Pleistocene ice-proximal glaciomarine sediments in boreholes from the Hebrides Shelf and Wyville-Thomson Ridge, NW UK Continental Shelf

Abstract

Synopsis Pleistocene sediments recovered in boreholes from the Hebrides Shelf and Wyville–Thomson Ridge indicate ice-proximal glaciomarine deposition in an outer shelf setting. The sediments are predominantly diamicts and in vertical profile display a general upward-fining trend. The lower part of the succession is characterised by a coarse, crudely stratified-to-massive, clast and matrix-supported diamict assemblage which is interpreted as an amalgamated sequence of debris flows. The upper part consists of finer, massive, matrix-supported diamicts deposited mainly from suspension but with a subsidiary input of ice-rafted material. Thin interbedded lag gravels and sandy sediment gravity flows form a minor component of the succession. This kind of succession is usually associated with a stationary or slowly retreating tidewater ice margin. The morphology of the outer shelf is characterised by a relict glaciated terrain; the sedimentary succession suggests that this is of submarine origin. These data indicate that at some time during the Pleistocene an ice-sheet extended out to the edge of the northern Hebrides Shelf and partly onto the Wyville-Thomson Ridge. The age of this glaciation is unknown but probably pre-dates the last Scottish ice-sheet (Late Devensian/Late Weichselian)