The Gollum channel system is the only major downslope sediment supplying system located on the Irish Atlantic margin, first described by Berthois & Brenot (1966). However, compared to its counterparts on the Celtic and Armorican margins, its structure and development is yet poorly understood. A variety of new data, collected during several campaigns from 1999 to 2006, has shed a new light on the upper reaches of this system. The most elaborate data set was collected on the upper slope of the Gollum Channel system. Additional to the RCMG high-resolution seismic profiling, campaigns organised by associated partners acquired multibeam bathymetry, TOBI side-scan sonar data and a long piston core in one of the channels.These data allowed to clearly distinguish two different channel settings. The main Gollum channel system is characterised by several deeply incised canyons with numerous slide scars on their flanks. Their pathways seem to be influenced by a structural control, creating a bayonet-shaped course. Upstream of this structural feature, the channel floor deposits are characterized by thick acoustically transparent units suggesting ponded turbidites or mass-wasting deposits. A long piston core, acquired by RN Marion Dufresne in 2001 (MD01-2464), however, only yields a small number of fine-grained turbidites in a muddy hemipelagic host sediment. This suggests that this system has known a relatively low activity during Quaternary times. Moreover, at the abyssal end of the slightly sinuous Gollum channel only a weakly developed deep-sea fan is found, confirming a low sediment supply. It was previously thought to be reworked by strong bottom current processes.In the northern part of the system, on the other hand, the Kings channels show an entirely different situation. Here the channels are broad and smooth with relatively gentle flanks. Along the longitudinal axis of the northernmost channel, an intra-channel levee is observed, suggesting a relatively higher activity compared with the more southern Gollum canyons. The most remarkable feature, however, is a large field of mass-wasting deposits and escarpments. This suggests a dramatic phase of slope instability within the Neogene. Until now, little evidence is found for the cause of this event. The evidence of pockmarks north of this area could invoke the mediation of fluid migration.Despite the absence of wells, the seismic stratigraphy of the Gollum channels could be linked with the relatively better constrained stratigraphy of the Belgica mound province in the north (Van Rooij et al., 2007; IODP 307 Expedition Scientists, 2005) through correlation with seismic profiles. This suggests the Gollum channel system probably started developing during a dramatic erosional event at the Miocene/Pliocene boundary. |
