Upper Viséan foraminiferal and algal diversity at Benburb, Northern Ireland as a tool of high-resolution biostratigraphy, and correlation of Late Viséan-Early Serpukhovian successions in Ireland and Britain

Abstract

Foraminifers and calcareous algae from three limestone units of the Viséan aged Tyrone Group were examined: Maydown Limestone Formation, Blackstokes Limestone Formation, and Blackwater Limestone Formation. The foraminifers recorded from the Maydown Limestone Formation are generally sparse with mostly long-ranging genera. Foraminifers recorded from the Blackstokes Limestone Formation are also sparse, but they suggest a latest Asbian age. Foraminiferal assemblages from the Blackwater Limestone Formation are more diverse and contain rare, but important taxa, confirming an early Brigantian age in intermediate members of the formation. The algal assemblages are generally sparse, but richer in the Blackwater Limestone Formation, where more commonly, early Brigantian taxa occur. Foraminiferal and algal diversity trends confirm that the lower and middle units of the Maydown Limestone Formation can be assigned to Cf6γ1‒Cf6γ2a zones, and the upper unit to Cf6γ2b. The Blackstokes Limestone Formation is assigned to Cf6γ2c. All these units are of late Asbian to latest Asbian age. The youngest Blackwater Limestone Formation is assigned to Cf6δ zone of early Brigantian age. Foraminiferal and algal trend analysis has highlighted the strong similarities between the Benburb succession and those in south Cumbria, northern England and Scotland. This implies that the Asbian–Brigantian boundary has now been moved to a lower horizon, at the base of the Tullymore Limestone Member, which is better recognized by means of algal and foraminiferal diversity, instead of by the occurrence of individual taxa. These zones show close correspondence with those documented from south Cumbria and the Pennines of northern England.