The Northwest Atlantic Mid-Ocean Channel of the Labrador Sea. IV. Petrography and provenance of the sediments

Abstract

The Northwest Atlantic Mid-Ocean Channel (NAMOC) of the Labrador Sea is associated with a 500 m thick sequence of well-bedded turbidites along the axis of the Labrador and Newfoundland basins and extends onto the western Sohm Abyssal Plain. The specific source areas of these terrigenous turbidites on the shelves and landmasses surrounding the Labrador Sea were not known hitherto because the morphological connections in the head region of the NAMOC with canyons on the slope are masked by young ice-rafted and bottom-current-transported sediments.Petrographic analysis of channel sands and gravels suggests a dominant Canadian source for the channel segment north of the confluence with the Imarssuak Mid-Ocean Channel (IMOC) based on the predominance of lower Paleozoic detrital carbonates. The IMOC provides sediment from sources around the West Reykjanes Basin, i.e., the east coast of Greenland and Iceland; however, source-specific minerals or rock fragments from the Tertiary alkali basalts of southwest Greenland were not detected. Anorthosite pebbles imply a Canadian rather than a Greenlandian source, based on the relatively low anorthite content (An25–45) of their plagioclases.In the silt- and clay-sized fractions turbidites are distinctly different from intercalated pelagic oozes by their high detrital carbonate and organic matter contents and low to zero contents of montmorillonite. Organic carbon concentrations (0.8–1.0%) of the muddy spill-over turbidites on the levees of NAMOC are sufficient for hydrocarbon source rocks; their association with coarse-grained channel sediments would make them interesting exploration targets if they occurred in shallower water in the subsurface.