Sediment-drift development on the continental margin off NW Britain

Abstract

The long-term record of sediment-drift development on the continental margin off NW Britain was investigated using seismic-reflection data calibrated with boreholes and short cores. These data indicate that the onset of bottom currents on the NW British margin occurred in the early late Eocene following a major phase of subsidence in the Rockall Trough and Hatton-Rockall Basin. Seismic reflection profiles reveal the downwarped and eroded surface of lower upper Eocene and older strata onlapped by middle to upper Cenozoic sediments. The latter consist predominantly of deep-marine contourites preserved both as mounded, elongate, and broad, sheeted, sediment drifts with associated sediment waves. Seismic-stratigraphical analysis of the drift succession has revealed a broad twostage depositional history. A vigorous bottom-current regime in the late Eocene to midMiocene interval was accompanied by significant lateral migration of sediment by upslope accretion onto the flanks of the basins, including the construction of the bulk of the Feni Ridge. Mid-Miocene tectonism modified the palaeoceanographic and sedimentary regime. In the ensuing mid-Miocene to Holocene interval, drift accumulation persisted in the axial and eastern part of the Rockall Trough whereas a largely erosional regime prevailed on its western margin. The overall locus of drift sedimentation shifted westwards onto the Rockall Plateau.

Investigations of the bottom current sculpted margin of Hatton Bank, NE Atlantic

“…The constructional furrows (Type 2) are also the result of changes in bottom-current activity and are thought to be upslope accreting elongated plastered contourite drifts with a moat forming where the core of the bottom current is located. Similar reflector configurations and drift moats are commonly found in the Feni Drift, on the northeast flank of Rockall Bank (Stoker, 1998).…”

“…The structural configuration of Rockall Plateau reflects the complex geological evolution of the region, which largely occurred during the Mesozoic to early Cenozoic continental rifting associated with the opening of the northeast Atlantic Ocean (Stoker, 1998). Break-up initiated between Greenland and Rockall at 57-56 Ma (Barton and White, 1997), during which a volcanic rifted continental margin was produced along the western edge of Hatton Bank forming a conjugate margin with East Greenland (Smith et al, 2005).…”

“…The confining of the current has the affect of reducing the sediment accumulation and promoting erosion to produce the furrows. Constructional furrows (or moats) are a common feature associated with many contourite systems such as the Feni Drift (Howe et al, 1994;Stoker, 1998) or the Faro-Albufeira contourite system (Llave et al, 2001). The continuous bottom-current flow allows the upslope accretion of the levee mounds with the current actively eroding the area upslope of the furrow and over time the moat will migrate upslope (Fig.…”

Untitled

“…This kind of changing seismofacies was observed for both the drifts at the Antarctic Peninsula (McGinnis and Hayes, 1995;Rebesco et al, 1996) and the Feni drift (Stoker, 1998). There, the different seismofacies also represent different stages within the development of the drifts.…”

“…Sediment deposited by or significantly affected by the action of bottom currents and wind driven surface currents leads to the formation of drifts, which lie parallel to continental margins (Stoker, 1998;Rebesco and Stow, 2000). Hence, our drifts are interpreted to be the result of a south setting current (AABW?…”