Geologic group in Ireland
TheRibband Group is ageologic group in south-easternIreland. It is the most extensivestratigraphic unit in this part of Ireland. It underlies much ofCounty Wexford. It overlies the Bray Group and Cahore Group. It is made up of medium to dark grey laminatedgreywackesiltstones andmudstones with occasional greenbeds.[1]Turbidite structures are locally prominent and the unit is dominantly adistal turbidite succession.Intercalatedvolcanic rocks are locally abundant. The ages of the rocks of the group range from the Cambrian[2] to the Ordovician,[3] MiddleCambrian-Llanvirn (Middle Ordovician).[4]
The Ribband group is one of the four EarlyPalaeozoic stratigraphic groups in SE Ireland. The others are: theBray group (made up of laterally-derivedflysch) which is conformably overlain by the Ribband Group; theDuncannon Group (a highly faulted, predominantly volcanic, platform sequence) whichunconformably overlies the Ribband Group except in the west; theKilcullen Group in theComeragh Mountains, which is composed of sand-dominant turbidites (lower Ordovician to at least theLlandovery Epoch of theSilurian) which areconformably underlain by the Ribband and Duncannon Groups. Thesediments of the Ribband group pass upward into the Kilcullen Group turbidites. This reflects a continuous period of flyschsedimentation.[4]
Although most of the Group is unfossiliferous (without fossils), locally sparsegraptolite faunas andacritarchs have been found. Their dating range from theDrumian stage of the Cambrian to the Early-Mid Ordovician.[5][6]
Geological formations related to the Ribband Group
[edit]The following is a classification by Brück & Molyneux (2011).
- TheAskingarran Formation forms a continuation of the Ribband Group which overlies it. Its top isfaulted against theTremadocian Ballyhoge Formation of the Ribband group. It is made up of black and grey laminatedsiltstones andmudstones with occasional greenbeds and common internal and external turbidite structures. It correlates with the Booley Bay Formation at Booley Bay and Clammers Point. These two formations comprise the oldest strata assigned to the Ribband Group.
- The Polldarrig Formation of the Cullenstown Group (which stretches north-eastwards fromCullenstown Strand toWexford town) is made up of grey and green, fine grained, laminatedgreywackes andshales and is the local equivalent of the Booley Bay Formation.
- TheBooley Bay Formation comprises much of the northern part ofHook Head (south County Wexford) and extends west ofWaterford Harbour (County Waterford).
- Thelithologies of theCahore Group are indistinguishable from those of the Booley Bay Formation. The group passes up northwards into the Ribband Group and the boundary between them is faulted. Unlike the Ribband Group, which extends into the Ordovician, it is entirely Cambrian.
- TheMaulin Formation (CountiesWicklow andCarlow) stretches 100 km southwards fromDublin Bay toCounty Carlow. It is made up of Ribband Group lithologies and includes dark greyphyllites, slates and thin greyquartzites. It is 900m thick in northern County Wicklow.
The BallymadderShear Zone (just east ofHook Head on the coast of southCounty Wexford), separates a to some extent different Cambrian succession immediately to the east to the one to its west. To its west the Clammers Point Unit (in theBannow area) exposes a coastal section comprising Cahore Group and Ribband Group sediments.
- ^Brück & Vanguestaine (2004)
- ^Brück & Molyneux (2011)
- ^Harper & Parkes (2000)
- ^abBrück et al. (1979)
- ^Vanguestaine & Brück (2008)
- ^Cocks et al. (2010)
- Various Contributors to the Paleobiology Database."Fossilworks: Gateway to the Paleobiology Database". Retrieved17 December 2021.
- Brück P.M., Gardiner P.R.R, T. J. Reeves T.J., Shannon P.M., Colthurst J.R.J., Feely M., Penney S.R., Smith D. G., and M. Vanguestaine M., 1979, South-east Ireland: Lower Palaeozoic stratigraphy and depositional history, Geological Society, London, Special Publications, Vol. 8, pp., 533-544[1]
- Brück P. M., Vanguestaine M., 2004, Acritarchs from the Lower Palaeozoic succession on the south County Wexford coast, Ireland: new age constraints for the Cullenstown Formation and the Cahore and Ribband Groups. Geological Journal, Vol. 39, pp. 199–224[2]
- Brück, P.M., Molyneux, S.G., 2011, Cambrian of Ireland, chapter 12 in: Rushton, A.W.A., Brück, P.M., Molyneux, S.G., Williams, M. & Woodcock, N.H., A Revised Correlation of the Cambrian Rocks in the British Isles, Geological Society, London, Special Report, 25, pp. 42–52.[3]
- Cocks, L.R.M., Fortey, R.A., Rushton, A.W.A. 2010. Correlation for the Lower Palaeozoic. Geological Magazine, Vol. 147, pp. 171–180.[4]
- Harper, D.A.T., Parkes, M.A. 2000. Chapter on Ireland in: A revised correlation of Ordovician Rocks in the British Isles. Geological Society of London Special Report, No 24, pp. 52–68.[5]
- McConnell B.J., Morris J.H., Kennan P.S., 1999, A comparison of the Ribband Group (south-eastern Ireland) to the Manx Group (Isle of Man) and Skiddaw Group (north-western England) in: Woodcock, N.H., Quirk, D.G., Fitches, W.R. BARNES, R.P. (eds) In Sight of the Suture: the Palaeozoic Geology of the Isle of Man in its Iapetus Ocean context, Geological Society, London, Special Publications, Vol. 160, pp. 337–343
- McIlroy D., Additional Ichnotaxa from the Flysch-Type Deposits of the Arenig Ribband Group, Co. Wexford, Ireland, 1999, Irish Journal of Earth Sciences, Vol. 17, pp. 103–113https://www.jstor.org/stable/30002288
- Rushton, A.W.A., Brück, P.M., Molyneux, S.G., Williams, M., Woodcock, N.H., 2011, A Revised Correlation of the Cambrian Rocks in the British Isles. Geological Society, London, Special Report Vol. 25, pp. 42–52.[6]
- Vanguestaine M., Brück P.M., (2008), A Middle and Late Cambrian age for the Booley Bay Formation, County Wexford, Ireland: New acritarch data and its implications. Revue de Micropalaeontologie, Vol.51, pp. 67–95[7]
Ireland
