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Abstract: The north-western Black Sea shelf is the widest continental shelf of the Black Sea, where the Danube delta/prodelta system includes important records on the Black Sea water level fluctuations. This study integrates newly acquired high-resolution single channel seismic reflection profiles and Calypso piston cores recovered along a transect extending from the Danube delta deep into its deep sea fan. The correlated results provide information on the Late Quaternary architecture of the Danube Black Sea shelf and on the role of global glacio-eustatic fluctuations on the building of the Danube delta/prodelta. The sedimentary sequences in the Black Sea are strongly affected by water level changes. For the whole duration of Late Glacial–Holocene period, the level of the Black Sea was controlled by the regional climate modifications rather than the global eustatic changes. The seismic sequences recognized on a very high-resolution seismic profile were dated by two Calypso piston cores. Based on the obtained data, during the Last Glacial Maximum the Black Sea was a land locked lake with the level below −120 m. In the course of the deglaciation the lake level rose up to −40 m, which is confirmed by occurrence of the prodelta lobes formed after the rise in water level originated from the melt water. Following the Younger Dryas, 11 000–8500 14C BP, there occurred a new level lowering to the level of −100 m, identified by the forced regression deposits recorded on the Romanian shelf. This last lowstand previously recognized by a pronounced shoreline with a characteristic beach profile and a belt of coastal dunes is also indicated by the prodelta at −100 m depth. All these coastal features as well as the incised anastomosed channel system remained preserved on the shelf resulting from a rapid ultimate transgression starting immediately after 8500 14C BP. [Copyright &y& Elsevier]

Abstract: This paper presents a 3D geometric interpretation of very high resolution seismic Chirp profiles acquired on the Romanian shelf during ASSEMBLAGE European Project. The results provide a solid record of the Black Sea Last Glacial Maximum (LGM) water level fluctuations. This pseudo-3D seismic interpretation shows that the Black Sea lacustrine shelf deposits form a significant basinward-prograding wedge system. On top of these prograding sequences is a set of sand dunes that delineates a wave cut-terrace like feature around the isobath −100 m. Landward of this dune field are small depressions containing barkhan-like bodies. The upper part of the last prograding sequence is incised by anastomosed channels which end in the Danube (Viteaz) canyon which are also built on the lacustrine prograding wedge. Ten stratigraphic units were distinguished and correlated with analyses of cores retrieved from this area. The results demonstrate that the first eight sequences represent lacustrine prograding wedges, the ninth sequence is the dune system itself and the tenth is a marine mud drape which covers the entire continental shelf. The lacustrine prograding wedges represent a lowstand deposit characterised by forced regression-like reflectors mapped from the pseudo-3D seismic data. Their hinge point corresponds to the wave erosion surface mapped around −100 m isobath on the multibeam mosaic. Dated cores give age control on this lowstand period, which lasted from 11 to 8.5 kyr 14C BP as implied by: (1) the continuously dry climatic conditions in the region inferred by high percentages of herbs and steppe elements determined from ASSEMBLAGE cores and, (2) the formation of dunes between 10 and 8.5 kyr 14C BP on the desiccated north-western Black Sea shelf at −100 m and (3) all of these covered by a marine mud drape confirming that the dune system is no longer active. The buried, anastomosed fluvial channels that suddenly disappear below 90 m depth, and a unique wave-cut terrace between 95 and 100 mbsl on the outer shelf are also consistent with a major lowstand base-level at around −100 m water depth. Preservation of sand dunes and the occurrence of small, buried incised valleys mark a rapid transgression within less than a century during which ravinement processes related to the water level rise had no time to significantly erode the seafloor. [Copyright &y& Elsevier]

Four of the 38 sediment cores, collected from the northwestern part of the Black Sea (French–Romanian BLASON Programme, 1998), were analysed in order to study the major hydrological and environmental change of the sea during the Holocene. This change was caused by the inflow of the marine Mediterranean waters into the freshwater basin of the Black Sea. Two cores from the northwestern shelf and two from the deep part of the sea, representing distinct sedimentary environments along the same profile, were chosen. Lacustrine sediments from deep-water cores and uppermost marine sediments in all studied cores are characterised by the presence of pyrite (FeS2), which indicates anoxic, sulphate reducing conditions in sediment and in water column (as it is observed now in the Black Sea). Pyrite formation in this anoxic environment takes place below the oxic/anoxic limit, by reduction and sulphidation of iron. The transition from freshwater to marine conditions is marked in all studied cores by the presence of ferrimagnetic iron sulphide––greigite (Fe3S4). Greigite is an intermediate mineral in the pyritisation reactions during early diagenesis, which can be preserved in the sediment if pyritisation cannot be accomplished, due to a high Fe/S ratio. In shallow water cores from the shelf, where marine transgression is marked by a discontinuity, greigite is present below and above it. This suggests that the anoxic, sulphate reducing conditions, allowing preservation of greigite, started in the sediment after marine transgression. In cores from the deep part of the sea, the transgression is represented by a level of sediments with high organic matter content (sapropel). The greigite is present only in the lower part of this level and its formation is related to the arrival of marine water. The presence of pyrite in the upper part of the lacustrine sediments indicates that anoxic conditions probably prevailed here during marine transgression. These results show the sensitivity of magnetic parameters to major environmental change in the Black Sea, and allow a correlation between cores from different depths, by recognition of greigite in the sediments marking the marine transgression. [Copyright &y& Elsevier]