Evidence for aqueous deposition of hematite- and sulfate-rich light-toned layered deposits in Aureum and Iani Chaos, Mars

Two new gray hematite-rich units have been found in Aureum and Iani Chaos, Mars, using data acquired by the Mars Global Surveyor Thermal Emission Spectrometer. These regions correspond with light-toned sulfate-rich deposits identified by the European Space Agency's OMEGA visible/near-IR spectrometer. Much of the light-toned material in Aureum and Iani Chaos is in the form of a capping unit similar to that seen in Aram Chaos. However, some light-toned material is also seen within the chaotic mounds, indicating that it was present before the formation of the chaotic terrains. The stratigraphy of the units in Iani and Aureum Chaos suggests that the capping and hematite-rich units must have been deposited after the formation of the chaotic terrains in the mid to late Hesperian, up to 1 Gyr after the formation of the light-toned outcrop in Meridiani Planum. The geologic contexts of these and other hematite- and sulfate-rich units in Aram Chaos, Valles Marineris, and Meridiani Planum indicate that they likely formed in similar environments under aqueous conditions. If this is the case, it suggests an active hydrological cycle lasting from the late Noachian to the late Hesperian.