Yardang geometries in the Qaidam Basin and their controlling factors

The hyperarid Qaidam Basin features extensive fields of yardangs (covering an area of ~ 40,000km2) sculpted in tectonically folded sedimentary rocks. We extracted the geometries of 16,749 yardangs, such as length-to-width ratio (L/W), spatial density, and spacing, from multi-source remote sensing data provided by Google Earth™. We classified the yardangs into four types based on their L/W: short-axis (1-2), whale-back (2-6), hogsback (6-10) and long-ridge (10 − 210). We interpreted the yardang geometries in the context of their geologic setting (bedding orientation, location along anticline crests or syncline troughs, and lithologic heterogeneity). Our results show that the yardang geometries in the Qaidam Basin are mainly controlled by the structural geology and rheology of the sedimentary rocks (e.g., strike and dip of bedding, the presence or absence of interbedded soft and hard beds, and structural position with folds), the angle between geomorphically-effective wind directions and the strike of bedding, and the relative cumulative wind shear force where two geomorphically-effective wind directions are present. Our analysis revealed the following: 1) nearly 69% of the yardangs with long-ridge and hogsback geometries are distributed in syncline areas whereas 73% of the yardangs with short-axis geometries are distributed in anticline areas; 2) the L/W ratio of yardangs exposed along the windward limbs of anticlines is lower than that of yardangs exposed along the leeward limbs; and 3) in the westernmost parts of the basin, yardangs are locally sculpted into mounds by two geomorphically-effective wind directions.