frequency motions varied along the canyon axis (Figure 6). There was a clear 

 increase in high-frequency (2 to 10 hr) motions toward the canyon head. The 

 Lydonia Canyon region is one of the few areas of the shelf where all 

 frequencies are important in describing the system. 



SEDIMENT TRANSPORT 



Distribution of surficial sediments and high-resolution seismic 

 reflection data suggests that very fine sand and silts and clays accumulate in 

 the head of Lydonia Canyon and on areas of the adjacent shelf. There is 

 little silt-plus-clay on the crest of the bank where currents are strong, but 

 as much as 75 percent of the total sediment is located on the slope where 

 currents are weaker (Figure 6). The data suggest a depositional environment 

 surrounding the canyon head. 



Silt-plus-clay content in the surficial sediments generally increased 

 with depth along the canyon axis (Figure 6). This overall trend was 

 interrupted at 300 to 400 m, where there is 30 to 40 percent silt-plus-clay. 

 At 500 m, sediments get coarser. Finally, farther down the canyon, sediments 

 get finer again. These distributions mirror current strengths: coarse 

 sediments where currents are strong, fine sediments where they are weaker. 

 However, current, sediment trap, and beam attenuation measurements show that 

 surficial sediments are reworked and suspended along the canyon axis to a 

 water depth of at least 600 m. Thus, although the texture suggests that fine 

 sediments may be accumulating, the axis is not tranquil at depths less than 

 600 m. 



The Georges Bank canyons are complex topographically, with steep walls 

 that are vertical in places. One must consider not only sediment types on the 

 canyon floor but also on the walls, which change in character from the deeper 

 to the shallower parts. 



Near-bottom current measurements on the slope from Baltimore Canyon to 

 Georges Bank (Csanady et al . 1988) show that, below 500-m water depth 



15 



