Source rock evaluation and source rock–hydrocarbon correlation in the Croatian part of Pannonian Basin System

The Croatian part of the Pannonian Basin System is located on its southern edge. It comprises the Hrvatsko Zagorje Basin and the North Croatian Basin, further divided into basins and subbasins traditionally termed depressions and subdepressions: the Mura, Hrvatsko Zagorje, Sava, Drava and Slavonija–Srijem Basin. All basins, except for the Hrvatsko Zagorje Subbasin, host a significant number of oil and gas production fields. Organic-rich source rocks with varying maturities are distributed throughout these basins. The primary source rocks in the Drava and Sava basins are Badenian and Pannonian marls and calcite-rich marls. In the Sava Basin, these source rocks are within the oil window. In the eastern and southern parts of the Drava Basin, the source rocks are either immature or within the oil window, while in the western and central parts they are within the gas window. The main source rocks of the Mura Basin are Eggenburgian marls and shales, which are within the gas window. The geochemical analyses presented in this paper, including biomarker fingerprinting and stable carbon isotope ratios, confirm a strong correlation between the oils and their source rocks throughout the Croatian part of the Pannonian Basin System.