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Foraminifera and Methane venting

Foraminifera and Methane venting. C ore sampling analyses, Hikurangi Margin, N.Z, SO191. This study tested for discernible imprints on the foraminiferal assemblage and on mineralization of foraminiferal tests from the methane-influenced environment. Hikurangi Margin seep sites.

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Foraminifera and Methane venting

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  1. Foraminifera and Methane venting Core sampling analyses, Hikurangi Margin, N.Z, SO191

  2. This study tested for discernible imprints on the foraminiferal assemblage and on mineralization of foraminiferal testsfrom the methane-influenced environment.

  3. Hikurangi Margin seep sites

  4. Geologic setting • Southernmost section of the 3000 km long Tonga–Kermadec–Hikurangisubductionsystem • Pacific plate is subducting beneath the Australian plate • Motion varies greatly: 100 mm/y in Tonga–Kermadec section, 40 mm/y in northern HikurangiMargin, 20 mm/y at southern end • anomalously thick (∼3 km) intricately deformed accretionary wedge • seep sites developed on crests of thrust ridges, underlain by thrust faults that act as conduits for fluids

  5. Methods • RV Sonne cruise 191-3, February-March, 2007 • TV-guided multi-corer • Sampled 7 sites from all three seep areas – Omakere Ridge, Rock Garden, Wairarapa plus one reference site from Omakere Ridge • Isotope analyses included biogenic carbonate (foraminiferal shells, clam shell) and inorganic carbonates (authigenic carbonate recovered from the same cores).

  6. Results Foraminiferal assemblage • 82 species • 16 occurred at all sites • all assemblages dominated by Uvigerinaperegrina • Agglutinate species occurred sparsely in seeps, but constituted 42% of the assemblage in the reference sample.

  7. Results – Foraminiferal density

  8. Results – species richness

  9. Diversity indices

  10. Isotope analyses • Six species • Stanford University Stable Isotope Laboratory on a Finnegan Kiel III carbonate device interfaced with an MAT 252 IRMS • University of Washington Department of Earth and Space Sciences Isotope Laboratory on a ThermoScientific Kiel III carbonate device attached to a Thermo- FinniganDeltaPlus IRMS • NBS 19 standard • Precision • Stanford - 0.05‰ for δ18O and 0.03‰ for δ13C • UW - 0.06‰ for δ18O and 0.03‰ for δ13C

  11. SEM imaging

  12. Isotope analyses C - Wairarapa

  13. Combined isotopes

  14. Conclusions • Assemblage data do not provide definitive mechanism for identifying or characterizing seep and non-seep sites. • Carbon isotope dataare clear in differentiating seep and non-seep cores. • Differences in variability and depletion of δ13C in foraminiferal carbonate appear to be correlated with differences in fluid-flow regimes. • Despite pristine appearance, there is a possibility of early diageneticalteration

  15. Thanks • Thanks to the officers and crew of RV SONNE and the scientific community on board who provided many stimulating discussions. • Funding: BMBF (the German Federal Ministry for Education and Research); Marsden Fund Council for government funding; University of Washington Department of Earth and Space Sciences Graduate Research Award. • David Mucciarone, Stanford University; Andrew Schauer, University of Washington, Ed Hare, Bruce Hayward, and Matthias Haeckel for pore water data.

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