.