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Geology of the Torquay district. Sheet description of the British Geological Survey 1:50 000 Series Sheet 350 Torquay (England and Wales)

By B E Leveridge, R C Scrivener, A J J Goode, and R J Merriman

Bibliographical reference: Leveridge, B E, Scrivener, R C, Goode, A J J, and Merriman R J. 2003. Geology of the Torquay district. Sheet description of the British Geological Survey, 1:50 000 Series Sheet 350 Torquay (England and Wales).

Authors: B E Leveridge, R C Scrivener, A J J Goode, and R J Merriman

The National Grid and other Ordnance Survey data are used with the permission of the Controller of Her Majesty’s Stationery Office. Licence No: 100017897/2003. Maps and diagrams in this book use topography based on Ordnance Survey mapping.

Copyright in materials derived from the British Geological Survey’s work is owned by the Natural Environment Research Council (NERC) and/or the authority that commissioned the work. You may not copy or adapt his publication without first obtaining permission. Contact the BGS Intellectual Property Rights Section, British Geological Survey, Keyworth, e-mail ipr@bgs.ac.uk. You may quote extracts of a reasonable length without prior permission, provided a full acknowledgement is given of the source of the extract.

(Front cover) Thatcher Rock viewed from Ilsham Marine Drive [SX 940 633] looking south-eastwards. Foreground cliffs are in the Meadfoot Group (undivided) and the island comprises rocks of the Daddyhole Member, Torquay Limestone Formation (Photographer B E Leveridge; GS1284).

(Back cover)

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Acknowledgements

M E Lewis contributed script on the hydrogeology of the district. M E Drummond mapped and researched part of the area during tenure of a University of Newcastle upon Tyne/BGS CASE studentship (1979–1982). He kindly provided his PhD thesis for incorporation of information into any subsequent BGS publication. Liberal reference has been made to his work for the dating for the members of the Brixham Limestone Formation and the Nordon Formation. Christine Castle also kindly gave permission to use data from her PhD thesis (1982) submitted to the University of Hull, regarding the ages of members of the Torquay Limestone Formation. Reference has been made to the work of H C Wilkinson, who kindly donated to BGS copies of his 1:10 560 scale field-slips of the Totnes area.

This report was edited by A A Jackson. Figures were produced by R J Demaine, P Lappage and G Tuggey, BGS Cartography, Keyworth.

Notes

The area covered by the geological Sheet 350 Torquay is referred to as ‘the district’. National grid references are given in the form [SX 890 125], all lie within the 100 sq km grid SX. Abbreviations in brackets refer to the symbols used on the geological map. The number given with the plate captions is the registration number in the British Geological Survey photograph collection.

Geology of the Torquay district—summary

This Sheet Description is an account of the geological map Sheet 350 Torquay, which lies within the county of Devon. The district has had a long association with geology as a science, and in the 19th century fossils from the limestones played a key part in establishment of the Devonian system. Today it has a high concentration of geological Sites of Special Scientific Interest.

The Upper Palaeozoic Devonian and Permian systems form the bedrock of the district. Sedimentary associations similar to those of the Torquay district occur across north-west Europe, formed in basins on the northern margin of the Rhenohercynian oceanic basin. Crustal extension and faulting during the late Silurian and Devonian resulted in the formation of graben and half graben. Continental rifting developed sequentially in a northerly direction; the southern basins filled with sediment while those to the north were still in the process of formation. Thus, sedimentation varied from basin to basin, and there is no single regional succession. In the Torquay district the sediments were deposited in the Looe Basin and in the adjacent South Devon Basin to the north. A change from terrestrial to marine sedimentation occurred in the Early Devonian in the Looe Basin, and marine conditions persisted throughout the remainder of the Devonian. Strata of the Mid and Late Devonian are characterised by grey and purplish red mudstone in the basins and by reef limestones and volcanic rocks on the intervening highs.

The Rhenohercynian basin closed during the Devonian, and deformation migrated northwards during the early Carboniferous with successive basin inversions, folding, cleavage and thrust development. The successions within the basins of the district were pushed out northwards on to the adjacent highs, and the deposits of the high were thrust onto adjacent basin sequences. When all basins of the province had closed late in the Carboniferous, continuing stress produced the second regional deformation. This was a synchronous event in the province, producing new structures in the Devonian rocks and in Dinantian rocks elsewhere in the region, and deforming the Silesian rocks to the north of the district. In Britain this deformation has commonly been regarded as the Variscan Orogeny.

Regional north-south extension and emplacement of granite followed at the end of the Carboniferous and in the early Permian. Permian depositional basins of the district were formed in this early post-orogenic phase. Rapid erosion produced torrential deposits, red breccias and sandstones, which filled the basins during the Permian.

There is little direct evidence of Mesozoic events in the district, but marine retreat features record a falling sea level from early Cainozoic times as a ‘staircase’ of wave-cut platforms; those platforms below 40 m OD are related to Quaternary events. Cave systems, such as Kent’s Cavern, were formed in Devonian limestone at levels that can be related to still-stands during marine regression: animal remains and artefacts found within the caves are of national importance. Periglacial head deposits of late Pleistocene (Devensian) age commonly infill the smaller valley bottoms or have been exposed on the cliffs by marine erosion. Low sea level during the Pleistocene glaciations caused the river systems to cut down to nearly 40 m below OD just offshore. Erosion and deposition during the Quaternary has produced head, fluvial and marine alluvium, which locally conceal the bedrock.

The Torquay district lies at the eastern end of the southwest England metalliferous province, but beyond the zone of tin and base metal deposits associated with the Dartmoor Granite so that the range of mineral deposits is restricted. Iron ore has been worked in the past and gold has been recorded. Other mineral products include building stone, roadstone and aggregate, brick making material, pottery clay and mineral pigments. These operations are now closed with the exception of the limestone quarry at Yalberton, which still produces a small quantity of stone.

Geological factors that have a bearing on land use and development are reviewed briefly in the Applied geology section. Attention is drawn to potential engineering hazards that have a bearing on future development in the district, for example concealed peat within alluvium and cavities within the limestone. Landslips are recorded in all of the major lithofacies that crop out along the coast and are a significant potential hazard in this popular holiday area. Additional sources of geological data are listed in the Information sources section and a Reference section is also included.

(Table 1) Geological succession of the Torquay district.

Chapter 1 Introduction

This Sheet Description presents an account of the geological map Sheet 350 Torquay. The district is underlain by Upper Palaeozoic rocks of Devonian age that are in part overlain unconformably by Permian deposits, mainly in the vicinity of Torquay and Paignton. Marine retreat features record a falling sea level from early Cainozoic times as a ‘staircase’ of wave-cut platforms; those platforms below 40 m above OD are related to Quaternary events. Cave systems, such as Kent’s Cavern, were formed in Devonian limestone at levels that can be related to still-stands during marine regression, and animal remains and artifacts within the caves are a feature of the later cave ‘earth’ deposits. Periglacial head deposits of late Pleistocene (Devensian) age commonly infill the smaller valley bottoms or have been exposed on the cliffs by marine erosion. Low sea levels during the Pleistocene glaciations caused the river systems to cut down to nearly 40 m below OD just onshore.

The Devonian sedimentary and volcanic rocks of this district lie eastwards along strike from those of the Plymouth district (Sheet 348; Leveridge et al., 2002). There, the rocks were recognised as having been deposited in fault-bounded basins and intervening highs which formed part of a continental passive margin sequence. Crustal extension and faulting during the late Silurian and Devonian lead to the formation of graben and half graben. This process of continental rifting developed sequentially in a northerly direction; the southern basins filled with sediment while those to the north were still in the process of formation. Because of this, sedimentation varied from basin to basin, and there is no single regional succession. Rift faults provided access for basaltic magma with volcanic rocks, enhancing the submarine highs; under suitable conditions extensive limestone reefs developed on these highs.

Similar sedimentary associations to those of the Torquay district occur across north-west Europe (Holder and Leveridge, 1986a) indicating a pattern of east-west trending basins forming the northern passive margin of the laterally extensive Rhenohercynian oceanic basin (Franke, 1989). That ocean basin closed during the Devonian, and deformation then migrated northwards through the passive margin during the Dinantian, with successive basin inversions, folding and thrusting. When the rift basins were closed, stress was transmitted synchronously through the province producing the late Carboniferous orogenic episode. The collapse of that orogenic edifice, regional north-south extension and granite intrusion followed at the end of the Carboniferous and in the early Permian. It was in this dynamic early post-orogenic phase of the history of the region that the Permian basins of the district were formed.

The geology of the district has long been a subject of study, and was reported on by Sir Henry T De la Beche in 1829, in an article ‘On the Geology of Tor and Babbacombe Bays, Devon’. This predated by several years his pioneering mapping of Devon, for the fledgling Geological Survey. The coastline, with its cliffs that show dramatic colour contrasts between the red-brown Permian rocks and the variable grey hues of the Devonian strata are of considerable scientific interest. Geological studies in the 19th and early 20th centuries included detailed investigations of the Devonian strata, particularly with regard to palaeontology, on the nature and age of the red beds, and on the cave deposits of Kent’s Cavern and elsewhere. Among the various workers, pre-eminent are the names of Pengelly, Champernowne and Ussher, the last of whom carried out the 1:10 560 scale mapping of the district for the Geological Survey. Ussher’s memoir (1903), rewritten by Lloyd (1933), remains the definitive publication on the general geology of the district. More recently, in the second half of the 20th century, important advances in the understanding of the geology of the district have been made by Laming (e.g. 1982), on the Permian red beds, and such as Selwood, House, Richter and Scrutton on the Devonian strata. At present, there are listed no fewer than 11 geologically related Sites of Special Scientific Interest (SSSI) in the Torbay area, which remains an important centre for geological teaching and research.

Administration of most of the district is by the Borough of Torbay Unitary Authority. The local economy relies on a variety of light industries and tourism; visitors are attracted by the combination of spectacular coastal scenery, family friendly beaches, and the climatic advantages of the district recognised as the English Riviera. Away from the conurbations, agriculture in the form of mixed farming is the main employment, benefiting from the mild and moist climate.

Chapter 2 Devonian

The Devonian System was proposed by Sedgwick and Murchison (1839) and substantiated on the basis of international correlation of marine and Old Red Sandstone fossils (Murchison and De Verneuil, 1841). The Torquay district figured prominently in those deliberations because of its marine fossils and the contemporaneous major survey work in the province by De La Beche (1839). Much later, appreciation that the marine deposits of the district represented both shallow marine platform and basinal deposits (e.g. Goldring, 1962) gave rise to the ‘Basin and Rise’ concept in south-west England. This was imported from the Rheinisches Schiefergebirge of Germany where the ‘Becken and Schwelle’ setting had been recognised at a much earlier date. More recently, Devonian rocks forming south Devon and much of Cornwall have been interpreted as representing the products and processes of an evolving rifted passive plate margin (Leveridge et al., 2002). That passive margin now lies just to the north of the Rhenohercynian Zone active plate margin tectonostratigraphic units of south Cornwall (Holder and Leveridge, 1986b).

The distribution of the successions in the Torbay district is shown in (Figure 1). As in adjacent districts, these successions characterise basins and highs of the passive margin. From south to north they are the Looe Basin Succession, the Brixham High Succession, the South Devon Basin Succession (southern sub-basin), the Torquay High Succession, and the South Devon Basin Succession (northern sub-basin). The successions are fault bound but largely parautochthonous; they represent the relative location of original basins and highs, but parts are detached from their root zones and are allocthonous. The formations present within the successions are shown in (Table 1).

The Nordon Formation is present in all successions, representing a background marine sedimentation, and ranges in age from the Eifelian (possibly uppermost Emsian) to the Frasnian (and probably Famennian). It is apparent from the mapping that the Torquay Limestone Formation, present in a series of thrust slices derived from the Torquay High, is equivalent to the East Ogwell Formation (Selwood et al., 1984) to the west and north-west across the Sticklepath Fault.

Looe Basin Succession

This succession (Table 1) in the southern third of the district comprises largely the major Lower Devonian lithostratigraphical divisions recognised and mapped across the south-west peninsula by Ussher (1890, 1907). These are now termed the Dartmouth Group and Meadfoot Group; the latter is generally subdivided into the Bovisand Formation and Staddon Formation (see Leveridge et al., 2002). It is succeeded by the early Mid Devonian Dittisham Member, of the long-ranging Nordon Formation, which is overlain by the Greenway Tuff Member of the Ashprington Volcanic Formation. The succession is disposed in three major northward-verging thrust nappes.

Dartmouth Group (Dm)

Elsewhere in the south-west of England, the group has been subdivided into formations (e.g. Dinely, 1966; Seago and Chapman, 1989) but within the Torquay district lithological associations are similar throughout and the group is undivided. This constitutes the southernmost thrust sheet: bedding is generally inclined southwards at moderate to steep angles, and is the right way up, so that the oldest rocks are in the bounding thrust hanging wall and the youngest rocks are to the south. Neither the base nor the top is seen in the Torquay district.

Mudstone dominates the group. It is red, purple and pinkish grey in colour, locally bioturbated, and occurs as thin beds or in units that may be over 10 m thick. Interlamination with grey-green siltstone and fine-grained sandstone is common. Siltstone and sandstone also occur in units that are up to 5 m thick, exceptionally up to tens of metres; these beds are generally grey-green in colour, but may also be red, bedding is thin to thick and the sandstone is fine to medium grained. Sedimentary breccia occurs sporadically, as thin to thick beds; clasts consist of mudstone and sandstone and are set in a silty mudstone matrix. Beds of pale quartzitic sandstone showing low-angle cross-lamination and basal scour structures occur.

Basaltic lava, tuff and associated hyperbyssal dolerite intrusions are prominent along the coast to east and west of the mouth of the Dart, but a lack of continuity precludes designation as a subdivision of the group.

The sedimentary rocks of the group are interpreted as having been deposited predominantly within perennial lakes in rapidly subsiding basins or as subaerial sheet-flood sands (e.g. Smith and Humphreys, 1991). The finer grained facies were deposited from suspension, whereas siltstone and sandstone units represent distal fluvial deposition from turbid underflows or by settlement in the lacustrine regime. The sedimentary breccias are the products of sporadic mass flow and indicate intrabasinal instability.

A Pragian (Siegenian), and possibly late Lochkovian (Gedinnian), age for the group is indicated by locally abundant fish remains (see House and Selwood, 1964).

Meadfoot Group (Mdt)

The Meadfoot Beds were defined as ‘bluish grey slates’ with hard grits in the 19th century by Champernowne (1881) at Meadfoot Beach, Torquay, and later confirmed as part of the marine Devonian by fossils. Ussher (1890, 1903, 1907) mapped these beds across the region, and subsequently the unit has been given group status. The group comprises two formations in its main crop (see Leveridge et al., 2002).

The Bovisand Formation (Bov) derives its name from Bovisand Bay in Plymouth Sound. In this district, the base is not exposed and upper contact with the Staddon Formation is faulted. Elsewhere, the formation rests conformably on the Dartmouth Group and it shows a transitional contact with the overlying Staddon Formation. The formation consists predominantly of grey mudstone, with laminae and beds of siltstone, sandstone and limestone, locally rich in macrofossils. Sandstone units, up to several tens of metres thick, comprise thin to thick beds of fine- to coarse-grained sandstone and thin grey mudstone interbeds. Westwards, two thicker mappable sandstone units are attributed member status (Leveridge et al., 2002) but within this area the structural relationships of mapped occurrences are not clear, and correlation along strike is uncertain. At the coast, the sandstone cropping at Southdown Cliff [SX 928 541] is inverted and that at Long Sands [SX 920 525] to the south is the right way up; these sandstones are probably part of the same unit exposed on opposite limbs of the Man Sands Antiform. Sandstone cropping out south-east of Croftland [SX 898 525] is possibly at the core of the structure and represents a second lower unit, but this is not confirmed.

The finer facies were deposited from suspension in quiet marine, shallow offshore to shelf environments. The bioclastic limestones represent reworked debris transported from shallow marine to offshore settings. The sandstones are interpreted as storm-generated turbidites and near shoreline deposits. The thick sandstone units are comparable with those along strike to the west that represent wave and storm-dominated shoreline facies (Jones, 1995).

The type section of the Staddon Formation (StG) is at Staddon Heights, some 30 km to the west in Plymouth Sound. It strikes east-west, and in this district, it is bound north and south by faults. To the south, the boundary is variably a thrust or reverse steep fault, and to the north its boundary is a low or moderate southerly dipping thrust. Much of the sequence appears to be inverted, but various levels of a dissected antiformal core or inverted limb appear to be represented along the crop. The formation consists predominantly of yellowish grey sandstone, which is fine to coarse grained and occurs in thin to thick, massive beds, commonly with parallel and low-angle cross-lamination. Interbeds consist of mudstone in the lower part of the sequence, and wispy interlaminated siltstone and fine-grained sandstone in the higher part; these may be grey, yellow, green or red.

Where the formation is exposed in the Dart valley, it shows similar bedforms and other sedimentary structures to those at the type section at Staddon Heights. A similar depositional environment is inferred, with an upward transition from a shallow marine setting, to deposition in standing water on a coastal plain or shallow marine embayment, and finally to an emergent fluvial regime with shallow channels and overbank deposits.

Biostratigraphical evidence principally micropalaeontological, shows the Bovisand Formation to be of Pragian-mid Emsian age, and the Staddon Formation to be late Emsian (see Leveridge et al., 2002).

Tamar Group

The Dittisham Member (DiM) of the Nordon Formation extends some 2.5 km to the west of Dittisham [SX 865 549] and 4 km eastwards to the outskirts of Brixham, being restricted along strike by overthrusting. It is essentially inverted, and is bound to the south by overthrust Staddon Formation, and to the north by the Greenway Tuff Member of the Ashprington Volcanic Formation. The Dittisham Member comprises dark bluish grey mudstone, with subordinate grey mudstone weathering greyish green, with thin beds of paler mudstone, laminae and thin beds of pale grey limestone, and sporadic thin shell coquinas. Towards the top lenses and thin beds of basic tuff are present.

The lithologies, stratigraphical and structural positions of the member are comparable to those of the Jennycliff (‘Slates’) division of the Saltash Formation in the Plymouth district where they succeed the Staddon Formation. It is similarly interpreted as quiet water sedimentation with periodic scouring currents that introduced bioclastic debris derived from the developing Brixham High to the north.

