Late Quaternary channel avulsions on the Danube deep-sea fan, Black Sea Auteur(s) : Popescu, Irina Lericolais, Gilles Panin, N Wong, H Droz, Laurence Éditeur(s) : Elsevier Résumé : 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. Marine Geology (0025-3227) (Elsevier), 2001-09 , Vol. 179 , N. 1-2 , P. 25-37 Droits : 2001 Elsevier Science B.V. All rights reserved http://archimer.ifremer.fr/doc/2001/publication-474.pdf DOI:10.1016/S0025-3227(01)00197-9 http://archimer.ifremer.fr/doc/00000/474/ | Partager |
Late Quaternary deep-sea sedimentation in the western Black Sea: New insights from recent coring and seismic data in the deep basin Auteur(s) : Lericolais, Gilles Bourget, Julien Popescu, Irina Jermannaud, Paul Mulder, T. Jorry, Stephan Panin, N. Éditeur(s) : Elsevier Science Bv Résumé : The Danube River Basin–Black Sea area represents a unique natural laboratory for studying the interplay between lithosphere and surface as well as source to sink relationships and their impact on global change. This paper addresses some information on the “active sink” of the system; i.e. the Danube deep sea fan and the Black Sea basin. The present study focuses on the distal sedimentary processes and the evolution of sedimentation since the Last Glacial Maximum. This is investigated through recently acquired long piston coring and shallow seismic data recovered at the boundary of influence of the distal part of the Danube turbidite system (to the north-west) and the Turkish margin (to the south). This dataset provides a good record of the recent changes in the sedimentary supply and climato-eustasy in the Black Sea region during the last 25 ka. This study demonstrates that the deep basin deposits bear the record of the Late Quaternary paleoenvironmental changes and that the western Black Sea constitutes an asymmetric subsident basin bordered by a northern passive margin with confined, mid-size, mud-rich turbidite systems mainly controlled by sea-level, and a southern turbidite ramp margin, tectonically active. Highlights ► Oceanographic results from survey carried out in the western Black Sea are presented. ► The Danube fan distal part: the Black Sea main depositional feature is described. ► This study is on the morphology and gravity sedimentation in the Black Sea deep basin. ► Data were collected at the boundary between the Danube fan and the Turkish margin. ► The dataset provide a good record of sedimentary supply and climato-eustatic changes. Global And Planetary Change (0921-8181) (Elsevier Science Bv), 2013-04 , Vol. 103 , P. 232-247 Droits : 2012 Elsevier B.V. All rights reserved. http://archimer.ifremer.fr/doc/00095/20637/18272.pdf DOI:10.1016/j.gloplacha.2012.05.002 http://archimer.ifremer.fr/doc/00095/20637/ | Partager |