The Lower Carboniferous Stratigraphy of the Omagh Syncline, Northern Ireland

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Abstract
Summary: The Omagh syncline is a large outlier of Lower Carboniferous rocks in Counties Tyrone and Fermanagh, Northern Ireland. The succession, about 8000 feet thick, is divisible into four lithologically distinct groups. At the base, resting unconformably on Dalradian rocks, is the Omagh Sandstone, a group of siliceous sandstones and conglomerates. It is confined to the eastern half of the outlier and its zonal position is indeterminable. The Claragh Sandstone which follows is characterized by abundantly felspathic sandstones. It overlaps the Omagh Sandstone in the west and rests on Dalradian and Moinian rocks. The fauna suggests a C 1 age. The third group, the Pettigo Limestone, is dominantly calcareous with a rich fauna indicating a C 2 S 1 age. The Clonelly Sandstone Group at the top of the succession, though mainly arenaceous, is more variable in lithology than the preceding groups. It is referred to the S 2 Subzone. The gentle folding of the Lower Carboniferous along an E.-W. axis is ascribed to Armorican compression, as is the development of four major faults by lateral slipping along NE.-SW. fault-planes. The source rocks of the Lower Carboniferous clastic sediments were the Moine and Dalradian rocks of the west and north. Virtually all the sediments were deposited in a marine environment. I. Introduction In North-West Ireland several extensive outliers of Lower Carboniferous rocks rest unconformably on an irregularly eroded surface of Dalradian and Moinian metamorphic rocks (Fig. 1). The outliers are the remnants of a once widespread covering of sedimentary rocks. One of the largest of the

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