Zastosowanie wskaźnika TAI (thermal alteration index) i analizy palinofacjalnej do określenia stopnia dojrzałości termicznej materii organicznej w utworach górnego permu i triasu w północnej części niecki nidziańskiej (Polska centralna)

Determining the thermal maturity of palynomorph based on their color is a method commonly used in hydrocarbon prospecting. The color of the outer membrane of miospores (exine) changes as a result of heating from pale yellow to black depending on the paleotemperature. Currently, there are many palynomorph color scales correlated with the value of vitrinite reflectance, temperature of burial and hydrocarbon generation stages. Due to the varied material, both in taxonomic and morphological terms, the author used the TAI AMOCO scale. Furthermore, the share of individual kerogen groups in palynofacies was analyzed in terms of their hydrocarbon potential. The Upper Permian and Triassic deposits from eleven boreholes located in the north part of the Nida Basin were investigated. They showed that the Triassic and in the Upper Permian samples from the Milianów IG 1 borehole, are dominated by the pale yellow to orange color of spores and pollen grains, corresponding to a TAI index from 1 to 4, i.e. the pre-generation, dry gas and the early oil generation windows. In turn, only the samples of the Upper Permian from the Pągów IG 1 borehole are dominated by the brown color of miospores, which corresponds to a TAI index from 4+ to 5, i.e. the peak oil prone. Dominant vitrinite reflectance Ro varies from 0,4% to 0,6%, so the degree of organic matter maturity in the Upper Permian and Triassic deposits is not very high, which indicates relatively low temperatures of sediment diagenesis (< 80°C). Analysis of palynofacies showed that the Upper Permian and Triassic deposits contain mixed and structural kerogen. Mixed kerogen, occurring in carbonate rocks, contains amorphous fine-scattered kerogen and “fluffy” of algae origin, as well as structural kerogen of terrigeneous origin, mainly exinite and vitrinite. Mixed kerogen is characterized by oil potential, whereas structural kerogen – by gas-oil potential.