Abstract This wide area of the Alpine–Himalayan belt evolved through a series of tectonic events related to the opening and closure of the Tethys Ocean. In doing so it produced the largest mountain belt of the world, which extends from the Atlantic to the Pacific oceans. The basins associated with this belt contain invaluable information related to mountain building processes and are the locus of rich hydrocarbon accumulations. However, knowledge about the geological evolution of the region is limited compared to what they offer. This has been mainly due to the difficulty and inaccessibility of cross-country studies. This Special Publication is dedicated to the part of the Alpine–Himalayan belt running from Bulgaria to Armenia, and from Ukraine to the Arabian Platform. It includes twenty multidisciplinary studies covering topics in structural geology/tectonics; geophysics; geochemistry; palaeontology; petrography; sedimentology; stratigraphy; and subsidence and lithospheric modelling. This volume reports results obtained during the MEBE (Middle East Basin Evolution) Programme and related projects in the circum Black Sea and peri-Arabian regions.

Abstract The Palaeozoic to recent evolution of the Tethys system gave way to the largest mountain chain of the world extending from the Atlantic to Pacific oceans – the Alpine–Himalayan Mountain chain, which is still developing as a result of collision and northwards convergence of continental blocks including Apulia in the west, the Afro-Arabian Plate in the middle and the Indian Plate in the east. This Special Publication addresses the main problems of the middle part of this system incorporating the Balkans, Black Sea and Greater Caucasus in the north and the Afro-Arabian Plate in the south. Since the Early Mesozoic a number of small to large scale oceanic basins opened and closed as the intervening continental fragments drifted northwards and diachronously collided with and accreted to the southern margin of the Eurasian Plate. Despite the remarkable consequences of this, in terms of subduction, obduction and orogenic processes, little is known about the timing and palaeogeographic evolution of the region. This includes the amounts of shortening and interplay between synconvergent extension and compression, development of magmatic arc and arc-related basins and the timing and mechanism of their deformation. The chapters presented in this Special Publication present new information that help to fill some of the gaps of the puzzle.

Abstract The Black Sea is generally thought to be a back-arc basin with active extension (rifting) beginning in late Early Cretaceous times – although some fundamental issues such as the presence or absence of a related magmatic arc and the orientation of the related, driving, subduction zone remain vaguely defined at best. However, as shown here, the regional structure of the Black Sea is consistent with that predicted by geodynamic models of modern back-arc basin formation, in which extension is driven by slab roll-back. This includes an asymmetric distribution of horst and graben structures in the back-arc basin, the distribution and spacing of which is related to the strength of the underlying lithosphere, which forms the hanging wall of the subduction zone. By analogy, the intrabasinal structure of the Black Sea as a whole is explicable as the consequence of a single phase of asymmetric back-arc basin formation, not two separate phases independently responsible for its western and eastern segments, and its underlying lithosphere is rheologically strong, as predicted by recent models of Precambrian Europe and present-day tomography.

Abstract A back-arc Black Sea Basin consists of two deep sub-basins – the West-Black Sea (WBS) and the East-Black Sea (EBS) – filled with thick sediments (up to 12–14 km), which are separated by the mid–Black Sea Ridge (MBSR) – a NW trending basement uplift structure. For a better understanding of the lithosphere structure of these two sub-basins, the authors made a comprehensive analysis of the available geological and geophysical data, including carrying out a three-dimensional (3D) gravity back-stripping analysis, a reinterpretation of a number of seismic refraction profiles as well as the re-evaluation of seismological data and local seismic tomography. Inferred differences in the basin architecture and lithosphere structure of the WBS and EBS can be explained by different affinities of the underlying crustal domains and by the peculiarities of their (Cretaceous and younger) rift and post-rift history. Rifting that led to oceanic crust formation in the WBS occurred within the continental crust of the Moesian Platform along Mesozoic sutures with adjoining accreted terranes. The EBS, most probably, formed within the Transcaucasus continental domain due to strike–slip movements along the MBSR. Underthrusting of the EBS oceanic lithosphere beneath the continental domain of the Scythian Platform led to the formation offshore of the Crimean orogen of accretional wedge of Sorokin Trough.

