Shatsky Ridge Research Articles

Contrasting lithospheric geophysical structure of the Black Sea subbasins: Relevance to testing geotectonic models for this mega depression

We present an integrated analysis of the geophysical parameters of the lithosphere of Black Sea basin obtained as a result of the interpretation of magnetic, gravity, thermal, deep seismic sounding and seismic-tomographic data. It first demonstrates inherent significant differences in geophysical parameters of lithosphere in the Western and Eastern Black Sea subbasins existing from the prerift stage. The set of reviewed parameters responsible for formation of the present-day lithosphere includes types of crust, depths to acoustic basement, configuration of subbasins, depths to Moho, heat flow and relief of the thermal-asthenosphere boundary (LAB), trends of main deep faults of the crystalline crust, their kinematic types, occurring linear magnetic anomalies, velocity pattern of subcrustal mantle. The above-mentioned parameters of the lithosphere are indicators of the age, geodynamics and driving mechanisms for opening of a subbasins. Oblique trends of the subbasins and the topography of Moho discontinuity in the west and east domains, oblique striking of pre-rifting Istanbul zone and the Shatsky Ridge and different trends of deep faults in the crystalline crust suggest distinct lithospheric structure existing from pre-opening of the Black Sea subbasins and different geodynamical conditions of its formation. The Odesa-Sinop-Ordu deep fault zone as a direct continuation of the Golovanivskaya suture zone of the Ukrainian shield and its slope, probably is of the Precambrian age. So it could be the tectonic boundary between two segments of pre-rift continental crust and between future subbasins. The examples illustrate how indicated parameters of the lithosphere can geophysically confirm the basic ideas of available models for geodynamics of the Black Sea.

Jurassic-Cretaceous magmatic arcs in the Eastern Black Sea: Evidence from geophysical studies and 2D modeling

The origin, tectonic development, and lithosphere structure of the East Black Sea Basin (EBSB) are governed by the evolution of the northern branch of the Tethys ocean. The most spectacular features of its evolution could retain their imprints in geophysical fields and models, which we used to constrain a geophysical transect for the crust and upper mantle crossing the EBSB and the Shatsky Ridge (SR) from the Eastern Pontides to the Northern Caucasus. 2D gravity and magnetic modeling, constrained by wide-angle seismic data, revealed thin high-density and high-velocity sub-oceanic crust of the EBSB with the Moho shallowing up ~20 km depth. A spectacular feature of the Black Sea magnetic field is the Alushta-Batumi anomaly (ABA) above the SR that could be an imprint of subduction-related Middle Jurassic magmatic arc, whereas the Cretaceous (in Eastern Pontides) magmatic arc manifests itself by a chain of magnetic anomalies on the southern shoreline of the Black Sea. The high-velocity heterogeneity, revealed by seismic tomography, could be an image of a slab due to Mesozoic (Middle Jurassic and Cretaceous) subduction of the northern branch of Neotethys ocean. It shows rather a flat subduction slab that plunges northwards from subcrustal depths south of Eastern Pontide to the depth of > 70–80 km below the SR. Middle Jurassic and Cretaceous subduction fronts are located closely in the region of Eastern Pontides, whereas the related magmatic arcs are spaced differently – over the SR for the Middle Jurassic arc and along the southern coastline for Cretaceous Eastern Pontide magmatic arc correspondingly. The latter could be caused by the opening of the EBSB in the Cretaceous that separated the eastern segment of the BS onto the Eastern Pontides – Arkhangelsky Ridge and the SR – Northern Caucasus domains.

Palaeo-stress regimes and structural framework during the Mesozoic-Cenozoic tectonic evolution of the Crimean Mountains (the northern margin of the Black Sea)

