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.
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
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.