EXPLORING AUSTRALIAN DRY LAKE SYSTEMS AS TERRESTRIAL ANALOGS FOR MARTIAN ACIDIC WEATHERING ENVIRONMENTS

This project is analyzing spectroscopic remote sensing data of acidic dry lake environments as possible terrestrial analogs of acidic Martian brines and weathering processes. Lakes Chandler, Deborah, and Gilmore, located in Western Australia, are among the rare terrestrial examples of dry lakes hosting evaporite minerals, such as jarosite and alunite, indicative of acidic conditions. The three dry lakes were chosen for study because of differences in local bedrock geology, which is a primary factor affecting brine compositions and related fractionation processes. Specifically, Lake Deborah is unusual in having komatiitic (ultramafic) rocks within its drainage basin, whereas Lakes Chandler and Gilmore are associated with more silicic rocks. Little is known about the distributions of evaporite mineral phases in these systems. Multispectral imagery acquired by the orbital Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER), as well as hyperspectral imagery from HyMap, an Australian airborne sensor, are being analyzed to map the evaporite mineralogy. These data are being compared with hyperspectral data of the Martian surface collected by the OMEGA and CRISM orbital imaging spectrometers.

Remote sensing information on the spatial distributions of acid playa minerals should help resolve questions concerning sources of acidity and related sedimentary processes, such as calcrete and silcrete development. Evaporite minerals formed near springs along playa margins often are especially interesting as these areas may reflect unusual local inflow sources, as well as brine compositional gradients and zones of mixing. Such hydrochemical gradients typically correspond to gradients in salinity, Eh and pH and offer a broad range of options for biological activity. We seek to answer these questions: Are any of the Martian deposits actual evaporites, or were they formed by some other process? Are there associated features, such as silcretes, which might be linked to aquifer chemistry, and even to possible biological mediation? If some Martian deposits are evaporites formed in playa-like settings, what are the best areas to search for fossil and chemical trace fossil preservation? How can we identify these areas using orbital remote sensing and rovers?