Abstract A ray-tracing modelling of seismic refraction data acquired in the 1960s has been undertaken on two north–south lines – Profile 25 in the western part of the Black Sea and Profile 28/29 crossing the Azov Sea and central part of the Black Sea. The velocity model along Profile 25 shows two domains interpreted as thin (5 km) high-velocity (sub-)oceanic crust below the deep-water part of the Western Black Sea (WBS) basin, covered by 12–13 km of Cretaceous and younger sediments, and a 39 km thick continental domain of the Scythian Platform and southernmost part of the East European Platform. They are separated by a high-amplitude normal fault, interpreted as being related to the opening of the WBS during Late Cretaceous rifting. The velocity model on Profile 28/29 shows what is interpreted as oceanic crust on the northwestern extremity of the Eastern Black Sea Basin (EBS) and thinned continental crust (Moho depths at 29 km) underlying the mid-Black Sea Ridge (MBSR) that separates the EBS and WBS. The basement of the MBSR comprises three units, which in an en echelon-like manner elevate southwards from a depth of 10–11 km beneath the Andrusov Ridge to 6 km on Arkhangelsky Ridge. An inclined seismic boundary at the Moho interface may be related to oblique rifting setting during the initial formation of the EBS.

Abstract Based on hydro-acoustic and geophysical observations, this paper presents an analysis of geomorphological and geological settings of gas methane occurrence on the NW shelf and upper continental slope, in the Sorokin trough and on the Kerch-Taman offshore, in the Black Sea. Gases are associated with seeps, mud volcanoes and gas hydrates. Evidence is given for the thermogenic nature of methane. The gas methane is of mostly abiogenic origin. Small gas releases may be produced by the decomposition of Quaternary organic material near the sea floor through the action of bacteria or biodegradation of redeposited thermogenic hydrocarbons. The origin of carbonate formations is related to degassing sedimentary layers. There is a possible role for deep faults in transporting gas to the sea floor. The gas hydrate stability zone in the Black Sea lies at minimum water depth of 600–650 m with its thickness up to 500 m.

Abstract Brittle tectonics analysis and stress tensor reconstructions allow us to better depict the Mesozoic and Cenozoic geodynamical evolution of the Eastern Balkanides which is characterized by a series of overimposed basin-systems. The Late Permian–Triassic corresponds to a wide carbonate platform with local embryonic troughs. During the Jurassic–Early Cretaceous period, the area, limited by regional unconformities, was at first dominated by the existence of a deep basin until the latest middle Jurassic, then by its gradual closure during the Late Jurassic–Early Cretaceous. Traces of these tectonic events are found as a result of brittle tectonic data analysis, especially in the Strandja Zone where NE–SW extension and ENE–WSW compression may be related to the Early Alpine phases of rifting and shortening, respectively. The Late Cretaceous–middle Eocene period was governed by the back-arc basin/island-arc system of East Balkan/Srednogorie zones. The inversion of these extensional zones occurred after the Maastrichtian, then important shearing and thrusting developed during the major shortening in the latest Middle Eocene. These Late Alpine tectonic phases were well characterized by brittle tectonics and the analysis of faulting in terms of stress tensors allows us to identify the main directions of extension of the rifting stage which is north–south to NNE–SSW, and the directions of compression of the Laramian and Illyrian phases, which are NE–SW and north–south, respectively. The relationships between folding and reverse and strike–slip faults are established as well as the occurrence of post-folding normal faults assigned to collapse process following the shortening.

Abstract The Eocene uplift and inversion of a part of the Black Sea margin in the Central Pontides, allows us to study the stratigraphic sequence of the Western Black Sea Basin (WBS). The revision of this sequence, with 164 nannoplankton ages, indicates that subsidence and rifting started in the Upper Barremian and accelerated during the Aptian. The rifting of the western Black Sea Basin lasted about 40 Ma (from late Barremian to Coniacian). In the inner, inverted, Black Sea margin, the syn-rift sequence ends up with shallow marine sands. The uppermost Albian to Turonian was a period of erosion or non deposition. This regional mid-Cretaceous stratigraphical gap might result from rift flank uplift, as expected in the case of a thick and cold pre-rift lithosphere. However, coeval collision of the Kargi Block, along the North Tethyan subduction zone at the southern margin of the Pontides, might also have contributed to this uplift. A rapid thermal post-rift subsidence of the margin occurred during the Coniacian–Santonian. Collision of the Kirşehir continental block commenced in Early Eocene time (zone NP12) giving rise to compressional deformation and sedimentation in piggyback basins in the Central Pontides, whereas the eastern Black Sea was still opening.

