The Curiosity rover investigates an aridification sequence in the layered sulfate-bearing unit.
Résumé
On Mars, prominent thick-layered sulfate-bearing deposits are observed at a number of late Noachian to late Hesperian locations (~3.5 Ga) [1]. Their apparent absence in older strata has led to the hypothesis that they represent ancient evaporites related to the global aridification [2]. In Gale
crater, the Curiosity rover is now exploring the Layered Sulfate-bearing unit (LSu), which is a hundreds of meters thick regional package of yet unknown origin within the Mt Sharp group (Fig. 1). Curiosity investigations can test whether its formation processes are similar to the Burns fm.,
another major sulfate-bearing strata documented by the Opportunity rover, or distinct such as a form of primary evaporites, syndiagenetic or later stage diagenetic precipitations with different aqueous conditions.
After exploring the mudstone-rich strata of the Murray and Carolyn Shoemaker fm. for about seven years, the Curiosity rover entered the LSu in 2021. Bedrock in the basal section is marked by diverse diagenetic overprints where sedimentary structures are less visible. In some places,
laminated mudstones or siltsontes associated with concretions and with mm-scale nodular features may present similarities to evaporitic textures previously observed in the Murray formation [3]. Further up, the rover imaged butte-forming outcrops (Fig. 1) and revealed a ~100-m-thick interval
with a transition into large-scale trough cross-bedded structures, the lithology, scale and thickness of which has never been observed before by the rover at such close range [4].
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