Interbedded Late Quaternary turbidites and contourites in Flemish Pass, off southeast Canada: Their recognition, origin and temporal variation

The recognition of contourite and turbidite deposits in deep-marine sequences can be challenging, as deposits may show similar sedimentary characteristics. In Flemish Pass, a small, 1100 m deep, perched basin along the southeast Canadian continental margin, both types of deposits occur. Late Quaternary sediments include thin sand layers interbedded with hemipelagic muds. The distribution, age, sedimentary structures and petrology of these sands were used to distinguish between turbidite and contourite deposits, which were then characterized by detailed grain size distribution for understanding the conditions leading to deposition of each type. Seven sediment facies each with a distinctive grain size distribution were recognized. They are 1—transported contourites, 2—winnowed beds, 3—possible jökulhlaup deposits, 4—sandy turbidites, 5—muddy turbidites, 6—hemipelagic sediment and 7—turbidites from well-sorted materials. Sand packets comprised of several stacked turbidite sand beds, some with erosive contacts, were correlated from the margin to the basin floor, showing clear distal fining, and creating a small lobe. The temporal distribution of the sand beds indicates that most turbidites and contourites were deposited at stadial to interstadial transitions. This linkage may be related to variations in the oceanic circulation in Flemish Pass, which winnowed turbidites and may have triggered turbidity currents by moving sands into canyon heads.