An Eifelian age has been attributed to fossils collected during the first survey of the district (Ussher, 1907).

Greenway Tuff Member (GyM) (part of the Ashprington Volcanic Formation) forms the uppermost part of the Looe Basin succession. This inverted volcanic sequence has a similar lateral extent to the underlying Dittisham Member, and is also overridden by the Staddon Formation on secondary flat-lying thrusts, to the east and west of Greenway. Its northern boundary is a northward-verging thrust. The member comprises basic tuff and basalt lava; the tuffs are dominant in the vicinity of Greenway, and the lavas are more prominent westwards in the lower half of the member. The tuff is grey to blue-green in colour, weathering ochre-brown, and is thinly to thickly bedded. Beds are variably crystal and lapilli rich, with beds of accretionary lapilli sparsely developed. Crude normal grading is common. The basalt lava and associated hyaloclastite occur in units up to several metres thick.

Brixham High Succession

The Brixham High Succession comprises those rocks that accumulated on the top and flanks of the elevated submarine area that formed with the development of the South Devon Basin half graben immediately to the north of the Looe Basin (Figure 2). Extensional rotation on a southerly inclined bounding fault to the north (compare with Leveridge et al., 2002) produced the southern sub- basin of the South Devon Basin and the Brixham High. All of the rocks occur within thrust nappes derived from that high during the main D₁ and D₂ deformation phases of the south-west England Variscan orogenesis. Northwards, the nappes have overidden much of the southern sub-basin of the South Devon Basin. They extend across the district from west of Totnes to Goodrington in Torbay, and to the south from Washbourne eastwards to Sharkham Point, near Brixham (Figure 1). It is also probable (see Chapter 6) that the thrust nappe of Meadfoot Group rocks disposed about Paignton was derived from the basement of the high rather than the Looe Basin. Within the nappes, there is a westwards transition by interdigitation from a predominantly limestone sequence about Brixham to a predominantly volcanic sequence about Ashprington.

Tamar Group

The Brixham Limestone Formation and the Ashprington Volcanic Formation of the Tamar Group interdigitate laterally (Table 1). The Nordon Formation and the Saltern Cove Formation, largely basinal deposits, also locally interdigitate with the limestone and volcanic formations within the Brixham High Succession.

Coastal section

The Brixham Limestone Formation (BxL) is subdivided in to members (Table 2) around the coastal section about Brixham, and at Goodrington, but these cannot be traced inland owing to the paucity of exposure.

The Sharkham Point Member (SP) (Brixham Limestone Formation) is the lowest member of the formation and exposed along the coast, running westwards from Sharkham Point [SX 937 946]. Inland it is present in isolated fault-bound crops but it is mapped in sequence in the vicinity of Sandridge [SX 806 565]. The base is not seen, but available evidence indicates that it lies offshore to the south, where it is overthrust by the Staddon Formation from the Looe Basin. The lowest part of the member on the coast is inverted, younging northwards. The central part, north of Sharkham Point, is folded into open to close upright folds, but with the ‘envelope’ the right way up and gently inclined northwards. The upper part of the member is inverted above a northward-verging minor thrust.

The lowest rocks exposed consist of interbedded reddened grey slaty mudstone and thin graded beds of limestone, which are shelly crinoidal packstone and wacke- stone. These are succeeded by blue-green thinly bedded lapilli tuffs, including accretionary lapilli, with limestone and mudstone interbeds. Overlying limestone is thinly bedded, becoming thickly bedded towards the top of the sequence. It comprises grainstone, packstone and wacke- stone, locally with abundant stromatoporoids.

The member was deposited in conditions that became shallower allowing shoals to develop and eventually a carbonate platform with patch reefs was established. The member is of early to mid Eifelian age (Drummond, 1982).

St Mary’s Bay Member (SMB) is part of the Nordon Formation, splitting the lower two members of the Brixham Limestone Formation. It backs St Mary’s Bay, and is mapped inland in a series of fault-bound blocks as far as Stoke Gabriel [SX 845 475]. Where the complete member is exposed, in the foreshore of the bay, it is generally overturned to the north except where parasitic folding occurs near the middle of the section.

The member consists largely of grey to dark grey slaty mudstone, weathering greenish grey and grey-buff. Limestone occurs as laminae, thin beds and lenticles, and the proportions in the lower part suggest a transition from the Sharkham Point Member, although the boundary is faulted. Also dispersed in the lower part of the member there are laminae and thin beds of tuffaceous siltstone and fine-grained sandstone. Limestone beds towards the top are coarsely bioclastic in part and some show normal grading. Dispersed macrofossils are present locally, and there is some bioturbation. The evidence suggests that the carbonate platform on which the Brixham Limestone accumulated was drowned as water depth increased and a supply of fine clastic sediment became available. Limestone beds towards the top of the member are interpreted as storm-derived sediments. The sequence is of mid to late Eifelian age.

The Berry Head Member (BHL) (part of the Brixham Limestone Formation) forms the headland at Berry Head and probably constitutes a significant part of the undivided formation extending a further 6 km westwards to north of Stoke Gabriel. The base is conformable with the St Mary’s Bay Member, but the top is not recognized as the Berry Head Member is thrust over the succeeding Churston Member to the south of Churston Cove [SX 9195 9695].

The lowest part of the Berry Head member comprises beds of rudstone and nodular limestone that pass up to thinly bedded grey wackestone and packstone with thin grey calcareous mudstone interbeds. Grey mudstone predominates locally. A transition from thin graded beds to thick laminar bedded crinoidal and stromatoporoid grain- stone and floatstone occurs in the central part of the member. The upper part comprises massive pale grey bindstone and floatstone.

The determined age range of the member is uppermost Eifelian to uppermost Givetian, but higher parts have not yielded definitive faunas (Drummond, 1982).

The Berry Head Member represents progradation of a biogenic bank complex; the lower storm-derived and flow- deposited carbonate clastic deposits pass up to massive beds of largely local reworked debris which is predominantly crinoidal and bound by laminar stromatoporids of a reefal flat.

The Goodrington Member (GD) of the Brixham Limestone Formation crops about Goodrington. There is no coastal section, but the beds are exposed in the footwall of a steep normal fault that runs along the cliff to the north of Broad Sands. Nearby inland roadside and quarry exposures provide a partial section. Interdigitated with this member are volcanic rock of the Ashprington Volcanic Formation and purplish red slaty mudstone of the Saltern Cove Formation. The member is bound in the Goodrington area by steep faults to the south and a northerly verging thrust to the north.

The lower part of the member comprises medium- to thick-bedded rudstone and floatstone with stromatoporoids and shelly fauna, and the upper part is thin- to thick-bedded micrite, with stromatoporoids (Amphipora). The member is dolomitic in part.

The age is not well constrained but has been attributed to the Givetian by Scrutton (1978). Drummond (1982) proposed a back-reef semi-restricted lagoonal depositional setting for the member.

The Churston Member (ChL) of the Brixham Limestone Formation is differentiated to the north-west of Brixham; it forms the coastal section between Fishcombe Cove [SX 920 569] and Broad Sands [SX 898 574]. Both southern and northern boundaries are thrust faults; it is overthrust by the Berry Head Member to the south and overthusts the Saltern Cove Formation to the north. Folds within the member take the form of a gently inclined northward-verging macroscopic fold with parasitic smaller scale structures.

Thinly interbedded slaty mudstone, crinoid wackestone, and lapilli tuff, low in the member are overlain by thin- to medium-bedded framestone and floatstone which pass up in to massive laminar stromatoporoid bindstone and float- stone, which is dolomitised in part.

The established age for the member is Frasnian, the oldest retrieved fauna being mid-Frasnian (Drummond, 1982). The sequence represents shoaling and establishment of a shallow high-energy platform and possible emergence.

At the top of the cliffs between Fishcombe Cove and Elberry Cove, the Churston Member passes up into the Saltern Cove Formation (SC) in a normal, right-way-up sequence. A broadly similar facies of the formation is seen at the base of the cliffs towards Elberry Cove, beneath an inverted sequence of limestone. Rather than simple folding of the formation boundary, the presence of low-angle faulting and relationships along strike indicate that this boundary at the base of the cliff is a significant thrust. The Saltern Cove Formation comprises thinly bedded calcareous red mudstone with thin beds of fine-grained tuff. It is the highest formation within the Brixham High Succession, and, overlying the limestone sequence, it is assigned a Frasnian age.

Inland

The limestone-dominant succession of the coast interdigitates with, and passes westwards into the predominantly volcanic sequence of the Ashprington Volcanic Formation. Extrusive volcanic rocks of this formation also extend into parts of the adjacent South Devon Basin succession and the Looe Basin (see above).

The Ashprington Volcanic Formation (AV) covers an area of about 30 km², extending from Totnes [SX 779 602] and Washbourne [SX 795 551] in the west to Longcombe [SX 835 600] and Dittisham [SX 865 553] in the east, and it is bounded by faults. The age of interdigitated limestone units suggest that there is a general younging northwards, but the top and base are not determined. Bedding is commonly moderate to steep, but the structural lower boundary of the formation is a flat-lying to gently inclined thrust. Thrust- bound outliers are present to the north around Totnes, and an inlier of Nordon Formation about Painsford [SX 802 568] appears to be a window through the thrust sheet.

The formation consists predominantly of basalt lava with subordinate volcaniclastic rocks. The lava flows are up to several tens of metres thick; most are well cleaved but the thickest units are poorly cleaved. The lava is dark grey- green where fresh, weathering to purple, red, and ochre yellow, particularly the well cleaved lava in the surface weathering zone. These weathered rocks superficially resemble the similarly coloured volcaniclastic rocks, hyaloclastite and bedded tuff, which form interbeds with the lava, and thicker sequences, particularly to the east. Tuffs are crystal or lapilli rich, locally agglomeratic with sporadic accretionary lapilli. Bedding of the tuffs varies from laminae to very thick; the thinner beds commonly show normal or reversed grading.

Limestone and grey or purplish red mudstone occur, interbedded with the volcanic rocks, particularly to the east, but elsewhere in structural and stratigraphical inliers.

The age range of the formation is interpreted as Eifelian to the Frasnian, based on the faunas of interdigitated and included limestones (see Ussher, 1907).

The formation is part of a significant persistent, possibly multicentre, volcanic edifice, predominantly of basaltic lava that is hyaloclastitic in parts, but with interdigitated and peripheral tuffs. It was deposited in a marine environment, interdigitating with platform and reefal limestone, but with evidence of emergence at times.

Meadfoot Group (Mdt)

The Meadfoot Group (undivided) crops out about Paignton, between 5 km and 10 km north of the main crop in the Looe Basin succession. The group is bound by a basal flat lying thrust or by steep faulting, and in places by the overlying unconformable Permian. The thrust sheet, previously considered to be a structural outlier from the main crop (Coward and McClay, 1983), is now considered, on the basis of its differing stratigraphy and lower metamorphic grade (see Chapter 4), to be part of the thrust stack derived from the Brixham High.

Mapping has not revealed the thicker sandstone facies typical of the Staddon Formation, as previously designated for this occurrence of the group. Interbedded sandstone and silty mudstone do form parts of the sequence as at the southern end of Goodrington Sands. There interbedded with units in which reddened grey silty mudstone predominates is a unit comprising silty mudstone and sandstone in similar proportions. The sandstone beds are up to 0.5 m thick, fine- to medium-grained, quartzitic, with parallel and low-angle cross-lamination. The mudstone is locally bioturbated, with sporadic coquinas of crinoid, brachiopod and bivalve debris.

On lithostratigraphical grounds, the sequence has been correlated with that at the classic Meadfoot Cliff type section, where a Pragian to Emsian age is established. A shallow marine shelf setting has been determined for this occurrence of the group (Richter, 1967).

South Devon Basin Succession (southern sub-basin)

The southern sub-basin succession is overthrust by the Brixham High deposits and substantially obscured in the district. The main crop is to the north of Totnes about Dartington, Marldon and Broadhempston. To the south, the sequence separating the overthrust Staddon and Ashprington formations about Washbourne to the west, and an inlier about Goodrington in the east, are considered to be part of this succession (Figure 1). All of the rocks of the sub-basin are within the Tamar Group.

Dartington area

Here the Nordon Formation (No) consists largely of mudstone, but also contains four limestone members (Drummond, 1982), and some basic volcanic rocks. The formation is bound to the north by steep faults and to the south by overthrust Ashprington Volcanic Formation. Within the formation the limestone units define large-scale folds that trend east to north-east, and thrusting occurs in the limbs (commonly overturned) of north-west-verging structures. The mudstone is grey to bluish grey, locally weathering buff and green and with purple and red staining near the outcrop of Permian rocks. It becomes calcareous where it is associated with the limestone and tuffaceous where it is associated with volcanic rocks. A fine siltstone interlamination occurs in places and elsewhere the mudstone appears to be structureless. Apart from the named members, limestone also occurs as laminae, thin beds and lenses. Dispersed corals and shells, are common, especially in the lower parts of the sequence. The volcanic rocks occur around Dartington and Uphempston, but are otherwise poorly exposed. They consist of fine to coarse-grained, bedded crystal tuff, which is green where fresh and an ochre brown colour where weathered. The limestone members are described in ascending stratigraphical order, determined on the basis of their conodonts (Drummond, 1982).

Bourton Limestone Member (BL) (Lower Eifelian) consists of dark grey, thin to medium bedded, crinoid wackestone and micrite; some beds show normal grading.

Marldon Limestone Member (ML) (Upper Eifelian to Lower Givetian) comprises thin to thick bedded pelloidal wackestone and packstone with thin grey mudstone partings, which pass laterally to more massive stromatoporoid floatstone or pelletoidal packstone. Corals and gastropods are locally common.

Dartington Limestone Member (DrtL) (Upper Givetian) is dark grey in colour but pale grey in the central part, thinly to thickly bedded and massive. It is muddy towards the top and base. Beds of micrite, wackestone, packstone, floatstone and rudstone are sharply defined, with normal grading and basal scour structures common.

Penny’s Wood Limestone Member (PWL) (Frasnian) comprises thinly interbedded grey to dark grey limestone and grey mudstone.

Parts of the Marldon and Dartington members may represent shoaling and local colonization of deposited carbonate banks. Otherwise the members are interpreted as largely derived carbonate mud and bioclastic debris that was transported by storm currents, turbidite and debris flows. The stratigraphical age of the members and their relationship to breaks in limestone deposition on the highs to north and south are illustrated in (Table 2).

Washbourne area

The Nordon Formation extends southwards from near Harberton [SX 779 592] on the western margin of the district to Washbourne [SX 797 547], and thence eastwards to East Cornworthy [SX 841 554]. It occurs as an inlier about Painsford [SX 801 568] within the main crop of Ashprington Volcanic Formation. The formation is bound to the south by overthrust Staddon Formation and to the north by the overthrust sheet of Ashprington Volcanic Formation. The limestone members are not seen here, but around Harbertonford, basic volcanic rocks, tuff and thin basalt lavas, occur within the formation as well as thin beds of sandstone that locally amalgamate into units a few metres thick. The grey mudstone locally contains dispersed solitary corals, and in places shell coquinas. An Eifelian age is attributed to these rocks on the basis of their shelly fauna (Ussher, 1907; Lloyd, 1933).

Goodrington area

A basin margin sequence that lies at a higher stratigraphical level than that seen in the Washbourne area occurs about Goodrington and is exposed in the coastal section between Waterside Cove and Broadsands. The Saltern Cove Formation is primarily a deposit of the basin, but here it interdigitates with peripheral deposits of the Brixham High. The red lithologies of the Saltern Cove Formation are coeval with the grey lithologies of the Nordon Formation elsewhere in the basin (Table 1).

In the coastal section, the fine-grained clastic lithologies of the Saltern Cove Formation rest on limestone, which in turn overlies a local expression of the Ashprington Volcanic Formation. The volcanic rocks here include lava and bedded tuff, and within this sequence there are sporadic interbeds of limestone, wackestone, packstone and floatstone. The limestone that lies immediately beneath the typical Saltern Cove Formation lithology is a thin- to medium-bedded stromatoporoid floatstone and crinoid wackestone with a single bed of stromatoporoid (Peneckiella salternensis {Scrutton, 1967}) framestone. The limestone is interpreted essentially as bioclastic debris apparently derived from the Brixham High carbonate platform; the framestone is indicative of shallowing and this may have been due to the emplacement of the volcanic rocks and the development of biostrome.

The Saltern Cove Formation (SC) consists largely of mudstone and fine-grained siltstone, which is red and reddish purple with local green reduction spots and some grey-green beds. Bedding varies from very thin (laminae) to thick, and normal grading is seen locally. Pale laminae of graded fine-grained limestone are developed sporadically. Breccias, up to 2 m thick, occur in the upper part of the coastal sequence at Saltern Cove and Waterside Cove, where dips increase northwards and are vertical in places. The breccias are both matrix-supported and framework- supported. Clasts consist largely of micritic limestone, coralline limestone and fine-grained volcanic rock, and limestone nodules and rounded blocks are present in the coarser beds. The coarse framework breccias show crude grading, and a limestone raft 3.8 m in length is exposed in one of the thicker matrix-supported breccia beds (Plate 1a). The limestone at the base of the Saltern Cove lithology is early Frasnian in age (Drummond, 1982). On the basis of the ostracods, ammonoids, and conodonts which they yield, the overlying beds range through Frasnian to Late Famennian (Ussher, 1903; House, 1963; Van Straaten and Tucker, 1972). The limestone clasts within the breccias yield conodonts indicating both Frasnian and Famennian ages (Van Straaten and Tucker, 1972; Drummond, 1982) where the host rock is of Famennian age.

