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



869 



Hasle (1959) have reported that the numbers of coccolithophorids in the upper 

 100-200 m of tropical to subantarctic waters are of the order of thousands/ml. 

 Bramlette (1958) estimated that in typical Quaternary calcareous ooze fi-om 

 the tropical Pacific, coccolithophorids constitute 10-15% of the total calcium 

 carbonate of the sediment, and that in many early Tertiary calcareous oozes 

 and chalks, coccoliths and related forms account for about 50% of the total 

 calcium carbonate. In recent years it has come to be generally recognized that 

 practically none of the calcium carbonate in deep-sea sediments is of inorganic 

 origin^electron microscope examination has revealed that the fine-grained 

 calcium carbonate previously loosely described as "impalpable" is formed 

 principally of fragments of coccolithophorids. "Coccolithophorids" in this 

 context is used to embrace the true coccolithophores, known from plankton 



e 



f 



g 



Fig. 1. Coccolithophorids and related forms, a-c, discoasters; d, pentalith of Braarvdo- 

 sphaera; e, f, rhabdoliths; g, h, coccoliths. 



samples, and other small calcareous bodies which are inferred to have been 

 formed by rather similar organisms. Quantitatively the most important of 

 these microfossils of uncertain affinities are the discoasters (Fig. la-c) — usually 

 flat, stellate bodies of approximately the same size as coccoliths, formed by a 

 group of organisms which are believed to have become extinct at about the end 

 of Tertiary time. 



Although information on the distribution of species is difficult to obtain 

 because of the difficulty of routine species identifications, Hentschel (1936) was 

 able to recognize different associations of coccolithophorids characteristic of 

 diff"erent water masses of the Atlantic. Preliminary results of Hasle (1959) 

 indicate that some of the species in Pacific plankton can be distinguished as 

 warm- water forms and others as cold-water forms, and that different species 

 live at different depths, at least within the upper 150 m in the equatorial 

 Pacific. Much more work on Recent plankton is required, however, before it 

 will be possible to make ecological interpretations of the abundant members of 

 this group in sediment cores. 



