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... in the sedimentary sequence (e.g., Ross, 1978). Wells located onshore and along the basin's margins (i.e., Georgia and Crimea) and wells drilled in the WBSB have been integrated by several studies, but correlations with the central EBSB stratigraphy are difficult (e.g., Sydorenko et al., 2017). ...
... ppt) between sea-level and 200 m below sea-level (bsl), and being almost constant from 200 m below sea-level to seafloor (Railsback, 2010;Stanev et al., 2014). Cores recovered at DSDP Hole 379A, located in the central Black Sea, shows sea surface chlorinity and salinity of 1.144% and 2.02%, respectively (Ross, 1978;Shishkina, 1978). At the borehole location it was observed that chlorinity drops to 0.27% at 32.4 mbsf, and salinity stays low up to 268 mbsf depth, fluctuating between 0.18 and 0.33%. ...
... The difference in salinity and chlorinity in sediments below seafloor from seawater at seafloor was interpreted as the freshening of the basins during late Pleistocene in the Black Sea (Shishkina, 1978). Similarly, low pore-water salinity of 0.5% was measured at the DSDP Leg 42B Hole 379A in the central Black Sea (Ross, 1978). This low salinity is due to dominant freshwater stages in the Quaternary deposits, corresponding to phases of isolation of the Black Sea (Popescu et al., 2006). ...
One of the key elements in passive continental margins and basins research is the understanding of how extensional processes initiate and evolve from rifting to breakup stage. These processes may vary spatially and temporally as result of the complex trade-off between spreading rates, lithospheric compositional variations, and along-axis changes in melt supply. Thus, extension may focus over one conjugate margin resulting in an along-axis change in rifting style. Lower crust and/or mantle exhumation may occur at hyper-extended areas, and along-axis changes in melt supply during spreading may result in varying amounts of magmatic intrusions within a highly extended continental crust. The resulting crustal structure and composition at rifted margins may therefore present a geophysical signature differing from what is normally expected for continental and oceanic crust, making it difficult to define the transition from the late stages of continental rifting to initial oceanic accretion. Nevertheless, a clear understanding of the stages defining passive continental margins and extensional basins evolution is key to unravel the mechanisms driving lithospheric extension, as well as the present-day configuration at these settings. Sedimentary basins formed in continental rifts and rifted margins also contain some of Earth�s major hydrocarbon fields. Constraining the evolution and dynamics of these fields gives insight into the timing of basin formation, sedimentation, trap formation, and heat-flow evolution, which are crucial for efficient hydrocarbon exploration. Passive continental margins are also relevant to the study of gas hydrates deposits, which are of interest not only for their potential as a future energy resource, but also for their implications on seafloor stability and their contribution to climate change. However, the dynamics driving their formation and evolution along passive margins is yet to be fully understood. This study provides an integrated geophysical investigation at one of the currently most debated extensional regions, the Eastern Black Sea Basin (EBSB). Here, the timing and dynamics of rifting and breakup processes and the resulting crustal configuration are still poorly constrained. This is due to the deep water setting and thick sedimentary infill, limiting direct sampling of deep sedimentary units and the ability of imaging the deep basin structures using conventional seismic imaging. The EBSB is also a frontier for oil and gas exploration due to the presence of a regional source-rock, the Oligocene-lower Miocene Maykop Formation. Thus, untangling the stages in basin evolution and defining the extent of different crustal basements is essential for modelling the maturity of the hydrocarbon systems in place. This study uses high-resolution, 2D long-offset seismic reflection data by Geology Without Limits (GWL) to investigate the deep tectonostratigraphic elements of the basin and the morphological character of its basement. Magnetic anomaly data are integrated to complement and guide seismic interpretation, defining the magnetisation character of morphologically different crustal domains. The combined analysis of tectono-stratigraphic and magnetic anomaly results provides new insights on the present-day crustal configuration, and on the timing and kinematics of rifting and breakup processes across the EBSB. The Black Sea is characterised by thermo-dynamic conditions which make this area favourable to gas hydrate formation. Gas hydrates have long been known in this area, with related evidence for Bottom Simulating Reflectors (BSRs) predominantly found in the western part of the basin (WBSB). Seismic data used in this study reveal new evidence for multiple BSRs along the NE margin of the EBSB, thus providing a new case study to investigate the physical nature of the identified BSRs, the presence and distribution of gas hydrates and/or free gas zones, and the mechanism(s) driving multiple BSRs generation. The long-offset nature of the seismic acquisition provides both reflected and refracted travel-time information that can be used in a tomographic approach, aiming to define a 2D velocity model within the shallow sedimentary section. To improve refracted arrivals, downward continuation is also applied to the seismic data. Results help to constrain velocity changes in sediments across the BSRs, which are interpreted as indicative for the presence of free gas and gas hydrate in the area. Velocities defined form travel-time analysis are also used to provide estimates of free gas and gas hydrate saturation in sediments using a forward effective-medium modelling approach. Results from this thesis contribute to the understanding of rifting evolution on both small-scale basins, such as the Black Sea, and fully developed passive continental margins. Similarly, results also contribute to the general understanding of gas hydrate evolution in the Black Sea as well as along other well-known gas hydrate regions.
... The only Mio-Pliocene stratigraphic archives (for scientific use) of the deep parts of the Euxinian (Black Sea) Basin have been obtained by the Deep Sea Drilling Project (DSDP) Leg 42B, which drilled three locations (379, 380/380A, 381) in the southwestern and central part of the basin ( Fig. 1; (Ross et al., 1978). The integrated studies from these wells have played a significant role in scientific discussions on the paleoenvironmental history of the Euxinian Basin and its connectivity with the Mediterranean Sea. ...
... E) was drilled at a water depth of ~2100 m (Shipboard Scientific Staff, 1978). The initial lithostratigraphic subdivision of the DSDP sediments was based on sediment lithology and chemistry, using biotic data as paleoecological indicator (Ross, 1978 (Stoffers and Müller, 1978;Hsü and Giovanoli, 1979). ...
... The initial correlation of the Pebbly Breccia to the Messinian event ( Fig. 2) was considered a working hypothesis at best (Ross, 1978), and has been seriously questioned by several authors. Kojumdgieva (1979,1983) claimed that the Pebbly Breccia deposits were of latest Khersonian age (~10-8.5 Ma). ...
Various hypotheses exist on the age and origin of the so-called “Pebbly Breccia” unit in the deep-sea record of DSDP Hole 380A of the Euxinian (Black Sea) Basin. Here, we present a detailed study of diatom and nannofossil assemblages of Hole 380A. Our diatom records show a characteristic sequence of appearance of markers species, which we can correlate to the recently established bio-magnetostratigraphic time frame of the Zheleznyi Rog section on the Black Sea coast of the Taman Peninsula (Russia). It shows that the Pebbly Breccia is sandwiched between Upper Maeotian deposits, and must have been deposited at an age between 6.7 and 6.3 Ma. The appearance of nannoplankton and the marine diatom association at above the Pebbly breccia (Unit IVc) suggests a short-term incursion of marine conditions. The age of Unit IVc, based on diatom data, is 6.3-6.1 Ma. The nannoplankton record is mainly represented by species that do not have stratigraphic value. The previously reported presence of Ceratolithus acutus in the Black Sea is explained by misinterpretation of destructed elements of ascidian spicules. We conclude that the Pebbly Breccia is not related to a desiccated Black Sea at Messinian Salinity Crisis times, but it corresponds to a late Maeotian episode of gravitational instability in the SW Black Sea region.
... Marine water is supplied to the Black Sea at times when Mediterranean sea-level is above the level of the sill in the Aegean/Sea of Marmara/Bosporus region. Salinity in the present-day Black Sea is in the range of 18-22 , with stagnant, anoxic bottom waters resulting from the density difference between the inflowing and outflowing waters (Ross, 1978b). At a Mediterranean sea-level lower than the Bosporus sill, the Black Sea turns into an isolated, freshwater basin and Black Sea water level will depend on the local hydrological budget (e.g., Major et al., 2002). ...
... The core is divided in nine subunits of terrigenous origin (Figure 1). Sediments are mainly dark greenish-gray to dark gray terrigenous mud, with occasional beds of silt, FIGURE 1 | Lithology and lithological units of DSDP leg 42B cores and map of the Black Sea region with DSDP Leg 42B drilling locations (Logs adapted from Ross, 1978b). Numbered locations indicate magnetostratigraphically dated late Miocene, Pliocene, and Pleistocene reference sections. ...
... sandy silt and sand. Graded bedding in the coarse lithologies suggests deposition in turbidity currents (Ross, 1978b). Fauna throughout the core is not age-diagnostic, but does describe paleoenvironmental changes (Shipboard Scientific Staff, 1978a). ...
The Miocene epicontinental Paratethys Sea of central Eurasia has experienced multiple restriction and reconnection events to the open ocean. Magnetostratigraphy is an important dating tool to better understand the temporal and spatial paleoenvironmental variations associated with these changes. Magnetostratigraphy in the Paratethys domain, however, is complicated by the presence of greigite (Fe3S4). Here, we report rock magnetic and X-ray fluorescence data of the Tisa section (Romania) which was previously magnetostratigraphically dated at the middle Miocene (base at 12.8 Ma and top at 12.2 Ma). This section comprises the Badenian Sarmatian Extinction Event (BSEE), which is marked by a major salinity change from marine to brackish environments, related to the opening of the connection between the Central and the Eastern Paratethys basins. In the marine Badenian sediments below the BSEE, the pyritization process is shown to be complete because of abundant sulfate supply. In the brackish Sarmatian deposits, four intervals with early diagenetic greigite are observed, and linked to insufficient sulfate in the water column. These four greigite intervals appear to correspond to maxima in the ∼100 kyr eccentricity cycle. We propose that increased fresh water from the Eastern Paratethys basin during eccentricity maxima restricted the sulfate availability in the Tisa area, leading to a reduced HS- production and enhanced greigite preservation. The early diagenetic formation of greigite enables a quasi syn-depositional recording of the paleomagnetic field, which allows reliable paleomagnetic dating in this section. Our results further suggest greigite as a potential indicator for salinity changes during marine/brackish transitions.
... Marine water is supplied to the Black Sea at times when Mediterranean sea-level is above the level of the sill in the Aegean/Sea of Marmara/Bosporus region. Salinity in the present-day Black Sea is in the range of 18-22 , with stagnant, anoxic bottom waters resulting from the density difference between the inflowing and outflowing waters (Ross, 1978b). At a Mediterranean sea-level lower than the Bosporus sill, the Black Sea turns into an isolated, freshwater basin and Black Sea water level will depend on the local hydrological budget (e.g., Major et al., 2002). ...
... The core is divided in nine subunits of terrigenous origin (Figure 1). Sediments are mainly dark greenish-gray to dark gray terrigenous mud, with occasional beds of silt, FIGURE 1 | Lithology and lithological units of DSDP leg 42B cores and map of the Black Sea region with DSDP Leg 42B drilling locations (Logs adapted from Ross, 1978b). Numbered locations indicate magnetostratigraphically dated late Miocene, Pliocene, and Pleistocene reference sections. ...
... sandy silt and sand. Graded bedding in the coarse lithologies suggests deposition in turbidity currents (Ross, 1978b). Fauna throughout the core is not age-diagnostic, but does describe paleoenvironmental changes (Shipboard Scientific Staff, 1978a). ...
