STRATIGRAPHY OF THE DEEP-SEA FLOOR 67 



Table III. Properties of Lithified Globigerma Ooze" 



" Based on samples taken on the Scripps Institution-U. S. Navy Electronics Labora- 

 tory Expedition in 1950. Velocities determined by the California Research Corporation 

 at La Habra, California. 



expect that the depth to lithification in a clay section and in a 

 calcareous ooze section should be, in general, within the depth 

 limits of 150 to 700 m, with an average depth around 300 to 400 m. 

 Almost everywhere there is a top layer of low-velocity material 

 which lies, on the average, within the limits noted above. The 

 work of Hill (1952, 1957), Hersey et al. (1952), Officer (1955), 

 Katz and Ewing (1956), Xafe and Drake (1957), and others indi- 

 cates that there is a fast changing velocity gradient to around 

 300 m, below which the gradient is less. Thus, refraction and re- 

 flection horizons commonly occur at depths from 400 to 800 m in 

 Atlantic sediments (Nafe and Drake, 1957). In the Atlantic and 

 adjacent seas Ewing and Ewing (1959) noted transformation to 

 shear waves, and refraction and reflection horizons presumed 

 to have taken place from semiconsolidated layers within the sedi- 

 ment column. In the Arctic Basin reflection arrivals are from 

 depths of 250-300 m with a\'erage inter\'al velocities of 2.04 

 km/sec (Crary and Goldstein, 1957). In the Pacific, in the north- 

 east red clay area there is an average first layer thickness of 290 m, 

 but in the east central Pacific calcareous area it is 330 m (Raitt, 

 1956). A reflection horizon also occurred in the same area at depths 

 between 200 and 300 m (Shor, 1959). In all oceans investigated 

 Gaskell et al. (1958) showed the presence, or probability, of a 

 topmost layer of low velocity. In many areas there are thicker 

 sections of 1 km or more recorded; in all but a few of these de- 

 terminations the writers do not exclude the possibility of masked 



