Pebidian Supergroup

The Pebidian Supergroup is an Ediacaran (i.e. late Precambrian) lithostratigraphic supergroup (a sequence of rock strata) in Pembrokeshire, west Wales. The term 'Pebidian' (along with Dimetian) was coined by geologist Henry Hicks in 1876 and published in a scientific paper in the Quarterly Journal of the Geological Society in the following year. It was named for Pebidiauc, an ancient local name for the St Davids area.[1]

Pebidian Supergroup
Stratigraphic range: Ediacaran
TypeSupergroup
Sub-unitsTreginnis, Treglemais & Penrhiw 'Groups', Caerbwdy Group, Ramsey Sound Group, Rhosson Group, Ogofgolchfa Group
Lithology
Primarytuffs
Othertrachytes, lavas, conglomerates
Location
Regionwest Wales
CountryWales
Type section
Named forPebidiauc
Named byHenry Hicks (geologist)

Outcrops

These rocks are exposed in the St David's peninsula in northwestern Pembrokeshire. One outcrop stretches east from Treginnis, wrapping around the north of St David's to Treglemais. Another underlies Hayscastle Cross with scattered outcrops elsewhere in the area.

Lithology and stratigraphy

The supergroup comprises at its base the Treginnis, Treglemais and Penrhiw 'Groups' of the Lower Pebidian which include trachytic and andesitic tuffs and halleflinta. Overlying these are the tuffs, lavas and conglomerates of the Caerbwdy Group, Ramsey Sound Group and the Rhosson Group. Uppermost i.e. youngest is the Ogofgolchfa Group which includes slates and tuffs. This whole assemblage has also been referred to as the Pebidian Volcanic Complex or Pebidian Volcanic Series.[2][3]

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References
  1. Sissingh, W. 2012 Rocky Roads from Firenze: History of Geological Time and Change 1650-1900 Utrecht Studies in Earth Sciences 020 ISSN 2211-4335 Utrecht University Chapter 9 Main sequences of rocks p533 The ISBN printed in the document (978-6266-305-7) is invalid due to an incorrect number of digits. retrieved 9 Oct 2013 from http://igitur-archive.library.uu.nl/geo/2012-1003-200424/Rocky-roads-Sissingh_USES-20120814-part%20III.pdf
  2. British Geological Survey 1:50,000 scale geological map sheets (England and Wales series) 209 St David's and 210 Fishguard.
  3. http://www.bgs.ac.uk/Lexicon/lexicon.cfm?pub=PN (BGS on-line lexicon of rock units)
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