Tectonic and stratigraphic aspects of the East Irish Sea Basin and adjacent areas: contrasts in their post-Carboniferous structural styles

Abstract

A revised geological map and lithostratigraphic correlation chart are presented for Carboniferous–Lower Jurassic strata in the East Irish Sea Basin (EISB) and contiguous basins of the NW–SE- to NNW–SSE-trending Clyde Belt. The significance of the exceptionally thick Triassic succession (4375 m) is documented in relation to other Triassic rifts of NW Europe. Basin margin faults within the Clyde Belt are basement-controlled and located either along the margins of exposed and concealed Ordovician–early Devonian buoyant granites, or orthogonal to earlier Paleozoic structures.Four basic and markedly different structural styles have been identified from seismic interpretation. The styles comprise: solitary Caledonoid-trending folds (typically elongate centroclines) with minimal NW–SE faulting (style 1); synthetic and antithetic fault systems in single NW–SE half-graben on the fringes of the Clyde Belt (style 2); linked half-graben with large tilted fault blocks and stacked Permo-Triassic halite detachments in the centre and north of the EISB (style 3); and small step-faulted tilt blocks without thick Permo-Triassic halites, but again forming linked half-graben, in the south and on the fringes of the EISB (style 4). The styles are largely independent of the age of the basin-fill, except style 3 which is restricted to Permian–Lower Jurassic successions.