Excess helium and argon of radiogenic origin in Mediterranean brine basins

Extraordinary helium and argon signatures were observed in a recently discovered brine lake district in the eastern Mediterranean Sea at water depths of similar to 3500 m, In the Urania Basin He-4 concentrations are enriched by a factor of up to 32 000 compared to normal seawater, Low He-3/He-4 ratios of 1 x 10(-7) and high Ar-40/Ar-36 ratios of up to 470 indicate a radiogenic source, These data represent by far the highest radiogenic supersaturations ever observed in an oceanic environment. We propose a new conceptional model assuming that the Urania Basin is fed by advective transport from a deep fluid reservoir below the Messinian evaporite sequence. The evaporite seal provides the unique condition for accumulating the extraordinary high amounts of radiogenic helium from deep sedimentary strata. Injection of radiogenic helium from brine pools like the Urania Basin may contribute significantly to the inventory of terrigenic helium in the deep waters of the eastern Mediterranean. (C) 1997 Elsevier Science B.V.