ALBERT

Description: The continental slopes of the Black Sea show abundant manifestations of gas seepage in water depth of

Description: Summary The origin of the Ionian Sea lithosphere and the deep structure of its margins remain a little investigated part of the Mediterranean Sea. To shed light on the plate tectonic setting in this central part of southern Europe, R/V METEOR cruise M111 set out to acquire deep penetrating seismic data in the Ionian Sea. M111 formed the core of an amphibious investigation covering the Ionian Sea and island of Sicily. A total of 153 OBS/OBH deployments using French and German instruments were successfully carried out, in addition to 12 land stations installed on Sicily, which recorded the offshore air gun shots. The aim of this onshore-offshore study is to quantify the deep geometry and architecture of the Calabria subduction zone and Ionian Sea lithosphere and to shed light on the nature of the Ionian Sea crust (oceanic crust vs. thinned continental crust). Investigating the structure of the Ionian crust and lithospheric mantle will contribute to unravel the unknown ocean-continent transition and Tethys margin. Analyzing the tectonic activity and active deformation zones is essential for understanding the subduction processes that underlie the neotectonics of the Calabrian subduction zone and earthquake hazard of the Calabria/Sicily region, especially in the vicinity of local decoupling zones.

Description: Cruise MSM34 of R/V MARIA S. MERIAN aimed to investigate a possible test site location for the German SUGAR project. The well sealed gas hydrate deposit should be accessible by the mobile drilling device MeBo 200. During the two legs of cruise MSM34 of R/V MARIA S. MERIAN regional 2D seismic surveying, high resolution 2D and 3D seismic imaging, geo-chemical sampling, heatflow measurements and long-term piezometer installations were undertaken. A grid of 28 2D seismic profiles was collected across the palaeo Danube delta. A number of inactive and partly buried channel systems could be mapped. Most of them were underlain by one or more bottom simulation reflectors (BSR) indicating the existence of gas hydrates. Based on the seismic brute stack images and the limits of the MeBo drilling device a prospective channel system with indications for possible gas hydrate formation at shallow depth (BSR, inverted strong amplitudes) could be identified in about 1500 m water depth. High resolution 2D seismic and 3D P-Cable seismic were used together with OBS deployments in order to allow structural mapping and physical description of the channel infill. Heatflow measurements and geochemical analyses of gravity and multi corer samples accompany these investigations. Neither the multibeam water column images nor Parasound records show any evidence of flares (gas bubbles in the water column) in this working area suggesting a well sealed hydrate reservoir. Active gas expulsion from the seafloor was observed at about 200 m water depth circling around a slump area. The base plane of the failed sediment volume builds the current seafloor at about 600 m to 700 m water depth. On regional 2D seismic profiles a BSR has been mapped underneath the slope failure with unexpectedly strong upward bending. High resolution 2D and 3D P-Cable seismic investigations with complementary OBS deployment will allow imaging the BSR outline. Moreover velocity analyses, heatflow measurements and geo-chemical samples will be available for a detailed description of hydrate distribution and sediment parameters. In a third working area high resolution 2D seismic reflection profiles were acquired across a fully buried channel system. Together with the regional seismic lines slope failure of the channel fill material can be studied across the slope extension of the system. In summary cruise MSM34 achieved all proposed aims. Based on new regional seismic acquisition two working areas were selected for 3D high resolution studies. Investigations of a promising location for a SUGAR pilot site will be supported by a test location for slope stability and analyses of fluid migration pathways in a buried canyon site.

Description: In the eastern Black Sea, we determined methane (CH4) concentrations, gas hydrate volumes, and their vertical distribution from combined gas and chloride (Cl−) measurements within pressurized sediment cores. The total gas volume collected from the cores corresponded to concentrations of 1.2–1.4 mol CH4 kg−1 porewater at in-situ pressure, which is equivalent to a gas hydrate saturation of 15–18% of pore volume and amongst the highest values detected in shallow seep sediments. At the central seep site, a high-resolution Cl− profile resolved the upper boundary of gas hydrate occurrence and a continuous layer of hydrates in a sediment column of 120 cm thickness. Including this information, a more precise gas hydrate saturation of 22–24% pore volume could be calculated. This volume was higher in comparison to a saturation calculated from the Cl− profile alone, resulting in only 14.4%. The likely explanation is an active gas hydrate formation from CH4 gas ebullition. The hydrocarbons at Batumi Seep are of shallow biogenic origin (CH4 〉 99.6%), at Pechori Mound they originate from deeper thermocatalytic processes as indicated by the lower ratios of C1 to C2–C3 and the presence of C5.

Description: The nature of the Ionian Sea crust has been the subject of scientific debate for more than 30 years, mainly because seismic imaging of the deep crust and upper mantle of the Ionian Abyssal Plain (IAP) has not been conclusive to date. The IAP is sandwiched between the Calabrian and Hellenic subduction zones in the central Mediterranean. To univocally confirm the proposed oceanic nature of the IAP crust as a remnant of the Tethys ocean and to confute its interpretation as a strongly thinned part of the African continental crust, a NE-SW oriented 131 km long seismic refraction and wide-angle reflection profile consisting of eight ocean bottom seismometers and hydrophones was acquired in 2014. A P-wave velocity model developed from travel time forward modelling is refined by gravimetric data and synthetic modelling of the seismic data. A roughly 6km thick crust with velocities ranging from 5.1km/s to 7.2km/s, top to bottom, can be traced throughout the IAP. In the vicinity of the Medina Seamounts at the southern IAP boundary, the crust thickens to about 9km and seismic velocities decrease to 6.8km/s at the crust-mantle boundary. The seismic velocity distribution and depth of the crust-mantle boundary in the IAP document its oceanic nature, and support the interpretation of the IAP as a remnant of the Tethys oceanic lithosphere formed during the Permian and Triassic period.