Although Neogene climate change reconstruction in central Asia is important for understanding global cooling, Asian monsoon evolution, and the Tibetan Plateau stepwise uplift during the Cenozoic, the paleoenvironmental evolution during the Paleogene in this region is still ambiguous due to a lack of corresponding continuous and complete terrestrial records with precise age constraints. Recently, a new fluvial sedimentary sequence with magnetostratigraphic ages spanning from ∼53 to 40 Ma was found in the Linxia Basin, NE Tibetan Plateau, thereby providing a window to understand Eocene climate change in the Asian interior. From this fluvial sedimentary sequence, we present early‐middle Eocene hydroclimate variations based on a combined method of rock magnetism and diffuse reflectance spectroscopy. Our results show magnetic enhancement of fluvial sediments at 51.7 Ma resulted from abundant single‐domain magnetite inputs from the surrounding mountains through strong erosion and transport in a relatively wet environment. Subsequently, at 47.6 Ma, magnetic weakening of floodplain sediments corresponds to an increase in hematite concentrations produced via low‐temperature oxidation in a prolonged dry environment. Comparisons of paleoclimatic proxies, such as organic geochemistry and rock magnetism from neighboring basins, tectonic deformation of the NE Tibetan Plateau, and sea level change in the Paratethys Sea suggest that the hydroclimate variation from relatively wet to dry climate in the early‐middle Eocene in this area was mainly controlled by global climatic change and probably superimposed by the uplift of the Tibetan Plateau.
Thick eolian loess sequences in arid Central Asia (CA) contain a wealth of information on the intensity variations of midlatitude westerlies and the aridification history of the nearby deserts. In this study, detailed lithologic and magnetostratigraphic investigations suggest that loess deposits on the western margin of the Pamir Plateau began to accumulate at around 2.7 Ma, representing the most complete and oldest loess‐paleosol sequence in western CA. The widely distributed continuous loess deposition in the region suggests a rapid desiccation of CA during the late Pliocene. A synthesis of the initial timing and spatial distribution of late Cenozoic eolian deposits on the Eurasian continent further demonstrates that the dramatic increase in global ice volume exerted a dominant role in the expansion of eolian loess deposits in CA, China, and Europe, and middle Pleistocene expansion is a crucial precondition for the establishment of modern distribution patterns of the Eurasian loess belt.
The Tibetan Plateau (TP) and its adjacent areas are located in the transitional zone of the high and cold mountainous regions, monsoonal humid regions, and arid regions of Central Asia. The TP is the highest plateau on Earth, with a complex terrain of plateaus, broad basins, high mountains, arid deserts and lakes. Due to its unique geographical location, the TP is influenced by the East Asian and Indian summer monsoons, and the Westerlies circulation (Chen et al., 2019;Machalett et al., 2008). Characterizing and interpreting the precipitation and temperature gradients across this vast region can potentially improve our knowledge of the effects of topography and atmospheric circulation on regional climatic patterns and the origins of dust outbreaks in the Asian interior. However, because of the sparse distribution of meteorological stations in the region, our understanding of the climatic gradients across the TP relies mainly on numerical simulations or satellite data. The climatic boundary (i.e., of precipitation and temperature) across the TP is still debated (
Although ventifacts are often utilized to determine past and present wind directions and sediment mobilities in arid, coastal, and periglacial environments, their morphodynamics have not been well understood. In this study, based upon the principles of classical mechanics, the abrasion rate of ventifact is analytically expressed by the elastic properties of rock or mineral components and the mass flux density of sediment transported by wind. The unknown abrasion coefficient can be estimated via wind tunnel experiments. The practicability of this novel formula is shown by the calculation of short-term abrasion depth of ventifacts over a desert pavement. It is expected that the current work will improve the quantitative reconstruction of paleo-environments and paleo-climates using ventifacts.
Thick eolian sediments in Eurasia, mainly distributed in the Chinese Loess Plateau (CLP), Central Asia and Europe, have long been intensively investigated as important and valuable terrestrial Quaternary paleoclimate and paleoenvironment media (Kukla, 1975;T. Liu, 1985;Dodonov, 1991;Forster & Heller, 1994). Over the past three decades, eolian loess deposits in these areas were widely used to explore the evolution of westerly and East Asian monsoons and the aridification of Asian inland (An, 2000;Fang et al., 2020;Guo et al., 2002), due to their continuous deposition, long timespan and high resolution. In fact, in addition to paleoclimate reconstruction, eolian loess deposits also contain physical erosion information of dust source regions. Continental erosion processes could modify the surface topography and the clastic materials in dust source regions (Haeuselmann et al., 2007), thereby exerting an important influence on the geochemical and mineralogical composition of loess deposits.
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