• The Crimean Mtns (CM) are divided into two parts by a NW-SE oriented main fault zone. • Two systems of E-W and of NW-SE oriented faults were reactivated since the Cretaceous. • The reactivated structures control the Cenozoic inversion of CM. • The model shows the major role of indenter during the Cenozoic inversion. This paper presents a chronology of tectonic events in the Crimean Mountains (CM) based on a micro- (palaeo-stress) and macro-scale (tectonic structures) structural analysis since the Cretaceous. Recent studies have attempted to fit the geology of the CM into the geodynamic context of the subduction of the Neotethys plate beneath the Eurasian margin; however, these attempts remain difficult and controversial as they are based dominantly on stratigraphic analysis. New structural analysis results indicate that structural development within the CM was largely determined by the influence of pre-existing structures that occurred long before the Cretaceous rifting in the Black Sea (BS). This could explain the features of the geological structure in the Western and Eastern CM separated by the Alushta–Simferopol Fault Zone (ASFZ). New palaeo-stress analysis allows us to identify the trends and timing of the Mesozoic–Cenozoic tectonic deformations with greater precision. Superimposing the low-magnitude seismicity (M ≤ 3) with structures defined on the established geological cross-sections permit the localization of currently active structures. Considering both recent scientific achievements concerning the geology of the CM and the results of this study, we propose a qualitative model of the formation of the BS Basin and its inversion in the context of the BS-Greater Caucasus (GC). In this model, the Shatsky Ridge (ShR), moving to the north, acts as an indenter deforming the CM and the GC. The results are of practical importance for geodynamic modelling and hydrocarbon exploration .

Crustal thickness in the Black Sea and surrounding region, estimated from the gravity data

In this research, the crustal thickness (Moho depth) variations in the Black Sea and surrounding region were calculated from the regional gravity anomaly data using an empirical equation. The data were obtained from the open source of Bureau Gravimétrique International (BGI) in digitized form. The gravity anomaly values are changing from −80 mGal in the onshore Black Sea region in Turkey to 260 mGal in the deeper parts of the sea. Maximum gravity anomaly indicates a consistent pattern in the offshore Black Sea and anomaly pattern follows the shape of the shoreline. The pattern is consistent with the deeper parts in the marine area and the eastern anomaly extends into the Russian territory between NW of Georgia and SE of the Crimean Peninsula. The crustal thickness map indicates almost the same trends. In this map, the minimum crustal thickness is about 10 km around the mid of the Shatsky Ridge, close to the coastal regions of SE Russia and the second thinnest (12 km) place is located around the Western Black Sea Basin. The maximum thicknesses are represented with the 34–36 km contours in the onshore Eastern Black Sea region and east of Anatolia. On the other hand, the maximum crustal thickness to the north can reach up to 28 km around the Sea of Azov and to the east. The thickness variations are generally related with the main tectonic trends in this region. The Analytic Signal (AS) and maxima points of the horizontal gradients (maxspots) maps constructed from the gravity anomalies are also prepared in this research to see if these anomaly trends follow the tectonic lines. The regions of maximum and minimum crustal thicknesses are well-consistent with the AS anomalies and boundaries of the bifocal thin crustal sections coinciding with the Eastern and Western Black Sea basinal parts are surrounded with the maxspots. The northern thick crustal region around the southern margin of the Indolo-Kuban Basin is also surrounded by the maxspots. It is possible to claim that the maxspots map from the horizontal gradient of Bouguer anomalies reflects the boundaries of the main tectonic units in the Black Sea Region. Particularly, southern boundary of the Scythian Platform, southern boundary of the Shatsky Ridge and Great Caucasus thrust are distinctive and easy to follow in the maxspots map.

The crustal structure of the transition from the East Black Sea Basin to the Shatsky Ridge from the reinterpretation of deep seismic sounding data on profiles 14-15-16

The paper represents the results of velocity modeling (ray-tracing modeling) performed for three deep seismic sounding (DSS) profiles 14, 15 and 16 acquired in the eastern part of the Black Sea more than 40 years ago. These profiles represent a system of radial profiles diverging from one common shot point in the East Black Sea Basin (EBSB) and crossing the Shatsky Ridge. The performed modeling showed that thin (~10 km) crystalline EBSB crust, with velocities increasing from 6,5 km/s in the basement to 7,0 km/s on the Moho (20—22 km), is overlain by sediments as thick as ~10 km. The continental crust of the Shatsky Ridge of ~30 km thickness comprises two layers — the upper crust (Vp=6,0÷6,5 km/s) as thick as 15 km and the 10 km thick lower crust (Vp =6,5÷7,0 km/s). The transition from thin EBSB suboceanic crust to the Shatsky Ridge continental crust occurs rather sharply, over an interval of ~25 km, where changes are observed in all crustal layers — from sediments to the Moho. The transition of the two types of the crust is ascribed by a lineament, parallel to the coastline of the eastern part of the Black Sea, and is associated with a collinear Alushta-Batumi magnetic anomaly of the same (NW) strike. These features may testify in favor of the tectonic nature of the transition zone, the formation and activation of which took place during the main stages of evolution of the study region — at the closure of Mesozoic Tethys ocean, during the riftogenic opening of the EBSB in Cretaceous, and during the Alpine orogeny in the compression setting. The wedge-like shape of the EBSB, expanding southeastward up to 160—180 km width, is consistent with the concept of riftogenic opening of the EBSB in the Early Cretaceous as a result of clockwise rotation of the Mid Black Sea Ridge.

