DIX Planetary Science Seminar

Observations of sedimentary rocks made by the Mars 2020 mission's Perseverance rover can be used to determine the depositional origin of ~3.5-billion-year-old sedimentary rocks in Jezero crater. Between March and June 2023, Perseverance acquired data on a sedimentary succession group of sedimentary rocks in the Jezero crater western fan known as the Skrinkle Haven member of the Tenby formation. Previously described from orbiter image data as the "curvilinear unit" because of its distinct planform geometry of sedimentary bodies, the original consensus hypothesis was that the Skrinkle Haven member was created through the lateral accretion of fluvial bars in a sinuous river. This study uses analyses of both rover and orbiter observations of the rocks' physical characteristics to test that hypothesis. Rover-scale images show that the Skrinkle Haven member is composed of two lithofacies: a well-cemented, medium-grained sandstone and a less-well-cemented conglomerate. Both lithofacies are uniformly planar-parallel bedded and steeply dipping at depositional angles up to ~30°, indicating that grain avalanching was the main bed-forming depositional process and that the sedimentary bodies were built through downstream accretion. Stratigraphic analysis suggests that the Skrinkle Haven member was deposited through the progradation of delta mouth bars, punctuated by downstream accreting fluvial bar deposition during intervals of aggradation and retrogradation. This interpretation implies the presence of a sustained, but dynamic, fluvial-deltaic depositional system in Jezero crater at the time of Skrinkle Haven member deposition