Modern and ancient extremely acid saline deposits: terrestrial analogs for martian environments?

Extremely acid (pH <1) saline lakes and groundwaters existed in the mid-Permian of the mid-continent of North America. Modern counterparts have been found in acid saline lake systems throughout southern Australia. We compare and contrast the Permian Opeche Shale of North Dakota and Nippewalla Group of Kansas to modern Australian salt lakes in southern Western Australia and in northwest Victoria. With the exception of some minor variations in pH, evaporite mineralogy, and water geochemistry, the Permian and modern systems are similar and characterized by: (1) ephemeral saline continental playas hosted by red siliciclastic sediments, (2) evaporite minerals, including abundant sulfates, (3) Al-Fe-Si-rich waters with low pH values, (4) acidophilic microbes, and (5) paucity of carbonates. The composition of these terrestrial systems is strikingly similar to compositional data returned from the martian surface. Specifically, both Earth and martian systems have high amounts of iron oxides and sulfates, and little, if any, carbonates. We propose that the modern and ancient terrestrial acid saline environments may be good analogs for possible environments on Mars.