Geography on Mars

• Third order of relief and deep time on Mars

• Geochemical periods (just to stir the pot)
• Phyllosian period: time of the phyllosilicate clays
• Up to late Noachian, when volcanism took off and pumped out so much sulfuric acid into the atmosphere
• These clays form in neutral or alkaline surface or subsurface waters
• Theiikian period: time of the sulfates
• Late Noachian/much of the Hesperian
• Sulfate minerals and evaporites form from a lot of water
• Acidic conditions (related to volcanism)
• Hydrated sulfates (gypsum, magnesium sulfate)
• Siderikian: time of iron oxidation
• Late Hesperian and the Amazonian
• Oxidation of iron-rich rocks