Spatial and Temporal Evolution of Rifting and Continental Breakup in the Eastern Black Sea Basin Revealed by Long‐Offset Seismic Reflection Data

AbstractThe age and distribution of the synrift and early postrift infill records the spatial and temporal distribution of extension and breakup processes in a rift basin. The Eastern Black Sea Basin (EBSB) is thought to have formed by back‐arc extension during Cretaceous to Early Cenozoic time. However, a lack of direct constraints on its deep stratigraphy leaves uncertainties over the time, duration, and location for rifting and breakup processes in the basin. Here we use the enhanced imaging provided by 2‐D long‐offset seismic reflection profiles to analyze the deep structural and stratigraphic elements of the EBSB. Based on these elements, we infer the presence of two distinct Late Cretaceous synrift units, recording initial extension (rift stage 1) over the continental highs (Shatsky Ridge and the Mid Black Sea High), followed by strain localization along the major basin‐bounding faults and rift migration toward the basin axis (rift stage 2). Overlying these units, Palaeocene(?)‐Eocene and Oligocene units show a synkinematic character in the NW, with evidence for ongoing extension until Oligocene time. Toward the SE, these sequences are instead postkinematic, directly overlaying a basement emplaced during breakup. We interpret the Palaeocene(?)‐Oligocene units to record the time spanning from the initiation of breakup (Late Cretaceous‐Palaeocene, in the SE) to the end of extension (Oligocene, in the NW). The first ubiquitously postrift infill is the Lower Miocene Maykop Formation. Our results highlight the along‐strike temporal variability of extension and breakup processes in the EBSB.

Towards а design of new generation digital seismic seabed seismographs – current state and future outlook

The paper presents the comparative characteristics of self-pop-up digital seabed seismometers that have been developed since the early 2000s. The requirements for the main technical characteristics that should be considered for developing the new-generation of self-pop-up seabed seismometers have been proposed. The microcontroller and reference frequency generator are the key parts for a seabed seismometer design. The paper provides the development results of these key components, which are essential for the seismometer performance (power consumption and functionality).
 A draft proposal for seabed seismic exploration project in the Russian sector of the Black Sea solving the current actual geological problems is presented. Implementation of the project will contribute to determination of the crystalline basement depth within the Shatsky ridge and the Tuapse depression; detection of P and S wave velocities in the lower part of sedimentary cover and in the basement, and to the refinement of the Earth’s crust thickness. The extension of regional seabed seismic lines from the Turkish to the Russian sector of the Black Sea will give the scientists a clearer picture of the Earth’s crust structure over the whole east Black Sea basin. The results of seabed studies will verify and improve the results of the Black Sea 2011 towed-streamer survey (with 10 km streamer) on the sedimentary cover structure and the Earth’s crust.

Effects of mesoscale eddies on behavior of an oil spill resulting from an accidental deepwater blowout in the Black Sea: an assessment of the environmental impacts.