Abstract Three fundamental stages of the Cretaceous–Neogene tectonic evolution of the Odessa Shelf and Azov Sea (northern margins of western and eastern Black Sea basins, respectively) have been documented from the analysis of reinterpreted regional seismic profiling and one-dimensional (1-D) subsidence analysis of 49 wells, for which the stratigraphic interpretation was recently revised. (1) An initial active rifting stage began within the Early Cretaceous (not later than Aptian–Albian times) and continued until the end of the Santonian in the Late Cretaceous ( c . 128–83 Ma). A system of half-grabens with mainly south-dipping normal faults developed on the Odessa Shelf at this time. The most profound faulting, accompanied by volcanic activity, occurred in the NE–SW orientated Karkinit-Gubkin rift basin at the boundary between the Eastern European and Scythian platforms. The footwalls of half-grabens were exposed above sea level and subject to erosion at this time. Active extensional processes affected the western part of Azov Sea and, while the onset and cessation of these cannot be tightly constrained, they are compatible with the well constrained results from the Odessa Shelf. (2) The second tectonic stage is one of passive post-rift thermal subsidence that lasted from the Campanian (Late Cretaceous) until the end of the Middle Eocene (83–38.6 Ma). (3) The third stage of basin evolution is one of inversion tectonics in a compressional setting. Discrete inversion events occurred at the end of the Middle Eocene, during the Late Eocene, during the Early Miocene and at Middle Miocene times ( c . 38.6 Ma, c . 35.4 Ma, c . 16.3 Ma, c . 10.4 Ma, respectively) and typical inversion structures developed on the Odessa Shelf, some parts of which were uplifted and significantly eroded (down to the Lower Cretaceous succession). The southern part of the Azov Sea, opening into the northernmost eastern Black Sea basin, subsided rapidly during this time; thereafter, until the Quaternary, rapid subsidence was limited to its southeastern part, which was incorporated into the Indolo-Kuban foreland basin of the Greater Caucasus orogen.

Abstract The Black Sea is an extensional back-arc basin developed along the northern active margin of the Tethys Ocean which was subducted northward from the Triassic to Miocene times. The Romanian Black Sea shelf is dominated by mid-Cretaceous extensional structures and their sedimentary cover, subsequently affected by Cenozoic compression. Here we analyse the post-Oligocene structural and sedimentological evolution of the shelf, based on Romanian oil industry data consisting of (1) 5300 line-km reflection seismic profiles situated on the shelf and continental slope; and (2) depth and lithostratigraphic information from 60 boreholes on the shelf. Our study provides evidence for a changing evolution of the shelf during a relatively short period of time directly related to the pre-Miocene period and the evolution of the Romanian onshore. Mio-Pleistocene subsidence of the Romanian Black Sea shelf is highly variable and is directly dependent on sediment input, tectonic activity as well as water-level fluctuations. Subsidence during the Badenian–Sarmatian and the Dacian–Quaternary was limited. In contrast, during the Pontian, shelf subsidence was progressively faster in the basinward direction. Subsidence on the outer shelf was much more significant than elsewhere on the shelf. Tectonically, the most active period during the Mio-Pleistocene was the Pontian. The Badenian–Sarmatian was largely quiescent and the Dacian–Quaternary saw a decrease in the Pontian tectonic activity, coming possibly even to a halt. From a sequence-stratigraphical point of view, eight systems tracts were identified for the Mio-Pleistocene sedimentary section. The Badenian-Sarmatian unit was attributed to a HST (highstand systems tract). The Pontian unit was subdivided into P1, P2, P3 and P4. Subunit P1, which was laid down on the slope at the time of deposition, is progradational and attributable to the lowstand wedge of a LST (lowstand systems tract). Subunit P2 is likewise also attributed to a LST, having the continental slope and the deep basin as palaeo-depositional environments. The reflection terminations and the wedge-shape of P3 suggest that it was deposited in the deep basin during a sea level lowstand. The next transgressive systems tract (TST) and HST developed during the deposition of P4. The boundary between P4 and the Dacian is represented by an erosional hiatus, which comprises the LST that follows the formation of the sequence boundary at the end of the Pontian. During the Dacian–Quaternary, the subsequent TST and HST were deposited on the inner and middle shelves. Sedimentation on the Romanian shelf during the Mio-Pleistocene period was thus strongly influenced by sediment input and subsidence, while sea level fluctuations played a lesser role. As sediment input is related to the evolution of the adjacent land and subsidence is dependent on sediment supply, tectonic activity and sea level fluctuations, these two factors are not totally independent.

