Dumke, Ines (2015) New insights into fluid flow and seep processes - Case studies from the North Atlantic and offshore New Zealand. (PhD/ Doctoral thesis), Christian-Albrechts-Universität, Kiel, 171 pp.

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Abstract

In this thesis, four fluid flow systems are studied in terms of their development, venting activity, and relation to past and current climate warming periods. The studies were accomplished by using a variety of geophysical methods, including 2D and 3D seismic, sidescan sonar, and sediment echosounder methods, as well as heat flow measurements, geochemical analyses, and numerical modelling. The first case study presents a fluid flow system early in its development, located north of the Knipovich Ridge on the western Svalbard margin. Gas hydrates in this region are more widespread than anywhere else in the eastern North Atlantic, indicating a substantial gas reservoir. The origin of the gas is discussed, as are the source rock potential on the Svalbard margin and the role of the Knipovich Ridge with respect to thermogenic gas production. Case study 2 focuses on a more developed fluid flow system, the Giant Gjallar Vent in the Norwegian Sea. This vent system is one of the largest in the North Atlantic and is characterised by two prominent conduits that terminate beneath the seabed. Based on new seismic data, the activity history of the vent is re-interpreted and implications on the future development of this structure are discussed. Case study 3 deals with a deviation from the classic fluid flow system: on the upper continental margin offshore Svalbard, fluid venting occurs without fluid conduits being present, as the reservoir crops out at the seabed. Seepage is linked to dissociation of gas hydrates, which is caused by seasonal fluctuations of bottom-water temperatures. The onset of periodic gas hydrate formation and dissociation is constrained from carbonate samples and discussed with respect to ongoing decadal-scale global warming. The fourth case study looks at cold seeps on the Hikurangi Margin offshore New Zealand, which represent a fully developed fluid flow system. Seafloor expressions imaged with sidescan sonar fall into four distinct types of backscatter pattern. These patterns are integrated with observations of seabed fauna and discussed with respect to cold seep development.

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