Sedimentary Fan Deposits in Jezero Crater Lake, in the Nili Fossae Region, Mars: Meter- scale Layering and Phyllosilicate-Bearing Sediments

Sedimentary deposits that are clearly related to valley networks on Mars are relatively unusual and have been recognized in only a few locations on Mars. However, such sediments have the potential to preserve an excellent record of the surface environment at the time of their emplacement, including data on the potential habitability of the surface, which makes them important targets of study for both orbital and landed missions. An exceptional example of valley network-derived sedimentary deposits is located in Jezero crater, a ~40-km diameter impact crater, northwest of the Isidis Basin near the Nili Fossae (centered at 77.6 E and 18.4 N). Two valleys debouch into this crater from the west and north, and each valley appears to have deposited a sedimentary fan. On the eastern end of the crater, an outlet valley is observed, and based on the elevation of the outlet valley, Jezero crater must have contained a sizeable lake at one time, with a volume of at least 250 km3, of comparable volume to terrestrial Lake Tahoe (V ~ 160 km3). The fan deposits have been interpreted as deltaic sediments, deposited into this lake. New data from MRO and other recent missions has motivated the reexamination of Jezero crater and its sedimentary deposits. Meter-scale layering is commonly observed on fan deposits in HiRISE data. Layers appear to dip gently (<10-15°) and outcrop in sinuous patterns. Many unconformities are discernable between packets of the layered material. We interpret these sediments as having been deposited via lateral accretion during meander migration, with observed unconformities resulting from numerous channel switching events on the fan. CRISM visible/near-infrared observations of the fan materials indicate that where these light- toned, finely-layered packets of sedimentary material are exposed, they commonly have spectra consistent with iron-magnesium phyllosilicate. Phyllosilicates are also found on the Jezero crater interior off the margins of the primary deposits. Given both the unique geological setting and mineralogy of the Jezero crater fan materials, it is a prime target for future landed missions, such as MSL.