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In Tunisia extracts from the Bahloul Formation are characterised by Pr/Ph ratios ranging from between 1.5 and 3, a moderate diasterane content, a
C27 sterane approximately equal to C29 sterane, a high C28/C29 sterane ratio (0.82-0.99), (El Euchi et al., 1997). The oil in the Nilde discovery is
also characterised by a moderate diasterane content, a Pr/Ph ratio close to 1 (L. Mattavelli et al., 1990), however it is by comparison highly enriched
in C29 regular sterane with still a relatively high C27/C29 ratio (0.84) but a low C28/C29 sterane ratio (0.43). The Bahloul eq. samples from north-
eastern Sicily have shown a similar C29 sterane content with a low C28/C29 sterane ratio ranging from 0.41 to 0.67. The Pr/Ph ratio in the latter
source rock differs from the Nilde oil (2.18 to 2.69 onshore Sicily), 0.98 in Nilde (Mattavelli et al., 1990), this is likely due to the different maturity
of the source rock (immature) with respect to the Nilde oil (peak mature).

All of the wells drilled in the inverted Messinian-Tortonian foredeep (exemplified by the Nilde discovery), indicate Cretaceous sequences could not
have generated significant quantities of hydrocarbons locally due to the lack of sufficient burial and the absence of organic rich facies. This suggests
generation of hydrocarbons must therefore have occurred within the adjacent thrust belt. Cenomanian-Turonian lithofacies in the Nilde area are not
consistent with the deposition of carbonate ramp deposits like the Bahloul Formation and are characterised by pelagic marls with planktonic
foraminifera (Trapanese eq. deposits). Geochemical data suggest the Nilde oil was generated by a source rock which was influenced by the
proximity of a shoreline and with possibly a limited input of terrestrial deposits. This is evidenced by the presence of diasteranes, stable carbon
isotope values which support the possibility of a limited terrestrial input, correlation with onshore source rocks characterised by a near-shore
environment of deposition. This would suggest the presence of shallow water carbonates of the Panormide unit in the offshore thrust belt and a
shallow water carbonate system leading to a deeper basin as observed in Sicily.

Tertiary Petroleum System

The Potential of the Numidian Flysch (Oligocene-Early Miocene)

Due to the absence of published analyses from the organic rich Numidian Flysch of Sicily, source to oil correlations were carried out using the
available geochemical data from the Numidian Flysch in Tunisia. Oil-source rock correlations based on δ13C for the aromatic and saturate fractions
indicate a good correlation between the Tunisian Numidian Flysch, the oil from the Gagliano field in eastern Sicily and the Madonna dell’olio seep
located in proximity of the village Blufi, about 30 km west of the Gagliano Field. Geochemical analyses of the Madonna dell’olio seep indicate the
oil has been generated by a carbonate source rock with an elevated clastic component.

Available geochemical data for the Gagliano Field (L. Mattavelli et al., 1990) also suggest generation from a carbonate source rock with a significant
clastic component as demonstrated by the presence of gammacerane, a relatively high C29 to C30 hopane ratio and the presence of diasteranes. This oil
is also characterised by a distinctive pattern of sterane distribution with a high C27/C29 ratio (1.25), (L. Mattavelli, 1990). By comparison the Madonna
dell’olio seep displays a C27/C29 ratio close to one, higher than any other source rock and bitumen analysed in Sicily.