RATE OF SEDIMENT ACCUMULATION 



The following discussion is based on radiocarbon dating of the TOTO sediments 

 by Ostlund et_a]_(1962) and data presented by Rusnak and Nesteroff (1962). 



Figure 10 shows the location of a few of the cores dated and the bulk rate of 

 sediment accumulation at these locations. Figure 11 gives the frequency of turbidity 

 current flows at selected locations. 



According to Ostlund et aj_(1962) the rates of sediment accumulation in the TOTO 

 are generally highest on the~bank slopes. Those deeper-water cores that show a rela- 

 tively high rate of accumulation are from the narrower sections of the channel, and, 

 therefore, tend to show a thicker accumulation for a given volume of supplied sediment 

 than is found in the broader reaches of the basin. 



The oldest sediment dated by Ostlund et_a_l_ (1962) in the TOTO was 26,275 years 

 ±570 years and was between 132 to 137 centimeters depth in the core. According to 

 a time scale presented by Ericson et aj_(1961) this date lies within the last glaciation. 

 Ericson et_a_l_ (1952) reported that Cretaceous sediments overlain by Pleistocene and 

 Recent sediments were encountered in a core taken at 3,383 meters just north of New 

 Providence Island. The authors accounted for the absent series by turbidity current 

 erosion of exposed Cretaceous sediments at a point not far from the core location. 



Sediments in the central area of the TOTO, apparently laid down through particle- 

 by-particle deposition, were termed by Rusnak and Nesteroff as pelagic sediments, and 

 they calculated a very slow rate of accumulation for this type sediment. The slow rate 

 of pelagic sediment accumulation becomes apparent by comparing the bulk sediment 

 accumulation per 1,000 years at various locations in Figure 10 against a range of 1 .5 

 to 3.0 centimeters per 1,000 years accumulation attributed to pelagic type sediments. 

 The balance of the sediments not accounted for by partlcle-by-particle deposition 

 during a 1,000 year period is assigned to turbidity currents. Frequently the turbldltes 

 are considerably older than the sediments over which they lie, indicating that an 

 accumulation of reef-derived and pelagic material builds up on the upper slopes of 

 the near-flank area, and, through various causes. Is released to flow down slope on 

 top of the material deposited contemporaneously with the buildup of near-flank 

 accumulations. 



From Figure 10 the rate of sediment accumulation can be seen to diminish north- 

 ward along the channel axis; likewise, frequency of turbidity current occurrence also 

 diminishes in the same direction (Fig 11). Consequently, as the present channel floor 

 continuously slopes in a direction coinciding with decreasing sediment accumulation, 

 it Is expected that the slope of the channel floor is in large part a deposltional gradient^ 

 rather than due primarily to some underlying structural mechanism. 



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