Inverted channel belts and floodplain clays to the East of Tempe Terra, Mars: Implications for persistent fluvial activity on early Mars

•Inverted sinuous ridges and candidate floodplain clays were found to the east of Tempe Terra on Mars.•The inverted ridges may represent exhumation of the channel belts and overbank deposits.•The findings imply prolonged fluvial activity on early Mars, potentially for tens of thousands of years. The climate on early Mars is one of the major unsolved problems in planetary science. It is unclear whether early Mars was warm and wet or cold and icy. Morphological features on Mars such as sinuous ridges could provide critical constraints to address this issue. Here we investigate several sinuous ridges to the east of Tempe Terra, located at the dichotomy boundary of the highland terrain and lowland plains and find these ridges may have recorded persistent fluvial activity on early Mars. Our analysis indicates that these ridges may represent exhumation of the channel belts and overbank deposits formed from meandering rivers over significant geologic time. Layered smectite-bearing minerals are distributed along the flank of the ridges, and could be detrital or authigenic floodplain clays. Our interpretation of the stratigraphic relationships indicates that the layered smectite-bearing materials lie between channel belt deposits, which has rarely been previously reported on Mars and supports the floodplain interpretation. Our results suggest a persistent warm period, perhaps triggered by volcanism, impacts, and/or variations in planetary obliquity, that persisted for a geologically significant interval (tens of thousands of years) during the Noachian period of Mars.