In the Plymouth district, the mudstone and siltstone of similar red lithologies have been interpreted as having been derived from terrestrial detritus introduced by turbid flow into the basin environment in which the grey lithologies represent the marine background settlement deposits. The breccia beds are mass flow and slurry deposits; the latter occur where there is little admixture of basinal mud with slumped shallow-water accumulations. Derived limestone clasts that yield fossils of Famennian age may indicate shallowing over the Brixham and Torquay highs and renewed carbonate sedimentation. However, it is more likely that the limestone clasts were derived from an active high on the north side of the South Devon Basin (Figure 1) and (Figure 2) related to the development of the Tavy Basin, after the drowning of the South Devon Basin highs and infilling of the basin (compare with Leveridge et al., 2002)

Torquay High Succession

The Torquay High Succession comprises essentially the limestone sequence of the Torquay Limestone Formation, to the east of the Sticklepath Fault, and its correlative to the west of the fault, the East Ogwell Limestone Formation (Selwood et al., 1984; (Table 1) and (Table 2). The Torquay Limestone Formation crops out on the headland Torquay, where it occurs within thrust sheets that also include parts of the Nordon Formation and the Meadfoot Group. Diagrammatic sketches of the reef development and subsequent faulting is shown in (Figure 4).

Torquay area

Meadfoot Group

The Meadfoot Group crops out along the northern shores of Tor Bay between Meadfoot Beach and Hope’s Nose, and to the west of Hope’s Nose towards Black Head. It extends beneath the eastern part of Torquay, forming the high ground between Wellswood and Babbacombe, in several fault-bound blocks. Sandstone units are locally prominent, but the presence of the Staddon Formation in Torquay has not been confirmed and the group has not been subdivided. The group comprises grey to dark grey mudstone and silty mudstone, with laminae and beds of sandstone, and sporadic thin beds of bioclastic limestone. The silty mudstone is commonly bioturbated with trace fossils, including Chondrites and Spirophyton. Fine- to medium-grained sandstone forms thin continuous beds, and coarse-grained sandstone forms lenticular beds. The latter show cross- bedding, basal scour and slump structures, and bioturbated tops. Locally amalgamated these beds form lenticular units up to 8 m thick with channel forms. Elsewhere isolated ball and pillow structures are common.

Shelly fossils indicate an Emsian age for these rocks (Ussher, 1903; Lloyd, 1933). The trace fossils indicate that the beds were deposited on a shallow marine shelf (compare with Richter, 1967). At times this was below wave action, and southward slumping together with the main channeling indicate the palaeoslope: the development of east-west-orientated channeling suggests tidal influence at certain periods.

Tamar Group

The Nordon Formation (No) (formerly the Eifelian Shales) in this succession includes the fine-grained clastic rocks overlying, and apparently succeeding, the undivided Meadfoot Group rocks on Hope’s Nose promontory. The formation consists largely of grey mudstone that weathers to grey-green and buff colours. Laminae and thin beds of fine-grained siltstone, weathering reddish brown, are dispersed throughout the sequence, but are more common in the lower part, and laminae and lenses of reddish grey muddy limestone are present towards its top.

An Eifelian age is attributed to the sequence on the basis of its shelly fossils, which include Spirifer speciosus (Lloyd, 1933).

Torquay Limestone Formation (TqyL) occurs within various fault-bound blocks within Torquay and to the east of the Sticklepath Fault. In places it is subdivided into members: nomenclature is that of Scrutton (1977a). Elsewhere the formation remains undivided.

Daddyhole Member (DhL) comprises thinly bedded to massive limestone, which is dark grey to grey in colour (Plate 1b). The thinner beds are largely detrital, the thicker beds consist of stromatoporoids and corals, commonly in growth position, or are micritic. In the Hope’s Nose area, massive units of lenticular limestone pass laterally and upwards, with disconformity, into thin beds. Calcareous mudstone and thin beds of tuff are sporadically developed within the member.

An early Eifelian (Polygnathus costatus partitus Zone) is attributed to these rocks, based on their conodont content (Castle, 1982).

Deposition of the Daddyhole Member was in quiet shallow conditions that allowed the build-up of a carbonate bank and establishment of patch reefs; there is evidence of some reworking and areas of more restricted carbonate deposition with only occasional periods of turbulence (compare with Scrutton, 1977a).

Walls Hill Member (WHL) is composed of pale grey, massive limestone beds with medium to thick bedding. Beds are micritic or coarsely bioclastic. In situ stromatoporoids constitute most of the massive beds. Matrix, where present, consists of corals and crinoid debris. The lower boundary of the member is taken at the base of lowest massive white limestone overlying dark grey thinly bedded limestone of the Daddyhole Member, seen at the base of the cliff at the northern end of Redgate Beach [SX 935 649]. Between the basal limestone and the typical facies there are several metres of thinly bedded red muddy limestone.

The member is Givetian in age. The limestone facies of the member represents major stromotoporoid reef development (Scrutton, 1977a).

Barton Limestone Member (BaL) consists of thick, massive beds of crinoidal and bioclastic grey limestone. Small stromatoporoids and large tabular corals are present in parts. Thinly bedded micrite is subordinate. In Lummaton Quarry [SX 915 665], lenticular beds with abundant brachiopods, gastropods and trilobites are known as the ‘Lummaton Shell Bed’ (see Ussher, 1907; House, 1963); it forms the base of the Barton Limestone Member overlying the Walls Hill Member. Higher parts of the sequence are present in Barton Quarry [SX 671 913] just to the north of the district. On the coast, the correlative limestone forms the cliffs at Babbacombe. It comprises medium to thin beds; the latter are dark grey, crinoidal and graded.

Macrofossils and microfossils from the Lummaton Shell Bed indicate a mid Givetian age, Maenioceras terrebratum Zone (House, 1963). Conodonts from Barton Quarry and the uppermost beds at Babbacombe indicate an early to mid Frasnian age (Lower Polygnathus asymmetrics Zone). Scrutton (1977a) interprets these beds as the deposits of ‘quite high’ energy conditions. The main body of the member appears to represent a patchwork of bioherms within worked crinoidal sand. A peripheral facies may be represented at Babbacombe.

Torquay Limestone Formation (undivided) (TqyL) is shown on the map in several large fault-bound outcrops around Torquay. It has not been attributed to members owing to the paucity of definitive fossils and because the rocks are of a different facies. Outcrops include the areas of Windmill Hill [SX 909 658] and Daison Hill [SX 913 657] near Hele, Stantaway Hill [SX 915 638], and Walden Hill [SX 915 638] and Braddon Hill [SX 920 639] north of Torquay harbour. Also included are the limestones of Petit Tor Downs [SX 926 663], Bishop’s Walk [SX 937 644] and Ilsham [SX 934 642] to the east.

Ussher (1907) recorded the transition between Eifelian and Givetian in the southern part of the sequence at Windmill Hill and Daison Hill where the strata dip gently northwards. This boundary has since been confirmed (Castle, 1982); it corresponds with the transition from grey, thinly bedded limestone with calcareous mudstone interbeds to pale grey, thickly bedded (up to 20 m), massive limestone. In Walden and Braddon hills, thickly bedded, massive pale limestone with corals, stromatoporoids and crinoid matrix have yielded a Givetian age, middle Polygnathus varcus Subzone (Castle, 1982). A break comparable with that between the Walls Hill and Barton Limestone members has not been recorded.

At Ilsham and Bishop’s Walk, the thickly bedded, massive micritic limestones have not yielded diagnostic faunas. Scrutton (1977b) equated them with the Walls Hill Member but this has not been confirmed. The Walls Hill Member in the type area at Oddicombe is overthrust onto slaty mudstone of the Nordon Formation. The limestone by Bishop’s Walk is overthrust onto Saltern Cove Formation above Anstey’s Cove.

The Petit Tor Downs limestone is faulted against the Saltern Cove Formation. It comprises thick, massive beds of packstone, floatstone and framestone with lenses and irregular masses of red silty mudstone. The upper part comprises interbedded limestone and red mudstone with large masses of limestone apparently surrounded by the mudstone. Condonts from the lower part indicate a Mid Devonian age and ammonoids retrieved from the upper part indicate the Mid Frasian Manticoceras cordatum Zone (House, 1963).

Ipplepen area

West of the Sticklepath Fault, strata of the Torquay High forms the southern parts of northerly verging thrust nappes that extend several kilometres northwards. The Torquay High succession forms an arcuate crop dissected by a fault on the southern side of Ipplepen, and occurs within fault- bound blocks about North Wilborough.

Tamar Group

The Nordon Formation (No) of the Torquay High is bound to the south by steep faults and is succeeded by the East Ogwell Formation. It comprises grey mudstone and silty mudstone, with dispersed siltstone laminae, thin limestone beds and lenticles, and dispersed organic debris, mainly brachiopods. Conodont determinations from near the top of the sequence indicate an early Givetian age (Selwood et al., 1984).

It is probable that this sequence of the Nordon Formation is an interdigitation within the East Ogwell Formation. The lower part of the latter is comparable with the Eifelian Chercombe Bridge Limestone in the adjacent Newton Abbot (Selwood et al., 1984), but does not crop out in the Ipplepen area owing to faulting of the contacts (Figure 4).

East Ogwell Limestone Formation (EOL) crops out mainly in the adjacent district to the north (Sheet 339 Newton Abbot; Selwood et al., 1984). The main part of the formation comprises pale to medium grey and greyish pink, thick bedded, massive limestone. It is coarsely bioclastic with corals, brachiopods and subordinate stromatoporoids in places, and elsewhere it is micritic with few fossils. The formation ranges in age from the Givetian to early Frasnian (varcus Zone to the Polygnatus asymmetricus Zone; Selwood et al., 1984). Two members are differentiated locally at the base, the Pulsford Member and the Blair Hill Tuff Member.

Blair Hill Tuff Member (BHT) occurs only locally at the base of the formation. It comprises bedded chloritic and calcareous tuff, green where fresh weathering brown and purple, fine to coarse grained, and locally lapilli rich; Middleton (1960) classified these rocks as keratophyre. The position within the sequence indicates that the member is early Givetian in age.

Pulsford Member (Pu) comprises grey to dark grey biomicritic limestone in thin lenticular beds, with thin interbeds of grey calcareous mudstone. The limestone is pelletal in places and elsewhere crinoidal debris is common. The member, where differentiated, rests conformably on the Nordon Formation sequence. Conodonts indicate an early to mid Givetian age (Polynathus varcus Zone; Selwood et al., 1984).

The limestone of the formation within district and in adjacent areas to the north represents a bioclastic carbonate platform build-up with local biohermal and reefal development (Scrutton, 1977a).

South Devon Basin Succession (northern sub-basin)

Rocks of the Nordon and Saltern Cove formations of the Tamar Group make up the succession of the northern sub- basin (Table 1). They are present in Torquay to the east and about Ipplepen to the west of the Sticklepath Fault. They are over-ridden by, or caught up in, thrust nappes associated with the Torquay High (Figure 2).

Torquay

Nordon Formation is present in the Ellacombe, Plainmoor, St Mary’s Church, Hele, Upton, and Torre areas of Torquay, and at Babbacombe. The overthrust Torquay Limestone Formation platform and reefal deposits of the Torquay High form fault-bound outliers closely associated with this sequence. In poorly exposed ground, the position of some of the limestone units is based on information from BGS archives, otherwise differentiation of limestone within the formation and that of the Torquay Limestone Formation is uncertain.

Grey mudstone forms the main part of the formation. Laminae and thin beds of siltstone and lenses of fine-grained sandstone occur sporadically. Tuff forms isolated lenses and basaltic lava is present at north Torre and in the cliffs below Babbacombe. Grey limestone that is thin- to medium-bedded with thin grey mudstone partings shows internal folding, and may be up to a few tens of metres thick locally.

In the cliffs between Babbacombe Beach and Oddicombe Beach, this part of the sequence has been informally referred to in literature as the ‘Babbacombe Slates’. Here dark grey and black pyritous mudstone is interbedded or closely interlaminated with the paler grey siltstone, and thin beds of limestone are present close to the contact with the overlying Barton Limestone Member.

The ‘Babbacombe Slates’ is the only part of the formation whose age is constrained: House (1964) recorded Lower Frasnian (Pharciceras lunulicosta Zone) ammonoids in the mudstone, and Castle (1982) attributed conodonts from the limestone beds to the Lower Frasnian (Lower Polygnathus asymmetricus Zone). The remainder of the formation appears to be of Mid Devonian age. Massive and thinly bedded limestone by St James’ Road [SX 912 651] has been assigned a Givetian age (Castle, 1982), but insufficient evidence is available for it to be firmly attributed to either the Nordon Formation or the Torquay Limestone Formation.

The high proportion of limestone in this sequence suggests that deposition occurred on the southern margin of the sub-basin, peripheral to the Torquay High.

Saltern Cove Formation (SC) crops out along the coastal section at Anstey’s Cove [SX 936 647], extending south- eastwards towards Black Head. It is bound to north, south and east by steep faults, overthrust by Torquay Limestone Formation, and intruded by the Black Head microgabbro (dolerite). It also crops from Petit Tor Beach [SX 927 624] south- westwards towards St Marychurch, where it is bound by steep north-west-trending faults. The formation here is overthrust by the Petit Tor Downs limestone to the south; to the north it is overlain unconformably by Upper (?) Permian breccia.

Purplish red slaty mudstone predominates on the slopes above Anstey’s Cove, but in the cove interbedded with the red mudstone are green silty mudstone with laminae and thin beds of dark grey mudstone and paler grey fine-grained siltstone that shows normal grading. Ussher (1903) reported nodular limestone within the slaty mudstone near the (thrust) boundary with the overlying Torquay Limestone Formation. In the cliff section between Anstey’s Cove and Black Head, and apparently beneath the microgabbro intrusion of Black Head, red and green slaty mudstone overlies limestone (up to 10 m thick), which is in faulted contact with underlying purple and green calcareous tuff.

The formation here was assigned to the Upper Devonian (Famennian) by Ussher (1903) and Lloyd (1933) on the presence of the ostracod Entomis serratostriata and bivalve Posidonomya venusta.

Ipplepen

Nordon Formation is restricted to small areas just to the south and east of Ipplepen. It consists of grey to dark grey slaty mudstone, finely interlaminated with fine-grained siltstone. A limestone unit dips gently northwards on the south side of Ipplepen, and small outcrops of tuff are present to the east of the village. The age of this sequence is uncertain. The east-west boundary with the Saltern Cove Formation to the north at Ipplepen is obscure and may be a fault.

Saltern Cove Formation is equivalent to the Whiteway Slate of Selwood et al. (1984), but that division included substantial tracts of grey and greenish grey slaty mudstone that would now be assigned to the Nordon Formation. The formation in the area comprises reddish purple and subordinate green and grey mudstone. Laminae and thin beds of fine-grained siltstone are present locally.

Ostracods recorded from the formation at Ipplepen include Martenella dichotoma, M. hemisphaerica, Richterina (R.) costata, R. (R.) striatula (Selwood et al., 1984), and indicate the M. hemisphaerica-dichotoma Zone (Upper Famennian).

Chapter 3 Permian

The Permian crops of the Torquay district comprise two sedimentary basins or cuvettes. The northernmost basin extends in to the adjacent Newton Abbot district (Sheet 339). The smaller southern basin underlies much of the conurbation of Paignton. In addition, there are a number of outliers that occur as far south as Brixham. Within the district, the Permian rocks include breccia and sandstone, mostly of characteristic red-brown colour, which rest with marked unconformity on the underlying Devonian rocks. One of the most striking aspects of the geology of the district is the contrast between the undeformed and generally gently dipping red beds, and the folded Devonian basement (Plate 2a).

From the time of the earliest geological studies of Torbay, the lack of fossils in the red beds led to some speculation about their stratigraphical position. The use of the terms ‘New Red Sandstone’ (Conybeare and Phillips, 1822) and ‘Red Sandstone Series’ (De la Beche, 1839) continued throughout the 19th century in the face of uncertainty as to whether or not these rocks belonged to the Permian or Triassic systems. To some extent, this uncertainty continues at the present day, for the stratigraphy developed for the Permian strata of the Newton Abbot and Exeter (Sheet 325) districts to the north cannot be correlated precisely with the red beds of Torbay. This stems partly from the laterally discontinuous nature of the breccia deposits and sandstone beds, and also from the complete absence of fossils and markers, such as the contemporaneous volcanic rocks of the Exeter district. It is generally considered (e.g. Durrance and Laming, 1982) that the red beds of the Torquay district represent some of the older parts of the Permian system, possibly extending into the latest Carboniferous. In the Crediton Trough of the Exeter district to the north, the Permian strata are placed in the Exeter Group; the older part that includes the Bow Breccia is separated by a marked unconformity from the younger formations of Mid to Late Permian age. Geochronological evidence from the Exeter Volcanic Rocks suggests that much of the older strata predate 290 Ma BP. On the timescale of Menning et al. (2000), which places the Permian-Carboniferous boundary at 292 Ma BP, it is likely that most of the red-bed sedimentation of the Crediton Trough can be accommodated within the Permian system. Here, by analogy it is also considered that most of the red beds (placed in the Exeter Group) are entirely of Permian age, with a broad correlation between the Torbay Breccia Formation (including the Corbyn’s Head Member) and the older part of the Crediton Trough sequence. The marked unconformity within the Permian of the Exeter district may or may not be present at the same level in the Torbay district. However, an unconformity does exist at the base of the Watcombe Formation (Plate 2b), which forms the lowest part of a younger suite of the Permian rocks of Torbay, analogous to the Whipton Formation of the Exeter district.

Torbay Breccia Formation (TB)

The Torbay Breccia Formation includes a number of stratigraphical units which have been described elsewhere, for example the Chelston and Paignton Breccias and the Livermead Formation (Durrance and Laming, 1982), but have not been mapped during this survey. As Ussher (1903) pointed out the identification of lithological units is possible at the coast, but inland the detailed stratigraphy is obscured by the urban developments of Torquay and Paignton.

Much of the formation consists of breccia and conglomerate, typically with individual units fining upwards from a coarse base that may show channeling into the underlying bed. The extent to which bedding is evident varies considerably; planar bedding predominates and crude cross- bedding is common in places. Clasts are predominantly rounded and consist of Devonian limestone or sandstone and slaty mudstone, with subordinate vein quartz, hornfels and chert. Quartz-porphyry clasts are present in many localities, and are particularly abundant at some, for example Livermead Head. The matrix is generally of red–brown colour and is predominantly sandstone with variable amounts of siltstone and mudstone. It is commonly cemented by iron oxide, and the rock is friable and rather soft weathering. Some breccias of the Paignton and Chelston areas also include a carbonate cement: these are much more indurated and have been worked locally for building stone. Substantial units of red sandstone are included within the Torbay Breccia Formation and these may show large-scale cross-bedding indicative of an aeolian origin. At the coast, these sandstones may be seen at Goodrington, where they exceed 35 m in thickness, and at Oddicombe Beach.

