Isotopic variations in the nitrogen of natural humic and bituminous organic substances

delta15N-values and nitrogen contents of a series of humic and bituminous organic sediments of different ranks were determined. The change of the isotopic abundance of nitrogen was investigated during heating in model experiments, using a gas flame coal. In the case of humic carbon coals the relative nitrogen contents vary from 0.8 to 1.4% and the delta15N-values from + 3.5 to + 6.3 parts per thousand increasing from the brown coal to anthracite ranks. During the coalification process both the delta 15N-values and the relative nitrogen contents do not vary continuously with the rank, but pass through maxima and minima. Model experiments using a gas flame coal show the same trend. Nitrogen with delta15N-values of + 2.8 or -7 parts per thousand was released in pyrolysis experiments, applying a gas flame coal and a steam coal at temperatures of 650 and 10000C, respectively. The investigated bituminous sediments yielded relative amounts of 0.1 to 0.8% with delta15N-values of + 4.2 to + 10.7 parts per thousand. The obtained results are discussed with respect to the elucidation of nitrogen genesis in natural gas deposits. (author)