Micas and clay minerals of muddy to clayey sediments from the Paleogene variegated shales, Polish Carpathians

The research was carried out on shales and mudstones of the Hieroglyphic Beds in the eastern part of the Dukla Unit. Samples of shales and mudstones were examined using optical microscopy, X-ray powder diffraction (XRD) and scanning electron microscopy (SEM). The chemical composition of minerals was studied by energy dispersive spectrometry (EDS). In order to obtain clay fractions of <2 μm and <0.2 μm the samples were prepared according to the standard Jackson method. Clay minerals preparations were air-dried, glycol vapour saturated and heated at 330ºC and 550ºC.
   Muscovite is the most common detrital mineral and the main component of the analyzed sediments. It occurs as mangled flakes, which underline the lamination of the host rocks. The EDS analyses have revealed fengite character of muscovites, which contain up 5.27 wt% of the Fe₂O₃. Biotite grains in most cases underwent chloritisation.
   The XRD analyses of the <2 μm have revealed the presents of illite, chlorite and mixedlayer minerals: illite/smectite and chlorite/smectite. Illite, in most cases, is the component of cement. Detailed characterization of illite/smectite was based on the diffractograms of the (0.2 μm fraction obtain from the XRD studies of glycol vapour saturated oriented preparation. The type of layer ordering in the mixed layered minerals was established according to the position of 001 reflection. R1 and R>1 are the characteristic types of the ordering in these minerals. They contain up to 30% of smectitic component in their structure. The presence of 1M and 2M1 politypes confirms the existence of both authigenic and detrital illite in the analysed clay material. The EDS investigation showed different amounts of Fe (from 5 to 30 wt% of Fe₂O₃) in illite or illite/smectite mixed layers.
   It was determined that only detrital chlorites appear in the studied sediments. They are often products of chloritisation of biotite. The XRD studies of the <2μm fraction displayed presence of chlorite and mixed-layer chlorite/smectite. It was confirmed during the EDS examinations, which revealed a considerable amount of K, which may derive from smectitic layers. Moreover, the EDS studies showed that chemical composition of chlorites varies considerably and that it is comparable to the composition of chamosite and ripidolite.
   The chemical composition of minerals occurring in the studied rocks indicates the complex diagenetic environment. The composition of the pelitic fraction (illite, illite/smectite, chlorite and chlorite/smectite) and a small amount of smectitic component in the ordered illite/smectite interstratifications (R1 and R>1) in particular, indicate the advanced degree of diagenesis.
   Acknowledgments: Studies were sponsored by the Ministry of Science and Higher Education (Grant No. N307 2846 33).