Hyperspectral VNIR imaging of microbialites from the alkaline lake Bagno dell’Acqua, Pantelleria island, Italy

Microbialites are organosedimentary, rock-like deposits, formed as a result of trapping and binding of sediment as well as mineral precipitation caused by microbial communities [1]. Fossilized terrestrial microbialites represent the oldest evidence of microbial life on Earth and therefore they are of great relevance for Astrobiology. Often fossil microbialites display typical morphological and compositional features which are highly diagnostic of microbial life [2]. These features can be identified via hyperspectral imaging which allows to map the distribution of the main mineral phases as well as organic matter (if any) [3]. In this work we investigated a few different microbialites from Lake Bagno dell’Acqua, Pantelleria, Italy. Lake Bagno dell’Acqua is an endorheic alkaline lake and was recently proposed as a Martian analog site due to close mineralogical similarities with some Martian terranes [4]. The microbialites were cut into thick slab and investigated with a combination of VNIR (350–2500 nm) hyperspectral imaging and μ-Raman spectroscopy. The VNIR imaging system was obtained by combining an ASD FieldSpec 4 Hi-Res with a micrometer X-Y stage. Hundreds of spectra were collected on densely spaced rectangular grids on the sample. The fiber optic bundle used to bring the scattered light to the spectrometer was adjusted in such a way to probe an area of about 0.45 (±0.05) cm2 in each measurement while each map covers an area of a few square centimeters. Raman scattering was used to support mineralogical determination from VNIR measurements. The proposed methodology allowed us to identify and map the distribution of the different phases in the investigated samples. Our results will support the data interpretation collected from rover’s instruments like Ma_MISS on Rosalind Franklin rover, which operate in a similar way [5].