Abstract

Sediment from short cores taken on the continental rise off Georges Banks show two facies which are best distinguished by clay mineral ratios. The green-gray material in the upper, Holocene section of the cores is carbonate and amphibole rich and has a montmonllonite/illite peak-area ratio which typically is greater than one. These characteristics serve to distinguish the upper facies from the red-brown Pleistocene sediment of the lower core section in which illite is the dominant clay mineral.

The clay mineralogy of the Pleistocene facies is consistent with a source in the Permo-Carboniferous red-bed area of the Canadian Maritime Provinces. This red lutite, which acts as a tracer for bottom current movement, was entrained on the continental rise by the Western Boundary Undercurrent and transported southwestward along the regional contours. The coarse fraction of this facies probably originated in down-slope processes along the entire continental margin under a regime of lower sea level and as ice-rafted debris.

The upper, Holocene facies cannot be linked o t any specific continental source, but it appears to have the sediment of the Labrador Sea as its immediate source. The montmorillonite-rich lutite is transported to the south parallel to the regional contours by the Western Boundary Undercurrent. The carbonate component consists of coarse Foraminifera which originate in the warm Gull Stream.

The character of the sediment and measurement of the predominant direction and speed of the bottom currents indicate that the Western Boundary Undercurrent is a significant factor in sediment transport and deposition on the east coast continental rise. A dispersal system parallel to the regional slope is confirmed to be operative for the fine sediment.

First Page Preview

First page PDF preview
You do not currently have access to this article.