STRATIGRAPHY OF THE DEEP-SEA FLOOR 71 



variations for a large number of dominantly shale sections, utilized 

 actual velocities from over seventy wells to form the Eocene and 

 Tertiary (post-Eocene) curves. In these the velocity increases from 

 about 2.1 km sec at 300 m to about 3.32 km /sec at 3000 m. 

 Because of the great amount of data in\^olved, they can be taken 

 as expectable variations of velocity with depth in Tertiary shale 

 sections. 



The previous discussion on consolidation, lithification, and 

 velocities now permits us to predict the situation present in a 

 noncalcareous, post-Cretaceous, clay section built up through a 

 long geologic 'time span. Throughout geologic time, a sediment 

 column, in an area of slow deposition, consolidation, and lithifica- 

 tion, would have, at the top of the column, about the same thick- 

 ness ot unlithified material. It has been shown that this would 

 ordinarily be of the order of 150 to 700 m with an average near 

 300 to 400 m. A natural consequence of this would be that the 

 thickness of the lithified portion of the column would gradually 

 increase while that of the topmost portion remained fairly constant. 



At the surface of the sediment the velocity should be of the order 

 of 1.5 km /sec (Fig. 8). The work of Nafe and Drake (1957) and 

 others in deep and shallow water indicates that the velocity gradi- 

 ent will increase with depth so that at about 300 m the velocity is 

 about 2.1 km /sec. Average velocity in the topmost, unlithified 

 section will be of the order of 1.8 km /sec. At about 300 m there 

 should be a conversion to shale (in line with our previous discus- 

 sions). There should be a lower, lithified section of clay shale which 

 varies greatly in thickness because it is being added to at the top 

 by the relatively constant-thickness upper layer. In this lower 

 layer the average \'elocity will \'ary according to the thickness of 

 the layer, but will be near 2.1 km/sec at the top as shown by 

 Faust (1951). It should be emphasized that these estimates are 

 only for a clay-shale section — any calcareous material will cause 

 the velocity to be higher. 



Two papers almost ideally illustrate the foregoing possibilities. 

 From studies by Officer and Ewing (1954) on the continental slope 

 south of Nova Scotia it can be seen that the velocities are much 

 closer to those expectable for a clay-shale section than for an un- 



