AAPG Geoscience Technology Workshop

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The Southeastern Margin of the Apulian Platform: Where and When?

Abstract

The Apulian Platform is one of the most prominent Mesozoic carbonate platforms of the Mediterranean area and is hosting some of the European major onshore oil fields. The characteristics of this carbonate platform are well known for the onshore area, where is characterized by shallow water sedimentation since Lower Jurassic until Cenozoic. The northwestern and northeastern carbonate platform margins are also outcropping in the Maiella and Gargano areas and were also identified in the seismic in the offshore. The outcropping slopes are characterized by steep escarpments during Lower Cretaceous, that were also identified in the subsurface by using 2D seismic data. The southeastern margin of the platform, however, is unclear as historically was considered to be in Albania in the Sazani tectonic zone and in the Greek islands of Cephalonia and Zakynthos (pre-Apulian zone auct.). In reality, the seismic data between Italy and Albania/Greece are showing that the typical seismic character of the Apulian shallow water carbonates is lost in a large sector that could be named as “Preapulian Basin”, which type section could be represented by the Paxi Gaios 1 well, drilled in Greece. The stratigraphic succession of this area is characterized by shallow water carbonate sedimentation, sometimes with evaporites, then a drowning during Upper Jurassic (Oxfordian/Kimmeridgian) and a Cretaceous basinal succession. The presence of this paleogeographic unit implies that during Upper Jurassic we got a disruption of the unity of the Apulian platform, with the development of some isolated buildups to the east that remained in shallow water conditions until Cenozoic. The presence of a partial drowning of the Apulian Platform during Upper Jurassic is something that was never evidenced before, and could be identified also in other marginal sectors like Aquila and Rovesti areas. This paleogeographic element is important also because the Jurassic interval is characterized by source rocks of good quality and capable of generating oil. It is currently not clear if the shallow water carbonates of the Sazani Zone are pertaining to an isolated platform coeval of the Apulian s.s., but we think an isolated carbonate buildup characterizes Cephalonia and Zakynthos . Understanding the geometry of the margins of these buildups or of the Apulian platform in Albania/Greece is very difficult and we investigated it in detail in the Sazani zone. Here the margin is highly deformed , with the Ionian basinal units overthrusting the shallow water carbonates: the margin is thus buried. In order to understand the margin geometry we performed also a 3D reconstruction of the Sazani zone, using outcrop and subsurface data. The margin is characterized by a steep slope (>30°) used as a ramp by the thrust faults. The resulting geometry is very similar to the ones of the northeastern margin of Apulia platform. Combining the source rocks of the Preapulian and Ionian Basins with the presence of these buildups create very favorable conditions for the presence of hydrocarbon accumulation in the offshore between Italy and Albania/Greece: the most critical factor, at the moment, is the presence of efficient seals capable of preserving hydrocarbon accumulations.