266 



Sediments 



the anomalous samples are immediately 

 above or below the depth where hydrogen 

 sulfide first appears in the cores. 



Data to be presented in later sections indi- 

 cate that both Santa Barbara and Tanner 

 Basins contain higher percentages of easily 

 oxidized components of organic matter than 

 do other basins. Partial oxidation of these 

 materials has evidently exhausted dissolved 

 oxygen in interstitial waters and, because of 

 the absence of burrowing animals in at least 

 Santa Barbara Basin, new supplies of oxygen 

 are not made available. In other basins the 

 slow rate of accumulation of organic matter 

 relative to inorganic sediments and the pres- 

 ence of burrowing animals result in more 

 complete loss of the easily oxidized compo- 

 nents of organic matter, without exhausting 

 the supply of dissolved oxygen in interstitial 

 water until enough time has passed that the 

 organic matter is buried to a depth of sev- 

 eral meters. Lack of dissolved oxygen in 

 interstitial water, or negative Eh there, rep- 

 resents a hostile environment for burrowing 

 and possibly for small surface-living animals 

 and for aerobic bacteria. Thus a mutual 

 interrelationship exists between animals and 

 oxygen content such that as long as the ox- 



ygen content permits burrowing animals to 

 Uve, their stirring activities increase the 

 oxygen content and this oxygen plus the in- 

 gestion of sediment markedly reduce the 

 organic content of the sediments. Probably 

 a decrease of oxygen to a level just below 

 the threshold value for burrowing animals 

 would produce an immediate catastrophic 

 decrease in oxygen content to zero values 

 that would cause difficulty in repopulating 

 the bottom. 



A plot of /jH against Eh for 23 well-dis- 

 tributed basin cores (Fig. 215) shows that 

 the points occupy a rather restricted area 

 with a general tendency at depth for pYi to 

 increase and Eh to become more negative. 

 In contrast, values from marshes, chiefly in 

 Newport Bay (Fowler, 1957; Stevenson and 

 Emery, 1958), are more widely scattered 

 but are usually of lower /jH than the basin 

 sediments. There is some slight overlap 

 with values for sea water, which generally 

 is of more positive Eh than are the sedi- 

 ments. Comparison with similar plots and 

 other data of Krumbein and Garrels (1952) 

 shows several fields of apparent chemical 

 stability in the basin sediments. For ex- 

 ample, the stable forms of iron should be 



^ SEA WATER 

 • BASINS 

 " MARSHES 



Figure 215. Interdependence 

 of /)H and Eh in basin (dots) 

 and marsh (circles) sediments 

 and in the overlying sea water. 



pH 



