Late Quaternary channel avulsions on the Danube deep-sea fan, Black Sea

Abstract

Analysis of new high-resolution seismic-reflection profiles, chirp profiles and previously published sidescan data, together with piston cores on the Danube Fan provide new insight into the recent sedimentation processes in the deep northwestern Black Sea. The latest channel-levee system on the Danube Fan developed probably during the Neoeuxinian lowstand (oxygene isotope stage 2) in a semi-freshwater basin with a water level about 100 m lower than today. Sediment supplied by the Danube was transported to the deep basin through the Viteaz Canyon, which was directly connected to the leveed channel of this system on the middle slope. Channel avulsion was common in the middle fan, as indicated by four main phases of bifurcation. Each phase developed after the same pattern: breaching of the lower and narrower left levee by turbidity currents, building of a unit of High Amplitude Reflection Packets (HARP) by the unchannelized flow while the former channel was abandoned, followed by initiation of a new meandering leveed channel. The northward migration through successive bifurcations is influenced by the asymmetry between levees, hence by the Coriolis effect. In the lower fan where the levees became too low to maintain a stable pathway for the turbiditic flows, channel migration occurred. Locations of HARPs and channels after bifurcation are controlled by the pre-existing bathymetry. Sedimentary deposits are confined between the high levees of unit 0 (the initial phase of the youngest channel-levee system) to the south, and the steep relief of the Dniepr Fan to the north. The HARPs of the most recent phase of avulsion are the most severely constrained by local topography and form a very narrow elongate structure that is at most half as thick as the previous HARPs. Their distal part is not covered by channel-levee systems and is visible both on sidescan mosaics and on chirp profiles and was sampled in core BLKS 98-20. Sea level controlled fan activity but the evolution of the last channel-levee system with several bifurcations during a single sea level lowstand suggests that the primary control of channel avulsion and sand delivery is probably autocyclic. The presence of important HARP sand bodies in the mud-rich Danube Fan is presumed by analogy with a similar seismic facies on the Amazon Fan and indicated by the sands cored in BLKS98-20. However, only drilling of the HARP units could verify this interpretation.

Connections Between Fluvial To Shallow Marine Environments and Submarine Canyons: Implications For Sediment Transfer To Deep Water

“…Republished with permission from the Geological Society of America, , their figures 3 and 4. (Ducassou et al 2009), the Danube (Popescu et al 2001), the Astoria (Carlson and Nelson 1969;Nelson et al 2009), the Var , the La Jolla (Covault et al 2007), and the Golo (Gervais et al 2006). In some cases there is one long-lived canyon (e.g., the Zaire), whereas in other cases multiple canyons may feed the fan at different times as fluvial avulsion and delta-lobe switching changes the location of pointsource sediment input (e.g., the Gulf of Lion, Berné and Gorini 2005).…”

Kinematics of back‐arc inversion of the Western Black Sea Basin

“…When the Dacian Basin was completely filled during the large scale Messinian Salinity Crisis (MSC) sea level drop, which took place in the Eastern Paratethys during the equivalent intra-Pontian times, large amounts of sediments were discharged into the Black Sea with typical progradational geometries (Figure 6). During periods of low-stands, the deep shelf incision observed along large canyons is associated with the formation of a thick succession of mass-transport and turbiditic deposits (in the sense of Posamentier and Walker [2006]) recorded along a number of deep-sea fans in front of modern rivers, like the Danube or Dnieper [Popescu et al, 2001].…”

Geological and morphological setting of 2778 methane seeps in the Dnepr paleo-delta, northwestern Black Sea

“…The northwestern Black Sea is dominated by a rather wide shelf (60-200 km) with a shelf break at 120 to 170 m water depth and canyon systems with large deepsea fan complexes, mainly developed during sea level lowstands (Winguth et al, 2000;Popescu et al, 2001). The main canyon systems in the western Black Sea are the Danube and Dnepr Canyons, each with their own typical morphology.…”

“…The main canyon systems in the western Black Sea are the Danube and Dnepr Canyons, each with their own typical morphology. The well-studied Danube Canyon (Popescu et al, 2001 differs from the Dnepr Canyon and other, smaller canyons because it indents the shelf over a distance of 26 km and has a unidirectional development. The Dnepr Canyon only starts from the shelf edge and deeply incises the upper slope (Wong et al, 2002).…”