Landscape Erosion, Karstic Activity and the Development of a Wetland in the Southern Bekaa Valley, Lebanon During the Last Glacial Period

Abstract

We present the results of the first multi-proxy sedimentological analysis of a sedimentary sequence recovered from Aammiq Wetland in the Bekaa Valley, Lebanon that spans the very end of the last interglacial and the last glacial period (~112 to ~35 ka BP). We show that the high authigenic carbonate content of the sediment that accumulated at the end of the last interglacial and the start of the last glacial period ~112 to ~86 ka BP was due to the significant influx of Ca enriched spring water. The concurrent low abundances of Si, Al and Ti probably reflect low levels of erosion in the watershed that was covered by arboreal vegetation. A shift in the hydrological system occurred around ~86 ka BP, which resulted in a lowering of water levels and the development of anoxic conditions, enabled the accumulation of organic matter. A transition from organic rich sediment to silty clay, coupled with an increase in Si, Al and Ti at ~63 ka BP records a reduction in organic productivity in the wetland and an increase in weathering and erosion in the watershed.