Abstract

Geophysical surveys since 1971 and sounding data reveal the morphology and structures of the southern Labrador Sea. Ran Ridge and older mid-Labrador Sea crustal basement are well-defined. The West Thulean Rise (pre-60 Ma BP), counterpart to the Thulean Rise of the Northeast Atlantic, extends between the Charlie Fracture Zone and Ran Ridge {anomaly 24). Topographic and basement structural relief along a fault (herein called the Leifur Eiriksson Fracture Zone), offsetting the Ran Ridge crest (60–45 Ma BP) at 57 °N, 45 °W, is correlated with magnetic anomaly trends. The pre-Thulean and Thulean time structures of the mid-ocean ridge and magnetic data isochrons define the initial spreading orientations of the Ran/Reykjanes Triple Junction. Seismic data extend the known area of the transparent, kilometre-thick sedimentary body in the southern central Labrador Sea, and a circular trend of elongate crests surrounding a vortex region lend definition to the proposed name, Gloria Drift. Dunal morphology is characteristic of the surface of the entire Gloria Drift, and is also revealed in the mid-layer (35 Ma BP) extending throughout the entire sediment blanket. Terrigenous clay deposits sculpted by the Northeast Atlantic Deep Water form the elongate drift crests. The crests mark the paths or perimeters of the moving and still water masses of the bottom water gyre and probable anticlockwise paleocirculation that developed the Gloria Drift. The Imarssuak Mid-Ocean Channel is controlled by mountains and lies within the presumed relic rift valley of Ran Ridge. The Deep Sea Drilling Project at site 113 on the flood plain of Imarsuak Channel recovered cores consisting of turbidite silts and sands, mixed with volcanogenic (Iceland?) materials, and heavy minerals and clay. At this site, the commencement of transport in the channel is correlated with the onset of glaciation in early Pliocene. North of the junction with Imarssuak Channel, the Northwest Atlantic Mid-Ocean Channel lacks the high reflectivity indicative of recent (Pleistocene) turbidite deposition; hence, we conclude that the main source for highly reflective turbidite silts and sands in the lower Northwest Atlantic channel is the Imarssuak Channel. Meanders in the Northwest Atlantic Channel between 52 °N and 56 °N compare almost equally in proportions of channel widths and meander wavelengths, to the northeast Atlantic's Maury Channel at the same latitude.

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