Eolian cannibalism: Reworked loess and fluvial sediment as the main sources of the Chinese Loess Plateau

Title of Publication: 
Eolian cannibalism: Reworked loess and fluvial sediment as the main sources of the Chinese Loess Plateau
Licht, A., Pullen, A., Kapp, P., Abell, J., and Giesler, N.
Publication Info: 
GSA Bulletin; May/June 2016; v. 128; no. 5/6; p. 944–956; doi: 10.1130/B31375.1; 9 figures; 2 tables; Data Repository item 2016026; published online 8 January 2016.

The loess and paleosol sequences of the Chinese Loess Plateau are composed of Quaternary dust, the origin of which has been the subject of considerable debate. Some recent U-Pb geochronological studies of eolian zircons have proposed the existence of two major wind pathways: from the north and northwest, through the Badan Jaran, Tengger, and Mu Us Deserts during interglacials, and from the west, through the Qaidam Basin during glacials. Others have emphasized the importance of Yellow River sediment supply in the Chinese Loess Plateau sediment budget. However, tracking dust source regions through U-Pb dating in a statistically robust manner is particularly complex given the similar age peaks in the age probability distributions of potential source regions in Central Asia. This paper presents 2410 new U-Pb ages of detrital zircons from wind-eroded strata, Quaternary eolian deposits, and modern river sands in central China in order to increase the robustness and the spatial resolution of zircon age distributions in dust source regions. We then propose a new mixture modeling technique to statistically address the contribution of these different sources to the Chinese Loess Plateau sedimentary budget. Our contribution estimates indicate that eolian supply to the Chinese Loess Plateau is dominated (60%–70%) by reworking of Yellow River sediment. Moreover, evidence of Qaidam Basin–sourced zircons (15%–20%) in both loess (glacial) and paleosol (interglacial) layers corroborates the existence of an erosive wind pathway through the Qaidam Basin during glacials and implies that a substantial portion of the interglacial dust is recycled from older glacial loess. We propose that sediment reworking of Yellow River sediment and older loess deposits by wind on the Chinese Loess Plateau homogenized the eolian zircon populations toward a glacial provenance due to higher (2–20 times) dust accumulation rates during glacials. These findings suggest that the Chinese Loess Plateau has evolved as a more dynamic landform than previous thought, where wind deflation, fluvial input, lateral transport, and accumulation of sediment are equally important. These internal reworking effects would then significantly bias the paleoclimatic interpretations based on eolian dust properties of the Chinese Loess Plateau.

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Figure 1. Schematic map of Central Asia, showing the modern, simplified dust-storm tracks and near-surface wind patterns (red arrows), throughout the (A) Mu Us, (B) Tengger, and (C) Badan Jaran Deserts, and the hypothetical “glacial” dust-storm track (blue arrows), through the Qaidam Basin and across northern and central Tibet (Pullen et al., 2011).