Investigating the Role of Amazonian Mesoscale Wind Patterns and Strength on the Spatial Distribution of Martian Bedrock Exposures. Issue 11 (18th November 2022)

• Record Type: Journal Article
• Authors: Gary‐Bicas, C. E.; Michaels, T. I.; Rogers, A. D.; Fenton, L. K.; Warner, N. H.; Cowart, A. C.
• Is Part Of: Journal of geophysical research. Volume 127:Issue 11(2022)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2022-11-18
• Subjects: Mars -- bedrock exposures -- material properties -- atmosphere -- erosional processes -- mesoscale; Planets -- Periodicals; Geophysics -- Periodicals; 559.9
• DOI: 10.1029/2022JE007496
• Languages: English
• ISSNs: 2169-9097

Abstract

Abstract: The Martian highlands contain Noachian‐aged areally‐extensive (>225 km 2 ) bedrock exposures that have been mapped using thermal and visible imaging datasets. Given their age, crater density and impact gardening should have led to the formation of decameter scale layers of regolith that would overlie and bury these outcrops if composed of competent materials like basaltic lavas. However, many of these regions lack thick regolith layers and show clear exposures of bedrock materials with elevated thermal inertia values compared to the global average. Hypothesized reasons for the lack of regolith include: (a) relatively weaker material properties than lavas, where friable materials are comminuted and deflated during wind erosion, (b) long‐term protection from regolith development through burial and later exhumation through one or more surface processes, and (c) spatially concentrated aeolian erosion and wind energetics on well‐lithified basaltic substrates. To test the third hypothesis, we used the Mars Regional Atmospheric Modeling System to calculate wind erosive strength at 10 regions throughout the Martian highlands and compared it to their thermophysical properties by using thermal infrared data derived from the Thermal Emission Spectrometer to understand the effect that Amazonian mesoscale wind patterns may have on the exposure of bedrock. We also investigated the effect of planet obliquity, Ls of perihelion, and atmospheric mean pressure on wind erosion potential. We found no evidence for increased aeolian activity over bedrock‐containing regions relative to surrounding terrains, including at the mafic floor unit at Jezero crater (Máaz formation), supporting the first or second hypotheses for these regions. Plain Language Summary: Several regions of Mars have exposed ancient bedrock materials (>∼3.6 billion years old) that should be buried underneath thick layers of granular material (regolith) that forms due to physical breakdown of the bedrock over prolonged periods of time. However, many regions lack regolith and have ancient bedrock exposures. One possible explanation for the spatial variability in bedrock exposure is that these rock materials break down into much smaller particles than typical Martian crustal materials, that are then carried away by wind, preventing a buildup of granular material. Another possible explanation is spatial variation in modern wind erosional patterns and strength. We used an atmospheric model and compared the spatial distribution of modeled wind strengths to that of exposed bedrock within the oldest regions on Mars to assess if there is any connection between exposed bedrock and Late Amazonian (250 Mya‐present) modern‐day wind patterns. We found no correlation between wind strength and exposed bedrock in these regions suggesting that material strength is the primary control on the present day distribution of bedrock exposure in Mars' older terrains. Key Points: There is no observed relationship between simulated Late Amazonian wind patterns and the spatial bedrock exposures Flat‐lying surfaces in craters have lower wind erosion potential (WEP) values than intercrater plains. Jezero crater floor had the lowest values Increased atmospheric pressure had the strongest effect on calculated WEP values