Decadal-scale soil redistribution along hillslopes in the Mojave Desert

This study estimates the relative magnitude of decadal-scale soil redistribution (i.e., soil loss or gain) by slope wash using ¹³⁷Cs inventories measured in 46 soil profiles at four study sites in the Ft. Irwin area of the Mojave Desert of California, USA. The variability in ¹³⁷Cs inventories on a <5 m scale suggests that even for the same topographic position, there is large variation in runoff generation and flow continuity. Smaller average ¹³⁷Cs inventories that are suggestive of higher relative erosion rates are associated with more gently sloping sites that have a lower percentage of surficial rock-fragment and vegetation coverage. Individual ¹³⁷Cs inventories from all four sites are positively correlated with the percentage of rock fragments in the upper soil profile. The increase in rock-fragment cover (i.e., soil armoring) with increasing slope gradient appears to negate any potential increase in transport effectiveness with increasing slope steepness. This armoring, together with the sandy-loam soil texture characteristic of steeper slopes, hinders runoff and slope-wash erosion. Our findings are supported by soil data that suggest that these patterns are persistent for longer timescales (i.e., centuries and millennia)

Linking coarse silt production in Asian sand deserts and Quaternary accretion of the Chinese Loess Plateau

The Chinese Loess Plateau (CLP) is a large, spatially well defined and persistent zone of loess accumulation developed near the fluctuating northwest margin of the East Asian monsoon. Many studies have analyzed its loess sediments to provide insights into paleoclimatic conditions. Although spatial and temporal variations in the grain sizes of CLP sediments are fundamental to this effort, controversy over the origin of the dominant coarse quartz silt has limited interpretations. Reexamination of the spatial pattern of grain-size distribution across the CLP and a field-scale experiment conducted in the Gobi Desert revealed a genetic association between the coarse silt fraction of the loess and primary production of coarse silt through eolian abrasion of sand in the proximal Mu-Us, Tengger, and Badain Jaran sandy deserts. Our results demonstrate the effectiveness of eolian abrasion of quartz sand in primary coarse silt production in Central Asia and identify this process as the most consistent with the wellrecognized systematic northwest-southeast depositional pattern of the CLP. We suggest that only abraded coarse quartz grains transported short distances by long-term persistent eolian activity can build up thick loess sequences to form a massive and spatially well defined loess plateau. These results decouple the production and transport of coarse silt and finer silt and clay particles, which have a more distant and wider provenance, changing the constraints on previous paleoclimatic reconstructions. © 2013 Geological Society of America

Rare earths release from dissolving atmospheric dust and their accumulation into crystallising halite. The dead-sea example

: The industrial extraction of Y and lanthanides (hereafter defined as Rare Earth Elements, REE) often requires the achievement of leaching procedures removing these metals from primary rocks and their transfer in aqueous leachates or incorporated in newly forming soluble solids. These procedures are the most dangerous to the environment in relation to the composition of leachates. Hence, the recognition of natural settings where these processes currently occur, represents a worthy challenge for learning how to carry out similar industrial procedures under natural and more eco-friendly conditions. Accordingly, the REE distribution was studied in the brine of Dead Sea, a terminal evaporating basin where brines dissolve atmospheric fallout particles and crystallise halite. Our results indicate that the shale-like fractionation of shale-normalised REE patterns in brines, inherited during the dissolution of atmospheric fallout, changes because of the halite crystallisation. This process leads to crystallising halite mainly enriched in elements from Sm to Ho (medium REE, MREE) and coexisting mother brines enriched in La and some other light REE (LREE). We suggest that the dissolution of atmospheric dust in brines corresponds to the REE extraction from primary silicate rocks, whereas halite crystallisation represents the REE transfer into a secondary more soluble deposit with reduced environmental health outcomes

Linking coarse silt production in asian sand deserts and quaternary accretion of the Chinese Loess Plateau

The Chinese Loess Plateau (CLP) is a large, spatially well defined and persistent zone of loess accumulation developed near the fluctuating northwest margin of the East Asian monsoon. Many studies have analyzed its loess sediments to provide insights into paleoclimatic conditions. Although spatial and temporal variations in the grain sizes of CLP sediments are fundamental to this effort, controversy over the origin of the dominant coarse quartz silt has limited interpretations. Reexamination of the spatial pattern of grain-size distribution across the CLP and a field-scale experiment conducted in the Gobi Desert revealed a genetic association between the coarse silt fraction of the loess and primary production of coarse silt through eolian abrasion of sand in the proximal Mu-Us, Tengger, and Badain Jaran sandy deserts. Our results demonstrate the effectiveness of eolian abrasion of quartz sand in primary coarse silt production in Central Asia and identify this process as the most consistent with the well-recognized systematic northwest-southeast depositional pattern of the CLP. We suggest that only abraded coarse quartz grains transported short distances by long-term persistent eolian activity can build up thick loess sequences to form a massive and spatially well defined loess plateau. These results decouple the production and transport of coarse silt and finer silt and clay particles, which have a more distant and wider provenance, changing the constraints on previous paleoclimatic reconstructions.</p

New chronology for the southern kalahari group sediments: implications for sediment cycle dynamics and early hominin occupation

The Kalahari Group covers an extensive part of the southern African continent and forms a low-relief landscape dominated by extensive unconsolidated sand. Current depositional models assume that the Kalahari Group sediments accumulated gradually throughout the Cenozoic, but an absence of absolute chronology beyond ~60 ka has left this premise untested. Here, we challenge this age model with new cosmogenic burial ages obtained from a 55 m section of Kalahari Group sediments at Mamatwan Mine near the southern edge of the Kalahari basin. Our results indicate that the majority of the existing section was emplaced rapidly at ~1 Ma. At this time the basin filled to its present level and established the Kalahari sand belts, which fostered the modern savannah. Our data suggest a dynamic landscape, with punctuated cycles of erosion and deposition, in contrast to the accepted concept of a stable basin filling slowly throughout the Cenozoic. The sedimentology and cosmogenic nuclide measurements from the lower Mamatwan Mine section reveal the existence of an extensive Early to Middle Pleistocene water body, persisting at least 420 ka prior to the rapid filling event at ~1 Ma. This water body is contemporaneous with a significant hominin occupation as evidenced by neighboring archaeological excavations. We thus provide the first evidence of association of the high-density hominin occupation in southern Africa with an extensive water body