SECT. 3] CKOSS -CORRELATION OF DEEP-SEA SEDIMENT CORES 837 



A . The Equatorial Suite 



Fig. 1 shows the positions of the cores, and Fig. 2 shows the faunal zones in 

 the cores in graphic form. The temperature or chmatic curve (heavy hne) is based 

 upon the abundance of Glohorotalia menardii and other temperature-sensitive 

 species. The subspecies G. menardii flexuosa (Koch) is especially abundant in 

 the flexuosa zone. Thus the heavy line represents primarily fluctuations in 

 faunal composition. In drawing the graphs these fluctuations have been 

 translated into climatic terms. Here it should be emphasized that the variations 

 in faunal composition are very strikingly apparent; their detection does not 

 depend upon careful counts or complicated statistical methods. For example, 

 the contrast between washed samples of Foraminifera from the uppermost zone 

 of "cold" climate and samples from the flexuosa zone is such that the difference 

 can be seen easily without taking the samples out of the vials in which they are 

 stored. The dashed line labeled "Top of Pulleniat. ohliquiloc. zone" in the 

 diagram of core V9-28, Fig. 2, marks the level in the cores above which the 

 planktonic species Pulleniatina obliquiloculata is rare (1-5 tests) or absent. 

 Below this level the species is very abundant ( > 100 tests in each sample). It 

 is again abundant in the uppermost post-glacial layer of these same cores. 



The light line representing coiling percentages of Glohorotalia truncatulinoides 

 has been drawn only where there is strong deviation to the left. Elsewhere in the 

 cores coiling is consistently between 90 and 100% to the right. Apparently twice 

 during the past 100,000 years a boundary between provinces of right and left 

 coiling dominance has swept back and forth across the equatorial region. If the 

 boundary line was essentially parallel to the core profile, it must have crossed 

 the positions of the various core stations at about the same time. If, on the other 

 hand, it moved from east to west and the rate of movement was slow, it must 

 have passed successively over the stations at appreciably different times. But 

 in that case the zones of left coiling in core A 180-72 would be thicker than the 

 corresponding zones in core V9-28, because station A 180-72 would then have 

 lain within the left coiling province an appreciably longer time than station 

 V9-28. Since no difference in thickness is discernible, we conclude that move- 

 ment of the boundary across all the stations took place virtually "instan- 

 taneously" or occupied a time interval which was so short as to be inappreciable 

 in terms of sediment accumulation at these stations. From this we infer that the 

 coiling zones in these cores are for practical purposes isochronous. 



Clearly evident in this suite of cores is the small variation in rate of sediment 

 accumulation from station to station. The almost exact equivalence of rates at 

 the extreme stations, Al 80-72 and V9-28, is particularly striking. This, together 

 with the fact that three other cores show closely similar rates, makes us believe 

 that, in these cores, we have examples of orderly accumulation by vertical 

 settling of particles with little or no interference from horizontal transportation. 

 Extrapolation of radiocarbon dates in various cores (Ericson and Wollin, 

 1956) and one direct dating by the ionium method (Urry, 1948) show that the 

 interval of warm climate represented by the flexuosa zone came to an end 



