Detection of organic carbon in Mars-analog paleosols with thermal and evolved gas analysis

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Authors

Adrian Broz , Joanna Clark, Brad Sutter, Doug W Ming, Briony H Horgan, Paul Douglas Archer, Lucas C.R. Silva

Abstract

Ancient, buried soils, or paleosols, may have been preserved in the geological record on Mars, and are considered high-priority targets for biosignature investigation. Studies of paleosols on Earth that are similar in composition to putative martian paleosols can provide a reference frame for constraining their organic preservation potential on Mars. However, terrestrial paleosols typically preserve only trace amounts of organic carbon. Moreover, the study of terrestrial paleosols is complicated by diagenetic additions of organic carbon, which can confound interpretations of their organic preservation potential. The objectives of this study were a) to determine whether organic carbon in Mars-analog paleosols can be detected with thermal and evolved gas analysis, and b) constrain the age of organic carbon using radiocarbon (14C) dating. Oligocene (33 Ma) paleosols from Oregon were examined with an instrument similar to the Sample Analysis at Mars Evolved Gas Analysis (SAM-EGA) instrument onboard the Mars Science Laboratory Curiosity rover. Trace amounts of organic carbon and fragments of organic molecules were observed in all samples. Total organic carbon (TOC) ranged from 0.002 - 0.032 ± 0.006 wt. %. Evolutions of organic fragments co-occurred with evolutions of CO2 from organic carbon decomposition. Like modern soils, the near-surface horizons of all paleosols had significantly higher TOC relative to subsurface layers. Radiocarbon dating revealed an organic carbon age of ~6,200 – 14,500 years before present, suggesting there had been late diagenetic inputs of organic carbon. This work demonstrates that near-surface horizons of martian paleosols are a potential high priority location for in-situ biosignature investigation.

DOI

https://doi.org/10.31223/X50G88

Subjects

Physical Sciences and Mathematics

Keywords

Paleosols, evolved gas analysis, SAM-EGA, organic preservation, radiocarbon

Dates

Published: 2021-12-16 13:25

Last Updated: 2021-12-20 22:57

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License

CC BY Attribution 4.0 International

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Conflict of interest statement:
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