title: Evidence for only minor contributions from bacteria to sedimentary organic carbon.
abstract: Because their molecular signatures are often prominent in extracts of sediments, bacteria are thought to be important contributors to petroleum source beds.  It has been shown recently, however, that abundances of biomarkers do not always reflect relative contributions to sedimentary organic carbon (Corg). The contribution of photosynthetic green sulphur bacteria to sediments can be assessed effectively because the diagenetic products of distinctive carotenoids from these organisms occur widely and their biomass is isotopically labelled, being enriched in 13C. We show here that, although sediments and oils from the Western Canada and Williston basins contain prominent biomarkers of photosynthetic bacteria, the absence of 13C enrichment in the total Corg requires that the bacterial contribution is in fact minimal. Although the importance of bacterial reworking of sedimentary debris cannot be doubted, we argue that our findings, when considered in conjunction with those from other settings, suggest that bacterial biomass may commonly represent only a minor component of total Corg in carbonaceous rocks.
authors.affiliation: Division of Marine Biogeochemistry, Netherlands Institute for Sea Research, Texel.
authors.forename: W A
authors.initials: WA
authors.lastname: Hartgers
authors.forename: J S
authors.initials: JS
authors.lastname: Sinninghe Damste
authors.forename: A G
authors.initials: AG
authors.lastname: Requejo
authors.forename: J
authors.initials: J
authors.lastname: Allan
authors.forename: J M
authors.initials: JM
authors.lastname: Hayes
authors.forename: J W
authors.initials: JW
authors.lastname: de Leeuw
mesh_terms: D002170:Canada; D002244:Carbon / Q000737:chemistry* / Q000378:metabolism; D002247:Carbon Isotopes; D002338:Carotenoids / Q000032:analysis; D019414:Chlorobi / Q000378:metabolism*; D000460:Chlorophyta; D004783:Environmental Microbiology; D019015:Geologic Sediments / Q000032:analysis* / Q000737:chemistry / Q000382:microbiology; D006838:Hydrocarbons / Q000032:analysis; D010578:Petroleum / Q000032:analysis / Q000382:microbiology*; D010788:Photosynthesis
chemical_list: D002247:Carbon Isotopes; D006838:Hydrocarbons; D010578:Petroleum; D002338:Carotenoids; D002244:Carbon