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Controls on the Petroleum Prospectivity of the Apulian Platform, Western Greece: Insights from field and subsurface data

John Underhill

Despite numerous oil seeps providing direct evidence that a working petroleum system exists in Western Greece, the region remains under-explored. Integration of onshore field exposures with subsurface data from the Ionian Islands, Epirus, Albania and Southern Italy, as well as offshore waters of the Southern Adriatic and Ionian Sea provides a new found basis by which to understand the tectonic and stratigraphic development of the area and its implications for petroleum exploration.

It has long been known that the Hellenide-Albanide region forms an integral part of the Tethyan passive continental margin. The Ionian area of Western Greece straddles the boundary between a para-authochthonous Pre-Apulian carbonate platform block and more basinal sequences of the Ionian Zone. The area subsequently got enveloped in a foreland fold-and-thrust system, which caused contractional telescoping of the former extensional system, as part of Alpine (Eurasian-African) collisional events. Recent work has shown how the nature of the Pre-Apulian-Ionian Zone contact changes from an original (Mesozoic) extensional fault system in the north-west to being a thrusted (and structurally inverted) one in the south (e.g. SE Kefalonia). The studies have also highlighted the boundaries rugosity, with clear evidence for depositional promontories and embayments along its length, something that also characterises the system in offshore waters of the Italian Adriatic.

Subsidence resulting from the Mesozoic development of the Tethyan passive continental margin and more especially, Cenozoic foreland basin subsidence ahead of the westerly migrating locus of the Hellenide (Alpine) thrust belt appear to be the main drivers for maturation of Mesozoic source rock intervals including the Lower Jurassic (Toarcian) Posidoniaschiefer and Cretaceous black shales of the Ionian Zone. Up-dip (westerly) migration of hydrocarbons is manifest in the occurrence of oil in thrust fault bound closures within the Albanides as well as along the unconformable (and locally karstified) contact between subcropping carbonates and draping mudstones of the basal (Oligo-Miocene) foreland basin (flysch) sequences or later Messinian evaporites. Whilst seepage along Hellenide thrusts and neotectonic structures formed due to outer-arc deformation, subduction roll-back and arc rotation demonstrates an increasing seal breach risk in onshore and more southerly areas (e.g. Lefkada, Kefalonia and Zakinthos), the challenge is there to identify areas in which trap integrity remains.

AAPG Search and Discovery Article #90161©2013 AAPG European Regional Conference, Barcelona, Spain, 8-10 April 2013