A large sedimentary basin in the Terra Sirenum region of the southern highlands of Mars

► Sedimentary basin in Terra Sirenum contains evaporites and phyllosilicates. ► Areal extent of at least 30,000 km2 and depth of approximately 200 m. ► Aqueous conditions early in the history of the planet dated to approximately 3.9 Ga. ► Normal and inverted fluvial channels with fan deposits at their termini.