The Curiosity rover is exploring Hesperian-aged stratigraphy in Gale crater, Mars, where a transition from clay-bearing units to a layered sulfate-bearing unit has been interpreted to represent a major environmental transition of unknown character. We present the first description of key facies in the sulfate-bearing unit, recently observed in the distance by the rover, and propose a model for changes in depositional environments. Our results indicate a transition from lacustrine mudstones into thick aeolian deposits, topped by a major deflation surface, above which strata show architectures likely diagnostic of a subaqueous environment. This model offers a reference example of a depositional sequence for layered sulfate-bearing strata, which have been identified from orbit in other locations globally. It differs from the idea of a monotonic Hesperian climate change into long-term aridity on Mars and instead implies a period characterized by multiple transitions between sustained drier and wetter climates.

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