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Yougui Song - One of the best experts on this subject based on the ideXlab platform.
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origin of loess deposits in the north tian shan Piedmont central asia
Palaeogeography Palaeoclimatology Palaeoecology, 2020Co-Authors: Yougui Song, Kathryn E Fitzsimmons, Xiuling Chen, Charlotte Prudhomme, Xiulan ZongAbstract:Abstract Loess deposits are widely distributed along the mountain Piedmonts of Central Asia. The transport processes and origins of Central Asian loess sediments remain poorly understood. Here we investigate the origin and formation of loess along the northern Piedmont of the Tian Shan based on trace element (including rare earth element) ratios and multidimensional scaling analysis. Our results indicate that the loess has undergone weak chemical weathering. Using a selection of geochemical fingerprinting techniques based on Pearson correlation and Kruskal–Wallis H tests, we establish a genetic link between alluvial-proluvial fans/plains, deserts, and loess along the Tian Shan Piedmont in northern Kyrgyzstan and southern Kazakhstan. The unsorted sediments on the Piedmont slopes and alluvial-proluvial plains are common sources for both deserts and loess to the north of the Tian Shan. Dune sediments are not the main source of the fine-grained loess. Origin and formation of Central Asian loess is strongly dependent on local topographic context and wind dynamics. Only once loess provenance and formation has been understood across both space and time can reliable interpretations of palaeoclimatic proxies in these deposits be made.
Jennifer Larsen - One of the best experts on this subject based on the ideXlab platform.
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Timing of surficial process changes down a Mojave Desert Piedmont
Quaternary Research, 2007Co-Authors: Kyle K. Nichols, Paul R. Bierman, Martha Cary Eppes, Marc W. Caffee, Robert C. Finkel, Jennifer LarsenAbstract:Abstract We measured 10 Be and 26 Al in 29 sediment samples to infer the history and millennial-scale rates of change down a low-gradient Piedmont, a common but enigmatic landform that dominates the Mojave Desert. Nuclide data suggest that a large volume of sediment was deposited on the proximal East Range Road Piedmont in Fort Irwin, California, ∼ 75,500 yr ago. Since then, this material has been stable or eroding slowly. In contrast, on the distal Piedmont (3.5 km from the upland source basins) soil stratigraphy suggests that there have been alternating periods of surface stability, erosion, and deposition over the last 70,000 yr. Nuclide data from samples amalgamated along cross-Piedmont transects suggest that long-term average down-gradient sediment speeds range from 9 cm yr − 1 near the uplands to 22 cm yr − 1 6 km down-Piedmont. These speeds are similar to 10 Be-estimated sediment speeds down three other Piedmonts in the Mojave Desert, suggesting that Piedmont surface morphologies dominated by shallow migrating channels have similar sediment transport rates. The timing of surface process change down the East Range Road Piedmont is determined by a combination of sediment available in the source basins, sediment transport rates, and the size of the Piedmont.
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Late Quaternary history of the Chemehuevi Mountain Piedmont, Mojave Desert, deciphered using 10Be and 26Al
American Journal of Science, 2005Co-Authors: Kyle K. Nichols, Paul R. Bierman, Martha Cary Eppes, Marc W. Caffee, Robert C. Finkel, Jennifer LarsenAbstract:We used the cosmogenic nuclides, 10 Be and 26 Al, as cosmic-ray dosim- eters to track sediment movement across the incised Chemehuevi Mountain Piedmont surface. The Piedmont extends 12 km from highland source basins to an ephemeral wash at the toe of the Piedmont. Nuclide activity in sediment from steep source basins and from the bedrock pediment allows us to estimate rates of sediment generation and thus the rate at which sediment is supplied to the Piedmont from weathering rock. Analysis of amalgamated sediment samples, collected along 4-km-long transects spaced at 1 km intervals from the mountain front provide context for understanding nuclide activity in sediment samples collected from two soil pits and demonstrate that sediment steadily moves down the channel network. Samples from the two soil pits allow for estimates of sediment deposition rates and thus further illuminate Piedmont history. Model results suggest that the Chemehuevi Mountains are eroding about 40 mm ky 1 whereas the mountain-proximal bedrock pediment and the interPiedmont Saw- tooth Range are eroding more slowly, 10 to 21 mm ky 1 and 9.5 mm ky 1 , respectively. Cosmogenic nuclide profiles in two soil pits suggest a complex history of deposition (at rates between 19 to 39 mm ky 1 ) and stability over the past 60 ky. A change in process from sediment deposition to sediment transport occurred distally on the Piedmont approximately 8 ky ago, while the mid-Piedmont Piedmont surface has been stable since the mid-Holocene. The incised Chemehuevi Mountain Piedmont is changing at rates similar to planar and uniformly active Piedmonts such as those adjacent to the Iron and Granite Mountains. All three Piedmonts have average sediment grain velocities of decimeters per year, long-term source basin erosion rates between 35 to 40 mm ky, depositional hiatuses around the Pleistocene-Holocene climatic transition from moister to drier conditions, and Pleistocene deposition rates of 18 to 39 mm ky. Such similarity in Piedmont behavior, despite clear differences in morphology and appearance, might suggest large scale geologic and climatic controls on the generation, transport and deposition of sediment in the Mojave Desert.
