Abstract
Loess accumulated in the Negev desert during the Pleistocene and primary and secondary loess remains cover large parts of the landscape. Holocene loess deposits are however absent. This could be due low accumulation rates, lack of preservation, and higher erosion rates in comparison to the Pleistocene. This study hypothesized that archaeological ruins preserve Holocene dust. We studied soils developed on archaeological hilltop ruins in the Negev and the Petra region and compared them with local soils, paleosols, geological outcrops, and current dust. Seven statistically modeled grain size end-members were identified and demonstrate that the ruin soils in both regions consist of mixtures of local and remote sediment sources that differ from dust compositions deposited during current storms. This discrepancy is attributed to fixation processes connected with sediment-fixing agents such as vegetation, biocrusts, and/or clast pavements associated with vesicular layers. Average dust accretion rates in the ruins are estimated to be ~0.14 mm/a, suggesting that ~30% of the current dust that can be trapped with dry marble dust collectors has been stored in the ruin soils. Deposition amounts and grain sizes do not significantly correlate with wind intensity. However, precipitation may have contributed to dust accretion. A snowstorm in the Petra region delivered a significantly higher amount of sediment than rain or dry deposition. Snowfall dust had a unique particle size distribution relatively similar to the ruin soils. Wet deposition and snow might catalyze dust deposition and enhance fixation by fostering vegetation and crust formation. More frequent snowfall during the Pleistocene may have been an important mechanism of primary loess deposition in the southern Levant.
Highlights
Widespread late Quaternary loess deposits can be found in the central and northern Negev desert
Diagnostic horizons show that all ruin soils are characterized by V-C profiles
Differences of pedogenic iron contents and magnetic properties, as well as contents of CaCO3, suggest that the ruin soils do not resemble re-deposited Pleistocene loess from the vicinity—at least not from the aprons that we analyzed. Based on their observation of a haboob dust storm, [77] suggested that part of the currently suspended and deposited dust in Israel is recycled Pleistocene loess, which is released due to agriculture in the northwestern Negev. While this might be true for current dust storms, it cannot be confirmed for the ruin soils that we studied—despite the very similar particle size distributions of Pleistocene loess and Holocene ruin soils
Summary
Widespread late Quaternary loess deposits can be found in the central and northern Negev desert. These testify to Pleistocene landscape changes, documented by variations of dust deposition, accumulation, and soil development [1,2,3,4,5,6,7,8,9,10,11,12]. Much less is known about dust settling and landscape changes during the Holocene, including how human activity interacted with climate fluctuations. This is partly due to a lack of Holocene sedimentary sequences. Avni et al [17] showed how natural incision of the Negev loess deposits during the Holocene led to landscape changes, which were slowed down by ancient agricultural terraces, as these controlled and reduced runoff
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