Throughout the Late Neogene, the Black Sea experienced large paleoenvironmental changes, switching between (anoxic) marine conditions when connected to the Mediterranean Sea and (oxic) freshwater conditions at times of isolation. We create a magnetostratigraphic time frame for three sites drilled during Deep Sea Drilling Project (DSDP) Leg 42B to the Black Sea (drilled in 1975). At the time, magnetostratigraphic dating was impossible because of the presence of the little understood iron sulfide mineral greigite (in sediments a precursor to pyrite) as magnetic carrier. Our rock-magnetic results indicate that only anoxic conditions result in poor magnetic signal, likely as a result of pyrite formation in the water column rather than in the sediment. The magnetostratigraphic results indicate that Hole 379A, drilled in the basin center, has a continuous sedimentary record dating back to 1.3 Ma. Hole 380/380A is subdivided into three consistent intervals, 0–700 mbsf, 700–860 mbsf, and 860–1075 mbsf. The top unit covers the Pleistocene but the magnetostratigraphy is likely compromised by the presence of mass transport deposits. The middle unit spans between 4.3 and 6.1 Ma and records continuous deposition at ~10 cm/kyr. The lower unit lacks the independent age constraints to correlate the obtained magnetostratigraphy. Hole 381 is drilled on the Bosporus slope and as a result, hiatuses are common. A correlation to the nearby Hole 380/380A is proposed, but indicates deposits cannot straightforwardly be traced across the slope. Our improved age model does not support the original interpretation based on these cores of a desiccation of the Black Sea during the Messinian salinity crisis.
... Early to Late Miocene sediments, sampled offshore Romania, comprise of mudstones (Robinson et al. 1995a;Spadini et al. 1996), with implied turbiditic layers observed in the seismic reflection profiles (Zonenshain & le Pichon 1986;Robinson et al. 1995a). Changes in water level and sediment drainage patterns, due to the uplift of the Carpathian Mountains during the Late Miocene, lead to the deposition of fluvial material and shallowwater limestones in this unit (Ross 1978;Robinson et al. 1996). The youngest sediments in the EBS, as recovered by gravity cores and drilling, comprise of clays with the occasional turbidite sequence (Ross 1978). ...
... Changes in water level and sediment drainage patterns, due to the uplift of the Carpathian Mountains during the Late Miocene, lead to the deposition of fluvial material and shallowwater limestones in this unit (Ross 1978;Robinson et al. 1996). The youngest sediments in the EBS, as recovered by gravity cores and drilling, comprise of clays with the occasional turbidite sequence (Ross 1978). The total thickness of top Cretaceous to recent sediment infill in the centre of the basin is 8-9 km (Shillington et al. 2008). ...
... For a shale lithology one would expect a velocity gradient in the upper sediments of ∼0.55 s −1 , while for a sand lithology one would expect a velocity gradient of 1-1.15 s −1 (Japsen et al. 2007). A gradient of ∼0.7 s −1 suggests a shale-dominated lithology, which is supported by results from a DSDP borehole on the mid-Black Sea high (indicated on Fig. 1) that found the shallow sediments were mostly clays interrupted by occasional turbidites (Ross 1978). The seismic velocity structure of the deeper sediments is dominated by a widespread and fairly continuous low-velocity zone. ...
... Ils prennent cependant en considération, dans leur modèle, la chute majeure du niveau marin (1500 m) datée du Sarmatien (10 Ma) proposée par Kojumdgieva [Kojumdgieva, 1983]. Cet auteur, appuyé par Robinson , rattache cette chute majeure du niveau marin à la "dessiccation" de la mer Noire proposée à la suite des découvertes du Leg DSDP 42B [Hsü, 1978b;Ross, 1978;(Paragraphe I-3.2.1.a). Comme j'y ai brièvement déjà fait allusion, la datation de cet événement est sujette à débat puisque Hsü et Giovanoli [Hsü et Giovanoli, 1979] le rattache de leur côté à la crise messinienne méditerranéenne (5 Ma). ...
... Ces indices se localisent dans deux bassins vestiges de [Ross et Neprochnov, 1978]. Au cours de ce leg DSDP, trois sites ont été forés ( Figure [Ross, 1978;Traverse, 1978]. ...
... Dans ce modèle, la faible profondeur d'eau du bassin au Messinien aurait permis la mise en place de sédiments détritico-évaporitiques qui n'auraient pris leur position actuelle qu'à la suite d'une subsidence plio-quaternaire catastrophique. Ross [Ross, 1978] et Hsü [Hsü, 1978b;Hsü et Giovanoli, 1979] en considérant l'histoire de la formation de la mer Noire telle qu'elle était ébauchée à l'époque (chapitre I-1.5), et surtout en soulignant l'absence d'enregistrement d'une subsidence d'une telle ampleur, ont cependant démontré que l'origine eustatique était à privilégier. ...
The Tertiary paleogeographic evolution of the Black Sea, within the paratethys realm, was characterised by several periodic isolation episodes. The eutatic responses of the Black Sea to these de-connexions, and especially those related to the Mediterranean Messinian crisis, are still not clearly established.
The high resolution seismic stratigraphy study we present is based on interpretation of multichanel HR seismic data correlated with drillings recovered on the occidental Black Sea margin. Our investigations were concentrated on the identification of erosional surfaces, interpreted as markers of eustatic falls, linked to the basin isolation phases.
On the Romano-Ukrainian shelf, the seismic profiles display six major discontinuities regarded as Tertiary erosional surfaces : (1) the surfaces underlined at the base of the Eocene (E), at the base of the Oligocene (O), in the Middle Miocene (M) and at the base of the Pontian (P); (2) and two intra-Pontian erosional unconformities (L.IPU and IPU).
On the other hand, the Messinian erosional surface was clearly identified on the Bulgaro-Turckish margin. Recent correlation between the Paratethysian and Mediterranean stratigraphic scale suggest that the IPU surface recognised on the Romano-Ukrainian shelf is equivalent to the Messinian erosional surface.
Among the five ante-Messinian erosional surfaces described, we interpret the M surface as the signature of a catastrophic sea level fall related to the Upper Burdigalian isolation phase. We propose that the four other surfaces correspond either to submarine erosion episodes, or to transgressive events.
The discovery of the Messinian erosional surface in Black Sea constituting the major result of this study, enables to validate the assomption about the Messinian Dessiccation of the Black Sea [Hsü and Giovanoli, 1979].
... Late Miocenetop Pliocene (11-1.8 Ma) sediments comprise sands and conglomerates mapped in north-eastern Turkey (Robinson et al., 1995b) and chalks, siderites, clays and limestones observed by the Deep Sea Drilling Project (DSDP) in the basin centre (Ross, 1978;Hsü & Giovanoli, 1980). Gravity cores and drilling (Ross, 1978;Robinson et al., 1996) indicate that the youngest sediments, top Pliocene-Present (1.8-0 Ma), comprise mostly clays, but they also include marls and occasional turbidites (Ross, 1978;Hsü & Giovanoli, 1980;Hiscott & Aksu, 2002). ...
... Ma) sediments comprise sands and conglomerates mapped in north-eastern Turkey (Robinson et al., 1995b) and chalks, siderites, clays and limestones observed by the Deep Sea Drilling Project (DSDP) in the basin centre (Ross, 1978;Hsü & Giovanoli, 1980). Gravity cores and drilling (Ross, 1978;Robinson et al., 1996) indicate that the youngest sediments, top Pliocene-Present (1.8-0 Ma), comprise mostly clays, but they also include marls and occasional turbidites (Ross, 1978;Hsü & Giovanoli, 1980;Hiscott & Aksu, 2002). ...
... Ma) sediments comprise sands and conglomerates mapped in north-eastern Turkey (Robinson et al., 1995b) and chalks, siderites, clays and limestones observed by the Deep Sea Drilling Project (DSDP) in the basin centre (Ross, 1978;Hsü & Giovanoli, 1980). Gravity cores and drilling (Ross, 1978;Robinson et al., 1996) indicate that the youngest sediments, top Pliocene-Present (1.8-0 Ma), comprise mostly clays, but they also include marls and occasional turbidites (Ross, 1978;Hsü & Giovanoli, 1980;Hiscott & Aksu, 2002). ...
Locating and quantifying overpressures are essential to understand basin evolution and hydrocarbon migration in deep basins and thickly sedimented continental margins. Overpressures influence sediment cohesion and hence fault slip in seismically active areas or failure on steep slopes, and may drive catastrophic fluid expulsion. They also represent a significant drilling hazard. Here, we present a method to calculate the pore pressure due to disequilibrium compaction. Our method provides an estimate of the compaction factor, surface porosity and sedimentation rate of each layer in a sediment column using a decompaction model and the constraints imposed by seismic data and geological observations. For a range of surface porosities, an ad hoc iterative equation determines the compaction factor that gives a calculated layer thickness that matches the observed thickness within a tolerance. The surface porosity and compaction factor are then used to obtain a density profile and a corresponding estimate of P‐wave velocity (V p ). The selected parameters are those that give a good match with both the observed and calculated layer thicknesses and V p profiles. We apply our method to the centre of the Eastern Black Sea Basin (EBSB), where overpressures have been linked to a low‐velocity zone (LVZ) at ca. 5500–8500 m depth. These overpressures were generated by the relatively high sedimentation rate of ca. 0.28 m ka−1 of the low permeability organic‐rich Maikop formation at 33.9–20.5 Ma and an even higher sedimentation rate of ca. 0.85 m ka−1 at 13–11 Ma. We estimate a maximum pore pressure of ca. 138 MPa at ca. 8285 m depth, associated with a ratio of overpressure to vertical effective stress in hydrostatic conditions (λ*) of ca. 0.7. These values are lower than those presented in a previous study for the same area.
... The responses of the Black Sea to the Tertiary, and particularly Messinian, global and nearby Mediterranean Sea level variations are still not clearly established. The Messinian desiccation of the Black Sea as proposed by Hsu [5] in the results of Leg DSDP 42B [13] was up to now still under discussion. ...
... Siege d'une forte sedimentation, cette plateforme represente une zone privilegiee pour I' enregistrement des processus sedimentaires, Pourtant, la stratigraphie absolue de cette zone reste f1oue. Pour Ie Ter- tiaire, les reponses du bassin euxinique (mer Noire) aux variations du niveau marin global et de la Mediterranee voisine, en particulier au Messinien, sont encore mal etablies, Faute de mise en evidence d'une surface d' erosion messinienne dans ce bassin, la manifestation de l'evenement messinien en mer Noire, propose par Hsu [5] lors des decouvertes du Leg DSDP 42B en 1975 [13], n'a jusqu'a aujourd'hui jamais ete c1airement demontree. ...
... La surface d'erosion messinienne M se correle avec Ie toit de l'unite des forages DSDP, caracterisant un milieu de depot supratidal-evaporitique, Une origine aerienne serait done a privilegier pour cette surface. Par ailleurs, les marges turques et roumaines sont considerees comme stables d'un point de vue tectonique a l'echelle des cinq demiers millions d'annees [5,12,13]. Le prolongement,jusqu'en pied de pente turque, de la surface d'erosion messinienne M ainsi que Ia profondeur des incisions contemporaines IPU.bis sous le plateau roumain temoignent done d'une chute du niveau marin d'ampleur exceptionnelle ayant affecte l'ensemble de Ia mer Noire a la fin du Messinien. Nous proposons que ces marques d'erosion constituent les traces de la surface d'erosion messinienne en mer Noire. ...
The stratigraphy of the Black Sea western margin is revisited through
seismic data acquired during two French-Romanian surveys. These data are
calibrated by industrial and DSDP drillings; they display several major
discontinuities regarded as Tertiary erosional surfaces. The major
seismic discontinuity underlines the base of Miocene formations and
corresponds to a composite surface including at least three erosional
phases ranging from Oligocene to Pontian times. Moreover, a Messinian
erosional surface is clearly identified. This is in agreement with the
Hsü's proposition [Palaeogeogr. Palaeoclimatol. Palaeoecol. 29
(1979) 75-93] suggesting a Messinian sea-level drop of Black Sea related
to the Messinian Salinity Crisis described in the Mediterranean Sea. To
cite this article: H. Gillet et al., C. R. Geoscience 335 (2003).
