I. D. Somerville, C. N. Waters, 2011. "NW Ireland", A Revised Correlation of Carboniferous Rocks in the British Isles, C. N. Waters, I. D. Somerville, N. S. Jones, C. J. Cleal, J. D. Collinson, R. A. Waters, B. M. Besly, M. T. Dean, M. H. Stephenson, J. R. Davies, E. C. Freshney, D. I. Jackson, W. I. Mitchell, J. H. Powell, W. J. Barclay, M. A. E. Browne, B. E. Leveridge, S. L. Long, D. McLean
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The Carboniferous rocks of NW Ireland extend from the western margin of the Dublin Basin (see Chapter 21), NW into Co. Roscommon as far as the Curlew Mountains, and further NW into Co. Leitrim and Co. Sligo, south Co. Donegal, and north Co. Mayo, north of the Ox Mountains (Fig. 54). All the rocks in the region belong to the Mississippian Subsystem.
Late Tournaisian, mostly continental or marginal marine facies, and Visean (Chadian-Asbian) shelf limestone of the Tyrone Group occur in counties Roscommon, Mayo, Leitrim, Sligo and Donegal within four structurally-controlled basins: the Carrick-on-Shannon Syncline, south of the Curlew Mountains; the Ballymote Syncline, between the Curlew Mountains to the south and the Ox Mountains to the north (Dixon 1972), extending NE into the Lough Allen Basin and the Cuilcagh Mountains farther to the east in Co. Leitrim; the Sligo Syncline north of the Ox Mountains (Oswald 1955); the Largymore Syncline, west of Killybegs and St John’s Point in south Co. Donegal. The Tyrone Group is followed by a mainly mudstone-rich sequence with an alternation of marine limestone, shale and sandstone (both marine and fluvio-deltaic) of late Visean to Namurian age (Leitrim Group).
The lithostratigraphy used here is based on a compilation and synthesis of existing published nomenclature. Unlike many other areas in southern Ireland, groups have been formally defined, combining related formations in similar depositional settings (e.g. shelf, ramp and basin).