Architecture of Fluvial and Deltaic Deposits Exposed along the Eastern Edge of the Western Fan of Jezero Crater, Mars

Early observations from the Perseverance rover suggested a deltaic origin for the western fan of Jezero crater only from images of the Kodiak butte. Here, we use images from the SuperCam Remote Micro-Imager and the Mastcam-Z camera to analyze the western fan front along the rover traverse, and further assess its depositional origin. Outcrops in the middle to lower half of the hillslopes comprise planar and inclined beds of sandstone that are interpreted as foresets of deltaic deposits. Foresets are locally structured in similar to 20-25 m thick, similar to 80-100 m long, antiformal structures interpreted as deltaic mouth bars. Above these foresets, interbedded sandstones and boulder conglomerates are interpreted as fluvial topset beds. One well-preserved lens of boulder conglomerate displays rounded clasts within well-sorted sediment deposited in overall fining upward beds. We interpret these deposits as resulting from lateral accretion within fluvial channels. Estimations of peak discharge rates give a range between similar to 100 and similar to 500 m3 s-1. By contrast, boulder conglomerates exposed in the uppermost part of hillslopes are poorly sorted and truncate the underlying beds. The presence of these boulder deposits suggests that intense sediment-laden flood episodes occurred after the deltaic foreset and topset beds were deposited, although the origin, timing, and relationship of these boulder deposits to the ancient lake that once filled Jezero crater remains undetermined. Overall, these observations confirm the deltaic nature of the fan front, and suggest a highly variable fluvial input. Early observations from the Perseverance rover of the Kodiak butte suggested a deltaic origin for the western fan of Jezero crater. Here, we use images from the SuperCam Remote Micro-Imager and the Mastcam-Z camera to analyze the western fan front along the rover traverse, and further assess its origin. We observe strata in the lower part of the fan front that we interpret as deltaic deposits formed below water in a lake. The strata of the upper part of the fan front contain sediments interpreted as fluvial deposits formed under various fluvial regimes, with some of them being deposited by the rivers that also fed the Jezero paleolake. Overall, these observations confirm the deltaic nature of the fan front, and suggest a highly variable fluvial input. New observations from the Perseverance rover of the western fan front confirm a deltaic origin Deltaic foresets in the lower fan front are organized as antiformal structures interpreted as delta mouth bars Sandstones and conglomerates in the upper part of the fan front suggest a highly variable fluvial input