Article: The conodont biostratigraphy of the Devonian Plymouth Limestone, South Devon
Conodont faunas from the Plymouth Limestone are indicative of levels ranging from the Middle Devonian patulus Zone to the Upper Devonian crepida Zone. The conodont faunas are described and compared with European counterparts, with which correlations are proposed. Although there are anomalies in some distributions, the conodonts have provided a tool for the dating and correlation of disjunct sections of Plymouth Limestone, and have enabled the elucidation of stratigraphical, palaeoenvironmental and structural aspects of the carbonates. Thus: the history of the Limestone began in the early Eifelian but was interrupted by a mid to late Eifelian volcanic episode; this was followed by the growth of a carbonate platform during the late Eifelian-mid Givetian. A late Givetian to early Frasnian carbonate maximum, which involved facies differentiation (more restricted environments are recognized in the east and south-east), was followed by an interval of widespread deepening (Lower asymmetricus Zone times). Deposition of massive Frasnian limestones ensued prior to local, mid Frasnian crevassing and further foundering in the early Famenman. The area is inferred to have stood as a topographic high within the late Devonian sea. The Limestone mass has been overfolded in the east but no inverted limb is recognized in the western outcrop.