Significance of primary hilltop loess in reconstructing dust chronology, accretion rates, and sources: An example from the Negev Desert, Israel

Abstract

[1] Although high-latitude loess sequences have been studied extensively for reconstructing past climates, loess in desert margins has been mostly overlooked. Moreover, many low-latitude loess studies have focused on secondary, reworked sequences for which paleoclimatic inferences are complicated owing to postdepositional processes acting under local control. In this respect, the spatial distribution of the loess and its different types are crucial. In this study, we differentiate primary and secondary loess using remote sensing and field criteria. We present remote sensing and geographic information system procedures for mapping loess distribution, in general, and for identifying pristine hilltop loess sequences in particular. Then, we present the mineralogical and textural analyses combined with optically stimulated luminescence ages of one such primary, hilltop loess sequence in the Negev desert that show that the late Pleistocene Negev loess started accumulating at $95 ka, much earlier than previously proposed ($70 ka). It was preceded by a previously unknown middle Pleistocene period of loess formation at $180-130 ka. The ages also suggest that the threshold of dust accretion rate needed for loess formation is $0.02 mm a À1 ($30 g m À2 a À1 ), a factor of 2 or more lower than previously thought (0.04 to 1.0 mm a À1 ). Our results also provide insights into causes of late Pleistocene loess accretion and its close association with regional dune field activity. The methodology for mapping the loess distribution may potentially be generalized to help understanding loess formation in other, more remote desert areas.

Origin of the Sinai–Negev erg, Egypt and Israel: mineralogical and geochemical evidence for the importance of the Nile and sea level history

“…They calculated percentages of these mineral species using a method by Dr. Amir Sandler of the Geological Survey of Israel (written communication, 9 August 2012), wherein the following factors are applied to XRD peak heights at two-theta, summed, and calculated as percentages: quartz, 26.6 , Â1.0; K-feldspar, 27.4 , Â3.0; plagioclase, 27.8 , Â3.5; and calcite, 29.4 , Â1.1. We followed this protocol with our XRD data in order to make direct comparisons with the loess mineralogical compositions reported by Crouvi et al (2009) and Enzel et al (2010). Mineral percentages calculated in this manner are consistent with major element chemistry.…”

“…Mineral percentages calculated in this manner are consistent with major element chemistry. Comparison with the Israeli loess mineralogy indicates that, for the most part, loess at Har Keren and elsewhere in Israel (Crouvi et al, 2009) is enriched in K-feldspar, plagioclase, and calcite, relative to quartz, when compared to these minerals in the Negev dunes (Fig. 19).…”

“…This hypothesis requires, therefore, that calcite and feldspars should be enriched in loess (relative to quartz) when compared to sands in the SinaieNegev erg. Crouvi et al (2009) andEnzel et al (2010) reported percentages of quartz, K-feldspar, plagioclase, and calcite in loess downwind of the SinaieNegev erg. They calculated percentages of these mineral species using a method by Dr. Amir Sandler of the Geological Survey of Israel (written communication, 9 August 2012), wherein the following factors are applied to XRD peak heights at two-theta, summed, and calculated as percentages: quartz, 26.6 , Â1.0; K-feldspar, 27.4 , Â3.0; plagioclase, 27.8 , Â3.5; and calcite, 29.4 , Â1.1.…”

Integrated Desert Terrain Forecasting for Military Operations

“…Results indicate that the source of coarse dust in the Negev's loess is the adjacent Sinai-Negev sand dunes, as opposed to previously suggested sources (Crouvi et al, 2008(Crouvi et al, , 2009. Combining the results from these hilltop sequences with results from additional field-based research concentrated on ancient stable surfaces located farther south, suggests that the earliest occurrence of very high dust accumulation rates in the Negev is ~180 ka.…”

The nature of the Pleistocene-Holocene palaeosols in the Gaza Strip, Palestine

“…The grain-size distribution in these soils reflects atmospheric dust that was supplied from the Sinai and the Negev deserts (Yaalon & Dan, 1974;Yaalon & Ganor, 1979;Dan et al, 1981;Ganor et al, 1991;Emzel et al, 2008;Crouvi et al, 2008;2009;2010). Aeolian dust from these deserts is still involved in the formation of all soils in Palestine (Dan & Yaalon, 1969).…”