Because of the environmental sensitivity of the Black Sea, as a semi-enclosed sea, any subsea oil spill can cause destructive impacts on the marine environment and beaches. Employing numerical modeling as a prediction tool is one of the most efficient methods to understand oil spill behavior under various environmental forces. In this regard, a coupled circulation/deepsea oil spill model has been applied to the Black Sea to address the behavior of the oil plume resulting from a representative hypothetical deepwater blowout. With climatological forcing, the hydrodynamic module based on DieCAST ocean circulation model realistically reproduces seasonally-varying circulation from basin-scale dominant structures to meso- and sub-mesoscale elements. The oil spill model utilizes pre-calculated DieCAST thermo-hydrodynamic fields and uses a Lagrangian tracking algorithm for predicting the displacement of a large number of seeded oil droplets, the sum of which forms the rising oil plume resulting from a deepwater blowout. Basic processes affecting the transport, dispersal of oil and its fate in the water column are included in the coupled model. A hypothetical oil source was set at the bottom, at the northwestern edge of the Shatsky Ridge in the area east of the Crimea Peninsula where the oil exploration/development is likely to be planned. Goals of the study are to elucidate the behavior of the subsea oil plume and assess scales of contamination of marine environment and coastlines resulting from potential blowouts. The two 20-day scenarios with the oil released by a hypothetical blowout were examined to reveal combined effects of the basin-scale current, near-shore eddies, and winds on the behavior of the rising oil plume and its spreading on the surface. Special attention is paid to the Caucasian near-shore anticyclonic eddy which is able to trap surfacing oil, detain it and deliver it to shores. The length of contaminated coastlines of vulnerable Crimean and Caucasian coasts are assessed along with amounts of oil beached and deposited.

Stratigraphy, structure and petroleum exploration play types of the Rioni Basin, Georgia

Abstract The Rioni Basin is an underexplored petroliferous basin located at the Georgian margin of the Black Sea flanked by two folded belts (the Greater Caucasus and the Achara–Trialet Belt). Whereas the stratigraphy of the northern onshore Rioni Basin has elements which are common with that of the offshore Shatsky Ridge, the southern onshore Rioni Basin segment is both stratigraphically and structurally akin to the offshore Gurian folded belt in the eastern Black Sea. In the northern basin segment, the existing oil fields (East and West Chaladidi) and an undeveloped oil discovery (Okumi) are related to either post-salt or pre-salt antiformal traps in detachment folds or in poorly understood stratigraphic pinchouts beneath a regional Upper Jurassic evaporite sequence. In the southern Rioni Basin, the oil in existing fields has either anticlinal four-way closures (Supsa) or a subthrust trap (Shromisubani) related to the leading edge of the north-vergent Achara–Trialet folded belt. Despite the long history of petroleum exploration in the Rioni Basin, these proven plays are not fully understood and systematically explored using modern technology. The existence of an Upper Jurassic regional evaporite seal highlights the possibility of pre-salt plays in the northern part of the basin.

Mesozoic to recent geological history of southern Crimea and the Eastern Black Sea region

Abstract We provide a synthesis of stratigraphic data to unravel the history of the geological evolution of South Crimea in the Mesozoic and Cenozoic. The South Crimea Orogen consists of three major mega-sequences: (1) the Triassic–Early Jurassic; (2) the Aalenian–Bathonian; and (3) the Callovian–Eocene. The Late Triassic–Early Jurassic deposits formed in the environment of a forearc basin and a remnant basin. The Aalenian–Bathonian deposits formed above subduction extension and a volcanic belt. Three main Callovian–Eocene tectonic units can be identified in South Crimea: (1) the South Crimean Shelf Basin; (2) the Sudak Deepwater Trough; and (3) the Alchak–Kaya Shelf Basin at the northern margin of the Shatsky Ridge. The Oligocene–Quaternary deposits are considered to be syn-orogenic. A description of the anticipated stratigraphic units on the Shatsky Ridge is suggested for the Middle Jurassic, Callovian–Late Jurassic, Neocomian, Aptian–Albian, Late Cretaceous–Paleocene, Eocene and Maykopian. We propose a model for the geological history of the Eastern Black Sea Basin. Graben formed during the Late Barremian–Albian at the location of the future Eastern Black Sea Basin and a phase of volcanism occurred in the Albian. The main phase of rifting and spreading of oceanic crust took place during Cenomanian–Santonian time. Supplementary material: A Google Earth kmz file of the location of the outcrops and sections is available at http://www.geolsoc.org.uk/SUP18850

The Black Sea basins structure and history: New model based on new deep penetration regional seismic data. Part 1: Basins structure and fill

