Aberystwyth Grits Group

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Aberystwyth Grits Group
Stratigraphic range: Llandovery Silurian
Wave-cut platform below Allt Wen - geograph.org.uk - 1751689.jpg
Turbidite sandstones and interbedded mudstones of the Aberystwyth Grits Group exposed on the foreshore below Allt Wen, near Aberystwyth
Type Group
Sub-units Trefechan Formation, Mynydd Bach Formation
Overlies Borth Mudstones Formation
Primary turbidite mudstones
Other sandstones
Region mid Wales
Country Wales
Type section
Named for Aberystwyth

The Aberystwyth Grits Group is a Silurian lithostratigraphic group (a sequence of rock strata) in mid Wales. The name is derived from Aberystwyth in northern Ceredigion where the strata are well exposed in coastal cliffs. The Group comprises the Trefechan Formation and the underlying Mynydd Bach Formation. The rocks of the Aberystwyth Grits Group have also previously been known as the Aberystwyth Grits Formation[1]


These rocks are exposed, along the Cardigan Bay coast both to the east and west of New Quay and northwards through Aberaeron and Aberystwyth to just short of Borth. They extend eastwards, though are usually obscured, in a belt of country between roughly 5 km and 10 km wide reaching from the coast. Much of the eastern boundary is defined by the Bronnant Fault.[2]

Lithology and stratigraphy[edit]

The Group comprises several hundred metres thickness of mudstone and sandstone turbidites laid down in the marine Welsh Basin during the Llandovery epoch of the Silurian period. Palaeocurrents indicating a source in the southwest have been recorded from throughout the group.[3]


  1. ^ "Aberystwyth Grits Group". The BGS Lexicon of Named Rock Units. British Geological Survey. Retrieved May 9, 2013. 
  2. ^ British Geological Survey 1:50,000 scale geological map (England & Wales) sheets 163, 177, 178, 194, 195
  3. ^ Howells, M.F. (2007). British regional geology : Wales (1st ed.). Nottingham: British Geological Survey. ISBN 978-085272584-9. [page needed]
  • London, P.F. Rawson. The Geological Society (2006). Brenchley, P.J., ed. The geology of England and Wales. (2. ed.). London: Geological Society Publishing. pp. 83, 89–90. ISBN 9781862392007.