31. CROSS-CORRELATION OF DEEP-SEA SEDIMENT CORES 



AND DETERMINATION OF RELATIVE RATES OF SEDIMENTATION 



BY MICROPALEONTOLOGICAL TECHNIQUES i 



D. B. Emcsoisr 



1. Introduction 



The new era in the study of deep-sea sediments which opened with the 

 invention of the piston corer by Kullenberg (1947) has taught us many things. 

 We now know that uninterrupted slow particle-by-particle accumulation should 

 never be taken for granted. On the contrary, experience at Lamont with 

 hundreds of cores has shown that when a core is taken without regard to bottom 

 topography it is more likely than not to contain evidence of slumping or catas- 

 trophic deposition by turbidity currents. Often the evidence for such interrup- 

 tions of orderly sediment accumulation is clear enough, as for example when the 

 normal sequence of foraminiferal lutite is broken by a layer of graded sand 

 containing parts of organisms of shallow- water origin. At other times, and 

 particularly when a part of the section has been removed by slumping, there is 

 no hint from the gross lithology of the core that the section is incomplete. This 

 is not surprising in view of the lithological uniformity of the Pleistocene section 

 and the mixing or blurring effect of burrowing by mud-feeders. How then is the 

 student of the deep-sea record of Pleistocene climatic changes to distinguish 

 between complete and incomplete records? The only satisfactory way of avoid- 

 ing confusion is to study suites of cores and to persist until layer-by-layer 

 correlations have been established between several cores. 



As a by-product of the cross-correlation of cores from the North Atlantic, 

 evidence has emerged that rates of sediment accumulation may vary greatly 

 from place to place apparently quite without the intervention of turbidity 

 currents. The plausible and virtually proven explanation is that deep oceanic 

 circulation, contrary to older ideas, is a fairly effective agent in the horizontal 

 transportation of fine sediment. This opens up the possibility of determining the 

 general direction of deep circulation wherever there are cores adjacent to a 

 seamount whose top has been swept by deep currents. An even more interesting 

 possibility is that of detecting changes in direction and velocity of deep circula- 

 tion during the Pleistocene and in connection with climatic changes. 



2. Methods of Correlation 



The stratigraphy of Pleistocene deep-sea sediments is pecuhar in its small scale 

 not only in the vertical dimension but also in the time dimension. For example, 

 the deep-sea stratigra])her must establish the time equivalence of zones which 

 are often no more than a few decimeters thick. Because of the short time inter- 



1 The laboratory work upon which this report is based was supiDorted by research 

 grants G4174 and G6540 from the National Science Foundation. 

 Lamont Geological Observatory Contribution No. .589. 



[MS received June, 1960] 832 



