Regional Depositional Age Assessment using Portable-OSL of Hand-Augered Aeolian-Fluvial Deposits along a chain of Small Dune-Dammed Basins in the Northwestern Negev Dunefield Margins, Israel&#160;
Authors: Greenbaum Noam , Robins Lotem , Joel Roskin 
Published: March 2024

Aeolian-Fluvial interactions range from aeolian- to fluvial-dominated processes, often resulting in unique morphologies and complex stratigraphies along dunefield margins. In the Northwestern Negev dunefield (Israel) desert, a key factor influencing transitions from aeolian- to fluvial-domination, is the basin size. While medium-sized (40-200 km2) and large (>200 km2) basins were breached before or during the early Holocene, small basins are still dammed by dunes. Often their surficial and buried palaeochannel is comprised of a sequence of remain of dune-dammed water bodies in the form of fossilized playas. Unlike medium and large basins, where incision exposes Aeolian-Fluvial deposits after the dune-dam breaching, small dune-dammed fluvial systems necessitate sampling techniques such as drilling into continuously aggrading Aeolian-Fluvial deposits to reconstruct the stratigraphy and interpret paleoclimate and palaeoenvironmental records. We demonstrate the potential of a SUERC Portable-OSL (port-OSL) for interpreting palaeo-records in small dune-dammed basins.The Shivta-East basin (3.3 km2) was hand-augered along an ephemeral stream's propagation path into the dunefield, at three disconnected playa-like sediments of seasonal dune-dammed waterbodies. At each dune-dammed waterbody sediments, samples were taken at 15-25 cm intervals and analyzed using the port-OSL reader. Their estimated ages were interpolated according to a calculated regional linear regression based on the northwestern Negev dunefield luminescence age database. This regression, generated by training a data set of thirty-two aeolian sand samples, analyzed for both OSL dating and port-OSL Net counts, accounts for 72% of the age variability, with a standard error of 3.4 ka between the model and the data. Due to the absence of modern-day OSL dated samples, the regression line was reconstructed for the LGM until the early Holocene. The regression model enables dating of the Last Glacial Maximum, Heinrich-1, and Younger Dryas sand incursions, previously described as the main active periods of the aeolian system.K-means cluster analysis based on the port-OSL signals, reveals three distinct clusters, which points to alternations of the sedimentary units, between sand and fluvial sourced fine-grained sediments. The three clusters are understood to reflect both the mineralogical composition and burial age of the deposits. The overlying cluster mainly consists of fine-grained sediments deposited in the dune-dammed waterbody, while the other two units are sandy deposits.Interpolation of the sandy samples from all three playas along the palaeochannel in the linear regression demonstrates that during the Heinrich-1 and Younger Dryas events, an aeolian-dominated environment dune-dammed the fluvial system, enabling aeolian sand deposition. Later, coevally with the fluvial system's propagation into the second (middle) dune-dammed waterbody, aeolian domination persisted until the Early Holocene generating the third and upstream dune-dammed waterbody.This study demonstrates the potential and limitations of the port-OSL reader combined with statistical methods for chrono-stratigraphic analysis of hand-augered samples collected from an altering depositional environment. The ability to rapidly estimated depositional ages and associated palaeoclimatic periods highlights the potential for further exploration of the port-OSL reader in different environmental settings.