An Aeolian Depositional Sequence Shaped by Near‐Surface Water at the Base of the Layered Sulfate Unit, Gale Crater, Mars

Abstract The basal strata of the orbitally defined Layered Sulfate unit (LSu) in Gale crater, Mars, marks the end of a major mineralogical transition from clay‐to sulfate‐bearing stratigraphy. This has previously been attributed to a period of significant aridification of Gale's climate. Here, we present ground‐based observations by the Curiosity rover of the sedimentary facies and architecture of the basal strata of the LSu, and reconstruct the past depositional environments. The succession predominantly comprises four members of the Mirador formation: the Contigo, Catrimani, Amapari, and Chenapau members. The Contigo member records the migration of simple aeolian dunes. The Catrimani and Chenapau members record a facies characteristic of wind‐ripple migration in aeolian sand sheets. Periodic damp sand sheet deposition is inferred through candidate adhesion structures and evaporite crystals. Evidence for periodic surface water occurs as lacustrine deposits (the Amapari member) and an embedded fluvial lens. Near‐surface water likely restricted the availability of loose sediment, suppressing dune formation and promoting the accumulation of a thick sandsheet succession that, at ∼60 m, exceeds known terrestrial equivalents. Deposition under these conditions would have required a continuously rising water table, but the rate of sediment accumulation was likely high enough for a predominantly aeolian environment. Contrary to earlier aridification models for the LSu, this basal succession likely records an overall aeolian environment controlled by a rising water table in Gale crater during the Hesperian.