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Department of Earth Sciences, Memorial University, St John’s, Newfoundland A1B 3X5, Canada
The Upper Hartfell Shale (including Anceps Bands A-E and the Extraordinarius Band) and the lowest Birkhill Shale have been extensively collected at Dob’s Linn revealing many forms previously unrecorded from Britain. The first two Anceps Bands (A and B) contain a distinct fauna from the following three (C-E) and two new subzones are suggested for the D. anceps Zone, an earlier D. complexus and a later P. pacificus Subzone, which should be more widely correlatable units. A major extinction occurred between Anceps Band E and the Extraordinarius Band (C? extraordinarius Zone) which contains only a few diplograptid species, as does the basal Birkhill shale (G. persculptus Zone). The O? acuminatus Zone commences at 1.6 m above the base of the Birkhill Shale with the first occurrence of A. ascensus while the monograptid A. ceryx appears at 1.9 m. The base of the O? acuminatus Zone is considered to be the most suitable horizon for the Ordovician-Silurian boundary.
