80 
50 
40 
30 
20 
WEIGHT PERCENT OF TOTAL SAMPLE 
7. 
“210 2I 
0-I05 
>1000 
M4-2 
VA, M4--'6 
M4-5-2 
(Ga50 » GOES NOEL oe) OD 
SEDIMENT -SIZE CLASSES, IN pm 
Figure 10A.—Weight percent of sediment in different size fractions of bottom sediment collected on cruise 4 at control station 
2, regional station 16, and site-specific station 5-2 on Georges Bank. 
for the drilling mud components by a combina- 
tion of sedimentation, sediment mixing, and 
erosion. 
A future followup of this study should be under- 
taken to determine the Ba concentration and the 
Ba/AI ratio in profiles by using the bulk sample. 
Comparison of profiles of the bulk sample and the 
fine fraction is necessary to determine the amount 
of Ba that is missed by the standard field sampling 
technique of collecting the upper 2 cm of sediment. 
In addition, longer core samples (30-40 cm) should 
be taken at the drill sites to determine whether the 
decrease in Ba concentration in the surface sedi- 
ment is due to actual removal or to downward 
mixing. 
21 
BARIUM INVENTORY AND DECREASE AT BLOCK 312 
The high density of stations and the frequent 
sampling at the drill site in block 312 allowed us 
to estimate the inventory of barium in the sedi- 
ments before, during, and after drilling. One objec- 
tive of this exercise is to determine how much of 
the Ba actually discharged by the drilling rig was 
deposited within 6 km of the drill site at the time 
of well completion. We were particularly interested 
in an estimate of the rate at which Ba concentra- 
tions decreased in the surface sediments after drill- 
ing was completed. The barium added by the drill- 
ing can be considered to be a tracer for sediment 
transport processes. Although barium sulfate has 
