Source rock potentiality of the late Miocene sapropelic layers of Gavdos island, Greece, based on geochemical and stratigraphic data

Positioned in a peculiar paleogeographic regime, near the Hellenic Trench, that is part of the still active subduction process in the eastern Mediterranean, Gavdos island, the southernmost part of Greece and Europe, offers insights, among others, into late Miocene sedimentary and tectonic processes. This study investigates the hydrocarbon generation potential of late Miocene sapropelic and mudstone/siltstones cyclic deposits through geochemical analysis of samples from two outcrops, namely the GL# and GC#. The GL# and GC# outcrops belong to the Tortonian and Messinian age respectively. GL# outcrop represents the lateral equivalent of the basal part of the main section originally described as Metochia-B, while GC# is a new outcrop (probably lateral linked to the Metochia-C), which covers part of the latest deposits that precede the Messinian Salinity Crisis (MSC) onset, firstly presented in this work. To evaluate the organic richness and hydrocarbon generation potential of these deposits, 59 samples were subjected to Rock-Eval VI pyrolysis. Results revealed that the potentiality varied from poor to fair, with most samples containing Type IV kerogen and limited occurrences of Type III, indicating minimal gas-prone source rocks. GL# outcrop samples, associated with the basal part of Metochia-B, exhibited lower organic richness compared to previous studies, reflecting deposition in a more marginal basin sector, where most probably oxygenation of the organic matter was more intense. GC# samples, representing the Messinian deposits, showed decreased organic matter productivity, potentially linked to environmental changes that prevailed prior to the MSC. This work fills a research gap in the geochemical characterization of Metochia-C sapropelic layers and further extends laterally previous analyses of Metochia-B. Although the geochemical signatures indicate limited onshore hydrocarbon potential, findings contribute to refining the hydrocarbon prospectivity map of the eastern Mediterranean. Further studies are essential to explore offshore prospects, where improved organic matter preservation is anticipated in more favorable depositional environments of the deeper sea. This study highlights the value of integrating stratigraphic and geochemical analyses for energy resource assessment in tectonically complex regions like Gavdos and its adjacent basins.