Investigation of the fate of nitrogen in Palaeozoic shales of the Central European Basin

Nitrogen geochemistry of Upper Carboniferous shales from the Central European Basin (CEB) was investigated by elemental analysis, stable isotope mass spectrometry and non-isothermal pyrolysis. Total N-contents of Namurian shales from four deep wells (4400-7000 m) in NE Germany ranged between 520 and 2680 ppm. Up to 90% of this nitrogen occurs as ammonium in minerals with delta N-15 values between +1 parts per thousand and +3.5 parts per thousand. Low nitrogen contents (down to 460 ppm) and high delta N-15 values (up to +5.6 parts per thousand) in one well in the basin centre suggest a large-scale release of nitrogen associated with isotopic fractionation. Pyrolytic liberation of N-2 from pelagic Namurian A shales of NW and NE Germany occurred at significantly lower temperatures than from paralic Namutian B shales and terrestrial Westphalian samples. On-line isotope analysis of N-2 liberated between 400 and 1200 degrees C indicates the presence of precursor pools with different thermal stability and nitrogen isotopic composition. (C) 2006 Elsevier B.V. All rights reserved.