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The AAPG/Datapages Combined Publications Database

CSPG Special Publications

Abstract


Canada's Continental Margins and Offshore Petroleum Exploration — Memoir 4, 1975
Pages 313-340
Atlantic Facing Margins

The Geology of the Irish Continental Margin and Some Comparisons with Offshore Eastern Canada

R. J. Bailey

Abstract

Gravity, magnetic and seismic surveys are beginning to reveal the general structure of the Irish continental margin. In the north (56°-54°N.), the margin exhibits a classic morphology, with a well-marked shelf break beneath which lies a buried marginal ridge of metamorphic (?) basement rock. This ridge appears to be limited by major faults crossing the margin at 56°N. and 54°50′N., the latter representing a possible offshore extension of the Great Glen Fault. To the south (54°-50° N.), the margin broadens to encompass a major deep-water embayment, the Seabight Trough, in which 5 km or more of Mesozoic to Recent sediment rest on thinned, quasi-oceanic crust. The trough is flanked on three sides by drowned continental crust. On the north, the Slyne Ridge has sustained some Mesozoic rifting, but is essentially a drowned east-west ridge of ancient Caledonian crystalline basement rock, bounded on the south (53°N.) by an old line of structural weakness. At its western extremity, the Slyne Ridge is contiguous with Porcupine Ridge, a continental “splinter” forming a western flank of the Seabight Trough. The eastern flank is formed by the mainland shelf edge, beneath which lies a buried ridge of ancient crystalline basement. Formation of the Seabight Trough by partial detachment of the continental fragment forming Porcupine Ridge remains a possibility, but simple pivotal motion about a point on the Slyne Ridge is not consistent with the inferred crustal structure beneath the Seabight Trough.

Hypotheses for the evolution of the North Atlantic suggest a former close conjunction between the Irish margin and its Canadian counterpart. Thus they might be expected to show geological similarities. A case can be made for correlation of the Cabot Fault and the possible offshore extension of the Great Glen Fault passing northwest of Ireland; and the imminent offshore convergence between the latter, the Highland Boundary line (?) and the above mentioned 53°N. line, suggests a possible offshore counterpart of the complex of faults bounding the Carboniferous rift of Newfoundland. Stratigraphic correlation of the marginal sedimentary sequences is to a large extent vitiated by the lack of paleontologic control on the seismp-stratigraphy of the Irish margin. However, the inferred chronology of deposition is generally in accord with that evidenced by offshore drilling adjacent to Canada’s east coast.


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