Statistical biostratigraphical analysis of graptolites from the Southern Uplands Terrane

Stratigraphical evaluation, including cluster-analysis, of more than 150 lower Caradoc graptolite-bearing localities from southern Scotland has failed to identify a discrete assemblage that can be used to recognise the Climacograptus bicornis peltifer Biozone. Instead, the lowermost Caradoc Nemagraptus gracilis Biozone is redefined as a partial range zone. It is succeeded by the Climacograptus bicornis Biozone, divisible into a lower Orthograptus apiculatus-Dicranograptus ziczac Sub-biozone, identified by the appearance of the eponyms together with the earliest occurrences of Amplexograptus leptotheca, Dicranograptus tardiusculus and several other graptolite taxa, and an upper wilsoni Sub-biozone, formerly the wilsoni Biozone, marked by the first appearance of Climacograptus wilsoni. Nemagraptus gracilis and Didymograptus superstes range through at least the lower part of the apiculatus-ziczac Subbiozone, but may be absent from the upper part of the sub-biozone, an interval that may equate approximately to the peltifer Biozone as formerly recognised. As recognised, the bicornis Biozone of Scotland is the approximate equivalent of the bicornis Biozone of North America and, at least in part, of the foliaceus Biozone of southern Britain. It is succeeded in Scotland by the clingani Biozone.