Sorting out Compositional Trends in Sedimentary Rocks of the Bradbury Group (Aeolus Palus), Gale Crater, Mars

Sedimentary rocks are composed of detrital grains derived from source rocks, which are altered by chemical weathering, sorted during transport, and cemented during diagenesis. Fluvio-lacustrine sedimentary rocks of the Bradbury group, observed on the floor of Gale crater by the Curiosity rover during its first 860 sols, show trends in bulk chemistry that are consistent with sorting of mineral grains during transport. The Bradbury group rocks are uniquely suited for sedimentary provenance analysis because they appear to have experienced negligible cation-loss (i.e., open-system chemical weathering) at the scale of the Alpha Particle X-ray Spectrometer bulk chemistry analyses based on low Chemical Index of Alteration values and successful modeling of >90% of the (volatile-free) targets as mixtures of primary igneous minerals. Significant compositional variability between targets is instead correlated to grain size and textural characteristics of the rocks; the coarsest-grained targets are enriched in Al2O3, SiO2, and Na2O, whereas the finer-grained targets are enriched in