This work is based upon results of interpretation of about 8872 km-long regional seismic lines acquired in 2011 within the international project Geology Without Limits in the Black Sea. The seismic lines cover nearly the entire Black Sea Basins, including Russia, Turkey, Ukraine, Romania and Bulgaria sectors. A new map of acoustic basement relief and a new tectonic structure scheme are constructed for the Black Sea Basins. The basement of the Black Sea includes areas with oceanic crust and areas with highly rifted continental crust. A chain of buried seamounts, which were interpreted as submarine volcanoes of Late Cretaceous (Santonian to Campanian) age, has been identified to the north of the Turkish coast. On the Shatsky Ridge, probable volcanoes of Albian age have also been recognized. Synorogenic turbidite sequences of Paleocene, Eocene and Oligocene ages have been mapped. In the Cenozoic, numerous compressional and transpressional structures were formed in different parts of the Black Sea Basin. During the Pleistocene–Quaternary, turbidites, mass-transport deposits and leveed channels were formed in the distal part of the Danube Delta.

Authigenic carbonate precipitates from the NE Black Sea: a mineralogical, geochemical, and lipid biomarker study

Carbonate precipitates recovered from 2,000 m water depth at the Dolgovskoy Mound (Shatsky Ridge, north eastern Black Sea) were studied using mineralogical, geochemical and lipid biomarker analyses. The carbonates differ in shape from simple pavements to cavernous structures with thick microbial mats attached to their lower side and within cavities. Low δ13C values measured on carbonates (−41 to −32‰ V-PDB) and extracted lipid biomarkers indicate that anaerobic oxidation of methane (AOM) played a crucial role in precipitating these carbonates. The internal structure of the carbonates is dominated by finely laminated coccolith ooze and homogeneous clay layers, both cemented by micritic high-magnesium calcite (HMC), and pure, botryoidal, yellowish low-magnesium calcite (LMC) grown in direct contact to microbial mats. δ18O measurements suggest that the authigenic HMC precipitated in equilibrium with the Black Sea bottom water while the yellowish LMC rims have been growing in slightly 18O-depleted interstitial water. Although precipitated under significantly different environmental conditions, especially with respect to methane availability, all analysed carbonate samples show lipid patterns that are typical for ANME-1 dominated AOM consortia, in the case of the HMC samples with significant contributions of allochthonous components of marine and terrestrial origin, reflecting the hemipelagic nature of the primary sediment.

Complex plumbing systems in the near subsurface: Geometries of authigenic carbonates from Dolgovskoy Mound (Black Sea) constrained by analogue experiments

Targeted sampling on the Dolgovskoy Mound (northern Shatsky Ridge) revealed the presence of spectacular laterally extensive and differently shaped authigenic carbonates. The sampling stations were selected based on sidescan sonar and profiler images that show patchy backscatter and irregular and discontinuous reflections in the near subsurface. The interpretation of acoustic data from the top part of the mound supports the seafloor observations and the sampling that revealed the presence of a complex subsurface plumbing system characterized by carbonates and gas. The crusts sampled consist of carbonate cemented layered hemipelagic sedimentary Unit 1 associated with several centimetres thick microbial mats. Three different carbonate morphologies were observed: (a) tabular slabs, (b) subsurface cavernous carbonates consisting of void chambers up to 20 cm 3 in size and (c) chimney and tubular conduits vertically oriented or forming a subhorizontal network in the subsurface. The methanogenic origin of the carbonates is established based on visual observations of fluids seepage structures, 13C depletion of the carbonates ( δ 13C varying between −36.7‰ and −27.4‰), and by thin carbonate layers present within the thick microbial mats. Laboratory experiments with a Hele–Shaw cell were conducted in order to simulate the gas seepage through contrasting grain size media present on the seafloor. Combined petrography, visual observations and sandbox simulations allowed a characterization of the dynamics and the structures of the plumbing system in the near subsurface. Based on sample observations and the experiments, three observed morphologies of authigenic carbonates are interpreted, respectively, as (a) Darcian porous flow through the finely laminated clayey/coccolith-rich layers, (b) gas accumulation chambers at sites where significant fluid escape was impeded by thicker clayey layers forming the laminated Unit1 and (c) focussed vertical fluid venting and subhorizontal migration of overpressured fluids released from (b). The Hele–Shaw cell experiments represent a promising tool for investigating shallow fluid flow pathways in marine systems.

