The BGS Lexicon of Named Rock Units — Result Details

Meldon Shale and Quartzite Formation

Computer Code: MQF Preferred Map Code: notEntered
Status Code: Full
Age range: Tournaisian Stage (CT) — Visean Stage (CV)
Lithological Description: Much of the outcrop occurs in the metamorphic aureole of the Dartmoor Granite with dark brown hornfelsed mudstone. The Formation comprises black shaly mudstones with variably abundant (locally exceeding 50%) thin beds (up to 15cm) and laminae of white and reddish brown quartzite. Radiolaria are abundant in the quartzites in the upper part of the Formation. A 26 to 61m-thick unit of thin-bedded to massive, locally cross bedded "keratophyric" tuffs and agglomerates is present in the upper part of the Formation.
Definition of Lower Boundary: The lower boundary is taken at the incoming of black mudstones with abundant thin beds and laminae of quartzite above the dark brown hornfelsed mudstones with scattered thin beds and lenses of pale green feldspathic siltstone of the underlying Meldon-Slate-with-Lenticles Formation. The Meldon-Slate-with-Lenticles Formation exhibits early ?D1 isoclines deformed by later more open D2 structures. As the Meldon Shale and Quartzite Formation exhibits only open folds, it is possible that the boundary between the two formations is a thrust. Further investigation is needed.
Definition of Upper Boundary: The upper boundary is taken at the incoming of internally structureless black argillaceous limestone beds, with subordinate black cherts and siliceous mudstones and mudstones of the overlying Teign Chert Formation above the thin-bedded mudstones and quartzites of the Meldon Shale and Quartzite Formation.
Thickness: 126 to 161m
Geographical Limits: Mainly limited to the Meldon Anticline of the Okehampton area (SX 59 94), central Devon. Mapped as far west as Launceston (SX 33 84) in thrust slices (BGS 1993) but the status of this crop needs further investigation.
Parent Unit: Teign Valley Group (TEVY)
Previous Name(s): Volcanic Group (-2327)
Upper Shale And Quartzite Group (-2945)
Lower Shale And Quartzite Group (-3562)
Lower Culm Measures (-77)
Alternative Name(s): none recorded or not applicable
Stratotypes:
Partial Type Section  Meldon Quarry, 2km southwest of Okehampton, central Devon. The Formation is exposed in several folds in the core of the Meldon Anticline. As the quarry is active, faces will vary with time. The entire sequence is usually exposed. The junction with the underlying Meldon Slate-with-Lenticles Formation is faulted but that with the overlying Teign Chert is exposed. Dearman, 1959. 
Reference(s):
Ussher, W A E. 1887. The Culm of Devonshire. Geological Magazine, Vol.24, 10-17. 
Dearman, W R. 1959. The structure of the Culm Measures at Meldon, near Okehampton, north Devon. Quarterly Journal of the Geological Society of London, Vol.115, 65-106. 
Edmonds, E A, Wright, J E, Beer, K E, Hawkes, J R, Fenning, P J, Freshney, E C, Lovelock, P E R, McKeown, M C, Ramsbottom, W H C and Williams, M. 1968. Geology of the country around Okehampton. Memoir of the Geological Survey of Great Britain, Sheet 324 (England and Wales). 
Selwood, E B. 1971. Successions at the Devonian-Carboniferous boundary between Boscastle and Dartmoor. Proceedings of the Ussher Society, Vol.2, 275-285. 
Ussher, W A E. 1882. The British Culm Measures. Proceedings of the Somerset Archeological and Natural History Society, Vol.38, 111-219. 
British Geological Survey, 1993. Tavistock. England and Wales Sheet 337. Solid and Drift 1:50 000 Provisional Series (Keyworth, Nottingham: British Geological Survey). 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
E323