Bardahessiagh Formation Explained

Bardahessiagh Formation
Type:	Formation
Age:	Ordovician
Region:	Northern Ireland
Country:	United Kingdom

The Bardahessiagh Formation is a geologic formation in Northern Ireland. It has been described from a locality lying about 3 km NNE of Pomeroy, south of Craigbardahessiagh. It is now known as comprising the former ‘Bardahessiagh Formation’,^[1] or Bardahessiagh Beds and the ‘Junction Beds’ that is underlain by a stratigraphical unit not recognised, until fieldwork by the Ulster Museum staff in 1992. The Bardahessiagh Formation is divided into three units, but the summit of the formation is not known. Field evidence indicates that the local top of the formation is characterised by a thrust contact with the Killey Bridge and Tirnaskea Formation (upper Katian and Hirnantian, respectively), exposed south of the Well Field, which lies 650 metres SSW of Craigbardahessiagh.

Constraints on the age of the formation is based on the brachiopod faunas and an upper Sandbian to lower Katian age has been proposed.^[2]

The Bardahessiagh Formation preserves a diverse and well-preserved assemblage of fossils. Only the brachiopods,^{[3] [4]} cephalopods,^[5] bivalves^[6] and kilbuchophyllid corals^[7] have been systematically described.

Based on the brachiopod faunas, the Bardahessiagh Formation has been interpreted as deposited in a transgressive regime, below storm-wave base environments, peaking in the second unit, with the presence of typical Sericoidea association (Candela 2001, 2006).

The integrity of the formation is currently endangered by excavation by locals using trenchers to dig irrigation ditches.

See also

• List of fossiliferous stratigraphic units in Northern Ireland

References

• Web site: Fossilworks: Gateway to the Paleobiology Database. ((Various Contributors to the Paleobiology Database)). 17 December 2021.

Notes and References

1. Mitchell, W. I. 1977. The Ordovician Brachiopoda from Pomeroy, Co. Tyrone. Monograph of the Palaeontological Society, London. (Publ. No. 545, part of vol. 130, for 1976).
2. Candela, Y. 2002. Constraints on the age of the Bardahessiagh Formation, Pomeroy, Co. Tyrone. Scottish Journal of Geology 38, 65–7.
3. Mitchell, W. I. 1977. The Ordovician Brachiopoda from Pomeroy, Co. Tyrone. Monograph of the Palaeontological Society, London. (Publ. No. 545, part of vol. 130, for 1976).
4. Candela, Y. 2003. Late Ordovician brachiopods from the Bardahessiagh Formation of Pomeroy, Ireland. Monograph of the Palaeontological Society, London. (Publ. No. 618, part of vol. 156, for 2002).
5. Evans, D. H. 1994. The Cephalopod fauna of the Bardahessiagh Formation (Caradoc Series) of Pomeroy, County Tyrone. Irish Journal of Earth Science, 13, 11–29.
6. Tunnicliff, S. P. 1982. A revision of Late Ordovician bivalves from Pomeroy, Co. Tyrone, Ireland. Palaeontology 25, 43–88.
7. Scrutton, C. T., Jeram, A. J. & Armstrong, H. A. 1998. Kilbuchophylliid corals from the Ordovician (Caradoc) of Pomeroy, Co. Tyrone: implications for coral phylogeny and for movement on the Southern Uplands Fault. Transactions of the Royal Society of Edinburgh: Earth Sciences 88 (for 1997), 117–26.