Tectonically Controlled Methane Escape In Lake Baikal

J. Klerkx1, M. De Batist2, J. Poort2, R. Hus2, P. Van Rensbergen2, O. Khlystov3 and N. Granin3

1 International Bureau for Environmental Studies, Brussels, Belgium; 2Renard Centre of Marine Geology, University of Ghent, Belgium; 3Limnological Instute, Siberian Branch of the Russian Academy of Sciences, Irkutsk, Russia

Abstract: Methane, which is at least partly stored in the bottom sediments of Lake Baikal as gas hydrates, is released on the lake floor in the deeper parts of the basin along major faults, forming venting structures similar to small mud volcanoes. The CH4 venting structures are considered to be the surface expression of escape pathways for excess CH4 generated by the dissociation of pre-existing hydrates. The existence of a local heat flow anomaly associated with the seep area is most likely due to a heat pulse causing the dissociation of the underlying gas hydrates. The heat pulse may be caused by upward flow of geothermal fluids along segments of active faults, possibly accelerated by seismic pumping. It is assumed that this fluid flow is tectonically triggered, considering that left-lateral strike-slip movements along the border faults act as a major factor in fluid accumulation: even a reduced lateral displacement is able to generate fluid flow in the compressional direction, resulting in fluid escape along faults directed along the main direction of extension. The tectonic effect may be coupled to the sediment compaction due to a high sedimentation rate in the area of mud volcanism. Both processes may generate a large-scale convective fluid loop within the basin-fill sediments which advects deeper gases and fluids to the shallow sub-surface. Even in the extensional tectonic environment of Lake Baikal, local compressional forces related to a strike-slip component, may play a role in fluid flow, accumulation and gas escape along active faults. The mechanisms that result in the expulsion of the CH4 in the Lake Baikal sediments are considered as an analogue of what could happen during CO2 sequestration in a similar tectonic environment.

Key words: Methane escape, mud volcanism, gas hydrates dissociation.

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