Bacteria and Bottom Deposits
Only brief mention can be made of the activities of bacteria in the processes of sedimentation on the ocean bottom. Further consideration
The activities of the various types of bacteria that occur in great abundance in the bottom sediments are believed to have a significant role in determining the character of the bottom deposits and the diagenesis of rock strata. Some of the results of chemical transformations wrought by these microorganisms are:
Formation of humus, a very stable organic end product of decomposition with a characteristic carbon-nitrogen ratio varying from 8:1 to 12:1 (Jensen, 1914).
Calcium precipitation in the presence of calcium salts and high pH.
It is believed by some investigators—Drew (1914), Bavendamm (1932), and others reviewed by Benecke—that bacteria in the sea are important agents in the precipitation of calcium carbonate in marine sediments and may therefore be of special geological importance. Many bacteria are known experimentally to produce an alkaline reaction in the presence of calcium and organic material, yielding ammonia. Such organisms may encrust themselves with areolas of calcium carbonate. The extent to which this type of precipitation can occur is still a moot question. Lipman (1929) was of the opinion that in the sea there can be no calcium precipitation because sea water does not contain sufficient concentration of calcium, but the general opinion seems to be that under certain natural conditions bacterial precipitation of calcium can and does occur in the sea, especially in bays in the tropics where there is an abundance of organic material.
Iron and manganese may be precipitated by bacteria that form sheaths of compounds of these metals (Harder, 1919). For example, they obtain energy from the oxidation of the soluble ferrous bicarbonate using the carbon dioxide liberated and precipitating ferric hydroxide.