Modulation of Seafloor Seepage by Faulting and Cracking of Deep Water Gas-Hydrate Systems at the Vestnesa Ridge, Fram Strait

Abstract:

Seepage of natural gas at the seafloor is a broadly observed phenomenon, associated with hydrate systems and/or with shallow gas accumulations in the sub-surface. Regardless the geological setting, global observations indicate that gas seepage is most often episodic. Seepage episodes may occur with a predictable short-term periodicity (e.g., by seasonal or tidal related pressure and temperature changes) or longer term periodicity (e.g., glacial-interglacial changes). But seepage episodes can be also irregular, modulated for instance, by cracking and faulting. Identifying the processes modulating seepage is fundamental for reconstructing seepage history and for analyzing potential implications of seepage from geological sources on past and present climatic anomalies. We document the overlapping influence of fault reactivation and possibly glacial-interglacial cycles on cracking and seepage evolution within the deep water (1-2 km water depth), > 60 km long, and gas hydrate-charged Vestnesa drift in Fram Strait. The Vestnesa drift consists of a ~125° striking eastern segment with active seepage, and a seemingly inactive ~100° striking western segment. While the eastern segment is vulnerable to deformation at the northward propagating Knipovich oceanic ridge, the westward segment is within the deformation field of the Molloy ridge and the Spitsbergen transform fault zone. High resolution 3D P-Cable seismic data reveal the link between gas chimney distributions and small scale curvilinear, nearly vertical sub-seabed cracks and faults that reflect the influence of regional tectonics on each drift segment. Our observation and analysis can be extrapolated to similar systems where the tectonic history may have implications for modern deformation and fluid flow evolution within sediment ridges, only detectable by high or very high resolution 3D acoustic data.