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Polygonal patterned ground is a dominant geomorphic feature in the McMurdo Dry Valleys, Antarctica. In central Beacon Valley, polygons are considered to be ancient expressions of stagnant surface processes and are thought to be stable for millions of years. However, the actual rate at which these polygons form and alter is not known. We describe a detailed cross section of a polygon, make several depth profiles of meteoric 10Be along this cross section, and use optically stimulated luminescence to date a few key samples at the center of this polygon. While confirming conclusions of previous studies that the polygon shoulders are stable on a 100 k.y. time scale and experience little vertical sediment mixing, our results also give clear evidence of eolian transport to the polygon center, leading to a sediment accumulation rate of 3 cm k.y.-1 over the past 15 k.y. Moreover, the data suggest that the accumulated material is locally derived, and, hence, surface erosion of the polygon shoulders must exist that cannot be recorded by meteoric 10Be. We conclude that polygon modification and soil accumulation under the apparent frozen conditions of Beacon Valley is an active and ongoing process. [ABSTRACT FROM AUTHOR]

Controversy exists regarding the sources of the eolian dust for the immense Loess Plateau of north-central China, the largest accumulation of windblown bess in the world. Because the bess accumulation rate, unit thickness, and particle size all decrease from northwest to southeast, it has long been thought that the northern deserts, especially the Mongolian Gobi, are the major bess source, a view supported by newly applied mineralogical provenance techniques (electron spin resonance, ESR). Here, we examine surface samples from the Gobi Desert and compare their magnetic and geochemical properties with those of last glacial bess samples from across the Loess Plateau region. The mineralogy, geochemistry, and magnetic properties of Gobi Desert samples are variable (most likely reflecting local lithobogical complexity), distinctive, and, critically, nonoverlapping with the notably homogenous characteristics of the last glacial boesses spanning the Loess Plateau. It is likelythat the source areas for the plateau encompass a much larger area than any one proximal desert region, in order to account for (1) the extreme degree of mixing, (2) the volume of bess generated and transported, and (3) the mineralogical and magnetic mismatch evident here between the Mongolian Gobi samples and the last glacial bess. [ABSTRACT FROM AUTHOR]

Formation of desert pavement and accretionary soils are intimately linked in arid environments. Well-sorted fallout scoria lapilli at Lathrop Wells (75-80 ka) and Red Cone (ca. 1 Ma) volcanoes (southern Nevada) formed an excellent parent material for pavement, allowing infiltration of eolian silt and fine sand that first clogged the pore space of underlying tephra and then aggraded and developed vesicular A (Av) horizons. Variations in original pyroclast sizes provide insight into minimum and maximum clast sizes that promote pavement and soil formation: pavement becomes ineffective when clasts can saltate under the strongest winds, while clasts larger than coarse lapilli are unable to form an interlocking pavement that promotes silt accumulation (necessary for Av development). Contrary to predictions that all pavements above altitudes of ∼400 m would have been reset in their development after late Pleistocene vegetation advances, the soils and pavements show clear differences in maturity between the two volcanoes. This indicates that either the pavements and/or soils develop slowly over many tens of thousands of years and then are very stable, or, if they are disrupted by vegetation advances, subsequent pavements are re-established with successively more mature characteristics. [ABSTRACT FROM AUTHOR]