J. R. Davies, I. D. Somerville, C. N. Waters, N. S. Jones, 2011. "North Wales", 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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Carboniferous strata within this region occur in the broad eastern flank of the north-south axis of the Clwydian Range from Prestatyn to Oswestry, sections within the Vale of Clwyd and the outlying districts around Llandudno, Menai Straits and Anglesey (Fig. 25). In NE Wales and the Welsh Borderlands the gently tilted Visean limestones are succeeded to the east by Namurian to Westphalian strata forming the Flint and Denbigh coalfields.
This region includes intermittent development of Tournaisian to Visean alluvial deposits (‘Basement Beds’). These are overlain by Visean ramp-to-shelf carbonates, present along the northern margin of the Wales-Brabant High, extending across North Wales (Clwyd Limestone Group). Visean to Namurian basinal deposits (Craven Group) occur on the north coast of North Wales (Fig. 25), deposited on the southern margin of the Irish Sea Basin (see Chapter 16). During the Namurian and Westphalian this region is represented by thick fluvio-deltaic successions, including the Millstone Grit and Pennine Coal Measures groups, in turn overlain by alluvial deposits of the Warwickshire Group.