Metamorphic evolution of carbonate-hosted microbial biosignatures

Claire Rachel Cousins, Sami Mikhail, Frédéric Foucher, Andrew Stelle, Frances Westall

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Microbial biosignature assemblages captured within mineral substrates experience extreme pressures (P) and temperatures (T) during rock burial and metamorphism. We subjected natural microbial biofilms hosted within thermal spring carbonate to six high pressure, high temperature (HPHT) conditions spanning 500 and 800 MPa and 200 to 550 °C, to investigate the initial petrographic transformation of organic and inorganic phases. We find biogenic and amorphous silica mineralises increasingly mature organic matter (OM) as temperature and pressure increase, with OM expelled from recrystallised calcite at the highest HPHT, captured within a quartz phase. Sulfur globules associated with microbial filaments persist across all HPHT conditions in association with microbially-derived kerogen. These data demonstrate how microbial material captured within chemically-precipitated sediments petrographically evolves in high grade rocks during their first stages of transformation.
Original languageEnglish
Pages (from-to)40-45
Number of pages5
JournalGeochemical Perspectives Letters
Publication statusPublished - 16 Jan 2020


  • Metamorphism
  • Biosignature
  • Carbonate
  • Microfossil
  • Raman spectroscopy
  • Kerogen


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