Sedimentology and stratigraphy of the fluvial-deltaic Skrinkle Haven member, Tenby formation, Jezero Crater, Mars

In 2023, the Mars 2020 Perseverance rover investigated the Skrinkle Haven mbr of the Tenby fm in the > 3.5-billion-year Jezero Crater western fan. This unit was interpreted from orbiter data as bank attached, lateral-accretion bars in a sinuous river on a muddy delta plain. To test that hypothesis, this study applied facies and stratigraphic analyses of both rover and orbiter data. Rover images show that the Skrinkle Haven member is composed of two lithofacies: a fine-grained sandstone and a pebble conglomerate. Both lithofacies are composed of structureless, ungraded, planar-parallel beds that have sharp, nongradational contacts and depositional angles up to ~ 30°. These characteristics indicate that grain flow was the main depositional process and that the sedimentary bodies were built through downstream accretion. Architectural analysis suggests that the Skrinkle Haven member was deposited primarily as delta foresets and mouth bars, with limited river bar deposition. The sequence stratigraphic analysis identified five maximum-flooding surfaces associated with relative-lake-level increases ranging from 5 to 25 m. In the sequences, deltaic strata prograded during normal and forced regressions. Some sequences have evidence for compensational stacking. Lake levels decreased through time both within sequences and throughout the duration of the Skrinkle Haven member deposition, from at least -2415 m in the oldest sequence to at most -2455 m in the youngest. The elevation range of the Skrinkle Haven member is below the modern Jezero Crater outlet breach, suggesting that the Jezero Crater lake basin was closed at that time. Overall, the Skrinkle Haven member records the deposition of a sandy to conglomeratic deltaic system that prograded into a closed lake basin during both forced and normal regressions. This type of fluvial-deltaic system is significantly different from the muddy delta topsets originally interpreted from orbiter data, because of the different implications for biosignature preservation and the paleohydrology of the Jezero Crater.