Cathodoluminescence-revealed diagenesis of carbonates and feldspars in Cergowa sandstones (Oligocene), Outer Carpathians

Cergowa sandstones (Lower Oligocene) have outstanding physical-mechanical properties, among the best of the industrial mineral deposits mined in the Polish Flysch Carpathians. Cathodoluminescence (CL) images of the Cergowa sandstones reveal luminescence coloursmainly in carbonates and feldspars, therefore these two groups of minerals were chosen in order to gain a better understanding of the processes that resulted in exceptionally strong cementation of the detrital components. Cathodoluminescence with cold cathode made it possible to detect the diagenetic features of carbonates and feldspars, to visualize relationships between the detrital grains and cements, and to suggest the processes responsible for their origin and their influence on the physical properties of the Cergowa sandstones. Three generations of pore-filling carbonate cement - calcite - that display brown, orange, and yellow colours observed in CL represent the diagenetic spectrum from eo- through mezo- to telodiagenesis. The feldspars underwent albitization and partial, or even complete, replacement by calcite. Dissolution of marginal parts of the mineral grains resulted in corrosion, which increased the contact surface between the grains and the cement. A combination of these processes resulted in exceptionally strong cementation of the Cergowa sandstones, which is expressed by their very high hardness and resistance to abrasion, freezing, and thawing.