Possible frost mounds in an ancient Martian lake bed

Circular to elongated mounds are observed in Gusev crater in the Aeolis subquadrangle of Mars. They are arranged in a large cluster and show different stages of evolution, from fresh to scar structures. Their morphology and morphometric ratios are comparable to those of terrestrial frost mounds. This study shows how the paleolacustrine environment of the Ma'adim Vallis/Gusev crater hydrogeologic system may have provided a suitable environment for the formation of frost mounds. Alternate hypotheses of formation including volcanism, fluvial erosion, and eolian erosion are discussed. Other features such as heavings, curvilinear troughs, hills, ridges, and depressions support the idea of a sediment/ice interaction. The typology of the mounds and plausible mechanisms for their formation are proposed. Their presence could support the model of a massive water body in Gusev during the Amazonian and provide indicators of paleoenvironmental conditions at the time of their formation. (C) 2000 Academic Press.