a) This line drawing and high-resolution seismic profile shows the nature and distribution of the Neogene strata in the west central Rockall Trough, with particular emphasis on the morphology and geometry of the eroded, upslope-prograding, RPb megasequence. On the seismic profile, the onlapping character of the sediment drift is well displayed. Significantly, this drift is now largely a relict feature having undergone extensive erosion since the early Pliocene. This erosion is manifest on the profile by the truncation of the internal reflections of the RPb drift at or near to present-day sea bed, the formation of an erosional scarp, and the separation of the basinal section from the slope deposits (Stoker 2002). The latter has resulted in the local exposure of Eocene strata. The line drawing emphasises this zone of early Pliocene–Holocene erosion as C10 is itself commonly truncated at the sea bed in the basin.
b) This high-resolution seismic profile shows further detail of the onlapping nature of the RPb megasequence on the slope of Rockall Bank. It also shows that the C10 angular unconformity is locally preserved on the slope, where it is draped by sediments of the overlying RPa megasequence. BGS borehole 94/1 tested the Neogene succession in this area (see
Fig. 13 for details).
c) This line drawing and high-resolution seismic profile shows the nature of the Neogene succession on the upper Hebrides Slope, in the area between the major depocentres of the Sula Sgeir and Barra/Donegal fans. In this area, the RPa megasequence consists of an acoustically layered, aggradational succession of sands and muds, which were deposited by a combination of downslope and alongslope processes (Leslie 1994). BGS borehole 88/7, 7A proved that the bulk of the RPa sediments were deposited under the influence of glacial activity on the adjacent shelf. The GU and C10 unconformities are well established at this site. The fragmentary nature of the RPb megasequence is also evident, having been extensively eroded on the shelf and upper slope. It is important to note that here the RPc/RPb boundary represents a hiatus between late Oligocene and mid-Miocene time, and is not directly equivalent to the C20 boundary, which is strictly a basinal event.
Reference
Leslie, A.B. 1994. Shallow Plio-Pleistocene contourites on the Hebrides Slope, northwest U.K. continental margin.
Sedimentary Geology, 82, 61-78.
Stoker, M.S. 2002. Growth and partial destruction of a Neogene sediment drift, western Rockall Trough.
In: Mienert, J. & Weaver, P. (eds), European Continental Margin Sedimentary Processes: An Atlas of Side-Scan Sonar and Seismic
Images. Springer Verlag, in press.
Stoker, M.S., van Weering, T.C.E. & Svaerdborg, T. 2001. A Mid-Late Cenozoic tectonostratigraphic framework for the Rockall Trough.
In: Shannon, P.M., Haughton, P.D.W. & Corcoran, D.V. (eds), The Petroleum Exploration of Ireland's Offshore Basins. Geological Society, London, Special Publication,
188, 411-438.
