Fig 1.
Digital elevation model (DEM) map of northern China.
Zone I-sandy loess; zone II-loess; zone III-clayey loess. The decrease in loess grains from northwest to southeast is consistent with the northwesterly winter monsoon winds over East Asia. The desert and mountains are indicated (adapted from [55]).
Fig 2.
Correlation map between multiple correlation coefficient (R2) and number of end-member (a), and three selected end members (b).
Fig 3.
Relative and accumulative frequency of 44 representative samples selected from the Sikouzi grain-size sequence are correlative to 3 end members in Fig 2, and their distribution in a C-M plot (red cross) is in contrast with that of the Mississippi river samples (gray triangles, [31]).
The former is parallel to line C = M while the latter shows an L shape.
Fig 4.
Grain size distribution of the Sikouzi fine samples in a C-M plot during past 20 Ma and during different time intervals.
Fig 5.
Variations of three end members of the Sikouzi grain-size sequence spanning the past 20 Ma plotted against paleomagnetic ages and its correlation with the integrated δ18O curve [37].
For each time interval, the solid line is linear fitting and the solid curve is averaging with a window width of 11 data points.
Fig 6.
Power (a) and evolutive (b) spectrums over the past 20 Ma on the detrended EM 2 data of Sikouzi grain-size record. Note that the 405-kyr period kept strong over the past 20 Ma and the 100-kyr period weakened since ~10 Ma.