Aeolian-fluvial sediments and landscapes along the northwestern Negev Dunefield (Israel) margins since the late Pleistocene

Abstract

<p>Dunefield margins are prone to changing domination between aeolian and fluvial systems. Dominating aeolian systems divert or block fluvial systems or/and reduce their erosional forces often leading to amplified sedimentation by a wide range of unique aeolian-fluvial (A-F) sediments. Other arid environments are mainly dominated by eroding ephemeral fluvial systems that usually characterized by sediment degradation.</p><p>The late Pleistocene encroachment of vegetated linear dunes into the northwestern Negev desert dunefield  (Israel) comprised a distinct period of aeolian domination upon ephemeral drainage systems originating in the loess-clad Central Negev highlands. This study analyzes the sediments, geomorphology and landscape evolution caused by A-F processes along dunefield margins, in particular sediments deposited by dune-dammed water bodies slightly upstream of the dunefield edge and between VLDs, using high-resolution field mapping, relative (portable) and absolute OSL dating, stratigraphy and sedimentological analyses. These sediments have been generally mapped as playa sediments, understood to be deposited in a fluvial-dominated environment.</p><p>Six main A-F sediment types were identified and interpreted: (a) Aeolian sand appears to be remnants of fluvial eroded VLD.  (b) Fluvial sand originates from dune erosion and deposited nearby. (c) Massive loam to silty-clay loam relates to abrupt changes in the hydraulic parameters (width/depth ratio and water losses through infiltration) which induce sudden change in flow velocity, resulting in unsorted massive deposits of upstream loess and other desert soil bedload. (d) Couplets, similar to the massive loam, contains loess and upstream sediments deposited in a standing water body. (e) Laminated silty-clay-loam units were identified only between VLDs. (f) High-energy fluvial deposits, which contain loam, sand and pebbles, with  a clear erosional boundary that mark the upstream edge of A-F sedimentation.</p><p>The landscape of the Negev dunefield margins developed since the late Pleistocene by short-term aeolian domination, which gradually changed into fluvial domination during the Holocene. Dune-damming depositions occurred during this transition. First outside the dunefield, then propagated downstream into the dunefield. Fluvial aggradation of A-F sediments resulted in a vast playa-like flats, that following dune-dam breaching underwent incision, let alone in small (~<20 km<sup>2</sup>) basins.</p>