The megaripples formed under the condition of multi-modal grain size distribution are considered to be intermediate-scale landforms between normal ripples and dunes. Field investigation shows that the megaripples in the Qaidam Basin are diverse in scale and shape, and a single mechanism seems to be unable to explain their formation. We propose that the formation of megaripples follows three evolution modes, presenting three states: transient, steady, and unstable. Transient megaripples are characterized by small scale, a small range of grain size and a short evolution cycle, which are the result of coarse grains gathering to the crest due to sand sorting; Steady megaripples are characterized by large scale, a wide range of grain size, stratified sedimentary structure and a long evolution cycle. The bimodal sand transport mechanism of the creeping of coarse particles caused by the impact of jumping fine particles shapes the surface armouring and stratified sediment; The scale and grain size range of the unstable megaripple is between the two. The strong wind causes the coarse particles to undergo a brief saltation movement, forming a small-scale secondary ripple. To test this hypothesis, we investigated their wind regime, morphology, grain size, sedimentary structure, and age. We find that the retardation effect of coarse particles relative to fine particles controls the erosion and deposition of megaripples and affects their scale and sedimentary structure. This will help us understand the coexistence of different scale ripples and Transverse Aeolian Ridges on Mars.The megaripples formed under the condition of multi-modal grain size distribution are considered to be intermediate-scale landforms between normal ripples and dunes. Field investigation shows that the megaripples in the Qaidam Basin are diverse in scale and shape, and a single mechanism seems to be unable to explain their formation. We propose that the formation of megaripples follows three evolution modes, presenting three states: transient, steady, and unstable. Transient megaripples are characterized by small scale, a small range of grain size and a short evolution cycle, which are the result of coarse grains gathering to the crest due to sand sorting; Steady megaripples are characterized by large scale, a wide range of grain size, stratified sedimentary structure and a long evolution cycle. The bimodal sand transport mechanism of the creeping of coarse particles caused by the impact of jumping fine particles shapes the surface armouring and stratified sediment; The scale and grain size range of the unstable megaripple is between the two. The strong wind causes the coarse particles to undergo a brief saltation movement, forming a small-scale secondary ripple. To test this hypothesis, we investigated their wind regime, morphology, grain size, sedimentary structure, and age. We find that the retardation effect of coarse particles relative to fine particles controls the erosion and deposition of megaripples and affects their scale and sedimentary structure. This will help us understand the coexistence of different scale ripples and Transverse Aeolian Ridges on Mars.

Megaripple, Aeolian processes, Qaidam Basin, Mars