Yardangs on Earth and implications to Mars: A review

Yardangs, as typical aeolian landforms, are extensively identified in arid/hyper-arid areas on Earth and other terrestrial bodies. In this review, based on analyses of Cmorphology, distribution, age, climate, and geologic condition of yardangs worldwide, we (1) assess the impacts of various controlling factors on yardang development to generalize a model based on morphology; (2) illustrate the climate-driven mechanism for yardangs; (3) propose a geomorphological evolutionary model of yardang fields; and (4) discuss potential implications of the above two models of yardang evolution on Earth to Mars. It is demonstrated that both deflation and abrasion work on yardang development, and it is the lithology to determine which one will be more effective. In addition, the wind action dominates the general aerodynamic form of yardangs, while non-aeolian factors account for the diversity in yardang morphology. Thus, a model including four stages and initiating mechanisms is generalized for yardang processes, from initiation to demise. The synthetic analyses of meteorological data, chronology, and paleoclimatic proxies show that yardang development is mostly controlled by westerlies, and would be accelerated during glacial periods and interrupted by lake formation during interglacial periods due to dry-humid fluctuations and changes in atmospheric circulation, driven by variations in solar radiation at orbital scales. This leads to the zonal distributions of yardangs near 30 degrees in both hemispheres. Depressions would be created or enlarged in yardang fields during glacial period, along with activities of dust release and transport, leading to aeolian deposition (e.g. loess) downwind. The depressions, then, could be turned into lakes during wet phase of interglacial period and evolved into newyardangs in the following glacial period due to wind erosion. This climate-controlled geomorphological process under glacial-interglacial cycles suggests that high accumulation rate in sediments from enclosed inland basins (e.g. the Qaidam Basin) doesn'tmean high-resolution climatic record due to the hiatus by wind erosion, indicating the significance of robust chronology establishment before any climatic correlation. Under the rules of Earth-based yardang evolution, it is potential to identify the specific level of development and explore the geomorphological processes as well as the climatic background for yardangs on Mars. (C) 2020 Elsevier B.V. All rights reserved.