Petrography and geochemistry of dispersed organic matter in the Oligocene source rocks of the central-western part of the Getic Depression, Romania

Abstract

The aims of this study include the evaluation and interpretation of Oligocene source rocks from the Central-Western part of the Getic Depression, Romania, and the identification of their maturation and their hydrocarbon potential. 24 argillite samples belonging to the source rocks were studied using organic petrography and geochemistry methods, including Rock-Eval pyrolysis, and the following sets of results were obtained: maceral diversity, values of vitrinite reflectance, thermal alteration index, and organic geochemical values. The Oligocene disperse organic matter contains both, humic and terrestrial organic matter, as well as sapropelic, marine, algal matter, represented by telalginite and lamalginite. Several anoxic deep marine water intervals were recorded in the Getic Depression. The samples are immature, with Tmax values ranging between 415 °C and 434.5 °C, and random vitrinite reflectance of 0.32% and 0.53%. The samples yield a total organic content between 0.55% and 5.71%, with a hydrogen index between 9 and 379 mg/g, showing two types of kerogen: a. mixed type II-III kerogen, indicating a generative potential for hydrocarbon and gas, and b. type III kerogen, indicating a gas generative potential.