Sedimentology of Acid Saline Lakes in Southern Western Australia: Newly Described Processes and Products of an Extreme Environment

Naturally acid saline systems with pH values between 1.7 and 4 are common on the Yilgarn Craton of southern Western Australia. a combination of physical and chemical processes here yield a previously undescribed type of modern sedimentary environment. Flooding, evapoconcentration, desiccation, and eolian transport at the surface, as well as influx of acid saline groundwaters, strongly influence these lakes. Halite, gypsum, kaolinite, and iron oxides precipitate from acid hypersaline lake waters. Shallow acid saline groundwaters affect the sediments of the lakes and associated mudflats, sandflats, channels, and dunes by precipitating early diagenetic halite, gypsum, iron oxides, clays, jarosite, and alunite. These modern environments would likely yield a rock record composed mostly of bedded red siliciclastic and reworked gypsum sand, alternating with less common beds of bottom-growth gypsum and halite, with alteration by early diagenetic features diagnostic of acid saline waters. This documentation of sedimentary processes and products of modern acid saline environments is an addition to the comparative sedimentology knowledge base and an expansion of the traditional models for classifying brines. Implications include better interpretations of terrestrial redbeds and lithified martian strata, improved acid remediation methods, new models for the formation and occlusion of pores, and the new setting for finding previously undescribed extremophiles

Field Observations and Lab Tests of Acid Brines: Implications for Past Deposition, Diagenesis, Erosion, and Life on Mars

Geochemical and mineralogical data obtained from lithified strata of Mars indicate that acid saline waters once existed on and just below its surface [1-5]. This confirms the interpretations of acid waters on Mars by Burns [6,7] based upon spectral signatures suggestive of jarosite and schwertmannite, as well as the theoretical work of Clark [8]. Acid saline environments on Earth are good analogs for martian lithified strata, especially those at Meridiani Planum [9,10]. In addition, acid brines may have been responsible for the formation of channels and some small craters on Mars [11,12]. We propose that acid brines should be considered possible agents of chemical sedimentation, diagenesis, and sediment transportation and erosion on Mars. Terrestrial acid saline lake systems are an uncommon, but natural, type of extreme environment. Here we summarize the characteristics of modern acid saline systems in Chile, Western Australia, and Victoria, Australia, and how they compare to martian strata. We also present both physical sedimentology and waterrock interaction experiments involving acid brines. Knowledge of the geology, geochemistry, and microbiology of terrestrial acid saline systems may lead to recommendations for future investigations of Mars and better understanding of its geologic evolution and search for possible past life