Sediment Redistribution on the Reykjanes Ridge: Seismic Evidence

Abstract

East-west seismic reflection lines obtained at 14-km intervals on the eastern flank of the Reykjanes Ridge reveal patterns of sediment cover controlled by the reaction of bottom-water movement to crustal topography. Bottom currents have piled sediment into drifts at a variety of scales. The largest of these is Gardar Drift, which is constructed along a fragmented basement ridge roughly 42 m.y. in age. Basement peaks with scoured and moated sedimentary envelopes, outcropping sedimentary strata, and dune topography indicate prevalent erosion and redeposition of bottom sediments. No conformable pelagic draping is anywhere visible in the surveyed area. Two prominent sediment reflectors occur on crust as young as 17 m.y. and 37 m.y., which sets a maximum limit on their ages. The younger reflector is highly variable in apparent reflectivity; it is well developed in fracture zones but is indistinct or absent on high-standing crustal blocks of equivalent age between fracture zones. The basement expression of these fracture zones is 12 to 45 m.y. in age and has been virtually smothered by the thickest sediment cover (1.75 km) observed in the survey area. Part of the fracture zone filling appears to be sediment redistributed by bottom currents, but the increased sediment smoothness and reflectivity in the fractures suggest localized turbid downslope flow within the ridge flank. In the last 5 to 10 m.y., coarse basaltic sand mainly from Iceland (at 64° N.) has been spread across a broad trough-contained fan southwest of the Iceland-Faeroes Ridge. At 58° N., the turbidite flow is funneled into Maury Channel, ultimately to be spread out onto the Biscay Abyssal Plain at and below 48° N., 1,600 km to the south.