... Early to Late Miocene sediments, sampled offshore Romania, comprise of mudstones (Robinson et al. 1995a;Spadini et al. 1996), with implied turbiditic layers observed in the seismic reflection profiles (Zonenshain & le Pichon 1986;Robinson et al. 1995a). Changes in water level and sediment drainage patterns, due to the uplift of the Carpathian Mountains during the Late Miocene, lead to the deposition of fluvial material and shallowwater limestones in this unit (Ross 1978;Robinson et al. 1996). The youngest sediments in the EBS, as recovered by gravity cores and drilling, comprise of clays with the occasional turbidite sequence (Ross 1978). ...
... Changes in water level and sediment drainage patterns, due to the uplift of the Carpathian Mountains during the Late Miocene, lead to the deposition of fluvial material and shallowwater limestones in this unit (Ross 1978;Robinson et al. 1996). The youngest sediments in the EBS, as recovered by gravity cores and drilling, comprise of clays with the occasional turbidite sequence (Ross 1978). The total thickness of top Cretaceous to recent sediment infill in the centre of the basin is 8-9 km (Shillington et al. 2008). ...
... For a shale lithology one would expect a velocity gradient in the upper sediments of ∼0.55 s −1 , while for a sand lithology one would expect a velocity gradient of 1-1.15 s −1 (Japsen et al. 2007). A gradient of ∼0.7 s −1 suggests a shale-dominated lithology, which is supported by results from a DSDP borehole on the mid-Black Sea high (indicated on Fig. 1) that found the shallow sediments were mostly clays interrupted by occasional turbidites (Ross 1978). The seismic velocity structure of the deeper sediments is dominated by a widespread and fairly continuous low-velocity zone. ...
Mud volcanism associated with the degassing of deeply buried sediments has been identified in the Black Sea and Caspian Sea. Sampling of mud volcano breccia and seismic imaging of the "roots" suggest the origin lies in the Maykop formation, an organic-rich shale deposited in the Oligocene/Miocene that constitutes the major hydrocarbon source rock in the area. High sedimentation rates, leading to rapid burial and undercompaction, combined with hydrocarbon generation are possible mechanisms for generating overpressure in this layer. To our knowledge the magnitude of this overpressure in the Black Sea has not been quantified. The excess pore- pressure can be estimated from seismic velocities, however the Maykop formation is too deep (4 - 7 km below the seabed) for accurate velocities to be obtained from conventional multichannel seismic data. In spring 2005, four new wide-angle seismic reflection/refraction profiles were collected across the Eastern Black Sea Basin that provide better constraints on the sediment and crustal velocity structure. The data are of high quality allowing multiple sedimentary phases to be identified and linked with coincident reflection data. We have used the seismic tomography code JIVE, which performs simultaneous inversion of reflections and refractions from multiple layers. The model shows a thick sedimentary package, ~9 km in the centre of the basin. A low-velocity zone that may be associated with overpressure occurs near the base of the sediments. It is ~4 km thick in the centre of the basin, with anomalous velocities of ~2.6-3 kms-1 within the zone and ~3.6 kms-1 above and below. The low velocity zone is fairly continuous across the eastern basin and can also be identified on a profile that crosses the Mid-Black Sea High into the western basin. Overpressure can be expressed in terms of effective stress (lambda); the ratio of excess pore pressure to lithostatic pressure. Using our velocity model, we estimate values of lambda of approximately 0.77±0.02, corresponding to pore pressures of ~45 MPa within the low velocity zone. If overpressure exists throughout the Maykop formation, as suggested by our data, it may be one of the largest overpressured regions in the world.
... A.7. Late Miocene (top of Sarmatian)-top of Pliocene Sands and conglomerates of Pliocene age have been drilled onshore Georgia and mapped in northeastern Turkey (Robinson et al., 1995b), though these units are typically non-marine and unlikely to be representative of lithologies in the basin center. Chalks, siderites, clays and limestone were recovered by DSDP drilling in the basin center (Ross, 1978;Hsü and Giovanoli, 1980). Interestingly, this interval also contains a thin unit comprising algal mats and peletal limestones, indicative of very shallow water depths (Ross, 1978;Hsü and Giovanoli, 1980;Kojumdgieva, 1983). ...
... Chalks, siderites, clays and limestone were recovered by DSDP drilling in the basin center (Ross, 1978;Hsü and Giovanoli, 1980). Interestingly, this interval also contains a thin unit comprising algal mats and peletal limestones, indicative of very shallow water depths (Ross, 1978;Hsü and Giovanoli, 1980;Kojumdgieva, 1983). Although interpretations regarding the age and causes of these deposits are controversial (Ross, 1978;Hsü and Giovanoli, 1980;Kojumdgieva, 1983), it appears that they correspond to a drop in sea level of over 2000 m, possibly related to Messinian desiccation event that affected the entire Mediterranean region (Hsü et al., 1973). ...
... Interestingly, this interval also contains a thin unit comprising algal mats and peletal limestones, indicative of very shallow water depths (Ross, 1978;Hsü and Giovanoli, 1980;Kojumdgieva, 1983). Although interpretations regarding the age and causes of these deposits are controversial (Ross, 1978;Hsü and Giovanoli, 1980;Kojumdgieva, 1983), it appears that they correspond to a drop in sea level of over 2000 m, possibly related to Messinian desiccation event that affected the entire Mediterranean region (Hsü et al., 1973). Because this desiccation was likely short-lived (100 kyr) (Hsü and Giovanoli, 1980), it is not included in the subsidence analysis presented in this paper. ...
To investigate the contribution of depth-dependent stretching to the formation of the eastern Black Sea, we examine this extensional basin using wide-angle seismic refraction data and subsidence analysis. Wide-angle seismic data can constrain variations in thinning within the crust, while subsidence analysis can extract information on thinning throughout the lithosphere. The eastern Black Sea is an ideal location for this study because it contains 8-10 km of sediments that record the Cenozoic subsidence history. In addition to providing generic insights into rifting processes, this study also provides new constraints on the controversial tectonic history of this region. New onshore-offshore wide-angle seismic refraction data were acquired in Feb.-March 2005 along four transects that survey thin crust in the center of the eastern basin, the mid-Black Sea High (a basement ridge that separates the eastern and western basins), Sinop Trough (a sub-basin south of the basin center), and the Turkish margin. Velocity models created by first arrival tomography (FAST) show that the crust thins abruptly from the margins into the center of the basin, from ~32-33 km to ~7-8 km over a lateral distance of only ~30 km, implying a stretching factor (beta) of ~4.5. Thin crust in the basin center is 7-9 km thick and has velocities consistent with either thinned continental crust or oceanic crust formed in a back-arc basin. We will present new velocity models created by joint reflection/refraction (JIVE) tomography that will provide further information on the affinity of crust in basin center and the structure of the margin. We have also analyzed the subsidence history using two strain rate inversion algorithms: 1) a model that assumes pure-shear extension, and 2) a model that allows extension to vary with depth without assuming the existence or form of depth-dependence. The results suggest that the stratigraphy of this basin can be explained by a predominantly pure-shear stretching history. The timing of opening has also been the subject of intense debate; our work indicates that extension likely continued into the early Cenozoic, as suggested by stratigraphic relationships and the timing of arc magmatism. The basin-wide pattern in stretching implied by our subsidence analysis suggests increasing extension to the east, which is consistent with the opening of the eastern Black Sea by the rotation of Shatsky Ridge away from the mid-Black Sea High. The beta derived from subsidence analysis (~4.8) is similar to that calculated from the crustal velocity model.
... Early to Late Miocene sediments, sampled offshore Romania, comprise of mudstones (Robinson et al. 1995a;Spadini et al. 1996), with implied turbiditic layers observed in the seismic reflection profiles (Zonenshain & le Pichon 1986;Robinson et al. 1995a). Changes in water level and sediment drainage patterns, due to the uplift of the Carpathian Mountains during the Late Miocene, lead to the deposition of fluvial material and shallowwater limestones in this unit (Ross 1978;Robinson et al. 1996). The youngest sediments in the EBS, as recovered by gravity cores and drilling, comprise of clays with the occasional turbidite sequence (Ross 1978). ...
... Changes in water level and sediment drainage patterns, due to the uplift of the Carpathian Mountains during the Late Miocene, lead to the deposition of fluvial material and shallowwater limestones in this unit (Ross 1978;Robinson et al. 1996). The youngest sediments in the EBS, as recovered by gravity cores and drilling, comprise of clays with the occasional turbidite sequence (Ross 1978). The total thickness of top Cretaceous to recent sediment infill in the centre of the basin is 8-9 km (Shillington et al. 2008). ...
... For a shale lithology one would expect a velocity gradient in the upper sediments of ∼0.55 s −1 , while for a sand lithology one would expect a velocity gradient of 1-1.15 s −1 (Japsen et al. 2007). A gradient of ∼0.7 s −1 suggests a shale-dominated lithology, which is supported by results from a DSDP borehole on the mid-Black Sea high (indicated on Fig. 1) that found the shallow sediments were mostly clays interrupted by occasional turbidites (Ross 1978). The seismic velocity structure of the deeper sediments is dominated by a widespread and fairly continuous low-velocity zone. ...
Although the Black Sea is one large depositional structure today, previous studies have shown that the basin can be divided into two sub-basins, which have different tectonic histories. There is a general consensus on the formation history of the Western Black Sea Basin but there is little agreement on the history of the Eastern Black Sea. In March 2005 we collected a series of onshore-offshore, wide-angle seismic refraction/reflection profiles throughout the basin to sample the crustal structure. Four lines were surveyed; Line 1 was a 470 km profile, shot along strike through the centre of the basin, Lines 3 and 4 were dip lines shot across the Mid-Black Sea High and one dip line (Line 2) was shot further to the east. Data quality is very good and deep arrivals can be typically detected to 100 km offset. These data will be combined with co-incident industry reflection profiles to constrain the extensional evolution of the Eastern Black Sea Basin. We present data from Line 1, which has been modelled to investigate the velocity structure of the basin. Line 1 has 34 ocean bottom seismometers, spaced at ~14 km, deployed along the profile with an additional seven seismometers deployed on land. The seismic source was an air-gun array with a total source volume of 3140 cu.in and the line was shot at a spacing of 60 s, equivalent to a spatial interval of about 120 m. A combination of ray-tracing and first-arrival seismic tomography has been used to create a 2D velocity model through the crust. The model shows that the basin has a thick sedimentary package (up to ~10 km thick) with velocities ranging from 1.6 - 4.2 km/s. These overlay a crystalline crust with velocities of 4.8 - 7.2 km/s, which thins to ~8 km thick in the deepest part of the basin. The model indicates the presence of a low velocity zone near the base of the sediment package. This anomalous layer stretches across most of the profile, with velocities as low as 3.1 +/- 0.12 km/s compared with sediment velocities of 3.9 km/s above. The most likely explanation for these low velocities is over pressurisation of pore-fluids leading to under-compaction of the sediments.
