The physics of wind-blown loess: Implications for grain size proxy interpretations in Quaternary paleoclimate studies

Újvári, Gábor; Kok, Jasper F.; Varga, György; Kovács, János

doi:10.1016/j.earscirev.2016.01.006

Cited by 178 publications

(83 citation statements)

References 295 publications

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“…The fact that Eolian sediments are transported near the saltation‐suspension threshold result is consistent with the relatively fine‐grained nature of bed sediment in the study site. The median grain diameter at 0.1 to 1 m above the ground was found to be ≈80–120 μm (Figure ), that is, small enough to be in modified saltation or short‐term suspension when u * exceeds 0.4 m/s for the smaller end of median grain sizes and when u * exceeds 0.7 m/s for the larger end of median grain sizes (Figure 8 of Újvári et al, ). These shear velocities are close to or within the range of geomorphically most effective shear velocities for the study site.…”

Section: Discussionmentioning

confidence: 93%

“…The median grain diameter at 0.1 to 1 m above the ground is in the range of approximately 80–120 μm. Grains of this size are expected to be in modified saltation (i.e., transported via semirandom trajectories influenced by both inertia and terminal velocity) or short‐term suspension when u * exceeds 0.4 m/s for the smaller end of median grain sizes and when u * exceeds 0.7 m/s for the larger end of median grain sizes (Figure 8 ofÚjvári et al, ). Both of these shear velocities are close to or within the range of geomorphically most effective shear velocities for the study site.…”

Section: Resultsmentioning

confidence: 99%

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Controls on Yardang Development and Morphology: 1. Field Observations and Measurements at Ocotillo Wells, California

et al. 2018

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Yardangs are streamlined hills formed in part by the erosive action of wind and wind‐blown sediments. Here we examine the controls on yardang development and morphology using the Ocotillo Wells State Vehicular Recreation Area (OWSVRA), California, as a study site. We measured the compressive strengths, strikes, and dips of bedrock strata, eolian sediment fluxes (including their vertical profiles and spatial variations around yardangs), and erosion rates derived from geologic constraints and multitemporal Terrestrial Laser Scanning (TLS). We used a combination of TLS‐based and airborne lidar‐based Digital Elevation Models (DEMs) to test the applicability of an asymmetric Gaussian function for characterizing yardang form and quantify the relationships among yardang lengths, widths, heights, spacings, and their controlling factors. Yardang aspect ratios are controlled by bedrock structural attributes, specifically by the tangent of the dip and the angle between the strike and the prevailing wind direction. Yardang spacings scale linearly with yardang width. Yardang heights increase as the square root of width such that larger yardangs tend to have gentler side slopes. Sediment fluxes reach a maximum in the troughs among yardangs, consistent with the hypothesis that yardang development involves the focusing of wind and wind‐blown sediments into troughs. The vertical distribution of eolian sediment flux follows a power law with an exponent of −2.5, a result consistent with an advection‐diffusion‐settling model of transport near the saltation‐suspension transition. Erosion rates are several mm/yr over time scales of ~100 and ~106 years.

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Section: Discussionmentioning

confidence: 93%

Section: Resultsmentioning

confidence: 99%

Controls on Yardang Development and Morphology: 1. Field Observations and Measurements at Ocotillo Wells, California

et al. 2018

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“…The sediments of the Chinese Loess Plateau (CLP) preserve a near-continuous continental record of Neogene climate changes Ding et al, 1994;Guo et al, 2002;Liu, 1985;Qiang et al, 2011). Although the grain size and dust accumulation of eolian deposits are valuable proxies for reconstructing the aridification and desertification of the Asian interior (Ding et al, 1995;Lu & An, 1998;Lu & Sun, 2000), the grain size of dust deposits is influenced by numerous factors such as wind strength and dust source changes; consequently, determining the main driver of grain size variations is a challenging task (Újvári et al, 2016;Vandenberghe, 2013). Records such as pollen assemblages and evaporites preserved in sedimentary basins in north China are also widely used as indicators of arid climates (Dupont-Nivet et al, 2007;Ma et al, 1998Ma et al, , 2005Zhao et al, 2015).…”

Section: Introductionmentioning

confidence: 99%

Expansion of Dust Provenance and Aridification of Asia Since ~7.2 Ma Revealed by Detrital Zircon U‐Pb Dating

Zhang

Stevens

et al. 2018

Geophysical Research Letters

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The relative importance of global cooling and Tibetan Plateau uplift in driving the aridification of Asia during the late Cenozoic is debated, largely due to the lack of appropriate proxy indicators. Here we address this problem by investigating changes in the source of Chinese loess and Red Clay, which is directly controlled by changes in the extent and distribution of the arid zone of Asia and the intensity of the East Asian winter monsoon, using zircon U‐Pb dating of 27 levels in a near‐continuous eolian sedimentary sequence in southern Chinese Loess Plateau. The results show that source regions expanded stepwise at ~7.2, ~2.6, 1.2–0.9 Ma, and at the Last Glacial Maximum. These changes were synchronous with global cooling and ice cover expansion in the Northern Hemisphere, suggesting that the drivers of aridification of the Asian interior were intimately related to global cooling in the late Cenozoic.

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“…For this site, we examined grain-size, environmental magnetism, and other spectrophotometric and geochemical proxies to reconstruct past climatic and environmental dynamics for the past 350,000 years. Grain-size composition is one of the most frequently used palaeoenvironmental proxies of loess sequences to infer changes in aeolian dynamics, sources of loess and pedogenesis17181920. Based on the principle of post-depositional formation of ultrafine magnetic particles during pedogenesis, environmental magnetism has also been successfully applied as a palaeoclimatic proxy in Eurasian loess6921.…”

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Tracing the influence of Mediterranean climate on Southeastern Europe during the past 350,000 years

Obreht

Zeeden

Hambach

et al. 2016

Sci Rep

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Loess-palaeosol sequences are valuable archives of past environmental changes. Although regional palaeoclimatic trends and conditions in Southeastern Europe have been inferred from loess sequences, large scale forcing mechanisms responsible for their formation have yet to be determined. Southeastern Europe is a climatically sensitive region, existing under the strong influence of both Mediterranean and continental climates. Establishment of the spatial and temporal evolution and interaction of these climatic areas is essential to understand the mechanisms of loess formation. Here we present high-resolution grain-size, environmental magnetic, spectrophotometric and geochemical data from the Stalać section in the Central Balkans (Serbia) for the past ~350,000 years. The goal of this study is to determine the influence of the Mediterranean climate during this period. Data show that the Central Balkans were under different atmospheric circulation regimes, especially during Marine Isotope Stages 9 and 7, while continental climate prevailed further north. We observe a general weakening of the Mediterranean climate influence with time. Our data suggest that Marine Isotope Stage 5 was the first interglacial in the Central Balkans that had continental climate characteristics. This prominent shift in climatic conditions resulted in unexpectedly warm and humid conditions during the last glacial.

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The physics of wind-blown loess: Implications for grain size proxy interpretations in Quaternary paleoclimate studies

Cited by 178 publications

References 295 publications

Controls on Yardang Development and Morphology: 1. Field Observations and Measurements at Ocotillo Wells, California

Controls on Yardang Development and Morphology: 1. Field Observations and Measurements at Ocotillo Wells, California

Expansion of Dust Provenance and Aridification of Asia Since ~7.2 Ma Revealed by Detrital Zircon U‐Pb Dating

Tracing the influence of Mediterranean climate on Southeastern Europe during the past 350,000 years

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