Molecular preservation in halite‐ and perchlorate‐rich hypersaline subsurface deposits in the Salar Grande basin (Atacama Desert, Chile): Implications for the search for molecular biomarkers on Mars

Abstract

[1] Similarities between the Atacama Desert (Chile) and Mars include extreme aridity, highly oxidizing chemistry, and intense ultraviolet radiation that promoted the photochemical production of perchlorates and nitrates. Concentration of these ions under hyperarid conditions led to the formation of nitrate-and perchlorate-bearing deposits in ephemeral lakes, followed by later deposition of chlorides and sulfates. At some locations, such as the Salar Grande, hypersaline deposits have remained unaltered for millions of years. We conducted a drilling campaign in deposits of the Salar to characterize the preservation state of biological molecules. A 5 m deep discontinuous core was recovered and subjected to multitechnique analysis including the antibody microarray-based biosensor LDChip300 and the SOLID (Signs Of Life Detector) instrument, complemented by geophysical, mineralogical, geochemical, and molecular analysis. We identified two units based on the mineralogy: the upper one, from the surface to~320 cm depth characterized by a predominance of halite and anhydrite, and the lower one, from 320 to 520 cm, with a drop in halite and anhydrite and an enrichment in nitrate and perchlorate. Organic compounds including biomolecules were detected in association with the different depositional and mineralogical units, demonstrating the high capacity for molecular preservation. Hypersaline environments preserve biomolecules over geologically significant timescales; therefore, salt-bearing materials should be high-priority targets for the search for evidence of life on Mars.Citation: Ferna´ndez-Remolar, D. C., et al. (2013), Molecular preservation in halite-and perchlorate-rich hypersaline subsurface deposits in the Salar Grande basin (Atacama Desert, Chile): Implications for the search for molecular biomarkers on Mars, J. Geophys. Res. Biogeosci., 118,[922][923][924][925][926][927][928][929][930][931][932][933][934][935][936][937][938][939]

Oxalate formation under the hyperarid conditions of the Atacama desert as a mineral marker to provide clues to the source of organic carbon on Mars

“…Detrital minerals (>80 wt % mineral content) dominate the lower unit, where clastic silicates (microcline, albite, riebeckite, and quartz) are associated with an ensemble of secondary saline components, including gypsum, anhydrite, and halite. In contrast to the heterogeneous lower unit, the upper unit is nearly pure halite, with very small amounts of gypsum [ Fernández‐Remolar et al ., ]. The upper halite‐rich materials correspond to the Soledad Formation, and the lower reddish detrital unit likely corresponds to proximal alluvial material interfingering with the lacustrine deposits of the Quillagua Formation [ Sáez et al ., , ].…”

“…It was filled over the course of three different depositional episodes [ Chong Dı́az et al ., ; Sáez et al ., ]: (1) the initial deposition of mixed red‐bed detrital and sulfate‐bearing sediments in the early to middle Miocene; (2) a second episode during the late Miocene with a detrital unit composed of siliceous breccias, gravels, marls, and diatomites known as the Quillagua Formation; and (3) a cap of massive precipitated chlorides known as the La Soledad Formation. The uppermost deposits were formed under extreme hyperarid conditions, which is considered to be a good analogue for the chloride‐bearing deposits of Terra Sirenum on Mars [ Fernández‐Remolar et al ., ]. Moreover, the general progression from siliciclastic to halide‐dominant sedimentation under increasingly hyperarid conditions bears some qualitative resemblances to the postulated formation history of the Terra Sirenum halide‐bearing deposits [e.g., Glotch et al ., ].…”

“…This is evidenced by the exceptional preservation of the sedimentary textures in primary anhydrite, which shows no signs of rehydration and would otherwise overprint and destroy the primary structures [ Pueyo et al ., ]. In addition, the presence of nitrate and perchlorate minerals, as well as very soluble halides (e.g., Br − , I − , and IO 3− minerals), accompanying halite and sulfates is further evidence of extreme conditions including water activity lower than 0.60 [ Fernández‐Remolar et al ., ]. Preservation of diverse biomolecules has been reported under these stressful extreme conditions, which suggests that rapid mineralization, low water activity, and basin subsidence are key factors to increase preservation rates for very labile biomolecules, such as nucleic acids [ Fernández‐Remolar et al ., ].…”

“…In this paper, we report the occurrence of the Ca‐bearing oxalates weddellite and whewellite preserved in ancient sedimentary deposits (>1 Ma–100 ka) in the Salar Grande basin in the Atacama desert, Chile. The Salar Grande is considered a good terrestrial analogue of halide‐bearing deposits in Terra Sirenum, Mars [ Chong Dı́az et al ., ; Sáez et al ., ; Fernández‐Remolar et al ., ]. Weddellite and whewellite are likely produced as biominerals at the margins of this basin through precipitation mediated by lichen activity.…”

The western Qaidam Basin as a potential Martian environmental analogue: An overview

“…Through the study of terrestrial analogues, we gain crucial information with respect to the ability of organisms to survive extreme conditions, as well as to the limits of life on Earth [Fairén et al, 2010]. Previous studies already analyzed microbial populations on Mars analogue environments [e.g., Fernández-Remolar et al, 2005;Clarke, 2006;Edwards et al, 2007;Fernández-Remolar et al, 2008;Foing et al, 2011;Fernández-Remolar et al, 2013]. The Atacama desert, considered one of the most similar places on Earth to Mars [Navarro-González et al, 2003], contains endolithic microorganisms within halite rocks [Wierzchos et al, 2006].…”