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The AAPG/Datapages Combined Publications Database

CSPG Special Publications


Canada's Continental Margins and Offshore Petroleum Exploration — Memoir 4, 1975
Pages 295-312
Atlantic Facing Margins

The Geology of the Irish Sea

J. E. Wright


The area described extends from the southwest coast of Scotland southwards to St. David’s on the southwest tip of Wales. The Irish Sea basin north of Anglesey is underlain largely by Carboniferous rocks except for an inlier of older, lower Palaeozoic slates on and around the Isle of Man. The Carboniferous is of Dinantian age on the Irish, Solway and North Wales coastal margins but Namurian and Westphalian sediments occur in the central part of the basin and in the Lancashire and Cumberland coalfields. The eastern part of the north Irish Sea carries a thick cover of Permo-Triassic rocks which extend seawards from the Cheshire and Solway Basins. These younger sediments include sandstones, mudstones and saliferous horizons and, on the basis of gravity surveys, have been estimated to range between 3 and 6 km in thickness. This should be compared with a thickness of about 3.2 km known from the adjacent land areas.

Shallow basement areas of lower Palaeozoic rocks extend westwards from Anglesey, southwestwards from Lleyn and northeastwards from the Wicklow coast of Ireland, separating the northern basin from the Mesozoic and Tertiary basins of Tremadoc and Cardigan Bays and St. George’s Channel. The Tre-madoc Bay Basin contains Tertiary and Mesozoic rocks penetrated to a depth of 1938 m by the Mochras borehole on the coast. To the southwest, the Cardigan Bay Basin contains Permo-Triassic and Jurassic rocks with no Tertiary cover. Farther to the west and south the St. George’s Channel Basin may contain Permo-Triassic, Jurassic and Cretaceous sediments below a thick Tertiary cover. This sequence is apparently affected by salt structures and may total about 6000 m in thickness.

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