Middle and Upper Devonian conodont biostratigraphy of the Torquay area, south Devon

Castle, Christine

Abstract

Localities and conodont faunas in the Torquay region are described, and the latter are assessed in terms of standard European Devonian conodont zonations, demonstrating that many of the divisions from the Middle Devonian partitus Zone to the Upper Devonian Ag. triangularis Zone are represented here. The stratigraphical history of the area (that is, that of the Torquay Limestone Group) is then discussed in the light of this information. The conodont associations show that deposition of the Daddyhole Limestone, the oldest member of the Group, began in the early Eifelian (lower partitus Zone) and continued into the early Givetian (upper ensensis Zone), but was interrupted by two deeper water, transgressive episodes in the c.costatus and low-mid ensensis Zones respectively; volcanic activity was associated with the first of these events. Accumulation of the massive, stromatoporoid, reefal limestones of the succeeding Walls Hill Formation began in the early Givetian (upper ensensis Zone) and, following a further deeper-water and partly-volcanic episode, a second cycle of reef development occurred in the mid Givetian Lower varcus Subzone. Both phases of reef growth produced some degree of facies differentiation. Regression of the reef began in mid-late Givetian times, and the massive, bioclastic Barton Limestone capped the subsiding reef, with localised concentrations of shells (Lummaton Shell Bed Member) developing in the basal parts of this formation around the Lower- Middle varcus subzonal boundary. Accumulation of the Barton Limestone continued from the Middle varcus Subzone to the mid Frasnian Lower asymmetricus Zone, when the environment deepened and brought about the transition to the Babbacombe Slates. Some area(s) may have formed local topographical highs from.the mid Givetian to the mid-late Frasnian, undergoing dissolution towards the end of this interval, but these area(s) subsided in the late.Frasnian Ag. triangularis Zone and deeper water conditions then prevailed throughout the Torquay district. The deep water ostracod-slate facies became established and continued into the late Famennian, when there was again volcanic activity.

Comparable limestone developments elsewhere in South-east Devon and in Plymouth are discussed, and previous work on the geology of the Torquay region, on Devonian conodont zonations and on Devonian conodonts in South-west England is reviewed. The Torquay conodonts are given a detailed systematic treatment, largely in terms of a form taxonomy. Some fifty-five taxa are identified in the faunas, representative of the ancyrodellids, icriodids, palmatolepids, polygnathids, schmidtognathids and spathognathodids: these are described and illustrated on twenty plates. Details of the individual localities and conodont faunas are to be found in the Appendix.

Citation

Castle, C. Middle and Upper Devonian conodont biostratigraphy of the Torquay area, south Devon. (Thesis). University of Hull. https://hull-repository.worktribe.com/output/4222083

• Thesis Type: Thesis
• Deposit Date: Jan 6, 2020
• Publicly Available Date: Feb 23, 2023
• Keywords: Geology
• Public URL: https://hull-repository.worktribe.com/output/4222083
• Additional Information: Department of Geology, The University of Hull
• Award Date: Aug 1, 1982