The BGS Lexicon of Named Rock Units — Result Details

Abergwilli Formation

Computer Code: ABGW Preferred Map Code: notEntered
Status Code: Full
Age range: Llanvirn Series (OE) — Llanvirn Series (OE)
Lithological Description: The Abergwilli Formation comprises interbedded, dark grey, micaceous burrow-mottled mudstone and laminated graptolitic mudstone with scattered thin sandstone beds and tuffs.
Definition of Lower Boundary: Base not seen during the current phase of survey but was previously taken at the first occurrence of "tuning fork" graptolites. (Strahan et al. 1909).
Definition of Upper Boundary: Upper boundary not seen during the current phase of survey but was previously taken at the base of the Didymograptus murchisoni bearing mudstones (now Felin Wen Formation) observed in a road bank opposite the corn mill in the village of Felin Wen (Strahan et al. 1909).
Thickness: Approximately 680m
Geographical Limits: The Abergwilli Formation is restricted in occurrence to an elogate belt along the southwestern margin of the Lower Palaeozoic Welsh Basin extending from aound Llandeilo in the east to Crosshands in the west. Possible correlatives, ascribed to the Didymograptus bifidus beds crop out farther south in the ground between St Clears and Whitland.
Parent Unit: Not Available (!)
Previous Name(s): Didymograptus Bifidus Beds (DBB)
Alternative Name(s): none recorded or not applicable
Reference Section  Road cutting adjacent to the A485 approximately 1.5km north of Abergwilli. The unit is named after the town of Abergwilli where sections of the Formation were described by Strahan et al. (1909). At present the best Reference Section seen through the Formation is exposed at SN2434 2225. 
Strahan, A, Cantrill, T C, Dixon, E E L and Thomas, H H. 1909. The Geology of the South Wales coalfield. Part 10. The country around Carmarthen. Memoir of the Geological Survey of England and Wales. [London: HMSO.] 
1:50K maps on which the lithostratigraphical unit is found, and map code used:
none recorded or not applicable