CLUES TO THE AEOLIAN HISTORY OF MEDUSA FOSSAE MATERIALS AS OBSERVED IN THE DUST-FREE WINDOWS OF THE OLYMPUS MACULAE, MARS

The Olympus Maculae are semicircular, generally low albedo features spanning ~1,400 km² within the aureole terrains, < 200 km from the western flank of Olympus Mons’ escarpment. These maculae exhibit elevated thermal inertia, ~no topographic relief, non-definitive spectra, and minimal surface dust in an otherwise dusty region. While their exact origin remains unclear, landforms in and around the maculae record complex aeolian, volcanic, and other geologic processes.

Here, we mapped and analyzed aeolian features, including yardangs and cross stratification, to characterize the paleoenvironment and materials of the maculae and to narrow possible reasons for their existence. Almost 3000 yardangs in and around the maculae, grouped by density clusters, were used to construct rose diagrams and show that there were three dominant wind directions toward the northeast (~55°), east (~80°), and southeast (~130°) with most dominant winds toward the northeast. Within the low-dust maculae, 5 meter-scale cross bedding is commonly associated with the hosting materials of Medusa Fossae Formation (MFF; Morris et al., 1994) materials. Intersecting concentric patterns within the cross-bedded layers, which are usually in the troughs of yardangs, suggests that the cross bedding may constrain past sediment transport within the maculae region. To understand the processes that may have created these patterns, we used an automaton model developed in Matlab (Rubin et al., 2006) to simulate environmental conditions that would generate cross bedding consistent with our observations. We found that the cross bedding closely resembles either climbing barchan dunes or festoon cross-lamination, where material is deposited into pre-existing troughs (McKee, 1979; Knight, 1929). These scenarios imply several generations of aeolian erosion and deposition inconsistent with a static landscape. Instead, the wide array of aeolian landforms and paleowind indicators is evidence that the Olympus Maculae and surrounding region offer unique insight into the material properties and dynamic evolution of this poorly understood region of Mars and the MFF. Future geomorphic and compositional research will seek to constrain the maculae’s formation and preservation, and to understand why they are dust-free.