Ancient hydrocarbon seeps from the Mesozoic convergent margin of California: Carbonate geochemistry, fluids and paleoenvironments

K. A. Campbell, Jack Farmer, D. Des Marais

Research output: Contribution to journalArticle

218 Scopus citations

Abstract

More than a dozen hydrocarbon seep-carbonate occurrences in late Jurassic to late Cretaceous forearc and accretionary prism strata, western California, accumulated in turbidite/fault-hosted or serpentine diapir-related settings. Three sites, Paskenta, Cold Fork of Cottonwood Creek and Wilbur Springs, were analyzed for their petrographic, geochemical and palaeoecological attributes, and each showed a three-stage development that recorded the evolution of fluids through reducing-oxidizing-reducing conditions. The first stage constituted diffusive, reduced fluid seepage (CH4, H2S) through seafloor sediments, as indicated by Fe-rich detrital micrite, corroded surfaces encrusted with framboidal pyrite, anhedral yellow calcite and negative cement stable isotopic signatures (δ13C as low as -35.5‰ PDB; δ18O as low as - 10.8‰ PDB). Mega-invertebrates, adapted to reduced conditions and/or bacterial chemosymbiosis, colonized the sites during this earliest period of fluid seepage. A second, early stage of centralized venting at the seafloor followed, which was coincident with hydrocarbon migration, as evidenced by nonluminescent fibrous cements with δ13C values as low as -43.7‰ PDB, elevated δ18O (up to +2.3‰ PDB), petroleum inclusions, marine borings and lack of pyrite. Throughout these early phases of hydrocarbon seepage, microbial sediments were preserved as layered and clotted, nondetrital micrites. A final late-stage of development marked a return to reducing conditions during burial diagenesis, as implied by pore-associated Mn-rich cement phases with bright cathodoluminescent patterns, and negative δ18O signatures (as low as -14‰ PDB). These recurring patterns among sites highlight similarities in the hydrogeological evolution of the Mesozoic convergent margin of California, which influenced local geochemical conditions and organism responses. A comparison of stable carbon and oxygen isotopic data for 33 globally distributed seep-carbonates, ranging in age from Devonian to Recent, delineated three groupings that reflect variable fluid input, different tectono-sedimentary regimes and time-temperature-dependent burial diagenesis.

Original languageEnglish (US)
Pages (from-to)63-94
Number of pages32
JournalGeofluids
Volume2
Issue number2
DOIs
StatePublished - Aug 13 2002

Keywords

  • Ancient hydrocarbon seeps
  • California Mesozoic
  • Carbonate geochemistry
  • Carbonate paragenesis
  • Stable isotopes

ASJC Scopus subject areas

  • Earth and Planetary Sciences(all)

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