Sulfate/carbonate relationships during the diagenesis of marine sediments: sedimentological study of the Eocene Sobrarbe delta (Spain) and thermodynamic modeling of the ODP/IODP data

This study focuses on the stability of sulfate and carbonate minerals during the early diagenesis of marine sediments (temperatures lower than 70°C and maximum burial depths of 2km). The first part presents the petrographic and geochemical study of dolomitic concretions containing calcite and sulfates (celestine, barite), in the Eocene Sobrarbe delta (Spain). We determine the order of precipitation and the conditions of formation of these minerals, during active tectonics. In the second part, the saturation state of the interstitial waters of marine sediments with respect to carbonate and sulfate minerals is calculated using the entire ODP/IODP data base (14000 samples). For sulfates (celestine, gypsum), saturation is common and characterized by chemical equilibrium. This work shows how water-rock interaction modelling can clarify the mechanisms of formation of diagenetic minerals in marine sediments.