Abstract
As a key global climate and dust archive, the nature of Chinese loess generation, transport and deposition remains debated. The lack of consensus on dust dynamics from sources to leeward regions fundamentally limits interpretation of the preserved past climate and dust record. Here, we investigate chronostratigraphic variability of aeolian deposits in upwind regions of the modern Chinese Loess Plateau (CLP) and attempt to understand dust dynamics that potentially affects loess deposition downwind. The strata consist of alternating layers of typical loess, well-sorted sand, and sandy loess, with obvious unconformities occurring at the transitions from loess to sand. We suggest that pre-existing typical loess in regions to the northwest of the modern CLP was eroded by wind, providing a significant source of homogeneous dust for the dust deposits downwind. The sand deposits interbedded with typical loess at the study sites suggests that proximal deserts have greatly expanded and contracted repeatedly prior to the Holocene. However, the spatial extents of the deserts, as inferred from the sections here, have not markedly diminished after the major expansion during the Last Glacial Maximum. Such a pattern of proximal desert dynamics plays an important role in regulating dust emission and transport, strongly affecting dust sequences on the CLP. Our results suggest a complex scenario of dust dynamics in upwind regions of the CLP at least over the Late Quaternary; the involved processes have to be considered when using conventional proxies from Chinese loess deposits to recover the history of climate and dust changes.
Highlights
As one of the world’s key climate archives, Chinese loess deposits have been widely used to decipher changes in continental environments and atmospheric circulation on various timescales (e.g., Hovan et al, 1989; Liu and Ding, 1998; Guo et al, 2002; Sun et al, 2012; Licht et al, 2014)
These findings call for urgent reassessments of changes in potential sources of Chinese loess, of accepted interpretations of climatic proxies applied to loess deposits, such as sedimentation rate and grain size, of Quaternary dust dynamics in this globally important dust emission region, and even exactly how the Chinese loess time series can represent large-scale climatic changes
Our results provide insights into dust dynamics in regions upwind of the Chinese Loess Plateau (CLP), which are crucial for understanding environmental and climatic changes recorded by loess sequences from the CLP and in constraining the specific dust source areas of one of the most important dust source regions in the world
Summary
As one of the world’s key climate archives, Chinese loess deposits have been widely used to decipher changes in continental environments and atmospheric circulation on various timescales (e.g., Hovan et al, 1989; Liu and Ding, 1998; Guo et al, 2002; Sun et al, 2012; Licht et al, 2014). Multiple erosional hiatuses during the past 300 ka, recorded by loess deposits at Jingbian, provide independent evidence that supports the hypothesis of loess cannibalization from CLP marginal areas (Stevens et al, 2018) These findings call for urgent reassessments of changes in potential sources of Chinese loess, of accepted interpretations of climatic proxies applied to loess deposits, such as sedimentation rate and grain size, of Quaternary dust dynamics in this globally important dust emission region, and even exactly how the Chinese loess time series can represent large-scale climatic changes. This means the potential for pre-existing loess to act as a dust source and for the influence of proximal desert activity on loess accumulation on the CLP remains unclear
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