CHAP. 33] THE PRESERVED RECORD: PALEONTOLOGY OF PELAGIC SEDIMENTS 



883 



samples obtained are disconformably overlain by a relatively thin Quaternary 

 cover. Apart from the Cretaceous and Paleocene on mid-Pacific seamounts 

 (Hamilton, 1956), the oldest known pelagic sediments from the Pacific Ocean 

 basin are two Middle Eocene outcrops on the Tuamotu Ridge (Riedel and 

 Bramlette, 1959). Eocene sediments have been reported in the Atlantic (Heezen 

 et al., 1959), and are believed to crop out also on the floor of the Indian Ocean 

 (Wiseman and Riedel, 1961). 



Fig. 12. Comparison of Quaternary (above the line) and middle Tertiary (Oligocene to 

 Lower Miocene, below the line) sediments at some localities ( x ) on the Pacific floor. 

 calc. = calcareous (microfossils); silic. = siliceous (microfossils); oz. = ooze. 



The spacing of the Tertiary pelagic sediment samples of any given age which 

 have been collected to date is not sufficiently close to permit drawing any but 

 the most generalized paleoceanographic conclusions. Certain interesting con- 

 clusions can be drawn, however, even from the gross microfossil content of 

 isolated Tertiary samples. Fig. 12 indicates the positions at which middle 

 Tertiary (Oligocene to Lower Miocene) sediments have been encountered in the 

 Pacific Ocean, and the nature of these middle Tertiary sediments at each 

 locality as compared with the type of sediment at present being deposited there. 

 It will be noticed that the contribution of calcareous microfossils at many 



