A gradual drowning of the southwestern Black Sea shelf: Evidence for a progressive rather than abrupt Holocene reconnection with the eastern Mediterranean Sea through the Marmara Sea Gateway

Core M02-45 recovered 9.5m of a similar to 12m-thick transgressive succession on the SW Black Sea shelf. The underlying transgressive unconformity, alpha, deepens toward the shelf edge, so that the coresite was never isolated from the open Black Sea. Fourteen radiocarbon dates indicate sedimentation from similar to 9.3 ka to the present, with only one hiatus at similar to 270 cm depth spanning similar to 4.5-2.5 ka. Three units are present in the core: Unit A (0-270 cm) = burrowed mud with laminated silt beds and mollusc shells of Mediterranean affinity (accumulation rate similar to 125 cm/ky); Unit B (270-525 cm) = silty mud with shelly interbeds containing Truncatella subcylindrica, Mytilus galloprovincialis, Parvicardium exiguum, Rissoa spp. and Modiolula phaseolina (rate similar to 85 cm/ky); Unit C (525-950 cm) = burrowed silty mud with graded beds of silt and fine sand, and shells of T subcylindrica, P. exiguum and Dreissena polymorpha (rate similar to 360 cm/ky). Unit C developed below storm wave base at a time when proponents of a catastrophic flood in the Black Sea claim that the shelf was subaerially exposed. Clearly it was not. Ostracoda of Caspian affinity indicate similar to 5 parts per thousand salinity until similar to 7.5 ka. Dinocysts and foraminifera confirm a low but rising salinity after similar to 8.6 ka. An increase of delta(34)S from similar to 5-30 parts per thousand through 8.4-7.6 ka is attributed to a first pulse of sulfate-rich Aegean water into an already high Black Sea, after which this sulfate was quantitatively precipitated as Sulfide. delta(34)S then dropped at similar to 8 ka to similar to-20 parts per thousand as dysoxia and water-column stratification were established because of the initiation of two-way flow through the Bosphorus. Earlier water exchange with the Mediterranean was likely impeded by strong Black Sea outflow which prevented easy access of the Aegean water mass. (c) 2006 Elsevier Ltd and INQUA. All rights reserved.