Abstract The Greater Caucasus (GC) forms a high Alpine fold-and-thrust belt on the southern margin of the East European Platform (EEP). The Triassic, and particularly, the Jurassic history of the Western Greater Caucasus region is important for our understanding of the palaeogeographic and tectonic evolution of the western Tethys area. In order to better constrain the nature and relevance of these events in the evolution of the region, which are classically described as the Late Triassic to Late Jurassic Cimmerian events, a field campaign in the Western Greater Caucasus was undertaken. Analysis of structural, sedimentological and petrological data from 41 sites in the Fore-Caucasus (Malaya Laba, Mount Tkhach-Belaya River), the Central Greater Caucasus (Georgievskoye, Otdaleni) and Southern Slope (Krasnaya Poliana) areas of the Western Greater Caucasus revealed that a broad asymmetric basin, with associated emergent volcanic islands, formed in the area in Jurassic times. Incipient back-arc rifting in Pliensbachian times was coeval with similar rifting episodes in the Pontides and South Caspian Sea areas. The synchroneity of these events may have been related to the renewal of the Tethys subduction to the south of the Eo-Cimmerian accretionary belt. Rift reactivation, with significant thinning of the continental lithosphere, occurred in the Aalenian. Despite the strong Alpine tectonic overprinting, some structural data confirms that the extension trend was east–west (almost parallel to the active margin) resulting in the formation of a series of pull-apart basins in the GC and the South Caspian region behind the Eastern Pontides–Lesser Caucasus subduction-related volcanic belt. In Bajocian times, subduction-related volcanic activity largely expanded from the Eastern Pontides–Lesser Caucasus to encompass the Transcaucasus, the southern part of GC and the Crimea region. Such widening of the volcanic arc was probably due to a shallowing of the northward subducting slab. In the back-arc GC region, this signalled the onset of the post-rift stage. The return of the slab to normal steepness resulted in subsidence in the back-arc region and in the GC with extensive accommodation space creation. This was subsequently filled by the Late Jurassic, Cretaceous and Cenozoic sedimentary successions.

Abstract The tectonic and geological evolution of Georgia and the Caucasus, on the whole, are largely determined by its position between the still converging Eurasian and Africa–Arabian lithosphere plates, within the wide zone of a continent–continent collision. The region in the Late Proterozoic–Early Cenozoic belonged to the now-vanished Tethys Ocean and its northern (Eurasian) and southern (Africa–Arabian) margins. Within this convergence zone there existed a system of island arcs, intra-arc rifts, back-arc basins characteristic of the pre-collisional stage. During syncollisional (the Oligocene–Middle Miocene) and post-collisional (the Late Miocene–Quaternary) stages, at the place of back-arc basins were formed fold and thrust belts of the Greater and Lesser Caucasus separated by the Transcaucasian intermontane lowland. Starting from the Late Miocene and as far as the end of the Pleistocene, in the central part of the region, simultaneously with formation of molassic basins and accumulation of coarse molasses there took place volcanic eruptions in subaerial conditions. According to the numerous data obtained during past decades we present a review on the lithological and structural characteristics of these collisional basins and on the coeval magmatic events.

Abstract The Greater Caucasus is Europe's highest mountain belt and results from the inversion of the Greater Caucasus back-arc-type basin due to the collision of Arabia and Eurasia. The orogenic processes that led to the present mountain chain started in the Early Cenozoic, accelerated during the Plio-Pleistocene, and are still active as shown from present GPS studies and earthquake distribution. The Greater Caucasus is a doubly verging fold-and-thrust belt, with a pro- and a retro wedge actively propagating into the foreland sedimentary basin of the Kura to the south and the Terek to the north, respectively. Based on tectonic geomorphology – active and abandoned thrust fronts – the mountain range can be subdivided into several zones with different uplift amounts and rates with very heterogeneous strain partitioning. The central part of the mountain range – defined by the Main Caucasus Thrust to the south and backthrusts to the north – forms a triangular-shape zone showing the highest uplift and fastest rates, and is due to thrusting over a steep tectonic ramp system at depth. The meridional orogenic in front of the Greater Caucasus in Azerbaijan lies at the foothills of the Lesser Caucasus, to the south of the Kura foreland basin.

