Novel saturated hexacyclic C34 and C35 hopanes in lacustrine oils and source rocks

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Abstract

Novel C34 and C35 hexacyclic hopanes having side chains with a pentacyclic or hexacyclic ring at C-22 are abundant in lacustrine oils and source rocks but almost absent from marine oils. The corresponding C34 and C35 hexacyclic hop-17(21)-enes were identified in thermally immature mudstones from Vietnam cored in the 500m deep ENRECA-3 well. All the novel hexacyclic compounds were unambiguously identified by comparison with synthetic standards. Traces of heptacyclic hopanes were detected in a lacustrine oil from Thailand. The C34 and C 35 hexacyclic hopanes have much longer gas chromatography (GC) retention times than the corresponding pentacyclic hopanes. They are isomerized faster at C-22 than the pentacyclic hopanes and their 22S/(22S+22R) ratio values at equilibrium are much higher (0.8 for C34). Precursors could be penta- and hexafunctionalised hopanoids in cyanobacteria and methanotrophs.

Original languageEnglish
Pages (from-to)107-118
Number of pages12
JournalOrganic Geochemistry
Volume87
DOIs
Publication statusPublished - 1 Oct 2015

Keywords

  • Biomarkers
  • Cyanobacteria
  • GC-MS
  • Hexacyclic hopanes
  • Hopanes
  • HPLC
  • Lacustrine oils
  • Methanotrophs

Programme Area

  • Programme Area 3: Energy Resources

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