Abstract_EANA2024-67

Abstract EANA2024-67

Detection and preservation of FTIR biosignatures in the microbialites of Lake Salda, a Jezero Crater analogue

Connor J. Ballard (1), Louisa J. Preston (1), Lewis Dartnell (2), Catherine Regan (1), Andrew Coates (1)

(1) Mullard Space Science Laboratory, Department of Space and Climate Physics, University College London, Dorking, UK (2) Department of Life Sciences, University of Westminster, 115 New Cavendish St. London, W1W 6UW

Accurately identifying organic geochemical signatures is a prominent theme in Martian surface exploration and wider astrobiology. To improve our chances of detection and minimise false negative or positive signatures, we must continue to scrutinise techniques used in the search for life through terrestrial analogue investigations.

The hydromagnesite (Hmg) deposits of Lake Salda can provide insights into the nature of biosignature detection and preservation on Mars, since they are representative of Mg-carbonate deposits at Jezero Crater. At Lake Salda, hydromagnesite is predominantly deposited through cyanobacterial microbialite formation. These deposits dominate ancient and recent lake deposits, which are interspersed with Fe/Mg phyllosilicates.

This work employs microscopy and FTIR spectroscopy as a reproducible and non-invasive technique to explore biosignature preservation in Mg-carbonate and Mg/Fe phyllosilicate deposits. We later correlate spectral features using VisNIR spectroscopy and remove excess hydration using lyophilization.

Microscopy demonstrates a variety of textures across microbialites at different localities. Cryptocrystallinity is a common grain texture amongst all Hmg microbialites at Lake Salda, with examples in fluvial input zones demonstrating carbonate precipitates with incorporated detrital bedrock grains. Ancient deposits found in a tired terrace system allow an opportunity to analyse samples which vary in age across ~ 14,000 years. The Mid-Terrace Microbialite (MTM) demonstrates a uniquely recrystallised botryoidal hydromagnesite cement, which alters the physical structure of the microbialite and has implications for the resultant spectra.

FTIR spectroscopy reveals strong hydration absorptions alongside minor organic signatures, including deoxyribose C-O stretching (1044cm-1) and phosphate backbone (PO2-) stretching (1220 cm-1) in organic rich samples. VisNIR spectroscopy identifies the inclusion of metal-OH ions (Fe, Mg, Fe) in both hydromagnesite microbialites and the Salda phyllosilicate deposits, while chlorophyl a (443 nm), carotenoids (498 nm), phycocyanin (629 nm) and chlorophyll b (687 nm) are identified in the microbialites.

Lyophilization reduces interstitial H2O absorptions (2800cm-1 – 3600cm-1) present in most microbialites, which obscure regions of key biosignature absorptions, including aliphatic hydrocarbons. The reduction in H2O intensity increases our ability to detect a strong 2923cm-1 band, assigned to the aliphatic CH2 V3 stretching mode, in the most organic rich samples.