ABSTRACT

The continental slope and rise, east of Newfoundland, accommodates two distinct gravel populations. The upper slope (300-700 m depth) population is characterized by unstained, granules to boulders of predominantly granitic and terrigenous sedimentary composition that show affinity to Paleozoic and Proterozoic rocks of Newfoundland and areas further north. The rise (2,500->3,000 m depth) population consists of iron- and ferromanganese-stained granules to cobbles composed mainly of carbonate that presumably has been derived from the high Canadian Arctic. The rise clasts are further distinguished in that they are finer grained, slightly more rounded and more altered by solution and/or boring organisms than their shallower water counterparts.

The upper slope gravel has been reworked from underlying sediments, and deposited from ice rafts, and both processes are probably continuing today. Gravel on the rise has been concentrated through winnowing of middle Holocene sediments by the Western Boundary Undercurrent which appears to have been operative as a winnowing agent since about 4,000 to 5,000 y BP.

The undercurrent has also affected the distribution of stained gravel which is most common and most intensely stained beneath a fast-flowing undercurrent core where environmental conditions resemble those documented for deep-sea, ferromanganese nodule fields.