Current-controlled sedimentation in a megatransform system: a case study of the Charlie–Gibbs Fracture Zone

The Charlie–Gibbs Fracture Zone is the main transform system in the North Atlantic Ocean. It serves as a primary deep-water gateway for the Iceland–Scotland Overflow Water current. Using high-resolution seismo-acoustic profiling, three types of contourite drift were identified in the valleys of the inactive fractures and active transform of the Charlie–Gibbs Fracture Zone: (1) channel-related drifts; (2) confined drift; and (3) plastered drift. The Iceland–Scotland Overflow Water current is the main agent controlling drift formation in the northern valley and eastern part of the southern valley, while it is suggested that the Denmark Strait Overflow Water or Lower Deep Water dominate in the western part of the southern valley. Examination of two sediment cores shows that the contourite drifts at least at their upper parts consist of alternating muddy and silty contourites and pelagic/hemipelagic sediments. The contourite deposition corresponds to the present interglacial interval. Pelagic/hemipelagic sedimentation prevailed during a glacial interval (marine isotope stages 3–2) and the last glacial/interglacial transition, corresponding with high ice-rafted debris input. The position of the highly productive Subarctic Front over the study area induced the formation of diatom ooze beds at the beginning of marine isotope stage 1 and high-carbonate pelagites during some intervals of marine isotope stage 3.