EVIDENCE FOR A BLACK SEA FLOODING EVENT

Ancient coasts of a Neoeuxine Black Sea lake lay at elevations down to 150 meters below today’s sealevel. Shorelines appear in maps and sonar images as wave-cut terraces, canyon-head cliffs, barrier bars, lagoons and coastal dune fields with dune shape, size and composition characteristic of wind-blown landscapes. Shore deposits consist of shelly sand, gravel and flattened, smooth cobbles with neritic fauna. Mussel shells are coated with algae. Rivers, whose channel deposits include sand and gravel with fluvial gastropods, meander across the Sea of Azov and much of the Black Sea’s continental shelf. One finds pans (small depressions that may have been ephemeral ponds) within vast dune fields. The bottoms of the depressions consist of mud, sand and red soil. Cores on the alluvial plain reveal desiccation cracks, plant roots and gypsum overgrowth on shells. Lake-floor mud contains freshwater mollusks, diatoms and dinoflagellates. These mollusks have ^87/86Sr compositions that are distinctly non-marine. Two periods of post-glacial lacustrine lowstand are recorded by AMS ¹⁴C dating of the shells. One occurs from 13.4 to 11 ky bp (uncorrected) and prior to the Younger Dryas. The other, from 10 to 8.4 ky bp, is early Holocene. Both lowstands are accompanied by the precipitation of carbonate mud (Seekreide) on the lake floor. At 8.4 ky bp the mollusk assemblage undergoes an abrupt shift to a marine composition. Desiccated substrates become blanketed with mud that builds an uniformly-thick drape across the submerged seascape. No coastal onlap is observed in the marine strata. Euryhaline fauna/flora (>12 o/oo salinity) from the Mediterranean replace oligohaline (1-5o/oo) Black and Caspian Sea species in a colonization event recorded by entirely new assemblages of benthic foraminifera, molluscs and dinoflagellates. According to pollen in these same cores, this repopulation accompanies a shift from a hot, dry coastal climate to one that is cooler and wetter. The working hypothesis which explains the rapidity of transformation from an isolated and shrunken lake to an expanded sea and fits best all of the data is a saltwater flood that took place when the rising global ocean spilled over the Bosporus barrier. This hypothesis is controversial and requires a critical appraisal.