Wavelet analysis of concentric crater fill surface ridges

Abstract

Concentric crater fill (CCF) are debris-covered ice deposits widespread in the mid-latitudes of Mars, which often exhibit ridges parallel to the crater walls. Surface ridges on debris-covered glaciers, which may be due to englacial or supraglacial debris transport, can provide insight into past climate variations. Alternatively, ridges may be related to non-climatic processes such as viscous buckle folding due to compression. We test the hypothesis that surface ridges on CCF are related to climate variations, driven by variations in orbital parameters, by identifying periodicities in CCF ridges and, where possible, comparing ratios of pairs of wavelengths to ratios of orbital periodicities. We identified wavelengths in surface ridges on concentric crater fill using wavelet analysis of profiles across HiRISE images and DTMs. For 68 % of CCF sites, we identified at least one significant wavelength, and identified a median wavelength of ∼33 m from brightness profiles. For elevation profiles, we found a median wavelength of ∼32 m. We identified only five cases with two wavelengths overlapping over a significant distance along profile that appeared to correspond to distinct periodicities. These rare cases did not have ratios clearly related to ratios of two orbital periodicities. Based on this, our results do not support the idea that CCF ridge spacing is related to orbital periodicities. We favor the possibility that CCF ridge spacing is instead due to buckle folding. The median wavelength of CCF ridges is consistent with buckle folding for a debris/ice viscosity ratio of 1–2 and a debris layer thickness of 6–8 m.