USING VNIR SPECTROSCOPY TO INTERPRET DISTRIBUTION AND FORMATION MECHANISMS IN ACID SALINE PLAYAS IN WESTERN AUSTRALIA: RELEVANCE TO MARTIAN PALEOLAKES

The initial discovery of phyllosilicates in Noachian terrains and sulfates in younger Hesperian terrains has been taken as evidence for a linear evolution in martian climate whereby an early clay-forming era with abundant water at neutral to alkaline pH was followed by a drier, more acidic period in which deposition of sulfate sediments dominated. However, with the increasing spatial resolution of orbital data and in situ investigations, the picture of Mars’ environmental history has become more complex, revealing paleolacustrine environments with widely varying geochemistries that indicate phyllosilicates and sulfates precipitated contemporaneously.

Playa lakes of Western Australia (WA), mostly groundwater-fed basins, hosting extremely acidic environments as well as neutral to alkaline systems, represent terrestrial analogs that provide opportunities to understand geochemical complexity and variability [e.g., Benison and Bowen, 2006; Bowen et al., 2012].

Here, we present the results of a field campaign integrating airborne hyperspectral data and laboratory analysis of samples from acidic saline playas in WA to better understand the formation and distribution of sequences of layered sulfate and phyllosilicate deposits on Mars and the interpretations that can be made from remote sensing. HyMAP VNIR airborne data were compared to quantitative XRD and ASD Fieldspec analysis of surface and shallow core materials. Spectral summary parameters were used to assess the sulfate and clay mineralogy of the large number of spectra collected along a core.

The results indicate that shoreline surfaces are dominated by detrital components with increasing clay and alunite at depth. Towards the central basin, gypsum increases in surface spectra but is swamped by the presence of detrital quartz in XRD. With depth, sulfates decrease and clays increase. Islands of mostly gypsum in the central playa have discrete interbedded layers of clay, which may indicate detrital contributions.

Remote spectral analysis provides sufficient identification and distribution of sulfate and clay components, and there is good agreement between remote and field analysis. However, developing models for depositional history requires information about specific mineralogy and formation mechanisms and the integration of in situ analysis.