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Abstract EANA2025-83


Microbially influenced evaporitic facies in the Makgadikgadi Pans (Botswana): insights for biosignature formation in Martian analogue environments

Tarozzi A. (1), Franchi F. (2),(3),(4), Gasparotto G. (1), Lesedi L. (3), Cavalazzi B. (1),(5)
(1) Department of Biological, Geological and Environmental Sciences, University of Bologna, Bologna, Italy (2) Dipartimento di Scienze della Terra e Geoambientali, Università degli Studi di Bari - Aldo Moro, Bari, Italy (3) Botswana International University of Science and Technology, Palapye, Botswana (4) School of Geosciences, University of the Witwatersrand, Johannesburg, South Africa (5) Department of Geology, University of Johannesburg, Johannesburg, South Africa


Evaporitic playa systems provide valuable terrestrial analogues for investigating the formation and preservation of biosignature under environmental conditions similar to those proposed for early Mars. The Makgadikgadi Pans in Botswana—among the largest evaporitic basins on Earth—combine hypersaline, alkaline, and seasonally dynamic conditions, making them an ideal natural laboratory for studying microbe–mineral interactions of astrobiology relevance. 

This study focuses on the surface salt crusts of Ntwetwe Pan, part of the Makgadikgadi Pans in Botswana, with the aim of characterizing their mineralogy, microtextures, and microbial structures, and evaluating their astrobiological relevance. Samples were collected along a 280-meter transect across salinity and moisture gradients. X-ray diffraction revealed halite as the dominant mineral, accompanied by widespread calcite and quartz, and by thenardite and trona in zones of elevated salinity. SEM-EDS analyses identified complex microfabrics—mineralized filaments, EPS-like matrices, and fine-grained coatings— indicative of microbial mediation in mineral precipitation and entrapment. A clear spatial pattern trend emerged: crusts from the margins were enriched in carbonates and exhibited well-preserved filament mineralization, while central samples, dominated by halite and trona, displayed poorer EPS preservation and weaker biosignature encapsulation. These findings underscore the role of environmental gradients in shaping the preservation potential of biosignatures. 

Along the transect, several features resembling potential biosignatures—such as spheroidal aggregates, acicular crystals, and vermicular cavities—were documented. Although some of them initially suggested a biogenic origin, their regular morphologies, lack of associated carbon, and mineralogical composition pointed instead to an abiotic origin likely due to rapid crystallization and dissolution–reprecipitation cycles under intense evaporative conditions. 

The Makgadikgadi Pans represent a valuable natural laboratory for refining biosignature detection strategies in Martian evaporitic environments such as Jezero Crater and Meridiani Planum. While rapid mineral precipitation in these systems may enhance microbial preservation, it can also generate abiotic features that closely resemble biogenic structures. This study reinforces the importance of a multidisciplinary approach—combining morphology, geochemistry, and mineralogy—in distinguishing true biosignatures, and provides critical insights for shaping the scientific goals of future astrobiology missions.

Acknowledgement: This study is a contribution to the Space It Up project funded by the Italian Space Agency, ASI, and the Ministry of University and Research, MUR, under contract n. 2024-5-E.0 - CUP n. I53D24000060005.