Dune Casts Preserved by Partial Burial: The First Identification of Ghost Dune Pits on Mars

Abstract

Eolian sediment transport is active on modern Mars and has been for billions of years. Dune fields dot the surface of the planet, and examples of preserved eolian strata confirm that dunes were active on ancient Mars. As is also true on Earth, most Martian eolian sandstones preserve only a small fraction of the strata that constituted ancient dunes, and whole dunes fields are rarely preserved. In this study, we focus on two fields of >300 pits each and compare the pit morphologies, scales, and orientations to modern Martian dunes. It is hypothesized that the pit fields studied in Noctis Labyrinthus and Hellas basin represent casts of dunes from two ancient dune fields that were partially buried in the Hesperian. The flood material concentrated in the interdune area then became indurated, while the loose eolian dune sands eroded away, leaving behind the ~102-m-scale dune-shaped pits or ghost dune pits. Modern barchan dunes in Oyama and Herschel craters are used for comparison to the pit fields, and the topography of these modern dunes is used to model pit morphologies after partial burial. Basalt flows and low-energy fluviolacustrine deposition are possible mechanisms for partial burial. The potential for eolian strata to be preserved within the pits at a once warm or water-rich interface makes the pits of interest for astrobiology. The inferred ancient dune fields record in their morphology a wind regime that differs from the modern and provide rare evidence of whole dune field preservation.