Stratigraphy of Dinantian rocks in WB3 borehole, Co. Armagh

Analysis of the 359m-deep Wilson's Bridge borehole, WB3, in County Armagh reveals an almost-complete local Dinantian succession. Seven lithological units are recognised and consist of alternating marine and non-marine carbonate and siliciclastic rocks. The succession ranges in age from late Courceyan (CM Biozone) to late Asbian, and for the first time in Northern Ireland there is biostratigraphical evidence for continuous sedimentation across the Courceyan-Chadian boundary. Chadian conodonts near the base of the section show close similarities with faunas from coeval rocks in the Northumberland Trough. The Pu Biozone is now recognised as being considerably thicker than was previously suggested. The Tournaisian part of the Armagh succession is similar to that in the Clogher Valley of County Tyrone but quite different from successions in the Kingscourt and Navan areas, south of the Longford-Down Inlier. The Viséan part of the succession is similar to that in counties Fermanagh and Tyrone, with open-marine limestones rich in corals and foraminifera of Arundian and late Asbian age, separated by deltaic sandstones yielding spores of TS to TC Biozone age (Holkerian to early Asbian). However, the Drumman More Sandstone Formation in Armagh is considered not to be a correlative of the Mullaghmore Sandstone Formation of north-west Ireland.