The base of the Torbay Breccia Formation is seen at the northern end of Saltern Cove, where coarse breccias, dominated by limestone and sandstone clasts (Plate 3a), rest on Lower Devonian mudstone and sandstone of the Meadfoot Group. At several localities to the south of the main Permian crops, Devonian limestone contains karst features infilled with red-bed deposits. Of these, the most striking is at Shoalstone Beach [SX 939 568], where ‘dykes’ within the Devonian Limestone are infilled with sandstone, siltstone and comb-layered carbonates. Towards the top of the Torbay Breccia Formation, for example at Oddicombe Beach and near Edginswell, steeper dips indicate tectonic tilting rotation, prior to the deposition of the Watcombe Formation. Exhumation of a strong pre-Permian topography has occurred in the St Marychurch area [SX 918 659] and remnants of the Torbay Breccia Formation were preserved prior to the deposition of the Watcombe Formation.

The breccia and sandstone of the formation are interpreted as debris flows (mostly in the northern part of the outcrop), flash flood deposits in braided river systems, and fluvial and aeolian dune sands.

The Corbyn’s Head Member (CH) has been named after the promontory, at the southern extremity of the Torquay Esplanade. In a section some 15.0 m thick, the lower strata consists of sandstone and the upper part of conglomerate. The sandstone varies in colour from purplish and reddish brown, to buff, pale grey and greenish grey (Plate 3b); it is medium to coarse and bedded. Individual sandstone beds vary considerably in thickness; most are less than 0.5 m. The sandstone beds are locally pebbly, with irregular seams of pebbles and cobbles, which form thin breccia or conglomerate beds in places. Clasts include sandstone, vein quartz, limestone, chert and quartz- porphyry. The sandstone beds commonly show cross- bedding and channeling, with lags of pebbles or very coarse-grained sandstone. Some beds of striking appearance consist of greenish grey or buff silty sandstone with intraformational clasts of red-brown mudstone. Thin beds of red-brown or grey-green mudstone are present in places, and may show desiccation cracks. Other thin beds of grey- green clay-rich siltstone, in the middle part of the succession, contain thin lenses, up to 40 mm long, rich in biotite flakes, many of which are euhedral. The conglomerates of the upper part of the section are framework-supported beds, with fairly well-rounded clasts up to cobble size, comprising red siltstone and sandstone, chert, limestone and red-stained quartz-porphyry.

The depositional environment of this member is interpreted as fluvial or delta plain with the sediments coarsening upwards in to alluvial fan deposits.

Watcombe Formation (Wat)

The Watcombe Formation has been mapped in the northern part of the district, where it rests, locally with marked unconformity, on the Torbay Breccia Formation. The Watcombe Formation is of variable lithology: much of the material inland is coarse breccia, with clasts of sandstone, slate and limestone in a poorly sorted matrix of sandstone, siltstone and mudstone (or ‘loam’ of earlier geologists such as Ussher). Clasts of quartz-porphyry are rare or absent. The shale-paste breccias described by Ussher as ‘dark red brown clunchy clay belonging to the Watcombe clay series’, were formerly worked for earthenware and the manufacture of bricks and tiles. Elsewhere there are units of brown mudstone and siltstone. At Petit Tor Beach, bedding units up to 2 m thick comprise muddy siltstone, with coarse-grade sandstone or fine breccia at the base, and interlaminated mudstone and fine-grained siltstone at the top. Iron-rich concretions and reduction spots are common in these units. Also present are impersistent interbeds of pale, medium-grained sandstone showing cross-lamination and basal flute moulds. These strata have not been encountered inland.

In the west of the formation, the breccias represent mainly debris flows. The finer mudstone units at the coast have sedimentary features that suggest deposition from turbid flows.

Petit Tor Member (PTB) is a breccia at the base of the Watcombe Formation; it rests unconformably on the Saltern Cove Formation. The member was formerly regarded as part of the Devonian limestone sequence, equivalent to the nearby Torquay Limestone Formation of Petit Tor Downs, which contains a similar range of fossils (e.g. House, 1963). The fossils are contained in limestone blocks, up to several metres across, or rafts and lenses of cleaved mudstone derived from the Saltern Cove Formation. Locally the clasts form a framework, elsewhere the breccia is matrix supported. In the coarse-framework breccia, where the long axes of clasts are parallel to the internal bedding, bedding within the clasts is locally parallel to the depositional bedding, which suggests a reason for the earlier interpretations. The haphazard orientation of pre-incorporation structures, bedding and cleavage, in some or a majority of clasts, plus the sandstone and siltstone matrix, indicates the nature of its origin. In the breccia, a crude bedding can be discerned in the sandstone and pebble matrix.

The breccia is very coarse-grained local talus, possibly deposited adjacent to contemporaneous faults that, locally, bounded part of the late Permian basin.

Oddicombe Breccia Formation (OBr)

The Oddicombe Breccia is restricted to a small area at the northern margin of the Torbay district. It rests conformably on the Watcombe Formation. In coastal sections to the north of the district, the Oddicombe Breccia is seen passing laterally into the Teignmouth Breccia; in the Newton Abbot district it is dominated by rounded clasts of Devonian limestone with some clasts of sandstone and quartz- porphyry in a matrix of hematite-stained silty sandstone. The bedding is mostly planar, commonly fining upwards and showing imbrication of the coarser basal clasts.

Chapter 4 Cainozoic

No deposits of Palaeogene or Neogene age have been recognised within the district, although the substantial deposits of the Bovey Basin are developed about the Sticklepath Fault complex a few kilometres to the north- west. In common with the rest of the south-west of England, marine retreat still-stand features that developed during these periods are ubiquitous, and can be mapped at intervals of a few metres from the highest levels down to the coast or valley bottoms. Only the lowest four features have been identified as of probable early Pleistocene age (Mottershead, 1977). These are platforms carved in solid rock that are gently inclined seawards and backed by solid cliffs (commonly degraded in part) at about 35 m, 20 to 25 m, 10 to 15 m and 2.5 to 5 m above OD.

Caves that are likely to be of Neogene age or older lie within the limestone formations and members above the lowest level of unconsolidated late Pliocene deposits of the province, at about 40 m above OD. Sandstone dykes and limestone cavity fills of crudely bedded pebbly sandstone (e.g. Saltern Cove) provide some evidence of the presence of rifts and caves formed during or before the Permian. Maxima in the height distribution pattern of Devon caves can be correlated with pronounced still- stands of sea level within the Palaeogene and Neogene at 130 m above OD and 70 m above OD indicating their active formation during these periods (see Leveridge et al., 2002). Within the district cavities and phreatic tubes above about 40 m can be seen (for example in quarries about Babbacombe within the Walls Hill Limestone Member) developed along faults, joints and bedding. They are also commonly encountered in borehole cores (BGS records).

Cave deposits

Several substantial cave systems have been recorded within the district in the past, some of which were subsequently removed by quarrying (Lloyd, 1933). Kent’s Cavern remains a cave complex of national importance because of its wealth of faunal remains and a record of human habitation, with flint axes attributable to the time of Homo heidelbergensis, extending back some 450 000 years. It is the oldest scheduled ancient monument in Britain. The entrances are at about 55 m and 58 m above OD; the system is thought to have been initiated 2 Ma BP in the Neogene. It comprises a complex of caverns, rifts along faults and phreatic tubes, with wall and ceiling decoration, multiphase roof breakdown and stalagmite formation, and flowstone floors. The crude stratigraphy present in the system is essentially of Quaternary age, and comprises interdigitated lithic breccia, cave earths, and stalagmite floors. The oldest animal remains within the breccia are of the cave bear (Ursus deningeri) dating back some 500 000 years. Other remains of animals that subsequently occupied the caves, fell in, or were washed into the caves include mammoth, rhinoceros, lion, hyena, horse, wolf and fox. Neanderthals and then Homo sapiens occupied the caves in the Ipswichian interglacial and Devensian glacial periods (125 000 to 12 000 years BP).

Raised-beach deposits

The earliest deposits, which are the lowest ones on the lower raised shore platforms, consist of coarse clastic deposits long recognised as raised-beach deposits (Godwin-Austen, 1842). They are present at several localities (see Lloyd, 1933) but only sufficiently extensive at Hope’s Nose (Plate 4a) to be recorded on the 1:50 000 scale map. The base of the Hope’s Nose deposit at 9 m above OD suggests that it occupies the second raised shore platform of the district, and indeed there are nearby remnants of the lower platform most of which has been removed by erosion. The deposit comprises thin to medium beds of carbonate-cemented sand with dispersed pebbles and pebble layers overlying a basal bed of limestone boulders and cobbles, which includes slate and quartz vein fragments, in a coarse sand matrix. Complete and fragmented shell fragments are locally abundant in the sandstone, with Ostrea being common. This sequence is about 4 m thick. It is overlain by unconsolidated fine- grained sand, possibly blown sand, up to 1.2 m thick. The succeeding 2 m or so of silty sand with rock fragments is a remnant of an overlying local head deposit. Such a sequence is typical of the lower raised shore platforms of the province. Small remnants of raised beach, at about 7 m above OD, overlain by blocky limestone head are present between Shoalstone Point and Berry Head.

Head

Head comprises poorly stratified or unstratified deposits of clay, silt, sand, gravel and locally derived angular lithic clasts, which may be up to block size, transported downslope by solifluction under Pleistocene periglacial conditions. The head mapped in the district is that forming the thicker deposits that in places occupy valley bottoms or mantle the coastal platforms between OD and about 35 m above OD around the coast, although in this district relatively little remains of these regional features. Significant head deposits are present as residual valley fill at Paignton [SX 891 619] and Torre Abbey [SX 908 638], and as raised platform deposits near Black Head [SX 937 645] and Kingswear [SX 893 503]. Elsewhere these main head deposits have been ascribed to the onset phase of the Devensian glacial period (Leveridge et al., 1990).

Head, or regolith, of local rock fragments in clay matrix also forms a mantling deposit in much of the district, developed mainly in early postglacial times. It is thin, generally less than 1 m thick, but exceptionally is 2 m on lower hill slopes.

Buried channels

The river valleys were overdeepened during the Pleistocene when sea level continued its retreat much below current levels (to >120 m below OD; see Evans, 1990). With regression after the late Pleistocene Devensian glacial period, alluvial deposition was active in the valleys, with the interplay of onshore and marine deposition at lower levels. At Maypool, near Dittisham, depths to solid rock is recorded in boreholes down to about 35 m below OD: downstream, at Kingswear, about 1.5 m of clay with boulders is succeeded by some 16 m of silt (Codrington, 1898). There are records of submerged forest; tree stumps rooted in grey clay that can be seen during exceptionally low tides along the beaches of Torbay (Lloyd, 1933). Radiocarbon dating of wood, from similarly located deposits in Cornwall, yielded an age of 4278 ± 50 years BP (Goode and Taylor, 1988). Within the alluvial spreads at Paignton, Goodrington and Torre Abbey, up to 6.5 m of peat is recorded in boreholes, within sequences that are up to 21 m thick. These comprise alluvial silt with lithic clasts, and towards the top there are interbedded and interlaminated silt and mud containing marine shells.

Fluvial deposits

River Terrace Deposits are present in the valleys of the River Dart and tributary streams above Totnes. The deposits consist of sand and gravel that contains clasts in variable proportions of slaty mudstone, limestone, basic volcanic rock and granite. A numbered sequence of terraces is not differentiated on the map, but minor featuring suggests that the lower terrace deposits extend some 2 km north of Totnes, and probably represent a separate terrace lower than the main terrace that lies to the west near Staverton. The upper surface of the deposits is very gently inclined downstream and towards the river. The superficial deposits rest upon a platform, or platforms, of solid rock, above the level of the modern (Holocene) river alluvium. The solid is exposed in small ‘cliff featuring’ between terrace deposits above and Holocene alluvium below. The age of the terrace deposits and solid terracing is uncertain, but the general height of the latter suggests correlation with the coastal Pleistocene raised shore platforms.

Alluvium is the deposit of modern river flood- plains, and is present along the valley floors of the rivers and larger streams in the district. The main tracts are above tidal reach on the River Dart and its tributaries about and to the north of Totnes. South of Totnes alluvial deposits are subject to reworking by marine processes. In much of the district, the alluvium can be divided into a lower unit of coarse gravel, and an upper unit of clay and silt, which may locally contain thin gravel beds or lenses of peat. Details of the alluvium of the River Dart and its tributaries are scarce: such records as exist suggest a maximum thickness of 3.0 m of silt and clay resting on up to 2.0 m of coarse gravel, which in turn rests on bedrock. The thicknesses of fine-grained sediment and gravel units are likely to be less for the alluvium of the minor streams.

Estuarine deposits

Tidal river and creek deposits flank the River Dart and occupy adjacent creeks. They include mud (clay), silt, sand, fine gravel, rock fragments and a variable organic content. Mud and rock debris derived from the solid and regolith of the riverside cliffs constitute the major part of these deposits, with sand and shell banks sparsely developed in the lower reaches.

Saltmarsh deposits are associated with small areas of saltmarsh established along the River Dart in its higher tidal reaches between Dittisham and Totnes. They comprise brown and grey silty clay, supplied by regular tidal inundation, and fixed by plant growth.

Marine deposits

Shoreface deposits contribute much to the tourist popularity of the district. The beaches of Oddicombe, Babbacombe and those of Torbay, Torre Abbey Sands, Paignton Sands, Goodrington Sands and Broad Sands consist of sand and gravel. The proportion of sand is generally larger to the south. The sand is predominantly quartz, with subordinate shell fragments and local lithic grains. A pale reddish brown hue is imparted by iron oxide staining inherited from the local Permian rocks.

Undifferentiated alluvium

The low alluvial tracts behind modern sea defences are shown as marine alluvium. In many cases, this is a thin silty clay and blown sand capping to terrestrial alluvium.

Offshore deposits

The disposition of sea bed sediments is based on British Geological Survey sampling in conjunction with Hydrographic Office charts. Sand predominates, but gravel rests directly upon solid rock to the north of Berry Head and forms a significant spread extending north-eastwards from the mouth of Tor Bay, and mud makes up subordinate areas eastwards from the centre of the bay mouth. The thickest development of deposits (over 15 m) is at the foot of a still-stand cliffline below about 25 m below OD and running north-south on the seaward side of the bay.

Landslip

See Applied geology

Artificial deposits

Made ground and worked ground in this district are mainly the Cut and fill deposits associated with the main railway line in the Littlehempston and Totnes areas, the coast line between Torquay and Kingswear and the newer dual carriageway sections of the A3022 and A380 Torbay by-pass.

Quarrying operations in the district have generally left little visible spoil. The variety of uses of the limestone, building stone, aggregate and lime burning consumed most of the rock quarried, and coastal quarries disposed waste in the sea. Those areas in the Hele district of Torquay where the clayey silts of the Watcombe Formation were formerly exploited for brick making and pottery (Ussher, 1903) have mostly been reclaimed and built upon by light industrial and retail developments. Mining spoil associated with the Sharkham Point ironstone workings has been thinly dispersed or infills small excavations in the limestone.

Domestic and construction waste makes up the substantial disused waste tip [SX 902 564] to the north-west of Hele; locally the waste is up to 12 m thick but may be thicker in places as it infills part of a head basin and former brick workings. There are several other disused tips in the district, for example on the alluvium at Goodrington [SX 888 594] and in disused quarries, for example in the Walls Hill Member at Babbacombe [SX 933 654]. Licenced tipping is currently active on the Nordon Formation on the lower slopes of the River Hems valley 1 km north of Totnes [SX 808 617]

Chapter 5 Igneous rocks

The main occurrences of extrusive igneous rocks of the district are described above as integral parts of the successions. As elsewhere in the passive margin ‘basin and high successions’ there is a close compositional, genetic and geographical relationship with associated hypabyssal intrusive rock, which in the Torquay district is microgabbro (dolerite).

Lower Devonian

Volcanic rocks form a prominent interdigitating and discontinuous sequence within the Dartmouth Group across the south-west of England It constitutes the ‘Whympston volcanic complex’ (Leake et al., 1992) in the adjacent Ivybrige district Sheet (349), and a significant part of the Bin Down Formation on the Plymouth district Sheet (350) farther west. In the Torquay district, the main crop is along and near the coast about Stoke Fleming and east of the mouth of the River Dart. Whereas the Whympston rocks comprise both acid and basic extrusives, in this district extrusive rocks, closely associated with dolerite sills, are essentially basaltic lavas and tuffs, although Ussher (1903) did report the presence of felsitic rock at Blackpool Sands. In some places the top of basic tuff units are silicified, possibly after sinter.

The Lower Devonian volcanic rocks consist largely of crystal tuff with relict vesicular glass fragments. The matrix is heavily altered, comprising chlorite, albite, carbonate and sericite.

Lavas are grey-green to pinkish grey in colour, massive or amygdaloidal. The rocks are porphyritic containing phenocrysts of plagioclase (albite-oligoclase) in a feldspar microlitic matrix with chlorite, calcite and disseminated iron oxides.

Microgabbro is variable but commonly comprises orthoclase and plagioclase (ophitic), clinopyroxene, ilmenite, and subophitic and intergranular augite. Secondary minerals are sphene, actinolite, prehnite, leucoxene and epidote.

Middle and Upper Devonian

The Ashprington Volcanic Formation (AV) forms a major part of the Brixham High Succession and subordinate marginal sequences in the adjacent Looe Basin and South Devon Basin (south). To the north, basaltic tuff and dolerite are associated with the late Middle and Upper Devonian Nordon Formation in the South Devon Basin about Dartington. Volcanic rocks are less prominent in the Torquay High Succession of the district than in the Brixham High Succession. The Blair Hill Tuff Member does appear to be part of a more extensive development of volcanic rocks associated with limestone in the Newton Abbot district (Sheet 339) to the north.

On the Torquay promontory, the Black Head dolerite and gabbro is intruded largely into the Upper Devonian Saltern Cove Formation, and is closely associated basic tuffs (and limestone) present in the cliffs a few hundred metres north of the head.

