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

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 Nemagrapt...

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Bibliographic Details
Published in:Geology (Boulder) 2015-09, Vol.43 (9), p.827-830
Main Authors: Parnell, John, Boyce, Adrian J, Davidheiser-Kroll, Brett, Brolly, Connor, Bowden, Stephen, Lindgren, Paula
Format: Article
Language:English
Subjects:
basalts
carbon
Europe
Fractionation
Geochemistry
Geological time
Great Britain
igneous and metamorphic rocks
Igneous rocks
Ireland
isotope fractionation
isotope ratios
isotopes
lava
Microbiology
Minerals
Ordovician
organic carbon
Paleozoic
Petrology
pillow lava
Radioisotopes
reduction
S-34/S-32
stable isotopes
sulfates
sulfur
United Kingdom
volcanic rocks
Western Europe
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Summary: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 in deep 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 where the basalt incorporated carbon during emplacement on the seafloor, microbial activity became sulfate limited.
ISSN:0091-7613
1943-2682
DOI:10.1130/G36937.1