The evolution of neogene-quaternary water-bodies in the Dead Sea rift valley

Abstract

During the late Neogene-Quaternary times the tectonic depressions along the Dead Sea transform accomodated several hypersaline to fresh waterbodies: the late Neogene Sedom lagoon and the Quaternary lakes of Amora, Samra, Lisan, Dead Sea and the Sea of Galilee. The sedimentary sections that were deposited at these water-bodies store the environmental conditions that prevailed in their watershed. The lakes are located between the Sahara-Arabia desert belt and the Mediterranean climate zone and their large watershed receives rains and detritus particles from these climatic regions. Thus, the sedimentary sections record the climate-hydrological conditions in the desert belt and Mediterranean climate zone during the late Neogene and the Quaternary Ice Ages. Over the past two decades extensive efforts were devoted to establish a precise and highresolution chronology for the environmental history of the water-bodies. The chronologies are mainly based on U-series, radiocarbon and oxygen isotope stratigraphy methods and provide the base for detailed geochemical and sedimentological reconstruction of the limnological-hydrological conditions in the watershed. The solutions that filled the lakes are mixtures of Ca-chloride brines that were originally formed in the late Neogene Kinnarot-Sedom lagoon and freshwater from the watershed. The mixing between these solutions is dictated by regional hydrological regime that in turn reflects the changes in the global climate patterns. The water balance in the lakes is reflected in their surface level and salinity. The precise chronology of the lacustrine sedimentary sequences allows the comparison with other global climate archives such as the ice cores and ocean temperatures and opens the way for understanding the global climate connection of hydrological changes in the Levant region. It appears that most of the rains in the lakes watershed are derived from the Mediterranean and reflect the climate-oceanographic conditions in the north Atlantic. Glacial periods were colder and wetter and interglacials were warmer and drier. Episodes of extreme aridity in the Levant region were accompanied by massive salt deposition at the shrinking lakes, e.g. at ~400 ka (MIS11); 130-120 ka (last interglacial MIS5e) and at 14-13 ka (the postglacial BÖlling-Allerod period). Nevertheless, various lines of evidence indicate on intrusions of wetness from southern sources into the Red Sea region-Arava valley during interglacials that are possibly related to the African monsoon. These wet intrusions could facilitate the migration of humans out of Africa along the rift valley. The lacustrine sedimentary sections indicate also on episodes of abrupt aridities that expanded over the sub-tropical regions from the Sahara to the Mediterranean (e.g. at ~3.5-3.3 ka, coinciding with the late Bronze cultural crisis). These events coincide with ice rafting episodes in the north Atlantic that were linked to solar minima events.