Fluvial features in the deep-sea: new insights from the glacigenic submarine drainage system of the Northwest Atlantic Mid-Ocean Channel in the Labrador Sea

Abstract

Side-scan sonar imagery and seismic profiles from the submarine drainage system of the Northwest Atlantic Mid-Ocean Channel (NAMOC) of the Labrador Sea reveal the presence of a variety of fluvial features in the deep-sea. The analogies extend from meso-scale features to the basin-wide drainage pattern. At basin-scale, the NAMOC submarine drainage system consists of downslope converging tributary canyons on the slope and yazoo-type tributary channels joining a central trunk-channel on the basin floor. In detail, the following fluvial features have been observed in NAMOC and its tributaries: meandering and braided channels and talwegs, point bars (some with meso-scale bedforms), terraces, wash-over fans, submarine hanging valleys and chute pools, and levee gullying and slumping. Some of these features are new and have not been recognised before in the deep-sea; others have not been documented in comparable detail previously. Although the similarity of deep-sea turbidite depositional features with fluvial features has long been recognised in the literature, fundamental differences exist between turbidite and fluvial facies associations, the most noticeable of which is the lateral juxtaposition of a meandering deep-sea channel and a submarine braidplain. The latter has only been established for a glacigenic submarine drainage system. The analogy with fluvial processes may be used in the quantification of flow processes of large-scale natural turbidity currents.