Tuff is subordinate in the Ashprington Volcanic Formation. Crystal, lapilli and, fine-grained tuff are present with sparse accretionary lapilli tuff, and hyaloclastite (fragmented highly vesicular basaltic glass derived from quenched lava). Tuff and hyaloclastite are severely altered and commonly cleaved. Typically they comprise pumice and crystal fragments (6 mm) replaced by white mica and chlorite, in a matrix of comminuted lava and ash, now replaced by chlorite and/or hematite. Secondary alteration is widespread; plagioclase is replaced by albite, white mica or calcite, pyroxene by chlorite or actinolite and Fe-oxide by hematite and/or titanite.

Lavas are dark grey-green where fresh and poorly cleaved; they are fine grained and porphyritic. Feldspar- basalt predominates consisting of albitic phenocrysts (up to 6 mm across) and smaller laths, some showing flow orientation, in a fine-grained matrix composed of secondary chlorite, calcite and prehnite: vesicles are infilled with albite, chlorite, calcite and quartz. Subordinate augite basalt is characterised by augite phenocrysts in a matrix of subhedral pyroxene and plagioclase laths with secondary minerals of epidote and actinolite.

Microgabbro/gabbro shows a similar composition to the lavas, varying between feldpar (albite and orthoclase) dolerite and augite dolerite. Generally they show a similar composition with ophitic and subophitic textures of clinopyroxene phenocrysts (up to 5 mm) enclosing plagioclase laths. Typical intrusions can be seen at Dartington and Black Head, where the feldspars are partly albitised oligoclase-andesine.

The extrusive and intrusive basic igneous rocks of the district compare with those elsewhere in the passive margin sequences of south Devon and central Cornwall. These are predominantly within-plate alkaline basalts with subordinate subalkaline basalt (Figure 3)a. Their isotopic and geochemical characteristics indicate derivation from a mantle source, Ocean Island Basalt-type magma, which in the continental plate setting is indicative of a strong extension (see Merriman et al., 2000). A proportion of the early Devonian rocks has calc-alkaline affinities (Figure 3)b, which has been attributed to contamination of mantle-derived magma during the early stages of continental rifting (Merriman et al., 2000).

Chapter 6 Structural geology and metamorphism

Ussher (1903) recorded cleavage and sketched folding and faulting in his observations of Devonian stratigraphical relationships in the area. He also inferred the presence of major thrusts to explain the relations between the Lower Devonian rocks overlying younger strata. In the revision of the Torquay memoir, Lloyd (1933) was less convinced of major thrusting preferring to interpret the structures as major northward overfolding. Vachell (1963) revived the thrust concept, attributing the Lower Devonian rocks about Paignton and Torquay to a northerly transported ‘Marldon Nappe’. In a subsequent detailed structural analysis of the district, Richter (1969) described cleavage, mesoscopic folds and faults, their orientations and sequence. He recognised four deformation phases: the first three of the four sequentially differentiated phases corresponding with the three main deformation phases of Leveridge et al. (2002), described as ‘southern domain’ structures characterising the Looe and South Devon basins in the Plymouth district. Richter recorded the main early phase of penetrative cleavage formation associated with asymmetric northerly vergent major and minor folds and related thrusting, a second phase of crenulation and fracture cleavage associated with northerly vergent minor folds, and a third phase of southerly vergent folding with minor thrusting. The significant role of thrusting in the district was subsequently re-emphasised by Coward and McClay (1983), who proposed thin-skinned tectonic models for a layer-cake stratigraphy. Importantly, the occurrences of the Meadfoot Group rocks about Paignton and Torquay were attributed to a major thrust nappe, derived from the south, with a minimum 13 km displacement.

Variscan structures

D₁ deformation

D₁ structures produced by the first major compressive deformation in the district include the ubiquitous cleavage (S₁), folds (F₁), thrusts and strike-slip faults. The folds range in scale from mesoscopic (minor fold: hand specimen to cliff size) to macroscopic (major folds that affect the mapped distribution).

S₁ cleavage

This is the first and main cleavage of the district, and is axial planar to F₁ folds. It is a slaty cleavage in argillaceous rocks, and a penetrative pressure-solution cleavage within the arenaceous rocks of the Lower Devonian. The volcanic and hyperbyssal intrusive rocks are commonly cleaved apart from the central parts of thicker flows and the larger microgabbro intrusions. Similarly, thin limestone beds carry a spaced pressure-solution cleavage but massive beds are generally poorly cleaved. As elsewhere in the region, the internal reorganisation and recrystallisation generating S₁ cleavage constitutes the main metamorphism of the rocks. In the southern part of the area where rocks are at epizonal metamorphic grade (see below) a grain lineation (preferred orientation of the long dimension of a mineral) is developed. It is parallel to the extension direction of clasts, burrows, and mineral aggregates in the plane of cleavage, and plunges to the south-south-east.

Cleavage has a modal east-north-east strike in the southern two thirds of the district; dip is to the south-south- east and increases southwards from gentle to very steep on the southern margin. To the north of Totnes, the strike of S₁ swings to the north-east and north on the northern margin of the district, with gentle dips to south-east and east, respectively. In the Torquay area there is no consistent pattern of cleavage orientation and dip direction between the various fault-bound blocks.

F₁ folds

Larger mesoscopic and major folds, in general, trend parallel to cleavage strike, having very gentle plunge. Over much of the area, the folds trend east-north-east or west- south-west. They are asymmetrical close to tight structures inclined gently to steeply, with cleavage, in the direction of cleavage dip. Typically, they have steeply inclined or over- turned short limbs and gently to moderately inclined long limbs (Plate 4b).

Vergence and facing is generally northwards, apart from the area to the north of Totnes where it is to the north-west or west. Incipient sheath folding is recorded locally (for example at Kingswear, Southdown Cliff, the cliffs above Babbacombe Beach and Anstey’s Cove), and minor folds may trend up to 90° from the modal direction and face east and west of the north-north-west extension azimuth.

There is a local divergence from the modal trend by some folds in the limestone. This is apparent in the Torquay area, where, apart from the effects of secondary rotation of the fault blocks, contrasting competence between thin bedded and massive limestone has resulted in disharmonic folding.

Major folding is evident to the north of Totnes, where limestone members are mapped and show a faulted synform and antiform with overturning in the common limb. The presence elsewhere of large-scale folding is indicated, for example, by the inversion of the Barton Limestone Member at Babbacombe, and the normal relationship of S₁ cleavage and bedding in the Saltern Cove Formation at Waterside Cove. The largest structure affects Meadfoot Group and Tamar Group of the Looe Basin succession south of the thrust contact with successions to the north. The hinge zone of the north-vergent antiform is between Man Sands [SX 923 534] and Long Sands [SX 922 527] within the Bovisand Formation. Part of the overturned northern limb forms Southdown Cliff (Plate 5a) which displays parasitic minor F₁ folding, coeval and later dislocations. The inverted limb includes much of the Staddon Formation, the Dittisham Member and the Greenway Tuff Member, a section locally in excess of 2 km in length.

NW-SE strike-slip faults

The Sticklepath Fault is mapped as a zone, 1 km wide, within which there are several faults. The trace of the main strand of the fault is beneath Torre railway station and Shiphay Hospital where post-Variscan movements have produced a fault zone some 10 m wide recorded in excavations. No definitive evidence of the age of the structure has been observed in the district. The Sticklepath Fault is one member of a set of regional north-west-trending faults that are attributed to syn- D₁ deformation (Leveridge et al., 2002). The relative positions of the Torquay and East Ogwell limestone formations indicate a cumulative residual minimum displacement of 5 km on the Sticklepath Fault; displacement is dextral and strike-slip.

Dextral displacements of 1 km or more are apparent along parts of north-west-orientated faults between Totnes and Pudcombe Cove [SX 912 505], Washbourne [SX 801 556] and Dartmouth, and though Abbotsleigh [SX 800 489]. Between the Broadhempston area [SX 80 66] and Sharkham Point, north-west faults are displaced by north-east-trending faults.

NE-SW faults

The north-east-trending faults range in orientation from north-north-east to east-north-east; many show sinistral displacement and/or downthrow to the north-west. Faults of this set terminate against or constrain the north-west- trending faults, suggesting penecontemporaneous development as a complementary set. On geometrical grounds the more easterly trends probably indicate later rotation by dextral displacement along the north-west-trending faults.

D₂ deformation

S₂ cleavage

The second phase cleavage is sparsely developed in the northern half of the area, but is significantly more common in the southern half of the district. It is a crenulation cleavage, generally spaced, only transposing the earlier S₁ fabric very locally. The cleavage has a modal east-north- east strike. Dips are variable within exposures but there is a progressive overall steepening southwards from moderate to vertical dips. Quartz veining is commonly associated with S₂, occupying cleavage planes where those are spaced. S₂ is an axial plane cleavage to F₂ folds.

F₂ folds

Folds of the second deformation are essentially minor structures in the district. They are open to close with rounded hinge zones, moderately to steeply inclined, commonly disrupted along cleavage. The folds are asymmetrical, modally verging north-north-westwards and plunging gently east-north-east or west-south-west. Thus they are largely coaxial with D₁ structures in the area (Plate 5a).

D₁ and D₂ thrust faults

The key role of thrusting in determining the disposition and juxtaposition of rocks of the ‘basin and high successions’ is indicated above. Mesoscopic thrust faults are observed, in association with F₁ and F₂ folds (Plate 5b), but those thrusts bounding major nappes are not well exposed. Attribution of major thrusts to D₁ and/or D₂, as in the Plymouth district (Leveridge et al., 2002), is generally not feasible here. The presence of the major thrust faults is generally indicated by stratigraphical and structural geometrical relationships, but faults with low to moderate dip have also been observed in borehole cores.

The Looe Basin succession is thrust northwards on to deposits of the Brixham High and adjacent South Devon Basin (Southern sub-basin). Between Dittisham and Brixham the uppermost deposits of the Looe Basin are preserved locally, but elsewhere these are overridden and occluded by the overthrust Staddon Formation. That boundary thrust is generally gently inclined, and, because of the occlusion, is regarded in large part as secondary out of sequence thrusting. The major antiformal folding and overturning of this upper part of the sequence is interpreted as a culmination (see below) anticline associated with the inversion and out-thrusting of the basin deposits during D₁. Thrusting between successions in this belt is thus considered to be a combination of D₁ and D₂ structures. Within the Looe Basin Succession, the boundary of the older Dartmouth Group with the underlying younger Bovisand Formation is interpreted as a thrust, both divisions in the vicinity of the boundary being the right way up, and boundary inclination commonly differing from bedding inclination.

The Brixham High limestone and volcanic rock divisions are similarly overthrust northwards. There are also significant thrusts within these sequences, as between the Middle Devonian Berry Head Member and Upper Devonian Churston Member of the main platform and biohermal sequence, and between the main body of Brixham Limestone Formation and the back reef Goodrington Member. To the west, the lower boundary of the Ashprington Volcanic Formation is generally gently inclined whereas bedding within the formation and in the underlying rocks dips moderately to steeply. The thrust sheet is interpreted as having been derived from the Brixham High, now overthrust by the Staddon Formation, with evidence displayed in the Dittisham area of its roots to the south. The thrust front of the nappe passes west to east through Totnes to Longcombe [SX 836 600] where it is displaced by steep faulting. It is probable that the main thrust nappe of undivided Brixham Formation continues south-eastwards. The flat-lying thrust-bound Meadfoot Group (undivided) about Paignton (Marldon Nappe of Vachell, 1963) thought to be derived from the main Meadfoot Group crop to the south by Coward and McClay (1983) is probably also part of the thrust nappe family derived from the Brixham High. This is because the Staddon Formation, essentially deposits of the Looe Basin (Leveridge et al., 2002) remain in sequence, and the lower metamorphic grade of these Meadfoot Group rocks (see below) is incompatible with derivation from the southern part of the district.

The overthrust nature of the Torquay High rocks in relation to basinal deposits of the South Devon Basin (northern sub-basin) is evident west of the Sticklepath Fault (Figure 4) where the limestone sheet boundaries are planar, and the juxtaposed rock sequences differ in age. East of the fault in the Torquay area, poor exposure and steep block faulting allow little direct observation of the low-angle thrust relationships in this multi-thrust sequence. Thrust juxtaposition of differing parts of the Torquay High Succession is observed in boreholes. Meadfoot Group rocks, again lower grade than those to the south, are included within the nappe family derived from the Torquay High, and are present within at least two thrust slices.

D₃ deformation

The third phase of deformation produced major folds and thrusts elsewhere in the region. It is weakly developed in this district: minor folds and a crenulation cleavage are attributed to this phase of deformation.

S₃ cleavage is developed only locally (e.g. St Mary’s Bay) as a spaced crenulation cleavage. It is gently inclined northwards.

F₃ folds are isolated small, mesoscopic, close, rounded fold couplets verging southwards. They are gently inclined with S₃ as axial plane cleavage.

Major folding of this phase is not evident within the district. However, the steepening southwards through the district of D₁ and D₂ structures is due to D₃ deformation. Unpublished BGS data shows that increasing intensity of D₃ structures southwards from the district to the Start peninsula is associated with a major southerly vergent antiformal fold of earlier structures, those structures being vertical or steeply overturned to the south.

Late Variscan and post-Variscan structures

The deformation of the district following the main compressive Variscan deformation is shown essentially by the faults. In addition to the faults described above other sets occur. The faults are moderate to steep. Significant trends are:

E-W faults are seen mainly where they control the distribution of Permian rocks, indicating significant movement during or after deposition of these rocks. In the Babbacombe area, the moderate northerly dip of the Lower Permian and the gentle northerly dip of the unconformable Upper Permian in an area constrained by east-west faulting suggests syndepositional movement on these faults. Significant also in this regard is the east-west-trending fault between Babbacombe and Shiphay; it bounds limestone in the Hele area, where bedding and cleavage have been rotated from a southerly to northerly dip.

N-S faults are not extensive structures but are locally numerous (e.g. Goodrington, and eastern Torquay), and terminate against or displace east-west faults. A near vertical fault of this general trend in the coastal cliffs between Broadsands and Saltern Cove has a fault gouge and brecciation up to 30 m wide in sub-zones indicative of polyphase movement. Locally, at Crystal Cove [SX 896 580], the whole of the fault zone is replaced by carbonate, reflecting its role as a major fluid pathway (Plate 6a).

NW-SE faults were established early in the deformation history of the district and were available subsequently, during appropriate stress conditions, for further dextral or sinistral strike-slip movement, or as normal faults. In this district, post-Variscan movement along these faults was significant as indicated by their displacements and disruption of the Permian sequence (see above).

Metamorphism

The deformed rocks of the district exhibit low-grade metamorphism as elsewhere within the Variscan sedimentary basins of south-west England (Warr et al., 1991). The metamorphic grade of pelitic rocks was determined during the revision survey of the district by Merriman and Kemp (2001). The Kubler Index of the illite crystallinity of some 97 samples is contoured in (Figure 5). The distribution of late diagenetic to epizone grades shows a general decreasing trend from south to north. This pattern appears to be modified by displacements on the north-west-trending faults to a degree not reflected in displacement of lithostratigraphical units, at least along the Dart Valley Fault. The regional metamorphism is largely a measure of the reconstitution of the rock body associated with the development of S₁ during D₁, but also reflects the initial burial and thickness of sedimentary overburden.

The epizone to the south is largely within the thrust nappes derived from the Looe Basin, but also includes the immediately adjacent, and probably overridden, areas to the north. These epizonal rocks were formed at temperatures of 300–350°C under a tectonic overburden of at least 7 km. The limited extent of high anchizonal rocks to the north includes rocks of the Brixham High and South Devon Basin (Southern sub-basin). The anchizonal grade implies burial under an overburden thickness of at least 5 km, generated by the Looe Basin inversion (see below) or during D₂ out of sequence thrusting.

Low anchizone rocks to the north include rocks from the Brixham High, South Devon Basin (Southern and Northern sub-basins). Isolated within that zone is a significant area of high anchizonal rocks to the north of Totnes, probably a reflection of the burial of older rocks in the deeper part of the southern half-graben basin of the South Devon Basin. Also within the low anchizone is the Meadfoot Group of the ‘Marldon Nappe’, an indicator that it was probably not derived from the Looe Basin.

The low anclizone and late diagenetic zone rocks of Torquay are the lowest grade rocks in the district, and include the oldest rocks in the Torquay High nappe family. The grade is indicative that the Meadfoot Group rocks of Torquay were not, in relative terms, deeply buried prior to derivation from the high. Corollaries are that they are not an extension of the ‘Marldon Nappe’, but may reflect dextral transport along the Sticklepath Fault from lower metamorphic grade rocks to the north. Fault reactivation may also have caused localised retrogression in some of these rocks.

Tectonic geology

The survey of the Torquay district has established its location in the southern part of the Rhenohercynian east-west passive margin (Figure 2) that rifted progressively northwards during the Devonian and Dinantian. The largely Lower Devonian Looe Basin succession is comparable to that established in the Plymouth district (Leveridge et al., 2002). The South Devon Basin differs from that to the west. The mid-basin high, the Torquay High, generated by sub-basin formation, was generally maintained in shallow water depths with biohermal and reefal production through the Mid Devonian in to the Late Devonian. Active reworking of the high produced significant limestone incursions in to the adjacent basinal areas. The local colonisation of these limestone deposits, and those derived from the Brixham High, within the southern sub-basin, suggests a basinal regime generally shallower than to the west. The volcanic and hyperbyssal rocks show a similar pattern of evolution as elsewhere along the margin (Figure 3). All are mantle-derived alkaline basalts typical of the rifting regime, but the Lower Devonian rocks have calcalkaline affinities, shown elsewhere to be due to crustal contamination characteristic of the early stages of continental rifting (Merriman et al., 2000).

During the early major deformation that migrated north-wards through Devon and Cornwall during the Dinantian, compression resulted in northward-verging folds, cleavage, thrusts and north-west-trending dextral strike-slip faults (Leveridge et al., 2002). The inversion of the Looe Basin within the district produced the Man Sands antiformal structure at the out-thrust front. With overloading on the Brixham High, capping deposits were then thrust off their basement, by shortcut thrusts, over deposits of the southern sub-basin of the South Devon Basin. A similar process subsequently affected the

Torquay High, with platform and reefal carbonates thrust northwards over deposits on the northern sub-basin. Later in the Carboniferous (Silesian), as the whole extensional rift system closed, continuing stress from the south produced the second northerly directed overriding deformation, which in the Torquay district was close to co-axial with the first. It is probable that the early thrusts were reactivated, and further transgessive flat-lying thrusts also developed associated with the early faults to transport some of the deposits of the highs still farther to the north (Leveridge et al., 2002).

