Diagenetic alteration of Badenian sulphate deposits in the Carpathian Foredeep Basin, Southern Poland : processes and their succession

The facies variation of the Badenian sulphate deposits in the Polish Carpathian Foredeep Basin reflects distinct depositional and diagenetic environments. In these environments the primary sulphate (mainly gypsum) was deposited and then underwent different pathways of diagenetic evolution, recognized on the basis of sedimentological, petrographic and geochemical studies. Diagenetic sulphate facies (anhydrite and secondary gypsum) formed in successive stages: syndepositional (the depositional stage), early diagenetic (at the surface and during shallow burial) and late diagenetic (during deeper burial and exhumation). Most anhydrite deposits show sedimentological and petrographic features characteristic of a diagenetic facies formed by replacement (anhydritization) of the precursor gypsum deposits. Four basic genetic models of anhydrite have been proposed: (1) syndepositional interstitial anhydrite growth de novo, (2) syndepositional anhydritization (via nodule formation and pseudomorphous replacement), (3) early diagenetic anhydritization (displacive anhydrite growth), and (4) late diagenetic anhydritization (replacive anhydrite growth). The succession of diagenetic processes and their paragenetic relationships within the Badenian sulphate deposits display a complex diagenetic evolution. Many controlling factors, such as a palaeogeographic setting, tectonic activity, geostructural constraints and physico-chemical changes of the pore fluids, related to sedimentary and diagenetic environments, have been involved in the sulphate diagenesis. The results may be applied to other ancient evaporite basins including the marginal gypsum deposits and anhydrite in the more buried, basinward part.