The structures beneath submarine methane seeps : seismic evidence from Opouawe Bank, Hikurangi Margin, New Zealand.

Netzeband, Gesa, Krabbenhöft, Anne, Zillmer, Matthias, Petersen, Carl Jörg, Papenberg, Cord and Bialas, Jörg (2010) The structures beneath submarine methane seeps : seismic evidence from Opouawe Bank, Hikurangi Margin, New Zealand. Marine Geology, 272 (1/4). pp. 59-70. DOI 10.1016/j.margeo.2009.07.005.

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Abstract

The role of methane in the global bio-geo-system is one of the most important issues of present-day research. Cold seeps, where methane leaves the seafloor and enters the water column, provide valuable evidence of subsurface methane paths. Within the New Vents project we investigate cold seeps and seep structures at the Hikurangi Margin, east of New Zealand. In the area of Opouawe Bank, offshore the southern tip of the North Island, numerous extremely active seeps have been discovered. High-resolution seismic sections show a variety of seep structures. We see seismic chimneys either characterised by high-amplitude reflections or by acoustic turbidity and faults presumably acting as fluid pathways. The bathymetric expression of the seeps
also varies: There are seeps exhibiting a flat seafloor as well as a seep located in a depression and small
mounds.
The images of the 3.5 kHz Parasound system reveal the ear-surface structure of the vent sites. While highamplitude
spots within the uppermost 50 m below the seafloor (bsf) are observed at the majority of the seep structures, indicating gas hydrate and/or authigenic carbonate formations with an accumulation of free gas underneath, a few seep structures are characterised by the complete absence of reflections, indicating a high gas content without the formation of a gas trap by hydrates or carbonates. The factors controlling seep formation have been analysed with respect to seep location, seep structure, water depth, seafloor morphology, faults and gas hydrate distribution. The results indicate that the revailing structural control for seep formation at Opouawe Bank is the presence of numerous minor faults piercing the base of the gas hydrate stability zone.

Document Type: Article
Keywords: seeps, bents, Seismics, methane, gas hydrate, mound, Hikurangi Margin, Opouwa Bank, Wararapa area, New Zealand
Research affiliation: OceanRep > GEOMAR > FB4 Dynamics of the Ocean Floor > FB4-GDY Marine Geodynamics
Refereed: Yes
Open Access Journal?: No
DOI etc.: 10.1016/j.margeo.2009.07.005
ISSN: 0025-3227
Projects: NewVents
Expeditions/Models/Experiments:
Date Deposited: 11 Nov 2009 12:07
Last Modified: 08 Aug 2017 09:52
URI: http://oceanrep.geomar.de/id/eprint/1341

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