The Record of Aqueous Alteration at Iazu Crater, Mars

We use CRISM hyperspectral data, HiRISE images and associated elevation maps, to characterize the mineralogy and stratigraphic setting of Iazu crater, a ~6 km diameter crater located ~25 km south of Endeavour crater in Meridiani Planum. A thick (~250 m) section of Burns formation layered hydrated sulfates is present on the rim and walls of Iazu crater. Comparisons to fresh Martian craters of the same size show that ~100 m of rim material has been removed by erosion. Iazu clearly formed during or after the emplacement of the Burns formation and thus preserves perhaps the best full Burns formation stratigraphic section. The Burns formation deposits stratigraphically and unconformably overlie the Noachian crust, which exhibits evidence of smectites. Within the underlying Noachian crust several layers of altered basaltic crust can be seen that are overlain by hydrated sulfates. The stratigraphic and mineralogic patterns show that the rocks exposed on the rim and walls of Iazu document the shift from formation of smectites to hydrated sulfates, beginning with several minor episodes and ending with a thick section of hydrated sulfates (i.e., the Burns formation). These rocks thus document the shift from aqueous alteration under relatively mild to extremely acidic and oxidizing conditions.