Geological imprint of methane seepage on the seabed and biota of the convergent Hikurangi Margin, New Zealand: box core and grab carbonate results

Campbell, Kathleen A., Nelson, Campbell S., Alfaro, Andrea C., Boyd, Sheree, Greinert, Jens, Nyman, Stephanie, Grosjean, Emmanuelle, Logan, Graham A., Murray, Gregory F., Cooke, Steve, Linke, Peter, Milloy, Sophie and Wallis, Irene (2010) Geological imprint of methane seepage on the seabed and biota of the convergent Hikurangi Margin, New Zealand: box core and grab carbonate results Marine Geology, 272 . pp. 285-306. DOI 10.1016/j.margeo.2010.01.002.

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Short box cores (to 30 cm bsf) and seafloor carbonate grab samples were acquired at mapped hydrocarbon seep sites (600–1200 m water depths) during the 2007 RV SONNE SO191 cruise on the Hikurangi Margin offshore eastern North Island, New Zealand, to evaluate the influence of methane seepage on sedimentologic, biotic, mineralogic and stable isotopic attributes of seabed sediments. Sedimentary horizons in the box cores consist of siliciclastic silts and sands, shell beds and nodular, microcrystalline aragonite bands up to 15 cm thick. The megafauna is dominated by infaunal to semi-infaunal chemosymbiotic bivalves (Calyptogena, Lucinoma, and Acharax), as well as associated worms and carnivorous and grazing gastropods. Burrows in silts, some occupied by worms or juvenile Acharax, mainly have simple morphologies more typical of high-energy, nearshore settings than deep-sea environments, while a few are large and sparsely branched with wall scratch marks inferred to be of decapod crustacean origin.

The box core silts and nodular carbonate samples vary in TOC content from 0.2 to 0.9 wt.%, carbonate content from 4 to 78%, and δ13C and δ18O values from − 50.3 to − 0.6‰ PDB and + 0.77 to + 3.2‰ PDB, respectively. Low carbonate content silt samples have the most enriched δ13C values, implying a seawater source for their pore water bicarbonate. Negative δ13C and positive δ18O values typify the nodular, microcrystalline aragonite bands, indicating formation during microbially mediated, sulphate-dependent anaerobic oxidation of methane (AOM) in a cold, near-seafloor environment, as is also supported by lipid biomarker data. A clear isotopic mixing trend of decreasing δ13C and increasing δ18O and carbonate content in the fine (< 100 µm) carbonate fraction of the host silts also has been reported from other methane seep provinces, and suggests a heterogeneous influx of methane-rich seep

Document Type: Article
Keywords: Hikurangi Margin, New Zealand, hydrocarbon seeps, chemosynthesis, Authigenic carbonates, mineralogy, Stable isotopes, lipid biomarkers
Research affiliation: OceanRep > GEOMAR > FB2 Marine Biogeochemistry > FB2-MG Marine Geosystems
Refereed: Yes
DOI etc.: 10.1016/j.margeo.2010.01.002
ISSN: 0025-3227
Date Deposited: 09 Feb 2010 15:43
Last Modified: 08 Aug 2017 09:02

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