Microbialite Biosignature Analysis by Mesoscale X-ray Fluorescence (μXRF) Mapping.

Area of Science:

• Astrobiology
• Geochemistry
• Planetary Science

Background:

• The Mars 2020 rover will utilize the Planetary Instrument for X-ray Lithochemistry (PIXL), a micro-X-ray fluorescence (μXRF) spectrometer, for biosignature detection.
• Understanding μXRF's capabilities in analyzing rock types and identifying biosignatures is crucial for the Mars 2020 mission's in situ science and sample selection.

Purpose of the Study:

• To test mesoscale chemical mapping using μXRF for biosignature interpretation in microbialites.
• To identify spatial distributions and elemental associations ('fluorescence microfacies') to infer the processes that formed compositional distributions in ancient stromatolites.

Main Methods:

• Utilized μXRF spectroscopy to analyze elemental distributions in Mesoarchean stromatolites from the Nsuze Group (2.98 Ga).
• Characterized five distinct fluorescence microfacies: laminated dolostone, laminated chert, clotted dolostone and chert, stromatolite clast breccia, and cavity fill.

Main Results:

• Analyzed elemental distributions to infer the formation processes of different microfacies.
• Laminated dolostone formed from microbial mats trapping sediment and precipitating carbonate. Laminated chert resulted from secondary silicification of microbial mats.
• Clotted dolostone and chert formed as mounds through mat growth and carbonate precipitation. Breccias filled erosional spaces, and cavities contained microquartz, Mn-rich dolomite, and calcite.

Conclusions:

• μXRF is effective for inferring genetic processes in rocks.
• μXRF can successfully identify biosignatures in compositionally heterogeneous rocks, supporting its use in astrobiological exploration.