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Glauberite is the most common mineral in the ancient sodium sulphate deposits in the Mediterranean region, although its origin, primary or diagenetic, continues to be a matter of debate. A number of glauberite deposits of Oligocene-Miocene age in Spain display facies characteristics of sedimentologic significance, in particular those in which a glauberite-halite association is predominant. In this context, a log study of four boreholes in the Zaragoza Gypsum Formation (Lower Miocene, Ebro Basin, NE Spain) was carried out. Two glauberite-halite lithofacies associations, A and B, are distinguished: association (A) is composed of bedded cloudy halite and minor amounts of massive and clastic glauberite; association (B) is made up of laminated to thin-bedded, clear macrocrystalline, massive, clastic and contorted lithofacies of glauberite, and small amounts of bedded cloudy halite. Transparent glauberite cemented by clear halite as well as normal-graded and reverse-graded glauberite textures are common. This type of transparent glauberite is interpreted as a primary, subaqueous precipitate. Gypsum, thenardite or mirabilite are absent in the two associations. The depositional environment is interpreted as a shallow perennial saline lake system, in which chloride brines (association A) and sulphate-(chloride) brines (association B) are developed. The geochemical study of halite crystals (bromine contents and fluid inclusion compositions) demonstrates that conditions for co-precipitation of halite and glauberite, or for precipitation of Na-sulphates (mirabilite, thenardite) were never fulfilled in the saline lake system. Primary gypsum (G) refers to the deduced original mineral association. The presence at present of secondary gypsum in all the formations is omitted. 444 J. M. Salvany et al.

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Thick halite intervals recovered by the Dead Sea Deep Drilling Project cores show evidence for severely arid climatic conditions in the eastern Mediterranean during the last three interglacials. In particular, the core interval corresponding to the peak of the last interglacial (Marine Isotope Stage 5e or MIS 5e) contains ~30 m of salt over 85 m of core length, making this the driest known period in that region during the late Quaternary. This study reconstructs Dead Sea lake levels during the salt deposition intervals, based on water and salt budgets derived from the Dead Sea brine composition and amount of salt in the core. Modern water and salt budgets indicate that halite precipitates only during declining lake levels, while the amount of 2 dissolved Na + and Claccumulates during wetter intervals. Based on the compositions of Dead 24 Sea brines from pore waters and halite fluid inclusions, we estimate that ~12-16 cm of halite 25 precipitated per meter of lake-level drop. During periods of halite precipitation, the Mg 2+ 26 concentration increases and the Na + /Clratio decreases in the lake. Our calculations indicate 27 major lake-level drops of ~170 m from lake levels of 320 and 310 m below sea level (mbsl) 28 down to lake levels of ~490 and ~480 mbsl, during MIS 5e and the Holocene, respectively. 29These lake leves are much lower than typical interglacial lake levels of around 400 mbsl. These 30 lake-level drops occurred as a result of major decreases in average fresh water runoff, to ~40% 31 of the modern value (pre-1964, before major fresh water diversions), reflecting severe droughts 32 during which annual precipitation in Jerusalem was lower than 350 mm/y, compared to ~600 33 mm/y today. Nevertheless, even during salt intervals, the changes in halite facies and the 34 occurrence of alternating periods of halite and detritus in the Dead Sea core stratigraphy reflect 35 fluctuations between drier and wetter conditions around our estimated average. The halite 36 intervals include periods that are richer and poorer in halite, indicating (based on the 37 sedimentation rate) that severe dry conditions with water availability as low as ~20% of present 38 day, continued for periods of decades to centuries, and fluctuated with wetter conditions that 39 spanned centuries to millennia when water availability was ~50-100% of present day. These 40 conclusions have potential implications for the coming decades, as climate models predict 41 greater aridity in the region. 42 3 Mediterranean, reflecting both natural variability and increased anthropogenic greenhouse gas 47 concentrations and predict up to 20% decreases in water availability by the end of the 21 st 48 century (

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