CHAP. 33] THE PRESERVED RECORD: PALEONTOLOGY OF PELAGIC SEDIMENTS 



871 



the relation between diatom species and assemblages and the main water 

 masses of the oceans. Cleve (e.g. 1900) was one of the first of a series of European 

 workers to show that different diatom assemblages are associated with the 

 different water masses of the North Atlantic. Hendey (1937) distinguished cold- 

 water and warm-w^ater floras in the near-surface waters of the Southern Ocean 

 and reported a relation between physical and chemical conditions of the en- 

 vironment and the morphology of diatom frustules; and Hustedt (1958) 

 investigated some of the South Atlantic and Antarctic diatoms in greater 

 detail. Semina (1958) and Karohji (1959), investigating plankton diatoms from 

 the northwest Pacific, traced a pronounced difference between the boreal 

 assemblage of the colder northern water and the warm-water assemblage of the 

 Kuroshio. In his study of the sediments of the tropical parts of the Pacific, 



Fig. 3. Silicoflagellates from pelagic sediments, a-c, Eocene; d, e, Miocene. 



Atlantic and Indian Oceans, Kolbe (1957) found the warm-water assemblage to 

 be similar in the three oceans, and different from the assemblages characteristic 

 of high latitudes. 



C. Silicoflagellaies 



The living organism comprises a small, flagellated cell with an associated 

 siliceous skeleton of hollow bars which form a spiny ring, variable in form and 

 in most species simply reticulated (Fig. 3). Silicoflagellates occur in all parts of 

 the oceans, and although their skeletons are found in almost all sediments 

 containing diatoms, they never constitute a significant proportion of the mass 

 of pelagic sediments. As a result probably of the small size of these organisms 

 (generally 10-50 [x), little is known of their biogeography (Gemeinhardt, 1930). 



D. Foramiiiifera 



The chambered tests of these protozoans, generally about 50-1000 y. in size, 

 are the major component of the calcareous microfossils in Quaternary pelagic 

 sediments. Most of the tests accumulating on the deep-sea floor are of plank- 

 tonic species (Fig. 4) which inhabit i^rinciiDally the upper part of the water 

 column, to a dejjth of 100-300 m. Tests of benthonic sjiecies, some of them 