The full inversion of the Culm Basin of North Cornwall and central Devon was associated with southerly out-thrusting and gravitational collapse south-wards. The third-phase structures in the district represent part of this process during which some of the earlier faults probably also became slides accommodating southerly transport.

Following the late Carboniferous compression, the north-south extensional rebound of the province was accompanied by intrusion of the granites (in the latest Carboniferous and early Permian times), backslip on earlier thrusts, and steep east-west faulting. It is probable that the east-west faults bounding the main Lower Permain crops in the district, about Paignton and to west of Torquay developed at this time with sedimentation off the sides and along the lengths of the troughs. There appears to have been rotation within these fault-bound blocks to produce the angular unconformity between Lower and Upper Permian rocks.

Within the district, there is no evidence of deformation later than the Early Permian. Strands of the Sticklepath Fault bound the Palaeogene/Neogene deposits of the Bovey Basin to the north, indicating movement on the fault during the Cainozoic (Tertiary), which may be responsible for the disruption of Permian rocks.

Chapter 7 Mineralisation

The Torquay district lies at the eastern end of the South- west England metalliferous province, but beyond the group of tin and base metal deposits that are genetically associated with the Dartmoor Granite. In consequence, the range of deposits and mineral occurrences are restricted and most derive from the movement of low-temperature hydrothermal fluids in and around bodies of Devonian limestone. The deposits included:

iron ore deposits of limonite and hematite as replacements, and filling cavities and fractures in the Devonian limestone
deposits of iron-rich ochre, probably as replacements in the Devonian limestone
gold-bearing carbonate veins in the Devonian limestone of Hope’s Nose

The iron ore and ochre were worked commercially during the 19th and early 20th centuries, though details of the occurrence and mineralogy of the deposits are sparse.

The most extensive workings were at Sharkham Point, Brixham, which furnished material for paint manufacture and harder iron ore for smelting. Between 1858 and 1914, some 300 000 tons were produced, but this figure probably includes output from other mines. At Sharkham Point, the ores were worked from open pits and underground galleries, drained by adit to sea level. The ores were irregularly developed along an east-west zone, some 600 m in length, in which faults trending approximately north-south and east-west have been mapped. The open pits in the western part of the district have been backfilled with waste, but in the east examples of the mineralisation can be seen in old mine workings. In places, there are well developed replacements of the limestone by hematite grading into unaltered rock. Elsewhere there are breccias of limestone, slaty mudstone and tuff, with localised replacements and botryoidal overgrowths of goethite, limonite and hematite. Some joint surfaces show aggregates and coatings of white or pale pink baryte crystals. The extent to which the mineralisation was controlled by faults is uncertain. It is clear that major vein structures are not present, but it is possible that the mineralisation was most strongly developed at the intersection of fractures, and this may represent the invasion of a palaeokarst system by ore fluids.

Other iron ore deposits were worked at Torre, Furzeham Common (Wheal Prosper), Parkham Hill (ochre), Rea Barn Hill (ochre): this list is not exhaustive. These deposits yielded iron ores of the Sharkham Point type, or iron oxide-rich clays (ochre) or a mixture of both. Much of the ochre and the softer varieties of iron oxides were used in the manufacture of anticorrosion paint (Howard, 2000), an industry that survived until the end of World War II.

The presence of native gold in narrow carbonate veins (Plate 6b), which cut through the Middle Devonian limestone of Hope’s Nose, was reported by Gordon (1922). Specimens collected by Sir Arthur Russell, and placed in the collection of the Natural History Museum and elsewhere, are of dramatic dendritic and fern-like aggregates of gold crystals in a matrix of calcite and dolomite (Russell, 1929). The veins, about 14 in number, comprise a swarm in which the components are separated by up to 20 m of host limestone; the mineralisation is restricted to the massive stromatoporoid reef facies of the Daddyhole Member, and is not seen in the overlying bedded limestone. Individual veins trend roughly east-west and are developed as irregular pods and lenses within steeply inclined fracture zones. Within the carbonate veins, the occurrence of gold is associated with buff to cream coloured calcite and dolomite, usually of saccharoidal texture. Cavities in the gold-bearing carbonate may be filled with yellow-brown iron oxide minerals, together with traces of goethite and hematite.

In his original account, Russell noted that certain of the gold specimens from Hope’s Nose contained high proportions of silver. This was later demonstrated to be in error by Clark and Criddle (1982), who demonstrated that high levels of palladium, rather than silver, is present in some of the gold specimens. They also recorded the rare palladium- arsenic-antimony minerals, isomertieite and mertieite-II, as inclusions in certain of the gold specimens. Scrivener et al. (1982) also recorded high palladium levels (up to 16 wt %) in some gold specimens from the locality. Further examination by Stanley et al. (1990) led to the identification of a suite of precious and base metal selenide minerals as minor components of a small number of the carbonate veins. Leake et al. (1991) have drawn attention to the complex concentric nature of palladium-rich zones in gold grains from Hope’s Nose, which is identical to that shown by Au-Pd-Pt grains collected in drainage geochemical surveys of the adjacent South Hams district of South Devon.

Metallogenesis

The mineralogy and ore textures of the iron and gold occurrences described above are consistent with mineral precipitation from low-temperature hydrothermal fluids. In the case of the Hope’s Nose gold occurrence, this is confirmed by fluid inclusion studies on quartz and carbonate (Scrivener et al., 1982), which indicate that the mineralising fluids were highly saline, calcium chloride-rich brines in the temperature range from 65º-120º. Such fluids are very similar to those responsible for lead-zinc-silver mineralisation in the north-south trending ‘crosscourse’ vein systems in the Variscan basement rocks of south-west England, and also to fluids which have produced replacement manganese ores in Late Permian breccias of the Exeter district (Scrivener et al., 1994). The high salinity and calcium chloride content of the ore fluids are typical of brines that form in deep sedimentary basins. It has been demonstrated that, in the case of the lead-zinc crosscourse deposits of south-west England, Permo-Triassic sediments were the hydrothermal fluid source, with a major episode of mineralisation in the Mid-Triassic (Scrivener et al., 1994). In the case of the Hope’s Nose gold veins, the ore mineralogy and textures, coupled with the proximity of the Permian unconformity, and the presence of basinal-type fluids, suggests formation during extensional fracturing, involving the migration of brine from superincumbent red-bed strata since removed by erosion.

In the case of the iron ore deposits of Sharkham Point, there is no evidence from fluid inclusion or geochronological studies. However the association of iron oxide minerals with baryte, the limestone host rock and the proximity of red beds, do suggest similarities with the Llanharry-Taff Wells mineralisation of south Wales. At Llanharry, the hematite-goethite ores were formed from highly saline fluids, at temperatures not exceeding 100ºC, with evidence for the presence of Ca/Mg chloride in the mineralising brines (Rankin and Criddle, 1985). In the Torquay district, both the gold and iron oxide mineralisation appear to be genetically linked to basinal brines, which accumulated in superincumbent red beds, and which migrated into the Devonian basement during extensional fracturing, possibly during the Triassic period. It is possible that the source of the gold and the iron may, at least partly, derive from interaction with Devonian volcanic rocks, and that the palladium derives from those of deeper mantle origin. In the neighbouring South Hams district, the widespread occurrence in stream sediments, of complex grains of gold, with platinum and palladium (Leake et al, 1991) may also be linked to the mantle-derived Lower Devonian alkali- basalts, and to fluid movements in a Permo-Triassic cover that was formerly present but subsequently removed.

Chapter 8 Applied geology

Geological factors that have a bearing on land use and development are reviewed briefly in this section.

The great variety of rock types of the district has furnished a similarly wide variety of mineral products, which include building stone, roadstone and aggregate, brick making material, pottery clay, mineral pigments and iron ore. These operations are now closed with the exception of the limestone quarry at Yalberton which still produces a small quantity of stone.

Building stone

The Devonian limestone of the area has been extensively exploited for building stone, large quantities of which were formerly exported from the coastal quarries. Massive blocks of this material can be seen in the local sea walls and other structures, while various coloured varieties were cut and polished for ornamental use as ‘Torquay marble’. Most of the ornamental limestones were worked from quarries at Ipplepen and Petit Tor. Blocks cut from quarries in the better cemented parts of the Permian breccias (invariably with dominant limestone clasts) have been used in the construction of walls, as have sandstones of early Devonian age. Devonian silty mudstone has found some local use in construction, and roofing slates were formerly quarried near Brixham.

Roadstone and aggregate

Roadstone has been worked from a number of quarries in Devonian dolerite and the harder parts of the volcanic rocks. The Devonian limestone can be used as a source of general aggregate; there is a small output at present.

Brick making material

The clay-rich parts of the Permian Watcombe Formation in the area around Hele were extensively worked for brick clay. Much of this material appears to have been a highly weathered breccia of reddened fissile mudstone fragments in a clay-rich matrix. The Watcombe Formation has also been worked for clay, which was used in the manufacture of terra cotta ware; the main sites for this clay were in the Newton Abbot district (Sheet 339) to the north. Other brick pits were opened in weathered fissile mudstone of early Devonian age near Claylands Cross, Paignton.

Aquifer vulnerability and pollution

The district ranges in elevation from sea level to over 180 m. Much of the area is drained by the River Dart and its tributaries, but the south and east are drained by small coastal rivers and the area around Eginswell in the north by a tributary of the River Teign. The water resources are regulated by the South West Region of the Environment Agency. The average annual precipitation decreases eastwards, varying from over 1400 mm on the high ground around Halwell Camp to less than 1000 mm over Hope’s Nose on the headland to the east side of Torbay (Meteorological Office, 1977). The average annual evapotranspiration is 536 mm (Thompson et al., 1981).

The regional groundwater flow is eastwards or south-eastwards towards the sea, reflecting the local surface water drainage pattern.

The north-eastern part of the area is covered by a hydrogeological map (Institute of Geological Sciences and South West Water, 1982). The best yielding aquifer in the district, is the gravels of the river terrace deposits (Table 3).

Typical analyses of groundwaters from the different formations are given in (Table 4). The groundwaters generally have short residence times in the aquifers. Sodium and chloride ion concentrations increase towards the coast. Locally, nitrate concentrations are elevated due to the agricultural use of nitrogen fertilisers.

River terrace deposits

Groundwater in the district is abstracted for public supply from two main sources: Brixham spring [SX 917 549] and the Littlehempston radial collector wells. The latter is licensed to abstract 5 932 000 m³/a from two radial collector wells at [SX 800 617] and [SX 805 626], plus an additional 16 boreholes. They penetrate about 9 m of superficial deposits of which the basal 7 m or so are saturated. Generally the aquifer comprises two sand and gravel horizons normally separated by about 1 m of silt, but locally this is up to 3 m thick. One of the boreholes [SX 8007 61277], penetrating 9.1 m of terrace deposits, struck water at a depth of about 2.4 m which rose to 0.8 m from the surface. It yielded 45 l/s for 5.2 m of drawdown, during a seven day pumping test in September 1960.

At Dartington Hall [SX 805 633] five one hour step tests in a borehole penetrating 5.5 m of gravel (of which 4.3 m were saturated), at rates increasing from 6.3 l/s to 11.4 l/s, produced a final drawdown of 2.8 m and pumping test analysis gave a transmissivity value of 155 m²/d. A series of wells into the gravels beneath the alluvium at Totnes [SX 80 61] yielded 7.6 l/s.

Water from the river gravels is generally soft, with total hardness less than 100 mg/l (as CaCO₃) and with a chloride ion concentration of less than 20 mg/l. As the aquifer is in hydraulic continuity with the rivers, it is liable to surface water pollution and potentially high suspended solids and nitrate concentrations. In 1930, trenches dug to the north-east of Dartington Hall, into the lower terrace, to capture induced recharge from the river encountered a strong flow from the higher terrace. The water had a high permanent hardness (285 mg/l as CaCO₃), implying that the water is probably fed from the Middle Devonian limestones to the west (Lloyd, 1933). One of the Littlehempston wells [SX 8048 6265] also, on occasions, had a relatively high total hardness (values varying from 75 to 265 mg/l (as CaCO₃) in 1964).

Other superficial deposits

High water tables can be expected in some of the superficial deposits, notably the alluvium, colluvial valley infill and the former salt marsh and lagoonal deposits along the coast (Geomorphological Services Ltd., 1988). These do not represent major groundwater resources, but the height of the water table is likely to act as a restraint on development.

Exeter Group (Permian)

The sandstones and breccias of the Exeter Group form potential aquifers with many old private supplies drawn from boreholes into the Torbay Breccia Formation in the Paignton area, but supplies have not been tested and yields are generally less than those encountered in the Dawlish area, farther north, where 5 l/s is common.

An old well, possibly as deep as 24.4 m, at the brewery in Paignton [SX 8857 6089] yielded 2.3 l/s from the Torbay Breccia Formation and a 1.2 m diameter and 2.1 m deep well also into the Torbay Breccia Formation at Well Street, Paignton [SX 8846 6093], formed part of the public water supply system for Paignton until 1907. The water level was reported always to be within 1.2 m of the surface even when pumping. However, a boring 80.5 m deep at the Paignton Steam Laundry [SX 8788 6004] drilled in 1909, through conglomerate into sandstone, was abandoned due to losing water at 15.8 m down. A spring and shallow well (Petit Tor) at Torquay Golf Course possibly the well-marked as Petit Well on 1:25 000 scale maps at [SX 9192 6640]) used to supply the brewery in St Marychurch with abundant water, however, it ran dry in times of drought. A two-day test at Avenue Road, Torquay [SX 9010 6475] on a 63 m deep borehole in Torbay Breccia Formation, yielded 1 l/s for 0.8 m of drawdown. Pumping test analysis gave the best estimate of the transmissivity value as 90 m²/d.

A borehole at Hele [SX 9066 6618] struck water at a depth of 83.8 m and yielded 0.6 l/s during a one-hour bailer test from the Watcombe Formation. However, a 30.5 m-deep borehole, also into the Watcombe Formation, at Torquay Golf Course [SX 9197 6657] had a water level only 2.1 m below the surface, but was easily pumped dry and never used.

Groundwater in the Exeter Group is hard but generally of good quality; it has a total hardness over 250 mg/l (as CaCO₃) in the breccias and sandstones and over 300 mg/l in the Watcombe Formation. Chloride ion concentrations exceed 50 mg/l near the coast (e.g. a spring at the English Riviera Centre in Torquay [SX 9085 6385].

Devonian

Devonian rocks underlie the majority of the district but only account for 4 per cent of the water licensed for use in the area. Groundwater occurs in joints and fissures. Yields are dependent on the number of dilated fissures a borehole intersects rather than the primary permeability of the rock, which is extremely low. Geological structure is an important control on fracture development and therefore borehole yields. Slaty mudstone initially tends to have a higher yield than sandstone as cleavage and joints are open in weathered zones near the surface. However, the yield from slaty mudstone is often only sustainable for short periods of time, and tends to decrease in dry weather.

Most of the formations have been utilised for small supplies. Yields from the mudstone formations are low, between 0.3 and 1.0 l/s being typical from 150 mm diameter boreholes, 30 to 45 m deep; dry boreholes are not unknown. Some yields from the Dartmouth Group, particularly around Stoke Fleming, are slightly higher; a 150 mm diameter borehole, 30.5 metres deep at Deer Park Hotel [SX 8638 4914] yielded 3.8 l/s during a two hour test in 1947 for 18.9 m of drawdown and another 150 mm diameter borehole, 38 m deep at Stoke Fleming [SX 8636 4868] yielded 1.5 l/s for 6.7 metres drawdown during an eight hour test in 1950. These higher yields reinforce the opinion that the Lower Devonian sandstones are too compact to yield water (Lloyd, 1933) and the fractured slate contains more groundwater. However, a 129.8 m deep borehole, probably into Dartmouth Group, in Dartmouth [SX 8647 5129] yielded no water. Small springs issuing from the Dartmouth Group south of Dartmouth were collected for water supply (Lloyd, 1933).

Springs from the Staddon Formation at Bosomzeal and Lapthorn historically supplied Dartmouth, the average flow was 3.2 l/s in summer and much greater in winter (Lloyd, 1933). This was supplemented by springs from the Bovisand Formation, tapped via adits into the sides of the valley between Old Mill and Hemborough supplying Dartmouth Naval College. Other springs issuing from the Bovisand Formation, supplied Kingswear Laundry [SX 889 516] with moderately hard water. The 26.3 m deep ‘Wayside Well’ at Dunstone Park [SX 8734 6214] into Meadfoot Group yielded a good supply (Lloyd, 1933).

Pumping tests have been carried out in the district Devonian slates. At Hillhead Farm, Brixham [SX 900 538] a 76.2 m deep borehole sited near the boundary between the Staddon and Bovisand formations yielded 0.2 l/s during a six-hour test for 11.0 m of drawdown and pumping test analysis gave a transmissivity value of less than 1 m²/d. A borehole 72.6 m deep at Hillhead Holiday Camp [SX 903 534] into the Bovisand Formation yielded 0.5 l/s for 23.6 m of drawdown during a one-day test; pumping test analysis indicated a transmissivity value of 1 m²/d.

A 106.7 m deep borehole into the Nordon Formation at Whiteways Cider Factory [SX 7843 6541] yielded 0.25 l/s when the borehole was 30.5 m deep but the water was lost when the hole was deepened.

At the Old Lion Brewery, Totnes [SX 8006 6039] a borehole 42.6 m penetrating 0.8 m of limestone within Nordon Formation, had a restwater level within 5.9 m of the ground surface, but did not yield a useable supply.

Water from the slaty mudstone has low total dissolved solids concentrations, similar in composition to the surface waters. The groundwater sources tend to be shallow and are vulnerable to surface pollution. The waters generally have a total hardness of less than 250 mg/l (as CaCO₃), and usually less than 150 mg/l.; the chloride ion concentration is generally less than 50 mg/l but increases around the coast, exceeding 100 mg/l locally. The waters from the slates generally are neutral (pH 6.5 to 7.7).

