Abstract
Based on the X-ray diffraction analyses of 150 bottom samples from the area of the Atlantic Ocean influenced by the Amazon River, trends in the clay mineral composition were observed. For the < 2 micron size fraction of samples from the mouth of the Amazon River for a distance of 1,400 kilometers along the shelf, montmorillonite shows a trend increasing from 27% to 40%, the kaolinite decreases from 36% to 32%, and the 10A mica decreases from 28% to 18%. Chemical alteration of clay minerals accounts for very little of these trends. Differential flocculation is shown not to be an important mechanism probably because of natural organic and metallic coatings which give all the clay minerals similar flocculating properties. The study shows the dominant mechanism responsible for the laterally changing composition of the clay minerals to be the physical sorting of sediment by size.
