Katodoluminescencja - niezbędne narzędzie w badaniach diagenezy piaskowców kambryjskich
Abstract
CATHODOLUMINESCENCE: AN ESSENTIAL TOOL IN DIAGENETIC STUDIES OF CAMBRIAN SANDSTONES OF NORTHERN AND EASTERN POLAND
Summary
CL study of Cambrian sandstones of the Polish part of the East European Platform (Fig. 8) made possible to reconstruct the primary textural features of strongly diagenetically altered quartz arenites (Fig. 3A, B). The study shows that the detrital material was loosely packed, with predominant point grain contacts. The quartz overgrowths originated during early diagenesis when mechanical compaction was weak. The silicification process occurred at least in two phases (Fig. 3D). During a later diagenetic phase pressure-solution of quartz grains occurred (Fig. 3F). CL observations allowed, in doubtful cases, to decide whether we are dealing with this process, or whether it is a process of overgrowths forming from opposite directions and resulting in development of compromise boundaries between them (Fig. 9). CL study of calcite cements proved their variation even within a single pore space (Fig. 2) or a single pseudomorph (Fig. 11D). The carbonatization processes were multi-phased what in turn resulted in a variability of cements (calcite, Fe-calcite, Fe-dolomite, ankerite, siderite). EDS point analyses of calcite cement showed that differences in luminescence colors of calcite result from varying MnlFe ratios (Fig. 7). CL photomicrographs proved the presence of calcite pseudomorphs after feldspars (Fig. 10B) and glauconite (Fig. 11D). If the amount of completely carbonatized feldspars is significant, such sandstones should be classified as diagenetic quartz arenites. This term reflects different, in this case more arkosic, primary composition of the sediment. CL study also showed that internal parts of siderite concentrations were dissolved and replaced by existing dolomite cement. CL appeared thus a very useful tool in the study of diagenetic processes altering Cambrian sands tones and made possible to assess these rocks from a new point of view providing better diagenetic and sedimentological interpretation of such rocks.
Summary
CL study of Cambrian sandstones of the Polish part of the East European Platform (Fig. 8) made possible to reconstruct the primary textural features of strongly diagenetically altered quartz arenites (Fig. 3A, B). The study shows that the detrital material was loosely packed, with predominant point grain contacts. The quartz overgrowths originated during early diagenesis when mechanical compaction was weak. The silicification process occurred at least in two phases (Fig. 3D). During a later diagenetic phase pressure-solution of quartz grains occurred (Fig. 3F). CL observations allowed, in doubtful cases, to decide whether we are dealing with this process, or whether it is a process of overgrowths forming from opposite directions and resulting in development of compromise boundaries between them (Fig. 9). CL study of calcite cements proved their variation even within a single pore space (Fig. 2) or a single pseudomorph (Fig. 11D). The carbonatization processes were multi-phased what in turn resulted in a variability of cements (calcite, Fe-calcite, Fe-dolomite, ankerite, siderite). EDS point analyses of calcite cement showed that differences in luminescence colors of calcite result from varying MnlFe ratios (Fig. 7). CL photomicrographs proved the presence of calcite pseudomorphs after feldspars (Fig. 10B) and glauconite (Fig. 11D). If the amount of completely carbonatized feldspars is significant, such sandstones should be classified as diagenetic quartz arenites. This term reflects different, in this case more arkosic, primary composition of the sediment. CL study also showed that internal parts of siderite concentrations were dissolved and replaced by existing dolomite cement. CL appeared thus a very useful tool in the study of diagenetic processes altering Cambrian sands tones and made possible to assess these rocks from a new point of view providing better diagenetic and sedimentological interpretation of such rocks.