High-resolution mapping and reflection profiling reveal a depositional fan on the Black Sea SW shelf fed from the Strait of Istanbul (Bosporus). The fan is constructed with an initial deposit of pebbles mixed with glacial and post-glacial shell debris. The pebbles are identical in their composition to quartzite and gabbro recovered in drill cores from the Bosporus Strait. Directly above the pebble layer are mollusks and foraminifera of Mediterranean provenance dated at 6.9 ka bp (uncorrected). Synchronicity between the onset of fan construction and arrival of Mediterranean fauna suggests an origin linked to the connection of the Black Sea's lake with the global ocean. The volume of the chaotic interior of the fan is comparable in magnitude to the volume excavated from the floor of the Bosporus Strait. We propose that when the exterior ocean breached the sill of this inlet, it transformed into an outburst of saltwater that gained energy as it enlarged the inlet. Torrents stripped the glacial and post-glacial covering from its pathway and scattered entrained debris in sheets and mounds as far away as the edge of the shelf. Even in areas where the pre-existing cover survived, its eroded surface attests to the passage of flooding water.