82 



Areas of poorly-or moderately-sorted sediments on the 

 basin slopes below the shelf are more widespread than on the 

 shelf o Here the moderately-and poorly-sorted sediments are 

 generally in the areas of the finest sediment. Slumping and 

 sliding are important here and probably are responsible for 

 the existing sorting. The accumulation of Foraminifera as 

 the coarse fraction of sediments may alter the grain-size 

 distribution enough to cause moderate to poor sorting. In 

 addition, silt and flocculated clays may settle out together, 

 and yet represent a wide range of particle sizes. 



Sediment along the courses of the submarine canyons is 

 usually moderately or poorly sorted. This may be caused by 

 the movement of sediment through the canyons by slumping or 

 sliding, both along the axis and down the side slopes. 

 Relation of Sorting to Depth 



Figure 25 is a graph of the average and median of the 

 sorting coefficients by depth intervals. The variation of 

 the sorting of sediments with depth is similar to that of 

 median diameters. Generally, the arithmetic mean of values 

 in each depth range is greater than the median, which indicates 

 a wider spread of values toward poorer sorting, 



A peak occurs in the curve in the 51-75 foot range where 

 patches of moderately-sorted sediment are located. From this 

 depth to 175 feet the curve is fairly uniform. This depth 

 range is over that portion of the shelf where most present- 

 day sedimentation probably occurs. Another peak is noted in 

 the 226-250 foot interval. This is due to the poor sorting 



