Regeneracja ziarn kwarcu w piaszczystych glebach korzeniowych w złożu węgla brunatnego Lubstów k. Konina

Abstract

FORMATION OF QUARTZ OVERGROWTH IN ARENACEOUS SEATEARTHS FROM THE LUBSTOW BROWN-COAL DEPOSIT (CENTRAL POLAND) Summary Silicified arenaceous seatearths were found to occur within the Adamow beds (Miocene of central Polish brown-coal formation), showing the features of fluvial sediments deposited in peri-outlet zones. Four forms of silica can be distinguished in them: grains of detrital quartz, overgrowths, authigenic quartz crystals and organo-mineral aggregates. Taking into account microstructural features, the sediments in question are silcretes of quartzitic type formed in early diagenetic stage under superficial conditions. They appear of top parts of each of sedimentation cycles distinguished, directly under brown coal beds. The relations between the above forms of silica indicate multi-stage character of silification process. They consist in superposition of overgrowths, closing of authigenic quartz crystals within these overgrowths and the presence of dissolution pits in overgrowths and in detrital grains. The source of silica was local dissolution promoted by participation of organic matter. Poorly crystalline silica was primarily bound in organo-mineral aggregates and mobilized after removal of organic substance, being subjected to recrystallization process, forming authigenic quartz crystals and overgrowths. The model of circulation of silica in the environment of formation of arenaceous seatearths within the Adamow beds is presented in Fig. 15.