Late Quaternary aeolian-fluvial palaeoarchives along dunefield margins

Abstract

<p>Aeolian-Fluvial (A-F) processes along dunefield margins document environmental changes in arid zones around the world. In the present study, at the northwestern Negev dunefield (Israel) margins, high-resolution chrono-stratigraphic analysis of marginal Vegetated Linear Dunes (VLDs) and fine-grained alluvial plains was conducted. Nineteen stratigraphic sections were analyzed in detail. Dating included pre-measurements using Portable Optically Stimulated Luminescence (POSL), which were used to decipher representative samples for OSL dating. Selected hearth and vegetation samples were radiocarbon dated as well.</p><p>A-F processes along dunefield margins may generate reliable and detailed palaeoarchives, by combining POSL and OSL analyses. VLDs, prone to defined periods of activation and stabilization, control a gradual and lagged shift from aeolian to fluvial domination in the dune-dammed dunefield margins, succeeding dunefield stabilization.</p><p>In an aeolian-dominated environment, either fully or partly dammed fluvial systems aggregate upstream-sourced sediments along the dunefield margins, forming an alluvial plain. Dune-dam waterbody deposits include three distinct types: (a) event-based couplets, (b) massive structureless loam and (c) fine-laminas. These deposits that may remain preserved for substantial times bury usually truncated dune remains. Aeolian deflation of fine-grained sediments from dune-dam waterbody deposits, percolated into adjacent marginal VLD, initiating pedogenic processes. Altogether, dune-dam impoundments were found to be spatially dynamic processes, in which the dune-dammed fluvial system gradually propagates downstream from the dunefiled margin into the dunefield. Each impoundment was generated by slightly or distinctly different A-F mechanisms depending on the location of the damming-dunes in relation to the dunefield margins.  </p><p>In the northwestern Negev, three major sand incursions into <180 km<sup>2</sup> fluvial systems during the LGM, Heinrich-1 and Younger-Dryas, resulted in localized and usually seasonal waterbodies, utilized by EpiPalaeolithic hunter-gatherers . This study also revelaed that during the early Holocene a climatic shift, which left a signature in the Mediterranean Basin in the form of Sapropel-1, was recorded along the dunefield margins, forming the last, upper and significant portion of the alluvial plains. This aggregative environment was also utilized by Neolithic and Chalcolithic man in some basins, locally reactivating VLDs. After dune-dam breaching, a fluvial-dominated environment developed, characterized by floodplain deposition, and scour and fill patterns.</p>