topographic high with a central valley and a gradual increase in 

 sediment thickness away from the high. If one can use the mean 

 sediment accumulation rates (Winterer and others, 1971) for the two 

 DSDP sites (62 and 63) during the past 15 m.y. (20m/m.y.) as repre- 

 sentative of accumulation rates throughout the Caroline Basin, then the 

 sediment thickness in the oldest part of this spreading area should 

 be about 300 meters. This agrees quite well with the seismic data. 

 On the other hand, the eastern profiles show a trough, in some cases 

 flanked by ridges, with relatively thick sediments extending up to, 

 and in some cases into, the trough. (2) Horizon X is absent in the 

 western profiles for some distance both south and north of the topog- 

 raphic high. In the east, on the other hand, it can be traced to 

 the trough from the south, and in some cases, to the north of the 

 trough. 



As pointed out by Vogt and others (1969), spreading discon- 

 tinuities such as those exhibited in this area may result from one or 

 more of the following processes: (1) Total stoppage and later reacti- 

 vation of a spreading center; (2) shift in the ridge axis; (3) change 

 in spreading rate; (4) change in spreading direction, and (5) change 

 in the mode of spreading (from normal to oblique) . From among these 

 causal mechanisms, no one can be selected with any degree of certainty 

 as the cause of the West Caroline Basin discontinuities. The sharp 

 change in sediment thicknesses across both the old-intermediate and 

 intermediate-young boundaries certainly indicate a drastic reduction, 

 if not a complete stoppage, in spreading rates, and are remarkably 



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