Subsidence mechanisms that may have controlled the evolution of the eastern Black Sea have been studied and simulated using a numerical model that integrates structural, thermal, isostatic and surface processes in both two- (2-D) and three-dimensions (3-D). The model enables the forward modelling of extensional basin evolution followed by deformation due to subsequent extensional and compressional events. Seismic data show that the eastern Black Sea has evolved via a sequence of interrelated tectonic events that began with early Tertiary rifting followed by several phases of compression, mainly confined to the edges of the basin. A large magnitude (approximately 12 km) of regional subsidence also occurred in the central basin throughout the Tertiary. Models that simulate the magnitude of observed fault controlled extension (β=1.13) do not reproduce the total depth of the basin. Similarly, the modelling of compressional deformation around the edges of the basin does little to enhance subsidence in the central basin. A modelling approach that quantifies lithosphere extension according to the amount of observed crustal thinning and thickening across the basin provides the closest match to overall subsidence. The modelling also shows that deep crustal and mantle–lithosphere processes can significantly influence the rate and magnitude of syn- to post-rift subsidence and shows that such mechanisms may have played an important role in forming the anomalously thin syn-rift and thick Miocene–Quaternary sequences observed in the basin. It is also suggested that extension of a 40–45 km thick pre-rift crust is required to generate the observed magnitude of total subsidence when considering a realistic bathymetry.
"Spadini et al. (1996, 1997) performed thermomechanical modeling of the Black Sea basin and suggested that the western Black Sea basin was formed by rifting of thick and cold lithosphere (200 km), the eastern Black Sea basin was developed by rifting of thin and warm lithosphere (80 km). Meredith and Egan (2002) represented the temperature at the base of lithosphere (125 km) as 1333 C throughout the basin's post-rift stage corresponding to the development of a more thermally mature lithosphere. According to the Verzhbitsky (2002) the lithospheric thickness of the western and eastern Black Sea basins calculated from heat flow data (60e65 km) corresponds to the thickness of the early Cenozoic oceanic lithosphere. "
[Show abstract][Hide abstract] ABSTRACT: The numerical results of thermal modeling studies indicate that the lithosphere is cold and strong beneath the Black Sea basin. The thermal lithospheric thickness increases southward from the eastern Pontides orogenic belt (49.4 km) to Black Sea basin (152.2 km). The Moho temperature increases from 367 °C in the trench to 978 °C in the arc region. The heat flow values for the Moho surface change between 16.4 mW m−2 in the Black Sea basin and 56.9 mW m−2 in the eastern Pontides orogenic belt. Along the southern Black Sea coast, the trench region has a relatively low geothermal potential with respect to the arc and back-arc region. The numerical studies support the existence of southward subduction beneath the Pontides during the late Mesozoic–Cenozoic.
"Active compressional deformation leads to the creation of a W–E trending system of canyons and ridges on the continental slope off Georgia (Klaucke et al., 2006; Meredith and Egan, 2002) in the Black Sea (Fig. 1a). On top of one of such ridges, a high-flux hydrocarbon seepage area, termed 'Batumi seep area' (41°57′N; 41°17′E, Fig. 1b), was recognized in about 840 to 860 m water depth (Klaucke et al., 2006) in the permanently anoxic Black Sea water body. "
[Show abstract][Hide abstract] ABSTRACT: Detailed knowledge of the extent of post-genetic modifications affecting shallow submarine hydrocarbons fueled from the deep subsurface is fundamental for evaluating source and reservoir properties. We investigated gases from a submarine high-flux seepage site in the anoxic Eastern Black Sea in order to elucidate molecular and isotopic alterations of low-molecular-weight hydrocarbons (LMWHC) associated with upward migration through the sediment and precipitation of shallow gas hydrates. For this, near-surface sediment pressure cores and free gas venting from the seafloor were collected using autoclave technology at the Batumi seep area at 845 m water depth within the gas hydrate stability zone.Vent gas, gas from pressure core degassing, and from hydrate dissociation were strongly dominated by methane (> 99.85 mol.% of ∑[C1–C4, CO2]). Molecular ratios of LMWHC (C1/[C2 + C3] > 1000) and stable isotopic compositions of methane (δ13C = − 53.5‰ V-PDB; D/H around − 175‰ SMOW) indicated predominant microbial methane formation. C1/C2+ ratios and stable isotopic compositions of LMWHC distinguished three gas types prevailing in the seepage area. Vent gas discharged into bottom waters was depleted in methane by > 0.03 mol.% (∑[C1–C4, CO2]) relative to the other gas types and the virtual lack of 14C–CH4 indicated a negligible input of methane from degradation of fresh organic matter. Of all gas types analyzed, vent gas was least affected by molecular fractionation, thus, its origin from the deep subsurface rather than from decomposing hydrates in near-surface sediments is likely.As a result of the anaerobic oxidation of methane, LMWHC in pressure cores in top sediments included smaller methane fractions [0.03 mol.% ∑(C1–C4, CO2)] than gas released from pressure cores of more deeply buried sediments, where the fraction of methane was maximal due to its preferential incorporation in hydrate lattices. No indications for stable carbon isotopic fractionations of methane during hydrate crystallization from vent gas were found. Enrichments of 14C–CH4 (1.4 pMC) in short cores relative to lower abundances (max. 0.6 pMC) in gas from long cores and gas hydrates substantiates recent methanogenesis utilizing modern organic matter deposited in top sediments of this high-flux hydrocarbon seep area.
Chemical Geology 01/2010; 259:350-363. DOI:10.1016/j.chemgeo.2009.10.009 · 3.52 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Paleowater depth observations suggest that a large sea level drop occurred in the Black Sea coeval with the Messinian salinity crisis in the Mediterranean Sea. This sea level drop would have induced vertical motions of the solid earth, which influenced strait dynamics with major implications for the hydrological regime of the region. Using three-dimensional flexure models we find that a sea level drop between 1730 and 2230 m is required to reproduce the observed paleowater depths. The models predict that uplift reduced the seaway connectivity between the Black Sea and the Mediterranean Sea (Aegean region) and between the Black Sea and the Caspian Sea (Stavropol Highlands). The Miocene Paratethys Sea consequently became fragmented, and the remaining subseas likely became more sensitive to climate change. This agrees with the discovery of erosional surfaces in the Caspian Sea and in the Pannonian Basin. To explain the synchronicity of the sea level lowering in the Black Sea and the Mediterranean, we speculate that a regional shift toward a drier climate occurred in response to the Messinian salinity crisis in the Mediterranean, which led to a fall in sea level within the Black Sea.
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