Spectral Properties of Chemical Sediments in Modern Acid Saline Lakes and Implications for Mars

Abundant zones of chemical precipitates including sulfates, iron oxides, and phylosilicates have been identified on Mars. Identification of these minerals, which are suggestive of formation and deposition in an aqueous setting, have been largely based on remotely acquired spectral data in both the short and long- range wavelengths. Here, we report on the sedimentological character and spectral properties of chemical sediments from acid saline lacustrine settings in southern Western Australia that have been identified as an important modern analog for past environments on Mars. Ephemeral saline lakes with acidic pHs (> 1.5) in this region are some of the only known lake systems that have naturally evolved to this extreme threshold. Strong spatial gradients in surface and shallow groundwater chemistry result in abundant heterogeneity in authigenic mineral types in the sediments, an observation which is consistent with observations on Mars. Spectral characterization of sediment from several different acid saline lakes in Western Australia show absorption features indicative of abundant and diverse sedimentary precipitates including a variety of sulfates, iron oxides, and phylosilicates. Spectral analyses, together with detailed field work and supplementary geochemical and mineralogical analyses from this environment may help to make more robust interpretations of spectral data from the acid saline deposits on Mars. The identification and spectral characterization of these minerals all within the modern acid saline lake settings suggests that extreme and multiple episodes of diagenesis are not necessary to produce this assemblage of minerals, and may not have been necessary on Mars. The sedimentary records being deposited and precipitated in these lake systems provide a valuable modern analog for interpreting depositional and early diagenetic processes the similar acid saline playa and groundwater systems that have existed in the past on Mars, and allow for evaluation for the preservation potential of extremophiles living within these systems.