Fivemiletown-Clogher-Aughnacloy-Benburb, Fermanagh-south Tyrone area, Carboniferous, Northern Ireland

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Mitchell, W I (ed.). 2004. The geology of Northern Ireland-our natural foundation. Geological Survey of Northern Ireland, Belfast.

W I Mitchell

Fivemiletown-Clogher-Aughnacloy-Benburb

Distribution of Carboniferous rocks in Co. Fermanagh - south Co. Tyrone. (P947821)
Lithostratigraphy of the Tyrone Group in the four regions of Co. Fermanagh-south Co. Tyrone. (P947933)
Geology of the Fardross stream section. (P947822)
Litho-, bio- and chronostratigraphy of the Carboniferous rocks in the Armagh area. (P947819)
Lithostratigraphy of the Tyrone Group in the Derrygonnelly - Marble Arch - Cuilcagh Mountain area. (P947934)

The Carboniferous rocks of this region are divided into three separate areas around Fivemiletown-Clogher, near Aughnacloy and at Benburb (P947821).

Fivemiletown-Clogher

Tyrone Group

The Ballyness and Clogher Valley formations (P947933) are exposed in conformable contact in the Cole Bridge River [H 443 523], 4 km north of Fivemiletown. The unfossiliferous Ballyness Formation comprises about 300 m of red and purplish red sandstone and conglomerate with clasts mainly of white quartz pebbles. The Clogher Valley Formation (400 m) is divided into lower and upper parts separated by a sandstone unit. The lower part is fenestral micrite, siltstone, sandstone, evaporite beds and grey mudstone with miospores indicating an early Chadian age. The upper part crops out [H 424 516] at Moysnaght, 4 km NNW of Fivemiletown, and consists of fossiliferous mudstone, siltstone, sandstone and thin crinoidal limestone with the early Chadian solitary coral Siphonophyllia cylindrica. The lower ‘member’ of the Ballyshannon Limestone Formation is exposed in Mullaghsillogagh quarry [H 424 504] 3 km northwest of Fivemiletown and contains corals such as Sychnoelasma konincki and is late Chadian.

The Fardross section (P947821) [H 523 486] [1], exposes five formations of the Tyrone Group (P947822). Mid- and late Arundian foraminifera including involutus stage Paraarchaediscus, Glomodiscus and Uralodiscus occur in the Bundoran Shale Formation, Mullaghmore Sandstone Formation and lower part of the Benbulben Shale Formation. Higher strata in the latter Formation contain the brachiopod Gigantoproductus sp. cf. semiglobosus and coral Lithostrotion decipiens (I. Somerville pers. comm.) and are early Asbian as are the succeeding Glencar Limestone and Dartry Limestone formations.

Aughnacloy

The stratigraphy of the Tyrone Group east and southeast of Aughnacloy is not defined accurately because of poor exposure (P947933). The oldest rocks of the Bundoran Shale Formation are exposed [1] in Drummond quarry [H 690 519], 2.5 km east of Aughnacloy. In the Oona Water [H 777 565] the Benbulben Shale Formation contains an Asbian macrofauna of corals and brachiopods. Thin mudstones in the succeeding Aughnacloy Sandstone Formation contain Holkerian-early Asbian miospores including Schulzospora campyloptera, an index taxon of the TC Biozone. Calcareous sandstone in Carricklongfield quarry [H 716 545] contains rare early Asbian corals and brachiopods. The Formation is equated with the Carland Sandstone Formation of east Co. Tyrone and Drumman More Sandstone Formation in Co. Armagh (P947819). The Maydown Limestone Formation exposed in Plaister quarry [H 676 539], 2.3 km NNE of Aughnacloy, contains an early Asbian macrofauna including Gigantoproductus sp. maximus group and Siphonophyllia benburbensis.

Benburb

Despite the proximity of rocks of the Armagh Group in Co. Armagh the late Viséan succession at Benburb [2] [3] lithostratigraphically more closely resembles the Tyrone Group succession in Co. Fermanagh and south Co. Tyrone. In the River Blackwater, 230 m of Asbian and Brigantian strata are exposed (P947933).

The Maydown Limestone Formation contains abundant Asbian corals and brachiopods and is exposed in Maydown quarry [H 817 518]. It includes lithologies that are typical in Co. Fermanagh of the change between the upper part of the Benbulben Shale, the Glencar Limestone and Dartry Limestone formations (P947934). Mudstones in the Carrickaness Sandstone Formation contain miospores of the late Asbian NM Biozone including the index taxa Raistrickia nigra and Triquitrites marginatus. The Asbian-Brigantian boundary is placed at the contact between the Glenview and Drumflugh limestone members in the Blackwater Limestone Formation[2]. Diagnostic Brigantian elements are rare in higher members but the typical bivalve Posidonia becheri is present.

References

  1. 1.0 1.1 Geological Survey of Northern Ireland 1982. Clogher, Northern Ireland Sheet 46. Solid Geology. 1:50 000. (Southampton: Ordnance Survey for the Geological Survey of Northern Ireland).
  2. 2.0 2.1 Mitchell, W I, and Mitchell, M. 1983. The Lower Carboniferous (Upper Viséan) succession at Benburb, Northern Ireland. Institute of Geological Sciences Report No. 82/12.
  3. Geological Survey of Northern Ireland 1984. Armagh, Northern Ireland Sheet 47. Solid Geology. 1:50 000. (Southampton: Ordnance Survey for the Geological Survey of Northern Ireland).