Aspects of the geology of the Malin Sea area

Abstract

Abstract A complex of sediment-filled graben and half-graben, separated by acoustic basement, occupy much of the northwest shelf of the British Isles. Some were established in the Late Carboniferous, but most were formed during a post-Hercynian tensional phase that adopted Caledonoid-trending structures in the basement. A major graben complex occurs in the Malin Sea area; flanked by the Coll-Tiree-Skerryvore-Stanton Banks basement ridge to the north and by the Islay-Donegal Platform to the south. Rock samples obtained by divers from the two basement ridges confirm their Precambrian character. Limited commercial multichannel reflection seismic data together with BIRPS WIRE lines and structural information supplied by Texaco suggest that the graben complex consists of three major depocentres: the Inner Hebrides Trough, the Malin Basin and the South Donegal Basin. To the west lies the Main Donegal Basin. This basin, in concert with the South Donegal Basin, evolved during the Carboniferous as a result of dextral strike slip movement between the Stanton Banks in the north and the Islay-Donegal Platform to the south. Sea bed core and dredge material and well data recovered from the graben complex indicate that the basin sediments include Upper Carboniferous, Permo-Triassic, Lower Jurassic, Middle Jurassic, with thick Cretaceous and Lower Tertiary in the far west. Periods of uplift and erosion restricted sedimentation during the late Mesozoic, whilst uplift and erosion in the early Tertiary was accompanied by extensive igneous activity, with the development of two plutonic centres and twelve other smaller intrusive igneous bodies. Tertiary sediments are inferred for the Blackstones Basin by analogy with similar sequences elsewhere in the Hebridean area. A thick Quaternary section, dominated by glaciomarine sediments, contains three of the five glacial cycles that constitute the Pleistocene in this area.