The Devonian limestones that crop in the northern half of the district, particularly near the coast around Torbay, are generally fault-bounded and are extensively recrystallised with little primary porosity. Their water-bearing capacity depends on a well-developed series of fractures and bedding planes that have been enlarged by solution. The effects vary from minor solution along joints to karstic features including dolines, solution pipes and hollows, and possible underground cave systems (Geomorphological Services Ltd., 1988). The solution pipes are commonly infilled with soil and limestone debris and hence do not always provide a rapid pathway for pollutants. The solution seems to be greater in the south in the Brixham Limestone on the Churston Ferrers plateau (where solution features more than 6 m deep have been identified) than in the Torquay Limestone around Walls Hill (Geomorphological Services Ltd., 1988). Caves seem to have formed preferentially along the coast as solution weathering features are absent from many quarry faces, although this could be due to the fact that the quarries are developed in good quality rock. No permanent surface streams exist on the limestone plateaux, the ephemeral nature of the streams indicating the presence of a subsurface drainage network within the limestone. The streams can be deeply incised with the valley sides forming limestone gorges at Galmpton, Brixham and Churston coves.

The limestones respond rapidly to recharge events as their storage capacity is limited, they also discharge water rapidly to the slates and the sea via submarine springs, for example the freshwater spring occurring a short distance offshore from Elberry Cove, north-west of Brixham.

Water tables in the limestones are generally discontinuous and controlled by the fracture systems and solution cavities. Borehole yields vary widely, depending on whether water-bearing fissure systems are encountered in what is locally a karstic aquifer, and there are some dry holes.

Springs frequently occur at the boundary between the mudstone and the limestone. A spring at the junction of Middle Devonian mudstone and limestone near the bend of Fleet Street into the Strand, burst its banks in 1930 flooding some shops (Lloyd, 1933). A spring at the junction of the Meadfoot Group and the Torquay Limestone on which Castle College in Torquay stands, historically supplied a brewery in Fleet Street (Lloyd, 1933). A spring at the base of the cliff below Manor Gardens at Meadfoot, provided water for medicinal purposes (Lloyd, 1933). The water is probably at least partially derived from limestone under Lincombe Hill as it is very hard with high concentrations of calcium and magnesium (Table 4).

There are several examples of better yielding wells occurring along faulted junctions with slaty mudstones. The public well at Goodrington [SX 88 58] sunk through the Saltern Cove Formation near the boundary with the Brixham Limestone Formation overflowed at a constant rate (Lloyd, 1933). A borehole 43 m deep into the Brixham Limestone beneath the Saltern Cove Formation in Primley [SX 8770 5928], struck water in the limestone at depths of 24.4 and 33.2 m and yielded 0.8 l/s.

A 152 mm diameter, 77.1 m deep borehole struck water at 60.7 and 69.2 m depth in the Torquay Limestone Formation beneath the Watcombe Formation; this yielded 0.8 l/s for 3.7 m of drawdown during a 20 day test. A borehole in Teignmouth Road, St Marychurch penetrating 97.2 m of Torquay Limestone beneath 6 m of Permian rocks supplied sufficient water for a brewery in 1912, while in 1875, a 194.6 m-deep borehole at Fleet Street in Torquay [SX 917 639] was abandoned after failing to obtain a supply in either the 102 m of Torquay Limestone Formation or the Nordon Formation below. It penetrated about 1 m of clay between the two formations, in a fault fissure, and this probably accounted for the absence of water (Lloyd, 1933).

Two pumping tests have been carried out in limestone to the south including the Brixham Limestone Formation. At Paignton Zoo [SX 880 597] a 60 m deep borehole through 20 m of Meadfoot Group struck water at 15, 20 and 23 m down. The hole was pumped at 2.3 l/s for 48 hours reducing the rest water level from 14.5 to 24 m. On analysis, it gave transmissivity values varying from 4 to 35 m²/d, the higher values being derived from the early data representing the dewatering of the overlying beds and the lower values from the later data reflecting the aquifer properties of the limestone. At Northern Telecom, Paignton [SX 8736 5838], a three-day test on a borehole 106.7 m deep penetrating 27.4 m of tuff underlain by 79.2 m of cavernous limestone with some fissile mudstone, of which only the bottom 32.3 m were not cased out, pumping at 3.4 l/s, for 2.4 m of drawdown gave a transmissivity value of 16 to 20 m²/d.

There are no data within the area for the East Ogwell Limestone Formation, however, just to the north of the district at Park Hill Farm, Ipplepen [SX 8431 6747] a 88.4 m deep borehole penetrating Whiteway Slate and Luxton Nodular Limestone above 6.1 m of highly permeable East Ogwell Limestone Formation, struck water at a depth of 73.2 m at the base of the Whiteway Slate. During a one-day test the yield was 6.8 l/s for 21.2 m drawdown. A 29-day intermittent pumping test with an average yield of 2.6 l/s, produced about 28 m of drawdown. The test was analysed and the transmissivity value calculated as 27 m²/d.

Water from the limestones is hard, with pH values over seven and bicarbonate ion concentrations of up to 300 mg/l. A large part of the outcrop of the limestone is along the coast where the aquifer is likely to be in hydraulic contact with the sea. Therefore sources could be contaminated by sea water with increased chloride ion concentrations caused by saline intrusion occurring as a result of groundwater abstraction reversing the natural hydraulic gradient. Tidal fluctuations in groundwater levels may occur.

Igneous rocks

The interbedded volcanic rocks and microgabbros also yield small supplies where they are unweathered and fractured. However where they are weathered, the resultant clays are of low permeability. The Devonian tuffs and lavas around Totnes were historically important for water supply. Springs issuing from the Ashprington Volcanic Formation on the southern slopes of the town used to supply 500 m³/d of water (Lloyd, 1933). Adits driven through volcanic rocks and associated slaty mudstone on the Follaton Estate farther west, intercepted springs; an adit at Follaton House yielded 91 m³/d in the summer of 1930. However, springs at the south-east side of Windmill Down tended to fail in time of a drought (Lloyd, 1933).

Yields from boreholes range from nothing from a 48.8 m deep borehole at Gilmore [SX 8283 5708] to 0.8 l/s for 1.8 m of drawdown during a two-hour test, from a 44.8 m deep borehole into tuff and slaty mudstone at Bowden Pillars Farm, Totnes [SX 8001 5913].

Water from the tuffs varies in chemical composition, depending on the lithology of the interbedded rocks. Total hardness is generally less than 250 mg/l (as CaCO₃).

Vulnerability to pollution

There are two main types of groundwater pollution, diffuse and point source. Diffuse pollution is caused by the application of fertilisers and pesticides; the rise in nitrate concentration in groundwater is an example of this and locally there is a nitrate problem in the shallow fractured aquifers of this area. Point sources of pollution such as landfill and leaking storage tanks also represent a threat to groundwater quality, particularly those sited on the Devonian limestones. The groundwater vulnerability to pollution from surface sources is shown on the map produced by the Environment Agency (1998).

Foundation conditions

Limestone solubility affects all of the limestone sequences to varying degrees. Around the coastal sections active cave formation and dissolution along fractures is evident, and there is reported evidence that site investigation boreholes encountered tidal movement of water onshore at depth within the Brixham Limestone Formation. Such movement of water is particularly relevant to any potential tunneling operations in Torquay. There, interthrust sequences that include limestone not cropping at surface are cut and bounded by faults, some of which are connected with the coast.

Other significant potential foundation hazards in the district occur where there is active dissolution by groundwater movement, and where voids have been produced in the long history of cavity formation (see Cainozoic).

Compressible ground Peat, up to 6.5 m thick, is encountered at depth in the alluvial tracts of Torre Abbey, Paignton and the Clennon valley at Goodrington. In the Chennon valley, the peat occupies a buried channel cut in alluvial clay with rock fragments, which runs north-south rather than along the local east-west length of the modern valley. The presence of this compressible material within the superficial sequences means that no significant constructional development can proceed without very thorough site investigations.

Slope stability within the Devonian rocks is dependent upon the depth of the excavation and its orientation with respect to the structural discontinuities such as bedding, cleavage, joints and faults within the rock. Within the upper weathered zone, shallow trenching is commonly unstable in the slaty fine-grained rocks, particularly where subparallel to the cleavage, owing to the opening of cleavage and cross-cutting joints. Because of the generally high concentration of structural discontinuities within the rocks, a detailed structure analysis is essential in all the deeper excavations and in all lithologies in order to identify the potential roles of plane failure, wedge failure and toppling failure.

Landslip

Landslips are recorded in all of the major lithofacies that crop out along the coast. Geological control on instability is a combination of bedding and cleavage plane discontinuities, joints and faults. The hazard potential of landslip in this popular holiday area is very significant.

Redgate Beach [SX 935 648] was closed at the time of the revision survey and is likely to remain so for any foreseeable future owing to active landslipping of the Torquay Limestone Formation. In the upper parts of the cliff above the beach, large limestone blocks that are tens of metres across have become detached along faults parallel to the cliff and related steeply inclined joints, and are moving eastwards downslope on subjacent clayey weathered slaty mudstone. The current backscarp of the slip is behind and west of the crest of the cliff-top hill, which makes a substantial volume of rock available for future migration and collapse seawards on to Redgate Beach.

At the northern end of Oddicombe Beach, the steep cliffs of Giant Rock [SX 926 660] in the Permian Torbay Breccia Formation are subject to toppling failure (which happened in 2001) on steeply inclined joints. Landslip deposits flanking the promontory impinge upon the popular tourist beach, where they are subject to erosion and remobilisation.

At St Mary’s Bay, the cleaved mudstone of the Nordon Formation strikes east-west through the beach section that trends north-south. The cliffs are degraded having been subject to a series of rotational slips in which both strike and dip are very variable, and there has been collapse on rotated and opened joints striking subparallel to the coast. The area of designated landslip is active.

Other coastal slips are also active in the sandstone and finer grained facies of the Bovisand Formation at Southdown Cliff, e.g. [SX 540 926] and the mudstone of the Dartmouth Group, e.g. Compass Cove [SX 884 494].

Inland landslips are relatively few and minor, but there are some active on steeper slopes, for example within the Permian along the Clennon valley west of Paignton [SX 865 612].

Information sources

Further geological information held by the British Geological Survey relevant to the Torquay district is listed below. Enquiries concerning geological data for the district should be addressed to the Manager, National Geological Records Centre, BGS, Keyworth. Geological advice for this area should be sought from the District Geologist, The Exeter Business Centre, Forde House, Harrier Way, Sowton, Exeter, EX2 7HU.

A Geoscience Data Index is available for consultation in BGS libraries and on the web site. This is a developing computer-based system that searches indexes to the collections. It has a backdrop based on the 1:250 000 scale maps. Available indexes include:

index of boreholes
outlines of British Geological Survey maps at 1:50 000 and 1:10 000 scale and 1:10 560 scale County Series
chronostratigraphical boundaries and areas from British Geological Survey 1:250 000 scale maps
geochemical sample locations on land
aeromagnetic and gravity data recording stations
land survey records

Maps

Geological maps

1:1 500 000
Tectonic map of Britain, Ireland and adjacent areas, 1996
1:1 000 000
Pre-Permian geology of the United Kingdom, 1985
1:625 000
Solid geology of the United Kingdom (south sheet), 1979 Quaternary map of the United Kingdom (south sheet), 1977 1:250 000
Sheet 50°N-04°W Portland, solid geology, 1983
Sheet 50°N-04°W Portland, sea bed sediments, 1983
1:50 000
Sheet 338 Dartmoor Forest Sheet 339 Newton Abbot Sheet 349 Plymouth
Sheet 350 Torquay
Sheets 355/356 Kingsbridge, Salcombe and Start Point
1:10 000/1:10 560
Details of the original geological surveys are listed on editions of the 1:50 000 geological sheets. Copies of the fair-drawn maps of the earlier surveys may be consulted at the BGS Library, Keyworth.
The maps covering the 1:50 000 Series Sheet 350 are listed below together with the surveyors' initials and the date of survey. The surveyors were A J J Goode, M T Holder, B E Leveridge, R C Scrivener, B J Williams and I Williamson. Mapping by M E Drummond of Newcastle University has also been incorporated in this sheet.
The maps are not published but are available for public reference in the libraries of the British Geological Survey at Keyworth, Edinburgh and Exeter, and the BGS London Information Office in the Natural History Museun, South Kensington, London. Uncoloured dyeline sheets or photographic copies are available for purchase from the BGS Sales Desk.

Geochemical maps

1:625 000
Methane, carbon dioxide and oil susceptibility, Great Britain (south sheet), 1995
Radon potential based on solid geology, Great Britain (south sheet), 1995

Geophysical maps

1:1 500 000
Colour shaded relief gravity anomaly map of Britain, Ireland and adjacent areas, 1998
1:625 000
United Kingdom aeromagnetic map (south sheet), 1965
1:250 000
Sheet 50°N-04°W Portland, aeromagnetic anomaly, 1978 Sheet 50°N-04°W Portland, Bouguer gravity anomaly, 1978
1:50 000
A geophysical information map (GIM) at a scale of 1:50 000 is available for this district. This shows information held in BGS digital databases, including Bouguer gravity and aeromagnetic anomalies and locations of data points, selected boreholes and detailed geophysical surveys.

Hydrogeological maps

1:625 000
Sheet 1 (England and Wales), 1977
1:100 000
Hydrogeological map of the Permo-Trias and other minor aquifers of South-west England, 1982

Mineral maps

1:1 000 000
Industrial mineral resources map of Great Britain, 1996

Books

British regional geology: south-west England. Fourth edition. 1975

Memoirs

Geology of the country around Dartmoor Forest (338) Sheet, 1912^‡1
Geology of the country around Newton Abbot (339) Sheet, 1913^‡2
Geology of the country around Newton Abbot (339) Sheet, 1984
Geology of the country around Ivybridge and Modbury (349) Sheet, 1912^‡3
Geology of the country around Torquay (350) Sheet, 1903^‡4: Second edition 1933^‡5
Geology of the country around Kingsbridge and Salcombe (355 and 356) Sheets, 1904^‡6

BGS technical reports

Technical Reports relevant to the district are described below. Most are not widely available but may be purchased from BGS or consulted at BGS and other libraries.

Biostratigraphy

There are biostratigraphical reports for the Torquay district. They are held as internal open file reports, by the Biostratigraphy Group of BGS, under the prefixes WH and PDL. Readers are recommended to contact the Chief Curator, BGS, Keyworth for access to these reports and to the palaeontological collections.

Metamorphism

One report is available on the ‘Metamorphism of the Palaeozoic rocks of the Torquay district, Devon, 1:50k sheet 350’. Internal Report, IR/01/184

Documentary collections

Boreholes

Borehole data for the district are catalogued in the BGS archives (National Geological Records Centre) at Keyworth on individual 1:10 000 scale sheets. For further information contact: The Manager, National Geological Records Centre, BGS, Keyworth.

BGS Lexicon of named rock units definitions

Definitions of the named rock units shown on BGS maps, including those shown on the 1:50 000 Series Sheet 350 Torquay are held in the Lexicon database, and is available on BGS web site http://www.bgs.ac.uk. Further information on the database can be obtained from the Lexicon Manager at BGS, Keyworth.

Material collections

Palaeontolological collections

Macrofossil and micropalaeontological samples collected from the district are held at BGS Keyworth. Enquiries concerning all the fossil material should be directed to the Curator, Biostratigraphy Collections, BGS, Keyworth.

Petrological collections

Hand specimens and thin sections of rocks from the district are held in the England and Wales Sliced Rock collection at BGS, Keyworth. A collections database is maintained by the Corporate Collections Management Programme at BGS Keyworth. The Programme Manager should be contacted for further information, including methods of assessing the database. Charges and conditions of access to the collection are available on request from BGS Keyworth.

Bore core collection

Samples and entire core from a small number of boreholes in the Torquay district are held by the National Geosciences Record Centre, BGS, Keyworth.

BGS photographs

Copies of photographs used in this report are deposited in the BGS Library, Keyworth. Prints and transparencies can be supplied at a fixed tariff.

Other relevant collections

Groundwater licensed abstraction, Catchment Management Plans and landfill sites

Information on licensed water abstraction sites, for groundwater, springs and reservoirs, Catchment Management Plans with surface water quality maps, details of aquifer protection policy and extent of Washlands and licensed landfill sites are held by the Environment Agency.

Earth science conservation sites

Information on Sites of Special Scientific Interest in the Torquay district is held by English Nature, Renslade House, Bonhay Road, Exeter EX4 3AW.

References

Most of the references listed below are held in the Library of the British Geological Survey at Keyworth, Nottingham. Copies of the references can be purchased, subject to current copyright legislation. BGS Library catalogue can be searched online at http://geolib.bgs.ac.uk

CASTLE, C. 1982. Middle and Upper Devonian conodont biostratigraphy of the Torquay area, South Devon. Unpublished PhD Thesis, University of Hull.

CHAMPERNOWNE, A. 1881. Notes on the find of Homalonotus in the red beds at Torquay. Geological Magazine, Vol. 6, 487–488.

CLARK, A M, and CRIDDLE, A J. 1982. Palladium minerals from Hope’s Nose, Torquay, Devon. Mineralogical Magazine, Vol. 46, 371–377.

CODRINGTON, T. 1898. On some submerged rock valleys in south Wales, Devon and Cornwall. Quarterly Journal of the Geological Society of London, Vol. 54, 251–278.

CONYBEARE, W D, AND PHILLIPS, W J. 1822. Outlines of the geology of England and Wales. (London: William Phillips.)

COWARD, M P, and MCCLAY, K R. 1983. Thrust tectonics of south Devon. Journal of the Geological Society of London, Vol. 140, 215–228.

DE LA BECHE, H T. 1829. On the geology of Tor Babbacombe and bays, Devon. Transactions of the Geological Society of London, Vol. 3, 161.

DE LA BECHE, H T. 1839. Report on the geology of Cornwall, Devon and west Somerset. Memoir of the Geological Survey of Great Britain.

DINELY, D L. 1966. The Dartmouth Beds of Bigbury Bay, south Devon. Quarterly Journal of the Geological Society of London, Vol. 141, 279–96.

