The Mars 2020 Perseverance rover has explored the escarpment at the front of the western fan in Jezero crater, Mars, where it encountered a variety of rock units as in-place outcrops and as loose pieces of rock separated from outcrops, or “float” rocks. Comparing float rocks to in-place outcrops can provide key insights into the crater’s erosional history and the diversity of units in the Jezero watershed that the Perseverance rover cannot visit in-situ. Here, we used multispectral observations from Perseverance’s Mastcam-Z instrument to investigate the lithology and origin of float rocks found on the western Jezero fan front (sols 415-707). We identified four textural classes of float rocks (conglomerates, layered, massive, and light-toned) and investigated their physical characteristics, spectral properties, and distribution to interpret their source and constrain their mode of transport. We found that the conglomerate and layered float rocks are highly spectrally variable and altered with differing ferric and ferrous signatures, and they likely derived from local sedimentary outcrops in the western fan front. Massive float rocks are the least altered, exhibit ferrous signatures, and could have derived from local outcrop sources or more distal sources in the Jezero watershed. Massive float rocks separate into two subclasses: massive olivine and massive pyroxene, which likely derived from the regional olivine-carbonate-bearing watershed unit and the crustal Noachian basement unit respectively. The unique light-toned float rocks have variable hydration and low Fe-abundance, but there are no local outcrop equivalent of these rocks in the western Jezero fan or crater floor.

We have studied the properties of the Nili Fossae olivine lithology from orbital data and in situ by the Mars 2020 rover at the Séítah unit in Jezero crater. We used the geochemistry collected by the rover’s instruments to calculate the viscosity and relative flow distance of the Séítah unit. Based on the low viscosity and distribution of the unit we postulate a ponded lava flow origin for the olivine rich unit at Séítah. We calculate an approximate depth for the cumulate layer of the lava pond based on the viscosity of the unit and model of Worster et al. (1993). We show that the resolution of orbital data is inadequate to map the phyllosilicate 2.38 μm band and demonstrate that it can be supplemented by in situ data from Mars 2020 SuperCam Laser Induced Breakdown Spectroscopy (LIBS) and reflectance observations to show that the low Al phyllosilicate in the olivine cumulate in the Séítah formation is either talc, serpentine, hectorite, Fe/Mg smectite, saponite or stevensite. We discuss two intertwining aspects of the history of the lithology: 1) the potential emplacement and properties of the cumulate layer within a ponded lava flow, using previously published models of ponded lava flows and lava lakes, and 2) the limited extent of post emplacement alteration, including phyllosilicate and carbonate alteration.

During the NASA Perseverance rover’s exploration of the Jezero crater floor, purple-hued coatings were commonly observed on rocks. These features likely record past water-rock-atmosphere interactions on the crater floor, and understanding their origin is important for constraining timing of water activity and habitability at Jezero. Here we characterize the morphologic, chemical, and spectral properties of the crater floor rock coatings using color images, visible/near-infrared reflectance spectra, and chemical data from the Mastcam-Z and SuperCam instruments. We show that coatings are common and compositionally similar across the crater floor, and consistent with a mixture of dust, fine regolith, sulfates, and ferric oxides indurated as a result of one or more episodes of widespread surface alteration. All coatings exhibit a similar smooth homogenous surface with variable thickness, color, and spatial extent on rocks, likely reflecting variable oxidation and erosional expressions related to formation and/or exposure age. Coatings unconformably overlie eroded natural rock surfaces, suggesting relatively late deposition that may represent one of the last aqueous episodes on the Jezero crater floor. While more common at Jezero, these coatings may be consistent with rock coatings previously observed in-situ at other landing sites and may be related to duricrust formation, suggesting a global alteration process on Mars that is not unique to Jezero. The Perseverance rover likely sampled these rock coatings on the crater floor and results from this study could provide important context for future investigations by the Mars Sample Return mission aimed at constraining the geologic and aqueous history of Jezero crater.

We have studied the observed properties of the Nili Fossae olivine-phyllosilicate-carbonate lithology from orbital data and in situ by the Mars 2020 rover at the Séítah unit in Jezero crater, including: 1) composition 2) grain size 3) inferred viscosity (calculated based on geochemistry collected by SuperCam (Wiens et al., 2022)). Based on the low viscosity and distribution of the unit we postulate a flood lava origin for the olivine-phyllosilicate-carbonate at Séítah. We include a new CRISM map of the phyllosilicate 2.38 μm band and use in situ data from Mars 2020 SuperCam Laser Induced Breakdown Spectroscopy (LIBS) and VISIR and MastCam-Z observations to show that the phyllosilicate in the olivine cumulate in the Séítah formation is either talc, serpentine, hectorite, Fe/Mg smectite, saponite or stevensite. We discuss two intertwining aspects of the history of the lithology: 1) the emplacement and properties of the cumulate layer within a lava lake, based on terrestrial analogs in the Pilbara, Western Australia, and using previously published models of flood lavas and lava lakes, and 2) the limited extent of post emplacement alteration, including phyllosilicate and carbonate alteration.