Geologic Characteristics Of Yardangs On Mars And Their Implications For Paleo-Environments

Wind-eroded ridges known as yardangs are common in most arid desert regions on Earth.They also have been reported on the other planets,i.e.Venus,Titan,and Mars,especially in the Aeolis-Zephyria Planum?AZP?region,west of the Medusae Fossae Formation?MFF?,which are abount of various yardangs.Previous investigations have reported their types,distributions and formations.However,the limited coverage of high-resolution images has constrained the size of research areas in previous studies,and small-sized yardangs of different types have been reported recently.Previous models only account for a few yardangs formations,and the evolution among different yardang types remain uncertain and demand further studies,which means that more analogue studies are required to better understanding the formation history and relevant climate environment of the martian region.As the largest yardang fields in China,Qaidam Basin is rich in various Mars-like yardangs,which can also shed light on the geological history of Mars.To fully understand the formation and evolution of Martian yardangs,we carried a detailed identification and investigation of yardangs in the Qaidam Basin on Earth and Aeolis-Zephyria region on Mars with multiple high-resolution images.Then,we conducted a comprehensive analysis and comprision study about their similarities and differences in morphologies and evolution models.And finally,combined with geomorphic features,regional volcanic activities and fluvial activities.we tried to explor the paleo-environments of AZP region on Mars.On the basis of their morphologies and distributions.we have classified the yardangs in the Qaidam Basin into 11 different types and sort them into 4 groups?Mesa group,Long-rdge group,Sawtoothed group,and Whaleback group?.Most of them are distributed in the northwestern and central eastern parts,with dominant orientations northwest to north-northeast and approximately west to east,respectively.The average aspect ratios for the Mesa group and the Whaleback group yardangs are nearly 3:1,while those for most of the Long-ridge group yardangs are greater than 5:1.The height of yardangs in the Qaidam Basin exhibit obvious type and regional differences.Most of them are below 20m,with an average value of 6.42 m.The evolution processes of yardangs in the Qaidam Basin can be divided into four stages?embryonic,adolescent,mature,and receding?,which indicates a full suite of cyclic yardang evolution,during which the evolution processes may have been interrupted at some stages due to differences in the competence of rocks and/or change of environment.The coverage area of yardangs in the AZP region is³.67×10⁵ km²,most of which are distributed in the Aeolis Planum,Zephyria Planum and the AZP central basin.We have identified 11 different types of yardangs in the AZP region and sort them into 4groups as well?Mesa group,Long-rdge group,Sawtoothed group,and Whaleback group?.The mean aspect ratios of the W group yardangs is about 3:1,and over 98%of them are less then 5:1.While over 81%aspect ratios of the L group yardangsare greater then 5:1.Most of the height?over 72.5%?of the yardangs is less than 100 m,with a mean value of72.86m.The orientation of yardangs in the e Aeolis Planum and the AZP central basin is NW-SE and S-N near the high land,while in the Zephyria Planum,the major orientatons are S-N,W-E,NE-SW,and SE-NW.The ages of post-formation modification of the ejecta are concentrated on 490-630Ma?Late Amazonia?,indicating a obvious decline of wind erosion rate.The original age the crater ejecta,partially covered by the MFF,is 3.48 Ga?early Heperian?,which means that the accumulated of the MFF material is earlier than Heperian,and the formation of yarangs should be later than that.The possibility formation age of the W-H type yardangs in the AZP central basin is earlier than520_-50⁺⁵⁰Ma from a creter covered on the MFF yardangs.Both of the yardangs in the Qaidam Basin on Earth and in the AZP region on Mars have similar morphologic and geometric characteristics,and may have experienced similar multi-stage evolution processes.The formation of the MFF material is discontinuous,and yardangs form within the breaks.The accumulation of MFF in the AZP region experienced at least four breaks and the prevailing wind regime has changed dramatically at least four times.