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Contemporaneous Deposition of Phyllosilicates and Sulfates; Using Australian Acidic Saline Lake Deposits to Describe Geochemical Variability on Mars

Wednesday, May 20, 2009
Baldridge (Jet Propulsion Laboratory)

Studies of the origin of the martian sulfate and phyllosilicate deposits have led to the hypothesis that there was a marked change in the Mars environment from neutral pH aqueous alteration in the Noachian to an acidic evaporitic system in the late Noachian to Hesperian. However, terrestrial studies suggest that two different geochemical systems need not be invoked to explain such geochemical variation. Western Australian acidic playa lakes have large pH differences separated vertically and laterally by only a few tens of meters demonstrating how highly variable chemistries can coexist over short distances in natural environments. We suggest that Australian analogs indicate diverse and variable aqueous environments on Mars where phyllosilicates and sulfates likely also formed in coetaneous depositional systems. In these systems, Fe and alkali earth phyllosilicates represent deep facies associated with upwelling neutral to alkaline groundwater, whereas aluminous phyllosilicates and sulfates represent near-surface evaporitic facies formed from more acidic brines.

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