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Crustal shortening onshore Sicily was accompanied by significant structural rotation which, according to paleomagnetic data, is in the order of 60 to
134 degrees clockwise in the northern portions of the thrust belt (F.Speranza et al.,1999). The rotation vectors are related to the opening of the
Tyrrhenian Sea and the retreat of the subducting Ionian plate. The current orientation of the onshore Tortonian-Messinian foredeep (trending
approximately east-west) is likely the result of this peculiar tectonic evolution, whereas offshore Sicily (Nilde area) a coeval foredeep is oriented
NE-SW to NNE-SSW, suggesting limited rotation occurred in the offshore (possibly in the order of 15-20 degrees clockwise).

The /DWH7ULDVVLFLiassic Petroleum System

Tectonic Setting of Hydrocarbon Seeps

A system of NE-SW oriented inverted faults in the offshore Tortonian-Messinian foredeep and foreland (exemplified by the Nilde Field) likely
initiated in the Late Triassic-Lias as extensional faults which were subsequently inverted during multiple compressive events occurring from the
Paleocene to the Early Pleistocene. The analysis of bitumen seeps onshore Sicily has shown all the samples are genetically related and are thought to
have formed from Late Triassic-Liassic intraplatform basins which are possibly oriented E-W at present day. These basins are not outcropping,
however their occurrence has been inferred from the distribution of seeps. An example of such intraplatform basin is provided by the Marineo Basin
drilled by Agip in 1992 (Marineo-1 well), which showed the presence of bitumen within Mesozoic sequences. Paleohighs linked to extensional
tectonics during the Late Triassic-Lias are still visible in some areas in western Sicily (i.e. M. Kumeta, M. Busambra), displaying a structural
orientation similar to the trend of the intraplatform basins. Structural restoration of the onshore sequences indicate these units were likely deposited
in lateral continuity with the offshore inverted foredeep foreland domain being characterised by an approximate NW-SE direction of extension
during the Late Triassic-Lias.

Geochemistry of Late Triassic-Liassic Source Rocks in Sicily

All the bitumen samples analysed in western Sicily (Figure 6) are heavily degraded oils very rich in asphaltenes. A carbonate source rock for these
hydrocarbons has been determined due to the absence of diasteranes, the dominance of Tm (17α(H)-22,29,30-trisnorhopane) over Ts (18α(H)-
22,29,30 trisnorneohopane), and the dominance of C29 hopane over C30 hopane. Other geochemical parameters, including sterane transformation
ratios, indicate these bitumens were generated by a fully mature source rock.

All the potential source rocks analysed in Sicily in this work are non-carbonate source rocks. Previous studies pointed out that the only carbonate
source rocks which are thought to occur in western Sicily are Late Triassic to Liassic in age. Significant petroleum potential could not be found in
any of the Late Triassic and Liassic samples in Sicily and it was therefore assumed that localised buried anoxic basins were the source of the
bitumen seeps. An example of such a basin is represented by the Marineo Basin drilled by Agip in 1992 (Marineo-1 well) which drilled through
slope facies of the Inici Formation (Modica Formation equivalent, Lias) with a fair petroleum potential (50 kg HC/t). The sequence underlying the
Inici Formation in this well, the Sciacca Formation (Late Triassic), may also be characterised by a fair petroleum potential as indicated by a TOC