AAPG Geoscience Technology Workshop

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Basin Inversion in the Central and Eastern Mediterranean: Structures From the Adriatic and Insight for Exploration in the Levantine Basin

Abstract

Inversion structures have a significant potential for hydrocarbon exploration representing important hydrocarbon plays in both mature and under-explored areas. Basin inversion, including a variety of positive inversion tectonic processes, controls the petroleum system elements from the initial extension up through the later contractional deformation. Permian to Mid-Jurassic rifting within the Tethyan realm led to the development of extensional fault systems that are nowadays recognized in both the Central and the Eastern Mediterranean as for example in the Adriatic Sea and in the Levantine Basin. Subsequently, these regions recorded contractional regimes from Late Cretaceous through Tertiary causing a switch in deformation and triggering widespread basin inversion phenomena. Here we present seismic examples of inversion structures taken from the well-known mature province of the Italian Adriatic Sea of Italy. Given the similar tectonic evolution, these examples may provide structural insights for the identification of prospective structures in the under-explored Levantine Basin, where inversion is still poorly documented. The Italian sector of the Adriatic is a long-established hydrocarbon province that recorded in the past a successful exploration history with two main proved plays represented by the biogenic gas in the shallow Pliocene-Pleistocene sequence and light-to-heavy oil and gas discoveries in the Cretaceous-Miocene carbonates. The Adriatic foreland belongs to the Adria continental block that, at present, extends northwest-southeast including, from north to south, the Po Plain, Istria, Adriatic basin, Gargano Promontory and the Apulian Peninsula. It represents a common foreland domain shared by three different thrust belts that developed in distinct times: the Apennines to the W/SW, the Southern Alps to the N/NW and the Dinarides-Albanides to the E/NE. This region records a polyphase tectonic history with repeated events of basin formation associated with normal faulting, reworked by compressional deformation. Normal faults connected to both rifting phases (Permian-Triassic and Jurassic) and to the syn-orogenic foreland flexure (Neogene) affected this area. In the Central Adriatic, compressive and transpressive deformation developed a NW-SE-trending (Mid-Adriatic Ridge). Seismic interpretation within the central sector of the Adriatic revealed that most of the compressional structures involving the carbonate sequence are thrust-related inversion anticlines that developed by the transpressional reactivation of pre-existing Permian-Triassic and Jurassic normal faults. Such structures, affecting the Triassic-Miocene carbonate succession and the Permian pre-carbonate sequence, present typical features of positive inversion tectonics. They appear as asymmetric harpoon-shaped anticlines facing toward the footwall and riding over high-angle blind thrust faults or as more symmetric features with conjugate up-thrusts. The positive basin inversion process involved both symmetric graben-like and asymmetric half-graben type Permian-Triassic/Jurassic basins suggesting a strong control of the pre-existing basin geometry on the inversion fold development. Moreover, the geometrical characteristics of this inversion structures are consistent with deep-rooted basement-involved deformation. Structural reconstructions reveal that inversion plays a significant role during the evolution of the Adriatic system. Various styles of inversion such as those here presented create different scenarios for assessing hydrocarbon prospectivity. Inversion structures developed ahead of thrust belts can serve to trap hydrocarbon expelled laterally from their generation kitchens within the advancing orogen. Furthermore, the inversion structures themselves may overlie hydrocarbon sources representing potential generation kitchens that could provide local oil and gas. By taking into account these key concepts of inversion, a reappraisal of the possible exploration targets may increase hydrocarbon prospectivity within regions of the Central-Eastern Mediterranean that experienced a similar tectonic evolution (e.g., Levantine Basin) unlocking potential for future exploration.