Holocene development and sediment transport on the northeastern Grand Banks of Newfoundland

Five sediment facies are recognized for the northeastern Grand Banks of Newfoundland based on sediment and bedform distributions (Barrie et al., 1984). Sediments from grab samples, boreholes and vibrocores obtained in each of these facies were examined fortexture, pebble lithology, mineralogy or sands, and quartz-grain surface textures. Results indicate a predominant locdi Tertiary and Cretaceous source of the material with a minor input from ice/iceberg rafting in the deeper shelf edge region. From the late Pleistocene-Holocene transgression to thepresent, the shelf surficial sediments have been highly reworked resulting in mature sand for wnich the various mineral size components.are hydraulically equivalent. The pretransgression subaerial surface can be laterally traced above -100m, the lowest stand of sea level, by the distinct change inheavy mineralogy from a dominance of garnet to ion hydroxide opaques, the intensity of quartz iron staining, and an increase in silt content. During the winter months, in a water depth of 70 m, the critical threshold of sand transport under oscillatory flow is exceeded up to 70% ot the time.Unidirectional velocities, 0.5 m above the seabed, are generally low with extreme velocities exceeding 0.45 m/sec. Both wave-generated and ocean currents have mean flow directions to the south-southeast. This motionresults in sediment transport in this direction and in the formation and movement of observed oscillation ripples, megaripples and sand waves (parallel to the bathymetric contours). The larger sand ridges also appear to respond to the southeasterly transport as evidenced by increasingly younger c14dates towards the southeast throughout the ridge. Investigations, including tracer sand studies are presentlyunderway to quantify the conditions under which these bedforms move.