Amapari Marker Band, Gale crater, Mars: Event horizon with highest bedrock iron and zinc concentrations detected by Curiosity’s Alpha Particle X-ray Spectrometer

Alpha Particle X-ray spectrometer (APXS) analyses of the distinct Amapari Marker Band (AMB), Gale crater, Mars reveal the highest, in situ, martian FeO and Zn abundances (47.51 wt%, 2.23 wt%), and elevated MnO associated with a lower rippled unit. APXS analyses also reveal a marked shift in provenance, to a generally basaltic composition, compared to the underlying Mg-sulfate-bearing strata, which persists into the overlying stratigraphy. The AMB also records a perturbation in the MgSO4-forming conditions present above and below. AMB chemistry could be consistent with a volcanic ash source; high metal concentrations resulting from volatile reactions within an ash cloud. Alternatively, syn- and/or post-depositional precipitation processes within a primary lake setting and/or a later diagenetic event or events may have played a role. Ongoing and future work will aim to further constrain processes responsible for deposition of the AMB, the high metal concentrations and its regional and global implications.