Periodic bedrock ridges on Mars

Abstract

[1] Evidence for sediment transport and erosion by wind is widespread over the surface of Mars today and was likely a major geomorphic process for much of its geological past. Although Martian surface features resembling aeolian dunes and ripples have been recognized since the Mariner and Viking missions, such features have been interpreted previously as active, indurated, or exhumed sedimentary forms. Here we report evidence based on High Resolution Imaging Science Experiment images that show some megaripple forms are eroded into cohesive substrate rather than being composed of loose granular material or fossilized dunes. Exposure of stratigraphic continuity within layered, cohesive material extending crest to trough through features with mean wavelengths of 18 to 51 m demonstrates the primarily erosional formation of what we term periodic bedrock ridges (PBRs). Hence some surfaces on Mars previously considered to be covered by winddeposited material are actually wind-carved exposures that offer windows into Martian history. PBRs lack the distinctive streamlining associated with wind-parallel yardangs and comparison of PBR orientation to yardangs, megayardangs, and active sedimentary dunes in the same vicinity confirm that these PBRs formed transverse to prevailing winds. Observed wavelengths of PBRs are comparable to those predicted by a simple model for erosional wavelengths of periodic transverse bed forms owing to the spacing of flow separations within the flow. Recognition of these transverse aeolian erosional forms brings up the question of how widespread Martian PBRs are and how many have been misinterpreted as active or indurated (fossilized) sedimentary dunes.

Gale crater: the Mars Science Laboratory/Curiosity Rover Landing Site

“…Sharp. Montgomery et al (2012) have recently inferred an erosional origin for landforms of similar appearance and scale elsewhere on Mars, which would be consistent with the north-south orientation of yardang-like structures carved into strata overlying the ridged material (Fig. 4(c)).…”

The birth and death of transverse aeolian ridges on Mars

“…Antidunes on Earth are both erosional and depositional and can be carved into planar surfaces. This might explain the appearance of deltoid‐like erosion of rock surfaces in Hellas (PSP_008427_1380) and the puzzling periodic bedrock ridges that resemble TARs but are clearly erosional in origin [ Montgomery et al ., ]. Erosion and dust deposition may be achieved by a common atmospheric process.…”

Formation of gravel-mantled megaripples on Earth and Mars: Insights from the Argentinean Puna and wind tunnel experiments

“…Indeed, the superposition relationships of such granule ripples with small craters along the MER Opportunity traverse path indicate that these bedforms have been static for on the order of 10 5 years (Golombek et al, 2010). This may also explain why some Martian large transverse bedforms are aligned, and apparently fixed upon, the crests of periodic bedrock ridges that have been hypothesized to form from aeolian erosion (Montgomery et al, 2012) (Fig. 1).…”