Acoustic evidence for shallow gas accumulations in the sediments of the Eastern Black Sea*

Abstract

The Black Sea contains immense gas accumulations. Exploration of gas accumulations is geologically and economically important because migration of methane in sediments may cause massive slope failures and the methane seeps may indicate deeper hydrocarbon reservoirs. Human activity both in and on the seafloor (oil industry) and natural activity (earthquakes, cyclones) trigger mechanisms for seafloor failure and gas release that may have a local and possibly global environmental impact. Recently, sonar and high‐resolution seismic surveys were carried out to obtain information about the effects of gas and gas‐filled sediments throughout the Turkish margin of the Eastern Black Sea, and shallow gas was detected on the subbottom profiler records. It continues about 25–65 m below the sea floor and is marked by bright and cloudy spots, sometimes pockmarks and acoustic voids. The lower section of the Turkish shelf is an extensive pockmarked plateau. The pockmarks are seen as circular structures with high backscattering on the sonar records.

Morphology of pockmarks along the western continental margin of India: Employing multibeam bathymetry and backscatter data

“…We speculate that uprising gas bubbles and gravitational pulls along the sidewall of the pockmarks might have initiated slumping. Similar events due to upward migration of gas were also recorded from the eastern Black Sea region (Ergün et al, 2002) and US Atlantic continental slope (Carpenter, 1981). The correlation between average slope angle of sidewall and relief of pockmarks (Fig.…”

“…Although, the backscatter over the whole study area varies widely from À26 to À57 dB, but within the pockmark itself, it is limited (À27 to À48 dB; Fig. 5d) and much higher (Ergün et al, 2002;Çifçi et al, 2003;Chand et al, 2009).…”

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

“…The Black Sea mud volcanoes, diapirs and cold seeps have been a target of investigation of numerous marine expeditions with the aim of investigating the mechanisms of hydrocarbon-rich fluids seepage (Ivanov et al, 1989;Ginsburg et al, 1990;Ivanov et al, 1992;Limonov et al, 1994;Woodside et al, 1997;Ivanov et al, 1998;Bohrmann and Schenck, 2002;Ergun et al, 2002;Kenyon et al, 2002). Differently shaped authigenic carbonates (slabs, chimneys, irregular, blocky) have been observed and sampled from various sites of the Black Sea Basin often associated with microbial colonies (Woodside et al, 1997;Peckmann et al, 2001;Thiel et al, 2001;Michaelis et al, 2002;Mazzini et al, 2004).…”

Geological and Geomorphological Factors and Marine Conditions of the Azov‐Black Sea Basin and Coastal Characteristics as They Determine Prospecting for Seabed Prehistoric Sites on the Continental Shelf

“…Lithologically, they are variable: clays, marls and occasional turbidites (for references, see Yanko-Hombach 2007a). High-resolution seismic and sonar images show primarily flat-lying, undisturbed sediments in the basin center, although the shallowest sediments often show disruption by gas (Ergün et al 2002;Shnyukov & Yanko-Hombach 2009). …”