EXPLORATION OF THE LOWER DELTA FRONT SUCCESSION IN JEZERO CRATER BY THE MARS 2020 PERSEVERANCE ROVER

The Mars 2020 Perseverance rover arrived at the base of the ancient delta in Jezero crater after completing the first year of its mission exploring and sampling aqueously altered igneous rocks that comprise the present-day crater floor. Perseverance had its first close encounter with sedimentary rocks on sol 422 at an outcrop called Enchanted Lake, then ascended the delta at an area called Hawksbill Gap. The ~20 m thick sequence comprising the lower half of the delta front has been split into 5 members (from base to top): Devils Tanyard, Hughes River Gap, Boston Knob, Hogwallow Flats, and Rockytop. The Devils Tanyard member is a recessively-weathering, planar laminated, fine- to medium-grained sandstone with strong phyllosilicate absorptions. Convolute laminations are interpreted as soft sediment deformation. Lenses of low-angle, cross-stratified, medium- to coarse-grained sandstone exhibiting scour and drape geometries and planar, thinly laminated gray potential mudstones are exposed for meters to tens of meters laterally within this member. The Hughes River Gap member is also a recessively-weathering, planar, very thinly bedded fine- to medium-sandstone, but lacks the facies diversity observed in the Devils Tanyard member. The overlying Boston Knob member is a thin interval of resistant gray rocks, which is likely a sandstone although an igneous origin is also being considered. The overlying Hogwallow Flats member contains­­ planar laminated to apparently massive, fine-grained sandstone to mudstone with distinct color variations, diagenetic textures, and a relatively high abundance of sulfate. Both depositional and diagenetic explanations for these variations are under consideration, but no evidence for subaerial exposure, e.g., mudcracks or crystal molds, has yet been observed in this or other members. The overlying Rockytop member is a coarse-grained to granule sandstone displaying poor sorting, imbricated clasts, and planar bedding. The sedimentary facies observed at both Enchanted Lake and Hawksbill Gap, coupled with the absence of thick sets of cross-stratified sandstone and lack of evidence for subaerial exposure, are most consistent with subaqueous deposition of a coarsening upward sequence by a series of broadly unconfined sedimentary gravity flows in a distal setting.