Abstract
A detailed biostratigraphy is established, using the high foraminiferal abundance and diversity at Trowbarrow Quarry, which is also proposed as a stratotype section for the late Asbian (late Visean), a substage not previously formally subdivided. The foraminiferal assemblages suggest that the early Asbian has to be revised, which has implications for the chronostratigraphy of many late Visean outcrops in Britain, which are probably erroneously interpreted.
From the upper part of the Park Limestone Formation at Trowbarrow Quarry, near the base of the section, the transition between foraminifers assigned to the early and late Asbian (Cf6 alpha-beta to Cf6 gamma subzones) is identified. The Urswick Limestone Formation contains excellent biostratigraphic records of many important taxa, enabling the subdivision of the formation into five foraminiferal assemblage zones for the late Asbian, namely Cf6 gamma 1a, Cf6 gamma 1b, Cf6 gamma 2a, Cf6 gamma 2b and Cf6 gamma 2c.
The last assemblage is currently recognized only in the North Pennines and at Trowbarrow. These assemblages enable revision of the stratigraphic range of many taxa used as biostratigraphic markers in Britain and Ireland.
Owing to its excellent foraminiferal record, the late Asbian subdivisions will significantly facilitate the reinterpretation of other well-known Asbian platform carbonate successions in Britain. Although there are some faunal differences, the base of the late Asbian can be confidently correlated to other European zonal schemes, with its base being equivalent to the base of the former V3b gamma or more recent MFZ14 foraminiferal zones of Belgium, and the base of the Mikhailovian Substage in Russia.