A Rock Record of Complex Aeolian Bedforms in a Hesperian Desert Landscape: The Stimson Formation as Exposed in the Murray Buttes, Gale Crater, Mars

Lithified aeolian strata encode information about ancient planetary surface processes and the climate during deposition. Decoding these strata provides insight regarding past sediment transport processes, bedform kinematics, depositional landscape, and the prevailing climate. Deciphering these signatures requires a detailed analysis of sedimentary architecture to reconstruct dune morphology, motion, and the conditions that enabled their formation. Here, we show that a distinct sandstone unit exposed in the foothills of Mount Sharp, Gale crater, Mars, records the preserved expression of compound aeolian bedforms that accumulated in a large dune field. Analysis of Mastcam images of the Stimson formation shows that it consists of cross-stratified sandstone beds separated by a hierarchy of erosive bounding surfaces formed during dune migration. The presence of two orders of surfaces with distinct geometrical relations reveals that the Stimson-era landscape consisted of large dunes (draas) with smaller, superimposed dunes migrating across their lee slopes. Analysis of cross-lamination and subset bounding surface geometries indicate a complex wind regime that transported sediment toward the north, constructing oblique dunes. This dune field was a direct product of the regional climate and the surface processes active in Gale crater during the fraction of the Hesperian Period recorded by the Stimson formation. The environment was arid, supporting a large aeolian dune field; this setting contrasts with earlier humid depositional episodes, recorded by the lacustrine sediments of the Murray formation (also Hesperian). Such fine-scale reconstruction of landscapes on the ancient surface of Mars is important to understanding the planet's past climate and habitability.