Dune-dammed waterbody, aeolian and fluvial sediment chronologies improve resolution of dunefield histories

Studies have demonstrated that >~100 absolute ages of aeolian sand at certain spatial/vertical resolutions are necessary for constructing a reliable chronological framework for palaeoenvironmental/palaeoclimatic interpretations of dunefield histories (Telfer and Hesse, 2013). As acquiring such an interpretable dataset demands significant resources, several approaches, such as portable-OSL-OSL age estimates, have attempted to partly overcome this necessity (Stone et al., 2019).

Encroaching dunes in the past and present, dam drainage systems. In arid environments this process generates proximal upstream, dune-dammed waterbodies. These waterbodies that are often seasonal, deposit distinct, low-energy, fluvial, fine-grained sediments (LFFDs), often as sedimentary couplets. When dry, the water-body deposits sustain a playa morphology. This recurring aeolian-dominated, aeolian-fluvial  process gradually leads to amplified LFFD accumulation, and partly reconfigures dunefield, and particularly dunefield margin, landscape evolution. In medium-sized basins (~10-200 km²) along the margins of the northwestern (NW) Negev desert dunefield of Israel, LFFD stratigraphic buildup gradually levels with dune-dam crest elevation, consequently leading to a dune-dam break outburst flood. The dune dam break in turn generates rapid fluvial incision of the LFFDS, reviving an open, fluvial-dominated environment in a transformed landscape (Robins et al., 2022,2023).

The INQUA DuneAtlas of global inland dunefield chronological data includes some dated samples that are non-dune sediments such as interdune and LFFD samples (Lancaster et al., 2016). However, the complementary contribution of such sediments to interpreting dunefield chronologies has not been fully assessed. Also, DuneAtlas sand samples dating to the LGM are sparse.

Here, we demonstrate for the NW Negev dunefield that OSL-dating, partly supported by port-OSL profiling, mainly of sandy units within LFFDs, improves the resolution and reliability of determining dunefield chronologies. The approach also gleans information on the morphological maintenance of existing dunes, and in some cases, reveals sand mobilization episodes that are absent in adjacent dated, dune cores.

Spatially dense, OSL-dated dune cores and sections of the ~10³ km²-sized NW Negev dunefield revealed that the dunefield was constructed in two main sand incursions and vegetated linear dune (VLD) buildup/extension periods – associated with the Heinrich 1 (H1) and Younger Dryas (Roskin et al., 2011). In this study, exposed OSL-dated LFFD sections along the upstream-facing, dunefield margins revealed that dune-dammed waterbodies partly to completely erode earlier dunefield-margin dunes but also preserve remains of eroded dunes between LFFD units. This partial preservation of aeolian deposits enables the construction of a reliable archive. The LFFD sections also revealed evidence of significant and initial dune incursion and damming during the LGM, intermittently recurring until the early Holocene (Robins et. al.). Early Holocene LFFDs may imply partial dune buildup or equilibrium-like dune maintenance, and/also, a significant lag between Younger Dryas dune-damming and dune-dam breaching. Altogether, dating dunefield LFFDs is proposed to be a primary approach for jointly studying dunefield and fluvial histories.

 

References

Lancaster, N., et al., 2016. QI 

Robins, L., et al., 2022. QSR 

Robins, L., et al., 2023. QSR

Roskin, J., et al., 2011. QSR 

Stone, A. et al. 2019. QG 

Telfer, M.W. and Hesse, P.P., 2013. QSR