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Amplified aeolian-fluvial sedimentation and landscape evolution along the southern margins of the northwestern Negev Dunefield (Israel) since the late Pleistocene

Amplified aeolian-fluvial sedimentation and landscape evolution along the southern margins of the northwestern Negev Dunefield (Israel) since the late Pleistocene

Mr. Lotem Robins
Dept. of Geography and Environmental Studies, University of Haifa, Israel

Interactions between aeolian and fluvial processes, are common in arid and semi-arid regions and generate unique combinations of sediments, stratigraphies and landforms. Dunes that divert or block a watercourse (dune dams) are a common aeolian-fluvial process, which occurs in dunefield margins.

Vegetated linear dune encroached from northern Sinai into the northwestern (NW) Negev desert, mainly during the Heinrich 1 and Younger Dryas periods. Each of these periods was followed by blocking of ephemeral drainage systems originating in the loess-clad Negev highlands. The dune damming led to a spatial strip of substantial short-term water-bodies along the newly-formed NW Negev dunefield margins, which resulted in Low energy Fluvial Fine Grain Deposits (LFFDs). These amplified aeolian-fluvial processes resulted in a unique water availability in this arid environment, which attracted Epipalaeolithic man.

This study analyzes the geomorphic and temporal processes of dune dam construction, maintenance, destruction and properties of the consequent water bodies in the NW Negev dunefield margins. The role of dune-damming process in landscape evolution is studied by: (a) mapping in detail the full spatial coverage of the LFFDs, (b) high-resolution stratigraphic documentation and relative (portable OSL) and absolute (OSL) dating, and (c) particle-size analysis. Stratigraphic sections were studied along ephemeral drainage systems of sizes ranging from single to hundreds of sq. km: Nahal Shivta (East), Nahal Raviv, Nahal Atadim and Nahal Besor at the Besor-Revivim confluence.

Between the late Pleistocene to the early Holocene these water bodies deposited 1-8 m thick sequences of LFFDs. The LFFD sediment appears as couplets and massive units. The couplet formation indicates ephemeral reservoir-like water body, while the massive unit indicates a higher fluvial energy. Both sediments comprised of local aeolian sand, fluvially reworked local dune sand and fluvial reworked loess.

The amplified LFFD accumulation combined with the dunefield stability were driving factors enabling the dune dams breaching and the consequent fluvial response and incision into LFFDs sequences. Sedimentological finds enable estimations of the amount of reworked loess deposited in the water bodies that may pertain to the late Pleistocene time-window of loess erodibility in the upstream Negev highland. These sequences since the middle Holocene until today appear as flat and fine-grained playa-like expanses, prone to enhanced dust entrainment. There is no evidence that the intensive Byzantine agricultural practices in the region utilized the LFFD surfaces for agriculture, probably due to their low permeability and high salinity.