A Tale of Two Seasons: The Geochemical Evolution of Acidic Hypersaline Lakes in Western Australia

Abstract

Analog environments on Earth such as the wide biogeochemical range spanned by the Western Australia Transient Lakes (WATL) present an opportunity to investigate what early lacustrine Martian environments could have been like, and understand how once active lake systems leave a record of their presence behind. From two field seasons, we present geochemical data from two endmember environments that are characteristic of lakes found across the Yilgarn Craton, and describe how these environments evolve overtime and affect habitability of the environment. The two endmember environments are: (1) surficial closed topographic basins, that do not show complex geology on the surface and (2) deeper incised settings exposing outcrops of varying lithology, which are driven by groundwater interactions and are dominated by clay minerals, quartz veins, and Fe oxides. Both environments contain thick salt deposits because of extreme wet-dry cycling that builds up salt pans over time, however, the Eastern Craton region shows even more distinct features. Specifically, some lakes in this region contain layered outcrops that show progressive weathering with depth, suggesting significant and extreme ongoing weathering.

We present our preliminary results from our field sites on the in-situ spectroscopy, XRF/XRD lab data of our samples, and the water chemistry data. Evidence shows that the surrounding kaolinite–quartz domains are possibly bleached white due to Fe loss and that Fe concentrations decrease from the upper to lower clay zone. Further geochemical results show elevated Fe, Si, and Al concentrations in this extreme system, indicative of extreme weathering and interactions with the acidic groundwater.

The WATL represents an area where acidic groundwater dominates the system as a whole and interacts with wet-dry cycles, which has implications for microbial life and preservation through time in a dynamic environment. We can leverage the geochemical results to inform the potential pathways for acidity generation (ferroylysis vs. sulfide mineral oxidation), which isn’t fully understood in the WATL systems. Thus, in these end-member environments we can better understand the geochemical evolution of these late-stage diagenetic environments, that went from a less saline, near neutral pH to one that is more acidic and saline.