Isotopic variations in dolomite concentrations from the Monterey Formation, California ( Miocene).

J. Hennessy, L. P. Knauth

Research output: Contribution to journalArticlepeer-review

54 Scopus citations


Isotopic analysis of dolomite concentrations from the Miocene Monterey Formation yields a covariance of delta18O and delta13C within every concretion analyzed. The total range for all concretions in delta18O (SMOW) is +27.3 per mille to +33.6 per mille. The total range in delta13C (PDB) is -10.2 per mille to +10.8 per mille. Variations of up to 3.6 per mille in oxygen and 12.2 per mille in carbon are encountered within a single concretion. Decreasing delta18O is interpreted in terms of increasing temperatures of formation as the concretion grows during burial. The Claypool and Kaplan (1974) model can be successfully used to interpret carbon isotope variations as the result of progressive concretion growth in the zones of microbial sulfate reduction, microbial methane production, and thermocatalytic decarboxylation. Multiple sampling of several concretions at a single outcrop yields a more complete early diagenetic history than by sampling only one concretion. Isotopic diagenetic profiles inferred from the dolomite concretions are similar to those seen in DSDP cores where deep-sea dolomitization is occurring today.-from Authors

Original languageEnglish (US)
Pages (from-to)120-130
Number of pages11
JournalJournal of Sedimentary Petrology
Issue number1
StatePublished - Jan 1 1985

ASJC Scopus subject areas

  • General Environmental Science
  • General Earth and Planetary Sciences


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