236 



Grim, Dietz, and Bradley (1949). Chlorite 

 is present in some analyses but is not abun- 

 dant. Probably far more important are the 

 clay minerals, illite and montmorillonite, 

 which together make up the bulk of the sed- 

 iment. Both may be green, and according 

 to Grim (1951) and Keller (1953) both are 

 responsible for the green color of many 

 shales. 



It is possible that some contribution to the 

 green color may be made by some ferrous 

 iron compound, but probably the chief color 

 effect of iron is in providing a red masking 

 effect at the sediment-water interface. Sedi- 

 ment at this position for a variable thickness 

 of 1 to 10 mm is soft, mobile, and brown. 

 Because this sediment is in contact with the 

 overlying water containing dissolved oxygen, 

 its iron can be present partly as a hydrated 

 ferric oxide (Strakhov, 1958). Later, when 

 this layer becomes buried a few centimeters, 

 it reaches a reducing environment and its 

 iron changes to a ferrous form, such as the 

 siderite reported by Grim, Dietz, and 

 Bradley (1949) to be present in the basin 

 sediments. The iron would then lose its red 

 color and allow the normal green of the clay 

 minerals to dominate. Supporting evidence 

 for this role of iron is the development of a 

 brown surface on samples of green mud 

 stored for a few days or weeks in incom- 

 pletely filled bottles and its easy removal by 

 treatment with stannous chloride. 



Deep-Sea Floor 



Only a few cores have been taken from 

 the deep-sea floor in the area of Chart I be- 

 yond the base of the continental slope, but 

 these are of interest because of their con- 

 trast to sediments of the continental border- 

 land. The sediments are red clay that is 

 typical of red clays elsewhere on the Pacific 

 Ocean floor (Table 12). One core, represent- 

 ing 5 meters of section, is uniform through- 

 out in general appearance — fine grain size, 

 high/'H, positive Eh, and low contents of 

 calcium carbonate and organic matter. 

 Another, 1 meter long, is red clay at the 

 bottom but is capped by 15 cm of gray mud 

 beUeved to be a turbidity current deposit 



Sediments 



from shallower water. Globigerina ooze 

 has been reported nowhere in abyssal depths 

 in the region, but it does occur in impure 

 form at several locaHties sampled near the 

 top of the continental slope. Since deep- 

 sea deposits are outside the field of concen- 

 tration of this study, the interested reader is 

 referred to the foUowing papers on deep-sea 

 sediments: Revelle (1944), Arrhenius (1952, 

 in press), Menard (1955), Revelle, Bramlette, 

 Arrhenius, and Goldberg (1955), and Gold- 

 berg and Arrhenius (1958). 



Source 



Sediments on the sea floor off southern 

 California are restricted to the following 

 possible sources: streams, wind, sea cliff 

 erosion, organic remains, and chemical 

 precipitates. The first three of these sources 

 are terrestrial and the last two marine. Even 

 though most of the computations must be 

 only approximations, estimates of the quan- 

 tities of sediment supplied by the various 

 sources are needed in order to be able to de- 

 termine their probable order of importance. 



Sediment supplied to the ocean by wind 

 is appreciable only during the Santa Anas, 

 the hot dry winds that blow seaward from 

 the desert for a few days each year. During 

 these days R/ V Velero IV and other ships 

 become coated with a layer of tan dust that 

 even works its way into closed cabinets. 

 Appreciable dust fall aboard ship has been 

 noted even as far offshore as San Nicolas 

 Island where 135 mg/sq yd was collected 

 on November 4, 1950. On several occasions 

 off Newport Beach the dust was seen float- 

 ing on the water. In an attempt to learn 

 more about this dust, Babcock (1957) col- 

 lected samples from eight cities in the Los 

 Angeles region after a Santa Ana wind- 

 storm by carefully sweeping 1 square yard 

 of the tops of automobiles in used car lots 

 in which the cars had been polished on the 

 previous day. The median diameters ranged 

 between 30 and 38 microns and averaged 34 

 microns (on a weight basis). The average 

 weight of dust at three stations near the 

 coast was 2.4 grams/sq yd, or 0.3 mg/sq 



