274 



Sediments 



genesis must be obtained. This has long 

 been recognized, but the approach has been 

 more that of speculation based on ancient 

 sediments than of collection of facts from 

 modern sediments and environments. 



Elemental Composition and C/N Ratio 



The elemental composition of organic 

 matter in sediments has so far proved impos- 

 sible to obtain with any accuracy, owing to 

 the difficulty of separating the organic mat- 

 ter from its enclosing sediment. A method 

 that has sometimes been used is to dissolve 

 away the inorganic grains with hydrochloric 

 and hydrofluoric acids and to analyze the 

 residue, correcting for the pyrite, excess ash, 

 and chlorine that also remain. An example 

 of such an analysis from Core 2989 in Santa 

 Catalina Basin (Table 22) was provided by 

 the Petroleum and Oil-Shale Experiment 

 Station, U. S. Bureau of Mines, Laramie, for 

 comparison with analyses of oil shales. The 

 final total organic content was 3.17 per cent 

 by dry weight of the original sample, nearly 

 as much as the original 3.32 per cent organic 

 carbon alone before treatment. Carbon in 

 the residue is 15.6 times nitrogen, whereas 

 in the original sample it was only 9.5, indi- 

 cating that at least 63 per cent of the nitro- 

 gen was lost during the removal of inorganic 

 grains. Although we might expect many 

 comparable analyses of phytoplankton to be 

 available, all that could be found were a 



rather unsatisfactory tabulation of analyses 

 by Vinogradov (1953) and some older analy- 

 ses of 1898 by K. Brandt (in Trask, 1937). 

 Vinogradov's data were supplemented in 

 Table 22 by the rather well-known compo- 

 sition of the human body. In spite of the 

 deficiencies in source data, comparison of 

 the various items in Table 22 shows that 

 natural alteration of the original organic de- 

 bris causes a progressive increase in the rela- 

 tive contents of carbon and hydrogen and a 

 decrease in oxygen and nitrogen. Similar 

 general changes were noted by Trask (1939), 

 ZoBell (1945), and Porfiriev (1955). With 

 coal the change from wood to anthracite is 

 accompanied by a progressive relative de- 

 rease in hydrogen as well as in oxygen and 

 nitrogen (Clarke, 1920, p. 763; Rankama and 

 Sahama, 1950, Table 8.7). 



The uncertainty in composition of total 

 organic matter in sediments is reflected by 

 an uncertainty in the ratio of total organic 

 matter to organic carbon. Trask (1932, 

 1937, 1939; Trask and Patnode, 1942, p. 43), 

 who studied the problem extensively, has at 

 various times advocated use of different 

 ratios (1.7, 1.8, and 1.8 to 1.9) for Recent 

 sediments and 1.6 for ancient rocks. In dis- 

 cussing the problem he pointed out that the 

 true ratio for any given sediment depends on 

 the nature of the source material and the 

 state of oxidation of the organic matter. 

 Emery and Rittenberg (1952) found that at 

 least the second factor is important for the 



Table 22 



Elemental Composition of Total Organic Matter 

 (Per cent dry weight) 



'Vinogradov (1953, Tables 83, 84). 



^Rankama and Sahama (1950, Table 8.4). 



^ After solution of detrital sediment, Orr and Emery (1956a). 



^ZobeU (1945); BaU, Whisman, and Wenger (1951). 



^ Oxygen by difference. 



