10Be dating of Neogene halite

Abstract

Direct radioactive dating of ancient halite formations is difficult because this mineral typically lacks conventionally datable material. We describe an attempt to date Neogene halite using the cosmogenic isotope 10Be (T1/2=1.39Ma). We dated marine-derived salt deposits from the Sedom and Amora (The Hebrew forms of Sodom and Gomorrah) Formations, Dead Sea basin, Israel. To verify whether Be is incorporated into marine halite we measured the stable isotope 9Be, 7Be (the short lived "cosmogenic brother" of 10Be having T1/2=53.3d), and 10Be in evaporation pans of sea-salt production plants. The data suggest that seawater beryllium is incorporated into the halite with a halite-brine distribution coefficient, (KD) of about unity. A 10Be/9Be decay curve constructed for Sedom Formation halite yielded an age that lies in the range of ~2-6Ma. The 10Be decay curve constructed for Sedom Formation halite yielded an age that lies in the range of 3-5Ma. This age is consistent with previous estimates of the Sedom Formation age. Furthermore, this age lies in the same range of 10Be in situ ages obtained on the lacustrine Erq El Ahmer Formation located in the northern Jordan Valley. This may imply that during the Mid Pliocene the Sedom Lagoon, the water-body that deposited the Sedom Formation, might have been already disconnected from the open sea. © 2013 Elsevier Ltd.