Multiple Evolution Modes of Megaripples in the Qaidam Basin

Aeolian landforms provide valuable insights into the planetary surface environment and its evolutionary history. In this study, the formation and evolution of megaripples in the Qaidam Basin and their relationship with the development environment are analyzed. By quantifying the wind environment, morphology, grain size distribution, sedimentary structure, and optically stimulated luminescence (OSL) age of megaripples, we propose for the first time that there are multiple megaripple evolution modes. Investigation revealed that three evolution modes were responsible for forming megaripples in different equilibrium states: transient, stable, and metastable. Well-sorted coarse sand grains accumulate on ridges and overlay poorly-sorted fine sand grains to form transient megaripples. Stable megaripples have alternating sedimentary bedding of coarse and fine sand grains. Metastable megaripples have a secondary ripple formation on the surface. Throughout their formation, coarse and fine sand grains undergo recombination. The response of coarse grains to the change in wind speed lags behind that of fine grains. This process controls the erosion and accumulation of megaripples and affects their size and sedimentary structure. The evolution mode, scale, and sedimentary structure of megaripples are influenced by the grain size range under the same wind conditions. The OSL ages of the coarse-grained megaripple sediments are less than 700 years. This study provides a fresh perspective on the coexistence of various sand ripples and transverse aeolian ridges found on Mars.