... Early to Late Miocene sediments, sampled offshore Romania, comprise of mudstones (Robinson et al. 1995a;Spadini et al. 1996), with implied turbiditic layers observed in the seismic reflection profiles (Zonenshain & le Pichon 1986;Robinson et al. 1995a). Changes in water level and sediment drainage patterns, due to the uplift of the Carpathian Mountains during the Late Miocene, lead to the deposition of fluvial material and shallowwater limestones in this unit (Ross 1978;Robinson et al. 1996). The youngest sediments in the EBS, as recovered by gravity cores and drilling, comprise of clays with the occasional turbidite sequence (Ross 1978). ...
... Changes in water level and sediment drainage patterns, due to the uplift of the Carpathian Mountains during the Late Miocene, lead to the deposition of fluvial material and shallowwater limestones in this unit (Ross 1978;Robinson et al. 1996). The youngest sediments in the EBS, as recovered by gravity cores and drilling, comprise of clays with the occasional turbidite sequence (Ross 1978). The total thickness of top Cretaceous to recent sediment infill in the centre of the basin is 8-9 km (Shillington et al. 2008). ...
... For a shale lithology one would expect a velocity gradient in the upper sediments of ∼0.55 s −1 , while for a sand lithology one would expect a velocity gradient of 1-1.15 s −1 (Japsen et al. 2007). A gradient of ∼0.7 s −1 suggests a shale-dominated lithology, which is supported by results from a DSDP borehole on the mid-Black Sea high (indicated on Fig. 1) that found the shallow sediments were mostly clays interrupted by occasional turbidites (Ross 1978). The seismic velocity structure of the deeper sediments is dominated by a widespread and fairly continuous low-velocity zone. ...
Wide-angle seismic data from the Eastern Black Sea have been used to determine the geological structure of the sediments, the entire crust, and upper mantle. Data were acquired using a combination of ocean-bottom seismometers (OBS), land seismometers, and a marine air-gun source, providing refracted and reflected energy recorded to offsets in excess of 100 km.
... Early to Late Miocene sediments, sampled offshore Romania, comprise of mudstones (Robinson et al. 1995a;Spadini et al. 1996), with implied turbiditic layers observed in the seismic reflection profiles (Zonenshain & le Pichon 1986;Robinson et al. 1995a). Changes in water level and sediment drainage patterns, due to the uplift of the Carpathian Mountains during the Late Miocene, lead to the deposition of fluvial material and shallowwater limestones in this unit (Ross 1978;Robinson et al. 1996). The youngest sediments in the EBS, as recovered by gravity cores and drilling, comprise of clays with the occasional turbidite sequence (Ross 1978). ...
... Changes in water level and sediment drainage patterns, due to the uplift of the Carpathian Mountains during the Late Miocene, lead to the deposition of fluvial material and shallowwater limestones in this unit (Ross 1978;Robinson et al. 1996). The youngest sediments in the EBS, as recovered by gravity cores and drilling, comprise of clays with the occasional turbidite sequence (Ross 1978). The total thickness of top Cretaceous to recent sediment infill in the centre of the basin is 8-9 km (Shillington et al. 2008). ...
... For a shale lithology one would expect a velocity gradient in the upper sediments of ∼0.55 s −1 , while for a sand lithology one would expect a velocity gradient of 1-1.15 s −1 (Japsen et al. 2007). A gradient of ∼0.7 s −1 suggests a shale-dominated lithology, which is supported by results from a DSDP borehole on the mid-Black Sea high (indicated on Fig. 1) that found the shallow sediments were mostly clays interrupted by occasional turbidites (Ross 1978). The seismic velocity structure of the deeper sediments is dominated by a widespread and fairly continuous low-velocity zone. ...
We present new data that explores the link between pore pressure and
seismic velocity to estimate the magnitude of the overpressure within
the deep sediments of the Eastern Black Sea basin. New wide-angle
seismic data, combined with coincident reflection data, have been
modelled simultaneously using the seismic tomography code, Jive3D, to
provide a well-constrained seismic velocity model of the sediments. Our
models reveal a widespread low-velocity zone at the depth of 5.5-8.5 km,
which is characterized by a velocity decrease from 3.5 to ~2.5 km
s-1. Using two separate methods that relate changes in
seismic velocity to changes in effective stress, we estimate pore
pressures of at least 160 MPa within the low-velocity zone. These pore
pressures give λ* values of 0.8-0.9 within the centre
of the basin and above the Mid-Black Sea High. The low-velocity zone
occurs within the Maikop formation, an organic-rich mud layer identified
as the source of mud volcanism in the Black Sea and South Caspian Sea.
... In modeling magnetic sources are assumed to occur in the crystalline crust because in the Black Sea the Curie temperature of the magnetite (578 C) is reached mainly below the Moho or sometimes above it [Starostenko et al., 2014]. The sedimentary cover is practically nonmagnetic on the NW shelf [Bezverkhov, 1988] and in the uppermost 1 km section of the 380 borehole [Ross, 1978]. In the deep-water part magnetic susceptibility information is not available. ...
... In contrast, density values of sedimentary rocks are practically unavailable in the deep-water basins of the Black Sea. Laboratory measurements were only performed on the samples from the youngest sediments of Pliocene -Quaternary age [Ross, 1978]. In this case, it remains only to apply velocity/density relationship using seismic data from the study area. ...
... Late Miocene-top Pliocene (11-1.8 Ma) sediments comprise sands, conglomerates (Robinson et al. 1995b), chalks, siderites, clays and limestones (Ross 1978;Hsü & Giovanoli 1980). Top Pliocene-Present (1.8-0 Ma) sediments, comprise mostly clays but they also include marls and occasional turbidites (Ross 1978;Hsü & Giovanoli 1980;Hiscott & Aksu 2002). ...
... Ma) sediments comprise sands, conglomerates (Robinson et al. 1995b), chalks, siderites, clays and limestones (Ross 1978;Hsü & Giovanoli 1980). Top Pliocene-Present (1.8-0 Ma) sediments, comprise mostly clays but they also include marls and occasional turbidites (Ross 1978;Hsü & Giovanoli 1980;Hiscott & Aksu 2002). Shillington et al. (2008) present a more detailed lithological description of the sediments and how they were identified. ...
Pore pressure above the hydrostatic (overpressure) is common in deep
basins. It plays an important role in pore fluid migration, represent a
significant drilling hazard, and is one of the factors controlling slope
stability and deformation in seismically active areas.
Here, we present an inverse model to calculate overpressure due to
disequilibrium compaction and aquathermal pressuring. We minimize a
function that contains the misfits between estimates from our forward
model and observed values using a non-linear least squares approach. The
inverse model allows the introduction of observed seismic and geological
constraints such as P-wave velocity (Vp) and density data,
and depth of the layer boundaries, for a better pore-pressure
prediction. The model output also provides estimates of: (1) surface
porosity, (2) compaction factor, (3) intrinsic permeability at surface
conditions, (4) a parameter controlling the evolution of the intrinsic
permeability with porosity, (5) the ratio between horizontal and
vertical permeability and (6) uncompacted thickness (so sedimentation
rate assuming known time intervals), for each sedimentary layer. We
apply our inverse approach to the centre of the Eastern Black Sea Basin
(EBSB) where the Vp structure has been inferred from
wide-angle seismic data. First, we present results from a 1-D inverse
model and an uncertainty analysis based on the Monte Carlo error
propagation technique. To represent the observed rapid change from low
Vp to normal Vp below the Maikop formation, we
impose a zero overpressure bottom boundary, and subdivide the layer
below the Maikop formation into two sublayers: an upper layer where the
rapid change is located and a lower layer where the Vp is
normal. Secondly, we present the results from a 2-D inverse model for
the same layers using two alternative bottom boundary conditions, zero
overpressure and zero flow. We are able to simulate the observed
Vp, suggesting that the low velocity zone (LVZ) at
˜3500-6500 m depth below the seabed (mbsf) can be explained by
overpressure generated due to disequilibrium compaction (>90 per
cent) and to aquathermal pressuring (<10 per cent). Our results
suggest that the upper sublayer, below the Maikop formation, behaves as
a seal due to its low permeability ˜0.3-2 × 10-14
m s-1. This seal layer does not allow the fluids to escape
downwards, and hence overpressure develops in the Maikop formation and
not in the layers below. This overpressure was mainly generated by the
relatively high sedimentation rate of ˜0.29 m ka-1 of
the Maikop formation at 33.9-20.5 Ma and an even higher sedimentation
rate of ˜0.93 m ka-1 at 13-11 Ma. We estimate a maximum
ratio of overpressure to vertical effective stress in hydrostatic
conditions (λ*) of ˜0.62 at ˜5200 mbsf associated
with an overpressure of ˜42 MPa.
... Accurate information on sediment density values within the deep part of the Black Sea Basin is extremely limited. Density measurements have only been made in the youngest sediments (Ross, 1978). Otherwise, averaged values of densities measured from samples of adjacent onshore areas as well as from general velocity/density relationships can be used. ...
... In the basin, two features are recognised from seismic data where a density ''layer'' taken to be the equivalent of the crustal ''granitic'' layer can be identified. The first is the Shatsky Ridge where the pre-Palaeocene basement occurs at a depth of 5.5 km Balavadze et al. (1975); Belokurov (1976); Ross (1978); Neprochnov (1980); Bezverkhov (1988); Belousov et al. (1988); Makarenko (1997). and at about 9 km an observed seismic boundary is interpreted as being the top of Jurassic sediments. ...
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.
... Therefore, it becomes important to investigate the Archangelsky Ridge, which is a continental crust intruded into the oceanic crust, which has a ridge appearance and is covered with sediment, with different techniques. There are many scientific studies using gravity data to investigate crustal and tectonic structure of the Black Sea basin (Balavadze and Mindeli 1964;Mindeli et al. 1965;Goncharov et al. 1972;Neprechnov et al. 1974;Ross 1978;Belousov et al. 1988;Buryanov et al. 1996Buryanov et al. ,1997Buryanov et al. ,1998Buryanov et al. ,1999aSpadini et al.1996;Sari and Ergun 2000;Cloetingh et al. 2003;Starostenko et al. 2004;Maden and Dondurur 2012). Belousov et al. (1988) found the oceanic crust thickness as 12 km in the Eastern Black Sea Basin (EBSB) and 5-6 km in the Western Black Sea Basin (WBSB) by taking the density as 2.97 g/cm 3 . ...
To investigate the crustal structure of the Archangelsky Ridge, gravity data obtained from the World Gravity Map (WGM2012) were analyzed using Total Horizontal Derivative (THD), Parker-Oldenburg (PO) inversion and Normalized Full Gradient (NFG) techniques. The THD method was applied to the Bouguer gravity after band-pass filtering in order to image the discontinuities. The maximum amplitude values of the THD were used to reveal the discontinuities caused by the density difference in the Archangelsky Ridge and its vicinity. In addition, the basement upper surface topography of the region was calculated and mapped with the inverse solution. Moreover, the presence of an uplift area in the northeast of the study area, as well as the elevation of the Archangelsky Ridge was determined. The depth to the Cretaceous aged sedimentary basement in the Sinop basin and on the Archangelsky Ridge approximately reaches 4 km and 1.6 km, respectively. The average upper surface depth of the basement is calculated as 5 km under the Eastern Black Sea Basin (EBSB). Finally, depth calculations were made using NFG method for the selected profiles and correlated with gravity inversion results. The depth results of the basement upper surface topography obtained from NFG and inversion methods are compatible with each other within ± 0.1 km error limits.
... There are no new well data available for this study, so we rely on published information to define the age and litho-stratigraphy of the interpreted sequences. The Palaeocene(?)-Eocene to recent EBSB infill is generally well known and considered as a postrift, based on onshore and offshore drilling (e.g., Ross, 1978;Sydorenko et al., 2017), whereas the age and distribution of the synrift sequences is much less constrained. Synrift units ...
