During the Silurian-Early Devonian, cephalopod limestone biofacies represent one of the best documented sedimentary deposits in the stratigraphic column. Reconstruction of the northern margin of Gondwana by means of cephalopod limestone biofacies also represents one of the most interesting topics of Early Palaeozoic palaeobiogeography.
Several authors have investigated the geographical position of various fossil groups during the Silurian-Early Devonian, including: nautiloid cephalopods (Crick 1990), bryozoans (Tuckey 1990), brachiopods (Cocks and McKerrow 1973; Boucot and Blodgett 2001), phytoplankton (Colbath 1990), ostracodes (Berdan 1990), higher land plants (Edwards 1990), palynology and plant dispersal patterns in the Ludford-Prídolí interval and Silurian-Devonian boundary (Richardson et al. 2001), Silurian stromatoporoids (Nestor 1990), Devonian stromatoporoids (Stock 1990), rugose corals (Pedder and Oliver 1990), algae (Poncet 1990), and Early-Middle Devonian gastropods (Blodgett et al. 1990). Nevertheless, in his discussion of Silurian biogeography Boucot (1990, pp. 191-196) noted that, "A number of potentially useful groups such as the nautiloids and stony bryozoans remain largely unstudied." As reported previously by Holland (1971, p. 70) "...The predominant impression is of cosmopolitan faunas, but this may be because outcrops of effectively observable Silurian rocks broadly follow the supposed Silurian equator. Platforms were apparently exceptionally large and geosynclines limited in the Silurian; the platforms comprise two "magnafacies," characterised by (a) shelly faunas and (b) graptolite-bivalve-orthocone faunas." (see also Cocks 2001). This latter represents the subject of this investigation.