Abstract Early Carboniferous–Eocene units exposed in the Arvin area document the development of the southerly, active continental margin of Eurasia. The oldest rocks exposed in the area are Early Carboniferous granites that regionally intrude schists and gneisses. The continental terrane rifted along the entire length of the Pontides (>1000 km east–west) during the Early–Middle Jurassic. Subsidence of the rift basin in the Artvin area was accompanied by terrigenous debris flows, turbidites and deep-sea radiolarian muds, and was associated with local extrusion of chemically ‘enriched’ basalts. Swarms of subduction-influenced basic, intermediate, to locally silicic dykes, intruded high-grade metamorphic basement within the rift. A basement horst within the rift was covered by condensed pink ammonite-bearing pelagic facies. Large volumes of subduction-influenced basalts erupted during the later stages of extensional basin development (Mid-Jurassic), associated with volcaniclastic sedimentation. The Artvin Basin is interpreted as a supra-subduction rift associated with incipient arc magmatism. The basin was stratigraphically inverted in response to Late Middle Jurassic ‘Neo-Cimmerian’ deformation. It was then partially eroded and covered by Upper Jurassic continental, to shallow-marine sediments, together with localized eruption of ‘enriched’ (non-subduction-influenced) basalts. The margin collapsed during the Late Jurassic–Early Cretaceous, initiating deposition of pelagic carbonates and mixed terrigenous, biogenic and volcaniclastic gravity flows. Subduction during the Late Cretaceous then constructed the east Pontide magmatic arc and a thick volcaniclastic fore-arc apron to the south. Supra-subduction-type ophiolites and accretionary melange formed within Neotethys to the south during the Late Cretaceous and were emplaced regionally northwards onto the leading edge of the Pontide active continental margin during the latest Cretaceous. Continental collision during the Mid-Eocene telescoped the distal part of the active margin which was emplaced northwards onto the east Pontide continental basement. The geological evolution of Artvin area correlates with the Pontides further west and with the southern and northern Transcaucasus to the east. Our favoured tectonic model involves long-lived, episodic, northward subduction of Tethys. Finally, there is no evidence of ‘Palaeotethyan’ ophiolites in the eastern Pontides region.

Abstract In the Lesser Caucasus three main domains are distinguished from SW to NE: (1) the autochthonous South Armenian Block (SAB), a Gondwana-derived terrane; (2) the ophiolitic Sevan–Akera suture zone; and (3) the Eurasian plate. Based on our field work, new stratigraphical, petrological, geochemical and geochronological data combined with previous data we present new insights on the subduction, obduction and collision processes recorded in the Lesser Caucasus. Two subductions are clearly identified, one related to the Neotethys subduction beneath the Eurasian margin and one intra-oceanic (SSZ) responsible for the opening of a back-arc basin which corresponds to the ophiolites of the Lesser Caucasus. The obduction occurred during the Late Coniacian to Santonian and is responsible for the widespread ophiolitic nappe outcrop in front of the suture zone. Following the subduction of oceanic lithosphere remnants under Eurasia, the collision of the SAB with Eurasia started during the Paleocene, producing 1) folding of ophiolites, arc and Upper Cretaceous formations (Transcaucasus massif to Karabakh); 2) thrusting toward SW; and 3) a foreland basin in front of the belt. Upper–Middle Eocene series unconformably cover the three domains. From Eocene to Miocene as a result of the Arabian plate collision with the SAB to the South, southward propagation of shortening featured by folding and thrusting occurred all along the belt. These deformations are sealed by a thick sequence of unconformable Miocene to Quaternary clastic and volcanic rocks of debated origin.

