Seal bypass at the Giant Gjallar Vent (Norwegian Sea): Indications for a new phase of fluid venting at a 56-Ma-old fluid migration system

• Published in: Marine geology Vol. 351; pp. 38 - 52
• Main Authors: Dumke, Ines, Berndt, Christian, Crutchley, Gareth J., Krause, Stefan, Liebetrau, Volker, Gay, Aurélien, Couillard, Mélanie
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01-05-2014; Elsevier
• Subjects: fluid pipe; Giant Gjallar Vent; Norwegian Sea; Ocean, Atmosphere; overpressure build-up; Sciences of the Universe; seal bypass; Vøring Basin; fluid pipe; seal bypass; Norwegian Sea; Vøring Basin; Giant Gjallar Vent; overpressure build-up; Voring Basin
• ISSN: 0025-3227; 1872-6151
• DOI: 10.1016/j.margeo.2014.03.006

The Giant Gjallar Vent (GGV), located in the Vøring Basin off mid-Norway, is one of the largest (~5×3km) vent systems in the North Atlantic. The vent represents a reactivated former hydrothermal system that formed at about 56Ma. It is fed by two pipes of 440m and 480m diameter that extend from the Lower Eocene section up to the Base Pleistocene Unconformity (BPU). Previous studies based on 3D seismic data differ in their interpretations of the present activity of the GGV, describing the system as buried and as reactivated in the Upper Pliocene. We present a new interpretation of the GGV's reactivation, using high-resolution 2D seismic and Parasound data. Despite the absence of geochemical and hydroacoustic indications for fluid escape into the water column, the GGV appears to be active because of various seismic anomalies which we interpret to indicate the presence of free gas in the subsurface. The anomalies are confined to the Kai Formation beneath the BPU and the overlying Naust Formation, which are interpreted to act as a seal to upward fluid migration. The seal is breached by focused fluid migration at one location where an up to 100m wide chimney-like anomaly extends from the BPU up to the seafloor. We propose that further overpressure build-up in response to sediment loading and continued gas ascent beneath the BPU will eventually lead to large-scale seal bypass, starting a new phase of venting at the GGV.
•The Giant Gjallar Vent is still active in terms of fluid migration and faulting.•The Base Pleistocene Unconformity acts as a seal to upward fluid migration.•Seal bypass in at least one location leads to a new phase of fluid venting.