Character, Rates, and Environmental Significance of Holocene Dust Accumulation in Archaeological Hilltop Ruins in the Southern Levant

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.

Composition of Modern Dust and Holocene Aeolian Sediments in Archaeological Structures of the Southern Levant

“…Apart from these differences, the archaeological soils of the various structures are strikingly similar. Although higher silt contents are evident in the Northern Negev, all profiles are dominated by calcareous silt, most likely of aeolian origin [19]. This is supported by the characteristics of current dust samples deposited with precipitation in the Petra region, which consist of calcareous silt loam.…”

“…The estimated annual sedimentation rates suggest that deposition on the monastery garden was nearly identical to the amounts that could be collected during one year of continuous sampling with the dust collectors on Jabal Haroun. It is slightly higher than sedimentation in the limestone terrace, and about the double of the deposition rate that was calculated for the hilltop ruin of the triclinium on Jabal Farasha [19]. The cistern cleanout spoil is hardly comparable to the other archives and off-scale, while Terrace 3 collected about 3.5 times the amount that was deposited in the adjacent Negev hilltop ruins [19].…”

“…The characteristics of the studied profiles partly depend on the types of the archaeological structures. All hilltop ruin soils exhibit a vesicular layer/V-horizon below a crust and clast pavement, which suggests that their substrates are largely aeolian sediments [19]. In contrast, V-horizons could not be discerned in terrace and cistern sediments.…”

“…Average sedimentation rates in the hilltop ruins were recently calculated [19] (pp. [12][13][14][15].…”

“…Here, we applied a revised bulk density of hilltop ruins soils, subtracting the soil skeleton (>2 mm), and using more conservative estimates of annual dust deposition, presented in Appendix B. The revision was applied to the previous estimates [19], as well. Accordingly, a minimum of~250 g m 2 a −1 dust was trapped by each of our standard marble dust collectors on Jabal Haroun.…”