Characterizing clay minerals in the Makgadikgadi Pans (Botswana): terrestrial analogue for Mars playa deposits

Terrestrial field analogues are crucial for preparing upcoming space missions and advancing our knowledge on extraterrestrial environments. They are extreme environments on Earth that share common characteristics with past or extant environments on other planetary bodies. The Makgadikgadi Pans in central Botswana, are a desiccated relic of a former giant lake system, Paleo-Lake Makgadikgadi. They are an evaporitic environment rich in hydrated minerals, characterized by ephemeral water bodies whose chemistry fluctuates over the wet and dry seasons leading to distinctive clay mineral and evaporite deposits on the pan floor harboring communities of extremophiles (Filippidou et al., 2024). Environments such as the Makgadikgadi pans are extremely relevant for the study of Mars habitability. In fact, clay minerals such as Fe/Mg smectites and chlorites have been detected on terrains across the Martian surface by remote sensing orbiters like the OMEGA instrument. These minerals, for their link with aqueous processes and for the potential of preserving microbial signature have strong implications for the study of the evolution of hydrology and paleo-environment on Mars.The goal of this study is to characterize clay minerals in the Makgadikgadi Pans using integrated analytical techniques, with the purpose of developing a criterion to help identify clay bearing strata formed authigenically within evaporitic environments of Mars and to distinguish them from those clay minerals formed under different physiochemical conditions (i.e. weathering profiles of basic volcanic rocks, impact-induced hydrothermal sites).In this study we will examine the vertical and spatial distribution of clay minerals from 15cm cores of shallow subsurface playa sediments along salinity profiles within the Kudiakam Pan, in the northern Makgadikgadi Basin. The analytical techniques used to characterize the clay minerals within the Makgadikgadi pans include X-ray Diffraction (XRD) and Near Infrared Spectroscopy to identify clay mineral types in oriented samples, Scanning Electron Microscopy (SEM) coupled with Energy Dispersive Spectroscopy (EDS) to examine clay morphology and for geochemical and elemental analysis of the clays and Raman Spectroscopy to investigate for adsorbed organic matter trapped within the clay layers.Preliminary data revealed that the superficial deposits from all cores of the Makgadikgadi pans contain interstratified illite-smectite (I/S) clay minerals showing a sharp peak at 12 . This may point to the evolution of pore water chemistry as expected in a playa environment. Further analysis using IR will constrain the clay mineral types and analysis by SEM-EDS will elucidate the differences in chemistry between samples. By analogy with the interstratified clay minerals found herein, we provide valuable ground truthing for astrobiological investigations and help assess the habitability of Mars.REFERENCES:Filippidou, S., Price, A., Spencer-jones, C., Scales, A., Macey, M. C., Franchi, F., Lebogang, L., Cavalazzi, B., Schwenzer, S. P., Olsson-Francis, K. (2024). Diversity of Microbial Mats in the Makgadikgadi Salt Pans, Botswana. Microorganisms, 12, 147.