The BGS Lexicon of Named Rock Units — Result Details

Saltash Formation

Computer Code: SAH Preferred Map Code: Slt
Status Code: Full
Age range: Emsian Age (DE) — Tournaisian Stage (CT)
Lithological Description: Dark grey and grey silty mudstone with variable but very subordinate amounts of laminae and thin beds of siltstone and sandstone. Bioturbation is locally present, especially in the lower part. There are scattered units of thin- to thick-bedded limestone (eg: Marble Cliff Limestone Member), thin- to thick-bedded sandstone (eg: Wearde Sandstone Member), basaltic lava (spilite), massive and bedded hyaloclastite, and bedded tuff (eg: St Germans Tuff Member).
Definition of Lower Boundary: The lower boundary is mainly thrust out in the east where it is assumed to overlie the Staddon Formation. In the west, on the north Cornish coast, it is taken at the incoming of dark and pale grey mudstones with scattered thin sandstones of the Saltash Formation above the sandstones and siltstones with subordinate mudstones of the underlying Bedruthan Formation.
Definition of Upper Boundary: The upper boundary is predominantly tectonic, except in the east in the Tamar valley, where it is taken at the incoming of dark grey cherts and siliceous mudstones of the Winstow Chert Formation above the mid grey silty mudstones of the Saltash Formation.
Thickness: 3900m on the north Cornwall coast. Comparable thicknesses are expected elsewhere.
Geographical Limits: From Trevose Head area (SW 86 76), north Cornwall to Torquay area (SX 93 65), south Devon.
Parent Unit: Tamar Group (TAMA)
Previous Name(s): Nordon Formation (NOSL)
Jennycliff Slates [Obsolete Name And Code: Use SAH] (JCS)
Plympton Slate Formation (In Part) (-4311)
Upper Devonian Slate (-4312)
Jennycliff Slate Formation (-3656)
Tempellow, Rosenum And Mileport Slate Formation (-1158)
Trevose Slate (-1159)
Trevose Slate Formation (TVS)
Nordon Slate (-2406)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Type Section  Cliff section. Mountbatten to Jennycliff Bay. 
Partial Type Section  River cliff on west bank of River Tamar, 380m southwest of the Tamar Bridge, at Saltash, east Cornwall. The section exposes folded silt-laminated grey mudstones, locally bioturbated, with scattered thin beds of sandstone and laminae of limestone. Units of basaltic lava and hyaloclastite are present as well as high-level basaltic intrusions. Neither the lower nor upper contacts of the Formation are exposed. 
Partial Type Section  River cliff section. Saltmill Creek to Sand Acre Bay. 
Reference(s):
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 countryside around Newton Abbot. Memoir of the British Geological Survey, Sheet 339 (England and Wales). 
Burton, C J and Tanner, P W G, 1986. The stratigraphy and structure of the Devonian rocks around Liskeard, east Cornwall, with regional implications. Journal of the Geological Society, London, Vol.143, 95-105. 
Hobson, D M. 1976. The structure of the Dartmouth antiform. Proceedings of the Ussher Society, Vol.3, 320-323. 
Pound, C J, 1983. The sedimentology of the Lower-Middle Devonian Staddon Grits and Jennycliff Slates on the eastern side of Plymouth Sound, Devon. Proceedings of the Ussher Society, Vol.5, 465-472. 
Chandler, P and McCall, G J H, 1985. Stratigraphy and structure of the Plymouth-Plymstock area: a preliminary revision. Proceedings of the Ussher Society, Vol.6, 253-257. 
Leveridge, B E, Scrivener, R C, Goode, A J J and Merriman, R J. 2003. Geology of the Torquay district - a brief explanation of the geological map. Sheet explanation of the British Geological Survey. 1:50 000 Sheet 350 Torquay (England and Wales). 
House, M R, Richardson, J B, Chaloner, W G, Allen, J R L, Holland, C H and Westoll, T S. 1977. A Correlation of Devonian rocks of the British Isles. Geological Society of London, Special Report No.8, Scottish Academic Press, Edinburgh. 
Burton, C J. 1974. A progress report on geological investigations in the Liskeard area of south-east Cornwall (abstract). Proceedings of the Ussher Society, Vol.3, 44-48. 
Kirchgasser, W T, 1970. Conodonts from near the middle/upper Devonian boundary in north Cornwall. Palaeontology, Vol.13, 335-354. 
Selwood, E B, Thomas, J M, Williams, B J, Clayton, R, Durning, B, Smith, O and Warr, L N, 1998. Geology of the country around Trevose Head and Camelford. Memoir of the British Geological Survey, sheets 335 and 336 (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). 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
E348