Xiulan Zong - One of the best experts on this subject based on the ideXlab platform.
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origin of loess deposits in the north tian shan Piedmont central asia
Palaeogeography Palaeoclimatology Palaeoecology, 2020Co-Authors: Yougui Song, Kathryn E Fitzsimmons, Xiuling Chen, Charlotte Prudhomme, Xiulan ZongAbstract:Abstract Loess deposits are widely distributed along the mountain Piedmonts of Central Asia. The transport processes and origins of Central Asian loess sediments remain poorly understood. Here we investigate the origin and formation of loess along the northern Piedmont of the Tian Shan based on trace element (including rare earth element) ratios and multidimensional scaling analysis. Our results indicate that the loess has undergone weak chemical weathering. Using a selection of geochemical fingerprinting techniques based on Pearson correlation and Kruskal–Wallis H tests, we establish a genetic link between alluvial-proluvial fans/plains, deserts, and loess along the Tian Shan Piedmont in northern Kyrgyzstan and southern Kazakhstan. The unsorted sediments on the Piedmont slopes and alluvial-proluvial plains are common sources for both deserts and loess to the north of the Tian Shan. Dune sediments are not the main source of the fine-grained loess. Origin and formation of Central Asian loess is strongly dependent on local topographic context and wind dynamics. Only once loess provenance and formation has been understood across both space and time can reliable interpretations of palaeoclimatic proxies in these deposits be made.
Marc W. Caffee - One of the best experts on this subject based on the ideXlab platform.
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Timing of surficial process changes down a Mojave Desert Piedmont
Quaternary Research, 2007Co-Authors: Kyle K. Nichols, Paul R. Bierman, Martha Cary Eppes, Marc W. Caffee, Robert C. Finkel, Jennifer LarsenAbstract:Abstract We measured 10 Be and 26 Al in 29 sediment samples to infer the history and millennial-scale rates of change down a low-gradient Piedmont, a common but enigmatic landform that dominates the Mojave Desert. Nuclide data suggest that a large volume of sediment was deposited on the proximal East Range Road Piedmont in Fort Irwin, California, ∼ 75,500 yr ago. Since then, this material has been stable or eroding slowly. In contrast, on the distal Piedmont (3.5 km from the upland source basins) soil stratigraphy suggests that there have been alternating periods of surface stability, erosion, and deposition over the last 70,000 yr. Nuclide data from samples amalgamated along cross-Piedmont transects suggest that long-term average down-gradient sediment speeds range from 9 cm yr − 1 near the uplands to 22 cm yr − 1 6 km down-Piedmont. These speeds are similar to 10 Be-estimated sediment speeds down three other Piedmonts in the Mojave Desert, suggesting that Piedmont surface morphologies dominated by shallow migrating channels have similar sediment transport rates. The timing of surface process change down the East Range Road Piedmont is determined by a combination of sediment available in the source basins, sediment transport rates, and the size of the Piedmont.
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Late Quaternary history of the Chemehuevi Mountain Piedmont, Mojave Desert, deciphered using 10Be and 26Al
American Journal of Science, 2005Co-Authors: Kyle K. Nichols, Paul R. Bierman, Martha Cary Eppes, Marc W. Caffee, Robert C. Finkel, Jennifer LarsenAbstract:We used the cosmogenic nuclides, 10 Be and 26 Al, as cosmic-ray dosim- eters to track sediment movement across the incised Chemehuevi Mountain Piedmont surface. The Piedmont extends 12 km from highland source basins to an ephemeral wash at the toe of the Piedmont. Nuclide activity in sediment from steep source basins and from the bedrock pediment allows us to estimate rates of sediment generation and thus the rate at which sediment is supplied to the Piedmont from weathering rock. Analysis of amalgamated sediment samples, collected along 4-km-long transects spaced at 1 km intervals from the mountain front provide context for understanding nuclide activity in sediment samples collected from two soil pits and demonstrate that sediment steadily moves down the channel network. Samples from the two soil pits allow for estimates of sediment deposition rates and thus further illuminate Piedmont history. Model results suggest that the Chemehuevi Mountains are eroding about 40 mm ky 1 whereas the mountain-proximal bedrock pediment and the interPiedmont Saw- tooth Range are eroding more slowly, 10 to 21 mm ky 1 and 9.5 mm ky 1 , respectively. Cosmogenic nuclide profiles in two soil pits suggest a complex history of deposition (at rates between 19 to 39 mm ky 1 ) and stability over the past 60 ky. A change in process from sediment deposition to sediment transport occurred distally on the Piedmont approximately 8 ky ago, while the mid-Piedmont Piedmont surface has been stable since the mid-Holocene. The incised Chemehuevi Mountain Piedmont is changing at rates similar to planar and uniformly active Piedmonts such as those adjacent to the Iron and Granite Mountains. All three Piedmonts have average sediment grain velocities of decimeters per year, long-term source basin erosion rates between 35 to 40 mm ky, depositional hiatuses around the Pleistocene-Holocene climatic transition from moister to drier conditions, and Pleistocene deposition rates of 18 to 39 mm ky. Such similarity in Piedmont behavior, despite clear differences in morphology and appearance, might suggest large scale geologic and climatic controls on the generation, transport and deposition of sediment in the Mojave Desert.
