Seismic stratigraphy of the West Shetland Drift: Implications for late Neogene paleocirculation in the Faeroe-Shetland gateway

The morphology and anatomy of a late Neogene contourite drift on the British margin of the Faeroe-Shetland Channel is investigated in unprecedented detail using industrial two-dimensional and three-dimensional seismic data. The West Shetland Drift is constructed by a succession of mounded, asymmetric strata that in the basin and on the midslope has accumulated on a regional unconformity of early Pliocene age. The midslope component of the drift system forms a 400 m thick convex, elongate sedimentary body that can be traced from the outlet of the Norwegian Channel and 250 km southwest along the Shetland margin. Contourite drifts occupying the basin are evident as a succession of sheeted-mounded and wavy migrating units intercalated by three mega-debrite sequences. The seismic architecture of the West Shetland Drift and tentative age estimates of its bounding surfaces suggests that it formed rapidly (∼5-10 cm kyr^-1) by alongslope transport of hemipelagic sediments derived from the NW European shelf. The change from erosion/nondeposition to enhanced contourite drift accumulation during the early Pliocene suggests that a moderate thermohaline current regime prevailed in the Faeroe-Shetland Channel prior to the main phase of Northern Hemisphere glaciation at 3.0-2.5 Ma. A reduction in meridional heat transport associated with a decrease in the flux of North Atlantic deep waters may have been an important factor for the growth of Northern Hemisphere ice sheets.