The BGS Lexicon of Named Rock Units — Result Details
Craig Y Llam Formation
Computer Code: | CYLF | Preferred Map Code: | notEntered |
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Status Code: | Pending Upgrade | ||
Age range: | Caradoc Series (O4) — Caradoc Series (O4) | ||
Lithological Description: | Massive, ash-flow tuffs, locally lapilli-rich, with subordinate rhyolites, mudstone debris flows and tuffaceous sediments. | ||
Definition of Lower Boundary: | A well exposed transition from disturbed or bedded mustones of the Tyr Gawen Formation to massive, locally nodular ash-flow tuffs. Contact disrupted in places by loading and fluidisation of underlying mudstone. | ||
Definition of Upper Boundary: | Well exposed. Transition from massive tuff, rhyolite or tuffaceous siltstones into mudstone. Contact placed where mudstone becomes dominant. | ||
Thickness: | 0-300m | ||
Geographical Limits: | Extends westwards from Cadair Idris as far as Ffridd Cocyn (6250 0450) where it dies out. | ||
Parent Unit: | Aran Volcanic Group (AVG) | ||
Previous Name(s): | Craig-Y-Llam Group [Obsolete Name And Code: See CYLF]
(CYLL)
Upper Acid Volcanic Group [Obsolete Name And Code: See CYLF] (UAV) Upper Acid Group [Obsolete Name and Code: Use CYLF] (-1470) Craig Y Llam Group [Obsolete Name and Code: Use CYLF] (-3344) |
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Alternative Name(s): | none recorded or not applicable | ||
Stratotypes: | |||
none recorded or not applicable | |||
Reference(s): | |||
Cox, A H. 1925. The geology of the Cadair Idris Range, (Merioneth). Quarterly Journal of the Geological Society of London, Vol. 81, 539-592. | |||
Cox, A H, and Wells, A K. 1921. The Lower Palaeozoic rocks of the Arthog-Dolgellau district (Merionethshire). Quarterly Journal of the Geological Society, London, Vol. 76, p. 254-324. | |||
Ridgeway, J. 1975. The stratigraphy of Ordovician volcanic rocks around the south and east of the Harlech Dome in Merionethshire, North Wales. Geological Journal, Vol.10, 87-106. | |||
1:50K maps on which the lithostratigraphical unit is found, and map code used: | |||
none recorded or not applicable |