EWING: ACOUSTIC PROPERTIES OF THE SEA FLOOR 



the middle of the ocean where there are less than 100 meters of sedi- 

 ment. The stippled area on either side has more than a kilometer of 

 sediment. Close to the continental margins on either side are as 

 much as 5 or 6 kilometers of sediment. 



Figure 6 is a similar display for the North Pacific Ocean. In 

 this area, and in several other localized areas, we now have more 

 detailed charts but this shows the general distribution. As in the 

 Atlantic, we find little sediment, less than 100 meters, in broad 

 areas. Sediments in the northeastern part are much thicker because 

 of a great addition of turbidite sediments (detrital sediments) . 

 There is a nice thick belt of sediments along the equator caused by 

 upwelling of deep water and high biogenic productivity. In the 

 western Pacific, we find a distinct case of a two-layer situation 

 with a thin layer of soft sediment overlying a much thicker layer of 

 very hard sediment, the hard sediment being a cherty limestone. 



Figure 7 shows the results of one of the JOIDES holes in the 

 western Pacific where we paid particularly close attention to several 

 factors. The reflection profile is traced on the right and next to 

 it are shown interval velocities. The lithologic section that was 

 cored is in the middle. This is a hole about 1,200 meters deep. 

 The heavy trace on the left is a plot of the age of the sediment 

 down the hole in millions of years. The dashed trace is the drilling 

 record in terms of drilling time in minutes per meter. 



We got nice correlations in the drilling record with the reflec- 

 tors at about 600 meters and 800 meters. Most of the upper 600 meters 

 of the section is just ooze, a microfossil ooze. At 600 meters, an 

 exceedingly sharp interface occurs where chert (flint) layers have 

 developed. This interface represents the rather abrupt transition 

 between soft sediment, that you can make a mud ball out of, and these 

 very hard chert layers that you can make arrowheads out of . 



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