The 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.
... The basin was a predominantly freshwater environment with possible phases of salinization. This is not surprising considering that the Black Sea was a lake during most of the Pleistocene (Ross 1978;Krijgsman et al. 2019). It is important to underline that the fluvial facies of the Porat Fm. are abruptly replaced by basinal mudstones, without deposition of intervening deltaic facies. ...
This paper studies the Porat Formation (Fm.), which was deposited along the NE margin of the Dacian Basin part of the East Carpathian foreland (ECF) during the Pliocene and Early Pleistocene. We use a review of stratigraphic data in combination with lithofacies and sedimentary architecture analysis to interpret the Porat Fm. as a large sandy alluvial basin infill with an aggradational structure, consisting of cyclic successions of shallow sandy high-energy braided rivers. Aggradation of the Porat Fan was governed by subsidence of the Dacian Basin, along with a northerly supply of water and sediment from the Carpathians. Along the southern margin of the area the fan entered the Reni–Izmail-Trough, which formed the periodically active gateway between the Black Sea and Dacian basins. Along this trough, the Porat Fm. is developed in a different facies, discerned as the Dolynske Member (Mb. 1), which accumulated in the channel of a large river interpreted as the paleo-Danube. According to mammal stratigraphy of the Porat Fm. this continental-scale river had reached the area by the Gelasian to early Calabrian. The Porat alluvial infill indicates a stable water supply from the Carpathians, which explains the ecologically mixed fauna in its deposits: moistened forested alluvial plain-valleys were present between the zonally semi-arid steppe interfluves. The Porat Fm. and the previously studied late Miocene Balta Fm. are key elements for further in-depth study of the terrestrial evolution (tectonic–sedimentary–relief) of the ECF and north-western Black Sea coastal regions.
... However, for NH 4 + in core C25, the low concentration in the upper part and the linear increase with depths ( Fig. 3) reveal that most of the surplus NH 4 + at site C25 is probably derived from deep sediment, deeper than collected interval. The + NH 4 in shallow pore water that come from deep sediments beside in situ production have also been reported in the Black Sea (Ross, 1978) and the Bay of Bengal (Mazumdar et al., 2014), where efficient molecular diffusions are indicated by quasi-linear increases of + NH 4 concentrations within tens of meters in depth. ...
... There are no new well data available for this study, so we rely on published information to define the age and litho-stratigraphy of the interpreted sequences. The Palaeocene(?)-Eocene to recent EBSB infill is generally well known and considered as a postrift, based on onshore and offshore drilling (e.g., Ross, 1978;Sydorenko et al., 2017), whereas the age and distribution of the synrift sequences is much less constrained. Synrift units ...
p>Estimating the degree of lithospheric stretching, and identifying the distribution of crustal types, are important elements in oil and gas exploration activity, because this information is used for thermal modelling of hydrocarbon maturation. The Eastern Black Sea Basin (EBSB) is a frontier basin for hydrocarbon exploration, but the deep-water setting (∼2200 m) and the presence of a thick sedimentary sequence (∼10 km) limit conventional seismic imaging. The EBSB is considered to be partially underlain by oceanic crust, but the distribution of crustal types and the structures accommodating the stretching are still poorly known. We use long-offset reflection seismic data, acquired in 2011 by Geology Without Limits and ION GXT, to image key elements of rift-basin settings such as thinned continental crust, tilted fault-blocks, syn- and post-kinematic sequences, the top of the acoustic basement and Moho. We differentiate the basement by examining seismic reflectivity patterns as an indicator of crustal type. We interpret variations in basement morphology to indicate the presence of a continent-ocean transition of enigmatic nature. This information will be used to further investigate the nature and thickness of the crust and to provide insights into mechanisms of continental extension and rifting in back-arc settings.</p
... The fan sedimentation ceased during lake level high-stands , when the Danube mouth occupied a vast shallow bay (Svitoch et al., 2000). During the Black Sea isolation, the sea (/lake) level oscillated independently relative to the global ocean, being directly influenced by the dry-wet cycles in Eurasia (Ross, 1978). This is proved by the good correlation between the number and ages of glacial-interglacial cycles in continental Europe with climatically-driven changes of the Black Sea (Zubakov, 1988;Eremeev et al., 1995). ...
The Black Sea climatically-driven level change is the main control of the Lower Danube incision and aggradation in the long-term subsiding setting of the Eastern Romanian Plain. The interglacial episodes of aggradation suggest a decreasing fluvial accommodation. While T4 terrace fill partially buried the cut terrace T5 in the upstream part of the studied area (Lower Danube-Argeş-Dâmboviţa), younger deposition did not compensate the previous incisions. Black Sea level fallings during glaciations were followed by Lower Danube incisions which propagated upward through knickpoints. Loess deposits can be correlated with these periods. Five episodes of incision were recognized based on terrace levels T5 to T1. Their ages and of the covering loess were obtained through optically stimulated luminescence (OSL) and were correlated with MIS 6 – MIS 3 and classic glacial chronological events (latest Rissian-middle Würmian). The maximum limiting age of Danube oldest terrace (T5) in the studied area is 141 ± 25 kyr, while of the youngest (T1) is 50 ± 6 kyr. The equivalent terraces on tributaries are younger. The time delays between terrace incisions on the Lower Danube system were estimated. The 32.7–15.9 kyr Danube floodplain deposits and the 5 kyr forests buried up to 7 m under Argeş floodplain suggest that younger than 44–40 kyr terraces may be buried.
... On glacial/interglacial timescales, sea-level fluctuations govern the connection to the Mediterranean Sea causing the hydrography of the Black Sea to alternate at least 12 times over the last 670,000 years between limnic and brackish stages (Ross, 1978;Badertscher et al., 2011). During interglacials, sea-level highstands favoured the connection to the Mediterranean Sea. ...
The Black Sea repeatedly experienced major hydrographic changes during glacial-interglacial transitions, with alternating limnic and brackish stages. While the redox conditions during the present Holocene brackish period (since ∼. 9,000. yr. BP) have been intensively studied, the redox evolution during the last interglacial, the Eemian (∼. 128,000-120,000. yr. BP), remains largely unexplored. With its at least 3. °C warmer climate and an up to 10. m higher global sea level, the Eemian could open a window into the future development of the Black Sea. This study provides a detailed comparison of the Black Sea redox evolution during Eemian and Holocene sapropel formation. We show that the redox conditions and associated geochemical processes in the Black Sea water column can strongly deviate from the Holocene when sea level and climate conditions are different. Mo/Al and Re/Mo as well as Mo and Fe isotope proxies record a comparatively uniform rise of the Eemian redoxcline culminating in pronounced euxinia. This scenario strongly contrasts with weaker euxinic conditions during the Holocene Unit II sapropel (∼. 8,000-2,500. yr. BP). Higher Mo/TOC ratios during the Eemian and Mo inventory considerations suggest a higher Eemian Mo availability, possibly due to an improved connection to the Mediterranean Sea. We conclude that higher temperatures, productivity, sea level-associated salinity changes, and corresponding higher sulphide levels were ultimately responsible for enhanced trace metal enrichment during the Eemian Black Sea sapropel stage.
... Due to very limited direct observations from the Black Sea itself, which are mainly limited to surficial sediments (Ross 1974(Ross , 1978Ross & Degens 1974;Ross et al. 1978), and due to the limited available seismic data (Finetti et al. 1988;Nikishin et al. 2015a, b), most of the tectonic models on the evolution of the Black Sea rely on data from the onshore areas rather from the basins themselves. Thus, any reliable data from this region play an important role in our understanding of the geological evolution of the Black Sea and surrounding tectonic units. ...
The Western Pontide Magmatic Belt consists of two different magmatic series corresponding to two distinct periods of intense volcanism, separated by a pelagic limestone marker horizon resting on a regional unconformity. The first stage of magmatism and associated extensional tectonic regime prevailed in the region between the Middle Turonian and Early Santonian. During the first stage, magmas were derived from a depleted mantle source containing a clear subduction signature. The extrusives intercalated with marine clastic sediments and pelagic carbonates associated with thick debris-flow horizons and olistoliths. Based on geochemistry and depositional features, the first stage is interpreted as an extensional ensialic arc setting developed in response to northwards subduction of the Tethys Ocean beneath the southern margin of Laurasia. During the Late Santonian, the volcanism stopped and the whole region suddenly subsided with the deposition of a thin, but laterally continuous, pelagic limestone horizon. This subsidence may imply the breakup of the Laurasian continental lithosphere and the beginning of oceanic spreading in the Western Black Sea Basin. The intensified extension is interpreted to be linked to the southwards rollback of the subducting slab. During the second stage in the Campanian, magmas were derived from two contrasting mantle sources: (1) a depleted lithospheric mantle enriched by a subduction component; and (2) an enriched asthenospheric mantle which is similar to that of the ocean island basalts (OIB). The depleted lithospheric source may be linked to the subcontinental lithospheric mantle of Laurasia, which was metasomatized by the previous Tethyan subduction event rather than by an active arc magmatism. Lavas derived from the depleted source are abundant throughout the stratigraphic column, whereas those from the enriched source dominate the end of the second stage. The presence of the alkaline lavas may indicate thinning of the lithosphere and upwelling of the asthenospheric mantle in the matured stages of rifting. We argue that the main cause of both rifting and temporal change in magma generation was the steepening and rollback of the northwards subducting slab of the Tethys Ocean. The aforementioned rollback also caused the Istanbul Zone to be moved to the south, and colliding with the Sakarya Zone in the south during the Maastrichtian. Based on geochemical, stratigraphic, palaeontological and sedimentary data, we suggest that the oceanic Western Black Sea Basin opened as an intra-arc basin during Turonian-Santonian time.
... Investigations by the DSDP permit comparison of Pleistocene, glacial, Holocene, and late Holocene apparent accumulation rates in the Black Sea basin. The Quaternary has been penetrated at three sites (Hsü, 1978a,b;Ross, 1978;Stoffers et al., 1978). Two of the DSDP sites were at widely separated locations in the deep basin floor; they have thicknesses of 620 and 640 m, respectively. ...
It has long been recognized that global Pleistocene-Holocene material fluxes are qualitatively distinct from those of the earlier Cenozoic and Mesozoic, but the full extent of the differences has only recently begun to emerge. Quantitative estimates of the masses of material eroded, transported, and deposited during the Pleistocene-Holocene have been difficult to obtain because of the lack of consistent information on the thicknesses and areal extent of the deposits on land and in shallow seas. Geologic maps commonly show extensive areas of Quaternary cover on older sediments, but information on the thickness of the tills, alluvium, and colluvium that make up these deposits is scattered throughout the literature and is often incomplete. Several major changes in the erosion-sedimentation regime have affected material fluxes. These have occurred in response to alternations in the climatic regime, to related changes in the sediment transport agents, to increasing amplitude of sea-level fluctuations, and to extensive regional tectonic uplift. The Pleistocene climatic regime results in alternations of glacial and temperate conditions at mid-and high latitudes, and arid and humid conditions at lower latitudes. Both types of change affect the rates of chemical weathering. At mid-and high latitudes the major transport agent alternates between glaciers and rivers. Glaciers are effective at removing, pulverizing, and transporting clastic sedimentary and low-grade metamorphic rocks, but less effective in attacking crystalline rocks. The glacial sediment is commonly transported uphill and deposited in such large quantities that it results in reorganization of the fluvial drainage systems. The Mississippi system of North America is an excellent example, the preglacial drainage having been truncated by two ice edge rivers, the Ohio and the Missouri. During times of deglaciation, supplies of fluvioglacial sediment often exceed the competence of the rivers, resulting in extensive alluviation. Both of these processes expose extensive areas of unweathered debris to soil-forming processes.
