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

Abstract

The Charlie-Gibbs Fracture Zone (CGFZ) is the main transform system in the North Atlantic Ocean. It serves as a primary deep-water gateway for the Iceland-Scotland Overflow Water (ISOW) 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 CGFZ: (1) channel-related drifts, (2) confined drift, and (3) plastered drift. The ISOW current is the main agent controlling drift formation in the northern valley and eastern part of the southern valley, while the Denmark Strait Overflow Water or Low Deep Water is suggested for 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 alternated muddy and silty contourites and pelagic/hemipelagic sediments. The contourite deposition corresponds to the present interglacial interval. During glacial interval (MIS 3-2) and the last glacial/interglacial transition, pelagic/hemipelagic sedimentation prevailed corresponding with high IRD input. The position of the highly productive Subarctic Front over the study area induced the formation of diatom ooze beds at the beginning of MIS 1 and high-carbonate pelagites during some intervals of MIS 3.