Quaternary desert loess and sandstone-loessite relationships in the geological record raise questions regarding causes and mechanisms of silt formation and accretion. In the northern Sinai-Negev desert carbonate terrain, only sand abrasion in active erg could have produced the large quantities of quartzo-feldspathic silts constituting the late Quaternary northwestern Negev loess. In the continuum of source (medium to fine sand of dunes) to sink (silts in loess) the very fine sand is unaccounted for in the record. This weakens the sand abrasion model of silt formation as a global process. Here, we demonstrate that, as predicted by experiments, abrasion by advancing dunes generated large quantities of very fine sand (60-110 μm) deposited within the dune field and in close proximity downwind. This very fine sand was generated 13-11. ka, possibly synchronous with the Younger Dryas under gusty sand/dust storms in the southeastern Mediterranean and specifically in the northern Sinai-Negev erg. These very fine sands were washed down slope and filled small basins blocked by the advancing dunes; outside these sampling basins it is difficult to identify these sands as a distinct product. We conclude that ergs are mega-grinders of sand into very fine sand and silt under windy Quaternary and ancient aeolian desert environments.
Bibliographical noteFunding Information:
We acknowledge E. Zilberman (Geological Survey of Israel) for field discussions. We thank the students of the Quaternary Field Methods classes (Institute of Earth Sciences, The Hebrew University of Jerusalem) who spent time in the Har Keren basins; among them, Israel Naaman found the radiocarbon sample and Alexis Rosenbaum, Navot Morag, and Sharona Shlomi initiated the stratigraphic analysis. The research was supported by the U.S. Army Research Office ( DAAD19-03-1-0159 ) grant to YE and RA (through PI E. McDonald, DRI) and by the United States–Israel Bi-National Science Foundation grant 2006-221 to RA and Alan Gillespie (UW). PSDAs were conducted by A. Lokshin and R. Krasilshikov and Z. Dolgin prepared the OSL and mineralogy by A. Sandler (all at the Geological Survey of Israel). Field assistance by Y. Rephael and Y. Mizrachi was crucial to the success of this research. Improvements of earlier versions of this manuscript by a colleague (A. Matmon, Hebrew U) and anonymous reviewers and by the associate (V. Holliday) and senior (D. Booth) editors are truly appreciated.
- Late Pleistocene
- Sand abrasion