MORPHOLOGY OF ALLUVIAL FANS AND FAN-LIKE FEATURES ON MARS AS AN INDICATOR OF DEPOSITIONAL ENVIRONMENTS (Invited Presentation)

The search for evidence of past life on Mars has focused on habitable aqueous environments that were active during the more favorable era of early Mars climate. Aqueous sedimentary depositional systems represent potential habitable environments and are preserved in the geologic record in many locations on the surface of Mars. A small number of individual locations have been analyzed in detail by rover missions. However, a global assessment of the extent and variability of these environments has not been fully tackled. Alluvial fans in particular, along with other fan-like features, are commonly preserved across much of the surface. This work expands the global Mars catalog of alluvial fan locations and classifies new and previously identified features based on morphologic characteristics, specifically plan-view shape, radial slope, and radial profile shape. Morphology is used to distinguish alluvial fans from fan-deltas, distributive fluvial systems, and other radial sedimentary features which form in different aqueous environments. Differentiating between different fan-like features is critical to understanding the scope and variability of different depositional environments. We identified a total of 775 alluvial fans, primarily distributed across the cratered highlands. We also classified a number of distributive fluvial features and “possible” alluvial fans based on morphologic characteristics. Features classified as “possible” alluvial fans have more complex morphologies, some of which are characteristic of fan-deltas. In addition, we observed benches and scarps on some of the possible alluvial fans that appear analogous to shoreline features seen on terrestrial fan-deltas in forced regression environments. Distinct shoreline features on fan-deltas allow us to estimate total water volumes of the crater lakes where the fan-deltas formed. In some cases, multiple shoreline benches on the same feature tell a story of water level changes in a forced regression crater lake. A more complete assessment of the depositional environments associated with alluvial fans and fan-deltas on Mars adds important context to our understanding of early Mars climate and surface water activity which may have hosted life.