The Circum‐Isidis Capping Unit: An Extensive Regional Ashfall Deposit Exposed in Jezero Crater
C. B. Hundal, John F. Mustard, C. H. Kremer, Jesse Tarnas, A. C. Pascuzzo
Abstract
Abstract Several mineralogically diverse regions across Mars are capped by dark‐toned rock formations emplaced during the Noachian‐Hesperian transition, an era encompassing a shift in volcanism from dominantly explosive to effusive. However, these caprocks' origins are uncertain, limiting insight into the nature of this shift. We explore the potential volcanic ash origin of a widespread (∼50,000 km 2 ) mafic caprock in the Circum‐Isidis region via an integrated photogeologic and remote‐compositional analysis. We also investigate whether this unit is genetically equivalent to a mafic rock formation exposed in the floor of Jezero Crater. We find: (a) the Jezero Floor and Capping Units are morphologically, stratigraphically, and compositionally similar, suggesting a shared formation mechanism, and (b) the tonal layering and draping characteristics of the Capping Unit are most consistent with a volcanic ash origin atop the ultramafic Olivine‐Rich Unit, also an ash. Our hypotheses can be tested by the Perseverance rover and studies of returned samples.