escarpment at 3,3°N. Profile 2 also shows an absence or severe 

 disturbance (the quality of the seismic record here is very poor) 

 between the axial valley (4.75°N) and 5.6°N and 3.8°N to the north 

 and south. Here again a short segment of intermediate sediment 

 thickness is seen to the south (between 3,4°N and 3.8°N). 



Profile 3 shows that the absent or disturbed sediment extends 

 southward to about 4°N from the valley at 5°N. Again there is some 

 indication of an intermediate thickness from 4°N southward to about 

 3.3 N. The northward extent of absent sediment seems to be 5.3°N. 



As indicated in Figure 5, on the western profiles horizon X is 

 only found well to the south of the axial valley, while Figure 4 

 shows that on the eastern profiles it can be traced to the trough from 

 the south, and continues northward of the trough (profiles 5 and 6). 



The area between profiles 3 and 4 (Fig. 4) seems to be the tran- 

 sition zone between the regime of undisturbed sediments flanking the 

 eastern trough, and absent or highly deformed sediments flanking the 

 axial valley to the west. As can be seen, there seems to be an area of 

 disturbed sediment extending about 30 km to the north and south of the 

 axial valley, but this does not compare to the 100 km or more missing 

 on profiles 1-3. Furthermore, the intermediate sediment thickness 

 zone does not appear on this profile or on those to the east (profiles 

 5-7). Profile 4 also shows a curious trough-like feature at 3.5°N, in 

 many respects similar to the northern trough. 



Figure 6 contrasts the thin sediment cover found on the northern 

 margin of the West Caroline Basin (profiles B and D) to the thick 

 sediments to the south (profiles E and F) . It also shows the rough 



16 