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Quantifying sediment transport on desert Piedmonts using 10Be and 26Al
Geomorphology, 2002Co-Authors: Kyle K. Nichols, Paul R. Bierman, Roger Leb. Hooke, Erik M. Clapp, Marc W. CaffeeAbstract:In situ produced 10 Be and 26 Al, measured in 40 sediment samples collected from the Iron and Granite Mountain Piedmonts, eastern Mojave Desert, provide a unique view of Piedmont modification processes and process rates over the 10 3 to 10 5 year time scale. Cosmogenic nuclide-based models suggest that the Iron and Granite Mountains generate 0.11–0.13 and 0.082–0.097 m 3 of sediment per year per meter of rangefront, respectively. The sediment moves down the Piedmont in an active transport layer (ATL), which is 20 to 30 cm thick (based on visual observations, measurements of depth to a buried B-horizon, cosmogenic nuclide data, and maximum ephemeral channel depths). Sediment in this layer is well-mixed vertically and horizontally on the 10 2 year time scale, indicating that the small ephemeral channels, which dominate the Piedmont surface migrate quickly. Interpretive models of increasing nuclide activities at depth in two pits suggest steady sediment deposition on the Piedmont (at rates between 17–21 and 38–45 m Ma � 1 ) until the late Pleistocene epoch, when a discontinuity to markedly lower nuclide activities in the isotopically well-mixed active transport layer suggests that deposition stopped, a significant change in Piedmont behavior. Nuclide activities in 10 amalgamated surface samples, each collected along a different 4-km-long transect, increase steadily away from the mountain front. Thus, we infer that sediment is uniformly dosed by cosmic rays as it is transported down the Iron and Granite Mountain Piedmonts. Interpretive models suggest that long-term average sediment speeds down the Iron and Granite Mountain Piedmonts are a few decimeters to a meter per year. D 2002 Published by Elsevier Science B.V.
Luca C Malatesta - One of the best experts on this subject based on the ideXlab platform.
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lag and mixing during sediment transfer across the tian shan Piedmont caused by climate driven aggradation incision cycles
Basin Research, 2018Co-Authors: Luca C Malatesta, Jean Philippe Avouac, Nathan D Brown, Sebastian F M Breitenbach, Jiawei Pan, Marie Luce Chevalier, Edward J Rhodes, Dimitri SaintcarlierAbstract:Transient sediment storage and mixing of deposits of various ages during transport across alluvial Piedmonts alters the clastic sedimentary record. We quantify buffering and mixing during cycles of aggradation-incision in the north Piedmont of the Eastern Tian Shan. We complement existing chronologic data with 20 new luminescence ages and one cosmogenic radionuclide age of terrace abandonment and alluvial aggradation. Over the last 0.5 Myrs, the Piedmont deeply incised and aggraded many times per 100 kyr. Aggradation is driven by an increased flux of glacial sediment accumulated in the high range and flushed onto the Piedmont by greater water discharge at stadial-interstadial transitions. After this sediment is evacuated from the high range, the reduced input sediment flux results in fluvial incision of the Piedmont as fast as 9 cm/yr and to depths up to 330 m. The timing of incision onset is different in each river and does not directly reflect climate forcing but the necessary time for the evacuation of glacial sediment from the high range. A significant fraction of sediments evacuated from the high range is temporarily stored on the Piedmont before a later incision phase delivers it to the basin. Coarse sediments arrive in the basin with a lag of at least 7 to 14 kyrs between the first evacuation from the mountain and later basinward transport. The modern output flux of coarse sediments from the Piedmont contains a significant amount of recycled material that was deposited on the Piedmont as early as the Middle Pleistocene. Variations in temperature and moisture delivered by the Westerlies are the likely cause of repeated aggradation-incision cycles in the north Piedmont instead of monsoonal precipitation. The arrival of the gravel front into the proximal basin is delayed relative to the fine-grained load and both are separated by a hiatus. This work shows, based on field observations and data, how sedimentary systems respond to climatic perturbations, and how sediment recycling and mixing can ensue.
