Petrologic studies of diagenetic history of coaly matter in the Podhale Flysch sediments, southern Poland

Marian Wagner


Common occurrences of terrigenic organic matter (both disseminated and accumulated in layers) in sedimentary rocks were observed. The flysch sediments in the Podhale Trough and in other parts of the Carpathians are inadequately recognised from coal petrologic point of view.

Studies were carried out in the eastern (2008) and western part (2009) of the Podhale Trough. Samples were collected from the exposures. Petrographic studies included microscopic observations of polished sections as well as mean random reflectance measurements of vitrinite (colotellinite) were done.

In the Podhale Flysch, coalified organic matter is represented mostly by vitrinite and, in microscopic scale, mainly by collotellinite. The common occurrence of coaly matter is revealed. It is well–visible in sandstones and mudstones, usually as the bedding planes. The amounts of coaly matter in clay minerals and carbonates are small.

Organic matter hosted in the Podhale Flysch strata represents diversified coalification ranks measured as random reflectance of vitrinite (colotellinite), which falls into the range from 0.49 to 1.00%. Such values are typical for low- to medium ranks of bituminous coal. Measurements of reflectance provided new data suitable for evaluation of thermal history of rocks in the Podhale Trough. The changes of vitrinite (colotellinite) mean reflectance of organic matter from the Podhale Flysch are relevant to the contents of crystalline illite – the recently applied geothermometer of diagenetic (katagenetic) transformations of clay minerals. If the thermal palaeogra- dient is known, random changes of reflectance of vitrinite can be used for estimations of both the maximum thickness of the Podhale Flysch during deposition and its later amount of erosion. It appears that estimation of ma- ximum thickness of the Podhale Flysch (i.e., depositional thickness after compaction) and the amount of erosion are almost identical with the estimations based upon the illitization of clay minerals.

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