INTEGRATED CONODONT AND GRAPTOLITE BIOSTRATIGRAPHY OF THE LOWER HARTFELL SHALE (SANDBIAN-KATIAN, LATE ORDOVICIAN), NEAR MOFFAT, SCOTLAND

Black graptolitic mudstones of the Lower Hartfell Shale are well exposed at Hartfell Spa near Moffat, Scotland. These strata span the Sandbian-Katian boundary within a well-established graptolite biostratigraphic framework (Zalasiewicz et al., 1995). Graptolites belonging to the Climacograptus bicornis Zone occur in the first 5.5 meters of the Lower Hartfell Shale. The FAD of Diplacanthograptus caudatus, which marks the base of the D. caudatus Zone and the base of the global Katian Stage, occurs at 5.5 meters above the base section. The FAD of Pleurograptus linearis, the index taxon for the overlying zone, occurs at 17.5 m above the base of the Lower Hartfell Shale. Conodonts were recovered from 9 horizons in the Lower Hartfell Shale: 3.7 m - Scabardella altipes; 5.8 m - Amorphognathus tvaerensis, Scabardella altipes, Dapsilodus sp., and Drepanoistodus suberectus; 6.0 m - Protopanderodus liripipus; 7.4 m - Oistodus sp. cf. O. venustus?; 8.1 m - Protopanderodus liripipus; 11.5 m - Protopanderodus liripipus, Periodon grandis (m element); 12 m - Scabardella altipes, Protopanderodus liripipus, Dapsilodus? sp., Periodon sp. (s element); 12.5 m - Protopanderodus liripipus; 16.8 m - Amorphognathus superbus, Protopanderodus liripipus. Amorphognathus tvaerensis is present 0.3 meters above the FAD of D. caudatus and A. superbus is present 9.4 meters above it. Thus, the A. tvaerensis Zone - A. superbus Zone boundary occurs within an interval of 9.1 meters in the D. caudatus graptolite Zone. These bedding plane co-occurrences provide more precise ties between graptolite and conodont biozonations and support the potential for additional resolution with further collecting at these and other localities.