The global distribution and morphologic characteristics of fan-shaped sedimentary landforms on Mars

Abstract

Fan-shaped sedimentary landforms on Mars are important geomorphic markers of past water flow and characterizing the distribution and morphology of these features can yield insights into the planet's climatic evolution. We present a new database of 1501 martian fan-shaped sedimentary landforms that builds upon previous surveys and uses Context Camera images. This comprehensive global survey includes both alluvial fans and putative deltas, which we term scarp-fronted fan deposits (SFDs), across the entire martian surface. We classified each fan-shaped landforms based on their morphology as alluvial fans, channelized SFDs, smooth SFDs, and terraced SFDs. Martian alluvial fans are highly concentrated in the high southern tropical latitudes while SFDs are more common near the equator. Both alluvial fans and SFDs are found at lower elevations than Late Noachian to Early Hesperian valley networks, suggesting a climatic change in the locations of stable liquid water. Alluvial fans within impact craters are preferentially located on north, south, and east facing slopes, and are concentrated near the location of highest rim topographic relief; together these observations support orographically-influenced precipitation and snowmelt as a runoff source. For every fan in the database we collected morphologic data, which we compare with terrestrial alluvial fans. Relationships between alluvial fan catchment and fan morphology vary little across the martian surface, suggesting relatively similar processes. Although stratigraphic evidence of a deltaic deposition is lacking, previously conducted experiments along with the depositional basins of the channelized and terraced SFDs generally support deltaic formation. Crater counts indicate that many alluvial fans are within Hesperian and Amazonian impact craters, indicating that significant fluvial erosion occurred during Mars' relatively recent history.