Structural decoupling in a convergent forearc setting (southern Crete, Eastern Mediterranean)

A multidisciplinary approach is used to investigate the structure of the southern Cretan margin, which is located in one of the most seismically active forearc regions in Europe. Bathymetric, seismic-reflection, and fault plane solution data were used to identify the main tectonic features on the margin, correlating their evolution with the main sedimentary sequences recognized on Crete. In contrast to the majority of forearc settings in the Pacific and Indian Oceans, southern Crete is a region of predominantly oblique movement above well-defined detachment zones. North-dipping thrust faults identified on seismic-reflection profiles reveal significant crustal shortening during the Miocene due to the westward propagation of the Hellenic fold-and-thrust system. In addition, east-dipping thrust faults rooted on top of pre-Neogene strata were also identified, but only a few of these thrusts affect Neogene to Holocene strata. Small-scale domes derived from evaporitic (Messinian) intrusions deform Pliocene–Quaternary strata. West- and east-dipping normal faults were also recognized within the Mesozoic and Cenozoic successions, and these are related to regional extension during forearc convergence. In such a setting, the fault-bounded continental slope of Crete effectively separates a region of uplift (Crete) from subsiding troughs to the south. Our work shows that structural segmentation at depth is complex, with multiple crustal levels recording contrasting styles of deformation and distinct moment-tensor solutions. This complexity derives from the oblique style of convergence recorded south of Crete, which reactivates distinct crustal levels depending on their rheology and relative degree of metamorphism inherited during Alpine compression. As a result, a strong correlation between seafloor morphology and transtensional movements is recorded in the upper 10–15 km of the crust, while transpression prevailed after the Serravallian below these depths

Triassic evaporites and the structural architecture of the External Hellenides and Albanides (SE Europe): controls on the petroleum and geoenergy systems of Greece and Albania

A combination of well data, seismic information on thrusting and tectonic shortening, plus analyses of the nature and depth of the Mesozoic units related to main detachment horizons (Triassic evaporites, flysch), are used to review, and further update the complex structural styles of the External Hellenides and Albanides Orogenic Belts, SE Europe. In the study area, the late Alpine orogenic evolution resulted in a structural architecture characterised by the successive westward thrusting of tectonic nappes (Gavrovo/Kruja, Ionian), with an imbricate tectonic style prevailing in all external zones. In the internal and central Ionian zone, imbricate thrusts and duplex structures are recorded, especially where about 24 km of stacked Mesozoic–Tertiary successions have been formed in Albania. Triassic evaporites, up to 3.5 km thick, acted as a detachment horizon for the internal deformation of the Ionian and Pre-Apulia zones (1.7–1.8 km thick in Greece), whereas the flysch unit of Upper Eocene–Oligocene (External Hellenides) and Oligocene–Aquitanian (Albanides) contributed to the deformation of the Ionian zone. In the Ionian zone, Triassic evaporites are laterally continuous and act as an effective seal unit when thrusted above Mesozoic carbonate/Tertiary units. Most of the oil and gas fields, oil shows and surface seeps have been developed in association with the relative more complex structure styles in the internal and the central Ionian zone of Albania and Greece. The Triassic evaporite detachment is detected at depths of 8–22 km in Albania, and about 5 km to 12–13 km in Greece. Thin and probably combination of thin- and thick-skinned deformation (SW Greece) of the Meso-Cenozoic succession above the Triassic evaporite and Permian sequences better depicts the complex structural architecture of the External Hellenides and Albanides, later affected by strike-slip tectonics and extensional deformation active since the Early Pliocene times. The main source rock levels, Lower Cretaceous shale/carbonate, Toarcian Posidonia and Triassic shales, are common in the Albanides and the Hellenides forelands. The thickness and Total Organic Carbon of these levels significantly increase in Albania, whereas trapping mechanism is almost the same and the Triassic evaporites play a significant role in both forelands. The hydrocarbon migration primarily followed developed thrust faults and important halokinesis, to charge fractured Cretaceous–Eocene carbonate reservoirs in the overthrust unit (Ionian zone), likely beneath the thrusted anticlinal belts. These sub-thrust structural models are related to the evaporites. Sub-thrust plays, referred to the autochthonous units (Apulia, Pre-Apulia/Paxos, Sazani zones), may also present reservoir potential in Albania and Western Greece. Upper Miocene and Pliocene deposits (sands) record reservoir potential in stratigraphic traps and good caprock characteristics in the Peri-Adriatic depression (Albania), whereas Messinian evaporites and clays may document seal potential for Upper Miocene sands in the southern areas of the Ionian Sea (Kyparissiakos Gulf, SW Kythira)

Deformation patterns in the southwestern part of the Mediterranean Ridge (South Matapan Trench, Western Greece)

Summarization: Seismic reflection data and bathymetry analyses, together with geological information, are combined in the present work to identify seabed structural deformation and crustal structure in the Western Mediterranean Ridge (the backstop and the South Matapan Trench). As a first step, we apply bathymetric data and state of art methods of pattern recognition to automatically detect seabed lineaments, which are possibly related to the presence of tectonic structures (faults). The resulting pattern is tied to seismic reflection data, further assisting in the construction of a stratigraphic and structural model for this part of the Mediterranean Ridge. Structural elements and stratigraphic units in the final model are estimated based on: (a) the detected lineaments on the seabed, (b) the distribution of the interval velocities and the presence of velocity inversions, (c) the continuity and the amplitudes of the seismic reflections, the seismic structure of the units and (d) well and stratigraphic data as well as the main tectonic structures from the nearest onshore areas. Seabed morphology in the study area is probably related with the past and recent tectonics movements that result from African and European plates’ convergence. Backthrusts and reverse faults, flower structures and deep normal faults are among the most important extensional/compressional structures interpreted in the study area.Presented on: Marine Geophysical Researc