Fluidaustritte an Schlammvulkanen und Cold Seeps sowie Fluidzirkulation des Don-Kuban Tiefseefächers (Kertsch Halbinsel, Krim, Schwarzes Meer)
Final Report Abstract
Despite delays in scheduling of the intended cruise with RV Poseidon, extensive sidescan sonar imaging of the continental slope offshore Kerch peninsula provided a first detailed look at the seafloor in this area. Mud volcanoes are not present nor are major cold seep sites besides the co-called Kerch flare. 3D-seismic P-cable data obtained during RV Poseidon cruise P427 provided a detailed view of the upper portion of the Kerch flare plumbing system. The seismic data indicate several surprising results. The Kerch flare consists of two, possibly three individual seeps that have their own separate and different feeder system. A small, rounded seep of 250 metres in diameter developed on the levee of slope canyon. The levee is dissected by near-vertical faults that are only tens of metres apart, but only one of these faults appear to have been used for vertical fluid migration. Similar faults have been identified on other levees in the study area, but without indications for fluid migration. A second, much larger seep developed both on the flanks of the levee and within the channel. It probably consists of two seeps that are fed by distinct near-seafloor gas accumulations. At these locations gas migration from depth is probably favoured by permeable channel-fill deposits. The original goals of the project have all been achieved. High quality sidescan sonar and high-resolution 3D-seismic data have been acquired on the Kerch continental slope in the Black Sea. However, the new data raised more questions than providing answers. To date, the surface observations and measurements of Römer et al. (2012) and the high-resolution backscatter data and subsurface seismic images are difficult to reconcile. Additional geochemical coring and heat-flow measurements could help in the interpretation, but access to the study has become almost impossible due to political developments. Still, several of the initial questions could be answered. In terms of fluid and methane emissions the Kerch slope is similar to the Dnepr slope despite being subjected to compressional forces. Typical elements of compressional regimes such as mud volcanoes are absent on the Kerch slope. Vertical fluid migration is controlled by both structural (faults) and stratigraphic (permeable horizons) processes. Fluid migration along coarse channel-fill deposits, however, appears to be the most prominent factor to accumulate gas in the shallow subsurface. We could not identify major gas hydrate reservoirs at depth. Whether this is due to the absence of such reservoirs, or due to difficulties in imaging these reservoirs and distinguish them from coarse-grained channel-levee deposits remains unclear.
