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Abstract

The late Neogene (Pliocene–Holocene) interval witnessed a significant change in sedimentation style across the UK Atlantic margin that culminated in its present morphological expression. The onset of change is marked by the creation of a regional, angular, erosional unconformity that can be traced from the Hebrides and West Shetland margins into the adjacent deep-water basins of the Rockall Trough and Faeroe-Shetland Channel. In the Rockall Trough, the unconformity is a submarine erosion surface that is dated as early Pliocene in age, between c. 3.85 and 4.5 Ma. On the Hebrides and West Shetland margins, the dating of the unconformity is slightly less well constrained and spans the latest Miocene(?)–early Pliocene (c. 5.5-3.8 Ma) interval. The formation of this unconformity may have resulted from the seaward tilting and subsidence of the shelf margin, which may have further modified the oceanographic circulation pattern in the adjacent basins. The sedimentary response to this event was relatively quick in the deep-water basins, which preserve a record of early Pliocene (post 3.85 Ma) to Holocene sediment-drift accumulation, albeit with a shift in the focus of sedimentation relative to the underlying strata. In contrast, major prograding wedges, which have contributed extensively to the construction of the Hebrides and West Shetland margins and to a lesser extent the Rockall Bank, date essentially from late Pliocene time and largely correlate with the influx of ice-rafted material to the margin. However, indications for a restricted lower Pliocene component to the shelf-margin succession suggest that this apparent delay or lag in sedimentation, relative to the basins, may be a natural response to the rate of denudation of the adjacent landmasses. The regional observations off NW Britain support the concept of Neogene tectonic uplift.

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