Chapter VII — 101 — Activities in Deposits 



duced nitrate to free nitrogen or ammonia, thereby creating conditions 

 sufficiently alkaline for the precipitation of both CaCOs and MgCOs with 

 the formation of limestone and dolomite. Oolithic formations were also 

 observed. 



Nadson (1928) believed that the bacterial reduction of sulfate also 

 contributes to the precipitation of carbonates: 



CaSO* + CH3COOH = CaCOa + H2S + H2O + CO, 



Whether CaCOg will be precipitated depends primarily upon the pK. The 

 destruction of the strongly acidic sulfate radicle tends to make conditions 

 more alkaline, but the effect of sulfate-reducing bacteria on the hydrogen- 

 ion concentration depends upon the nature of the organic matter used as 

 a source of energy, as well as upon the concentration and form of calcium 

 sulfate. RiTTENBERG (1941) and others have found that under certain 

 conditions the media in which sulfate reducers are growing become pro- 

 gressively more acidic because the organic matter which is being utilized 

 as a source of energy is oxidized to organic acids in sufficient concentra- 

 tions to offset the effect of the sulfate which is reduced. 



Drew (191 i, 1913) attributed the precipitation of CaCOs in the sea 

 largely to the action of denitrifying bacteria according to the following 

 reaction in which hydrogen and carbon are derived from the anaerobic 

 oxidation of organic matter: 



Ca(N03)2 + 3 H2 -f- C = CaCO, + 3 H2O + N2 



His conclusion was based primarily upon experiments in artificial media 

 and the observation of large numbers of denitrifying bacteria in tropical 

 seas where there was evidence of limestone formation. Believing that the 

 process was fairly specific, Drew (191 2) named the organism involved 

 Bacterium calcis. This organism was more thoroughly described by Kel- 

 LERMAN and Smith (1914) who classified it as Pseudomonas calcis. It is 

 closely related or identical to marine denitrifiers described by Gran 

 (1901), Baur (1902), Feitel (1903), and Parlandt (191 i). 



Kellerman and Smith (1914) confirmed Drew's observations on the 

 precipitation of CaCOa in nitrate media by Pseudomonas calcis. They 

 found further that ammonia production either from protein or nitrate 

 decomposition resulted in CaCOa precipitation : 



Ca(HC03)2 + 2 NH4OH = CaCOs 4- 2 H2O -|- (NH4)2C03 



Other microorganisms may be instrumental in the process by oxidizing 

 the calcium salts of organic acids, leaving calcium and CO2 which, in the 

 presence of water, unite to form CaCO.3. These observations were con- 

 firmed and extended by Kellerman (1915a). Kellerman and Smith 

 (1916) found halophlllc lime-precipitating bacteria in Great Salt Lake 

 which resembled those isolated from the sea. 



Berkeley (191 9) failed to find any evidence of denitrification (liber- 

 ation of free nitrogen from nitrate) by bacteria in sea water collected off 

 Vancouver Island. In artificial media, however, the bacterial reduction 

 of nitrate resulted in the precipitation of CaCOs. Berkeley attributed the 

 precipitation of CaCOs in sea water primarily to the bacterial oxidation 

 of organic calcium salts: 



Ca(C00CH3)2 + 4 O2 = CaCOa -1- 3 CO2 + 3 H2O 



LrpMAN (1924) has questioned the ability of Pseudomonas calcis or 

 other denitrifying bacteria to precipitate CaCOs from pure sea water 



