906 EMILIANI AND FLINT [CHAP. 34 



mixing is believed to range from a few to several centimeters, and corresponds 

 to a time span of a few thousand years. The time resolution of the events re- 

 corded by the sediment is thus decreased to a few thousand years, from a 

 theoretical limit of only a few years. The loss of resolution is inversely propor- 

 tional to the rate of sedimentation, being greatest for the more slowly accumu- 

 lating sediments. Therefore undisturbed sediments accumulating at higher 

 rates generally yield a record of comparatively greater detail. 



Stratigraphic study of Globigerina ooze cores involves a variety of methods. 

 Of direct interest to Pleistocene research is the study of those parameters which 

 have been most affected by repeated glaciation of the continents. These para- 

 meters are the micropaleontology of the pelagic foraminiferal faunas; the 

 oxygen-isotopic composition of foraminiferal shells; the weight percentage of 

 Foraminifera relative to bulk sediment (possibly only in the Atlantic and 

 adjacent seas); and calcium-carbonate percentages (only occasionally). 



The living species of pelagic Foraminifera number about 25, of which 15 are 

 common. Spectrographic and X-ray analysis of 1 1 species showed that the shell 

 material is nearly pure calcite with only about 0.11% of strontium (Emiliani, 

 1955b). A small amount of organic material is also present. The common 

 species can be grouped as follows with respect to temperature preferences (data 

 from Phleger et ah, 1953; valid for the Atlantic and possibly also for the other 

 oceans; cf. Bradshaw, 1959): 



1 . Species abundant in low latitudes : 



Globigerina eggeri 

 Globigerinoides sacculifera 

 Globorotalia menardii menardii 

 Globorotalia menardii tumida 

 PuUeniatina obliquiloculata 



2. Species abundant in middle latitudes: 



Globigerina bulloides 

 Globigerina inflata 

 Globorotalia hirsuta 

 Globorotalia scitula 

 Globorotalia truncatulinoides 



3. Species abundant in high latitudes: 



Globigerina pachyderma 



4. Species abundant in both low and middle latitudes: 



Globigerinella, aequilateralis 

 Globigerinita glutinata 

 Globigerinoides conglobafa 

 Globigerinoides rubra 

 Orbulina universa 