At lower latitudes the alternation of arid and humid climates results in alternating cycles of alluviation and incision in river valleys as well as an alternation of soil-forming processes.
The late Cenozoic-Pleistocene glaciations resulted in a series of sea-level falls of increasing amplitude. Erosion of exposed unconsolidated clastic shelf sediments and consequent isostatic compensation has resulted in large masses of sediment being off-loaded from the continental shelves onto deep-sea fans and abyssal plains by turbidity currents. Modern continental shelves with clastic sediments are adjusted to the Pleistocene low stands of sea level. The present widespread development of estuaries is a result of this condition.
Interglacials are too short and the sediment supply is too small to allow shelves to build back to equilibrium grade with high sea-level stands. Although during the interglacials a few large rivers can build deltas to the shelf break and spill sediment into the deep sea, most estuaries do not fill with sediment before the next sea-level fall. In contrast, carbonate sediments become cemented by fresh water infiltration when sea level falls and, as a result, carbonate-dominated shelves and banks reflect equilibrium with high sea-level stands.
Carbonate extraction from the ocean is at a maximum as shallow shelf seas flood during the late stages of deglaciation.The largest supplies of clastic sediment come from the largest regional uplifts, the Tibetan Plateau-Himalayas and western North America. Evidence suggests that both of these regions were uplifted in the late Pliocene and Pleistocene. Their uplift may be the ultimate cause of the onset of continental glaciation and the global climatic alternations that have characterized the Earth's recent past.
Pleistocene-Holocene fluxes do not reflect the long-term state of the planet but are the result of a set of unusual conditions. It is, however, against this rapidly changing background that future global change will take place.
... However, diagnostic fossils were practically absent and diagenetic formation of magnetic greigite (Fe3S4) minerals complicated reliable magnetostratigraphic dating (Hsü and Giovanoli, 1979). The tentative dating of the more than 1000 m of Black sea sequence was thus considered a working hypothesis at best (Ross, 1978b). ...
The Black Sea and Caspian Sea are the present-day remnants of a much larger epicontinental sea on the Eurasian continental interior, the Paratethys. During the late Miocene Messinian Salinity Crisis (MSC), a unique oceanographic event where 10% of the salt in the world's ocean got deposited in the deep desiccated basins of the Mediterranean, the Paratethys Sea was connected to the Mediterranean Sea. Unlike the Mediterranean, no salt is known to have been deposited in the Paratethys region at this time, yet a similar mechanism of deep desiccation (with a water level drop of up to 2 km occurring at 5.6 Ma) has been proposed in the past to explain the late Miocene and Pliocene Paratethys basin evolution.
... Although Zubakov (1988) provided an excellent basis for a climatostratigraphic correlation of the Black Sea record to the global oxygen-isotope scale for the last 1 Ma, allowing determination of several saline and freshwater events coinciding with glacial-interglacial cycles, detailed insights into high-resolution dynamics of older Terminations, like T II, are sparse due to the lack of well constrained and complete sediment cores (e.g. Ross, 1978;Quan et al., 2013). By contrast, T II and Eemian studies worldwide established innovative concepts for a regional and global point of view during the last decades. ...
... 1972;Neprechnov vd. 1974;ross 1978;Belousov vd. 1988;Buryanov vd. ...
Gravity anomaly map of the study area, which includes Turkish Margin of the central Black Sea, shows a negative gravity anomaly in the Sinop and Eastern Black Sea sub-basin and a positive gravity anomaly over the Archangelsky Ridge. The amplitudes of these anomalies are approximately 50, 30 and 100 mGal along the Sinop and Eastern Black Sea sub-basins and over Archangelsky Ridge, respectively.
Full horizontal derivatives of the Bouguer anomaly map have been computed in order to determine tectonic structure of the study area, and the maximal amplitudes of horizontal derivatives have been mapped. The linearities with horizontal derivative amplitudes in between 3.00- 6.50 mGal/km indicate the major tectonic structure in NWSE direction separating Archangelsky Ridge from Sinop and Eastern Black Sea sub-basins. There are also parallel linearities running along the both flanks of the ridge represented by medium-magnitude horizontal derivative amplitudes. These linearities are interpreted as sub-parallel normal fault blocks towards the Eastern Black Sea basin. An elongated anomaly along the main Archangelsky Ridge gravity anomaly is observed especially on the second derivative map, and it is interpreted as secondary uplift of the Archangelsky Ridge.
Using power spectrum method, depths of Moho and Conrad discontinuities, and sedimentary basement are computed to be 29.5 km, 11.2 km and 4.2 km, respectively. Furthermore, the basement depth corresponding to the Cretaceous basement of the pre-rift rocks of the Black Sea from 3D inversion is computed as 4 km in the Sinop basin, while there are approximately 1 km thick sedimentary unit over the Archangelsky Ridge.
... Although Zubakov (1988) provided an excellent basis for a climatostratigraphic correlation of the Black Sea record to the global oxygen-isotope scale for the last 1 Ma, allowing determination of several saline and freshwater events coinciding with glacial-interglacial cycles, detailed insights into high-resolution dynamics of older Terminations, like T II, are sparse due to the lack of well constrained and complete sediment cores (e.g. Ross, 1978;Quan et al., 2013). By contrast, T II and Eemian studies worldwide established innovative concepts for a regional and global point of view during the last decades. ...
... It is difficult to postulate the role of abiotic processes in extracting dissolved silica from the surface waters of the Black Sea basin, although it has been suggested that sorption reactions involving dissolved silica and suspended sediments are a likely buffering mechanism in controlling silica concentrations in fresh water environments (Edwards and Liss, 1973;Mayer and Gloss, 1980). Diatoms constitute nearly 50 to 60 percent of the bulk of the two siderite units in the Black Sea section (Ross, 1978). Such an abundance of diatoms indicates that the silica cycle of the Neogene Black Sea was principally driven by biologic activity. ...
It has been hypothesized that finely disseminated, soft,
wheat-like grains of siderite in the sideritic muds of the PlioPleistocene
section of the Black Sea are "sub-aqueous precipitates"
(Hsu and Kelts, 1978). In an attempt to quantify this hypothesis, we (1)
investigated the chemistry, mineralogy, and isotopic composition of
the siderites and associated calcite and (2) developed a thermodynamic
model of endogenic siderite precipitation (that is, directly precipitated
from the water column) driven by sequential evaporative concentration
of acidic, dissolved or~anic-carbon, and iron-rich waters. Considering
the average com.Position of the present-day Satilla drainage of the
southeastern Umted States as approximating the composition of the
waters that fed the Neogene Black Sea and allowing this water to
evaporate isothermally at 25°C in equilibrium with atinospheric C02
(PC02 = l 0-3.5 attn), we calculated the aqueous concentrations at which
various carbonate phase5 would precipitate out of the system. It is
shown that evaporation of this water to roughly one-twelfth of its
original volume can result in precipitation of the pure endmember
siderite alone. Relating our geochemical and modeling results to the
details of Black Sea climatostratigraphic and evolutionary history during
the times of deposition of the siderite units, we corroborate the
qualitative arguments of Hsu and Kelts (1978). We also conclude that
climate was the chief forcing function in transforming episodically the
calcite-precipitating eutrophic water masses of the Plio-Pleistocene
basin to one of siderite ptecipitation. Based on our model calculations
of the thickness of siderite precipitated per cm2 of basin area, we
further predict that the observed laminae/interbeds of siderite could be
a composite of several microlayers of siderite and clays.
... The location of the Black Sea, between Europe and Asia, makes its water level dependent on Eurasian climatic fl uctuations . This inland sea is a perfect present-day example of a marginal basin where connection changes dramatically with sea level (Ross, 1971Ross, , 1978 Ross et al., 1970; Ross and Degens, 1974; Ryan et al., 2003 Ryan et al., , 1997). The Black Sea is at present the world's largest anoxic basin, making it an important modern analogue for past anoxic conditions, while during the last glacial period, it was a low-salinity oxygenated lake, isolated from the Mediterranean (Deuser, 1972Deuser, , 1974 Lericolais et al., 2006b; Wall and Dale, 1974). ...
This paper presents geophysical and core data obtained from several marine geology surveys carried out in the western Black Sea. These data provide a solid record of water-level fluctuation during the Last Glacial Maximum in the Black Sea. A Last Glacial Maximum lowstand wedge evidenced at the shelf edge in Romania,Bulgaria, and Turkey represents the starting point of this record. Then, a fi rst transgressive system is identifi ed as the Danube prodelta built under ∼40 m of water depth. The related rise in water level is interpreted to have been caused by an increase in water provided to the Black Sea by the melting of the ice after 18,000 yr B.P., drained by the largest European rivers (Danube, Dnieper, Dniester). Subsequently, the Black Sea lacustrine shelf deposits formed a signifi cant basinward-prograding wedge system, interpreted as forced regression system tracts. On top of these prograding sequences, there is a set of sand dunes that delineates a wave-cut terrace-like feature around the isobath -100 m. The upper part of the last prograding sequence is incised by anastomosed channels that end in the Danube (Viteaz) canyon, which are also built on the lacustrine prograding wedge. Overlying this succession, there is a shelfwide unconformity visible in very high-resolution seismic-refl ection profi les and present all over the shelf. A uniform drape of marine sediment above the unconformity is present all over the continental shelf with practically the same thickness over nearby elevations and depressions. This mud drape represents the last stage of the Black Sea water-level fluctuation and is set after the reconnection of this basin with the Mediterranean Sea.
... Positively, these recent studies have demonstrated that the Black Sea semi-enclosed basin constitutes one of the most interesting research zones for high-resolution paleoclimatological and paleoenvironnemental reconstructions. Since the DSDP drillings (Ross, 1978b; Ross and Neprochnov, 1978; Ross et al., 1978), the lithology and mineralogy of deep sediments from the Black Sea have been well studied (i.e. Degens and Ross, 1974; Ross, 1978a; Major et al., 2002b; Strechie et al., 2002; Bahr et al., 2005 Bahr et al., , 2006 Major et al., 2006; Giunta et al., 2007; Ryan, 2007; Bahr et al., 2008 Bahr et al., , 2009 ). ...
The Danube River Basin–Black Sea area represents a unique natural laboratory for studying the interplay between lithosphere and surface as well as source to sink relationships and their impact on global change. This paper addresses some information on the “active sink” of the system; i.e. the Danube deep sea fan and the Black Sea basin. The present study focuses on the distal sedimentary processes and the evolution of sedimentation since the Last Glacial Maximum. This is investigated through recently acquired long piston coring and shallow seismic data recovered at the boundary of influence of the distal part of the Danube turbidite system (to the north-west) and the Turkish margin (to the south). This dataset provides a good record of the recent changes in the sedimentary supply and climato-eustasy in the Black Sea region during the last 25 ka. This study demonstrates that the deep basin deposits bear the record of the Late Quaternary paleoenvironmental changes and that the western Black Sea constitutes an asymmetric subsident basin bordered by a northern passive margin with confined, mid-size, mud-rich turbidite systems mainly controlled by sea-level, and a southern turbidite ramp margin, tectonically active.
... De Mid-Basin Highs waren bedekt met een dunne laag van pelagische mergelachtige sedimenten (ROBINSON et al., 1996). (MURATOV et al., 1978;ROSS, 1978;SCHRADER, 1978;KOJUMDGIEVA, 1983). De waterdiepte in het centrum van het bekken was gereduceerd tot enkele honderden meters, zodat de afzetting van fluviatiel materiaal plaatsvond tot diep in het bekken. ...
