Ancient Winds, Waves, and Atmosphere in Gale Crater, Mars, Inferred From Sedimentary Structures and Wave Modeling

Wave modeling and analysis of sedimentary structures were used to evaluate whether four examples of symmetrical, reversing, or straight-crested bedforms in Gale crater sandstones are preserved wave ripples; deposition by waves would demonstrate that the lake was not covered by ice at that time. Wave modeling indicates that regardless of atmospheric density, winds that exceeded the threshold of aeolian sand transport could have generated waves capable of producing nearshore wave ripples in most grain sizes of sand. Reversing 3-m-wavelength bedforms in the Kimberley formation are interpreted not as wave ripples but rather as large aeolian ripples that formed in an atmosphere approximately as thin as at present. These exhumed bedforms define many of the ridges at outcrops that appear striated in satellite images. At Kimberley these bedforms demonstrably underlie and therefore predate subaqueous beds, suggesting that a thin atmosphere existed at least temporarily before subaqueous deposition ceased in the crater. The other three candidate wave ripples (Square Top, Hunda, and Voe) are consistent with modeled waves, but other origins cannot be excluded. The predominance of flat-laminated (non-rippled) beds in the lacustrine Murray formation suggests that some aspect of the lake was not conducive to formation or preservation of recognizable wave ripples. Water depths may generally have been too deep, lakebed sediment may have been too fine-grained, the lake may have been smaller than modeled, or the lake may have been covered by ice.

Automated summary

Wave modeling and sedimentary structure analysis suggest that some bedforms in Gale crater sandstones may be preserved wave ripples, indicating that the lake was not covered by ice. However, other bedforms are interpreted as aeolian ripples formed in a thin atmosphere. The presence of predominantly flat-laminated beds in the lake suggests that conditions were not conducive to the formation and preservation of recognizable wave ripples, possibly due to deep water, fine-grained sediment, or ice cover.