--> Gas hydrates and genetic link between Miocene seafloor methane seeps and underlying fluid conduit plumbing, East Coast Basin, New Zealand
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AAPG Asia Pacific Region Geosciences Technology Workshop:
Gas Hydrates – From Potential Geohazard to Carbon-Efficient Fuel?

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Gas hydrates and genetic link between Miocene seafloor methane seeps and underlying fluid conduit plumbing, East Coast Basin, New Zealand

Kathleen A. Campbell1, Campbell S. Nelson2, Stephanie L. Nyman2, Jens Greinert3,4, David A. Francis5, and Stephen D. Hood1


1School of Environment, University of Auckland, Private Bag 92019, Auckland 1142, New Zealand
2School of Science (Earth Sciences), University of Waikato, Private Bag 3105, Hamilton 3240, New Zealand
3GEOMAR Previous HitHelmholtzTop Centre For Ocean Research Kiel, Wischhofstrasse 1-3, D-24148 Kiel, Germany
4Christian-Albrechts University Kiel, Institute of Geosciences, Ludewig-Meyn-Str. 10-12, 24098 Kiel, Germany
5P.O. Box 30-819, Lower Hutt 5040, New Zealand, New Zealand


April 15-17, 2019 – AAPG Asia Pacific Region Geosciences Technology Workshop: Gas Hydrates – From Potential Geohazard to Carbon-Efficient Fuel?, Auckland, New Zealand

Posted: June 30, 2019

Abstract

Methane-derived authigenic carbonates in Miocene bathyal mudstones in eastern North Island, New Zealand, are typically expressed as either sub-seafloor conduit concretions or as seafloor seep limestones, the former interpreted to mark subsurface fluid pathways and the latter typically fossiliferous with a chemosynthesis-based biota. Rarely are both types exposed in a single location; consequently, any potential genetic link between them is usually inferred. Petrography and stable carbon (δ13C) and oxygen (δ18O) isotopes allow exploration for evidence of direct ties between paleo-conduit concretions and limestone build-ups formed from ancient methane seepage. The authigenic carbonate components present include texturally varied microcrystalline calcite, fibrous aragonite, and granular, blocky and bladed calcite crystals, especially infilling once-open central conduits within the concretions and in vugs and veins in the limestone. Their δ13C values typically range from –52 to –20‰ VPDB indicating that anaerobic oxidation of methane (AOM), possibly mainly of thermogenic origin, was a primary process during carbonate precipitation in North Island paleo-seeps. Additionally, some components show a range of relatively less depleted δ13C values, suggesting a diminished methane supply and increasing influence from marine bicarbonate. δ18O values range widely from –6 to +4‰ VPDB, consistent with pore fluid evolution associated with gas hydrate formation and dissociation events and/or temperature shifts with burial. Petrographic and isotopic similarities in cement components and concretions at Rocky Knob, east of Gisborne, the largest Miocene seep complex in New Zealand, suggests a genetic tie between paleo-fluid plumbing and seafloor manifestations of methane seepage, with derivation from the same fluids albeit in different parts (i.e. sub-seafloor vs seafloor) of the seep complex.

AAPG Datapages/Search and Discovery Article #90348 © 2019 AAPG Asia Pacific Region Geosciences Technology Workshop, Gas Hydrates – From Potential Geohazard to Carbon-Efficient Fuel?, Auckland, New Zealand, April 15-17, 2019