Chapter VII 



ACTIVITIES OF MICROORGANISMS IN 

 BOTTOM DEPOSITS 



Bacteria are important chemical and geological agents in bottom de- 

 posits, not so much because they are indispensable to any one process, but 

 rather because they help to accelerate many processes. The vast num- 

 bers, physiological versatility, and almost universal distribution of bac- 

 teria in recent marine sediments help to account for the long-range 

 effectiveness of their work. 



In general, the geological activities of bacteria are neither specific nor 

 confined to a limited number of species. The metabolic products of 

 practically all bacteria have some effect upon their geological environ- 

 ment. Evidence of their early creation (bacteria probably being one of the 

 first forms of life on the earth) indicates that they have had an enormous 

 span of time in which to exert their profound influences. Controlled lab- 

 oratory experiments with samples of bottom deposits under environ- 

 mental conditions simulating those on the sea floor demonstrate that bac- 

 teria could be functional in situ, or in the environment in which they 

 occur. This, together with the correlation of the numbers and kinds of 

 microorganisms with chemical, physico-chemical, and geological condi- 

 tions found in sediments, clearly shows that microorganisms are instru- 

 mental in the modification and diagenesis of the sediments. 



Calcium carbonate precipitation : — According to estimates by 

 Vaughan (1924), marine sediments contain an average of 20 per cent of 

 calcium carbonate in the form of limestone, while the entire earth's crust 

 contains only about 6 per cent. Almost pure CaCOs is being deposited in 

 certain parts of the sea, and in most bottom deposits precipitated CaCOs 

 serves as an important conglomerating or cementing material. While 

 large quantities of CaCOa are deposited in the skeletal remains of animals 

 and by calcareous algae (Clock, 1923), the activities of heterotrophic 

 bacteria contribute to the process in various ways. 



Murray and Irvine (1889) attributed the precipitation of CaCOs to 

 the reaction of ammonium carbonate with calcium sulfate : 



(NH4)2C03 -H CaSOi = CaCOs -|- (NH4)2S04 



Ammonium carbonate originates from ammonia and CO2 resulting from 

 the microbiological disintegration of nitrogenous organic substances. 



In an obscure Russian publication which escaped attention until his 

 observations were published in German (Nadson, 1928), Nadson (1903) 

 showed that the bacterial production of ammonia from proteinaceous 

 materials promotes the precipitation of CaCOs in Lake Weissowo. Pro- 

 teus vulgaris, Bacillus mycoides, Actinomyces albiis, Bacterium albo-luteum, 

 and Bacillus salinus were the principal organisms involved. Ammonia 

 production tends to increase the pH of water and thus promotes the pre- 

 cipitation of CaCOs (MoBERG et al., 1934). Besides liberating ammonia 

 from proteinaceous materials, certain organisms observed by Nadson re- 



