Preserved barform deposits in the Carolyn Shoemaker formation, Gale crater, Mars

The early environmental history of Mars is encoded within the planet's record of sedimentary rocks. Since 2012, the Curiosity rover has been ascending Mount Sharp, Gale crater's central mound, making detailed observations of sedimentary strata exposed there. The primary depositional setting represented by the rocks examined thus far has been a perennial lake, represented by the mudstones and sandstone lenses of the Murray formation. Here, we report on the sedimentology of outcrops examined in the Carolyn Shoemaker formation, which sits stratigraphically above the Murray formation. We interpret strata exposed in the eastern Knockfarril Hill, Glasgow, and Mercou members of the Carolyn Shoemaker formation to represent river bars in ancient alluvial and coastal settings based on sedimentary structures, stratal geometries measured from photogrammetric data, and erosional morphology. The transition from a lacustrine to a fluvial depositional setting records the aggradation and progradation of coastal rivers into what was previously the extent of the Gale lake system. This may have occurred due to the shrinking of the lake over time due to climate, or local three dimensionality in shoreline evolution, such as the formation of a new sedimentary lobe following a channel switch.