Tyrone Group
Tyrone Group | |
---|---|
Asbian – Carboniferous) | |
Type | Group |
Unit of | Carboniferous Limestone Supergroup |
Sub-units | Dartry Limestone, Glencar Limestone, Benbulben Shale, Mullaghmore Sandstone, Bundoran Shale, Ballyshannon Limestone, Clogher Valley and Ballyness formations |
Underlies | Leitrim Group |
Overlies | Fintona Group |
Thickness | ~2400m |
Lithology | |
Primary | limestones |
Other | sandstone, conglomerates, mudstone, shale |
Location | |
Country | Northern Ireland |
Extent | County Fermanagh, County Tyrone |
Type section | |
Named for | County Tyrone |
The Tyrone Group is a
Constituent geological formations
In stratigraphic order (youngest/uppermost at top), its constituent
Dartry Limestone Formation
Traditionally known as the Upper Limestone, the
- Carn Limestone
- Cloghany Limestone (a bioclastic crinoidal grainstone between 0.5 and 1.25m thick)[5]
- Carrickmacsparrow Limestone (a crinoidal
- Cloghan Hill Limestone (30-50m thick, mud mounds amidst shales, silts and limestones, includes bioherms)[7]
- Knockmore Limestone (between 0-290m thick, lenticular mounds of grey micrites)[8]
In the Irish Republic, this rock sequence is known as the Bricklieve Limestone Formation.
Glencar Limestone Formation
Benbulben Shale Formation
Known previously as the lower part of the Middle or Calp Limestone and of the Upper Calp Shale, this 60-120m thickness of mudstones with fossil-rich grey limestones and thin calciturbidites and sandstones make up the formation.
Mullaghmore Sandstone Formation
Variously known in the past as the Middle or Calp Sandstone, Upper Calp (Macnean) Sandstone and Clonelly Sandstone Group, about 200m thickness of brown to grey sandstones interbedded with mudstones and siltstones make up this formation.[11] A thin band extends southwest and northeast from Scotstown in County Monaghan whilst a broader band is found east of Lough Macnean Lower, running north to Derrygonnelly. A narrow outcrop runs northeast-southwest through Manorhamilton. The most extensive area is around Lough Melvin west to Mullaghmore Head and including Inishmurray. A further band wraps south towards Sligo. There are other outcrops west of Ballyshannon, around Mountcharles from Lough Bradan Forest to the shores of Lower Lough Erne.
Bundoran Shale Formation
Known variously in the past as the Middle or Calp Limestone, or Lower and Middle Calp Shales, this 80-450m thickness of dark grey mudstones with layers of bioclastic limestone includes at its base, the Skea Sandstone Member (a.k.a. the Dowra Sandstone Member).
Ballyshannon Limestone Formation
Formerly known as the Pettigo Limestone Group or the Lower Limestone, this 120-450m thickness of blue-grey limestones with interbeds of silty shale, includes the Gortnaree Sandstone Member at its base.. There are further outcrops around Sligo Bay and southwest from Manorhamilton. In the Irish Republic, this rock sequence is known as the Oakport Limestone Formation.
Clogher Valley Formation
The formation which comprises peritidal limestones and shales [14] is evident in the Castlecaulfield area and extends from Ballygawley through Clogher to the Fivemiletown area. The outcrop also extends southwest from the Tempo area to south of Lisbellaw and along the northeast edge of Enniskillen to the eastern shores of Lower Lough Erne.
Ballyness Formation
Formerly known by various names including the Lower Carboniferous Sandstone, Basal Clastics and Calciferous Sandstone, the formation comprises about 300m thickness of red sandstones and quartz conglomerates.[15] Though much obscured by superficial deposits, its outcrop extends from the countryside north of Donamore southwestwards towards Clogher and in the area between Fivemiletown and Fintona. A further outcrop extends northwest from Lisbellaw to Ballycassidy and the eastern shores of Lower Lough Erne.
References
- ^ https://www.bgs.ac.uk/lexicon/lexicon.cfm?pub=TYRO BGS Lexicon of named rock units
- ^ Geological Survey of Northern Ireland 1991, 1:50,000 scale geological map sheet NI 44,56 and 43 ‘’Derrygonelly’’
- ^ "BGS Lexicon of Named Rock Units - Result Details".
- ^ "BGS Lexicon of Named Rock Units - Result Details".
- ^ "BGS Lexicon of Named Rock Units - Result Details".
- ^ "BGS Lexicon of Named Rock Units - Result Details".
- ^ "BGS Lexicon of Named Rock Units - Result Details".
- ^ "BGS Lexicon of Named Rock Units - Result Details".
- ^ "BGS Lexicon of Named Rock Units - Result Details".
- ^ "BGS Lexicon of Named Rock Units - Result Details".
- ^ "BGS Lexicon of Named Rock Units - Result Details".
- ^ "BGS Lexicon of Named Rock Units - Result Details".
- ^ "BGS Lexicon of Named Rock Units - Result Details".
- ^ "BGS Lexicon of Named Rock Units - Result Details".
- ^ "BGS Lexicon of Named Rock Units - Result Details".
- I.C. Legg, T.P Johnston, W.I. Mitchell & R.A. Smith (1998). Geology of the country around Derrygonnelly and Marble Arch, Memoir of the Geological Survey of Northern Ireland, Sheet 44, 56 and 43 (Northern Ireland) (1. ed.). London: The Stationery Office. pp. 6–25. ISBN 0118845314.)
{{cite book}}
: CS1 maint: multiple names: authors list (link