The global distribution of depositional rivers on early Mars

Sedimentary basins are the archives of ancient environmental conditions on planetary surfaces, and on Mars they may contain the best record of surface water and habitable conditions. While erosional valley networks have been mapped, the global distribution of fluvial sedimentary deposits on Mars has been unknown. Here we generated an eight-trillionpixel global map of Mars using data from the NASA Context Camera (CTX), aboard the Mars Reconnaissance Orbiter spacecraft, to perform the first systematic global survey of fluvial ridges?exhumed ancient deposits that have the planform shape of river channels or channel belts, but stand in positive relief due to preferential erosion of neighboring terrain. We used large fluvial ridges (>70 m width) as a conservative proxy for the occurrence of depositional rivers or river-influenced depositional areas. Results showed that fluvial ridges are as much as 100 km long, common across the southern highlands, occur primarily in networks within intercrater plains, and are not confined to impact basins. Ridges were dominantly found in Noachian through Late Hesperian units, consistent with cessation of valley network activity, and occurred downstream from valley networks, indicating regional source-to-sink transport systems. These depositional areas mark a globally distributed class of sedimentary deposits that contain a rich archive of Mars history, including fluvial activity on early Mars. 2005). There has yet to be a systematic survey of fluvial ridges?exhumed ancient fluvial deposits (Burr et al., 2009; Williams et al., 2009, 2011, 2013; DiBiase et al., 2013; Davis et al., 2016, 2019; Cardenas et al., 2018; Hayden et al., 2019; Balme et al., 2020)?across the entire surface of Mars, which may potentially hold a yet richer record of environmental conditions than the topographic record of eroded valley networks. Unlike the surface of Earth, which is continually modified, Mars has had minimal tectonic activity and experienced cold and hyperarid conditions since valley network cessation (Fassett and Head, 2008a), which has led to the preserva

Automated summary

This study conducted the first systematic global survey of fluvial ridges on Mars using data from the NASA Context Camera, revealing their widespread distribution across the southern highlands and intercrater plains, representing ancient fluvial deposits that may offer a rich archive of Mars history, including fluvial activity on early Mars.