The lithified aeolian dune field adjacent to the Apollinaris Sulci, Mars: Geological history and paleo-wind record

Abstract

A lithified aeolian dune field in the Apollinaris Sulci region of Mars presents a unique opportunity to study ancient aeolian processes and paleo-wind conditions during an earlier episode of martian climate history. The ancient dunes occur inside an eroded, partly-filled impact structure. The petrified dune field retains its original geomorphology and has south-, south-southeast-, and south-southwest-facing lee slopes, indicating dominance of a north-to-south paleo-wind direction. The preserved dunes have crescentic and marginal barchan morphologies with crestlines ranging from 100 m to 7 km in length. To the north of the preserved dunes, the yardangs of the Apollinaris Sulci, eroded into strata of the Medusae Fossae Formation, have an average orientation (azimuth) of 169°. The yardangs are interpreted to form from reversing winds along this orientation, in contrast with the northerly winds that formed the paleodunes. The observed paleodunes, yardangs, modern bedforms, and abundant dust cover collectively demonstrate that the climate has changed over time. Certain, heavily eroded, slopes on the paleodunes show crest-parallel lineations interpreted as exposed cross strata. Second-order bounding surfaces within the strata provide evidence that the meter-scale, superimposed bedforms migrated across some lee faces when the dunes were active. This potentially reflects preservation of ancient bedforms analogous to the “large martian ripples” commonly observed on active martian dunes today. In the paleo-interdune spaces, linear ridges and grooves are interpreted as preserved paleo-transverse aeolian ridges. The juxtaposition of these three common martian bedforms – dunes, transverse aeolian ridges, and large martian ripples – all preserved in close proximity, suggests Mars in the Hesperian epoch was subject to similar aeolian dynamics as are observed today.