... De Mid-Basin Highs waren bedekt met een dunne laag van pelagische mergelachtige sedimenten (ROBINSON et al., 1996). (MURATOV et al., 1978;ROSS, 1978;SCHRADER, 1978;KOJUMDGIEVA, 1983). De waterdiepte in het centrum van het bekken was gereduceerd tot enkele honderden meters, zodat de afzetting van fluviatiel materiaal plaatsvond tot diep in het bekken. ...
... m depth) by the high-resolution pollen record of Popescu (2006). The present results covering the entire Pliocene and Lower Pleistocene of this section significantly change the previous chronostratigraphy (Hsü, 1978;Muratov et al., 1978;Ross, 1978) and demonstrate the interest of high-resolution pollen analyses in the Black Sea. ...
The Early Pliocene corresponds to a global warm climate documented by marine & terrestrial records. Reconstruction of climatic parameters, based on terrestrial proxies, indicate at European mid-latitudes a MAT higher of about 1-5°C than today and MAP higher of about 400-1000 mm. This global warm situation was interrupted between 4.7 - 4.5 Ma by a cooling event related to small fluctuations of the Antarctic ice-sheet that modify the floristic assemblages. according to pollen recors, the Northern Mediterranean area is characterized by dominance of arboreal pollen, suggesting a dense forest cover, on contrary to the Southern Mediterranean where herbs were prevalent, signifying a widespread development of open vegetation during the early Pliocene. Such a contrast in landscape between the North and the South of the Mediterranean is to be related to the latitudinal gradient in humidity. In the North Mediterranean area, the vegetation organization was also closely linked to the relief. Coastal plains were inhabited by Taxodiaceae swamps replaced in some places by marshes. With respect to the geographic position, several plant ecosystems can distinguished: (1) salt marshes, along the Atlantic coastline (zone A); (2) marshes mostly made of Cyperaceae evidenced on the Mediterranean coastline. Such juxtaposed assemblages resemble the modern vegetation of the Mississippi Delta and Florida. Peculiar vegetation assemblages characterize the Mediterranean coastal plains. In the southeastern Mediterranean region (Zone B), the open vegetation was composed by herbs including subdesertic elements. Mediterranean xerophytes are only numerically represented in the area of Tarragona and Sicily, their assemblage resemble the modern thermo-mediterranean formation. Close to the mountains (Zone C) vegetation is organized according to an altitudinal gradient. The low altitude vegetation was composed by Taxodiaceae (Sequoia) while Cathaya and Cedrus dominated the mid-altitude belt. Abies and Picea developed in higher altitude. The Eastern Europe vegetation (zone D) was characterized by coexistent warm-temperate forests and open ecosystems. Some megathermic and mega-mesothermic elements were persisting. Mediterranean xerophytes were indentified in few amounts in the Eastern Europe, showing a slight increase according to the latitudinal gradient. Site 380A (Black Sea) provides relatively high percentages of Artemisia growing in Anatolia, which increased again during the cooler periods. Anatolia probably represents the origin of the repeated steppe expansions which occurred in Europe at each glacial phase. Finally, the Nile region (zone E) documents the presence of savannah (composed mainly by Poaceae and Cyperaceae) including some subdesertic taxa. Nile riparian forests preserved several tropical-subtropical elements.
... m depth) by the high-resolution pollen record of Popescu (2006). The present results covering the entire Pliocene and Lower Pleistocene of this section significantly change the previous chronostratigraphy (Hsü, 1978;Muratov et al., 1978;Ross, 1978) and demonstrate the interest of high-resolution pollen analyses in the Black Sea. ...
Climate characteristics (temperature, rainfall, seasonality) of Europe were already documented by several pollen records (Suc et al., 1995; Fauquette et al., 1999; Popescu, 2006; Fauquette et al., 2007; Jiménez-Moreno et al., 2007). Two new pollen records at high chronological resolution of the whole Pliocene (5.33 - 2.6 Ma) and early Pleistocene (DSDP Site 380 in the southwestern Black Sea and Wólka Ligezowska in southern Poland, at 42 and 51° North latitude, respectively), provide detailed information in two key-regions. DSDP Site 380 pollen diagram shows a continuous competition between thermophilous forests and Artemisia steppes, while thermophilous-mesophilous forests contrast with coniferous boreal forests then the latter with toundra-park at Wólka Ligezowska (Popescu et al., accepted). The narrow relationship between Site 380 pollen curves (especially the "thermophilous elements / steppe elements" ratio) and the oxygen isotope reference ones allows (1) to accurately characterize the cyclic evolution of climate progressively leading from warm to glacial conditions along a 10° in latitude gradient in Europe, and (2) to define phytogeographical provinces with their distinction both in mean annual temperature with respect to latitude and in seasonality (temperature, precipitations) according to their geographic location.
... Investigations by the DSDP permit comparison of Pleistocene, glacial, Holocene, and late Holocene apparent accumulation rates in the Black Sea basin. The Quaternary has been penetrated at three sites (Hsü, 1978a,b;Ross, 1978;Stoffers et al., 1978). Two of the DSDP sites were at widely separated locations in the deep basin floor; they have thicknesses of 620 and 640 m, respectively. ...
It has long been recognized that global Pleistocene-Holocene material fluxes are qualitatively distinct from those of the earlier Cenozoic and Mesozoic, but the full extent of the differences has only recently begun to emerge. Quantitative estimates of the masses of material eroded, transported, and deposited during the Pleistocene-Holocene have been difficult to obtain because of the lack of consistent information on the thicknesses and areal extent of the deposits on land and in shallow seas. Geologic maps commonly show extensive areas of Quaternary cover on older sediments, but information on the thickness of the tills, alluvium, and colluvium that make up these deposits is scattered throughout the literature and is often incomplete.
Several major changes in the erosion-sedimentation regime have affected material fluxes. These have occurred in response to alternations in the climatic regime, to related changes in the sediment transport agents, to increasing amplitude of sea-level fluctuations, and to extensive regional tectonic uplift.
The Pleistocene climatic regime results in alternations of glacial and temperate conditions at mid- and high latitudes, and arid and humid conditions at lower latitudes. Both types of change affect the rates of chemical weathering. At mid- and high latitudes the major transport agent alternates between glaciers and rivers. Glaciers are effective at removing, pulverizing, and transporting clastic sedimentary and low-grade metamorphic rocks, but less effective in attacking crystalline rocks. The glacial sediment is commonly transported uphill and deposited in such large quantities that it results in reorganization of the fluvial drainage systems. The Mississippi system of North America is an excellent example, the preglacial drainage having been truncated by two ice edge rivers, the Ohio and the Missouri. During times of deglaciation, supplies of fluvioglacial sediment often exceed the competence of the rivers, resulting in extensive alluviation. Both of these processes expose extensive areas of unweathered debris to soil-forming processes. At lower latitudes the alternation of arid and humid climates results in alternating cycles of alluviation and incision in river valleys as well as an alternation of soil-forming processes.
The late Cenozoic-Pleistocene glaciations resulted in a series of sea-level falls of increasing amplitude. Erosion of exposed unconsolidated clastic shelf sediments and consequent isostatic compensation has resulted in large masses of sediment being off-loaded from the continental shelves onto deep-sea fans and abyssal plains by turbidity currents. Modern continental shelves with clastic sediments are adjusted to the Pleistocene low stands of sea level. The present widespread development of estuaries is a result of this condition. Interglacials are too short and the sediment supply is too small to allow shelves to build back to equilibrium grade with high sea-level stands. Although during the interglacials a few large rivers can build deltas to the shelf break and spill sediment into the deep sea, most estuaries do not fill with sediment before the next sea-level fall. In contrast, carbonate sediments become cemented by fresh water infiltration when sea level falls and, as a result, carbonate-dominated shelves and banks reflect equilibrium with high sea-level stands. Carbonate extraction from the ocean is at a maximum as shallow shelf seas flood during the late stages of deglaciation.
The largest supplies of clastic sediment come from the largest regional uplifts, the Tibetan Plateau-Himalayas and western North America. Evidence suggests that both of these regions were uplifted in the late Pliocene and Pleistocene. Their uplift may be the ultimate cause of the onset of continental glaciation and the global climatic alternations that have characterized the Earth's recent past.
Pleistocene-Holocene fluxes do not reflect the long-term state of the planet but are the result of a set of unusual conditions. It is, however, against this rapidly changing background that future global change will take place.
... Even with a Çanakkale outlet above − 65 m, eustatic sea level was sufficiently high in sub-stages MIS-5a, MIS-5c and MIS-5e to establish an assemblage of marine molluscs and foraminifera. The global ocean even penetrated into the Black Sea via the Strait of Istanbul to introduce species of marine foraminifera and diatoms recovered in the DSDP cores from the basin floor and molluscs exposed in outcrop on Karangatian terraces (Ross, 1978;Hsü, 1978;Kaplin et al., 1993;Chepalyga, 1995;Ryan et al., 2003;Kaplin and Selivanov, 2004). A Çanakkale outlet as shallow as −60 m would cause the SoM to revert to lacustrine conditions in sub-stages MIS-5b and MIS-5d. ...
Chirp sub-bottom profiling, multibeam bathymetric mapping and a combination of faunal and isotopic analysis of molluscs and foraminifera in sediment cores on the northern shelf of the Sea of Marmara (SoM) provide evidence of sea-level excursions, water exchanges between the adjacent Mediterranean and Black Seas, and oscillating salinity over the last 160 ka bp. During the marine isotope stages MIS-2, MIS-3, MIS-4 and MIS-6 the SoM disconnected from the Mediterranean Sea and evolved into a lake. During MIS-1, MIS-5 and MIS-7, the SoM reconnected and became salty once again. Sapropels formed shortly after each invasion of Mediterranean saltwater observed in our cores. Concurrent suboxic–dysoxic conditions prevailed over quite shallow substrates on the shelf.Ancient shorelines are pervasive at − 85 m on the northern shelf and in the region of Prince Islands coincident with the elevation of the modern bedrock sill in the Çanakkale (Dardanelles) Strait. At times when global (eustatic) sea level dropped below this sill, the surface of the SoM stabilized at its outlet and freshened. Thus this particular shoreline is interpreted as the edge of the most recent SoM lake that existed from about 75 ka bp to 12 ka bp. The freshening is observed in very light (− 6‰) values of δ18O measured on freshwater molluscs and the complete absence of foraminifera.Two brief lacustrine episodes during MIS-5 suggest that the level of the Çanakkale outlet might have been as shallow as − 50 m in the past, a likelihood supported by submerged terraces along its margins bounding the modern central channel and the presence of an euryhaline biofacies in Unit L4.1 corresponding to MIS-5b. δ18O profiles and carbon-14 dating show that salinification of the SoM and the blossoming of bioherms evolved rapidly after the latest connection with the Mediterranean at 12 ka bp. However, freshening proceeded more slowly once the connection was severed.