Topography of the crust–mantle boundary beneath the Black Sea Basin

A map of Moho depth for the Black Sea and its immediate surroundings has been inferred from 3-D gravity modelling, and crustal structure has been clarified. Beneath the basin centre, the thickness of the crystalline layer is similar to that of the oceanic crust. In the Western and Eastern Black Sea basins, the Moho shallows to 19 and 22 km, respectively. Below the Tuapse Trough (northeastern margin, adjacent to the Caucasus orogen), the base of the crust is at 28 km, whereas in the Sorokin Trough, it is as deep as 34 km. The base of the crust lies at 29 and 33 km depths respectively below the southern and northern parts of the Mid-Black Sea Ridge. For the Shatsky Ridge (between the Tuapse Trough and the Eastern Black Sea Basin), the Moho plunges from the northwest (33 km) to the southeast (40 km). The Arkhangelsky Ridge (south of the Eastern Black Sea Basin) is characterised by a Moho depth of 32 km. The crust beneath these ridges is of continental type.

Tectonic paleostress fields and structural evolution of the NW-Caucasus fold-and-thrust belt from Late Cretaceous to Quaternary

The NW-Caucasus fold-and thrust belt essentially corresponds to the inverted western Flysch Zone of the Great Caucasus Mountains, a deep basin that developed from Late Jurassic to Eocene times between the Scythian Plate to the north and the Transcaucasian terranes to the south (the Shatsky Ridge, SW of the NW-Caucasus zone). The Flysch Basin was strongly affected by compression in Late Eocene times, when the characteristic WNW trending folds and thrusts of the NW-Caucasus belt developed (some authors regard the main compressive deformation as Miocene in age). By means of remote sensing analysis, we elucidate the geometry of major structures in the belt: WNW trending south-vergent thrusts and folds, and major vertical and transverse NNE–SSW to NE–SW deep fault zones. The later structures are interpreted as ancient faults that were active during the development of the Flysch Basin. Paleostress investigations reveal seven main tectonic episodes in the evolution of the NW-Caucasus since Late Cretaceous. Combining structural interpretation, remote sensing analysis and paleostress field reconstruction, we propose a model for the structural evolution of the belt. During the Late Cretaceous–Paleocene, the western Caucasus zone was under transtensional regime with an E–W to NE–SW trending σ 3 that generated oblique normal movements along NNE–SSW transverse faults and WNW–ESE margins of the Flysch Basin. This tectonism could correspond to rifting related to the formation of the Eastern Black Sea Basin. At the Paleocene–Eocene boundary, a transpressional event with an E–W to NW–SE trending σ 1 developed and the NNE–SSW to NE–SW trending faults could have been inverted. This event could correspond to an attenuation in the Eastern Black Sea Basin formation or to the incipient accretion of the Transcaucasian terranes. During the Eocene, another E–W to NW–SE oblique extension (-transtensional event) affected the Flysch Basin that could be related to a known rifting phase in the Eastern Black Sea Basin. Strong NNE–SSW to NE–SW compression characterises Late Eocene tectonism. The fold-and-thrust belt developed at this time as a result of the direct collision of the Shatsky Ridge with the Scythian Plate. A NE–SW extension followed the Late Eocene event, related to basin development around the newly formed fold belt. A WNW–ESE oblique contraction affected the belt during the early Miocene as the result of Arabian Plate convergence with the Caucasian system. The latest inferred event is a compressional regime, with NNW–SSE trending σ 1 that is affecting the NW-Caucasus belt from Sarmatian times until the present. Under this oblique compression, the belt has deformed as in a dextral shear zone and the thrust surfaces have acquired lenticular shapes. This study highlights the occurrence of oblique movements in the NW-Caucasus area prior to and after the dominant Late Eocene compression. From the Late Cretaceous until the Eocene, the structural development of the NW-Caucasus was closely related to the evolution of the Eastern Black Sea Basin. From the Late Eocene until Quaternary times, it was rather related to the Arabia–Eurasia plate convergence.

How many Pacific hotspots are fed by deep-mantle plumes?

