Clay sediments derived from fluvial activity in and around Ladon basin, Mars

The morphology and mineralogy of light-toned layered sedimentary deposits were investigated using multiple orbital datasets across the Ladon basin region, including within northern Ladon Valles, southern Ladon basin, and the southwestern highlands of Ladon basin. Light-toned layered deposits are particularly widespread in Ladon Valles and Ladon basin, ranging laterally for distances over 200 km, with the thickest exposure (54 m) located at the mouth of Ladon Valles. The restriction of layered sediments below a common elevation (−1850 m) in Ladon Valles and Ladon basin and their broad conformable distribution with bedding dips between 1 and 4° favor a lacustrine environment within this region during the Late Noachian to Early Hesperian. The Ladon layered deposits have spectral signatures consistent with Mg-smectites, even when the morphology of the layering varies considerably in color and brightness. These phyllosilicates were most likely eroded from the highlands upstream to the south, but the lacustrine environment may have also been favorable for in situ alteration and formation of clays. The southwestern highlands also display light-toned layered deposits within valleys and small basins. These sediments predominantly have signatures of Mg-smectites, although we also identified Fe/Mg-smectites and additional hydrated phases in some deposits. One of these altered deposits was found within a younger Holden crater secondary chain, possessing a Late Hesperian to Early Amazonian age for valleys and sediments that postdate the deposits within Ladon Valles and Ladon basin. Phyllosilicate signatures were also detected in the ejecta from two fresh craters that exposed highland materials upstream of Arda Valles, revealing that the highlands are clay-bearing and may be the most plausible source of the clay-bearing fluvial-derived sediments found within the valleys and basins downstream. Some of the highland deposits are likely coeval to similar clay-bearing sediments found to the south within Holden and Eberswalde craters, indicating late, widespread fluvial activity and deposition of allochthonous clays within the broader Margaritifer Terra region when Mars was thought to be colder and drier.