Source of biodegraded oil seep and bitumen rock-impregnations from the Sicilian Orogen and Foreland (Italy): Rock-Eval 6/7S and GC-MS approach

Abstract

Hydrocarbons have been known in Sicily for centuries from oil seeps and bitumen-impregnated limestones, which were exploited in the 19^th and early 20^th centuries. In the 1950s, several shallow wells were drilled in the Sicilian Foreland with the aim of hydrocarbon production. The study focuses on oil and bitumen seeps in Sicily, southern Italy. The oil seeps occur on the surface in Madonna dell’Olio (MA) in the Madonie Mountains in northern Sicily. They are also present as bitumen-impregnated porous carbonates in the Ragusa Formation on outcrops and in the subsurface in the Hyblean Foreland in southeastern Sicily (Streppenosa, Castelluccio, and Tabuna mines). Oil seeps introduce hydrocarbons into the natural environment, where biodegradation occurs. As biodegradation increases, the organic sulfur content increases, while the proportion of pyrolytic organic sulfur within total organic sulfur decreases. The Rock-Eval’s Multi-Heating Rates method shows that the Ragusa bitumen is dominated by the heavy fraction, in contrast to the diesel oil dominance of MA. Distinct oil families represent individual sources: carbonates in the Sicilian Fold-and-Thrust Belt, and shales and carbonates in the Ragusa Hyblean foreland. The distribution of biomarkers indicates an early oil window for both the MA and Ragusa fluids, with MA hydrocarbons slightly more mature than Ragusa ones.