Ancient Martian Aeolian Sand Dune Deposits Recorded in the Stratigraphy of Valles Marineris and Implications for Past Climates. Issue 9 (31st August 2020)

• Record Type: Journal Article
• Authors: Chojnacki, Matthew; Fenton, Lori K.; Weintraub, Aaron Robert; Edgar, Lauren A.; Jodhpurkar, Mohini J.; Edwards, Christopher S.
• Is Part Of: Journal of geophysical research. Volume 125:Issue 9(2020)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2020-08-31
• Subjects: sand dunes -- sedimentary deposits -- Valles Marineris -- paleoclimates -- aeolian bedforms; Planets -- Periodicals; Geophysics -- Periodicals; 559.9
• DOI: 10.1029/2020JE006510
• Languages: English
• ISSNs: 2169-9097

Abstract

Abstract: Aeolian sediment transport, deposition, and erosion have been ongoing throughout Mars's history. This record of widespread aeolian processes is preserved in landforms and geologic units that retain important clues about past environmental conditions including wind patterns. In this study we describe landforms within Melas Chasma, Valles Marineris, that occur in distinct groups with linear to crescentic shapes, arranged with a characteristic wavelength; some possess slope profiles analogous to modern sand dunes yet show evidence for lithification. Based on the features' dimensions, asymmetry, and spatial patterns relative to modern equivalents, we interpret these landforms to be two classes of aeolian bedforms: decameter‐scale megaripples and sand dunes. The presence of superposed erosional features and depositional units indicates that these landforms were cemented and likely ancient. Melas paleodunes are found atop Hesperian‐aged layered deposits, but we estimate them to be younger, likely lithified in the Amazonian period. Although a range of degradation was observed, some paleodunes are >10 m tall and maintain steep lee sides (>25°), an uncommon scenario for terrestrial examples as other geologic processes lead to dune obliteration. The preserved paleobedform geometries are largely consistent with those of modern aeolian indicators, suggesting no major shifts in wind regime or contributing boundary conditions. Finally, we propose that their appearance and context require sequential periods of dune migration, stabilization following catastrophic burial, cementation, differential erosion, exposure, and burial. The presence of wholly preserved duneforms appears to be more common on Mars compared to the Earth and may signal something important about Martian landscape evolution. Plain Language Summary: Wind‐driven sand dunes are common on modern Mars, and the presence of certain sedimentary rock layers indicates that these landforms occurred there in the past. Here, we explore features in the canyons of Valles Marineris that show characteristics frequently attributed to dunes, yet evidence for their lithification and burial is clear. Their horizontal extent, height, shape, slopes, and collective spatial patterns led to our interpretation of them as lithified dune fields. The heavily eroded appearance along with superposed elements such as craters and boulders led to the conclusion that these are relatively ancient landforms. Despite this erosion, this level of preservation is rare for terrestrial sand dunes due to erosion and tectonics, thus providing an opportunity to reconstruct the various factors contributing to their history. Understanding the circumstances that led to the preservation of these ancient duneforms will yield crucial information regarding planetary sedimentary processes and the geologic history of the region. Key Points: Sedimentary deposits were identified in Valles Marineris and interpreted as ancient aeolian dune fields with a range of preservation states Their preservation indicates a complex history with periods of migration, burial, stabilization, cementation, exhumation, and erosion Paleodune morphologies compared with modern indicators suggest no major shifts in wind regime have occurred since their stabilization