A 250 ka sedimentary record from a small karstic lake in the Northern Levant (Yammoûneh, Lebanon) Paleoclimatic implications

Abstract : The Levant, influenced by both the Mediterranean Sea and the Saharan–Arabian deserts, is a key region for understanding climatic changes in response to glacial/interglacial boundary conditions that have greatly affected regional hydrology. Here, we present the first long-term paleoenvironmental record from the northern Levant, presently much wetter than the southern Levant. Our record derives from the multi-proxy study of a sediment core (36 m long) retrieved from the small intra-mountainous, tectonic basin of Yammoûneh (Lebanon), which is mainly supplied by karstic springs.Sediments consist of a thick accumulation of brownish to greenish clayey silts, interrupted by intervals of whitish marls composed of CaCO3 rich material. The core chronology is based on radiometric dating (14C and U/Th) and paleomagnetic techniques. The sedimentary sequence spans approximately the last two glacial–interglacial cycles (~ 250 ka). Carbonate content is relatively high throughout the profile due to a perennial input of detrital calcite from the watershed, but varies significantly. The marls are mostly composed of authigenic and biogenic calcite and reflect lacustrine environments with high carbonate productivity during peaks of interglacial periods. Their occurrence suggests low physical erosion of the basin slopes which were covered by arboreal vegetation, and intense karstic water circulation under warm and relatively wet conditions, in agreement with pollen data. The clayey silts are dominated by quartz and clay minerals, and a few amounts of K-feldspars and dolomite. They are characterized by high concentration in magnetic particles, and high relative concentrations of Si, Al, K and Fe considered as strictly of detrital origin. Due to the carbonated nature of the watershed, quartz and K-feldspars are attributed to eolian origin from a distal source. The clayey silt intervals generally suggest palustrine conditions with abrupt flows responsible for runoff-derived material, or subaerial environments and low local water availability in particular during the Last Glacial Maximum. High Si/Al and K/Al ratios, during interglacials, are attributed to relatively high eolian dust contribution due to the decrease of local detrital inputs.Our study reveals significant differences between Yammoûneh and lake records from the Dead-Sea basin (southern Levant), the latter showing high/low levels during glacial/interglacial periods. These hydrological differences might reflect either changes in the North–South (NS) rainfall gradient in response to the development of the northern ice sheet and the southward migration of the westerly belt, or local factors, i.e., a decrease in efficient precipitation and water availability at Yammoûneh during the coldest glacial periods (e.g., the Last Glacial Maximum), due to water storage by ice caps on the Mount Lebanon range and frozen soils in the Yammoûneh basin.
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Anne-Lise Develle, Françoise Gasse, Laurence Vidal, David Williamson, François Demory, et al.. A 250 ka sedimentary record from a small karstic lake in the Northern Levant (Yammoûneh, Lebanon) Paleoclimatic implications. Palaeogeography, Palaeoclimatology, Palaeoecology, Elsevier, 2011, 305 (1-4), pp.10-27. ⟨10.1016/j.palaeo.2011.02.008⟩. ⟨hal-01516171⟩

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