Fig. 2

Evidence for an aeolian origin of the studied red clay. a Field photograph of alternating reddish-brown clay and grey caliche nodule layers. b Mineral composition from X-ray diffraction results from bulk sediments for the studied red clay in Altun Shan, compared with Quaternary loess and red clay from Shilou⁶¹ (SL) on the Chinese Loess Plateau. c, d Average major and trace element distributions for the studied red clay from Altun Shan compared with red clay from Qin’an⁶². e Grain size distributions for the studied red clay from Altun Shan. f Scanning electron microscope image of representative quartz grains that illustrate the angular morphology of the grains