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The AAPG/Datapages Combined Publications Database
AAPG Special Volumes
Fohrmann, M., A. R.Gorman, and I. A. Pecher,
Seismic Characterization of the Fiordland Gas-hydrate Province, New Zealand
Miko Fohrmann1, Andrew R. Gorman,2 Ingo A. Pecher3
1Department of Geology, University of Otago, Dunedin, New Zealand; Present address: Institute of Geological and Nuclear Sciences (GNS), Lower Hutt, New Zealand
2Department of Geology, University of Otago, Dunedin, New Zealand
3Institute of Geological and Nuclear Sciences (GNS), Lower Hutt, New Zealand
The authors gratefully acknowledge the University of Otago for funding the project. Furthermore, M. Fohrmann deeply acknowledges the Jack Bradshaw fund for financial support. Special thanks to the Institute of Geological and Nuclear Sciences (GNS), the National Institute of Water and Atmospheric Research (NIWA), and the New Zealand Ministry of Economic Development for providing access to the seismic reflection data. Reviews of an earlier version of this manuscript by Matthew Hornbach and John Townend greatly improved this chapter.
Occurrences of bottom-simulating reflectors (BSRs), related to the presence of gas hydrates, previously have been observed across a widespread zone on the active continental margin associated with the incipient Puysegur subduction zone, southeast of the South Island of New Zealand. However, unlike New Zealand's other large gas-hydrate province located on the active Hikurangi margin, east of the North Island, the Fiordland BSRs have not been described in terms of their seismic characteristics or distribution. Five seismic reflection data sets are analyzed here to identify a region of BSRs covering approximately 2200 km2 (849 mi2). The BSRs identified in this region exhibit classic characteristics indicative of a reflector at the base of the gas-hydrate stability zone: (1) they predominantly have a negative polarity, implying a decrease in acoustic impedance; (2) they crosscut strata; and (3) they have a variable amplitude-versus-offset response, indicating the presence of free gas below the reflector. Localized regions of acoustic blanking may be observed at some points above strong BSRs. The lack of information on the sedimentary characteristics of the Fiordland margin limits our ability to quantify the gas-hydrate deposits in this province. However, a significant proportion (16%) of the mapped region contains structural and stratigraphic features that can focus the upward flow of fluids and may therefore correspond to regions of increased hydrate concentrations.
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