Combined control of bottom and turbidity currents on the origin and evolution of channel systems, examples from the Porcupine Seabight

Abstract

The Gollum Channel System (GCS) and Kings Channel System (KCS) are situated at a key location on the eastern side of the Porcupine Seabight to provide valuable insight into British-Irish Ice Sheet dynamics and sediment supply to the Belgica cold-water coral mound province. These channel systems are the most efficient pathways for particles from the Irish Shelf edge to the Porcupine basin. The spatial and temporal variability of their activity are, therefore, likely to have significant regional consequences. However, the sedimentary processes involved in the evolution of both systems have not yet been comprehensively studied. Here, bathymetric, 2D seismic reflection and oceanographic data are used to reconstruct and compare the interplay between along-, across- and downslope processes through geomorphologic and seismic stratigraphic analyses. The initial seafloor topography of the systems was shaped in the late Miocene-late Pliocene by intense northward-flowing bottom currents during the first phases of the composite RD1 erosion event. The bases of the KCS and GCS were eroded by downslope-flowing turbidity currents during the last phase of the RD1 event. Sediment transport within the channels was probably most active during Quaternary glacial periods of lowered sea levels, and sediment carried downslope by turbidity currents was likely pirated and transported northwards by contour currents. Therefore, the channels are proposed to have been of major importance as a source of sediment and nutrients for the Belgica cold-water coral mounds and associated sediment drifts to the north. The GCS and KCS represent an area where bottom currents, turbidity currents, slope failures and hemipelagic processes have interacted throughout the Neogene and Quaternary.