Regolith of the Crater Floor Units, Jezero Crater, Mars: Textures, Composition, and Implications for Provenance

Abstract

A multi‐instrument study of the regolith of Jezero crater floor units by the Perseverance rover has identified three types of regolith: fine‐grained, coarse‐grained, and mixed‐type. Mastcam‐Z, Wide Angle Topographic Sensor for Operations and eNgineering, and SuperCam Remote Micro Imager were used to characterize the regolith texture, particle size, and roundedness where possible. Mastcam‐Z multispectral and SuperCam laser‐induced breakdown spectroscopy data were used to constrain the composition of the regolith types. Fine‐grained regolith is found surrounding bedrock and boulders, comprising bedforms, and accumulating on top of rocks in erosional depressions. Spectral and chemical data show it is compositionally consistent with pyroxene and a ferric‐oxide phase. Coarse‐grained regolith consists of 1–2 mm well‐sorted gray grains that are found concentrated around the base of boulders and bedrock, and armoring bedforms. Its chemistry and spectra indicate it is olivine‐bearing, and its spatial distribution and roundedness indicate it has been transported, likely by saltation‐induced creep. Coarse grains share similarities with the olivine grains observed in the Séítah formation bedrock, making that unit a possible source for these grains. Mixed‐type regolith contains fine‐ and coarse‐grained regolith components and larger rock fragments. The rock fragments are texturally and spectrally similar to bedrock within the Máaz and Séítah formations, indicating origins by erosion from those units, although they could also be a lag deposit from erosion of an overlying unit. The fine‐ and coarse‐grained types are compared to their counterparts at other landing sites to inform global, regional, and local inputs to regolith formation within Jezero crater. The regolith characterization presented here informs the regolith sampling efforts underway by Perseverance.

Diverse Lava Flow Morphologies in the Stratigraphy of the Jezero Crater Floor

“…Differences in the chemistry of the regolith further highlights the variances in rock composition between on one side the Artuby and Rochette members, and on the other the stratigraphically higher Máaz rocks exposed near the OEB landing. We see that the regolith near Artuby, which is likely sourced from weathering of local bedrock, is spectrally distinct from typical regolith at the OEB landing (Figure S3 in Supporting Information S1; see also Cardarelli et al, 2022;Vaughan et al, 2023).…”

Mineralogy, Morphology, and Emplacement History of the Maaz Formation on the Jezero Crater Floor From Orbital and Rover Observations

“…However, the broad band is centered at shorter wavelengths, closer to 1,000 nm, and the smooth areas also show an additional upturn near 2,500 nm that we attribute to the long edge of the HCP ∼2,000 nm band, which is not observed in any of the average SuperCam bedrock spectra. Instead, both SuperCam and CRISM spectra of fine regolith on the crater floor show broad absorptions centered near 1,000 and 2,100 nm consistent with HCP (Mandon et al., 2023), suggesting that regolith is contributing to the CRISM signature (Mandon et al., 2023; Vaughan et al., 2023). Thus, we hypothesize that the typical spectrum of the smooth areas is a mixture of Rochette and Artuby member bedrock (i.e., broadly similar to the Chal and Nataani members; green spectra in Figure 5a) and fine regolith (light blue spectrum in Figure 5a).…”

“…The Maaz formation may be a source for at least some of the local fine regolith (Vaughan et al., 2023). Mastcam‐Z spectra of fine‐grained regolith exhibit a broad band centered >900 nm consistent with pyroxene, and similar weak bands are found in Mastcam‐Z spectra of abrasion patches throughout the Maaz formation.…”

Overview and Results From the Mars 2020 Perseverance Rover's First Science Campaign on the Jezero Crater Floor

“…Erosion would have also removed substantial amounts of material from the Máaz formation in order to explain the present-day variance in topography and surface textures that may have resulted in the delineation of up to five distinct members. Erosion of the Séítah formation to liberate olivine grains (Figure 16e) and subsequent transport of these grains likely explains the prevalent occurrence of olivine grains found in Máaz formation regolith (Vaughan et al, 2023;Wiens et al, 2022).…”

“…The team also searched for rocks along the drive to perform compositional analyses with SuperCam LIBS and VISIR to see if there was an identifiable contact in the form of a transition from olivine-bearing Séítah formation rocks to olivine-poor Máaz formation rocks. Up until this point in the mission, olivine had never been detected in rocks, only in soils in the Máaz formation (e.g., Vaughan et al, 2023;Wiens et al, 2022). However, two observations along the base of Artuby ridge, on rock targets Entrevaux (sol 173) and Aiguines (sol 178) (Figure 12) were significant because olivine was identified in the SuperCam LIBS (via a ratio of Fe + Mg/Si converging towards 2) and VISIR data (via olivine's one micron reflectance feature).…”