904 EMILIANI AND FLINT [CHAP. 34 



other components intimately mixed with it may have been largely or even 

 entirely derived from reworking. Generally, the relatively heavy shells of 

 pelagic Foraminifera can settle undisturbed on a given portion of the ocean floor 

 while the finer biogenous components (coccoliths, diatoms, Radiolaria), and 

 especially the much finer mineral particles settling at the same time through 

 the same water column, may be moved away by bottom currents and may be 

 replaced by similar components reworked from adjacent areas. In such cases 

 the reworked components are older than the undisturbed component or 

 components. 



The local factors which importantly affect marine-epicontinental sedimenta- 

 tion are integrated in the pelagic environment. The "background noise" is thus 

 greatly reduced and an undisturbed section of deep-sea deposits can yield 

 invaluable information on the conditions prevailing when the sediments were 

 being deposited. The conditions include those on the ocean floor, in the water 

 column above, at the ocean surface, in the atmosphere, on land areas, and 

 possibly on the sun and in the interplanetary space. In addition, the occurrence 

 itself of sedimentary disturbances (turbidity-current deposits, winnowing, etc.) 

 in a column of otherwise undisturbed deep-sea sediments may yield information 

 on the factors causing the disturbances. Thus, the repeated and extensive 

 occurrence of graded and non-graded layers of sand and silt in North Atlantic 

 cores (Ericson et al., 1952, 1955, 1961) which generally contain normal deep-sea 

 clays and oozes in their uppermost portions demonstrates that turbidity cur- 

 rents across the continental slope bordering the North Atlantic basin on the 

 west were far more frequent during the last glacial age than in postglacial time. 

 Totally undisturbed deep-sea sediments (that is, sediments in which all the 

 components are undisturbed as defined above) are probably a rare occurrence. 

 In cores oi Globigerina ooze in which the foraminiferal component is undisturbed, 

 the undisturbed character of the finer components (e.g. fine-carbonate fraction 

 and clay) can be considered as proved if parameters measured on these correlate 

 with similar or even different parameters measured on the foraminiferal com- 

 ponent. Thus the demonstrated correlation between Mg percentages in the fine- 

 carbonate component and paleotemperatures measured on the foraminiferal 

 component in deep-sea cores from the Caribbean shows that the fine-carbonate 

 component is undisturbed (Wangersky, 1958; Rosholt et al., 1961). 



The facility with which information obtained from the various sedimentary 

 components of undisturbed deep-sea cores can be interpreted varies greatly. 

 The foraminiferal record can be interpreted easily by the various methods 

 discussed below, while the record offered by clay mineralogy is still difficult to 

 interpret. This is unfortunate, because red clay accumulates at rates far lower 

 than those of foraminiferal oozes, and can be sampled to far greater ages than 

 the latter. The record offered by coccoliths, diatoms and Radiolaria is still 

 besieged by taxonomic difficulties and also by the facility with which the very 

 light skeletons and skeletal elements of these organisms can be reworked, not 

 only from neighbouring areas of the ocean floor but also from distant lands 

 (cf. Kolbe, 1954, 1955, 1957, 1957a; Riedel, 1957, 1959; Riedel and Bramlette, 



