The BGS Lexicon of Named Rock Units — Result Details

Posidonia Beds

Computer Code: POS Preferred Map Code: notEntered
Status Code: Index Level
Age range: Visean Stage (CV) — Visean Stage (CV)
Lithological Description: At the top of the Teign Chert, shales containing Posidonia becheri are overlain by interbedded shales, cherts and thin limestones. A band with spirally striate goniatites is present above the beds containing Posidonia.
Definition of Lower Boundary: Boundary with main part of Teign Chert taken at level where well-bedded cherts become predominant.
Definition of Upper Boundary: Conformably succeeded by the Ashton Shale (basal member of the Crackington Formation). The boundary is reflected in the topography, with the Teign Chert (including the Posidonia Beds) forming prominent features.
Thickness: 30-45 metres.
Geographical Limits: Middle Teign Valley, Devon.
Parent Unit: Teign Chert Formation (TCH)
Previous Name(s): Spara Bridge Formation (-1764)
Alternative Name(s): none recorded or not applicable
Type Section  Road section west of Lower Ashton, Devon. Detailed section (in cherts with subordinate siliceous shales, with tuffs and scarce limestone). Given in Selwood, et al, 1984, p 69. 
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). 
Chesher, J A, 1968. The succession and structure of the Middle Teign Valley. Proceedings of the Ussher Society, Vol.2, 15-17. 
1:50K maps on which the lithostratigraphical unit is found, and map code used: