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Several maturation parameters were determined for a 5800-m-thick Neogene sequence in the Pannonian basin of southeastern Hungary. The oil window was found to start at 3450 m corresponding to a vitrinite reflectance of about 0.7% Ro. This is typical of a mixture of Type II-Type III kerogen such as occurs in the U.S. Gulf Coast. The carbon preference index (CPI) of n-alkanes in the rock extracts also approaches 1.0 at this depth. Hydrocarbon generation appeared to continue to the bottom hole depth of 5800 m with an oil generation minimum or gap occurring in the 5000-5400 m interval that might be due to a change in the nature of the organic matter. Two isomerizations of biological marker compounds, the shift of steranes from 20(R) to 20(S) and of hopanes from 22(R) to 22(S) were found to reach equilibrium at 4000 and 3000 m, respectively, just prior to the threshold of intense oil generation. Also, the C29-monoaromatic steranes were converted almost 100% to C28-triaromatic steranes prior to this depth.

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