CHAP. 34] THE PLEISTOCENE RECORD 905 



1959). Thus information from deep-sea sediments, pertinent to Pleistocene 

 history, lias been garnered largely from the foraminiferal component. 



Disregarding accessory components, normal Globigerina ooze consists essen- 

 tially of shells of pelagic and benthonic Foraminifera, coccoliths, Radiolaria, 

 diatoms and clay. Generally these various components amount to most of the 

 dry weight of the bulk sediment. Globigerina ooze accumulates at rates varying 

 from less than a centimeter to several centimeters per thousand years, depend- 

 ing upon rates of supply of the various components from the water column 

 above, and upon bottom conditions such as currents, morphology and post- 

 depositional solution. Following the invention of the j)iston corer by Kullenberg 

 (1947), sections of deep-sea sediments as long as 20 m or more were obtained 

 from the ocean floor. In the absence of a reliable method of dating Globigerina 

 ooze beyond the range of the ^sipa-SSOTh method (about 200,000 years), cores 

 showing sedimentary disturbances are difficult to use for the reconstruction of 

 Pleistocene events, because a sedimentary section representing unknown time 

 may have been added or removed by each disturbance. Elisions are most 

 common on the to]3s and steep sides of deep-sea mounds, whereas additions 

 occur on the floors of depressions. Thus, the most convenient place to sample 

 the ocean bottom for undisturbed sections are the sides of gentle deep-sea 

 mounds. 



Research on Globigerina ooze cores that seem undisturbed upon megascopic 

 inspection revealed that major unconformities are common in deep-sea sedi- 

 ments, especially in the Atlantic basin. Thus many of the long Globigerina 

 ooze cores that have been described in detail show at least one major un- 

 conformity, below which older Pleistocene, Tertiary or even Cretaceous sedi- 

 ments occur (cf. Ericson et al., 1961). Indeed, the stratigraphically longest core 

 so far described from the Atlantic and adjacent basins, containing no major 

 unconformities, is a core from the central Caribbean which is only 9 m long. 

 Major unconformities seem to be absent from a suite of five eastern-equatorial- 

 Pacific cores described by Arrhenius (1952). Two of these cores (nos. 58 and 62) 

 may reach back in time about a million years through continuous sedimentary 

 sections. Unfortunately these cores do not seem to be as easy to interpret 

 from the point of view of Pleistocene events as the Atlantic cores, as explained 

 below. 



Globigerina ooze does not accumulate below 4800 m in the Atlantic and 4300 m 

 in the Pacific, where post-depositional solution of the carbonate material is 

 already important. The depth at which post-depositional solution becomes 

 appreciable may have varied during the Pleistocene in response to climatic 

 changes, especially in the Atlantic and adjacent seas where significant tem- 

 perature changes of the bottom water have been noticed (Emiliani, 1955, 1958). 

 During the Tertiary, when the bottom temperature of the oceans was higher, 

 Globigerina ooze accumulated in some of the areas where only red clay has been 

 accumulating during the Pleistocene (Revelle et al., 1955). 



Globigerina ooze, which accumulates largely on aerobic bottoms, is constantly 

 reworked by bottom organisms. The sedimentary thickness affected by this 



