Mutzl, J. ; Lenz, O. K. ; Landmann, G. ; Hinderer, Matthias (2015)
Palynology and micropalaeontology of Holocene lacustrine sediments of the Layla Lakes in central Saudia Arabia and implications for palaeoenvironment and palaeoclimate.
Geo Berlin 2015. Berlin (04.10.-07.10.2015)
Konferenzveröffentlichung, Bibliographie

Kurzbeschreibung (Abstract)

The Layla Lakes in central Saudi Arabia, located 300 km south of Riyadh, are fed by groundwater, but dried up in the late 1980’s due to extensive groundwater use, revealing a series of 23 sinkholes in the Jurassic Hith formation. In one of them with a size of 400x100 m and a depth of 10 m several samples were taken during a field campaign in 2011. Furthermore a sediment core was drilled near the sinkhole, revealing a lacustrine succession of 10.8 m. Mineralogical and geochemical analyzes show two distinct types of sedimentation: Sediments with an average con- tent of 85% calcite (carbonates) and sediments, which consist almost entirely of gypsum and anhydrit (sulfates). The carbonates precipitated when the exchange between groundwater and lake water was too large to achieve supersaturation of gypsum, while the sulfates mark periods of strong evaporation with limited rates of water exchange. First radiocarbon ages of mollusc shells and U/Th dating of carbonates indicate that the sedimentary succession covers 6000 years. Autochthonous microfossil assemblages comprise pollen, spores, diatoms, freshwater algae, testate amoebae, phytoliths and other non-pollen palynomorphs and offer the application of various multi-proxy methods to reconstruct palaeoclimate and palaeoenvironment in the center of Saudi Arabia in detail, a region, where such a complete sedimentary record is unknown so far. First XRF and visual analyses of sediment composition show at least four changes between arid and more humid phases based on the frequency of carbonate and sulfate sediments. A first palynological analyses show that during the humid phases the groundwater inflow was higher than the loss of lake water by evaporation. With increasing lake level large floodplain environments evolved, which were covered by a vegetation mainly composed of grasses and sedges. During dry phases the lake level decreased significantly and the vegetation was replaced by plants that were adapted to arid conditions.

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