Ma'adim Vallis, Mars: Insights into episodic and late-stage water activity from an impact crater

Alluvial fans, a form of sedimentary deposit reported on Mars, offer insight into the evolution and nature of fluvial activity on the planet. Additionally, the region's preserved mineralogy can also be used to study its hydrological history. In this context, we discuss the diverse geomorphology and mineralogy of an unnamed crater that formed on the eastern wall of Ma'adim Vallis, Mars. Ma'adim Vallis is an irregular-shaped, flat-floored valley incised due to the outflow of water from the Eridania basin. The rim of the unnamed crater is breached at multiple locations and it hosts an alluvial fan of an area similar to 50 km(2). The CRISM spectral signatures show Mg-rich olivine and Mg-rich smectite. Mg smectite was plausibly transported through water or formed in situ while the underneath terrain was rich in Mg olivine. The crater retention age on the ejecta of the unnamed crater is 3.7 Ga which suggests that the crater likely formed during the Noachian-Hesperian period boundary or earlier. This unnamed crater probably witnessed the last episode of water activity in the Vallis, which was most likely fed by water overflowing from a resurged early Hesperian water activity in Eridania Basin. This study substantiates episodic, late- stage water activity in Ma'adim Vallis, and the unnamed crater formed on the floodplains of the Vallis providing an excellent opportunity for future landing missions to explore astrobiological significance of the region.