DRUMMOND, M E. 1982. The geology of Devonian limestones of the Brixham-Dartington area, South Devon. Unpublished PhD Thesis, University of Newcastle.

DURRANCE, E M, and Laming, D J C. 1982. (editors) The geology of Devon. (Exeter: University of Exeter.)

ENVIRONMENT AGENCY, 1998. Policy and Practice for the Protection of Groundwater, Groundwater vulnerability of South Devon, sheet 49

EVANS, C R D. 1990. United Kingdom offshore regional report: geology of the western English Channel and its western approaches. (London: HMSO for British Geological Survey.)

FRANKE, W. 1989. Tectonostratigraphic units in the Variscan belt of central Europe. Geological Society of America, Special Paper, No. 230, 67–90.

GEOMORPHOLOGICAL SERVICES LTD. 1988. Applied Earth Science Mapping for Planning and Development: Torbay, Devon

GODWIN-AUSTEN, R A C. 1842. On the geology of the south-east of Devonshire. Transactions of the Geological Society of London, Series 2, Vol. 6, 433–429.

GOLDRING, R. 1962. The bathyl lull: Upper Devonian and Lower Carboniferous sedimentation in the Variscan geosyncline. 75–98 in Some aspects of the Variscan Fold Belt. Coe, K (editor). (Manchester: University Press.)

GOODE, A J J, and TAYLOR, R T. 1988. Geology of the country around Penzance. Memoir of the British Geological Survey, Sheets 351 and 358 (England and Wales).

GORDON, W T. 1922. Native gold at Torquay, Devonshire. Nature, Vol. 109, 583.

HOLDER, M T, and LEVERIDGE, B E. 1986a. Correlation of the Rhenohercynian Variscides. Journal of the Geological Society of London, Vol. 143, 125–134.

HOLDER, M T, and LEVERIDGE, B E. 1986b. A model for the tectonic evolution of south Cornwall. Journal of the Geological Society of London, Vol. 143, 141–147.

HOUSE, M R. 1963. Devonian ammonoid successions and facies in Devon and Cornwall. Quarterly Journal of the Geological Society of London, Vol. 119, 315–321.

HOUSE, M R. 1964. A new goniatite locality at Babbacombe and its problems. Proceedings of the Ussher Society, Vol. 1, 125–126.

HOUSE, M R, and SELWOOD, E B. 1964. Palaeozoic palaeontology in Devon and Cornwall. 45–86 in Present views of some aspects of the geology of Cornwall and Devon. HOSKING, K F G, and SHRIMPTON, G J (editors). (Truro: Royal Geological Society of Cornwall.)

HOWARD, B. 2000. The Torbay Paint Company. (Dartmouth: History Research Group.)

INSTITUTE OF GEOLOGICAL SCIENCES AND SOUTH WEST WATER. 1982. Hydrogeological Map of the Permo-Trias and other minor aquifers of South West England, 1:100 000

JONES, N S. 1995. Shallow marine sedimentation in the Lower Devonian Meadfoot Group (Bovisand Formation) from the Whitsand Bay area, with sedimentological notes on other Devonian strata examined within the area. British Geological Survey Technical Report, Stratigraphy Series, WH/95/210R.

LAMING, D J C. 1982. The New Red Sandstone. 148–178 in The geology of Devon. DURRANCE, E M, and LAMING, D J C (editors). (Exeter: University of Exeter.)

LEAKE, R C, BLAND, D J, STYLES, M T, and CAMERON, D G. 1991. Internal structure of south Devon Au-Pd-Pt grains in relation to low temperature transport and deposition. Transactions of the Institution of Mining and Metallurgy. Section B (Applied Earth Science), Vol. 100.

LEAKE, R C, BLAND, D J, STYLES, M T, and ROLLIN, K E. 1992. Exploration for gold in the South Hams district. British Geological Survey Technical Report, WF/92/2 (BGS Mineral Reconnaissance Programme Report 121).

LEVERIDGE, B E, HOLDER, M T, and GOODE, A J J. 1990. Geology of the country around Falmouth. Memoir of the British Geological Survey, Sheet 352 (England and Wales).

LEVERIDGE, B E, HOLDER, M T, GOODE, A J J, SCRIVENER, R C, JONES, N S, and MERRIMAN, R J. 2002. Geology of the Plymouth and south-east Cornwall area. Memoir of the British Geological Survey, Sheet 348 (England and Wales).

LLOYD, W. 1933. The geology of the country around Torquay (second edition). Memoir of the Geological Survey of Great Britain, Sheet 350 (England and Wales).

MENNING, M, WEYER, D, DROZDZEWSKI, G, VAN AMEROM, H, and WENDT, I. 2000. A Carboniferous Time Scale 2000: discussion and use of geological parameters as time indicators from central and western Europe. Geologisches Jahrbuch, A 156, 3–44.

MERSCHEDE, M. 1986. A method of discriminating between different types of mid-ocean ridge basalts and continental tholeiites with the Nb-Zr-Y diagram. Chemical Geology, Vol. 56, 207–218.

MERRIMAN, R J, and KEMP, S J. 2001. Metamorphism of the Palaeozoic rocks of the Torquay district, Devon, 1:10 000 Sheet 350. British Geological Survey Internal Report, IR/01/184.

MERRIMAN, R J, EVANS, J A, and LEVERIDGE, B E. 2000. Devonian and Carboniferous volcanic rocks associated with the passive margin sequences of south-west England; some geochemcal perspectives. Proceedings of the Ussher Society, Vol. 10, 77–85.

METEOROLOGICAL OFFICE. 1977. Average Annual rainfall (millimetres), International Standard Period 1941–1970, Southern Britain, 1:625 000

MIDDLETON, G V. 1960. Spilitic rocks in south-east Devonshire. Geological Magazine, Vol. 97, 192–207.

MOTTERSHEAD, D N. 1977. The Quaternary evolution of the south coast of England. 299–320 in The Quaternary History of the Irish Sea. Geological Journal Special Issue, No. 7.

MURCHISON, R I, and De VERNEUILL, E. 1841. On the geological structure of the northern and central regions of Russia in Europe. Proceedings of the Geolocical Society of London, Vol. 3, 398–408.

RANKIN, A H, and CRIDDLE, A J. 1985. Mineralizing fluids and metastable low-temperature inclusion brines at Llanharry iron deposit, South Wales. Transactions of the Institution of Mining and Metallurgy. Section B (Applied Earth Science), Vol. 94, 126–132.

RICHTER, D. 1967. Sedimentology and facies of the Meadfoot Beds (Lower Devonian) in south-east Devon (England). Geologische Rundschau, Vol. 56, 543–561

RICHTER, D. 1969. Structure and metamorphism of the Devonian rocks south of Torquay, south-east Devon (England). Geologische Mitteilungen, Vol. 9, 393.

RUSSELL, A. 1929. On the occurrence of native gold at Hope’s Nose, Torquay, Devonshire. Mineralogical Magazine, Vol. 22, 159–162.

SCRIVENER, R C, COOPER, B V, GEORGE, M C, and SHEPHERD, T J. 1982. Gold-bearing carbonate veins in the Middle Devonian Limestone of Hope’s Nose, Torquay (Abstract). Proceedings of the Ussher Society, Vol. 5, 186–188.

SCRIVENER, R C, DARBYSHIRE, D P F, and SHEPHERD, T J. 1994. Timing and significance of crosscourse mineralization in SW England. Journal of the Geological Society of London, Vol. 151, 587- 590.

SCRUTTON, C T. 1967. Marisastridae (Rugosa) from south-east Devonshire, England. Palaeotology, Vol. 10, 266–79.

SCRUTTON, C T. 1977a. Facies variations in the Devonian lime-stones of eastern South Devon. Geological Magazine, Vol. 114, 165–193.

SCRUTTON, C T. 1977b. Reef facies in the Devonian of eastern south Devon. Memoires, Bureau de Recherches Geologiques et Minieres, Vol. 89, 125–135.

SCRUTTON, C T. 1978. Eastern south Devon. 27–49 in International symposium on the Devonian System (PADS 78). A field guide to selected areas of the Devonian of south-west England. SCRUTTON, C T (editor). (London: Palaeontological Association.)

SEAGO, R D, and CHAPMAN, T J. 1989. The confrontation of structural styles and the evolution of a foreland basin in central southwest England. Journal of the Geological Society of London, Vol. 145, 789–800.

SEDGWICK, A, and MURCHISON, R I. 1839. Classification of the older stratified rocks of Devonshire and Cornwall. Philosophical Magazine, Vol. 14, 241–260.

SELWOOD, E B, EDWARDS, R A, SIMPSON, S, CHESHER, J A, HAMBLIN, R J O, HENSON, M R, RIDDOLLS, B W, and WATERS, R A. 1984. Geology of the country around Newton Abbot. Memoir of the British Geological Survey, Sheet 339 (England and Wales).

SMITH, S A, and HUMPHREYS, B. 1991. Sedimentology and depositional setting of the Dartmouth Group, Bigbury Bay, south Devon. Journal of the Geological Society of London, Vol. 148, 235–244. STANLEY, C J, CRIDDLE, A J, and LLOYD, D. 1990. Precious and base metal selenide mineralization at Hope’s Nose, Torquay, Devon. Mineralogical Magazine, Vol. 54, 483–493.

THOMPSON N, BARRIE I A, AYLES M, 1981. The Meteorological Office Rainfall and Evaporation System: MORECS, Met. Office Hydrological Memorandum No. 45, 72pp

USSHER, W A E. 1890. The Devonian rocks of south Devon. Quarterly Journal of the Geological Society of London, Vol. 46, 487–517.

USSHER, W A E. 1903. The geology of the country around Torquay. Memoir of the Geological Survey of Great Britain, Sheet 350 (England and Wales).

USSHER, W A E. 1907. The geology of the country around Plymouth and Liskeard. Memoir of the Geological Survey of Great Britain, Sheet 348 (England and Wales).

VAN STRAATEN, P, and TUCKER, M E. 1972. The Upper Devonian Saltern Cove goniatite bed as an intraformational slump. Palaeontology, Vol. 15, 430–438.

VACHELL, E T. 1963. The structure of the Torbay region - the Marldon Beacon nappe. Proceedings of the Ussher Society, Vol. 1, 59–60.

WARR, L N, PRIMMER, T J, and ROBINSON, D. 1991. Variscan very low-grade metamorphism in south-west England: a diastothermal and thrust related origin. Journal of Metamorphic Geology, Vol. 9, 751–764

WINCHESTER, J A, and FLOYD, P A. 1977. Geochemical discrimination of different magma series and their differentiation products using immobile elements. Chemical Geology, Vol. 20, 325–343.

Figures, plates and tables

Figures

(Figure 1) Devonian successions in the Torquay district.

(Figure 2) Devonian rift basins and highs in the Torquay district and adjacent areas.

(Figure 3) Classification and tectonic discrimination of Devonian igneous rocks of the Torquay district.

(Figure 4) Diagrammatic sections of the thrust sheets of the Torquay High. a. Devonian limestone platform and reef development separating the northern and southern sub-basins of the South Devon Basin, Late Devonian. b. Inversion and thrust displacement of the successions within the district and adjacent area west of the Sticklepath Fault, late Variscan. Other structures, barring the late fault separating the Torquay High and Southern Sub-basin successions, are omitted.

(Figure 5) Contoured metamorphic map of white mica crystallinity (Kubler) indices for the Torquay district.

Plates

(Plate 1a) Saltern Cove Formation, Saltern Cove [SX 8956 5866]: large limestone clast (3.8 m in length) in matrix-supported breccia bed. Viewed from south (GS1285).

(Plate 1b) London Bridge [SX 923 627] viewed from the south-east. Cliffs in the Daddyhole Member, Torquay Limestone Formation, showing thinly bedded and thicker lenticular bedded facies. Steeply inclined beds about the bridge and cliff base (right) form inverted limbs, and gently inclined beds of the main cliff, the common right way up limb of northward verging F₁ folds. (GS1286).

(Plate 2a) Lower Permian Torbay Breccia Formation resting unconformably on the Lower Devonian Meadfoot Group (undivided) at Goodrington [SX 8954 5873], viewed from south. (GS1287).

(Plate 2b) The Upper Permian Petit Tor Breccia Member (central feature) resting unconformably on the Upper Devonian Saltern Cove Formation (to left of centre) at Petit Tor Beach [SX 9365 6648]. Succeeding Watcombe Formation and Oddicombe Breccia Formation (feature top right) dip gently northwards. Direction of view towards the west-north-west (GS1288).

(Plate 3a) Corbyn’s Head Member of the Torbay Breccia Formation at Corbyn’s Head: purple and green sandstone beds with sporadic granule and pebble intraclasts, showing parallel lamination and low-angle cross-bedding [SX 9075 6322]. Direction of view towards the south-west (GS1289).

(Plate 3b) Torbay Breccia Formation at Goodrington [SX 8957 5878]: thick beds of purple breccia with interbeds of reddish brown sandstone. Clasts, showing imbrication, are largely locally derived limestone. Direction of view towards the west (GS1290).

(Plate 4a) Pleistocene raised-beach at Hope’s Nose [SX 9475 6330]. Direction of view towards the south-west (GS1291).

(Plate 4b) Overturned limb of the northward-verging Man Sands Antiform, Southdown Cliff [SX 9285 5410] viewed from the east. Sandstone facies of the Bovisand Formation defines these mesoscopic folds (GS1292).

(Plate 5a) Gently inclined northward-verging tight D₁ fold couplet refolded by steeply inclined D₂ folds in limestone of the Berry Head Member, Brixham Limestone Formation, cliff south of Berry Head [SX 9423 5615] (GS1293).

(Plate 5b) Overturned anticlinal F₁ fold verging north-westwards displaced along low-angle thrust at Hope’s Nose [SX 9471 6332] (GS1294).

(Plate 6a) Major north-south fault zone near Crystal Cove [SX 896 580], view from the south. Middle Devonian Goodrington Limestone Member of the Brixham Limestone Formation (left) separated from the reddish brown sandstone of the Torbay Breccia Formation (right) by some 25 m of crystalline calcium carbonate occupying the fault zone (GS1295).

(Plate 6b) Dendritic native palladian gold from a carbonate vein in Middle Devonian limestone at Hope’s Nose Torquay. The delicate gold crystals have been exposed from the calcite host by etching with dilute mineral acid. Specimen is 15 mm in length and is in the collection of Torquay Natural History Society. (Photograph J S Jones) (GS1296).

(Back cover)

Tables

(Table 1) Geological succession of the Torquay district.

(Table 2) Biostratigraphy of the limestones of the district. 1 Current at time of determination; 2 Based on M E Drummond (1982); 3 Based on C Castle (1982); 4 Based on Selwood et al. (1984). NB. Stage attribution amended further due to the revision of the Givetian/Frasnian boundary by the International Commission on Stratigraphy in 1985. ≡ calcareous mudstone; Br Breccia; ls limestone; LSB Laminated Shell Beds; vv tuff

(Table 3) Licensed groundwater abstractions for the Torquay district (in Ml/a).

(Table 4) Chemical analyses of water from the Torquay district.

Tables

(Table 3) Licensed groundwater abstractions for the Torquay district (in Ml/a).

	Statutory water undertaking	Private water supply	Agriculture (excluding spray irrigation)	Spray irrigation	Industry	Total
Drift	6068.4 (2)	434.1 (4)	54.7 (12)	6.8 (1)		6564.0 (19)
Exeter Group (breccias and conglomerates)		3.7 (2)	11.9(2)	9.0 (1)		24.6 (5)
Exeter Group (Watcombe Formation)			0.2 (1)	4.3 (1)		4.5 (2)
Devonian limestones		0.2 (1)	31.7 (11)		150.0 (3)	182.0 (15)
Norden Formation		8.1 (4)	106.1 (59)		0.5 (1)	114.7 (64)
Meadfoot and Dartmouth Groups		16.8 (10)	110.7 (48)	4.5 (1)		132.0 (59)
Tuffs and lavas		2.1 (5)	138.4 (24)		0.2 (2)	140.7 (31)
Total	6068.4 (2)	465.1 (26)	453.6 (157)	24.6 (4)	150.8 (6)	7162.4 (195)

Geology of the Torquay district. Sheet description of the British Geological Survey 1:50 000 Series Sheet 350 Torquay (England and Wales)

British Geological Survey

Acknowledgements

Notes

Geology of the Torquay district—summary

Chapter 1 Introduction

Chapter 2 Devonian

Looe Basin Succession

Dartmouth Group (Dm)

Meadfoot Group (Mdt)

Tamar Group

Brixham High Succession

Tamar Group

Coastal section

Inland

Meadfoot Group (Mdt)

South Devon Basin Succession (southern sub-basin)

Dartington area

Washbourne area

Goodrington area

Torquay High Succession

Torquay area

Meadfoot Group

Tamar Group

Ipplepen area

Tamar Group

South Devon Basin Succession (northern sub-basin)

Torquay

Ipplepen

Chapter 3 Permian

Torbay Breccia Formation (TB)

Watcombe Formation (Wat)

Oddicombe Breccia Formation (OBr)

Chapter 4 Cainozoic

Cave deposits

Raised-beach deposits

Head

Buried channels

Fluvial deposits

Estuarine deposits

Marine deposits

Undifferentiated alluvium

Offshore deposits

Landslip

Artificial deposits

Chapter 5 Igneous rocks

Lower Devonian

Middle and Upper Devonian

Chapter 6 Structural geology and metamorphism

Variscan structures

D1 deformation

S1 cleavage

F1 folds

NW-SE strike-slip faults

NE-SW faults

D2 deformation

S2 cleavage

F2 folds

D1 and D2 thrust faults

D3 deformation

Late Variscan and post-Variscan structures

Metamorphism

Tectonic geology

Chapter 7 Mineralisation

Metallogenesis

Chapter 8 Applied geology

Building stone

Roadstone and aggregate

Brick making material

Aquifer vulnerability and pollution

River terrace deposits

Other superficial deposits

Exeter Group (Permian)

Devonian

Igneous rocks

Vulnerability to pollution

Foundation conditions

Landslip

Information sources

Maps

D₁ deformation

S₁ cleavage

F₁ folds

D₂ deformation

S₂ cleavage

F₂ folds

D₁ and D₂ thrust faults

D₃ deformation