Seismic geomorphological reconstructions of Plio-Pleistocene bottom current variability at Goban Spur

High-resolution single channel sparker reflection seismic data revealed the presence of large-scale sediment waves nearby DSDP Site 548, located on Goban Spur. They developed in a gentle terraced environment which contrasts with the canyon-incised Celtic margin, and the relatively smooth Porcupine Seabight to the north. Based upon the morphological characteristics of the observed seabed and buried sediment waves, energetic alongslope bottom currents are thought to be the driving mechanism for the sediment wave development. These currents are driven on their turn by an enhanced internal tide regime that could be attributed to the introduction of the Mediterranean Outflow Water. The DSDP Site 548 downhole geophysical data and the seismic stratigraphic analysis allowed the differentiation of three sequences that relate to evolutionary stages since the
lower Pliocene. The sequences are bounded by local erosional events, associated with mass wasting events, which seem to occur roughly synchronously to major northern hemisphere glaciations, respectively during the Lower Pleistocene (~2.5 to 2.15 Ma), and the Middle Pleistocene (~0.45 Ma). The lower sequence (from ~4.5 to ~2.15 Ma) shows no morphological evidence of bottom-current driven sedimentation. It is however settled over a smooth erosional surface which could indicate the introduction of the Mediterranean Outflow Water. The intermediate sequence is characterised by large-scale sediment waves that have gradually developed in close association with palaeo-seafloor irregularities. It is inferred that the sedimentation resumedwith a relative bottom current energy increase. The youngest sequence recorded active sedimentwave formation, similar to the
previous sequence. Although the Goban Spur sediment waves cannot be regarded as contourite drifts as such, their stratigraphic evolution corresponds to other well-documented contourite depositional systems, influenced by the Mediterranean Outflow Water.