Long offset seismic reflection data reveal the presence of four Bottom Simulating Reflectors (BSR0-3) within folded sediments of the Tuapse Trough, along the NE margin of the Eastern Black Sea Basin (EBSB). Multiple BSRs are observed in other sites worldwide, however, their origin and formation mechanisms are still debated. Here, we investigate the formation mechanisms of the EBSB multiple BSRs based on their seismic character and on their physical properties derived from reflected and refracted arrival seismic velocities. Seismic reflection data are downward continued to enhance refracted arrivals. A 2D travel-time velocity model of the sub-seabed, using combined travel-times from non-downward-continued reflected and downward-continued refracted signals, shows variations in the physical properties at the BSRs and nearby sediments. The P-wave velocity (VP) increase of 1.55-1.72 km/s between the seafloor and BSR0 (258 mbsf) reflects normal compaction trends in sediments, whereas the VP of 1.75-1.83 km/s between BSR0 and BSR1 (360 mbsf) is higher than that expected for sediments at that depth. Beneath BSR1, a VP decrease from 1.83 km/s to 1.61 km/s occurs within a 70-80 m-thick layer including BSR2 (395 mbsf) and extending to BSR3 (438 mbsf). Beneath BSR3, VP increases. Based on an analytical model linking seismic velocity to physical properties, these VP trends can be explained by a gas hydrate saturation from 0 to 2% between the seafloor and BSR0, reaching 4 ± 2% just above BSR1. A free gas saturation of up to 20-25% is estimated within the low-velocity zone between BSR1 and BSR3. BSR1 likely represents the present-day base of the gas hydrate stability zone (BGHSZ), which aligns with the theoretical BGHSZ assuming a geothermal gradient of 26-30˚C/km. Based on seismic polarities and results from travel-time analysis and rock physics modelling, we suggest that hydrate dissociation and recycling processes may explain the negative polarity of BSR2 and BSR3, which are still visible due to the presence of relict gas, and inferred higher gas hydrate saturations close to the present-day base of the stability zone at BSR1. Also, structural and stratigraphic controls seem to have favoured focused free gas flow and hydrate formation at the top of an anticlinal structure, thus likely controlling multiple BSR generation in the EBSB.
Gas Hydrates (GH) study in Bulgaria started in 1999 with a simple model of gas hydrate stability zone (GHSZ) of the Black Sea methane hydrates. The Model was developed and still developing. The last model works with 27 parameters including effects from sea level and climate change. Model for the Bulgarian Exclusive Economical Zone (BEEZ) of the Black Sea shows details of the structure and parameters of the Bulgarian GH and conditions for their exploration.
The model is applied for interpretation of the changeable activity of hydrocarbon emissions of mud volcanoes and long term thermal monitoring of Dvurechenskii Mud Volcano.
A new express method for estimation of the maximum GH deposits from seismic records is created. The
processing of available seismic records shows new prospects and challenger tasks for GH study.
This work is in the frames of the next international projects: GEOHYDAT, EUROSEISMIC, ASSEMBLAGE,
CRIMEA, GEO-HYDRATE, GEOHAZARDS, BLACKSEASPAN, BLACKSEA-CASPEANHEATFLOW,
SUBVENT, DEEPWATER-MULTIPHASEPUMP, GEO-METHANE, SUGAR, PERGAMON.
In the last project is creating model of the GHSZ of the Arctic Ocean.
In 2000 was created a draft "Bulgarian Program for Gas Hydrates: Research and Development" which still is
without expected results. The Program could be a base for hydrocarbon independency of Republic Bulgaria.
Many gas seepages, temperature, pressure, salinity, anoxic environment and high source gas potential of the Black Sea indicates that the Black Sea might have huge potentials for biogenic and thermogenic gas hydrates. However, the last important parameter to consider gas hydrate as an energy source is the type of sediments. Coarse marine sands are considered as good hydrate reservoirs because of high porosity and high permeability. Only very limited data is available related to the types of lithology of the Black Sea sediments. Hence, in this study, the literature data (especially the drilling and coring data of DSDP Leg 42B program) about gas seepages, temperature gradient, pressure gradient, salinity, anoxic environment and high source gas potential, and the types of the sediments in the Black Sea were investigated and analyzed. Although gas seepages, temperature gradient, pressure gradient, salinity, anoxic environment and high source gas potential of the Black Sea are appropriate for producible gas hydrate reservoirs, the sediments of the Black Sea appear to be generally fine grained with high clay content. Sandy-silt and silty sand layers in turbidites of the Black Sea might be potential producible hydrate reservoirs but these sediments are fine. As well as turbidites, separate thin sand layers might be potential gas hydrate reservoirs as an energy source in the Black Sea.
The samples used in this study are mollusc shells that were obtained from core sediments taken at 60 m water depths from the Southern Marmara Sea, close to the Kapidag Peninsula. The ages of samples ranged from Late Pleistocene to Early Holocene. In two cores, analysis were carried out on mollusc fossils for δ18O and δ13C isotopes. The δ18O and δ13C values of molluscishells ranged between 0.20‰ and -3.0‰ and 0.08‰ and 0.81‰, respectively. δ18O and δ13C display independent and different values that are inversely related with each other. The lowest δ18O values are associated with highest δ13C values. The variations in oxygen and carbon isotopic values are independent from each other and reflect changes in palaeogeographic environment. The varying isotopic temperature values between 13.0°C and 27.6°C proves changing palaeoenvironmental conditions in the basin. The isotopic temperature and δ13O and δ13C data for the Late Quaternary times (for W2-H L!) in the Marmara Sea are obtained in this study for the first time.
Draining a territory almost twice the Black Sea area, the Danube River is the most important sediment supplier of this marine basin. Presently the Danube River determines the sedimentation on the northwestern Black Sea shelf area. The Danube influence extends down to the deep sea floor. In turn the Black Sea strictly controls the sedimentation of the Danube material through the sea level variations. Danube Delta is acting as a regulator of the sediment transfer between the Danube River and the Black Sea. The three factors -river, delta and marine basin- make up a well-established geosystem. Our present interest will concentrate on the sedimentary cycle including the Romanian Carpathians source area, the Lower Danube transport agent and the western Black Sea accumulation basin (Fig. 1).
Geological and paleoceanographic studies in the Marmara and Black Seas indicate that climate changes during the Quaternary modified coastlines and influenced prehistoric human life there. The effect of active tectonics on coastal modification is poorly known, however, and much less appreciated. This paper summarizes field evidence and relevant literature for the Marmara region in an effort to explore the modifying role of active tectonics on the area's coastlines. The Marmara region is a tectonically very active belt in northwestern Turkey with an extensive paleogeographical evolution related to escape tectonics and development of the strike-slip North Anatolian Fault (NAF). Here, east-west and northeast-southwest oriented depressions have created lakes, marshes, and fluvial systems since the Late Pliocene and Pleistocene along splays of the NAF concurrent with Plio-Pleistocene uplift and denudation. Post-Pleistocene uplift and denudation, accompanied by seismic movements during historical times, have formed wide alluvial plains suitable for human settlement. The distribution of Paleolithic sites exclusively on high terraces, and the total absence of pre-Bronze Age (5000 to 3000 BP) sites, are particularly noteworthy in the area, which includes the Bosphorus, Izmit Bay, Sapanca Lake, and the Sakarya River. Active tectonics continue to reshape the region, as is plainly demonstrated by the 1999 Marmara earthquake sequence.
In all aquatic environments, nitrogen cycling within the water column is strongly influenced by oxygen. We hypothesize that the nitrogen isotopic composition (δ15N) of organic matter deposited in the sediments is a proxy for the redox state of the water column at the time of deposition. We tested the hypothesis by measuring the bulk sedimentary δ15N values in a drill core from the Black Sea, a basin that alternates between oxic, less saline conditions and anoxic, marine conditions on glacial–interglacial time scales. We reconstructed these changes in Black Sea redox conditions using sedimentary δ15N, total organic carbon (TOC), total nitrogen (TN), redox-sensitive metals, and micropaleontological data from a deep-sea core (DSDP Site 380). The sedimentary data reveal that during the transitions between oxic and anoxic conditions, δ15N values increased relative to the preceding and succeeding quasi-steady-state oxic and anoxic periods. The results indicate that the reciprocal transitional states from anoxic to oxic conditions were accompanied by intense denitrification; during the quasi-stable oxic and anoxic states (characterized by glacial fresh water and interglacial marine conditions) nitrification and complete nitrate utilization, respectively, dominate the nitrogen cycle. While other factors may influence the δ15N record, our results support the hypothesis that the variations in nitrogen isotopic composition of organic matter are strongly influenced by changes in redox state in the Black Sea subphotic zone on glacial–interglacial time scales, and can be explained by a relatively simple model describing the effects of oxygen on the microbial processes that drive the nitrogen cycle in marine ecosystems. Our model suggests that the nitrogen isotopic composition of marine sediments, on geological time scales, can be used to reconstruct the redox state of the overlying water column.
The Holocene history of the Danube Delta has been studied using 14C analyses of faunal material. The principal phases of development include: (1) initial Letea Caroarman spit, 11,700–9800 yr B.P. in its central part, 8800-5500 yr B.P. in its southern part; (2) Sf. Gheorghe I Delta, 8900-7200 yr B.P.; (3) Sulina Delta, 7200-2000 yr B.P., and (4) Sf. Gheorghe II Delta-Chilia Delta 2000 yr B.P.-present. Other smaller-scale features have also been dated, including secondary deltas (Coşna and Sinoe Deltas) and littoral bars. Age determinations carried out on whole samples were erratic and it was found that individual species had to be separated and dated. In all cases, the older dates were of transported material whereas the younger dates gave the true age of the formation.
Three holes were drilled during the 1975 DSDP Leg 42B drilling the Black Sea. A section from Hole 380, at 2107 m water depth on the western edge of the abyssal plain, is 1074 m thick, and provides the most complete stratigraphic section. Dating of the sediments is based upon (1) fossil evidence from pollen, crustaceans, benthic foraminifera, and diatoms, (2) correlation with climatic changes and with unusual isochronous events that have been dated elsewhere, (3) paleomagnetic data, and (4) estimates of sedimentation rate.The history of Black Sea sedimentation recorded by the DSDP cores includes black shale sedimentation during the Late Miocene, followed by periodic chemical sedimentation from Late Miocene to Early Quaternary, and a change to dominantly terrigenous sedimentation from the Middle Quaternary. These hemipelagic and turbiditic sediments were deposited in lacustrine and brackish marine environments. The Messinian sediments, however, consist of stromatolitic dolomite, oolitic sands, and coarse gravels, deposited in supratidal and intertidal environments. The intercalation of the shallow-water sediments in a deep-water sequence suggests a drastic lowering of the water-level within the Black Sea basin during the Messinian so that the edge of the present abyssal plain was then the edge of a shallow lake.The Messinian draw-down phase of the Black Sea was in existence for about 100,000 years during the Lago-Mare stage of the salinity crisis. The evaporated waters formed an alkaline lake before it was drowned by a brackish marine transgression correlative to the Trubi transgression of the Mediterranean.
This paper presents a time-dependent variable-size box model for the total fluid and salinity balances of the Black Sea. In addition to the advective flows due to rivefine and Mediterranean inputs of water, the model accounts for entrainment flows which are parameterized using the theory of Ellison and Turner (1959) and employs a modified version of the Gargett (1984) formulation for eddy diffusivity in describing cross-pycnocline mixing flows. The variable volume of the boxes permits explicit simulation of the replacement of the preexisting late Pleistocene lake water by the inflow of denser Mediterranean water. Our results indicate that the time needed to displace the old deep water with new saltier water is 2000 years or less. Because of the effects of mixing, the salinity of both the surface and deep waters requires a greater time interval to obtain present-day values, i.e., ~4000 years if the inflow of Mediterranean water is constant in time at its present value and ~6000 years if this input changes with time in approximation to the rate of sea level rise. The occurrence of the marine coccolithophorid Emiliania huxleyi in the Holocene sapropel layer requires a minimum surface salinity of 11 ø/oo, which takes some 1600 to 3100 years to develop. This range is a result of the uncertainty in the history of the Mediterranean water input. The model is also employed to investigate the freshening of the Black Sea after cutoff of Mediterranean input. The salinity of both surface and deep waters is found to fall below 11ø/oo Copyright 1989 by the American Geophysical Union.
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