The onset of the Permo-Carboniferous glaciation: reconciling global stratigraphic evidence with biogenic apatite δ¹⁸O records in the late Visean

The δ¹⁸O values of phosphatic microfossils recovered from NW Ireland are used to determine the timing and magnitude of cooling associated with the onset of the Carboniferous glaciation. Microfossil fish δ¹⁸O_apatite demonstrates a +2.4‰ (V-SMOW) shift, which, once corrected for δ¹⁸O_seawater changes owing to evolving ice volumes, equates to an approximate 4.5 °C reduction in equatorial sea surface temperature between the earliest Asbian and the mid-Brigantian (late Visean). Both conodont and microfossil fish δ¹⁸O_apatite indicate stabilization of an ‘icehouse’ climate during the Brigantian and into the Serpukhovian. Substantial late Visean cooling identified herein is in good agreement with global glacioeustatic records.