The Pacific plate is usually considered to host 14 hotspots, but most of this volcanism does not seem to originate from deep-mantle plumes. To reach this conclusion, we tried to establish how many of the seamount alignments on the Pacific plate correspond to classic hotspots, i.e., long-lived hotspots linked to oceanic basaltic plateaus. We retraced the tracks of the 14 Pacific hotspots by using (1) the absolute stage poles representing the Pacific plate absolute motion since 145 Ma, (2) an updated compilation of radiometric ages of seamounts and oceanic plateaus totaling 266 seamounts or islands, (3) the detailed bathymetry of the Pacific Ocean, and (4) the present locations of the hotspots. This analysis allowed us to correlate only three hotspots with the beginning of their tracks possibly corresponding in space and time to an oceanic plateau: Easter to the eastern Mid-Pacific Mountains, Louisville to the Ontong Java plateau, and, with less confidence, Marquesas to Hess Rise and Shatsky Ridge. In addition, the Hawaii hotspot has produced long-lived volcanism. These four are the only classic hotspots on the Pacific plate. However, seven hotspots present short tracks (,35 m.y.) that cannot be traced to an oceanic plateau and thus are not related to any deep-mantle phenomena: Foundation, Macdonald, Pitcairn, Rarotonga, Rurutu, Samoa, and Society. The two northeast Pacific hotspots, Kodiak-Bowie and Cobb, and the Caroline hotspot are unclassifiable because of close proximity to a subduction zone where the prior history of volcanism has been lost.

Petroleum geology of the Black Sea

The Black Sea comprises two extensional basins formed in a back-arc setting above the northward subducting Tethys Ocean, close to the southern margin of Eurasia. The two basins coalesced late in their post-rift phases in the Pliocene, forming the present single depocentre. The Western Black Sea was initiated in the Aptian, when a part of the Moesian Platform (now the Western Pontides of Turkey) began to rift and move away to the south-east. The Eastern Black Sea probably formed by separation of the Mid-Black Sea High from the Shatsky Ridge during the Palaeocene to Eocene. Subsequent to rifting, the basins were the sites of mainly deep water deposition; only during the Late Miocene was there a major sea-level fall, leading to the development of a relatively shallow lake. Most of the margins of the Black Sea have been extensively modified by Late Eocene to recent compression associated with closure of the Tethys Ocean. Gas chromatography—mass spectrometry and carbon isotope analysis of petroleum and rock extracts suggest that most petroleum occurrences around the Black Sea can be explained by generation from an oil-prone source rock of most probably Late Eocene age (although a wider age range is possible in the basin centres). Burial history modelling and source kitchen mapping indicate that this unit is currently generating both oil and gas in the post-rift basin. A Palaeozoic source rock may have generated gas condensate in the Gulf of Odessa. In Bulgarian waters, the main plays are associated with the development of an Eocene foreland basin (Kamchia Trough) and in extensional structures related to Western Black Sea rifting. The latter continue into the Romanian shelf where there is also potential in rollover anticlines due to gravity sliding of Neogene sediments. In the Gulf of Odessa gas condensate has been discovered in several compressional anticlines and there is potential in older extensional structures. Small gas and oil discoveries around the Sea of Azov point to further potential offshore around the Central Azov High. In offshore Russia and Georgia there are large culminations on the Shatsky Ridge, but these are mainly in deep water and may have poor reservoirs. There are small compressional structures off the northern Turkish coast related to the Pontide deformation; these may include Eocene turbidite reservoirs. The extensional fault blocks of the Andrusov Ridge (Mid-Black Sea High) are seen as having the best potential for large hydrocarbon volumes, but in 2200 m of water.

Crustal structure in the Kamchatkan segment of the pacific transition zone

Based on deep seismic sounding data, a velocity model of the Earth's crust has been developed for the Kamchatkan segment of the Pacific transition zone. The velocity difference in the structure of the continental and oceanic blocks of the Earth's crust is shown. It has been revealed that these crustal blocks join each other along the deeply inclined fault zone. This zone is located 120 km northwest of the axis of the deep-sea trench. It separates the high-velocity block of eastern peninsulas and bays of Kamchatka from the low-velocity block of the Shatsky Ridge. The latter may be considered to be a contact zone between the continental and oceanic crust. The crust of the regions of Recent volcanic activity in Kamchatka has a number of specific features, such as: a complex heterogeneous structure of the basement; relatively high velocity values in the crust and low values in the upper mantle; anomalous behaviour and velocity inversions related to the complex alternation of sedimentary-volcanogenous and intrusive rocks and zones of hydrothermal alterations; and the possible presence of magma chambers of different types within the crust and the crust-mantle transition zone.