| Formation fluids in the Lower Cretaceous Mannville Group and associated horizons were collected and compiled to identify the causes and controls of a recognised P;Isotope and chemical systematics of the collected waters are consistent with mixing as a dominant control on major element chemistry. Biogenic sulphate reduction (RSR) is recognised as a major, although not the only, factor accounting for high levels of oxidized carbon and sulphide found in the waters. Chemical and isotopic composition of dissolved sulphur species and bicarbonate are consistent with BSR coupled with re-oxidation of sulphide, precipitation of pyrite and a complex association of bicarbonate producing processes, including methanogensis, dissolution of carbonate minerals and cross formational migration of gases.;Geochemical thermodynamic models suggest that cation exchange reactions between clay minerals exert an underlying control on relative ion ratios. The oxidation-reduction relationships of the waters are indicative of possible metastable equilibria between carbonate minerals, dissolved inorganic and organic carbon and long chained hydrocarbons in petroleum. |
