586 KAPLAN AND RITTENBERO [CHAP. 23 



phosphorus is Hberated. This value agrees reasonal)l,\ well with what one would 

 calculate on the basis of the mineralization of plankton of average composition. 

 The assum])tion has been made (Redfield, 1958a) that phosphate release occurs 

 as a result of decomposition of photosynthetic organisms in the water column, 

 ])robably by bacterial action. However, using average values given by Caspers 

 (11)57. ])p. 821, 823) for oxygen, H2S and P2O5 with depth, it is possible to 

 obtain a range of values for the oxygen equivalents to ])hos])horus ratio, and a 

 I'atio of a])])roximately 1)00 is obtained from average data for stagnant fjords 

 (Fleming and Revelle, 1931)). It is suggested here, and elaborated on more fully 

 in the section on diagenesis, that phosphorus release, in some areas at least, 

 occurs most actively at the mud-water interface. 



2. Physical Aspects of Sedimentation 



A. Sediment Types 



In discussing sediment types we will follow the suggestion of Emery (1952) 

 that the sediments in the neritic environments, particularly the continental 

 shelf, be given a generic classification according to the dominant cause of de- 

 position. The principal sediment types thus classified are listed below with 

 brief comments. Although the relative importance of each is largely a local 

 phenomenon, the importance in present day basin sedimentation generally 

 increases toward the last mentioned, 



a. Eolian 



These are wind-borne deposits of silt to fine sand that may be of particular 

 importance in regions where sand dunes are well developed along a coast or 

 where deserts reach the ocean. Visual observation of this means of deposition 

 was made by Darwin (1887), and more recently Rex and Goldberg (1958) 

 showed such an origin for certain deep-sea sediment components. Eolian sand 

 grains would jjrobably be well rounded and distinguishable from other sedi- 

 ments; Eolian silts would be difficult to recognize on this basis. 



b. Volcanic 



There are a limited number of locations where vulcanism occurs directly 

 adjacent to neritic areas. Basins in the vicinity of such areas, namely Iceland, 

 Alaska, New Zealand, Japan and Southeast Asia, could receive considerable 

 volcanic contribution. Volcanic ash was described by Kuenen (1943) and Neeb 

 (1943) from many of the Moluccan basins, and more recently by Worzel (1959) 

 in the east Pacific. 



Ash from submarine vulcanism may also contribute to basin sediments. 

 Submarine seepage of hot springs may be responsible for chemical deposition 

 of lime, silica or even manganese (Niino, 1959); these are more properly classi- 

 fied under authigenic sediments. 



