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

Abstract

We present a combined geomorphologic, multispectral, and geochemical analysis of crater floor rocks in Jezero crater based on data obtained by the Mast Camera Zoom and SuperCam instruments onboard the NASA Mars 2020 Perseverance rover. The combined data from this analysis together with the results of a comparative study with geologic sites on Earth allows us to interpret the origins of rocks exposed along the Artuby ridge, a ∼900 m long scarp of lower Máaz formation rocks. The ridge exposes rocks belonging to two morphologically distinct members, Artuby and Rochette, both of which have basaltic composition and are spectrally indistinguishable in our analysis. Artuby rocks consist of morphologically distinct units that alternate over the ridge, bulbous, hummocky, layers with varying thicknesses that in places appear to have flowed over underlying strata, and sub‐planar thinner laterally continuous layers with variable friability. The Rochette member has a massive appearance with pronounced pitting and sub‐horizontal partings. Our findings are most consistent with a primary igneous emplacement as lava flows, through multiple eruptions, and we propose that the thin layers result either from preferential weathering, interbedded ash/tephra layers, ʻaʻā clinker layers, or aeolian deposition. Our analyses provide essential geologic context for the Máaz formation samples that will be returned to Earth and highlight the diversity and complexity of geologic processes on Mars not visible from orbit.

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

“…Earth‐based geochronology studies of the samples will help to determine the age of emplacement of these igneous members relative to one another and to the Isidis basin and Jezero crater‐forming events, as well as constraining the nature of Jezero resurfacing events and subsequent exhumation and erosion. The Máaz and Séítah formations are igneous in origin (e.g., Farley et al., 2022; Liu et al., 2022); Séítah represents an olivine‐rich cumulate formed from differentiation of a large melt or magmatic body, and the Máaz formation likely represents a separate series of lava flows emplaced on top of Séítah, with possible minor contributions from pyroclastic or airfall deposits (Alwmark et al., 2023). Geochronology and geochemical analysis of the returned samples will help to refine the petrologic histories of the Séítah and Máaz formations. Both the Máaz and Séítah formation rocks show evidence for multiple distinct episodes of aqueous alteration, although not in an extensive open system.…”

“…Rocks of the Máaz formation also exhibit flow-like morphologies (Figure 5d), vesicular textures (Figures 5e,9f,and 11d), and layering, particularly within the Artuby member (Figures 9f and 13d). A minor contribution from pyroclastic or aeolian materials, intercalated with lava flows, is possible for the Artuby member, as observations of thin, recessive layers framing more bulbous portions (e.g., Figure 9c) are difficult to attribute to effusive processes (Alwmark et al, 2023). Though initially considered part of the Séítah formation due to its geographic occurrence, the Content member may instead represent lava flows as well, based on its similar composition to upper Máaz (Section 5.1.2) and its pitted texture (Figure 17c), which is difficult to reconcile with a cumulate origin (Wiens et al, 2022).…”

“…There was again no significant difference in composition between the two members, similar to what was observed at Mure (Wiens et al., 2022). The team was especially interested in the nature of the layered Artuby member and whether its origins were sedimentary or igneous (Alwmark et al., 2023). Conversations about future investigation of the Artuby member would continue throughout the campaign and result in the investigation of the adjacent Rimplas outcrop (Section 4.9) during the return trip back to OEB.…”

“…Textural and geographic studies may indicate that different events created the upper Máaz and lower Máaz members. The broader geographic extent and thinner layering observed in the lower Máaz (Artuby and Rochette) members could indicate low‐viscosity flows (Alwmark et al., 2023), whereas the upper Máaz members have a more limited geographic distribution and less layering, potentially indicating a smaller volume of lava with higher viscosity (Horgan et al., 2022). RIMFAX subsurface profiles and observations of extended erosion and tectonic modification of and lower Máaz may also indicate that an extended period of time passed before upper Máaz was emplaced on top of lower Máaz (Horgan et al., 2022).…”

The Complex Exhumation History of Jezero Crater Floor Unit and Its Implication for Mars Sample Return

“…However, the in situ investigation of the dark floor unit (Alwmark et al., 2023; B. Horgan et al., 2022; Sun et al., 2022) revealed that the Máaz formation is layered and comprised of five different members, with different properties that could influence erosion and crater retention. The primary spatial extension of these sub‐units is not known even if some margin of potential lava flow may have been identified (Alwmark et al., 2023; B. Horgan et al., 2022). It may complicate the history we are presenting here: once exposed to bombardment, these different subunits may have eroded at different rates.…”