Basins and Troughs 



235 



Table 1 8 



Chemical Composition of Sediments Expressed as Oxides, 



PER CENT 



pa U S 



CQ H 



iH rt o ■» 



.5 O " - 



c« 



(^ c3 O ^ 



■5 



C/3 



■ rl- ro 



C/D -g ^ 



S t" ii 



.S e^ u 



*i ^ l-< 



S ^ c) 



O r ) U 



ON 



2s 



5 S 



SOS 



ii 3 cL 



u ^ e 



ili 0) CS 

 00 w — 



c 



TD =^ :2 



O "S c 



D C ns 



t^ O c« 



O oi - 



£,ON fN 



y c 3 



CQ Oi <N 



2 «{ S 



■o c — 



- u a. 



O w2 



J3 on 



C/5 -^ 



sections of many still-wet core samples were 

 assigned color symbols using the National 

 Research Council's Rock-Color Chart de- 

 veloped by Goddard and others (1948). 

 Nearly all the color measurements fell in 

 the range between 5 7 3.5/2 [5 7 = hue, 

 3.5 = value (lightness), 2 = chroma (satura- 

 tion)] and 3G7 4/3. However, some sam- 

 ples from Santa Monica Basin were assigned 

 to the color region near 4BG 3/1. Few of 

 the "values" were higher than 4 or lower 

 than 3, and the "chromas" ranged between 

 1 and 3. These colors might best be de- 

 scribed as gray yellow-green to gray bluish- 

 green. No relationship to oxidation-reduc- 

 tion potential or to hydrogen sulfide was 

 evident; in fact, the bluish-green cores were 

 the only ones free of hydrogen sulfide 

 throughout. When the muds are dried, the 

 only obvious color change is one of value, 

 which increases about two points (becomes 

 lighter). When wetted again, the color re- 

 turns approximately to the original. 



Sediments of all the basins off southern 

 California are green, they are high in calcium 

 carbonate, hydrogen sulfide is present in 

 some sediments at the surface or at least at 

 depth but it does not influence the color, 



the basins are areas of somewhat restricted 

 circulation, and the coast is bold with few 

 rivers. Thus it is evident that the character- 

 istics of Blue Mud and Green Mud as indi- 

 cated by Murray and Renard are not defini- 

 tive or even mutually exclusive, a conclusion 

 that has been reached in other studies of 

 marine sediments. As suggested by Revelle 

 (1944, p. 15), these names should not be 

 used any longer as genetic terms but only 

 as descriptive of the actual color of muds. 

 In this sense all the fine-grained sediments 

 off" southern California must be termed green 

 muds. 



Among the factors usually considered as 

 yielding the greenish color of many marine 

 sediments are clay minerals, fine-grained 

 green minerals such as glauconite and 

 chlorite, reduced iron, and pigments. The 

 latter, pigments, is most easily eliminated as 

 a factor because little or no color change 

 could be detected in sediment samples after 

 more than 90 per cent of the green pig- 

 ments had been extracted during laboratory 

 studies of the distribution of green pigments 

 (Orr, Emery, and Grady, 1958). Fine- 

 grained glauconite has not been reported in 

 the basin silts and clays, although sought by 



