Diagenesis as a function of redox conditions in nature : a comparative survey of certain organic and inorganic compounds in a oxic and anoxic Baltic Basin
Sediments from Baltic basins, the relatively well aerated Bornholm Basin and the poorly aerated Gotland Deep, were collected in order to see what effect a relative lack of oxygen at the sediment-water interface has on the diagenesis of organic material deposited in nature. From hydrographic considerations one can assume that the Gotland Deep has a perennial deficiency of oxygen when compared to the Bornholm Basin. This was also shown from the manganese (HARTMANN, 1964) content in the two sediments. Both sediments were also found to have a similar mineral composition and particle size distribution. That they were of a similar age could be shown by the fact that they both had a relatively large amount of organic material (GRIPENBERG, 1955) and similar concentrations of ammonia. Since the two basins have different rates of primary productivity, it was necessary to adjust the quantitative results with a compensating factor. This factor was based upon the pristane, a highly stable hydrocarbon, content, and it was determined that the Bornholm Basin had a primary productivity 1.5 times as high as the Gotland Deep. Quantitatively the lower oxygen concentrations in the Gotland Deep resulted in the preservation of more total soluble amino acids, fatty acids, hydrocarbons, and organic carbon. In addition a greater percentage of the total organic carbon in the Gotland Deep was, in a non-condensed form. Qualitatively no major difference was found in the distribution in the two sediments of the total soluble amino acids (with the possible exception of tyrosine), fatty acids, or hydrocarbons, however unsaturated fatty acids and hydrocarbons showed considerable difference in their qualitative distribution. The low oxygen basin was found also to contain considerable more unsaturated compounds, and its material seemed to have been less influenced by bacteria, as determined by a higher linear/iso fatty acid ratio. A study of the fatty acids and hydrocarbons that were released from the mineral matrix of the sediments by acid digestion, indicates an additional preservative effect in that a still greater degree of unsaturation was present and in that the linear/iso ratios were higher. This preservative effect in the relatively well aerated basin was either less or absent
