Enhanced microbial activity in carbon-rich pillow lavas, Ordovician, Great Britain and Ireland

Research output: Contribution to journalArticle


There is extensive evidence for the microbial colonization of seafloor basalts in the modern ocean and in the geological record. The sulfur isotope composition of pyrite in the basalts commonly indicates marked isotopic fractionation due to microbial sulfate reduction. Sections through the Nemagraptus gracilis zone (Ordovician) in Great Britain and Ireland are characterized by both widespread pillow lavas and organic-rich seafloor sediment, allowing an exceptional opportunity to assess whether the availability of organic carbon influenced the extent of microbial activity in the basalts indeep geological time. Whole-rock data from basalts at 10 localities show that there is a relationship between sulfur isotopic composition and the carbon content of the basalt. At two localities where organic carbon was entrained in the basalt, isotopic compositions are heavy compared to compositions in carbon-poor basalt, implying that microbial activity exhausted the supply of seawater sulfate. In most basalt, microbial activity was limited by the supply of carbon, but wherethe basalt incorporated carbon during emplacement on the seafloor, microbial activity became sulfate limited.


  • John Parnell
  • Adrian J. Boyce
  • Davidheiser Kroll Brett
  • Connor Brolly
  • Stephen Bowden
  • Paula Lindgren
External organisations
  • University of Aberdeen
  • Scottish Universities Environmental Research Centre
  • University of Glasgow
Research areas and keywords

Subject classification (UKÄ) – MANDATORY

  • Geology
Original languageEnglish
Pages (from-to)827-830
Number of pages4
Issue number9
Publication statusPublished - 2015
Publication categoryResearch
Externally publishedYes