Devonian ammonoid successions and facies in Devon and Cornwall

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Abstract
The ammonoid successions in the Devonian rocks of the Torquay, Chudleigh, and Padstow areas of Devon and Cornwall are described and it is shown that representatives of all the German Devonian ammonoid Stufen occur in south-west England. The ammonoid successions demonstrate significant facies changes within the Middle and Upper Devonian among the areas discussed. In the Torquay area the zone of Anarcestes lateseptatus is recognizable in the Calceola Shales, and in the massive Givetian limestones two ammonoid faunas occur, a lower zone with Maenioceras molarium and an upper zone with M. terebratum. The main Lummaton Shell Bed includes the fauna of the terebratum Zone. Limestone sedimentation probably continued into the Lower Frasnian, but the Manticoceras cordatum and Crickites holzapfeli zones are represented at Saltern Cove by thick argillaceous developments: it appears that at Torquay these zones may be reduced in thickness. An ostracodslate facies follows immediately above the holzapfeli Zone; ostracod evidence shows that this facies continues into the Upper Famennian. A similar Middle Devonian succession, but without ammonoids, is developed at Chudleigh, but the Upper Devonian sequence is a reduced one of nodular limestones and slates with nodules in which the Manticoceras, Cheiloceras, Platyclymenia, Clymenia, and Wocklumeria Stufen occur. The name Mount Pleasant Series is proposed for the Famennian sequence, which is 170 ft in thickness. This Upper Devonian facies is thought to be comparable with the German schwellen facies in contradistinction to that at Torquay, which is of becken type. The Middle Devonian in the Padstow area is predominantly of slate facies with minor calcareous developments in the Eifelian and Givetian. Three main goniatite faunas can be recognized within the Middle Devonian. Good goniatite faunas of the Frasnian cordatum Zone occur in banded slate facies and these are overlain by a thick series of ostracod-bearing slates. It is evident that the ostracod facies enters at a lower level than at Torquay. The following new species of goniatites are described: Archoceras ussheri, Ponticeras pedderi, and Protornoceras foxi.

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