Abstract Similar geological, petrological, geochemical and age features are found in various Armenian ophiolitic massifs (Sevan, Stepanavan and Vedi). These data argue for the presence of a single large ophiolite unit obducted on the South Armenian Block (SAB). Lherzolite Ophiolite type rock assemblages evidence a Lower–Middle Jurassic slow-spreading rate. The lavas and gabbros have a hybrid geochemical composition intermediate between arc and Mid Ocean Ridge Basalt (MORB) signatures which suggest they were probably formed in a back-arc basin. This oceanic sequence is overlain by pillowed alkaline lavas emplaced in marine conditions. Their geochemical composition is similar to plateau-lavas. Finally, this thickened oceanic crust is overlain by Upper Cretaceous calc-alkaline lavas likely formed in a supra-subduction zone environment. The age of the ophiolite is constrained by 40 Ar/ 39 Ar dating experiments provided a magmatic crystallization age of 178.7±2.6 Ma, and further evidence of greenschist facies crystallization during hydrothermal alteration until c . 155 Ma. Thus, top-to-the-south obduction likely initiated along the margin of the back-arc domain, directly south of the Vedi oceanic crust, and was transported as a whole on the SAB in the Coniacian times (88–87 Ma). Final closure of the basin is Late Cretaceous in age (73–71 Ma) as dated by metamorphic rocks.

Abstract In order to improve our understanding of the palaeogeographic and geodynamic evolution of the Tethyan realms preserved in the Lesser Caucasus we here review the existing data for the sedimentary cover of ophiolites preserved in Armenia. Particular attention is given to those dated sedimentary rocks that are in direct genetic contact with ophiolitic lavas, as they provide constraints for submarine oceanic activity. The oldest available ages come from the Sevan–Akera suture zone that point to a Late Triassic oceanization. Data from both the Sevan and Vedi ophiolites provide evidence for Middle Jurassic (Bajocian) submarine activity, that continued until at least the Late Jurassic (Mid/Late Oxfordian to Late Kimmeridgian/Early Tithonian), as dated recently in Stepanavan and in this study for the Vedi ophiolite.

Abstract The stress indicators describing the recent (provided by active tectonics framework) and palaeo-stress (provided by micro-fault kinematics and volcanic cluster) patterns show the scale and temporal changes in stress states since the beginning of Arabian–Eurasian collision. The recent stress derived from the active fault kinematics in the Lesser Caucasus and adjacent area corresponds to a strike–slip regime with both transtension and transpression characteristics. The kinematics of active structures of various scale are conditioned by tectonic stress field with general north–south compression and east–west extension. The distribution of Neogene to Quaternary volcanic cluster geometries and micro-fault kinematic data evidence the time and orientation variability of the stress field since the beginning of the Arabian–Eurasian collision. In addition to the general north–south compression orientation, two other – NW–SE and NE–SW – secondary orientations are observed. The first one was dominant between the Palaeogene and the late Early Miocene and the second one has prevailed between the Late Miocene and the Quaternary. Since the continental collision of Arabia with Eurasia the tectonic stress regime in the Lesser Caucasus and adjacent area changed from compression (thrusting and reverse faulting) to transtension-transpression (strike–slip faulting with various vertical components).

Abstract Five different deformation phases have been recognized in the SE Anatolian orogen and the Arabian Platform based on palaeostress inversion studies using fault-slip data sets. The timing and duration of these phases are determined using various criteria including the age of the affected strata, syndepositional structures, cross-cutting structures and overprinting slickensides. The oldest deformation phase is characterized generally by NE–SW-directed extension. The extension is thought to have resulted from slab-roll back processes during the Maastrichtian to Middle Eocene interval ( c . 60 Ma to 40–35 Ma). The second deformation phase is characterized by east–west to NW–SE-directed compression and thought to result from cessation of roll-back processes possibly due to subduction of younger oceanic crust or increase in the convergence rate between Africa and Eurasia during the post-Middle Eocene to Late Oligocene interval ( c . 40–35 Ma to 25 Ma). The third deformation phase is characterized by east–west to NW–SE-directed extension possibly due to slab detachment that initiated in Iran and migrated westwards during the latest Oligocene to Middle Miocene period (25–11 Ma). The fourth deformation phase is characterized by approximately north–south-directed compression due to collision and further northwards indentation of Arabian Plate by the end of Middle Miocene (11–3.5 Ma). The fifth and present deformation phase is characterized by NE–SW compression which might result from tectonic re-organization in the region since the Middle Pliocene ( c . 3.5 Ma to recent).