New algal and foraminiferal assemblages and evidence for recognition of the Asbian-Brigantian boundary in northern England

Abstract

SUMMARY A detailed micropalaeontological analysis (foraminifera and calcareous algae) has been made of the Brigantian Basal Stratotype section at Janny Wood in the Stainmore Trough, and sections in the Rookhope, Allenheads, Feizor and Back Scar boreholes on the Alston and Askrigg blocks of northern England. The sections contain a complete composite succession from the upper Asbian to the Pendleian. Using the first appearances, last appearances and the acmes of the foraminiferal and algal taxa, it is possible to recognize eight assemblages in the shallow-water platform facies of the Alston and Askrigg blocks. Several taxa occur earlier in the Janny Wood section (Stainmore Trough) than in the boreholes on the adjacent blocks and many common taxa in what is currently regarded as the highest Asbian part of the Janny Wood section are more typical of the Brigantian. All the palaeontological data suggest that the Birkdale Limestone and possibly the Robinson Limestone in the Janny Wood section could be Brigantian, although there is an absence of basal Brigantian foraminiferal markers (e.g. Loeblichia and Janischewskina). Nevertheless, the basal Brigantian Stratotype boundary could be moved from its current position at the base of the Peghorn Limestone to a lower level, preferably at the base of the Birkdale Limestone.