The BGS Lexicon of Named Rock Units — Result Details

Treffynnon Group

Computer Code: TRF Preferred Map Code: Trf
Status Code: Pending Upgrade
Age range: Ediacaran Period (AD) — Comley Series (EC)
Lithological Description: Felsic pyroclastic and extrusive rocks interbedded with shallow water sediments. Lithologies comprise volcanastic breccias, crystal tuffs, porphyritic rhyolitic lavas and thinly interbedded quartzose sandstones, tuffs, lapillistone and mudstone.
Definition of Lower Boundary: Not defined - contacts mostly faulted.
Definition of Upper Boundary: Unknown - unconformably overlain by mudstones and sandstones of the Solva Group (Cambrian)
Thickness: Unknown - at least 15m proved in boreholes around Llandeloy.
Geographical Limits: Pembrokeshire.
Parent Unit: Not Applicable (-)
Previous Name(s): none recorded or not applicable
Alternative Name(s): none recorded or not applicable
Stratotypes:
Reference Section  Quarries in village of Treffynnon. Williams, T G. 1934. 
Type Area  Around Treffynnon, near St. David's, Pembrokeshire, South Wales. 
Reference(s):
Williams, T G. 1934. The Precambrian and Lower Palaeozoic rocks of the eastern end of St David's Precambrian area Pembrokeshire. Quarterly Journal of the Geological Society, London, Vol.90, 32-75. 
Allen, P M and others. 1985. Exploration for porphyry-style copper mineralisation near Llandeloy, southwest Dyfed. Mineral Reconnaissance Programme Report No 78, British Geological Survey, Keyworth, Nottingham, 99pp. 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
E209