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Abstract

Here we present our analysis of HiRISE imaging revealing the presence of scour marks, curvilinear and parallel-sided furrows, and chains of linked and overlapping pits over the larger Martian basins basins, along with meter-sized boulders distributed in clusters and circular mounds, present as isolated features and also in clusters, and covered with small boulders. We show that the association of scour marks with clusters of boulders and mounds can be related to the dual processes of ice keel scouring and ice rafting of both glacial and non-glacial detritus. These processes are well documented on Earth, where they result in distinctive morphologies and sedimentary patterns recognizable on the ocean floor, comparable to those we identified on Mars. The Martian outflow channels may have been subject to erosion and deposition associated with glacial action or ice streaming within ancient ice sheets, including upstream glaciation in the form of moraines, till deposits, eskers, and kame and kettle topography. Icebergs formed at the glaciers termini would have calved seaward of the grounding lines and drifted across the cool northern oceans, carrying with them supraglacial and englacial debris that was deposited on the seafloor as they melted and ablated. Where they ran around, the icebergs created distinctive grooves, chains of craters and mounds on the seafloor all over the Martian lowlands. We conclude that these features can be interpreted as proxy indicators of the former presence of icebergs and sea ice floating in ancient cold oceans on Mars.