Organic inclusions in salt. Part 3. Oil and gas inclusions in Cambrian evaporite deposit from East Siberia. A contribution to the understanding of nitrogen generation in evaporites

Halite in Cambrian KCl-deposits from the southern part of the Siberian platform, which have been thermally overprinted by dolerite intrusions, commonly contains inclusions dominantly composed of CO2 and less commonly, host inclusions composed of hydrocarbons. Four types of hydrocarbon inclusions have been identified in samples taken from locations devoid of dolerite intrusions. These are (1) monophase gaseous inclusions (i.e. N2, CH4 or N2–CH4), (2) aliphatic oil inclusions, (3) two-phase (L1+L2) hydrocarbon-brine inclusions and, (4) N2-hydrocarbon inclusions. The area where the N2-rich inclusions occur is associated with ammonium-free K-chlorides. By comparing different types of K-salt environments, the origin of the nitrogen could be identified. First, ammonium ions are produced by deamination of organic matter and stored in K-chlorides, and thereafter N2 is released from NH4–K-minerals by oxidation in zones rich in iron oxides and/or by 40K radiolysis.