The BGS Lexicon of Named Rock Units — Result Details

Torpoint Formation

Computer Code: TPT Preferred Map Code: Tpt
Status Code: Full
Age range: Frasnian Age (DR) — Famennian Age (DA)
Lithological Description: Brownish purple to purplish red cleaved mudstone and fine-grained siltstone, yellowish to blue-green, fine- to coarse-grained siltstone and fine-grained sandstone. Colour mottling and transposition of colour by fluids may occur near faults. Green reduction spots are sporadically formed.
Definition of Lower Boundary: Not seen.
Definition of Upper Boundary: In the Tavy Basin: A transition from the purplish red slaty mudstone of the Torpoint Formation into the greenish grey slaty mudstone of the Tavy Formation. Also interdigitates with the Saltash Formation in the South Devon Basin.
Thickness: Not known.
Geographical Limits: The Torpoint Formation dies out in the Liskeard area on the west side of the Plymouth 348 Sheet but continues eastward onto the Ivybridge (349) Sheet.
Parent Unit: Tamar Group (TAMA)
Previous Name(s): Plympton Slate Formation (-3090)
Purple And Green Slates (-1874)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Type Section  Cliff section. Torpoint Ferry to north side of Yonderberry Point. 
Reference(s):
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). 
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). 
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. 
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. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
E348 E349