Figure 1

Environmental setting of the study area. (a) Map of China showing the major atmospheric circulation systems: EAWM - East Asian Winter Monsoon and EASM - East Asian Summer Monsoon. (b) Digital elevation map of northern China showing the northeastern Tibetan Plateau, the Yellow River and the Yinchuan Plain. The map was generated using ArcGIS 10.0 (https://www.arcgis.com/features/), elevation data were obtained from the Digital Elevation Model (DEM) (90 m × 90 m), provided by the International Scientific & Technical Data Mirror Site, Computer Network Information Center, Chinese Academy of Sciences (http://www.gscloud.cn). (c) Geological map showing the location of drill core PL02. Figure 1a and c were all produced using CorelDraw Graphics Suite 2017 (http://www.coreldraw.com/cn/?topNav=cn).