SECT. 3] 



PELAGIC SEDIMENTS 



691 



Recent deep-sea sediments have been observed in several instances, both in the 

 Pacific (Bramlette, unpublished) and in the Atlantic (Correns, 1937; Radczew- 

 ski, 1937). Extensive dolomitization is observed to occur at the interface of 

 basaltic intrusions, such as the one encountered in the experimental Mohole off 

 Guadalupe Island. 



CaCO, 



4000 



00% 



5000 



6000 

 m 



Fig. 20. Average carbonate content as a function of water depth in the Atlantic and 

 Pacific, demonstrating the effect of total rate of deposition on the rate of solution of 

 calcium carbonate at the ocean floor. Under similar depth conditions the ultimate 

 carbonate content of the sediment is, on the average, higher in the Atlantic than in 

 the Pacific. This is due to more rapid burial of the sediment in the Atlantic Ocean, 

 which, per surface area, receives considerably more solid and dissolved material from 

 the continents than does the Pacific. (From Revelle, 1944.) 



Much detrital carbonate appears to be carried by wind into the pelagic 

 environment. Calcite and dolomite are often the dominant components of 

 eolian dust, which occasionally also contains small amounts of breunnerite 

 (Radczewski, 1937). In Mediterranean sediments, calcite is the dominant 

 eolian material (Norin, 1958). In deep pelagic sediments most of the fine-grained 

 eolian calcite is dissolved, but in areas with a heavy eolian fallout and a high 

 preservation of accumulating carbonates, eolian calcite and dolomite might be 

 quantitatively important. 



