Geochemistry of Upper Miocene–Lower Pliocene source rocks in the Hellenic Fold and Thrust Belt, Zakynthos Island, Ionian Sea, western Greece

Abstract

The southwestern margin of the Hellenic Fold and Thrust Belt, situated along the southern edge of the Dinarides-Albanides-Hellenides continental convergent zone, has been studied in terms of its hydrocarbon generating potential. The Upper Miocene–Lower Pliocene (Tortonian to Zanclean) clastic sedimentary succession at Zakynthos Island provides an excellent opportunity to evaluate the source rock potential of such a system. Twenty seven mudstone samples were analyzed using organic geochemical techniques such as, Rock-Eval pyrolysis, bitumen extraction, open-column chromatography and gas chromatography–mass spectrometry. The obtained data indicate that the sedimentary sequence contains units with sufficient organic material of good enough quality to be considered as potential source rocks. The input of terrestrial organic material and associated gaseous generating potential is indicated by: (1) Rock-Eval pyrolytic yields and calculated values of hydrogen and oxygen indices, (2) n-alkane distribution with dominant long-chain components, (3) high terrigenous to aquatic organic material ratios, (4) odd to even predominance values, (5) low sulfur content and (6) occurrence of gammacerane. The kerogen is immature as evidenced by: (1) Tmax and production index values, (2) odd to even predominance values, (3) low diasterane to sterane and Pr/Ph ratios, (4) low 20S/(20S + 20R) and ββ/(ββ + αα) sterane ratios and (5) presence of gammacerane.