Organic Constituents 



287 



Santa Monica, and Santa Catalina Basins 

 yielded oil amounting to 9.5, 7.7, and 9.5 per 

 cent of the total organic matter, respectively. 

 This is 19 to 36 times the amount extracted 

 by solvents from otherwise untreated sedi- 

 ments. 



Gases 



In addition to their solid and liquid con- 

 stituents, sediments also contain greater or 

 lesser quantities of gases of various kinds. 

 Detailed studies of these gases awaited the 

 development of mass spectrometer tech- 

 niques during the past decade. Samphng 

 also presented a problem because gases bub- 

 bling up from the bottom consist only of the 

 gases that had not yet dissolved in the water, 

 and they provide no measure of gases pres- 

 ent in the sediments. Recently Emery and 

 Hoggan (1958) combined a special collecting 

 device and use of a mass spectrometer to 

 analyze gases present between the surface 

 and a depth of 375 cm in sediments of Santa 

 Barbara, Santa Monica, and Santa Catalina 

 Basins and between the surface and 45 cm 

 in marshes at Newport Bay and Seal Beach. 

 A weighted coring device made of short 

 lengths of steel pipe coupled together was 

 dropped into the bottom sediment, recovered 

 aboard ship, and disassembled and capped 

 inside a large plastic bag in which atmo- 

 spheric gases had been replaced with helium. 

 At the laboratory of Richfield Oil Corpora- 

 tion, Wilmington, Cahfornia, the gases were 

 extracted under vacuum from the capped 

 lengths of pipe. The most abundant gases 

 were determined directly in the mass spec- 

 trometer; the rest of them had first to be 

 concentrated in a liquid nitrogen bath. Per- 

 centages of various gases were converted to 

 milliliters per hter of interstitial water using 

 nitrogen as a standard gas with a concentra- 

 tion assumed to be the same as in overlying 

 water. Ammonia, not determined by mass 

 spectrometer, was added from earlier meas- 

 urements on nearby cores by Rittenberg, 

 Emery, and Orr (1955); hydrogen sulfide was 

 also present in some samples but was not 

 measured. Carbon dioxide was measured, 

 but probably not reliably because of com- 



plexities of the carbon dioxide-carbonate 

 system. 



The results for Santa Barbara Basin (Fig. 

 230) show that ammonia and methane domi- 

 nate at depth, but higher representatives of 

 the methane series and even some aromatic 

 volatile hydrocarbons are also present. At 

 depth the weight of methane is about equal 

 to the weight of all heavy nonvolatile hydro- 

 carbons that were separated by chromatog- 

 raphy (Table 27). In oil fields also the 

 weight of hydrocarbon gases is about equal 

 to the weight of petroleum. However, in the 

 Recent sediments of Santa Barbara Basin 

 the ratio of methane to ethane is about 

 100,000 to 1, in contrast to the 4-to-l ratio 

 that is typical of oil field gases. Results in 

 the other basins showed an increase of meth- 

 ane with depth but to maximum concentra- 

 tions of less than 0.2 per cent of those found 

 in Santa Barbara Basin. Evidently the nega- 

 tive Eh and other conditions are more favor- 

 able for the production of hydrocarbon gases 

 in Santa Barbara Basin than in the other 

 basins or in marshes. None of the hydro- 

 carbon gases was detected in samples of sea 

 water above the basins, so they must have 

 been produced by diagenesis of organic mat- 

 ter at the bottom. In support of this con- 

 clusion, bacteria and fungi have recently 

 been discovered to be capable of producing 

 hydrocarbon gases higher than methane 



CUMULATIVE ML GAS/L WATER 



200 300 400 



Figure 230. Composition of dissolved gases and volatile 

 organic materials in interstitial water of sediments in 

 Santa Barbara Basin. Note the increase with depth of 

 most gases. 



